Structural Analysis with Autodesk® Revit® Structure Models
Mike King – Odeh Engineers, Inc.
SE2564
More than seven years ago, we started our first Autodesk Revit Structure software projects with the
promise that we would be able to send our models to the analysis package of our choice, size all our members, bring
it all back into Revit, and save ourselves countless hours of work. All these years later, we’re still working on it. The
good news is that we’re a lot closer. Revit Structure 2012 offered a totally redesigned analytical model that is identical
to that found in Autodesk® Robot™ Structural Analysis. Revit Structure 2013 further improves on 2012 in truly
beneficial ways. We will look at how the Revit analytical model relates to the physical, which settings affect design,
and how things translate between packages. We will show you best practices for a couple of tools as well as tips and
tricks to streamline the workflow and truly capitalize on this promise of Building Information Modeling (BIM).
Learning Objectives
At the end of this class, you will be able to:
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Visualize and manipulate the Revit Structure analytical model and explain how the physical and analytical models
interact
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Round-trip models and member sizes to external analysis packages
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Examine load paths and member reactions using Revit Extensions
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Reduce duplication of effort and increase productivity when modeling
About the Speaker
Mike King is a software engineer proficient in Microsoft® .NET technology. He has a
background in civil/structural engineering and in-depth experience in .NET development of all
types. He has worked to customize AutoCAD® from Visual LISP® and VBA to ObjectARX®
and Microsoft .NET, and has significant experience with the Revit® Structure API. At Odeh
Engineers, Inc., he has developed both line-of-business applications, such as a corporate
intranet that incorporates CMS, CRM, and PM functionality, and specific-needs applications
such as custom tablet PC tools for documenting field conditions. At Odeh Engineers Mike has
collaborated with Autodesk on a number of subscription based Revit extensions.
kingm@odehengineers.com
Structural Analysis with Revit Structure Extensions
Introduction
Target Audience
I just want to make it clear that this class is really for structural engineers. I firmly believe that
maintaining and properly using the analytical model in Revit should be the responsibility of the
project engineers, not the drafter. It should be considered on a par with any other design
software package.
Outline
Topic
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Analytical Modeling in Revit Structure
Analysis Extensions
Autodesk® Robot™ Structural & Autodesk 360 Structural Analysis
Bentley RAM Structural System & ETABS from CSI Berkeley
Integration Level
Fully Integrated
Well Integrated
Getting better!
We’re going to start out with a fairly comprehensive discussion of the Revit Analytical Model,
which is fundamental to getting any analysis tool to work either within Revit or via a link. After
that we’ll look at the structural analysis and design extensions available with your subscription,
and then we’ll look at Autodesk® Robot™ Structural Analysis Professional and Autodesk 360
Structural Analysis. Finally, we’ll take a quick look at links to RAM Structural System from
Bentley and ETABS from CSI Berkeley.
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Structural Analysis with Revit Structure Extensions
Structural Analytical Model
Historical Challenges
Different programs from different companies have evolved over many years. They have
separate assumptions, limitations and internal representations. They specialize in different
types of design, support different codes and standards and often focus on specific markets.
Analytical models are often stick frame style simplifications of real buildings. It isn’t necessary
to include every single element. Different engineers design different things in different programs
(gravity, lateral, connections, foundations, infrastructure, etc.). There is no well supported
comprehensive industry standard. Despite all that, we’ve decided that all programs should be
able to seamlessly transmit all of their modeled data from any one to any other even as new
versions come out and products change. Honestly, why would that work? It’s a tremendous
development challenge for companies that often have no strong incentive to let you bring your
work to a competitor’s application.
What Changed?
Autodesk acquires Robobat in 2006 showing a real commitment to the structural engineering
discipline as a market focus. Suddenly the incentive and means exist for one company to really
make this work. They have knowledge of both ends of the process and the resources to get it
done. In the 2012 versions Robot Structural Analysis and Revit Structure share a common
analytical model format. In Revit 2013 the tools to interact with this analytical model have been
further refined. This means, at a fundamental level, they can express the same things in the
same ways. Developers working on interoperability have access to the guts of each program in
a way no 3rd party could. The advent of Autodesk 360 Structural Analysis and a growing suite of
structural analysis and design extensions that run directly in Revit show this focus is paying off.
Workflow
Expect to:
 Put a qualified skilled engineer in charge of the Revit analytical model
 Spend time maintaining the analytical model
 Keep a set of analytical views setup for review
 Model for your desired target link / application
 Invest time reading the manual, learning the quirks
This isn’t a free ride; no one can alleviate the design engineer from the responsibility of
understanding and maintaining the analytical model that express their design intent. There is no
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Structural Analysis with Revit Structure Extensions
one right way to interpret the physical model of a structure, you need to tweak and clarify. The
time saved is in coordination and remodeling, and the accuracy and integration is worth it.
Suggested Roles:
 Drafter: Setup and maintain views, documentation, sheet setup, details, markups
 Junior Engineer: Physical modeling, connections, system design, analytical adjustments
 Senior Engineer: Analytical model review, design intent, structural analysis link
 Principal: Project review, initial planning, consistency checks, standards
Setup Analytical Views
For each plan, section, elevation and 3d view you have, you should have an analytical view.
Turn on linear analytical element end differentiation in the Structural Settings  Analytical
Model Settings dialog box
Setup analytical model end colors in Visibility and Graphics
Create a view template to maintain your preferred settings, feel free to experiment and modify
as needed to see exactly what you need to.
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Structural Analysis with Revit Structure Extensions
Use sectioned 3d views to inspect individual floors, frames or sub-structures in 3d to fully
understand the framing conditions being modeled.
The goal of analytical views is to reduce clutter and cut to the heart of the structural model.
Remove anything and everything you don’t need and simplify as much as possible. You should
be able to see what you need to at a glance to make it more likely you’ll check often and notice
issues.
Analytical Considerations
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Analytical / physical relationship
Materials
Loads
Boundary conditions
Revit attempts to infer the analytical model from the
physical, it’s not always right! Check it and, when
needed, fix it. Make sure all your structural elements
have structural materials applied. Model whatever loads
you want to design for then apply boundary conditions
on your model
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Structural Analysis with Revit Structure Extensions
Toggling Analytical Model
All structural elements have an “Enable Analytical
Model” setting in their structural properties. Turn this
off to remove an element from analytical consideration
entirely. Some elements also have a Structural setting;
this older setting also turns off the analytical model.
Turning off the structural setting also prevents you from
adding reinforcement to concrete elements that
support it.
Horizontal Stick Framing Properties
When the analytical model is activated, horizontal stick
frame elements expose a variety of properties on their
analytical model.
Analyze As
Specify Gravity or Lateral, controls how this is used in
design. Check specific links for support.
Start / End Releases
Fixed, Pinned and Bending Moment (fixed against
torsion) are available by default. User defined gives
complete (maybe excessive) control, not all analytical
tools will use this (Robot / 360 Structural Analysis do).
Note that there are also Start/End Connection
properties on the physical model that can be set to
None, Cantilever Moment or Moment Frame. These
settings affect some tools (e.g. Composite Design
extension, RAM Structural System) and are used for
construction documents.
Rigid Links
For beams, you can set this to Yes, No, or From Column. From Column
means, essentially, respect the columns setting for this property. Rigid Links
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Structural Analysis with Revit Structure Extensions
are infinitely stiff weightless connections that can be formed between a beam and a column
representing an eccentric connection.
You can also manually create rigid links between any two analytical nodes using the Analytical
Link button on the Edit Analytical panel that becomes visible when Analytical Adjust is clicked.
Analytical Alignment
These settings allow you to override the default analytical model placement relative to the
physical model. You can assign the analytical model to either follow the physical location line or
snap to a grid line or other reference. Later on we’ll look at directly grip editing the analytical
model.
Columns & Braces
Most analytical properties are similar to beams. Rigid links
setting is either on or off. Alignment options can be specified for
both the XY (horizontal) plane and the Z axis (vertical). Again,
those points can be grip edited.
Floors
Either one-way or two-way, alignment methods can be specified
or perimeter edited manually.
Wall Elements
Configure as gravity, lateral or both. Analytical projection relative to the physical model is
editable as is the top and bottom projection.
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Structural Analysis with Revit Structure Extensions
Foundations
Elements can be analyzed as either foundations or slabs on grade. A foundation element can
accept load, slabs on grade only support themselves.
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Structural Analysis with Revit Structure Extensions
Analytical Settings
Understanding the analytical settings tab is key to successfully auditing and maintaining your
analytical model.
Automatic Checks
 Model validated as you work
 Best enabled when model is stable
 Manual checks not available when active
 Remaining settings on this tab relate to these two checks
Tolerances
 Relate to analytical / physical model relationships
 Left column: warnings occur during checks
 Right column: Placement of analytical model when set to auto-detect
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Structural Analysis with Revit Structure Extensions
Circular Reference Check: Trigger warning for circular bearing chain
Analytical / Physical Model Consistency Check
Controls specific consistency checks performed during analytical / physical check (either
automatic or manual). Distances shown here are dependent on tolerances specified above.
Analytical Model Visibility: Leave this on, it’s useful.
Structural Materials
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Must be assigned to all structural elements
Structural materials have Assets with the aspect set to Physical in the Material Browser
Structure Property Sets are pre-populated, can be edited
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Structural Analysis with Revit Structure Extensions
Assigning Structural Materials
 Can be Instance or Type parameter
 Materials and Finishes (instance parameter)
 Assigned / layer on layered elements (e.g. walls)
Loads
Modeling loads in Revit ensures all analysis products are using common criteria.
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Structural Analysis with Revit Structure Extensions
Load Cases
Load case has a name, which can be anything desired. Natures can be created and called
anything desired as well and associated with cases. Categories are fixed in product and must
be assigned to each case. Unfortunately the default set of cases seems very redundant. Case
SNOW1 is of Nature Snow and Category Snow Loads… why? Well you can have many
different “dead loads” that you might want to schedule, filter or tag according to different criteria.
You might want to create load combinations that only include some. Each load defined in your
Revit model is of exactly one load case.
Load combinations allow the definition of any number of different (generally code required)
factored or unfactored load case combinations.
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Structural Analysis with Revit Structure Extensions
Modeling Loads
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Hosted (by analytical element) or unhosted (independent)
Point, line or area
Reaction: means they are the result of another element, considered “internal loads”
Load case assigned from above
Oriented to desired work plane
Point and Line can represent any combination of force vectors on three axis and moment
vectors on three axis
Area loads can only represent force, still three axis
Line loads may be uniform or linearly sloped
Area loads may be constant or sloped in one or two directions with control points
Not all tools support all load
Hosted loads automatically cover the analytical element they are assigned to. Points are
assigned to one end of a linear element (a node). Lines are assigned to the full length of any
analytical element. Areas are assigned to any surface element and follow it.
Recommendations
 Use hosted area loads when possible (very helpful)
 Other types of hosted loads, less often useful
 Use unhosted area loads for things like snow drift, storage rooms, etc.
 Keep loads as simple as possible, Revit can model far more than most analysis tools
can understand
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Structural Analysis with Revit Structure Extensions
Boundary Conditions
Boundary conditions are used to represent things like foundations, adjacent buildings or other
constraints that represent the edge of your analysis area. They are designed essentially absorb
force or moment applied to them.
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Structural Analysis with Revit Structure Extensions
Structural Analysis Extensions
Revit Structure extensions are available with your Revit subscription through your subscription
management portal. They are easy to use, focused and work completely within your Revit
model so there’s no link troubles to worry about. For that reason, they are the most tightly
integrated of any of the analysis / design tools available. Unfortunately they are also very
limited in scope so they are no replacement for a full feature analysis and design application.
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Available at no additional cost with subscription
Work within Revit
Seamless integration
Focused, easy to use
Limited functionality
Recommended for:
o Quick checks
o Schematic design phase
o Response to changes after main design
Composite Design
This tool is suitable for composite or non-composite design of
wide flange steel beams under composite concrete on metal
deck. This type of design is very common in US markets and
makes effective use of concrete in compression and steel in
tension (for positive moment regions). November 2011
update adds support for cantilevered and multispan beam
design as well as dramatically improving performance and
fixing a number of bugs. Quick checks of single beams to full
floor design, settings driven, uses Revit loads, assigns studs,
camber, beam size and reactions back to Revit model.
Incorporates many of the features of the Static Analysis of
Beams module for a larger selection and includes its own load
takedown algorithm.
Conceptual Form Simulation
This tool allows analysis of arbitrarily loaded complex
conceptual forms. It is suitable for finite element analysis of
stresses, deformations and reactions of arbitrary 3d shapes.
Floor Vibrations Analyzer
Suitable for use after composite designer has been used to
select steel sizes. Using AISC Design Guide 11 this tool can
check a variety of acceleration drivers and sensitivity factors
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Structural Analysis with Revit Structure Extensions
for an entire floor using automatically detected bays with assigned occupancy types. No design
is possible, strictly a serviceability or human-comfort check.
Gravity Column Designer
 Design any selected wide flange or HSS column for loads with optional eccentricity
 Point loads from Revit or can be assigned within the tool
 Bracing and fixity at each level can also be assigned.
Load Takedown
 Distributes loads across floor systems to beams, columns and eventually foundations or
boundary conditions throughout your structure
 Useful for determining reactions and applied loads for a variety of design purposes
 Requires careful validation by engineer
Static Analysis of Beams, Frames, Slabs and Trusses
Purely analysis tools useful for feeding reactions, stresses and internal forces to other design
programs (including spreadsheet based calculators).
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