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Autodesk Structural Engineering Curriculum 2013Instructor GuideUnit 4: Extending BIM for Structural Analysis and Design
ContentsUni t Overview ................................................................................................................... 2
Overview ....................................................................................................................... 2Objectives ..................................................................................................................... 2
Lesson 1: Theory of Physical and Analy tical Objects ................................................... 3Lesson Overview .......................................................................................................... 3Revit Extensions & Robot ............................................................................................. 4
Exercises Overview .......................................................................................................... 5
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Unit Overview
OverviewThis unit provides an overview of the analytical model in AutodeskRevitStructure software. It highlights
the differences between the physical and analytical model, and then introduces powerful structural
extensions you can add to Revit Structure. The unit includes a brief review of modeling in Revit Structure
followed by an introduction to the concept of linking to third-party analysis programs. In addition, the unit
introduces structural loads, load cases, and load combinations.
Estimated Duration: 3:00 hours
ObjectivesAfter completing this unit, students will be able to:
Define the Revit Structure analytical model.
Know the differences between physical and analytical models.
Understand the basic concept of structural loads, load cases, and load combinations.
Understand how the basic tools work in Revit Structure related to using Building Information
Modeling for structural analysis.
Understand the relationship between analysis software, such as AutodeskRobot software, and
BIM applications such as Revit Structure.
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Autodesk Structural Engineering Curriculum 2013Instructor GuideUnit 4: Extending BIM for Structural Analysis and DesignLesson 1: Theory of Physical and Analyt ical Objects
Lesson 1: Theory of Physical and AnalyticalObjects
Lesson OverviewAutodesk Revit Structure is a Building Information Modeling (BIM) application. All elements of the structural
model are controlled by one unifying, underlying database that controls the entire physical and analytical
model. Bidirectional associativity of the two structural models means a change to a physical object in one
view changes the associated analytical object.
With BIM, we endeavor to capture, preserve, and reuse information for downstream applications. The
benefit of this approach is higher-quality output and greater productivity with less effort (less cost). Revit
Structure elements are controlled through parametric relationships between the physical and analyticalmembers. For example, the analytical column is typically centered in the physical column geometric center.
When you move the physical column, the analytical column moves as well, keeping its relationship to the
physical columns geometric center.
In Revit Structure, an analytical model is a simplified 3D representation of the full engineering description of
a structural physical model. The analytical model consists of those structural components, geometry,
material properties, and loads that together form an engineering system. Revit creates the analytical model
automatically while you create the physical model, and you can export to analysis and design applications.
In the following illustrations, the left view represents the physical model, and the right view represents the
analytical model.
Figure4.1:Thephysicalmodelisontheleftandtheanalyticalmodelisontheright.
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From the Structural Settings dialog box, choose the Analytical Model Settings tab to adjust how Revit
Structure performs certain tasks on the analytical model.
Figure4.2:TheStructuralSettingsdialogbox.Automati c Checks: When enabled, automatic support checking provides a warning when a member is not
supported. This setting is useful when most of the structure has been modeled, and you want to know if
changes made to the model cause elements to become unsupported. Note: Enabling this setting during theearly stages of a project will show a significant number of elements unsupported during model creation and
can be misleading and unhelpful.
Tolerances: Set tolerance limits for horizontal and vertical analytical model automatic adjustment. For more
information, see Revit Structure Help for Automatic Adjustment of the Analytical Model (Auto-Detect).
Revit Extensions & RobotAutodesk Revit Extensions for Autodesk Revit Structure 2013 software provide a full range of benefits to
enhance the software. Users of these extensions can benefit from their ease of use, helping them be more
productive and agile while working on projects. This unit will specifically address the Autodesk Robot
Extensions used in Revit Structure.
AutodeskRobot Structural Analysis Professional software (Robot) is a feature-rich structural analysis and
design software application capable of modeling and analyzing virtually any type of structure, no matter how
advanced the geometry conditions. Robot is an ideal analysis companion for BIM software, and it links with
Revit Structure. Using Robot enables Revit Structure users to directly analyze their models without
oversimplifying or interfering with the 3D building model to satisfy the restrictions of their chosen analysis
solution.
Historically, the workflow for design engineers involved interpreting architectural drawings and making their
analytical model from these drawings, constantly checking and rechecking the correlating models. The finite
element model from the engineer typically runs on its own platforms and does not interface with any BIM
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software. Autodesk revolutionized this process by introducing Robot and continues to improve on the robust
link between Robot and Revit.
These extensions provide a vehicle to perform less complicated calculations in Revit, as well as producing
professional reports for documenting the work. Not only does Robot interface with Revit but it links with
many other software applications using a technique known as Interoperability. This enables models, or
fragments of models, to be seamlessly moved on a common platform, ensuring the finite element model is
the exact same as the physical model. The robust link creates a platform where you can model elements
and conditions in whatever software is easiest to use and provides enough options for more complicated
tasks. The following exercises highlight only a few of the many extensions available to Autodesk
Subscription customers.
Exercises OverviewTo complete the following exercises, students will need online access to the Autodesk BIM Workshop
(www.autodesk.com/bimworkshop). Click on the Structural Engineering tab and select Unit 3. They will also
need headphones if they are in a lab setting among other computers.
Exercise 4.1: Composite Beam Design
This extension is for the Composite Steel Beam design. The slab and all beams must be associated with the
same level.
The basic functionalities of the extension:
Interactive design of the composite beams: This option enables users to design selected members
according to their own configurations. In this case, a dialog box is displayed and users can set their
configurations, check results of their design, or accept the design.
Automatic design of the composite beams: This option enables users to design members according
to selection and their own configurations. The design is done automatically according user settings.
This exercise uses the model SE_Unit4_Excercise1_Start.rvt.
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Figure4.3:Compositebeamdesignmodel.
Figure4.4:Interiorcompositebeammodel.In this example, we look at designing an interior composite beam to span 30' with a beam spacing of 8'
using the minimum number of 3/4" diameter x 3" stud shear connectors. The slab is 5" thick with f'c =3 ksi
(n=9) concrete. The beam is to be constructed without shores. The beam must support a ceiling of 7 psf,
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partitions and other dead load of 25 psf, and a live load of 150 psf. The steel beam uses A992 Steel with 50
ksi yield strength. This example uses AISC Load and Resistance Factor Design (LRFD). The beam in
question is outlined in the figure above. The initial beam is a W21x62.
Questions fo r Exercise 4.1
Using the composite beam extension, what is the most economical beam design by weight of steel beam?
Answer: W16x26 with 52 studs; however, even though it satisfies code requirement, this design requires alot of studs. It is not the most economical design when the stud welding labor is considered.
What is the most economical beam in terms of minimum amount of studs and stud welding labor that is 16"
deep?
Answer: W16x31. This is a better deign because it used almost half the number of shear studs, which
reduces field labor on the beam. The 5 pounds per foot of beam over 30 feet costs less than the cost of the
additional studs that the W16x26 design requires. For comparison, consider steel at $1.50 per pound and
each stud cost of $10 per installed stud. Also point out to student that steel and labor prices can vary greatly
due to market conditions and regional workforces. For engineers to have economical designs, they must
always maintain a good dialog with local fabricators, erectors, detailers, and steel suppliers to understand
pricing of their design.
What is the lightest 18"-deep beam that satisfies the design?
Answer: W18x35
What is the lightest non-composite beam that satisfies the design?
Answer: W21x44
Overall, which of the above designs is best and why?
Answer: W16x26 with 26 studs.
Why does the module have -0.256 for the dead load? (Reference the image below.)
Answer: This is the sum of the 8 tributary width multiplied by the dead load of 32 psf.
Figure4.5:Referencepicturedeadload.
Why does the module have -0.600 for the live load? (Reference the image below.)Answer: This is the sum of the 8 tributary width multiplied by the dead load of 150 psf.
Figure4.6:Referencepictureliveload.
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Exercise 4.2: Load Takedown
Using the Load Takedown extension, you can perform a simulation of load takedown for vertical forces and stresses caused
by these forces in vertical elements of a structure defined in Revit Structure.
You can load necessary information from Revit Structure:
Geometry
Material parameters Supports
Loads
Load cases
Load combinations
All results are presented in appropriate tables and on diagrams.
Assumptions:
Visualization of vertical forces includes:
o For columns: vertical force Fx
o For walls: a sum of vertical forces on the top edge of an element
Stresses are calculated using the following formula: vertical force/cross-sectional area.
This exercise uses the model SE_Unit4_Exercise2_Start.rvt.
Questions fo r Exercise 4.2
When is the Load Takedown tool useful?
Answer: It helps in calculating load on structural members when all the framing has simple frame connections with
nonredundant structures.
Are there times when the Load Takedown tool should not be used?
Answer: The Load Takedown tool is not accurate when the system is an indeterminate system with interdependent load path
that vary with each members stiffness.
Figure4.7:Structuralbeamsystem.
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Figure4.8:Tributaryareas.Exercise 4.3: Static Analysis o f Slabs
The static analysis of slabs extension enables performing static analysis of a slab defined in a Revit
Structure model.
You can load necessary information from Revit Structure, including slab geometry, constraints/supports,
load cases, load combinations, and loads. Results obtained for a defined slab model are displayed in the
graphical (maps of a selected quantity) and tabular form.
In addition, obtained results with data concerning the analyzed slab may be presented in the form of a report
(in the HTML format); a report for a slab can be printed, saved to a file, or sent to a MicrosoftExcelor
Word document.
This exercise uses the model SE_Unit4_Exercise3_Start.rvt.
Questions fo r Exercise 4.3
When is the Slab tool useful?
Answer: It is very helpful on concrete floor systems for a quick evaluation of a given load.
Why are the individual column reactions different for each column when you compare the results from the Load Takedown to
to those of the Slab Analysis tool?
Answer: The Load Takedown tool only works on simple span framing type construction. It could not accurately address the
highly indeterminate two-way concrete slab system shown in this example.
Is the total load on the structure the same when you compare the sum of the reactions of the Load Takedown tool and the su
of the reactions on the Slab Analysis tool?
Answer: Yes, this is required to satisfy the laws of equilibrium on the system as a whole. The sum of the total forces
transmitted through the structural system must be the same. However, the internal force distribution was different in the two
tools because the Static Analysis of Slabs tool accounted for the indeterminate slab structure.
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Figure4.9:Slabdesign.
Exercise 4.4: Static Analysis o f Beams
This extension enables you to perform static analysis of a single or multispan beam defined in a Revit
Structure model. It utilizes information directly from Revit Structure such as: beam geometry,
constraints/supports, load cases, load combinations, and loads. Results are displayed in both graphical
(diagrams) and tabular form. In addition, results may be presented in the form of a report (in the HTML
format). The report for a beam can be printed, saved to a file, or sent to an Excel or Word document.
This exercise uses the model SE_Unit4_.Exercise4_Start.rvt
Questions fo r Exercise 4.4
Use the beam in the model of exercise 4.1 with the Static Analysis Beam tool to create a report.
Answer: Compare these results with those of the composite beam tool used earlier.
Calculate by hand and then draw the beam load, shear, moment, and deflection diagrams, and then
compare them to the report you made in step a above.
Answer: Have the students turn these in, and compare them to the results of the analysis tool.
Figure4.10:StaticBeamtool.Exercise 4.5: Revit to Robot Link
Using the latest links available from many of the available analysis programs, you can create new models in
Revit Structure or your analysis software using the information available in the other program. In many
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cases, all geometric and design information, including materials, family instances, walls, slabs, openings,
grid lines, boundary conditions, footings, loads, and load combinations can be created, updated, or deleted
in either of the two programs using the information available in the other program.
In this exercise, you will export a model to Robot and perform several calculations using both the robust
analysis capabilities of Robot and hand calculations.
This exercise uses the SE_Unit4_.Exercise5_Start.rvt.
Using the Revit to Robot Link, export the model to Robot.
Explore the loads, materials, and structural elements created in Robot from the link.
Ask the students if anyone took the time to read further about how to use Autodesk Robot
Structural Analysis Professional in the Help files and Getting Started documentation.
Figure4.11:Robotdesignexample.