Eriksson Culvert v4
Analysis and Design of Precast and Cast in Place Concrete Culverts
in Accordance with LRFD, LFD, AREMA or CHBDC Specifications
User Manual
version 4
Copyright Notice
Copyright © 2010-2018 by Eriksson Software, Inc. All rights reserved. No part of
this material may be reproduced or transmitted in any form or by any means
without written permission.
Eriksson Software, Inc.
http://www.erikssonsoftware.com
e-mail: TechSupport@eriktech.com
Table of Contents
1
GETTING STARTED ...................................................................................................................... 1
1.1
1.2
1.3
1.6
2
TUTORIAL PROBLEMS ................................................................................................................. 4
2.1
2.2
2.3
3
OUTPUT OPTIONS..................................................................................................................... 83
VIEWS...................................................................................................................................... 83
PRINTING ................................................................................................................................. 88
STATUS BAR ............................................................................................................................ 88
ENGINEERING THEORY ............................................................................................................. 89
5.1
5.2
5.3
5.4
5.5
5.6
5.7
5.8
5.9
5.10
5.11
5.12
5.13
5.14
5.15
5.16
6
PROGRAM MENU ...................................................................................................................... 34
TOOL BAR ................................................................................................................................ 34
INPUT DIALOG BOXES ............................................................................................................... 34
GETTING RESULTS..................................................................................................................... 83
4.1
4.2
4.3
4.4
5
TUTORIAL 1: FOUR SIDED PRECAST BOX ..................................................................................... 4
TUTORIAL 2: THREE-SIDED PRECAST BOX CULVERT .................................................................. 19
TUTORIAL 3: PERMIT VEHICLE WITH HL-93 ................................................................................ 25
PROGRAM INPUT ........................................................................................................................ 34
3.1
3.2
3.3
4
INTRODUCTION ........................................................................................................................... 1
PROGRAM FEATURES ................................................................................................................. 1
INSTALLATION AND SET UP ......................................................................................................... 2
STARTING A DESIGN ................................................................................................................... 2
SUPPORTED SPECIFICATIONS ................................................................................................... 89
MATERIAL PROPERTIES ............................................................................................................ 89
STRUCTURAL MODEL ................................................................................................................ 90
APPLIED LOADS ........................................................................................................................ 92
LIVE LOAD................................................................................................................................ 94
FLEXURAL STRENGTH ............................................................................................................... 96
SHEAR STRENGTH .................................................................................................................. 100
CRACK CONTROL ................................................................................................................... 104
FATIGUE ................................................................................................................................ 105
DISTRIBUTION REINFORCEMENT .......................................................................................... 106
SHRINKAGE AND TEMPERATURE REINFORCEMENT................................................................ 107
BAR SCHEDULE .................................................................................................................. 108
LOAD RATING ..................................................................................................................... 110
END REGIONS .................................................................................................................... 114
RETAINING WALL DESIGN .................................................................................................... 115
STRIP FOOTINGS FOR 3-SIDED CULVERTS ........................................................................... 118
APPENDIX .................................................................................................................................. 120
6.1
6.2
6.3
6.4
6.5
6.6
APPENDIX 1: GLOSSARY AND NOTATION .................................................................................. 120
APPENDIX 2: FIRST TUTORIAL PROBLEM .................................................................................. 122
APPENDIX 3: SECOND TUTORIAL PROBLEM .............................................................................. 135
APPENDIX 4: THIRD TUTORIAL PROBLEM (FINAL RUN – TEXT REPORT ONLY) ............................. 147
APPENDIX 5: REFERENCES ..................................................................................................... 159
AGENCY LIST ......................................................................................................................... 160
INDEX ................................................................................................................................................. 163
1 Getting Started
1.1
Introduction
Eriksson Culvert is a Microsoft Windows-based program for the design or analysis of single and
multiple-cell precast or cast in place concrete culverts in accordance with either the AASHTO LRFD
Specifications, 5th Edition (2010) and 6th Editions (2012), the 2013 Interims to the LRFD 6th Edition,
the 7th Edition (2014, including the 2015 and 2016 Interims), the AASHTO Standard Specifications,
17th Edition (2002), AREMA 2010, or CSA-S6-06.
Developed in the C# language in the .NET Framework, Eriksson Culvert incorporates a state-of-theart computational engine to perform extremely fast, real-time calculations. Its rich set of features,
including hot code switching, permits the designer to investigate many design types and freely switch
between the supported specifications instantaneously at any time during the design process.
Eriksson Culvert was created specifically for the Microsoft Windows environment. Full support is
provided for all Windows features. All Windows are scrollable. Eriksson Culvert’s interface takes full
advantage of Windows’ power and flexibility to give you better control over the design process.
1.2
Program Features
System
 MS Windows XP/Vista/7/8/10
 C# in .Net Framework
 DRM based
Design Specifications
 AASHTO LRFD (5th - 8th Editions)
 AASHTO Standard (STND)
 AREMA
 CHBDC
Operational Modes
 Fully-automatic design
 Analysis mode
Geometry
 Precast and cast-in-place
 Single to four cell culverts
 4-sided, 3-sided, Type I and II
 V-bottom slab
 Span, height, length
 Slab and wall thicknesses
 Haunch widths
 Culvert skew and skewed ends
Material Properties
 Concrete properties
 Normal or lightweight concrete
 Rebar properties
 Exposure type
 Soil properties
Eriksson Culvert V4 User Manual

Slope Factor
Loads
 LRFD HL-93
 HS & H trucks
 Flexible dead loads
 Fully customizable vehicle library
 Multiple trucks in a single design
Load & Resistance Factors
 Code specified
 User-defined
 Load modifiers
Reinforcement
• Rebar and mesh
 Top, bottom, side cover
 Bar sizes
 Bar spacing
 Shear steel
 Improved mesh support
Output
 Highly graphical
 True 3D OpenGL rendering
 Detailed text reports
 Results graph
 Results grid with clipboard copy
1
1.3
Installation and Set Up
Click here to go to our YouTube channel to see videos on getting started with Eriksson Software
products and other tutorial videos.
1.4
Starting a Design
As mentioned earlier, to start Eriksson Culvert, run Eriksson Culvert.exe. However, the easiest way
to start Eriksson Culvert is to launch it through the Programs folder of the Start menu, which should
be located in the lower left-hand corner of your screen.
When Eriksson Culvert is first started, two basic options are available. Either a new design can be
started or a previous job can be re-opened.
To start a new design, double click on one of the default start files in the middle section of the start-up
screen. There are five different culvert types available to start a design from, four-sided, three-sided,
two-cell, type I, or type II. Clicking once on any of these buttons will show the file preview summary,
double clicking will open the file.
Screen 1-12
To open a saved file, you can click on the “show file explorer” button to easily navigate through
Eriksson Culvert files stored locally on your computer. Alternatively you can click the “open file” button
on the left side of the screen to open the traditional Windows file explorer.
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Only one job is permitted to be open at a time in Eriksson Culvert. Accordingly, when a new job is
opened, the current job is automatically closed. If any changes have been made to the current job,
the user will be presented with the option of saving the current job first.
Once a design has been started, you can go back to the start-up screen by clicking on the “new” button on the
tool bar; or open an existing file by clicking on the “open” button.
Screen 1-13
Screen 1-14
Required Input
The input for Eriksson Culvert is organized into logical groups of data. Each group is entered via one
or more dialog boxes of information. The main groups are as follows:
1.
2.
3.
4.
5.
6.
7.
Project Settings – Job description, governing specification and operation mode
Culvert Properties – Culvert dimensions and material properties
Loads – Applied static loads, and seismic options
Load & Resistance Factors – Override load & resistance factors as necessary
Analysis Options - Specify run-time changes to basic assumptions and equations
Reinforcement – Edit properties of rebar at any position
Shear Steel – Enable and add shear steel for Analysis
When a new job is started, the input boxes in the above dialog boxes will each be initialized to
reasonable default values.
Program Computations
Eriksson Culvert automatically updates its calculations whenever an open dialog box is closed using
the OK button for that dialog box. Calculations are also recomputed when a previous job is restored.
Because of its extremely fast 32-bit calculation engine, Eriksson Culvert’s recalculation times are
typically less than a few seconds.
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2 Tutorial Problems
2.1
Tutorial 1: Four Sided Precast Box
Problem Overview
A complete start-to-finish design using Eriksson Culvert will be demonstrated in this chapter. The job
is a typical precast four sided box culvert, which will be designed in accordance with the LRFD 6th
Edition Specifications. Below are the input values for the problem.
Governing Specifications
AASHTO LRFD 6th Edition
Culvert Dimensions
Clear Span
Clear Height
Length
Fill Depth
Skew
Top Haunch
Bottom Haunch
=16 ft
=8 ft
=8 ft
=1.99 ft
=0 deg
=8 in
=8 in
Reinforcement Covers
Top Slab Cover = 2 in
Bot. Slab Cover = 1 in
Ext. Walls Cover = 1 in
Box Concrete
f’c = 5.0 ksi
f’ci = 4.5 ksi
wc = 0.150 kcf
Reinforcement
fy = 60 ksi
Dead Load
Soil Density
= 0.12 kcf
Lateral Soil Loads
Max. Equiv. Fluid Press. = 60 pcf
Min. Equiv. Fluid Press. = 30 pcf
Live Load
HL-93 (LRFD)
Figure 2-1: Plan and Elevation Views of the box culvert for Tutorial 1.
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Data Preparation
Most input fields in Eriksson Culvert’s interface were designed to minimize the preliminary work that
must be done by the engineer prior to running the program.
Eriksson Culvert automatically computes the self-weights of both the slab and the walls.
Entering Data
To begin the tutorial, start Eriksson Culvert by accessing it though the Programs folder of the Start
menu. Click the Start button in the lower left-hand corner of the screen, highlight the Programs folder,
highlight the Eriksson Culvert icon, and click the icon. Note that due to differing versions of Windows,
some of the following screen shots may look different on your system.
The startup screen will appear, select the project titled “four-sided” and double-click to open the file.
Screen T1-1
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Screen T1-2
Once the job has been loaded, a design is performed based on the the current job data, and four
tabbed views are displayed, with the main view slected as the current view. This view is a graphic
view of the primary data for the job. This data includes the slab clear span and clear height,
calculated wall and slab thicknesses, materials properties, loads, and rebar schedule. The screen
shot above shows the top of four scrollable pages included in this view.
The other views are Text Report, Results Graphs, and 3D Rendering. You can access these views by
clicking on their respective tabs.
Data input in Eriksson Culvert is accomplished via standard Windows dialog boxes (DBs). These are
organized around logical groupings of data. Depending on whether a job was initialized using one of
Eriksson Culvert’s default jobs, a previously created seed file, or some other file, a number of DBs will
need to be opened and the relevant changes made to the data. Dialog boxes can be opened via the
menu at the top of the screen or via buttons, which are located on the toolbar.
To begin the revision process for the job we have just initialized, we will revise the descriptive
information for the job. On the toolbar, located near the top of the screen, click the Project Settings
dialog box button, which looks like this:
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Screen T1-3
Notice that in its initial state, it contains no information other than “[New job]”.
Before proceeding, however, an important resource of Eriksson Culvert’s to learn about is its help
system. When any dialog box is open, you can press the F1 key on your keyboard to immediately get
specific help about the current dialog box. Press the F1 key to view the help screen for the Job
Information dialog box.
Each dialog box’s help screen contains detailed information about the input required for that dialog
box. Later, during the more complicated input areas, this will prove to be an invaluable reference.
Aside from the context-sensitive help, there are also help topics dealing with the general operation of
the program and engineering theory as well. To access those areas, click the Contents tab located in
the left pane of the help screen. Do that now.
Screen T1-4
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To view the contents of each major section, click the plus sign to the left of the the book icon next to
the item of interest and one or more subtopics will appear. For example, under the Design and
Analysis section, topics related to the underlying operation of the program are contained.
To close the Eriksson Culvert help system and return to the Job Information dialog box, click the “X”
in the upper right-hand corner of the help window.
Screen T1-5
Enter the job information shown above, using the Tab key to move from field to field.
Now the bottom portion of the window is where you will set all of the design information, e.i. governing
specification and the operating mode.
Our job will be in accordance with LRFD 6th Edition Specifications, and the first pass will be in design
mode. These options happen to be the default settings for this dialog box. To accept these values,
click the OK button.
In Design Mode, the program selects some or all of the slab and wall thicknesses, and fills the rebar
schedule. In Analysis mode, the user selects the slab and wall thicknesses, and sets most of the
rebar sizes and spacing.
Open the Culvert Properties Dialog Box by clicking its button, which looks like this:
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Screen T1-6
The culvert physical properties (clear span, clear height, etc.) and material properties are specified in
the Culvert Properties dialog box. All of the culvert dimensions, including rebar covers, are entered
into the two tabbed pages. The design type (3 or 4 sided) and boundary conditions are also defined in
this DB.
Since we are in Design Mode, the slab and wall thicknesses are labeled as minimum values. You
may input either zero for these values, or some value greater than zero. If you assign a value greater
than zero, the program requires at least a minimum value of 3 inches for all members. Additionally,
the program also checks any minimum value greater than zero for reasonableness based on the clear
span and the clear height, in order to obtain reasonable values in the design phase.
The next dialog box we will look at is the static loads dialog box. Click on the static load dialog icon
on the toolbar (it looks like a vertical point load), or select ‘Static Loads’ from the Input menu.
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Screen T1-7
In the Static Loads dialog box, you specify the static loads applied to the culvert. Take a moment to
review the load types and values shown above, referring to the help system or Chapter 3 for details.
Click the OK button.
The next dialog box we will look at is the moving loads dialog box. Click on the load dialog icon on
the toolbar (it looks like a truck), or select ‘Moving Loads’ from the Input menu.
Screen T1-8
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The live load vehicle type we will be using is an LRFD HL-93. To view the details of the live load, click
the “Properties” button. Close that dialog box when you are finished viewing it.
For most design mode jobs, this is probably the extent of the input that you need. However, for this
tutorial, we will also look at the Analysis Options dialog box. Click on the following icon to access this
window:
Screen T1-9
Screen T1-10
Before we look at the results of the design, note the area at the bottom of the screen. This is called
the status bar. The two panes at the right side of the status bar contain information about the design.
From left to right, they are defined as follows:
1. Design Mode: Indicates the mode of operation (Design or Analysis)
2. LRFD 6th Ed: Currently selected design specification
All of the data input for this job has now been addressed. At this point, completion of the design
consists of viewing the calculation results and and making refinements to the input data as
necessary.
Getting Results
Eriksson Culvert incorporates an extremely fast and efficient calculation engine. On a typical PC,
recalculation times are typically less than a few seconds. This results in the ability of the program to
perform real-time calculations. That is, whenever a revision to the input data is made, calculations
are automatically updated in the background, and the results are quickly made available to view in
multiple formats.
The practical result of Eriksson Culvert’s method of performing calculations is that after editing the
input, you can immediately view the effects on the design. As we’ll see, in addition to the main view
there are three other ways to view results:
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1. Text report
2. Graphs
3. 3D rendering view
Besides the main view and graphs, one additional design view mode is available in Eriksson Culvert,
which is the text mode. Click the Text Report tab to open this view.
Screen T1-11
This view of the results gives several pages of data. The first pages are a reprint of the input data,
followed by a complete listing of all shears and moments, along with the values at the critical
sections, and the rebar schedule. Note that in the critical section table all of the allowable values are
greater than the applied values.
The text window shows the top of the detailed text report. This report is 8 pages in length and so will
not completely fit on the screen. Along the right-hand side of the screen there is a scroll bar that
permits you to very easily and smoothly scroll and review the results. The rectangular-shaped button
currently positioned at the top of the scroll bar is called the “thumb.” You can click and hold on the
thumb and move your mouse toward you to fluidly scroll down the page. Also on the right hand side
of the page is a navigation tab that allows you to easily jump to a specific portion of the output by
simply clicking on a link.
Tip: You can gauge the size of a report by glancing at the size of the thumb. The ratio of the vertical
height of the thumb to the total length of the scroll bar is the same as the height of the view area to
the total length of the text report
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Scroll the text view to the position shown below, or click on Design Results.
Screen T1-12
The text screen above has been scrolled to show the top of the third page of the text report. The
design results starts here, with the reinforcment bar schedule.
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Screen T1-13
The reinforcement bar schedule is followed by the unfactored moments and shears table. Note that
there are two unfactored tables. The first is the table of all loads used in the design. The second
table is a listing of all live loads checked by the program. This may include the design truck, the
tandem load, and the lane load.
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Screen T1-14
The serviceability check is next, followed by the output at the critical sections.
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Screen T1-15
The last part of the printout shows the load combination results at the tenth points.
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Screen T1-16
Now is a good time to obtain a printout. You can actually get a printout at anytime during the design.
(Note, however, that until the job has been saved, it does not have a filename, so “Eriksson
Culvert1.etcx’ will be shown as the filename at the top of each page of each report.) To bring up the
Print dialog box, click “File” then “Print” or press CTRL+P.
Screen T1-17
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The Print Dialog Box applies to the active window. In our case, the text view is the active one. You
can also preview the report before you print by accessing Print Preview from the File menu.
The complete printouts for the two main windows for this Tutorial are included in Appendix 2 of this
manual.
Saving Your Data
Saving your data permits you to recall the job at a future time for review and possible editing.
Screen T1-18
To save the data for our example, we will use the Save button or select the Save option on the File
menu. Since we have not yet given this job a name, the Save As dialog box will appear.
Note that once a name has been entered, if you pick the Save option, the Save As dialog box will not
appear again. So, if you desire to change the name of the job, you must actually pick the Save As
option from the File menu.
Eriksson Culvert’s data files use the extension “.etcx,” which Eriksson Culvert will supply for you. So
enter “Tutorial1” as the job name and click the Save button.
To close the current job, select “Close Project” from the File menu.
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2.2
Tutorial 2: Three-sided Precast Box Culvert
Figure 2-2: Plan and Elevation Views of the three sided culvert for Tutorial 2.
Problem Overview
This Tutorial problem will provide an overview of entering and designing a three-sided single cell
precast box culvert. In Tutorial 1, we addressed every dialog box that required input for the job. In this
problem, however, we will only discuss the differences between four-sided and three-sided culverts.
Start Eriksson Culvert as before and begin a new three-sided job by double clicking on the “ThreeSided” default file.
Eriksson Culvert V4 User Manual
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Screen T2-1
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Screen T2-2
Once the job has been loaded, a design is performed based on the the current job data, and the main
view of Eriksson Culvert is displayed. The screen above should appear. Note the plan view and
typical section. This is a three-sided culvert. Scroll through these three pages of information and
review the job parameters before proceeding.
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Screen T2-3
Open the Culvert Properties dialog box, as shown above.
[Note: From this point on, if it is not explicitly stated, open and close the required dialog boxes as
necessary to match the screens shown.]
Note that the ‘design type’ has been set to three-sided; this disables several input boxes on this DB
that relate to input for the bottom slab. Also notice that the ‘support type’ option is enabled.
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Screen T2-4
Click the “Text Report” tab to view the detailed text report as shown above.
Scroll down to the section entitled “Design Results”. In this section will be a warning.
Note that for a three-sided culvert, the program calculates and prints the pinned reactions applied to
the structure, along with a warning about the foundation and a reminder to check the shipping and
handling.
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Screen T2-5
Before closing this tutorial, open the ‘help’ menu at the top of the screen. From here you are able to
contact technical support, check for updates, view change logs, and access the QC document.
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2.3
Tutorial 3: Permit Vehicle with HL-93
Figure 2-3: Plan and Elevation Views of the box culvert for Tutorial 3
Problem Overview
This Tutorial problem will provide an overview of entering and designing a box single cell precast box
culvert with both an HL-93 truck and a typical permit vehicle. In the previous tutorials, the dialog box
fields were already filled out for you. In this tutorial, you will have to do some data entry to see the
final results.
Start Eriksson Culvert as before and begin a new job by opening the Initialize New Design dialog box.
Screen T3-1
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Double-click on the “Four-sided” button to start the project.
For this tutorial we will check both HL-93 and a permit vehicle. While we are using typical
assumptions with our permit vehicle, the user is reminded that not all permit vehicles are treated the
same. Please check with your governing authority for the proper design assumptions to use with
specific permit vehicles.
A full design can easily be accomplished with just a single run of Eriksson Culvert. To start with,
make sure you are in Design Mode.
Screen T3-2
Open the Culvert Properties dialog box and change the clear span, clear height and length to match
the input below.
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Screen T3-3
Then access the Moving Loads Dialog Box. The default problem only has one truck, the HL-93.
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Screen T3-4
To add a permit vehicle, click the Add Truck to List button. The truck library screen will be displayed.
Screen T3-5
Select the NYSDOTPermit vehicle and then press OK. You will be returned to the Moving Loads
Dialog Box.
Back on the Moving Loads window, we must now configure the trucks.
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Screen T3-6
Configure each truck as needed by selecting that truck in the list, and then making any needed
corrections in the parameters to the right. For this design, we only need to configure the permit
vehicle. Highlight the permit vehicle in the list, and then change the vehicle type to Permit Vehicle,
and the load combination to Strength II. You may also need to change the rating load factor, but we
will leave it at 1.35. Note that this load factor will only be applied to the rating calculations. There is a
separate design load factor that will be applied to the flexure and shear calculations (which can be
accessed through the load and resistance factors dialog box).
Screen T3-7
We also need to remove the lane load. Note that parameters at the bottom of this dialog box are not
specific to an individual truck but will be applied to all trucks.
Press OK and look at the text report
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Screen T3-8
The thicknesses and the critical section summary tables will display the controlling truck
To save space we use key values for the truck names, in this case, the HL-93 is displayed as AA and
the permit truck is displayed as AB in the critical section tables
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Screen T3-9
The thicknesses of the various members can be seen on the Main View.
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Screen T3-10
Change the operating mode to Analysis Mode.
Screen T3-11
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Switching to Analysis Mode will freeze the reinforcement based on the controlling truck and fill depth.
Pressing OK will again complete the analysis. Scan the critical section table of the text report to
make sure that there are no design deficiencies. Note that the program does this for you
automatically, and posts the results in the design deficiency list next to the text report. If there are no
deficiencies detected, then the deficiency list will not be present. If there are any deficiencies, then
upgrade any of the reinforcement steel as necessary.
Screen T3-12
That completes this tutorial on mixing permit vehicles with the HL-93 truck to produce an adequate
structure.
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3 Program Input
This section of the manual explains each screen, dialog box, or other data entry method into which
data is entered into the program. In general, data is entered into dialog boxes. These can be
accessed via the program menu or via the tool bar. In many cases individual dialog boxes contain
buttons, which open one or more additional dialog boxes.
3.1
Program Menu
The program menu, located in the upper area of the screen, organizes the main features of the
program. Each menu item contains one or more submenus.
Screen 3-1
The main menu items are as follows:






3.2
File – Gives access to the file and printing functions of the program
Input – Organizes and gives access to the primary input dialog boxes
Results – View results not represented in tab views in a selectable grid
Libraries – Access the reinforcement size/spacing pairs library
Window – Contains functions that allow you to manipulate Eriksson Culvert’s windows
Help – Provides access to the help system and link to contact tech support
Tool Bar
The tool bar, or button bar, contains a series of buttons, each with a specific program function
assigned to it. Most of the important program features contained in the menus have been assigned to
buttons for quick and easy access to them.
Screen 3-2
The picture or icon on each button gives you a clue about its function. To find out what a specific
button does, move your cursor over it and a small rectangular box ( a “tool tip”) will appear. A more
detailed description will also appear in the status bar at the bottom of the screen.
3.3
Input Dialog Boxes
Input for Eriksson Culvert is organized into a series of dialog boxes. Each dialog box and its contents
are described below.
Project Settings
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Screen 3-2
Project Name
Name of project (30 characters maximum).
Task
Task name (30 characters maximum). Should describe the location and possibly type of culvert
being designed.
Client
Client name (20 characters maximum).
Job Number
Job number (15 characters maximum).
Designer
Initials of the designer (4 characters maximum). This will appear in the top right-hand corner of each
page of printed reports.
Specifications
Select either AASHTO LRFD 5th Edition, LRFD 6th Edition (with or without the 2013 Interims), LRFD
7th Edition (including the 2015 and 2016 Interims), LRFD 8th Edition, AASHTO Standard
Specifications (STND), AREMA, or CHBDC (CSA-S6-06). You may freely switch between any of the
specifications at any time. However, if you do, you should review all data for the job to ensure that
any assumptions the program had to make during the switch to one of the other specifications are
valid. Note, however, that switching specifications does not automatically switch the truck, the user
will have to manually re-select the appropriate truck. If you do select Standard or AREMA
Specifications then you can select the Method as either Load Factor (LFD) or Service Load (ASD) .
Program Operation
Select either Design Mode or Analysis Mode. This will determine the basic operating mode of the
program. In Design Mode the program will design the culvert according to user-specified input. In this
mode the program will determine the appropriate culvert properties such as reinforcement, slab
thickness, and wall thickness. Member thicknesses can be ‘fixed’ in the Analysis Options dialog box
to freeze the slab and wall thicknesses so that only the reinforcement will be designed. In Analysis
Mode the program will analyze the culvert according to the user-specified input and program
designed values. In this mode the user can adjust the reinforcement and review analysis results. The
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program will not automatically adjust parameters such as reinforcement, slab thickness, and wall
thickness.
Two items need to be discussed at this point. First, if you want to switch reinforcement types (either
from rebar to mesh, or from mesh to rebar), you must first switch the program operation to Design
Mode. You can then switch the reinforcement type. This is done to allow the program to fill the
internal reinforcement schedule with the appropriate type of reinforcement. Second, you may only
indicate that shear steel is active in Analysis Mode. Currently the program does not design the shear
steel for you, and member thicknesses are determined during Design Mode assuming that the
concrete resists the entire applied shear. Note that shear steel is not required, it is merely available
as an option during an analysis.
State/Agency
Select the agency that governs the current design. Known settings typically used for that agency will
be set as the current settings when the OK button is pressed. When an agency is selected, the values
that will be changed are shown in the window to the right.
Screen 3-3
Type of Culvert
Select either Precast or Cast-in-place culvert. The selection will affect the Culvert Properties input
screen. For example precast culverts are limited to 60 feet length while cast-in-place culverts can be
any length and only cast-in-place culverts can have end skews. Also, specific code provisions may
impact cast-in-place design differently than precast. See the Engineering Theory for a detailed
discussion of any potential differences between culvert types.
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Culvert Properties
Physical Dimensions
Screen 3-6
Name
Input a name for the culvert. This is for your information only, and is not used by the program in any
fashion.
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Culvert Properties
No. Boxes
Input the number of boxes, between 1 and 4.
Design Type
Select the type of culvert to be designed, either three of four sided.
Support Types
Select the type of supports to model the culvert. This option is only enabled if three-sided is
selected for the design type. The options are pin-roller, pin-pin, and fixed-fixed (note that fixedfixed is only available for cast-in-place culverts.
Clear Span
Input the culvert clear span as the dimension in the horizontal or x-direction of the open area of
the culvert. Typically this is measured between the inside faces of adjacent walls parallel to the
span of the top and bottom slabs.
Clear Height
Input the culvert clear height as the dimension in the vertical or y-direction of the open area of the
culvert. Typically this is measured between the inside face of the top slab and the inside face of
the bottom slab (or the bottom of the walls for 3-sided culverts).
Length
Input the culvert section length as the distance between joints, measured along the culvert
centerline. If your culvert has no joints, then input the entire length of the culvert. This value is
used in the creation of the bar schedule in both Design and Analysis Modes. The culvert length
will also be used as live load distribution width for fill depths less than 2 feet (STND and AREMA),
if the assigned length is less than the calculated distribution width.
Eriksson Culvert is a design program, not a detailing program; the bar lengths in Eriksson Culvert
are primarily for estimation purposes and are meant to provide a means to compare design
options. Actual drawing and production demands may require adjustments to bar lengths to
accommodate local codes and construction practices or plant specific production methods.
Fill Depth
Input either a single fill depth or a range of fill depths. If analyzing the culvert over a range of fill
depths then values for the maximum fill depth, minimum fill depth, and increment must be input.
The culvert will then compute fill depths from the minimum depth to the maximum depth at the
value of the increment, inclusive of both the maximum and minimum values. If the value of 1.99 ft
is between the maximum and minimum values then it will also be included in the analysis. For
example, if the minimum value is specified as 0 ft, the maximum values is specified as 2.3 ft, and
the increment as 0.5 ft, then the fill depth values included in the analysis will be: 0.0, 0.5, 1.0, 1.5,
1.99, 2.0, and 2.3 ft.
Use Range of Fill Depths
Check this box to input a range of fill depths.
Fill Depth/Max. Fill Depth
Input the fill depth value if analyzing culvert at a single fill depth or input the maximum fill
depth if analyzing the culvert over a range of fill depths.
Min. Fill Depth
Input the minimum fill depth if analyzing the culvert over a range of fill depths.
Increment
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Input the increment value for the range of fill depths. If the difference between the maximum
and minimum fill depths is not evenly divided by the assigned increment, then the last
increment checked will be smaller.
Slab and Wall Dimensions
Variable/Fixed Thicknesses
In Design Mode you have the option to choose between variable and fixed thicknesses for all
members:
If “variable” is selected ETCulvert will select the most efficient thickness for each member during
the design process. Note that next to this option is “Min. Thickness”; by specifying a value for this,
ETCulvert will not select a member thickness smaller than this value. You may input 0 here, in
which ETCulvert will use a minimum of 3”.
If “fixed” is selected ETCulvert will not size the member, and instead use the value specified in
the “Thickness” option. Note that the minimum thickness you can enter is 3”.
In Analysis Mode, enter the exact values for the slabs and walls. Note that some agencies
impose specific minimum slab thicknesses. If you have not selected any specific governing
agency, then the minimum thickness of all members is 3 inches. Note that in analysis mode, you
may not change the member thickness flag (fixed or variable) for any member. Also, based on
the clear span and clear height, the program may require you to input a member thickness in
excess of the absolute minimums. This is to insure that the program can assign rebar that fits
within the section.
Added Thickness for Bottom Slab
Input additional thickness for the bottom slab needed for a V-Bottom in the bottom slab at the
intersection of the bottom slab and the side walls. This is also sometimes called a “fish bottom”.
Top Haunch
Input the X (horizontal) and Y (vertical) dimensions for the top haunch if there is one. To form a
45 degree haunch use the same dimension for both X and Y. Both top haunches will have the
same dimensions.
Bottom Haunch
Input the X (horizontal) and Y (vertical) dimensions for the bottom haunch if there is one. To form
a 45 degree haunch use the same dimension for both X and Y. Both bottom haunches will have
the same dimensions.
Note that the use of the haunch in the analysis is dependent on the options selected on the
Analysis Options page. See the discussion on that page for how the haunch can be used in the
analysis.
Skew Angle
Culvert
Input the culvert skew angle defined as the centerline of culvert relative to a perpendicular to the
over roadway, in degrees.
Skewed culvert orientation is used to satisfy right-of-way constraints and/or staged construction
requirements on skewed alignments. In the event a skewed orientation is necessary, skewed
details are normally provided at the extreme ends or at staging lines of culvert construction. This
allows the majority of the culvert length to remain square and retain similar reinforcement details.
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When using the STND and AREMA Specifications, this input is used to determine the live load
distribution width for culverts, under less than 2 feet of fill. When using the LRFD and CHBDC
Specifications, this input is used to determine vehicular traffic direction in relation to main
reinforcement, for all fill heights.
The program treats skewed cast-in-place and precast end details quite differently.
When a cast-in-place culvert has a skewed end detail, the program cuts transverse reinforcing
bars to their required length so they fit the geometry of the skewed end. The correct bar lengths
are determined by the program from the skew input parameters for Left End Skew and Right End
Skew, which are inputs for cast-in-place culverts only. The cut transverse bars are assumed to
be supported by a top slab edge beam and bottom slab cut-off wall along the skewed end of the
culvert barrel. The bar schedule output by the program for a skewed end cast-in-place culvert
adjusts for all the cut transverse reinforcement.
For cast-in-place culverts under all specifications, run the program with the perpendicular clear
span and the appropriate roadway and culvert end skews.
When a precast culvert has a skewed end detail, transverse reinforcement is assumed to be
splayed to fit the geometry of the skew. This splaying of reinforcement in a unit increases the
length of the reinforcing bars and the clear span of the unit. As a result of the differing skew
philosophies used in each specification, we offer the following recommendations:
For a STND or AREMA Specification run, square precast units should be run with the
perpendicular clear span and appropriate roadway skew angle, however, skewed precast units
should be run with the skewed clear span and a roadway skew angle of zero degrees.
For an LRFD or CHBDC Specification run, square precast units should be run with the
perpendicular clear span and appropriate roadway skew angle, however, skewed precast units
should be run with the skewed clear span, a single lane of traffic parallel to main reinforcement
and a roadway skew angle of zero degrees. Note that the bar schedule output by the program for
a skewed end precast unit is actually the bar schedule of a square unit. The size/spacing pairs
and some of the lengths will be correct, but other lengths and most of the weights will be larger
than actual construction.
Left End
For cast-in-place culverts only, input the skew angle for the left end of the culvert defined as the
angle between the left face of the culvert and the centerline of the culvert (‘LEFT SKEW’ in the
following diagram).
Right End
For cast-in-place culverts only, input the skew angle for the right end of the culvert defined as the
angle between the right face of the culvert and the centerline of the culvert (‘RIGHT SKEW’ in the
following diagram).
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Reinforcement Cover
Input values for the exterior cover dimensions for the top slab, bottom slab, and exterior walls. The
cover is measured from the outside surface to the edge of the first steel bar. The fourth and fifth cover
values are used for the rebar cover on the interior of the top slab and the interior of the bottom slab,
respectively. The final cover value is used for the interior cover of all walls (which includes both faces
of interior walls).
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Material Properties
Screen 3-7
Concrete
The 28-day concrete strength (f’c), the density of the concrete, the modulus of the concrete (Ec), and
the type of concrete may be specified. The modulus of elasticity of the concrete is automatically
recomputed when changes are made to either the strength or the density. However, concrete
modulus may be overridden. The program uses LRFD 5.4.2.4-1 for this calculation.
The concrete type may also be designated as normal, sand-lightweight, or all-lightweight. LRFD
defines lightweight concrete as concrete containing lightweight aggregate and having an air-dry unit
weight not exceeding 0.120 kcf. However, if a unit weight is specified as being less than 0.120 kcf
and it is desired that the concrete be treated as lightweight for design purposes, the concrete type
must be explicitly changed by the user. Note that under the LRFD 7th Edition, you can no longer
select the concrete type, rather it is selected for you based on the unit weight, and will either be
Normal Weight (>135 pcf) or Lightweight (< 135 pcf).
Mcr Factors
These factors are the gamma factors present in the new Mcr equation introduced in the 6th Edition
(LRFD Eq. 5.7.3.3.2-1). Currently Eriksson Culvert only uses the first and third gamma factors.
CHBDC uses neither of these factors.
Fr Factors
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Here the user can change any of the multiplication factors used in calculating the modulus of rupture
(Fr). The first factor is the generic normal weight concrete factor used in both the 5th and 6th Editions
of LRFD, along with STND. The second factor is only used in the 5th Edition for the minimum steel
cracking moment. The lightweight concrete factors are used in all editions of LRFD prior to the 7th
Edition, along with STND and AREMA. The 7th Edition only uses the first factor, and uses this factor
for both normal and lightweight concrete. CHBDC uses none of these factors.
Reinforcing Steel
Input values for the yield strength (fy), allowable stress, and modulus of elasticity (Es) of the
reinforcing steel. The reinforcing diameter is used by the program to compute the depth to the
reinforcement during the design phase. For the calculations of the critical section values, Eriksson
Culvert uses the actual diameter of any the calculated or assigned flexural reinforcement. However,
in Design Mode, at the time the program settles on a specific member thickness, the size of the
reinforcing is not known, therefore the ‘reinforcing diameter’ is used to approximate the thickness of
one layer of reinforcement. If you are using mesh, then the default value of 1 inch may be too large.
You can also define the yield strength of the shear steel here as well. Note that if you switch from
rebar to mesh, the program will automatically change the steel yield as well, defaulting to 60 ksi for
rebar and either 65 or 70 ksi for mesh. However, the yield strength of the shear steel will not be
changed.
Soil
Input a value for the density and Poisson’s ratio of the soil.
Exposure Factor
Select the exposure factor to be used for the Culvert. If using LRFD Specification the available values
are Class 1 Exposure, Class 2 Exposure, and User-Defined. If User-Defined is selected, then you
must input a value for Gamma-e. If using Standard or AREMA Specifications the program selects the
appropriate value of Z for the user, based on the culvert type (cast-in-place or precast). The values
selected by the program reflect the values in the specification. They may be overridden by the user.
LRFD does not specify the exposure factor to be used. CHBDC uses a maximum crack width for
service load checks, which functions similarly to an exposure factor.
Soil-Structure Interaction
Select either Compacted Fill, Uncompacted Fill or a User-Defined value. If User-Defined is selected,
then you must input a value for Fe. Note that for compacted or uncompacted fills, the Fe value listed
is used as the maximum possible value, assuming an embankment type of installation. The actual Fe
value used by the program may be less than this. If you set the type of interaction to User-Defined,
then the program uses whatever value you input for Fe. This is useful for trench installations, so you
can calculate the actual Fe based on the soil conditions and input that value here. CHBDC uses both
a vertical arching factor and a horizontal arching factor based on the installation type (B1 or B2).
Slope Factor
Select either Granular Soil, Other Soil Types, or User-Defined. If User-Defined is selected, then you
must input a slope factor. The slope factor is used for fill depths greater than 2 feet to calculate the
live load distribution factor. Note that if you change the specification, then this value may be changed
by the program as well. CHBDC uses a fixed value of 1.75 for the slope factor.
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Static Loads
Screen 3-8
Live Load
Compute Depth of LL Surcharge
For the LRFD specification, the user can select this option to let the program calculate the height
of the live load surcharge depending on the fill depth and the height of the culvert. Where the
user has selected to analyze a range of fill depths, the value of the live load surcharge will also
change.
Depth of LL Surcharge
Input the value for the depth of the live load surcharge. This value will be used for all fill depths.
Track Width
For AREMA, the track width can be input here. Note that under AREMA the truck gage width will
not be used.
Apply LL Surcharge At Fill Depths Greater Than 2 Feet
Normally the program only applies a live load surcharge when the fill depth is less than 2 feet. By
selecting this option you can force the program to apply live load surcharge at all fill depths. If
you want to force the program not to apply any live load surcharge for fills less than 2 feet, then
set the depth of the live load surcharge equal to zero.
Neglect LL for fill depths greater than 8 feet and greater than span length
Check to have analysis neglect live load for fill height greater than 8 feet and the clear span.
Apply LL Surcharge when LL is neglected
Check to have analysis apply loading due to live load surcharge even when live load is neglected
due to fill depth.
Dead Load
Additional Uniform Dead Load
Input an additional uniform dead load. This load is applied to the one foot wide culvert structural
model. In other words, to convert an area load to the proper distributed load, simply multiply by 1
foot.
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Future Wearing Surface
Input the weight of a future wearing surface (if any), which is also applied to the one foot wide
culvert structural model.
Concentrated Loads
Input up to three additional concentrated line loads. For each load, input the magnitude of the
load and the location from the centerline of the left most wall.
Lateral Soil Loads
Equivalent Fluid Pressures
For LRFD, STND and CHBDC, input the maximum and minimum equivalent fluid pressures for
lateral earth loads. The default for the maximum is 60 psf, and the default for minimum is 30 psf.
The maximum value will be used in those load combinations where the program is calculating the
maximum inward pressure on the walls, and the minimum is used where the program is
calculating the minimum inward pressure (or maximum outward pressure). The exceptions are
LRFD 5th Edition, where the program matches the perceived intent of the 1st Edition of the MBE,
and uses the minimum load factor, EHmin, to calculate the minimum inward pressure, and
CHBDC, which uses EHmin as well.
Lateral Pressure Coefficients
For AREMA, assign the maximum and minimum lateral pressure coefficients.
Fluid Pressures
Consider Internal Water Pressure
Check to have analysis consider internal water pressure. The program will use either the full
height of internal water pressure or no water pressure. Internal water is assumed to have a unit
weight of 62.4 pcf.
Internal Pressure Head
Input the pressure head you would like applied to the interior of the culvert. Note that this option is
only enabled if “consider internal water pressure is selected”.
Check Buoyancy
If this option is selected, Eriksson Culvert will perform a buoyancy check.
Seismic Loads
Include Seismic Loads
Select this option if you would like ETCulvert to perform a seismic analysis.
Peak Ground Acceleration (PGA
Enter the peak ground acceleration in the horizontal direction.
Ground Shear Modulus
Enter the ground shear modulus.
Slip Interface
Select the slip interface, the options are “no slip” and “full slip”.
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Moving Loads
Screen 3-9
Truck Analysis List
A list of trucks that have been added to the analysis. The user may select whether or not to include
each of these truck by checking or unchecking the box next to its name. Note that you must have
included at least one truck to analyze. Clicking on the truck’s name itself will select the truck and
display the assigned design and rating parameters to the right.
Add Truck to Analysis
This button will take the user to the Vehicle Library, where you may select a new truck to add to the
truck analysis list.
Properties
This button will take the user to the Vehicle Properties dialog box, where you will be able to edit the
highlighted vehicle’s properties.
Load Configuration
This button takes the user to a standard Windows open file dialog box where you will be able to select
and import a previously saved truck configuration file.
Save Configuration
This button takes the user to a standard Windows save file dialog box where you will be able to save
the currently displayed truck configuration.
Vehicle Design and Rating Parameters
The Vehicle Design and Rating Parameters allows the user to modify the following properties for the
selected truck in the analysis truck list (to the left).
Vehicle Type
The user has the option of setting the vehicle type to be either design, legal, or permit, and
modifying the rating load factors. Depending on the specification, all vehicle types may or may not
be available. Note that these live load factors will only be applied to the ratings calculations.
There are separate design live load factors that will be applied to the flexure and shear
calculations (which can be accessed through the Load and Resistance Factors dialog box).
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Override MPF
User can select to override the MPF factor for a single lane under LRFD only. If the user selects
to override the MPF, the program will then restrict the moving load analysis to a single lane,
regardless of the assigned overall culvert width.
Design Load Combinations
For LRFD, select either a Strength I or Strength II design. For STND or AREMA, the user can
select between Group I or Group IB. CHBDC users only have one design load combination
available.
DLA/Impact
The user has the option to select whether they want to Eriksson Culvert to compute or if they
want to specify the percent DLA. If selected, input a new factor as a percentage. This impact will
be applied at all fill depths and for any number of axles.
Traffic Direction
Select the direction of the lanes relative to the main reinforcement. The lanes can be placed as either
parallel or perpendicular to the main reinforcement. The most common traffic direction for a box
culvert is parallel. Use the perpendicular direction to model storm drains that run parallel to streets
and roads. Under LRFD and CHBDC, the perpendicular direction may also be used to account for
skewed culverts.
Max Number of Lanes
Select how the max number of lanes is to be determined. Select Computed by Program to have
Eriksson Culvert determine an appropriate value for max number of lanes or select Specify Number
of Lanes to choose a value from 1 to 4. Note that with some combinations of fill depth and traffic
direction the number of lanes is set to 1 internally and cannot be changed. Also, if the user selects a
Strength II load combination, the program will set the number of lanes equal to 1, and again in this
case this value cannot be overridden by the user. Under AREMA the number of lanes is always
equal to 1, and cannot be overridden by the user.
Include Lane Load
Check to have the lane load included with the live load. Note that there is no option to neglect the
lane load in the vehicle properties input window, although you can achieve the same result by setting
the lane load equal to zero.
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Vehicle Properties
Screen 3-10
Vehicle Name
A text label used to identify the vehicle. Use only letters, numbers, and/or the underscore character
(_) when entering a name, as this name will be used as the library file name.
Truck
Specify the various properties of the main vehicle load. As the values for the truck are adjusted a
Profile View and Plan View of the truck will be updated. The Profile View shows the relative weights
of each axle and the Plan View shows a footprint of the truck.
Axles
Specify the number of axles, their weights, and spacings. Click the up and down arrow next to
No. of Axles to increase or decrease respectively the number of axles. Changing the number of
axles will adjust the number of rows in the Axle Weights and Axle Spacings grids. In the Axle
Weights grid specify the weight for each axle. To change the axle weight, click on the desired
axle row in the grid. In the Axle Spacings grid specify the minimum and maximum spacing
between each pair of adjacent axles.
Tire Contact Area
Input the length and width of the tire contact area. Width is defined as the direction parallel to the
centerline of the axles and length as the direction perpendicular to the centerline of the axle.
Gage Width
Input the gage width, which is the distance between the centerlines of the wheels, as measured
perpendicular to the centerline of the truck. Note that the gage width is not used in AREMA.
Tandem
Include Tandem
Check this box for the effects of the tandem load to be included in the design, which would
normally be the case for the HL-93 (LRFD).
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Axle 1 Weight
Input the weight of Axle 1.
Axle 2 Weight
Input the weight of Axle 2.
Axle Spacing
Input the spacing between Axle 1 and Axle 2.
Lane Load
Uniform Load
Enter the magnitude of the uniformly-distributed load (line load) to be considered in the lane load
portion of the analysis. The assigned lane load input will be divided by the lane width to convert
this value to a ‘strip’ load.
P-Moment
The point load used in conjunction with the uniform load for determining maximum effects. This
value is not used for one cell box culverts.
P-Shear
The point load used in conjunction with the uniform load for determining the highest shears. This
value is not used for one cell box culverts.
Combine
Choose how to combine the loads. The first option will combine the loads as Truck + Lane or Tandem
+ Lane, which is required by the LRFD Specification. The second option will apply the loads
individually as Truck or Tandem or Lane, and is usually used for any design under the Standard
Specification.
Save To Vehicle Library
Click this button to save the vehicle as defined in this dialog box to file to be used in the Vehicle
Library. The Vehicle Library is placed by default in the user’s Documents folder. This path will be
shown by default in the Save dialog so the vehicle can be saved to the user’s Vehicle Library folder.
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Vehicle Library
Screen 3-11
Vehicle properties can be saved to a vehicle library file to be used in other culvert designs. Eriksson
Culvert will install five files for trucks as defined in the LRFD, Standard Specifications and CHBDC:
HL-93, HS-20, HS-25, CL-625 Design, and CL-625-ONT Design. Additional vehicles can be added
from the Vehicle Properties dialog box. The vehicle library files will be located by default in the user’s
Documents folder in the folder “Eriksson Software\Eriksson Culvert\Vehicle Library.” This folder will
be shown initially whenever accessing the vehicle library either to save files from the Vehicle
Properties dialog box or to open files from this dialog box. A user can choose to browse to other
folders to either save or open vehicle library files in other locations.
Folder
The path to the currently selected folder is displayed here. Initially this will show the path to the user’s
Documents folder\Eriksson Software\Eriksson Culvert\Vehicle Library\. Eriksson Culvert will create
this folder and use it by default. To navigate to other folders that contain vehicle library folders, click
the Browse button to open a Windows Browse for Folder dialog box.
Vehicle Library Files
A list of vehicle library files in the current folder is shown here. Click on any of them to display the
properties of the vehicle.
Vehicle Properties
Displays the properties of the vehicle selected in the Vehicle Library Files list. This mirrors the Vehicle
Properties dialog box except the values cannot be edited, only viewed.
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Load and Resistance Factors
Screen 3-12 (for LRFD)
Screen 3-13 (for STND and AREMA)
Screen 3-14 (for CHBDC)
Locked/Unlocked
By default the form will be locked. Click this button to unlock the form to edit the values on the form.
Load Factors
For LRFD and CHBDC, input load factors for the various load cases. For STND and AREMA, input
Gamma, Beta-D, and Beta-L values. Note that these live load factors will be used for flexure and
shear calculations only. For ratings calculations, the program will use the live load factors assigned
on the Moving Loads dialog box.
Resistance Factors
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For LRFD, input values for Shear and Moment, along with the compression and tension values for the
points on the internal P-M diagram. For STND and AREMA, input values for Shear and Moment as
well as P-M Diagram values for Slabs, Exterior Wall, and Interior Wall. For CHBDC, the user can
assign values to both the phi factor for concrete and the phi factor for steel.
The STND Specification strength reduction phi factors are listed as 0.90 for flexure, 0.85 for shear,
0.75 axial compression (spirals) and 0.70 axial compression (ties). These have been used as a basis
when selecting the default values for the P-M diagram used internally by the program to calculate the
flexural resistance of the various members of the culvert.
A phi factor of 0.85 is the default for slabs. For shorter spans in the range of 12 feet or less, shear
will usually control the slab design so a value of 0.85 was selected. For longer spans where flexure
controls, the user has the option of increasing the phi factor to 0.90 for a less conservative design.
A phi factor of 0.70 is the default for interior walls. Interior walls take the majority of the axial forces
on multi-cell (multi-span) structures so a phi factor for axial compression was selected. It can be
assumed horizontal wall reinforcement behaves more like “ties” than “spirals”, so the lower value phi
factor of 0.70 is used.
A phi factor of 0.80 is the default for exterior walls. Exterior walls of culverts behave more like beamcolumns than pure compression or pure flexural members. The default value of 0.80 is midway
between a pure compression member (phi = 0.70) and a pure flexural member (phi = 0.90) for
exterior walls.
For LRFD, the phi factor for moment is actually a variable number based on the location on the P-M
curve. The value assigned here is used to in the preliminary estimate of the area of steel required in
design mode, and to calculate the area of steel needed to satisfy minimum steel requirements (Mcr).
This value is also used to calculate the flexural capacity when the user selects the analysis option
‘Ignore Axial Thrust’, and in this instance a variable phi is not calculated.
Load Modifiers
For LRFD only, input values for Ductility, Redundancy for Dead Load, Redundancy for Live Load, and
Importance.
Capacity Modifiers
For LRFD only, input values for Condition and System modifiers.
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Analysis Options
Screen 3-15
Live Load Analysis
Automatically Set Traffic Direction to Account for Skew Effects
For LRFD and CHBDC, check this box to have the analysis automatically set the traffic direction
perpendicular to the main reinforcement when the skew is greater than 15 degrees for all fill
depths, regardless of the Lane Direction setting for the Vehicle Properties. The Lane Direction
setting will be used otherwise. Uncheck this box to have the analysis use the Lane Direction
setting for all skew angles. For STND, the program always adjusts the distribution width to
account for skew effects when the fill depth is less than 2 feet, see the discussion in Engineering
Theory.
Include Impact on Bottom Slab
Check to include impact on the bottom slab. This option was included to have the live load
results more closely equal the previous PCANY Culvert program, which included impact on the
bottom slab.
Limit Distribution Width to Culvert Length for Fills Greater Than 2 Feet
Check to have the moving load calculations limit the live load distribution width to the culvert
length if the fill is greater than 2 feet deep.
Limit Distribution Width to Culvert Length for Fills Less Than 2 Feet
Check to have the moving load calculations limit the live load distribution widths to the culvert
length if the fill is less than 2 feet deep.
Combine Axle Overlaps for Fills Greater Than 2 Feet
Check to have the moving load calculations combine axles that overlap when the fill depth is
greater than 2 feet. If unchecked, the axle loads will be applied to the top slab as is, and will be
allowed to overlap where the axle spacing is less than the fill depth multiplied by the fill slope.
Note that this option is no longer valid when using LRFD 2013 Interims and later.
Following is an example of the effects of the combine axle overlaps option in Eriksson Culvert.
The example shows results for only the first three axles of the NYSDOT permit vehicle for an 8
foot fill depth using LRFD specifications.
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Live Load Distribution when analysis option “Combine Axle Overlaps for Fills Greater Than 2
Feet” is not checked.
Live Load Distribution when analysis option “Combine Axle Overlaps for Fills Greater Than 2
Feet” is checked
Always Distribute Wheel Load
Under LRFD, for fill depths less than 2 feet, wheel loads may be assumed to be directly on the
top slab, or they may be distributed through the fill. Checking this option will distribute the load
through the fill. If this option is not checked, then the program will place the wheel load directly
on the top slab. Also, if you are using the ASTM charts to select your steel, you will need to use
this option to match the model used to create the charts. Note that STND and CHBDC requires
that the wheel load is always placed on the top slab for fill depths less than 2 feet.
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Axle Increment for Analysis
Input the number of axle increments to be used in the moving load analysis. Assigning a high
number will greatly slow down the moving load analysis. The minimum value allowed is 10,
which places the axles at the tenth points on each cell. The default value is 20.
Reinforcement
Individual Top and Bottom Slab Design
Check to perform individual top and bottom slab design. If not checked, the governing slab will be
used to determine thickness and steel area.
Individual Interior and Exterior Wall Design
Check to perform individual interior and exterior wall design. If not checked, the governing wall
will be used to determine thickness and steel area.
Distribution Slab Has Been Provided
If checked the program will assume that a separate distribution slab has been placed on top of
the top slab, and therefore no distribution steel will be necessary in the box itself. This will only
apply to designs will fill depths less than 2’.
Always Include Distribution Steel
If checked the program will always calculate and display distribution steel, even when the fill
depth is greater than or equal to 2 feet. If unchecked, the program will only calculate distribution
steel for fill depths less than 2 feet. Note that even if distribution steel is not calculated, some
minimum reinforcement may be used.
Epoxy
Select which bars you would like epoxied, the options are ‘none’, ‘top steel if fill < 2ft’ and ‘all
steel’. If ‘top steel if fill < 2ft’ is selected the program will always assume the top layer of steel in
the top slab is epoxy coated for fill depths less than 2 feet. Otherwise, all steel in the culvert is
assumed to be uncoated at all fill depths. If ‘all steel’ is selected, the program will assume all steel
is epoxy coated at all fill depths.
Max. As used in Vc Calcs
In LRFD, when the shear capacity of the concrete is calculated using the iterative approach in
Appendix B5, a preliminary estimate of the reinforcing steel is based on moment demand. Then
the area of steel is used to calculate the shear capacity and checked against the shear demand.
If the preliminary estimate of the area of reinforcing steel is unsatisfactory the program enters a
loop inside the shear calculations to increase the area of steel until this requirement it met. This
area of steel should be limited to around 2.0 in2/foot for practical purposes, and can be adjusted
up or down here. If this limit of the reinforcing steel cannot be satisfied then the program
increases the member thickness, recalculating the structural steel demand, and re-starts the
shear demand loop.
Live Load Deflection Criteria
Select the live load deflection criteria. Live load deflections of single cell culverts are compared with
the clear span divided by either 800 or 1000. The user can also define their own criteria by selecting
‘User Defined’.
Slenderness
Select Check Slenderness and input a K Factor to have the analysis perform a slenderness check.
Structural Analysis Modeling
Use Haunches in Top Slabs
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If this option is selected then the stiffness of the haunches (if any) are incorporated into the
structural model at the ends of the top and bottom slabs. This will cause a redistribution of the
top and bottom slab moments from the center to the ends. Also, if you are using the ASTM
charts to select your steel, you will need to use this option to match the model used to create the
charts.
Use Haunches in Walls
If this option is selected then the stiffness of the haunches (if any) are incorporated into the
structural model at the top and bottom of the exterior walls. This will cause a redistribution of the
wall moments mid-height to the top and bottom of the walls. This modification is not applied to
the interior wall (if any) as it has little to no effect on the structural analysis. Also, if you are using
the ASTM charts to select your steel, you will need to use this option to match the model used to
create the charts.
Support Fixity (3-sided only)
Here the user has 2 or 3 options for the support boundary conditions used in the structural model.
The first two options are pinned/pinned and pinned/roller. The pinned/pinned condition is the
default, and is the most common type of construction for precast culverts.
If your 3-sided culvert has a span to depth ratio exceeding 4 to 1, we recommend that you
investigate the support condition using a pinned/roller model, in addition to the default support
condition of pinned/pinned. When you select this option, the program places a roller at the left
support, and a pin at the right support, which will cause the shear and moment to be removed
from the walls. Field observations have shown that large span to depth ratios may result in
potential lateral translation of supports, resulting in larger top slab positive moments than are
predicted using a pinned/pinned support model. Additional top slab tension reinforcement is
necessary for these larger bending moments to mitigate tension cracking on the underside of the
top slab. Note that the shear and moment diagrams are symmetrical regardless of which support
model you select.
For cast-in-place 3-sided culverts, there will be a third support condition available, that of
fixed/fixed.
Critical Section
Consider Haunches
Select this option to have haunches considered in the selection of the location of the critical
section. If haunches are specified and this is checked then the program will design the member
using moment and shear values beyond the face of support in accordance with whether or not the
user has selected to extend the critical section (see below). If this is not checked then the
program will design the member using moment values at the face of the intersecting members
and shear values at the dv (or d for STND) from the face of the intersecting members regardless
of the specified haunch lengths. This will provide a more conservative design.
Extend Critical Section
If haunches are specified and this option is checked then the program will position the critical
section for shear at a distance of dv(d) beyond the end of the haunch. If left unchecked, then the
critical section for shear will be placed at a distance of dv(d) from the face of the intersecting
member. For flexure, if this option is selected, then the critical section is located at the
intersection of the haunch and the constant depth member (basically the end of the haunch). If
unchecked, then the critical section for flexure is taken at the point at which the depth of the slab
plus haunch is 1.5 times the depth of the slab.
Note that if this option is selected, the user is assuming that the face of support is located at the
end of the haunch. This extension will only be applied to haunches that form an angle of less
than 45 degrees to the supporting face.
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Use Max Moment w/ Max Shear
The shear analysis will either use the maximum moment or the corresponding moment. If
checked, the maximum moment at the face of the wall will be used in the interaction between Vu
and Mu to calculate the shear capacity of the member. If unchecked, the moment at the critical
section for shear will be used instead.
Use Haunches for Flexure and Shear
By default the haunch is only used to position the critical section, although the haunch may also
be used to stiffen the corners of the structural model. By selecting this option, the user may also
direct the program to use the haunches in the calculation of the flexural and shear resistance.
Flexure
Use Eq. 12.10.4.2.4a-1
If checked, the flexural moment capacity is calculated using LRFD Eq. 12.10.4.2.4a-1. The
program applies a factor to the Nu term in the equation, thereby allowing the user to ignore the
effects of axial thrust if desired. Note that this equation is modified in CHBDC. See the theory
section for the revised equation.
Ignore Axial Thrust
If unchecked, the flexural moment capacity is taken from a location (based on the applied P) on a
P-M diagram built internally by the analysis routine for AASHTO Codes. If checked, the flexural
moment capacity is set to where the P-M diagram crosses the horizontal axis (P = 0), causing Ma
(allowable) to be equal to Mu (pure flexure) in the printout. Also if checked, the variable phi will
not be calculated under LRFD, and will be set to that which the user has input on the Load and
Resistance Factors page.
Shear
Always Check Iterative Beta
If checked, the program will calculate the shear capacity of the concrete using the iterative beta
method in LRFD Appendix B5. This value is then compared to the shear capacity already
calculated using the internal decision table (see Section 5.7) and the larger of the two values is
used for the current member.
Use LRFD 5.14.5.3
If checked, the program will calculate the shear capacity of the top slab of a 3-sided culvert with
more than 2 foot of fill using LRFD 5.14.5.3, which is usually only used in 4-sided culverts.
However, some states allow this provision to be used for 3-sided culverts as well.
Environmental
Apply Environmental Durability Factors
If checked, the program will calculate the and apply the environmental durability factors (as
defined in ACI-350) to the flexural demand.
Exposure
Select the appropriate exposure option for your design, the options are ‘normal’ and ‘severe’. This
is used in computing the environmental durability factors, defined in ACI-350.
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Reinforcement
Screen 3-16(Design Mode - Rebar)
In Design Mode only the reinforcement type can be changed. Select either Rebar or Mesh. If you
select Mesh then select either Smooth (W) or Deformed (D) mesh. You can only switch the
reinforcement type when the program is in Design Mode. This is to allow the program to properly fill
the internal reinforcement schedule.
For the calculation of longitudinal steel in Design Mode, the user has three options. If they select to
follow the specifications for this area, then the program will use a decision tree that is based on the
governing specification. If they choose to always use the percentage of the cross section area, then
the program will ignore shrinkage and temperature steel and only calculate the area of the
longitudinal steel based on a percentage of the cross-section area. Finally, they have the option of
always using the shrinkage/temperature steel, which forces the program to calculate and use the
shrinkage and temperature steel area for longitudinal steel.
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Screen 3-17(Design Mode - Mesh)
If the user selects mesh, there are additional options available that will determine what line wires and
cross wires the program selects. The user can select either a 2 sheet or a 4 sheet configuration for
both the interior and exterior sheets. The graphic below displays these layouts. Note that for the 4
sheet layout, the user also has the option of no laps for the inner cage (similar to the rebar layout for
the inner cage).
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The most common configuration is a 2-sheet layout with wall laps for the interior sheets, and a 2sheet layout with slab laps for the exterior sheets. In general, you should not put laps in tension
zones, although this is not a code requirement.
For both mesh and rebar, the user has the option of assigning a minimum base reinforcement for
both flexural and longitudinal steel. This was added to allow users to follow the provisions of the 7th
Edition of LRFD where a minimum steel provision has been added for both directions and both the
interior and exterior faces. In addition, the user also has the option of using the same calculated
minimum reinforcement in each face by checking the ‘Maximize’ box. If this option is left unchecked,
then the calculated (or assigned) minimum reinforcement is distributed evenly between each face
(i.e., ½ of the minimum reinforcement is placed in each face). Finally, the user also has the option of
using the individual member thicknesses (or not) to calculate the minimum steel. If this option is
checked, the program uses the individual member thicknesses to calculate minimum steel, otherwise
the program uses the largest thickness of all members.
Screen 3-18 (Analysis Mode - Rebar)
When operating in Analysis Mode only the reinforcement can be edited. The user can edit the bar or
wire size and spacing for each group of bars as defined by location within the culvert. If using mesh
reinforcement then you can set the number of levels to one or two for many of the mesh locations. To
switch reinforcement types you must first change the program mode to Design Mode.
User Defined Longitudinal Steel
Check this to be able to edit the bar or wire size and spacing for longitudinal steel. If this box is
checked then the analysis will not design the longitudinal steel but will instead use the values defined
in the grid. If not checked, then the program will calculate the longitudinal steel based on the options
previously discussed under Design Mode.
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Screen 3-19 (Analysis Mode - Mesh)
For mesh users operating in analysis mode, you have a range of inputs available. Note that the A
and B marks are always line wires, while the C marks are cross wires. In addition, the base wires
extend the full length of the sheets, while the nested zones and adder sheets are only present in
specific locations. See the graphic below.
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The nesting zones are treated in Eriksson Culvert as additional line wires spaced between the base
line wires, while adder sheets are separate small sheets that are in addition to the base sheets, and
are connected with only a few cross wires.
Shear Steel
Screen 3-20
Check Include Shear Steel to include shear steel in the culvert. The shear steel must be designed by
the user. The shear steel is defined for four areas: the top slab exterior cells, the bottom slab exterior
cells, the top slab interior cells, and the bottom slab interior cells.
To define the shear steel zones for any area first set the number of zones. Then for each zone input
the area of steel (in2/ft) and the length for that zone. The distance from the left end of the area to the
start and end of the zone will be automatically calculated and shown. Zones cannot extend past the
end of the clear span. The length of the clear span is shown at the top right.
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Shear steel can be added by the user to reduce the slab thickness. Even though you may define
shear steel in both Design and Analysis modes, the program will only include the effects of shear
steel in Analysis Mode. In Design Mode, the members thicknesses will be determining assuming
that the concrete alone will resist the applied shear. Slab thickness reduction, if possible, may be
investigated in Analysis Mode.
Reinforcement Size/Spacing Library
Screen 3-21
The Reinforcement Size/Spacing pairs dialog box allows the user to modify the reinforcement
sizes/spacing pairs for both rebar and mesh used internally in the design algorithm. Click the
‘Include’ column to include/exclude a bar or wire size. To input or edit spacings, click on any row to
display the current spacing for that bar or wire size. When editing spacings, the list to the right will be
automatically updated and sorted from smallest area/unit width to largest.
Reinforcement Type
Allows the user the option of viewing and modifying the size/spacing pairs in US Customary or Metric
units. This does not change the reinforcement type used in Eriksson Culvert – this can only be
changed on the Reinforcement dialog box.
Units
Allows the user the option of viewing and modifying the size/spacing pairs in US Customary or Metric
units.
Add/Delete Wire
When editing mesh, you can add or delete wires in the first list by clicking the add wire or delete wire
buttons. This will allow the user to add intermediate wire sizes that are not in the default list.
Save
This button takes the user to a standard Windows save dialog box where they will be able to save the
reinforcement size/spacing pairs configuration for future use. Note that the program stores all
reinforcement types into the same library file (rebar and mesh).
Open
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This button takes the user to a standard Window open file dialog box where they will be able to select
and import a previously saved reinforcement size/spacing pairs configuration.
Cancel
Exit this window and discard any changes.
Okay
Exit and use the reinforcement size/spacing pairs as defined in this window.
Tip: For mesh users, if you want the design algorithm to properly accommodate nested line wires,
you should not use spacings of less than 4 inches
Vehicle Library
Screen 3-22
Selecting the Libraries|Vehicles menu option displays the input window shown above. This is the
same library screen as is accessed via the Moving Loads input window. However, here you can
create a new truck or edit an existing truck using the ‘New Truck’ and ‘Edit Truck’ buttons. Both
options will take you to the vehicle properties screen, where you can create a new truck or edit an
existing truck, and then save it back to the library.
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Retaining Walls
Eriksson Culvert now contains a module to assist in the design of wing walls, which are designed as
retaining walls:
Screen 3-23
This new window is comprised of three panes. The left hand pane contains four input tabs, the center
pane contains two output tabs, and the right hand pane contains the design summary and report
navigation tree.
Project Tab
Screen 3-24
Properties
Name
Input a name for the retaining wall. This is for your information only, and is only used for the text
report.
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Date
Input a date for the retaining wall. This is for your information only, and is only used for the text
report.
Description
Input a description for the retaining wall. This is for your information only, and is only used for the
text report.
Analysis Options
Backfill Lateral Earth Pressure Theory
Choose a lateral earth pressure theory to use. The options are explained in the theory section.
Include Bearing Pressure
Indicates whether the bearing pressure should be included in the analysis as a force. This will be
represented as a distributed load acting on the footing.
Include Sliding Pressure
Indicates whether the sliding stress should be included in the analysis as a force. This will be
represented as a distributed horizontal load acting on the bottom of the footing.
Properties Tab
Screen 3-25
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Stem
Height
The height of the stem measured from the surface of the backfill.
Thickness
The thickness of the stem at the top of the retaining wall.
Change in Toe
The total tapering amount of the toe, measured at the base of the stem.
Change in Heel
The total tapering amount of the heel, measured at the base of the stem.
Footing
Thickness
The thickness of the footing.
Toe Length
The length of the toe. Measured from the base of the stem.
Heel Length
The length of the heel. Measured from the base of the stem.
Soil
Depth Backfill
The depth of the backfill. Measured from the surface of the base subgrade.
Slope Backfill
The slope of the backfill surface.
Concrete
Unit Weight
The unit weight of the retaining wall concrete.
Elastic Modulus
The elastic modulus of the concrete.
Sliding Friction Angle
The angle of friction between the retaining wall and the concrete
Backfill
Friction Angle
The angle of internal friction of the backfill soil.
Dry Unit Weight
The dry unit weight of the backfill soil.
System
Length of Wall
The total length of the wall.
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Reinforcement Tab
Screen 3-26
Reinforcement List
Displays a list of all available reinforcement types supported by the retaining wall analysis. These
include US Customary, Soft Metric, and Canadian. Currently the retaining wall analysis only supports
rebar.
Reinforcement Type
Separate input pages are available, one for the flexural steel, and one for the shrinkage and
temperature steel. Both pages are identical in the input available to the user.
Auto Design Reinforcement
The selection of this option will tell the program to automatically design the rebar size spacing pairs
for the given reinforcement. It will automatically set the cover of the flexural steel to 3 inches.
Reinforcement Parameters
Cover
The cover of the reinforcement for the selected area.
Bar Size
A drop down box of available bar sizes.
Bar Spacing
The spacing of the bars.
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Surcharge Tab
Screen 3-27
New
Expands the input to allow the definition of a new surcharge load.
Edit
Expands the input to allow for editing of the currently selected surcharge load in the list.
Delete
Deletes the currently selected surcharge load.
New Surcharge
Screen 3-28
The interface for the input of a new surcharge load. These loads are assumed to be uniform loads.
Load Type
A drop down box for selecting the type of load. Either ES (a permanent earth surcharge load) or
LS (a transient live load).
Load Magnitude
The magnitude of the surcharge load. Assumes positive is downward.
Edit Surcharge
Screen 3-29
An interface for editing the selected surcharge.
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Visualization Tab
Screen 3-30
Provides a sketch of the retaining wall. This sketch will be automatically updated as you change the
dimensions.
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Report Tab
Screen 3-31
Provides a text report of the summary inputs and the results. To print the report press Ctrl+P.
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Summary and Navigation Pane
Screen 3-32
Provides as a summary of the design (green pass and red fail) and serves as links to jump to the
corresponding section in the report.
When the Visualization tab is active, the summary pane contains an additional box at the bottom to
allow the user to turn on and off various parts of the sketch.
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Strip Footings
Eriksson Culvert now contains a module to assist in the design of strip footings. Pressing the footing
icon on the tool bar brings up the following window:
Screen 3-33
This new window is comprised of three panes. The left hand pane contains four input tabs, the center
pane contains two output tabs, and the right hand pane contains the design summary and report
navigation tree.
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Project Tab
Screen 3-34
Properties
Name
Input a name for the strip footing. This is for your information only, and is only used for the text
report.
Date
Input a date for the strip footing. This is for your information only, and is only used for the text
report.
Task
Input a task for the strip footing. This is for your information only, and is only used for the text
report.
Client
Input a client for the strip footing. This is for your information only, and is only used for the text
report.
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Job Number
Input a job number for the strip footing. This is for your information only, and is only used for the
text report
Description
Input a description for the strip footing. This is for your information only, and is only used for the
text report.
Analysis Options
Include Pedestal
Check if the strip footing contains a pedestal which the wall sits on.
Subgrade Soil Type
Selected the type of soil the subgrade sits on (changes bearing pressure calculation).
Load and Resistance Factors
Load Factors
Inputs to allow manual override of the load factors
Resistance Factors
Inputs to allow manual override of the resistance factors
Properties Tab
Screen 3-35
Physical Dimensions
Wall Thickness
The width of the keyway on the top of the strip footing.
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Pedestal Width
The width of the pedestal.
Pedestal Height
The height of the pedestal.
Slab Width
The width of the strip footing.
Slab Thickness
The thickness of the strip footing.
Slab Length
The total length of the strip footing.
Concrete Properties
Weight
The unit weight of the concrete.
Strength
The compressive strength of the concrete.
Elastic Modulus
The elastic modulus of the concrete.
Aggregate Size
The aggregate size of the concrete.
Soil Properties
Weight
The unit weight of the soil.
Bearing Strength
The bearing strength of the soil.
Inner Fill
The inner fill height of the footing.
Outer Fill
The outer fill height of the footing.
Sliding Friction Angle
The angle of friction between the footing and the subgrade.
Reinforcement Properties
Yield
The yield strength of the reinforcement.
Elastic Modulus
The elastic modulus of the reinforcement.
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Reinforcement Tab
Screen 3-36
Reinforcement Type
Two options which choose whether to use rebar or mesh for reinforcement.
Rebar / Mesh Type
Displays a list of all available reinforcement types supported by the strip footing analysis. These
include US Customary, Soft Metric, and Canadian.
Flexure Reinforcement
Auto Design
If checked Eriksson Culvert will pick a bar size and spacing from the reinforcement library
Bottom Long. Reinforcement
Bar Size
The bar size of the reinforcement for the selected area.
Spacing
The spacing of the reinforcement for the selected area.
Cover
The cover of the reinforcement for the selected area.
View Reinforcement Library
Click to access the size/spacing pairs library available in Eriksson Culvert.
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Loading Tab
Screen 3-37
Loading Conditions
Contains to drop down boxes which contain all of the truck/fill depth combinations from Eriksson
Culvert.
Add
Expands the input to allow the definition of a new load.
Edit
Expands the input to allow for editing of the currently selected load in the list.
Delete
Deletes the currently selected load.
New Load Case
Screen 3-38
The interface for the input of a new load. These loads are assumed to be point loads acting at the
center of the strip footing on the top surface.
Load Type
A drop down box for selecting the type of load.
X Component
The x-component of the applied load.
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Y Component
The y-component of the applied load.
Edit Load Case
Screen 3-39
An interface for editing the selected load.
Visualization Tab
Screen 3-40
Provides a sketch of the strip footing. This sketch will be automatically updated as you change the
dimensions.
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Report Tab
Screen 3-41
Provides a text report of the summary inputs and the results. To print the report press Ctrl+P (or
press File|Print).
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Summary and Navigation Pane
Screen 3-42
Provides as a summary of the design (green pass and red fail) and serves as links to jump to the
corresponding section in the report.
User Options
Screen 3-43
Eriksson Culvert Reinforcement Library Files Location
Displays the folder used for storing Eriksson Culvert vehicle library files. This is the initial folder
accessed in the Vehicle Library dialog. This folder defaults to the "Eriksson Software\Eriksson
Culvert\Live Load Library" folder in the user's Documents folder. Click the Browse button to change
the default folder.
Eriksson Culvert Live Load Configuration Library Files Location
Displays the folder used for storing Eriksson Culvert vehicle library files. This is the initial folder
accessed in the Vehicle Library dialog. This folder defaults to the "Eriksson Software\Eriksson
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Culvert\Reinforcement Library" folder in the user's Documents folder. Click the Browse button to
change the default folder.
Eriksson Culvert Vehicle Library Files Location
Displays the folder used for storing Eriksson Culvert vehicle library files. This is the initial folder
accessed in the Vehicle Library dialog. This folder defaults to the "Eriksson Software\Eriksson
Culvert\Vehicle Library" folder in the user's Documents folder. Click the Browse button to change the
default folder.
Default Settings
Here you can set the default units and user initials. These will be set for each new project file, but will
not affect existing data files.
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4 Getting Results
4.1
Output Options
Output can be obtained from three places:
1. Tabbed Views
2. Printer
3. Status Bar
4.2
Views
There are five distinct views:
1.
2.
3.
4.
5.
Main View
Text Report
Results Graphs
3D Rendering
Results Grid
Main View
The main view displays a limited set of input, along with the reinforcement schedule and several
reinforcement views.
Screen 4-1
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Text Report
The text report contains a reprint of all of the input data, along with detailed design or analysis results.
Screen 4-2
There are two panes on the right hand side of this window. The navigation pane, which is always
visible, allow the user to both navigate quickly to a specific point in the report, and to adjust which
portions of the text report will be displayed.
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Screen 4-3
The second pane is only visible where there are asterisks in the report. The text report flags design
deficiencies by use of asterisks. This second pane contains a list of every point in the report where
this is an asterisk. You can navigate to each place by simply clicking on a line in this pane.
Screen 4-4
The user can export the text report to a text file by selecting Export Text Report from the File menu.
Tip: You can increase or decrease the text size in the text report by using a combination of the
control key and the mouse wheel.
Results Graphs
Multiple graphs available for moment, shear, and axial force diagrams in all members for all load
types.
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Screen 4-5
3D Rendering
The culvert under design can be rendered in 3D. Eriksson Culvert utilizes a sophisticated, true 3D
graphical rendering window. State-of-the-art OpenGL graphics are incorporated directly into Eriksson
Culvert.
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86
Screen 4-6
Reset View
Click one of the four buttons to reset the view to Elevation (Front), Plan (Top), Side (Right), or Top
Right. This feature is helpful if you have panned the view away from the culvert so that it is no longer
visible and you wish to quickly bring it back into view.
Visible Items
Select from the list of visible items to turn them on or off in the view.
Mouse Controls
The 3D view is a live view, which means that it can be rotated, panned and zoomed using the mouse.
The mouse controls are present in the upper center of the viewing screen. Click on the controls (from
left to right) to perform the following actions: Zoom Window, Zoom, Pan, Rotate, and Zoom Fit. To
quickly rotate the drawing to show specific faces or edges click on the cube in the upper right hand
corner.
Results Grid
Screen 4-7
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87
The Results Grid is accessed from the Results menu. The Results Grid shows the same data as the
Results Graph (and some data not shown in the Results Graph) but shows the raw data in a grid. The
user can select the Member and Load Type data to be shown. If using a range of fill depths than the
user can also select the fill depth. The grid will show the Location along the member, the moment(s),
shear(s), and axial force(s).
This data can be copied to the clipboard to be pasted into any application that also uses the clipboard
like a spreadsheet. Use the mouse to select a range of cells to copy, then press Ctrl+C.
4.3
Printing
You can print the current results of your design at anytime. To print, select Print from the File menu
or click the printer icon. The Print dialog box that corresponds to the active window will appear.
Screen 4-8
Print
The Print dialog box permits you to specify which printer currently configured on your system you
want to send the results to. You can also preview this output by selecting Print Preview.
4.4
Status Bar
Screen 4-9
The status bar is comprised of two panes. The leftmost pane contains the current program operating
mode, Design or Analysis. The rightmost pane contains the current specification.
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5 Engineering Theory
5.1
Supported Specifications
Eriksson Culvert supports the AASHTO LRFD Specifications and the AASHTO Standard
Specifications for Highway Bridges, along with the AREMA and CHBCD Specifications. The following
specific versions are supported:
Supported Specification
LRFD Specifications
Standard Specifications
AREMA Specification
CHBDC Specifications
Edition/Interim
5th edition (published in 2010)
6th edition (published in 2012)
2013 Interims to the 6th Edition
7th Edition (published in 2014)
2015 and 2016 Interims to the 7th Edition
8th Edition (published in 2017)
17th edition (published in 2002)
2010 edition (published in 2010)
CSA-S6-06 edition (including all 3 Supplements)
The selected design specification can be freely changed during the design process. Access to the
specifications type is provided in the Project Settings dialog box. When the specifications are
changed, design parameters that are specification-dependent and which have been designated as
“automatic” (e.g., load and resistance factors) will be automatically updated to reflect the particular
design specifications selected. As a result, it is recommended that when the governing type of
specifications is switched, the input data and results be carefully reviewed to understand the full
extent of the changes.
The AREMA Specifications are mostly identical to the STND Specifications. We will only point out the
differences between those two specifications in this section. Also, any reference to LRFD will
generally mean all of the LRFD specifications listed above. If any of the LRFD specs differ, this will
be noted.
5.2
Material Properties
Lightweight Concrete
Concrete type can be normal weight, sand lightweight, or all lightweight (in CHBDC, these categories
are referred to as normal-density, semi-low density and low density). The LRFD Specs define
lightweight concrete as having an air-dry density not exceeding 0.120 kcf. However, it is up to the
user to explicitly designate a concrete type as lightweight in the Materials Properties page of the
Culvert Properties dialog box. Note that this has changed in the 7th Edition. Now the program will
select either Normal Weight or Lightweight depending on the assigned unit weight (the user may not
assign concrete types). For unit weights greater than or equal to 135 pcf, the program will treat the
concrete as Normal Weight. For unit weights less than 135 pcf, the program will treat the concrete as
Lightweight. In addition to weight calculations, designating a concrete type as lightweight will
influence three other areas of the calculations:
1. Modulus of rupture
2. Resistance factor for shear
3. Tensile and shear capacity of concrete
(LRFD 5.4.2.6)
(LRFD 5.5.4.2)
(LRFD 5.8.2.2)
The following moduli of rupture are computed by Eriksson Culvert:
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Condition
Normal wt. concrete, minimum reinforcement
Normal wt. concrete, minimum reinforcement
Sand-lightweight concrete
All-lightweight concrete
All concrete types
Normal-density concrete
Semi-low-density concrete
Low-density concrete
fr (ksi)
0.37√f’c (5th Edition)
0.24√f’c
0.20√f’c
0.17√f’c
0.24√f’c (7th Edition)
0.40√f’c (CHBDC)
0.34√f’c (CHBDC)
0.30√f’c (CHBDC)
For normal weight concrete, the resistance factor for shear, φv, is 0.90. For both types of lightweight
concrete φv is set to 0.70, but has been increased to 0.80 in the 6th Edition, and to 0.90 in the 7th
Edition. For CHBDC, φs (steel) is 0.90, and φc (concrete) is 0.80.
In accordance with LRFD Article 5.8.2.2, if lightweight concrete is specified, all occurrences of the
term “√f’c” within LRFD Articles 5.8.2 and 5.8.3 are modified by the following factors:
Concrete Type
Normal weight
Sand-lightweight
All-lightweight
Factor
1.00
0.85
0.75
Modulus of Elasticity
The modulus of elasticity of the culvert concrete are computed by default using the following
equations:
E c = 33,000 w 1c.5 f c'
(LRFD 5.4.2.4-1)
Ec = 120,000 wc2.0 f c'0.33
(LRFD 5.4.2.4-1, 7th Edition)
(CHBDC 8.4.1.7)
where, wc, γc = unit weight (i.e., density) of concrete
f’c = specified concrete strength
The user can of course override the program calculation of this value. Further discussion of other
materials properties is included under the appropriate sections within this chapter of the user manual.
5.3
Structural Model
The method of analysis is the displacement or stiffness method. The structure is represented by a
matrix consisting of member stiffnesses. These are derived for three possible movements at the
ends of members: vertical, horizontal, and rotational. The following boundary conditions are then
applied to the matrix for a box culvert:
No vertical displacement at the outside ends of the bottom slab.
No lateral displacement at the right end of the bottom slab.
For a three sided culvert the following boundary conditions are applied to the matrix:
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No vertical or lateral displacement at the bottom of both walls.
An optional roller (which allows lateral displacement only) may be placed at the bottom of the
left wall.
Figure 5-1: Structural idealization models for a box and three sided culvert.
Additionally, hinges in the walls for type 1 and 2 culverts are modeled as pin connections.
Figure 5-2: Structural model for a type 2 culvert
Figure 15-3: Structural model for a type 1 culvert with joints located at the top of the wall
Through matrix manipulation, the true displacements at the ends of each member are computed for
each given loading condition. Then the exact end moments and forces are determined using the
computed displacements. These moments and forces are used to develop stresses, proportion
reinforcement, or alter member depth. If member depth is altered, its effect is reevaluated in the
above manner.
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The length of each member for analysis purposes will be from centerline to centerline of the
supporting members. Moments at the geometric centers of members, moments at faces of support or
moments within and at the ends of fillets (haunches) built monolithic with the member and support
may be selected for member design.
It is assumed that loading applied to the top slab will be uniformly distributed over the whole bottom
slab. This is a reasonable assumption since a mat of granular material is usually placed beneath the
bottom slab for the culvert to lay on. More refined assumption appears impractical due to the lack of
precise soil information for each site.
Analysis results are reported for the each member at 10th points along the member, measured from
centerline of supporting member to centerline of supporting member. Eriksson Culvert provides two
methods of presenting numerical results: graphs and text reports.
5.4
Applied Loads
Vertical Loads
The Dead Load on the top slab consists of soil weight plus the weight of the concrete slab. The
program is capable of analyzing additional uniform dead load as well as accepting up to three (3)
extra concentrated dead loads.
The program complies with STND Articles 16.6.4.2 and 16.7.4.2 (Modification of Earth Loads for Soil
Structure Interaction) for embankment installations (see also LRFD 12.11.2.2). These Articles state
that the earth loads described in STND Article 6.2 may be used if they are multiplied by a soilstructure interaction factor, Fe, that accounts for the type and condition of installation.
The soil-structure interaction factor, Fe, is not applicable if the Service Load Design Method is used.
For CHBDC, the program uses the Vertical Arching Factor from Table 13 in Section 7.8.4.2.3, which
depends on the installation type, B1 or B2.
Horizontal Soil Pressures
The program will not only investigate the maximum lateral earth pressure but will also investigate the
minimum lateral earth pressure acting on the outside walls. This is an AASHTO loading condition to
check for maximum positive moments in the top and bottom slabs. For STND and LRFD, the
program used an equivalent fluid pressure method to calculate the horizontal soil pressure, not the
soil weight. For AREMA, the program uses the soil weight multiplied by the minimum and maximum
lateral pressure coefficients. For CHBDC, the program uses the unit weight of the soil in conjunction
with the Horizontal Arching Factors from Table 7.11, again depending on the installation type.
Internal Water Pressure
Water pressure inside the culvert barrel can reverse the wall moments and add to slab positive
moments and may be checked. The program is able to use full height of water pressure and no water
pressure as two loading cases. Internal water pressure is taken as 62.4 pcf.
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Figure 5-2: Typical static loads applied to a culvert under design
Load Combinations
Load combinations are created based on code requirements. Generally, they are broadly grouped
into service and strength categories.
Service Combinations
Service combinations are primarily for the Service Load Design Method and for serviceability checks
Strength Combinations
Strength combinations are checked for shear and flexural strength.
For STND and AREMA, we only have one load combination to check:
Loading = 1.3(DL) + 2.17(L+I)
Loading = 1.4(DL) + 2.33(L+I)
(STND)
(AREMA)
In the above equation, DL includes concrete, soil and water dead loads.
For LRFD, we check three load combinations:
For maximum vertical load on the roof and maximum outward load on the walls,
DCmax + DWmax + EVmax + EHmin + (LL+IM)max + WAmax.
For minimum vertical load on the roof and maximum inward load on the walls,
DCmin + DWmin + EVmin + EHmax + LSmax
For maximum vertical load on the roof and maximum inward load on the walls,
DCmax + DWmax + EVmax + EHmax + LSmax + (LL+IM)max
For CHBDC, we check five load combinations:
For maximum vertical load on the roof and minimum horizontal inward on the walls,
DCmax + DWmax + EVmax + (LL+IM)max + EHmin + WAmax
For maximum vertical on the roof and maximum horizontal inward on the walls,
DCmax + DWmax + EVmax + (LL+IM)max + EHmax + WAmin
For minimum vertical on the roof and maximum horizontal inward on the walls,
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DCmin + DWmin + EVmin + EHmax + WAmin
For maximum vertical on the roof and maximum horizontal inward on the walls,
DCmax + DWmax + EVmax + LSmax + EHmax + WAmin
For minimum vertical on the roof and maximum horizontal inward on the walls,
DCmin + DWmin + EVmin + LSmax + EHmax + WAmin
5.5
Live Load
The live load vehicle definition of Eriksson Culvert is very flexible and therefore very powerful. It
permits most load types encountered in highway and railroad bridge design to be modeled. Several
predefined vehicle types are included as default trucks in the vehicle library. The primary vehicle
types for all specifications are discussed below:
H and HS Loadings
Eriksson Culvert can model all H and HS loadings. These vehicles consist of an axle load portion or a
lane load portion. The axle load portion of the H series consists of a pair of axles that are fixed in
spacing. However, the HS series axle load consists of three axles: the front pair of axles is fixed and
the rear pair is variable in spacing.
Separate analyses are performed for the axle load and lane load analyses. The results of each
analysis are compared for moment and shear at each location under consideration along the
structure and the governing value is adopted.
HL-93 Load
The HL-93 load consists of the following three distinct parts, as defined in Art. 3.6.1.2 of the LRFD
Specifications:



Design Truck: Three axles of 8 kips, 32 kips, and 32 kips spaced a 14 (fixed) between the front
axles and variable between 14 and 30 ft between the rear axles.
Design Lane: Uniform load of 0.64 klf.
Design Tandem: Pair of 25-kip axles spaced at 4 ft (fixed).
As with all vehicles, separate analyses are performed for each vehicle component. However, what
distinguishes a live load analysis performed under the LRFD Specifications as compared to the
Standards Specifications is the manner in which the components are combined. Under LRFD, the
results of the design truck are compared to the results of the design tandem, and the governing
values are adopted. These combined results are then added to the results of the lane load analysis.
Note that whether the results of the truck analysis and the lane load analysis are to be combined in
an “AND” or an “OR” fashion is specified by clicking the respective radio button in the Combine group
at the bottom of the Vehicle Properties dialog box.
Live Load may be neglected when the depth of fill is greater than or equal to 8 feet, and exceeds the
span length of a single culvert, or exceeds the total width of multiple culverts. Additionally the lane
load may be turned off, as lane loads are typically not applied to many types of buried structures.
Cooper E80 Load
As per AREMA 2.2.3, the recommended live load for each track the Cooper E80 loading with no lane
or tandem load. The longitudinal distribution of the axle loads are to be limited by the axle spacing.
The transverse distribution of the axles loads are to be limited by the extent of the structure. The
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94
program assumes only one track on a structure, and the direction of the track must be placed parallel
to the main reinforcement.
CL-625/CL-625-ONT Load
Per CHBDC 7.8.4.3, the live load shall be the trucks in Section 3, and shall include the dynamic load
analysis as specified in Section 3.8.4.5.2. The truck definition file shipped with the program includes
one large axle (Axle 4), and 2 smaller axles in the tandem (Axles 2 and 3). Of course, the user may
define their own CHBDC truck that includes all of the axles.
Fill Depths < 2 Feet
When the culvert has traffic running directly on the top slab, wheel loads are distributed as in ordinary
bridges. This is also done when the height of fill on the culvert is less than 2 feet.
When the traffic direction is parallel to the main reinforcement, the program will distribute wheel loads
over a slab width, E, equal to 4 + 0.06S, where S is the perpendicular distance between wall
centerlines. See STND 3.24.3.2. For LRFD, the equation is the same (see 4.6.2.10.2), but here S is
defined as equal to the clear span. Note that the program calculates this width for one wheel only, for
both STND and LRFD. Also, note that the program will only use one traffic lane, with the appropriate
MPF. For CHBDC, we use the same live load distribution as is found in the 6th Edition of LRFD.
When the traffic direction is perpendicular to the main reinforcement, the program calculates a
distribution length based on the desired specification, and then places as many axles as possible on
this width. Again, this distribution width may be limited by the culvert length. Additionally, more than
one lane may be placed on the culvert, depending on the magnitude of the clear span. Due to
complex placement of wheel loads for the perpendicular case specified in the AASHTO specification
each lane is assumed to be 10 feet wide. This conservative assumption may result in increased
flexural and shear demands on the structure depending on the clear span. For example Figure 5-3
shows the maximum live load distribution used in Eriksson Culvert for a 40 foot clear span when the
number of lanes is allowed to be computed by the program. However, if the user feels that this is too
conservative, they may limit the number of lanes placed on the culvert in the Loads dialog box.
Figure 5-3: Live load distribution for perpendicular traffic travel
The user may elect to not limit the distribution width to the culvert length. In this case, the user is
responsible to insure proper shear transfer between adjacent culvert sections. Note that in STND
there is an absolute limit of 7 feet for the distribution width. This absolute limit cannot be overridden
by the user.
Fill Depths >= 2 Feet
When the height of fill is greater than or equal to 2 feet, wheel loads are distributed over areas having
sides equal to 1.75 (for STND and CHBDC), and 1.15 for LRFD, times the depth of fill. This is
outlined in STND 6.4.1, CHBDC 6.9.6, and LRFD 3.6.1.2.6. When these wheel loads overlap, the
entire truck load is distributed over the length of the distributed truck. As with fill depths less than 2
feet, the user can force the program to limit the total width of distribution to a maximum of the
supporting slab, or they may allow the distribution width to be exceed the width of the supporting slab.
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Note, however, that limiting the distribution width equal to the width of the supporting slab may be
overly conservative, and in any case is not required by any of the specifications supported by
Eriksson Culvert.
The method of analysis is similar regardless of the traffic direction (with one exception, as noted
below). For all specifications, the program considers two, three and four adjacent vehicle lanes and
selects the critical case. Appropriate lane reduction percentages are used for the three and four lane
loading cases.
When the traffic direction is perpendicular, under the last paragraph of LRFD 3.6.1.2.6, if the live load
and impact moment, based on the distribution of the wheel load through earth fills, exceeds the live
load and impact moment calculated according to LRFD 4.6.2.10 (equivalent strip method for fills < 2
feet), the latter moment shall be used. Therefore, when the fill depth is greater than or equal to 2
feet, and the traffic direction is perpendicular, then Eriksson Culvert runs the moving live load analysis
twice, one with the assigned fill depth, and once with a fill depth equal to 0.
Live Load Distribution in AREMA
In AREMA, all fill depths are treated the same for live load distribution. The live load distribution
factor is taken as 1.0 for the transverse direction. For the longitudinal direction, the program assumes
that each axle load is distributed over a length of 5 feet.
In AREMA, the fill depth must be at least 18 inches in depth (AREMA 16.1.1).
Skew Effects
Both specifications mention the need to account for the effects of skews, but do not provide any
details for implementation. For STND, if the design span exceeds 6.0 / sin(θ), where θ is the skew
angle, the distribution width is reduced by multiplying the cosine of the skew angle for fill depths less
than 2 feet. Culverts with skews in excess of 60 degrees are designed for a skew of 60 degrees. For
LRFD, when the skew angle is greater than 15 degrees for all fill depths, the program places the
traffic lanes in the perpendicular direction. Note that these effects may be turned on and off via the
Analysis Options dialog box.
Live Load Surcharge
Live load surcharge is automatically applied by the program for fill heights less than 2 feet.
Surcharge should be applied by the user whenever the culvert is under live load influence for fills ≥ 2
feet. Surcharge need not be applied when live load may be neglected in accordance with AASHTO
Article 6.4.2.
Impact Factors/Dynamic Load Allowance
For STND, the Live Load Impact is in accordance with Article 3.8.2.3. For the LRFD Specs, a value
of 0.33 is assumed for the dynamic load allowance in accordance with LRFD Table 3.6.2.1-1. This
value is only applied to the wheel load component of the live load. For AREMA, the impact factor is
assumed to be 60% at a fill depth of 18 inches decreasing linearly to 0% at a fill depth of 10 feet, see
AREMA 16.4.4. For CHBDC, the dynamic load allowance for box type structures shall be the value
obtained from Section 3.8.4.5.3.
5.6
Flexural Strength
For both the LRFD and the STND Specifications, the following procedure is used to compute the
required area of steel at three critical sections of each member (left/bottom end, midpoint, and right
top end). At the ends of the member, the critical section for the following flexure calculations may be
taken at the face of the intersecting members, within a haunch (LRFD C5.7.3.2.1 and STND 8.8.2),
and at the toe of a 45 degree haunch (LRFD 12.11.4.2 and STND 16.7.4.5).
1)
Compute the loading using the code specified load factors (see Section 5.4 of this manual).
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A concrete stress of 0.85f’c will be assumed uniformly distributed over an equivalent
compression zone bounded by the edges of a cross section and a straight line located
parallel to the neutral axis at a distance a = Β1 (c) from the fiber of maximum compressive
strain.
2)
β1=0.85 or β 1 = 0.85
but
)
(
0.05 fc' 4000
for
1000
f c' greater than 4000 psi,
β1 cannot be less than 0.65
3)
No compression steel is considered and all tension steel is assumed to be in 1 layer
4)
Assume As
Set Ru =
[
0.85fc'
ρ=
M
φbd 2
]
 
1 − 1 − 2Ru
  0.85fc'
 




0 .5 



fy
ρb =
0.85 β 1fc' (87000 )
(
f y 87000 + f y
)
ρ ≤ 0.5 ρ b where ρ ≥ 0.002
Better economy is achieved when ρ = 0.5 ρ b instead of 0.75 ρ b
As = ρbd
5)
Compute Mu (Pure Flexure)

a 

M u = φ  As fs  d − 
2 


where:
As f y
a=
0.85fc' b
[
]
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and φ = 0.95 for 3-sided precast and φ = 1.0 for 4-sided precast
(note: under LRFD, phi is excluded in the above equation for Mu, as it is present in the P-M diagram)
Compute Po (Pure Compression)
6)
[
(
)
Po = φ 0.85f c' Ag − Ast + Ast f y
]
where:
Asy = As + As,min
and φ = 0.7
(note: under LRFD, phi is excluded in the above equation for Po, as it is present in the P-M diagram)
Standard Specification:
Compute Pb and Mb (Balanced Condition)
7)
(
Pb = φ 0.85fc' 12ab − As f y
)

T a
M b = Pb eb = φ 0.85fc' 12ab  − b
2 2


T 

 + As f y  d − 
2 


where:
0.003E s β 1d
and T = member thickness
ab =
0.003E s + f y
For slabs, phi = 0.85, for exterior walls, phi = 0.8, and for interior walls, phi = 0.7.
8)
Assume straight line relationship between pure compression and balanced condition and
balanced condition and pure flexure.
 M − Mu
M a =  b
Pb



Pa + M u for Pa < Pb

M a = M b for Pa = Pb
 P − Pa 
M b for Pa > Pb
M a =  o

 Po − Pb 
LRFD:
7)
Compute Pc and Mc (limit of compression controlled section, and Pt and Mt (limit of tension
controlled section). Here phi is variable, depending where on the P-M diagram you fall. For
the compression controlled area, phi is 0.75. For the tension controlled area, phi is 0.9. For
the transition zone, phi will vary between 0.75 and 0.9 (see LRFD Article 5.5.4.2.1).
Pc = 0.85 f c'bβ1 (
ε cu d s
) − As f y
ε cu + ε c
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ε cu d s  T β1 ε cu d s 
T

) − (
)  + As f y  d s − 
ε cu + ε c  2 2 ε cu + ε c 
2

ε d
PT = 0.85 f c'bβ1 ( cu s ) − As f y
ε cu + ε T
M c = 0.85 f c'bβ1 (
M T = 0.85 f c'bβ1 (
8)
ε cu d s  T β1 ε cu d s 
T

) − (
)  + As f y  d s − 
ε cu + ε T  2 2 ε cu + ε T 
2

Under LRFD, there are three parts to the P-M curve, that between pure compression and the
compression controlled limit, that between pure flexure and the tension controlled limit, and a
third line that transitions between the two limits. As with STND, a straight line is assumed
between major points on the curve.
 P − Pa 
M c for Pa > Pc
M a =  o

 Po − Pc 
M a = M c for Pa = Pc
 M − Mc 
(Pa − PT ) + M C for PT < Pa < Pc
M a =  T
 PT − Pc 
M a = MT for Pa = PT
 M − Mu
and M a =  T
PT


Pa + M u for Pa < PT

For both codes, the program then iterates until the allowable moment is greater than the applied
moment.
For both STND and LRFD, the user also has the option of using 12.10.4.2.4 to calculate the flexural
resistance using:
where g = 0.85 bf’c
For CHBDC, the above equation is modified as follows:
where g = αφc bf'c, and α = maximum (0.67, 0.85 - 100 / 1000 * f'c (psi))
Minimum Eccentricity
Minimum eccentricity is be checked for all members.
e=
M
P
If e is less than 1", then e is set equal to 1".
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If e is less than 0.1(T), then e is set equal to 0.1(T), where T = member thickness.
Slenderness
Slenderness is checked for walls only.
Kl
Slenderness may be neglected if
< 22 , where
r
K = 2.0, l = box culvert clear height, and r =
0.3T
12
Walls are designed using the factored axial load, Pu, and a magnified factored moment, Mc, defined
by:
M c = δM , where M = Design Moment
and
δ =
Cm
  Pu
1 − 
  φPc
Pc =
EI =




≥ 1.0 , where C m = 1.0 , and φ = 0.7
π 2 EI
(Kl )2
Ec Ig
[2.5(1 + β d )]
, where β d = Dead Load Moment / Maximum Total Moment
Deflections
The maximum live load deflection in the top slab is calculated for single cell boxes only. This live load
deflection is compared to the deflection limitation specified in the input and, if needed, the thickness
of the top slab is increased until the deflection criterion is met.
Maximum Steel
The STND Specification specifies that mild reinforced concrete members shall be designed so that
the reinforcement ratio shall not exceed 0.75 of the balanced reinforcement ratio (STND 8.16.3.1).
This approach is used for CHBDC as well.
LRFD uses a unified approach which is built into the P-M diagram.
Minimum Steel
Both STND and LRFD require that a sufficient amount of reinforcement be present in the culvert
element to develop a moment of 1.2 times the total moment required to crack the culvert element. If
the flexural resistance is at least 1/3 greater than that required by analysis, then this limit may be
ignored. Minimum flexural reinforcement (parallel to the span) is calculated as 0.002bh for all
specifications.
5.7
Shear Strength
Concrete Shear Strength
The shear stress (fv) is computed as follows:
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100
fv =
Vu
φbd
where b = 12 inches and Φ = 0.90
At the left end or right end of a member where sections are located less than a distance d from the
face of the support, they will be designed for the same shear, V, as that computed at a distance d.
For LRFD, substitute dv for d. Note that in LRFD C5.13.3.6.1 (2nd Paragraph), the design section may
be taken at a distance dv past the end of the haunch.
In the case of Vee-Bottom culverts, where the bottom slab is thickened at the walls to provide a “fish
bottom”, the appropriate additional thickness (at a distance d from the wall) is used to calculate the
shear capacity of the bottom slab. The bottom slab member is still assumed to be prismatic with a
thickness equal to that at mid-span for flexural design at all locations.
For the Standard Specifications, the allowable concrete shear stress is computed as follows:
For fill height less than 2 feet:
v c = 2 f 'c
or
Vud 
'
v c = 1.9 f ' c + 2500 ρ 
 ≤ 3 .5 f c
 M 
ρ = reinforcement ratio =
whichever is greater.
V d
As
and u ≤ 1.0
bd
M
For fill height greater than or equal to 2 feet (and AREMA):
V d 
v c = 2.14 f ' c + 4600 ρ  u  ≤ 4 fc'
 M 
with v c min = 3 f ' c
Per LRFD 5.14.5.3, the provisions of 5.8 apply to fill depths less than 2 feet for both the sidewalls and
the slabs. Eriksson Culvert calculates the shear resistance of the concrete using the simplified
approach as allowed in LRFD 5.8.3.3, and assumes a beta value of 2.0 (except when the member
thickness is greater than or equal to 16 inches, see below). This leads to the calculation of Vc and
Vc,max as follows (Vp is equal to zero as this is a non-prestressed member):
Vc = 0.0316 β f ' c bv d v
(LRFD Eq. 5.8.3.3-3)
Vc,max = 0.25f ' c bv d v + V p
(LRFD Eq. 5.8.3.3-2)
Where the member thickness is equal to or greater than 16 inches or the member is in tension, the
program uses the iterative approach in Appendix B5 for the calculation of beta used in Eq. 5.8.3.3-3,
due to the lack of transverse reinforcing assumed in the design algorithm. A value is assumed for
theta, which is used in Eq. B5.2-1. From this we can use Table B5.2-1 to look up a new value for
theta. This process is repeated until successive values for theta are approximately the same. Once
the calculations for theta have converged, theta is used in Table B5.2-1 to obtain a value for beta.
The proper selection of the governing provision in LRFD can summarized by the following flow chart:
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4-sided structure
Fill depth >= 2 feet
Use 5.14.5.3 for slabs
Use 5.8.3 for walls
If wall thickness >= 16” or member is in tension, use 5.8.3.4.2 (beta
calculated using App. B5)
If wall thickness < 16”, use 5.8.3.4.1 (beta is a constant 2.0)
Fill depth < 2 feet
Use 5.8.3 for all members
If member thickness >= 16” or member is in tension, use 5.8.3.4.2 (beta
calculated using App. B5)
If member thickness < 16”, use 5.8.3.4.1 (beta is a constant 2.0)
3-sided structure
Any fill depth
Use 5.8.3 for all members
If member thickness >= 16” or member is in tension, use 5.8.3.4.2 (beta
calculated using App. B5)
If member thickness < 16”, use 5.8.3.4.1 (beta is a constant 2.0)
Note that the iterative beta method (beta calculated using Appendix B) is actually usable in all
situations, regardless of the member thickness or location.
For most culverts, moment and axial force demands are calculated on a preliminary estimate of each
member thickness. The area of reinforcing steel is determined based on moment demand and the
corresponding section depth is checked for shear capacity. If the depth is insufficient the loop reiterates and this process is performed until all requirements are met.
However, when the section depth is greater than 16 inches the flexure reinforcing steel affects the
calculation of the shear strength and causes the strain to vary. If the usual design approach (as
detailed in the preceding paragraph) is followed then every iteration increases the member depth,
reduces the flexural steel, and increases the strain. This increase in strain reduces the provided
shear stress. The increase in strength in shear from every depth increment is overcome by the
decrease in Beta which causes the loop to not converge and continue until the maximum shear strain
is met or the maximum number of iterations is performed. This process produces inefficient design
results in which large member thicknesses are produced.
Therefore the design of flexural steel reinforcing for members greater than 16 inches are controlled by
the demands of shear and not moment. The new process used by Eriksson Culvert for such member
proceeds as follows:
1. Once the member thickness reaches 16 inches, a preliminary estimate of the reinforcing steel
is based on moment demand. Then the area of steel is used to calculate the shear capacity
and checked against the shear demand. If the preliminary estimate of the area of reinforcing
steel is unsatisfactory the program enters a loop inside the shear calculations to increase the
area of steel until this requirement is met. This area of steel should be limited to around 2.0
in2/foot for practical purposes (note that this upper limit can be adjusted by the user). If this
limit of the reinforcing steel cannot be satisfied then the program increases the member
thickness, recalculating the structural steel demand, and re-starts the shear demand loop.
2. When the member thickness is fixed, the program then checks the steel reinforcing and
member thickness for moment demand requirements.
3. Proceed to check all other requirements such as service stress limits.
For fill depths greater than 2 feet, the horizontal slabs the provisions of Article 5.14.5.3 shall apply.
Note that this section uses de instead of dv.
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
A V d 
Vc = 0.0676 fc' + 4.6 s u e  bd e
bd e M u 

(LRFD Eq. 5.14.5.3-1)
Vc,max = 0.126 fc' bv d e
In all specifications, Mu can either be taken as that which occurs at the critical section for flexure
design, or as that moment that is present at the critical section for shear (‘corresponding moment’).
For CHBDC, Vc can be found from the following:
The value of β can be determined using one of the methods in Section 8. Eriksson Culvert uses the
general method.
Shear Stirrups
Shear stirrups are only taken into account during Analysis mode. In Design mode, the program
assumes that the shear is resisted by the concrete only.
LRFD
The capacity of the defined shear steel area can be determined by:
Vs =
Av f yv d v
s(tan(θ ))
(LRFD Eq. 5.8.3.3-4)
where theta is assumed to be 45 degrees
The program then checks for the maximum capacity of the shear steel using:
Vs max = Vn − Vc
where Vn ≤ 0.25fc' bv d v
(LRFD Eq. 5.8.3.3-2)
Finally, the program finds the maximum spacing of the shear stirrups, which depends on the shear
stress in the concrete, which can be calculated by:
vu =
Vu
φbv d v
for v u < 0.125fc' , smax is the lesser of 0.8 * dv or 24 inches
for v u ≥ 0.125fc' , smax is the lesser of 0.4 * dv or 12 inches
Standard Specification
The capacity of the defined shear steel area can be determined by:
VS =
Av f yv d
s
(STND Eq. 8-53)
The program then checks for the maximum capacity of the shear steel using:
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103
Vs,max = 8 f ' c bw d
(STND 8.16.6.3.9)
Finally, the program finds the maximum spacing of the shear stirrups.
s max = d / 2 < 24
(STND 8.19.3)
if Vs > 4 f ' c bw d , then s max = s max / 2
(STND 8.16.6.3.8)
CHBDC
Per Section 7.8.8.2.3, if Vc is less than Vu at any section, shear stirrups shall be designed to satisfy:
5.8
Crack Control
LRFD
Under the LRFD Specification the stress in the spacing of the individual tension steel bars must be
less than a required value as specified LRFD 5.7.3.4. First, the stress in the tension steel is
calculated. This stress is used to calculate the required spacing of the tension steel using the
following equation:
s reqd =
700γ e
− 2d c
β s fss
(LRFD Eq. 5.7.3.4-1)
In LRFD, there is no limit on dc (distance between the center of the layer of steel closest to the
tension face and the tension face itself) in the cracking analysis. Therefore, to prevent the calculation
of a negative sreqd, the cracking analysis limits the calculation of dc similar to that in the STND
Specification, that is, an upper limit of 2 inches is placed on the concrete cover used in the calculation
of dc.
The cracking parameter γe is assigned by the user, however LRFD does not give any guidance as to
the magnitude of this value for culverts. To bypass the cracking check, that is, to prevent cracking
from controlling the design, set γe to a very large value.
Standard Specifications
For the STND Specification service check (16.6.4.7 and 16.7.4.7), the stress in the tensile steel is
again calculated, which is then compared to an allowable stress as calculated by the following:
fs =
z
≤ 0.6 f y
β (d c A)1 / 3
(STND Eq. 16-19 - CIP)
where β is equal to:
β = 1+
dc
0.7d
fs =
z
(d c A)1/ 3
≤ 0.6f y
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(STND Eq. 16-24 - Precast)
104
Where A is the effective tension area of concrete surrounding the flexural tension reinforcement and
having the same centroid as that reinforcement, divided by the number of bars. The cracking
parameter Z is assigned by the user. The STND Specification suggests a value of 155 for Z for CIP
construction, and 98 for precast. To bypass this check, that is, to prevent cracking from controlling
the design, set Z to a very large value, although keep in mind that there is still an upper limit on fs of
0.6fy. AREMA suggests a Z of 170 for members in moderate exposure conditions and 130 for
members in severe exposure conditions.
CHBDC
Per Section 8.12.3.2, the crack width shall be calculated as follows:
where kb shall be taken as 1.2 for components with epoxy-coated reinforcing steel and 1.0 for all
other components, and βc shall be taken as 1.7
srm shall be calculated as follows:
where kc = 0.5,
db = diameter of bar (mm)
ρc = ratio of area of steel (As) to effective tension area of concrete (Act). The depth of Act shall
be taken as the lesser of 2.5 times the distance from the extreme tensile fiber to the centroid of the
tension steel, or, 1/3 the distance from the neutral axis to the extreme tensile fiber
εsm shall be calculated as follows:
where fs = stress in reinforcement at the serviceability limit state (i.e., service load),
fw = stress in reinforcement under conditions causing initial cracking
Per 8.4.1.8, the cracking strength for normal density concrete shall be taken as:
And fw can be calculated using fcr and the thrust in the member by first calculating:
The program then uses this moment to determine what the stress in the reinforcement (fw) would be
at this moment value.
5.9
Fatigue
LRFD
Fatigue check is not required in LRFD under Article 5.5.3.1.
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105
Standard Specification
The fatigue stress limits on reinforcement due to the repeated application of live loads are
necessitated by the high reinforcement stresses resulting from Load Factor Design and the high
allowable stresses for Grade 60 reinforcement in Service Load Design. These limits have a
substantial effect for culverts under low fill heights. AASHTO Article 8.16.8.3 is followed.
The range between a maximum and minimum stress in straight reinforcement caused by live load
plus impact at service load shall not exceed:
ff = 21 − 0.33fmin + 2.4 , where f f = stress range
and
fmin = algebraic minimum stress level, tension positive, compression negative
At a section where stress is not reversed:
fs =
M
, where M = live load moment range
As jd
At a section where stress is reversed:
fs =
+M
(tensile part of stress range)
As jd

d' 
  k −  
d 

− M

 1− k 



 (compressive part of stress range)
fs' =
As jd
Total stress range = fs + fs'
In many cases, with low fill heights, the area of the flexural reinforcement is increased to satisfy the
fatigue serviceability requirement.
CHBDC
Per 7.8.10, box culverts with depths of cover less than 0.6m (23.62”) shall be checked for fatigue
requirements (8.5.3.1). Per 8.5.3.1 the stress range in straight bars shall not exceed 125 MPa. The
program applies this stress range to all bars.
5.10 Distribution Reinforcement
LRFD
When the fill depth is less than 2 feet, see Article 9.7.3.2, in which the distribution steel must be equal
to or greater than the following percentage of the flexural steel:
For primary reinforcement parallel to traffic:
% Steel =
100
, where S is the design span
S
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106
For primary reinforcement perpendicular to traffic:
% Steel =
220
, where S is the design span
S
When the fill depth is greater than 2 feet, Article 5.15.4.1 states that distribution steel is not required.
Therefore, Eriksson Culvert uses shrinkage and temperature steel as a minimum check.
Standard Specification
According to Section 6.5, when the depth of the fill exceeds 2 feet, reinforcement to provide for the
lateral distribution of wheel loads in not required. Top slabs with less than 2 feet of fill must have
distribution steel that satisfies the following percentage of the flexural steel:
%Steel =
1
, where S is the design span
S
For both specs, when the fill depth is less than 2 feet, the program uses epoxy coated bars in the top
face of the top slab when requested by the user. Note that this is a requirement in most states.
CHBDC
Per 7.8.12.1 (a), top slabs of box sections having a depth of cover of less than 0.6m shall be provided
with distribution reinforcement in accordance with 8.18.7, to be placed near the inside of the bottom
face of the slab.
Per 8.18.7, distribution reinforcement shall be placed transverse to the main reinforcement. The
amount of distribution reinforcement as a percentage of the main reinforcement shall be:
For main reinforcement parallel to traffic:
%Steel = 55 / √S, maximum 50%, where S = effective span length in meters
For main reinforcement perpendicular to traffic:
%Steel = 120 / √S, Maximum 67%, where S = effective span length in meters
5.11 Shrinkage and Temperature Reinforcement
LRFD
For 4-sided precast structures, use the greater of 5.10.8 or 0.002Ag, except that 5.10.8 does not
apply to sections less than 16 feet in length. For 3-sided structures, see 12.14.5.8, which requires a
minimum of 0.002Ag. Article 5.10.8 does not apply to 3-sided structures. LRFD does not provide any
guidance for fill depths greater than 2 feet, therefore the program applies the above logic, as other
minimum steel requirements will probably control in the design.
For CIP structures at all depths, see Article 5.10.8.
Standard Specification
For 4-sided precast structures, use the greater of 0.125 in2/ft (8.20), or 0.002Ag (16.7.4.8), however
note that 8.20 does not apply for structures with lengths under 16 feet. For 3-sided precast
structures, see 16.8.5.8 (0.002Ag), however, 8.20 does not apply for any length structure. While
there is no guidance for fill depths greater than 2 feet, the program applies the same logic as listed
above, as it is likely that other minimum steel criteria will ultimately control.
For CIP structures at any fill depth, see 8.20.
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CHBDC
Per 7.8.11.2, the minimum area and maximum spacing of shrinkage and temperature reinforcement
shall be in accordance with Table 7.18. In Table 7.18, precast box culverts with a depth of cover
equal to or greater than 0.6m shall have a minimum area of reinforcement of 300 mm2/m, at a
maximum spacing of 250mm above the principal reinforcement on the inside face.
5.12 Bar Schedule
The following is a list of all the possible bar marks that may appear in the output.
A1
Top corner (flexural reinforcement).
A2
Bottom corner (flexural reinforcement).
A100
Top slab, inside face transverse (flexural reinforcement).
A200
Bottom slab, inside face transverse (flexural reinforcement).
A300
Top slab, outside face transverse (flexural reinforcement for multi-cell
culverts, temperature steel for single cells).
A400
Bottom slab, outside face transverse (flexural reinforcement for multi-cell
culverts, temperature steel for single cells).
B1
Exterior wall, inside face vertical (flexural reinforcement).
B2
Exterior wall, outside face vertical (flexural reinforcement used in
combination with A1 and A2 bar if a U-bar is not used).
C1
Top slab, bottom slab, and wall longitudinal
(temperature reinforcement).
C100
Top slab, inside face longitudinal (distribution reinforcement).
C200
Bottom slab, inside face longitudinal (distribution reinforcement).
Reinforcement Types
STR
Straight
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L-BAR
L-shaped
U-BAR
U-shaped
Bar sizes range from #4 to #11. Bar spacings range from 2 inches minimum to 12 inches maximum.
The program uses the actual reinforcing bar diameter when locating design reinforcement. For mesh,
the program supports mesh sizes from 2.5 to 45, in both smooth and deformed types. Mesh can be
spaced at 2 inches through 12 inches.
When the clear height of the box is greater than 6 feet, bar marks A1, A2, and B2 are arranged to
have the same spacing so that Class C splices may be supplied.
When the clear height of the box is less than 6 feet, the program will omit the B2 bar and bar marks
A1 and A2 will have the same spacing and overlap with a Class C splice.
When the culvert is multiple cell, bar marks A300 and A400 will match the above spacing.
Some fabricators prefer to combine bar marks A1, A2 and B2 or A1 and A2 into one large U-shaped
bar instead of separate bars and this is acceptable.
When single cell boxes have clear spans less than 5 feet, the program will combine bar marks A1 and
A300 into one U-shaped bar for the top mat of the top slab and bar marks A2 and A400 into one Ushaped bar for the bottom mat of the bottom slab. This U-shaped bar will be given bar mark A1 for the
top slab and A2 for the bottom slab and will be displayed as a U-BAR in the bar schedule.
It should be noted that when fill heights are less than 2 feet, epoxy-coated reinforcement is required
in the top mat of the top slab in most states. This affects bar marks A1, A300 and C1. When epoxycoated bars are used, their bar marks will be displayed as AE1, AE300 and CE1 in the bar schedule.
For mesh, the design algorithm adds two additional bar types, C2 and C3. These wires are not
necessitated by the analysis, rather they represent the assumed cross wires for the A1 and A2 wires,
respectively. They are not editable in Analysis Mode, and can safely be ignored.
For ASTM charts, use the following conversions for AS1 – AS8.
ASTM
AS1
AS2
AS3
AS4
AS5
AS6
AS7
AS8
Eriksson
Culvert
A1/A2/B2
A100
A200
B1
C100
C1
A300
A400
Splice Length Chart
The program will compute and print splice lengths for bar marks B1, B3, C1, C100 and C200 as per
AASHTO Specifications. Bar splices for bar marks A100, A200, A300 and A400 will be printed only if
the required bar length exceeds 60 feet.
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5.13 Load Rating
LRFR Analysis
When the user selects the 5th Edition of LRFD as the governing specification, the calculation of each
load rating follows the procedure outlined in The Manual for Bridge Evaluation (MBE), First
Edition/2008 by AASHTO. This section was primarily designed for load rating bridge superstructures,
and gave no guidance on several conditions that apply to culverts. These conditions include vertical
and horizontal soil loads, water pressure and horizontal live load surcharge. These loading conditions
can create reversed effects to individual members of the culvert. For example, horizontal earth
pressures produce opposite top slab moments compared to vertical live loads and gravity loads. Also,
vertical loads on the top slab can reduce soil pressure effects on the exterior walls. Consequently all
of these actions must be considered when calculating the ultimate resistance in the numerator of the
load rating equation. Therefore Eriksson Culvert adopted a load rating equation that is identical to the
Equation 6A4.2.1-1 given in the 2nd Edition of the MBE for culverts and is shown below. In this
equation, live load surcharge is considered a transient load derived from the presence of a vehicle
axle positioned adjacent to the edge of the culvert that creates additional soil pressure and is
therefore placed in the denominator. Also note that in the first edition of the MBE, it was assumed
that the max/min effects of the horizontal earth load is produced using the load factors for EH. This is
the method used when the user selects the 5th Edition of LRFD as the governing specification.
When the user selects the 6th Edition of LRFD, the calculation of each load rating follows the
procedure outlined in The Manual for Bridge Evaluation (MBE), Second Edition/2010, by AASHTO
(including all interims up through 2014). Support for culverts was added with the 2013 Interims in
Article 6A.5.12.4. The new load rating equation, 6A.5.12.4-1 (shown below), is equivalent to the
procedure currently contained in Eriksson Culvert, with one exception. The new MBE states that
max/min effects for horizontal earth loads shall be produced via the ratio of the maximum and
minimum equivalent fluid pressures (basically the method followed in STND).
RF =
C ± γ DC ( DC ) ± γ DW ( DW ) ± γ EV ( EV ) ± γ EH ( EH ) ± γ WA (WA)
γ LL ( LL + IM ) ± γ LS ( LS )
In summary, when the governing specification is LRFD 5th Edition, the load factors for EH are used in
the load combinations and rating equations. When the governing specification is LRFD 6th Edition,
the ratio of the maximum and minimum fluid pressures are used for EH instead.
A load rating is produced at the 3 critical sections of each member of a culvert. The controlling rating
of either shear or moment is shown in critical sections table in the text report output. If the value of the
live load shear or moment is zero for a member the load rating output is zero, and shown to the user
as NC, meaning Not Calculated or Not Checked. Also, in the walls at the mid-height, if there is no
negative live load moment, then the negative critical section is not rated. Similarly, if there is no
positive live load moment at wall mid-height, then the positive critical section is not checked. If the
load rating exceeds 99.0, the rating output is shown as 99.00. If live load exists at one of the critical
sections while the dead load action is in excess of the capacity of a member a negative factor will be
shown.
Load Rating in Design Mode
The program initially calculates the reinforcing steel required and member thicknesses to satisfy the
shear, axial and moment demand on each section. Following this computation the requirements of
minimum reinforcing steel and fatigue stress limits are checked for adequacy on the reinforcing steel
and increased if necessary. Once a final steel reinforcing area is calculated, a trial bar size and
arrangement is checked against crack control requirements until satisfactory. This finalized pattern
is then displayed in the output and used for calculating the moment inventory and operating load
ratings for each member and each members thickness is used to obtain the shear inventory and
operating ratings.
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Load Rating in Analysis Mode
Here the reinforcing area and member thickness are defined to the program in the culvert properties
dialog box. The program performs checking of all appropriate limit states and a rating for both
moment and shear is calculated. The moment rating is based on the allowable moment capacity of
each member while, the shear rating is calculated based on the total shear capacity of each member
including both concrete and shear steel.
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5.14 End Regions
Cast-in-place construction allows for the easy formation of edge beams and cut-off walls for the
support of the cut reinforcement. Cut reinforcement is not assumed for precast construction as
precast forms do not easily accommodate edge beams and cut-off walls. The following suggested
edge beam and cut-off wall reinforcement and dimensions must be verified by the designer and
increased if necessary.
In situations where a skewed culvert unit may control slab thickness requirements for the project,
designers are encouraged to investigate edge beam design, in accordance with the LRFD
Specifications, as an alternative to increasing slab thickness. In addition, if the skewed unit is located
at the fascia of the bridge, the Multiple Presence Factor, MPF, may be reduced from a value of 1.2 to
1.0.
Cast-in-place culverts with skewed ends require additional stiffening of the top and bottom slabs by
what is most commonly called an "edge beam" in the top slab and a "cut-off wall" in the bottom slab.
An edge beam is very similar to a headwall in that it may be used to anchor guide railing posts or
retain earth fill. Its main purpose, however, is to stiffen the top slab of cast-in-place culverts that lose
their rigid frame action as a result of having a skewed end. A cut-off wall will stiffen the bottom slab
as well as prevent water from undermining the culvert. A cut-off wall is usually required on culverts
with no skew also.
For single cell cast-in-place culverts with skewed ends use a minimum 1'-6" wide by 1'-0" high
(measured from the top of the top slab) edge beam for the top slab. The end of the bottom slab is
suggested to have a minimum of a 1'-6" wide by 4'-0" high (measured from the bottom slab invert)
cut-off wall placed directly beneath it.
The single cell edge beam should have a minimum of 4 - #8 longitudinal bars (bar marks S1 and/or
S2) in the bottom of the top slab. The cut-off wall should have a minimum of 4 - #8 longitudinal bars
placed in the top of the bottom slab. In addition, the top slab edge beam should have a minimum of 4
- #5 longitudinal bars (bar marks G1 and/or G2) placed as shown below with #5 stirrups at 1'-0"
centers. Note that the S1 bars are intended for both edges, if the edges have the same skew, and
the left edge otherwise. The S2 bars are intended for the right edge The same logic is applied to the
G1 and G2 bars.
For multiple cell cast-in-place culverts with skewed ends it is suggested to use a 1'-6" wide by 1'-0"
high edge beam for the top slab. The end of the bottom slab should have a minimum of a 1'-6" wide
by 4'-0" high cut-off wall poured directly beneath it.
The multiple cell edge beam is typically reinforced with a minimum of 8 - #6 longitudinal bars (bar
marks S1 and/or S2). A minimum of 4 - #6 bars are usually placed in both the top and bottom of the
top slab edge beam as well as in the top and bottom of the bottom slab cut-off wall. In addition, the
top slab edge beam should have a minimum of #5 stirrups at 1'-0" centers.
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5.15 Retaining Wall Design
Lateral Earth Pressure
The magnitude of the lateral pressure, per geotechnical engineering theory, is
is the vertical stress of the soil and is the coefficient of lateral earth pressure. This
Where
coefficient depends on the state of the soil. If the wall does not deflect it is at rest, if the wall deflects
away from the soil causing the pressure it is considered active, and if the wall deflects towards the
soil causing the pressure it is considered passive. Note: Different specifications require different
deflects to be considered active/passive.
At Rest Earth Pressure
When the soil is considered at rest, the coefficient of lateral earth pressure, , can be found to be
where,
is the angle of internal friction of the soil.
The angle the pressure acts on, measured from the horizontal is
where,
is the slope of the surface we are finding the lateral pressure on, taken from the y-axis with positive
being clockwise and
is the slope of the backfill
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Rankine’s Active Earth Pressure
Rankine earth pressure theory was developed under the assumption that no friction exists between
the wall and the soil. Using this theory we can find to be
where,
is the slope of the backfill,
is the slope of the surface we are finding the lateral pressure on, taken from the y-axis with positive
being clockwise,
is the angle of internal friction of the soil and
is
The angle the pressure acts on, measured from the horizontal is
where,
is the slope of the surface we are finding the lateral pressure on, taken from the y-axis with positive
being clockwise and
is the slope of the backfill
Coulomb’s Active Earth Pressure
Coulomb’s active earth pressure theory accounts for wall friction and can be used on retaining walls
with granular backfill. Using Coulomb’s active earth pressure the lateral earth pressure coefficient can
be found as
The angle the pressure acts on, measured from the horizontal is
where,
is the slope of the surface we are finding the lateral pressure on, taken from the y-axis with positive
being clockwise,
is the slope of the backfill and
is the angle of friction between the interface of the soil pressure.
Rankine’s Passive Earth Pressure
Rankine earth pressure theory was developed under the assumption that no friction exists between
the wall and the soil and that the interface is vertical. Using this theory we can find to be
where,
is the slope of the backfill and
is the angle of internal friction of the soil
The angle the pressure acts on, measured from the horizontal is
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where,
is the slope of the surface we are finding the lateral pressure on, taken from the y-axis with positive
being clockwise and
is the slope of the backfill
Surcharge Loading
All surcharges are assumed to be uniform infinite loads applied to the surface of the backfill. For
uniform loads the magnitude, , assumes the not attenuate through the soil and thus all points under
the soil the vertical stress is increased by . This also translates to an increase in lateral pressure by
using the selected lateral earth pressure theory.
Bearing Pressure
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The bearing pressure is added as a force to the system acting on the bottom of the foundation. The
bearing pressure however is unique depending on the loads being applied, thus each load
combination has a unique bearing pressure. The location of this bearing pressure depends on the
eccentricity, e, of the reaction which comes from the overturning analysis. The pressure distributions
follow LRFD in that they are rectangular when on soil and trapezoidal when on rock.
Sliding Stress
The sliding stress is added as an axial force acting upon the bottom of the slab. It’s magnitude is the
. This will result in a compressive force in the toe and a tensile force in the heel.
5.16 Strip Footings for 3-Sided Culverts
Supported Specifications
The strip footing module comes with support for AASHTO LRFD 6th edition with 2013 Interims. The
strip footing module will only be available if Eriksson Culvert has this specification selected.
Loads
Vertical Loads
The Dead Load consist of the soil weight plus the weight of the concrete slab (slab and pedestal).
The program is capable of accepting any number of additional loads which act at the center of the
keyway. The depth of the keyway is assumed to be zero for the analysis.
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Applied Loads
The applied loads are automatically acquired from the reactions of the three-sided culvert (from
Eriksson Culvert). The strip footing module stores a loading condition for each truck / fill depth
combination and will design the strip footing to satisfy all of the loading conditions. The user also has
the ability to modify / add / delete any of these loads if they desire.
Bearing Pressure
A trapezoidal distributed load is applied to the bottom of the strip footing. This load is picked in order
to enforce equilibrium on the system and thus varies depending on the load combination we are
checking.
Load Combinations
The strip footing module checks all possible load combinations from the loads on the system. For
each load combination the analysis is performed and the controlling cases are reported.
Flexural Strength
The flexure strength is calculated assuming singly reinforced member with a uniform concrete stress
block. Thus, the following equation is used,
where
When selecting reinforcement the bar size / spacing pairs is iterated through until the pair with the
lowest area of steel (which exceeds demand) is found.
Shear Strength
One Way Shear
The one way shear capacity is found using the general procedure defined in LRFD Appendix B5. The
strip footing module checks two critical sections’ one way shear capacities. Those being at the left
and right hand side of the pedestal / keyway (if no pedestal) extended by the shear depth, . The
controlling load combination and their shear capacities and shear demands are reported.
Two Way Shear
The strip footing module also checks to make sure the wall loading will not cause a two-way shear
failure of the slab. For this check the critical section is on each side of the pedestal / keyway (if no
. This module assumes the strip foot ends at the
pedestal) extend by half of the shear depth,
. The shear capacity is then
end face of the wall. Thus, , the shear perimeter, is
found using LRFD Equation 5.13.3.6.3-1.
Shrinkage and Temperature Reinforcement
The strip footing module automatically chooses shrinkage and temperature reinforcement for the
user. This reinforcement is designed in order to meet the requirements set by LRFD section 5.10.8.
The selected reinforcement is reported in the text report.
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6 Appendix
6.1
Appendix 1: Glossary and Notation
Note: Generally, only terms specific to Eriksson Culvert are defined below. Items contained in the
program interface and/or on printout that are not defined below are either standard industry
nomenclature or are defined in the AASHTO LRFD Specifications or AASHTO Standard
Specifications.
A.F.: Axial Force.
As: Area of flexure reinforcing steel
Av: Area of shear reinforcing steel
Bot: Bottom.
cg: Center of gravity.
CIP: Cast in Place
CL: Center Line
Corr.: Corresponding.
Dist.: Distance.
Dynamic Load Allowance (DLA): An allowance for increasing the effects of live load per LRFD.
Comparable to the impact factor in the Standard Specifications.
Ec: Elasticity of the concrete.
Ext.: Exterior.
Eq./Equiv.: Equivalent.
Es: Elasticity of the steel (rebar).
f’c: The 28-day strength of the concrete.
Fss: Stress in the steel.
FWS: Future wearing surface. The portion of the weight of the future wearing surface apportioned to
the beam under design.
fy: Yield stress of the reinforcing (i.e., rebar).
Hor. Leg/H Leg: Horizontal leg.
Haunch: The build-up directly over the beam. In Eriksson Culvert, the haunch includes only the
additional slab concrete located directly above the top of the precast beam but below the bottom
surface of the slab. The haunch’s weight and its contribution to section properties are
automatically computed.
Impact Factor: An allowance for increasing the effects of live load per Standard Specs. Comparable
to the dynamic load allowance in LRFD.
Ind.: Individual.
Int.: Interior/Internal.
IR: Inventory rating.
LL: Live load.
Longitud/Longit: Longitudinal.
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Lt: Left.
M: Moment
Ma: Allowable Moment
Mu: Ultimate Moment
Max: Maximum.
Mdl,Vdl: Moment/shear due to dead load plus soil load plus FWS.
Mid: Mid-point.
Min: Minimum.
Mll,Vll: Moment/shear due to live load.
M-PT: Member 10th point.
Msp,Vsp: Moment/shear due to horizontal soil pressure plus live load surcharge.
Mwp,Vwp: Moment/shear due to water pressure.
NC: Not Calculated
No: Number
phi*Vn: Maximum shear resistance.
OR: Operating rating.
Press.: Pressure.
Qty: Quantity.
Reinf: Reinforcement
Resist Factors: Resistance factors. See phi-M, phi-V.
Rt: Right
Skew Angle: The skew angle, θ, of the bridge. This is the reduction of a 90o angle between the
longitudinal axis of the beam and an imaginary line through the supports of all the beams. A skew
angle of zero indicates that the beams are at right angles to the supports. Used in distribution
factor calculations per LRFD.
Spac: Spacing
V: Shear
Vc: Shear Resistance provided by concrete
Ver. Leg/V Leg: Vertical leg.
Vs: Shear resistance provided from shear steel
Wgt: Weight.
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6.2
Appendix 2: First Tutorial Problem
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6.3
Appendix 3: Second Tutorial Problem
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6.4
Appendix 4: Third Tutorial Problem (final run – Text Report only)
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6.5
Appendix 5: References
AASHTO, Standard Specifications for Bridge Design, 17th edition, American Association of State
Highway and Transportation Officials, Washington, D.C. 2002.
AASHTO LRFD Bridge Design Specifications, 5th edition, American Association of State Highway and
Transportation Officials, 2010.
AASHTO LRFD Bridge Design Specifications, 6th edition, American Association of State Highway and
Transportation Officials, 2012, with 2013 Interims.
AASHTO LRFD Bridge Design Specifications, 7th edition, American Association of State Highway and
Transportation Officials, 2014, with 2015 and 2016 Interims.
AASHTO LRFD Bridge Design Specifications, 8th edition, American Association of State Highway and
Transportation Officials, 2017.
AREMA 2010, American Railway Engineering and Maintenance-of-Way Association, 2010.
ACI Committee 318, Building Code Requirements for Structural Concrete (ACI 318-05), American
Concrete Institute, Detroit, 2005.
CSA-S6-06 Canadian Highway Bridge Design Code, Canadian Standards Association, 2006, with 3
Supplements.
PCA, Notes on ACI 318-05 Building Code Requirements for Structural Concrete (ACI 318-05),
Portland Cement Association, Chicago, 2005.
PCI Industry Handbook Committee, PCI Design Handbook, 6th Ed., PCI, Chicago, 2004.
Young, Warren, Roark’s Formulas for Stress and Strain 6th Edition, McGraw-Hill, Texas, 1989, 736
pages
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6.6
Agency List
Currently, Eriksson Culvert supports the following agencies:
NYSDOT
SDDOT
Iowa DOT
Nevada DOT
ACPA
ASTM 1433
ASTM1577
MnDOT
Following is a summary of the changes to the input and the internal calculations for the support of the
various supported agencies.
NYSDOT STND:
For skewed culverts with less than 2 feet of fill, if the design span exceeds
6.0
, where θ is the
sin θ
skew angle, live load wheel loads are magnified by reducing the distribution slab width, E, by
multiplying by the cosine of the skew angle. Culverts with skews in excess of 60 degrees shall be
designed for a skew of 60 degrees.
For fill heights less than 3 feet, the impact fraction is calculated as
50
≤ 0.3 , where S is the
(S + 125)
centerline distance between adjacent walls.
NYSDOT LRFD:
For skewed culverts with less than 2 feet of fill, if the skew angle is greater than 15 degrees, and the
program is set to automatically account for skews, then the traffic is placed perpendicular to the span
of the culvert. Also, the lane load is distributed as per the latest NYSDOT Blue Pages.
NYSDOT General:
The following analysis options are set:
Automatically Account for Skew Effects
Limit Distribution Width for Fills Less Than 2 Feet
Limit Distribution Width for Fills Greater Than 2 Feet
Combine Axle Overlaps for Fills Greater Than 2 Feet
Use Max Moment w/ Max Shear
Extend Shear Section
True
True (STND), False (LRFD)
False
True
True
False
The following material properties are set:
Soil weight
Concrete weight
Lateral earth pressure
= 120 pcf
= 150 pcf
= 60 pcf max., 30 pcf min.
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Precast concrete strength
= 5000 psi
Cast-in-place concrete strength = 3000 psi
The reinforcing bar covers for precast box culverts are set to:
Exterior concrete cover top slab
Exterior concrete cover bottom slab
Exterior concrete cover walls
Interior concrete cover s
2"
1"
1"
1"
The reinforcing bar covers for cast-in-place box culverts are set to:
Exterior concrete cover top slab
Exterior concrete cover bottom slab
Exterior concrete cover walls
Interior concrete cover
2"
3"
2"
2"
The following minimum exterior wall thickness requirements are used in the design phase:
Clear Span (CS)
CS < 8 ft
8 ft ≤ CS < 14 ft
14 ft ≤ CS < 20 ft
CS ≥ 20 ft
Exterior Wall Thickness (EWT)
EWT ≥ 6 in
EWT ≥ 8 in
EWT ≥ 10 in
EWT ≥ 12 in
Interior wall thicknesses are set to a minimum of 6 inches during the design phase.
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SDDOT general:
Material Properties:
All bar covers are set to 1 inch except for the interior of the bottom slab which is set to 1.5 inches.
Soil-Structure interaction factor is set to 1.15 (User Defined).
Concrete strength = 4.5 ksi, and the elasticity is set to 3865.2 ksi.
Loads:
Override the calculation of lanes by the program and set equal to 1.
Minimum equivalent fluid pressure is set to 20 pcf.
Analysis Options:
Ignore Axial Thrust
Check Slenderness
True
False
All members have a minimum thickness of 7 inches.
Phi for flexure is set to 0.90.
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Index
A
Agency List, 169
Agency Support, 46
Applied Loads, 101
B
Bar Schedule, 117
Beam weight, 12
Begin a new design, 12
Bottom Slab Support, 50
C
Calculations, 10
Clear Height, 48
Clear Span, 48
Client, 45
Concrete Properties, 51
Copyright Notice, 2
Crack Control, 113
Critical Section Options, 64
Culvert Properties, 48
Culvert Type, 46
D
Data Preparation, 12
Dead Load, 53
Deflections, 63, 110
Designer, 45
Dialog Boxes
Analysis Options, 60
Culvert Properties, 17, 47
Initialize New Design, 44
Job Information, 45
Job Information, 14
Load and Resistance Factors, 59
Loads, 18, 53, 54
Material Properties, 51
Print, 98
Project Settings, 15, 45
Reinforcement, 65
Reinforcement Size/Spacing Library, 71, 72
Results Grid, 97
Retaining Walls, 73, 82
Shear Steel, 70
User Options, 90
Vehicle Library, 58
Vehicle Properties, 56
Distribution Reinforcement, 116
Distribution Width, 61, 104
Dynamic Load Allowance, 106
Eriksson Culvert V4 User Manual
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End Regions, 123
Engineering Theory, 99
Equivalent Fluid Pressure, 54
Exposure Factor, 52
F
F1 key, 6, 14
Fatigue, 115
Fe Factor, 52
File types, 4
Fill Depth, 48
Fill Depth/Max Fill Depth, 48
Flexural Strength, 106
Flexure Options, 64
Fluid Pressures, 54
Fr Factors, 51
Future Wearing Surface, 53
G
Getting Help, 6
Getting Started, 1
Glossary, 129
Graphical Results, 95
H
Haunches, 49
Help system, 6, 15
I
Increment, 48
Input Dialog Boxes, 43
Installation and set up, 2
J
Job Number, 45
L
Lane Load, 57
Lateral Soil Loads, 54
Length, 48
Lightweight Concrete, 99
Live Load, 53
Live Load Analysis, 103
Live Load Analysis Options, 61
Load Combinations, 102
Load Factor, 45
Load Factors, 59
163
Load Rating, 59, 119
M
Main View, 92
Material Properties, 99
Maximum Steel, 110
Mcr Factors, 51
Member Thickness, 48, 65
Minimum Eccentricity, 109
Minimum Fill Depth, 48
Minimum Steel, 110
Modulus of Elasticity, 100
O
On-line help, 14
Open a previous job, 12
Output Options, 92
P
Physical Dimensions, 47
P-Moment, 57
Program Features, 1
Program Menu, 43
Program Operation, 46
Project Name, 45
P-Shear, 57
R
References, 168
Reinforcement Cover, 52
Reinforcement Options, 62
Resistance Factors, 59
Retaining Walls, 124
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Service Load, 45
Shear Options, 64
Shear Stirrups, 112
Shear Strength, 110
Shrinkage and Temperature Reinforcement, 117
Skew Angle, 49
Slenderness, 63, 109
Slope Factor, 52
Span CL-to-CL, 48
Specifications, 45, 99
Starting a design, 7, 10
Strength combinations, 102
Strip Footings, 127
Structural Model, 100
Structural Modeling Options, 63
T
Table of Contents, 3
Tandem, 56
Task, 45
Text Report, 93
Three D Rendering, 95
Tool Bar, 43
Truck, 56
Tutorial 1, 11, 131
Tutorial 2, 29, 144
Tutorial 3, 35, 156
Tutorial Problems, 11
U
Uninstalling Eriksson Culvert, 5
Use Range of Fill Depths, 48
User name, 4
164