CE-422
STRUCRUTAL DESIGN AND DRAWING
OPEN ENDED PROBLEM ON 3D COMPUTATIONAL MODEL ON ETABS
BY
MUHAMMAD DANISH NADEEM (CE-16205)
SEC: B
BATCH: 2016-2017
DEPARTMENT OF CIVIL ENGINEERING
NED UNIVERSITY OF ENGINEERING AND TECHNOLOGY
KARACHI, PAKISTAN
TABLE OF CONTENTS
Page
No.
 ABSTRACT
3
 MODEL INITIALIZATION
3
 DEFINING GRID LINES AND STORY DIMENSIONS
4
 DEFINING MATERIALS
5
 DEFINING SECTIONS
6-8
 DRAW SECTIONS
8
 JOINT RESTRAINTS
9
 DEFINE LOADS
9-10
 DIAPHRAGM
10-11
 CLADDING
11
 MESH SIZE
12
 APPLYING LOADS
13-15
 LOAD COMBINATIONS
15-16
 MASS SOURCE
16
 NO. OF MODES FOR MODAL ANALYSIS
17
 CONCRETE FRAME DESIGN PREFERENCES CHECK
17
 RUNNING ANALYSIS
18
 DESIGN CHECK
18-19
 RESULTS
19-30
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 ABSTRACT
ETABS, which stands for Extended 3D Analysis of Building Systems, is an engineering software developed by
“Computers and Structures” and Ashraf Habibullah is the inventor along with his many other software; like SAP 2000,
CSiBridge, SAFE, etc. ETABS is primarily used to analyze and design a multi-story building with great ease and in a
very short time as compared to when done manually by hand calculations.
In this report, A computational model on ETABS 2016 Ultimate 16.0.0 is developed for a 3-story RC building structure
subjected to gravity as well as lateral loads (Wind and Earthquake loads) Using UBC-97 provisions, based on linear
static analysis. Concrete of 3000 psi compressive strength and A615Gr60 steel of 60,000 psi yield strength is used in
the structure. Number of bays in X and as well as in Y direction is set to 3 with a typical story height of 12ft.
 MODEL INITIALIZATION
By selecting a new model, a model initialization window is appeared on the screen from which Units and steel and
concrete design codes can be selected.
Using ACI 318-14 Design Code for Concrete as UBC-97 is no longer supported by the version used. However, later on
in the report, for wind and earthquake loads, UBC-97 is still available to be selected and load combinations and
strength reduction factors are defined and replaced manually with respect to UBC-97 provisions.
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 DEFINIG GRID LINES AND STORY DIMENSIONS
According to the Roll No. (CE-16205), spacing in x-direction as 25ft and in y-direction as 20ft were set as required
based on the last and 2nd last digit of the roll no. respectively. Number of grid lines in x and y directions and also number
of stories and their height is also shown in the figure below.
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 DEFINING MATERIAL
From the Define drop down list, material properties were selected which displayed Define Materials window. From
here we can add new material or also already pre-defined material can be modified as well. Using add new material
option, added concrete of 3000psi compressive strength. Desired A61Gr60 steel was already present which did not
need any modification.
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 DEFINING SECTIONS
By going to Define > Section Properties > Frame Sections, Frame Properties window is displayed from where new
section properties can be added or already defined section properties by software can be used.
By clicking on add new property option, desired sections for beams and column were added using rectangular
concrete sections for both beams and columns as shown in the picture below.
The reason why torsional constant, or can also be named as polar moment of inertia and moment of inertia along x
and y are reduced is that when beam is under loading then some crack formations are to be expected which reduces
the moment of inertia of beams so that’s why it’s reduced to 0.01% and 35% and is according to the design codes.
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Now Slabs can be defined by going to Define > Section Properties > Slab Sections. Here, by adding new property
option, 8” thick slab of following properties and name was defined.
 DRAW SECTIONS
Sections can be drawn using the quick access tool bar at the left corner. In the model, the sections were drawn using
quick draw column, beam and floor. From the bottom bar, All Stories option was activated to apply the sections to all
other story levels as well. It could have also been done using Replicate feature which is found in Edit drop down list
or can be directly accessed using shortcut command “Ctrl + R”.
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 JOINT RESTRAINTS
Joint Restraints were applied as Fixed by switching to base level and
selecting all of the base joints then going to Assign > Joints > Restraints
 DEFINE LOADS
Loads were defined by going to Define > Load pattern as follows:
Lateral Earthquake Loads (Both in X and Y directions) were modified as follows by assuming the structure belongs to
the category of standard occupancy structures class and Structural system is concrete intermediate moment resisting
frame (IMRF) both in X and Y directions.
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Lateral Wind Loads (same for both in X and Y directions) were modified as follows:
 DIAPHRAGM
Function of a diaphragm is to transmit the lateral loads to vertical resisting elements of a structure like shear walls or
frames. Here, floor acts as diaphragm and for lateral loads, Concrete floors are permitted to be idealized as rigid.
As the concrete slabs are very stiff as compared to the stiffness of the frames; therefore, the in-plane deformations of
the diaphragm are negligible as compared to the horizontal deflections of the frames and such diaphragm can be
classified as Rigid.
Therefore, diaphragm is defined as rigid by going to Define > Diaphragm > Modify/Show Diaphragm.
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To assign rigid diaphragm to floors, first selected all the floors by going to Select > Object Type and then selected floors
from the list and then closed that window.
Then went to Assign > Shell > Diaphragms and DIAPHRAGM RIGID was selected from the list and was applied to all
the floors.
 CLADDING
To apply wind loads, Cladding has to be drawn for which I went to Draw > Auto Draw Cladding and used floors option
to draw the walls between the floors.
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 MESH SIZE
In order to use finite element analysis, Meshing is to be carried out. Finite element method reduces the degree of freedom
from infinite to finite with the help of meshing. For irregular structures, Manual meshing of slabs is generally done.
Automatic Meshing of slab can also be applied and it reduces analysis run time as well.
Manual meshing was done in the model by selecting all the slabs from select similar objects command and was meshed
into 12 by 12 elements in both the direction as shown in the figure.
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 APPLYING LOADS
Loads were applied by going to assign > Frame loads and as well as Shell loads command. Dead loads are automatically
computed by the software based on the dimensions and density of structural members assigned to them. Although,
additional superimposed dead load needs to be calculated of the non-structural elements like floor finishes and partition
walls.
Super imposed dead load applied on slab by floor finishes can be calculated manually or can be taken directly from the
UBC-97 manual.
In the model, for the slabs, 25psf of superimposed dead load is applied because of floor finishes which are 2in thick and
density of RCC was taken as 150 pcf by going to Assign > Shell Loads > Uniform. The calculation is shown below:
Superimposed dead load = 150 x 2/12 = 25psf
Similarly, Live load of 60 psf was assigned to slabs of Story 1 & 2. For roof level (Story 3), lower value of Live
load was taken and only 20 psf of live load was applied on the slab of Story 3.
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Now for the application of wall loads as dead loads on frames, density of cement concrete wall was considered to
be 0.145k/ft3. As the wall in 8in thick and the clear height between the floors is 12ft and beams have depth of 2ft.
therefore height of wall is 12ft – 2ft = 10ft. Now dead load of wall is calculated as follows:
Dead load of walls: 10 x 8/12 x 0.145 = 0.97 k/ft2
This dead load is only applied to the frames of 1st and 2nd story only as there are no walls are considered above the
story 3.
Now wind loads were applied in both the x and y directions on the model using shell objects (Claddings) as follows by
going to Assign > Shell Loads > Wind Pressure Coefficients.
•
For X direction (Windward face):
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•
For X direction (Leeward face):
Wind Loads in Y direction were also applied in the similar manner.
 LOAD COMBINATIONS
Load Combinations were added manually by going to Define > Load Combinations > Add New Combo.
Page | 15
Here is shown how one of the many load combinations were defined manually:
 MASS SOURCE
We have to define the Seismic load which is to be used for seismic calculations by going to mass source window. It is
represented by W in IBC, UBC and some other American Codes. This weight is not only used for Seismic Analysis but
as well as for Wind Pressure Analysis as well. So, it can be said that mass source command is used for calculating center
of mass of the diaphragm and is used by any type of lateral load which uses that center.
In the model, 100% of dead load is considered; whereas, in this case, live load could have been neglected but still 25%
of live load is considered as well as shown.
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 NO OF MODES FOR MODAL ANALYSIS
As no. of modes = 3 x no. of stories; therefore, 9
modes are used for this analysis.
Modal case type used = Eigen.
 CONCRETE FRAME DESIGN PREFERENCES CHECK
In the ETABS Ultimate 16.0.0 version, UBC-97 Design Code is not available for concrete frame designing so ACI 31814 was selected instead but some of the factors like load combinations (which were defined manually in the previous
steps) and strength reduction factors were changed/replaced according to the UBC-97 provisions as shown in the picture
below, highlighted as red.
Page | 17
 RUNNING ANALYSIS
The defined model in the ETABS can be analyzed very easily within few seconds by clicking Run Analysis command
or by simply pressing F5 which is a shortcut key for it.
The model will show axial, shear, bending moment diagrams and deflected shape, story drifts and displacements etc.
according to the defined sections, materials, gravity and lateral loads, and their combinations and design codes used.
Here the deflected shape and moment diagram due to dead load are shared but others important tables and all are shared
after the design check which is the next step.
 DESIGN CHECK
Design check can be started by going to Concrete Frame Design > Start Design/Check or by just simply pressing
Shift+F6. In this stage, it was checked that if all the members were passing or not under the defined loads and their
combinations and designing is also according to the code used. By Display Design Info command, following results
can be obtained.
Page | 18
After running the design check, it’s to be verified if all the members have passed the design requirements or not
which is done with the help of Verify All Members Passed command.
Reactions at the bottom, Axial, shear, bending moment diagrams, displacements, story drifts for different load types
and combinations can be viewed like shared one below for dead loads. Support reactions window can easily be
accessed by pressing F7 key and Frame forces window by Pressing F8 key.
 RESULTS
•
Reactions, Axial, In-plane Shear and Bending Moment diagrams for dead loads: -
Support Reactions
Axial forces diagram
Page | 19
In-Plane Shear Forces Diagram
In-Plane Bending Moments Diagram
Page | 20
•
Deformed Shapes for First Three Modes: -
Mode 2
Mode 1
Mode 3
Page | 21
Page | 22
•
Deflection in Slab and Moments due to Deal Loads: -
Vertical Displacement (Uz) for story 2
Moment 11 (Story 2)
Page | 23
Moment 22 (Story 2)
Page | 24
•
Story Shears, Max Story Displacements and Drifts: -
Page | 25
•
Rebar Percentage, Longitudinal & Shear plus Torsional Reinforcing: -
Longitudinal Reinforcement
Shear Plus Torsional Reinforcement
Rebar Percentage
Page | 26
•
Detailing: -
From Model Explorer Window, Detailing and drawings of different structural members can be viewed. Some of the
many drawings and detailing from the model are as follows.
Page | 27
Page | 28
•
Detailed Summary for Most Critical Beam and Column: -
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