Workflows for Analysis and Design Using Autodesk® …aucache.autodesk.com/au2011/sessions/4166/class... · Workflows for Analysis and Design Using Autodesk® Revit® Structure and

Workflows for Analysis and Design Using Autodesk®

Revit® Structure and Add-ons Thomas Fink – SOFiSTiK AG

SE4166

This class will present an overview of SOFiPLUS, an interface for structural analysis based on AutoCAD® and explain how it complements Autodesk® Revit® Structure. You will learn how to maximize benefits from Revit Structure 2012 by leveraging its new analytical model. We will also discuss the importance of working with partial models (slabs/shear walls, etc.) and code checking for single parts of the building (columns, slabs, etc.).

About the Speaker

After receiving his diploma in structural engineering at Technical University in Munich, Thomas has

worked in structural engineering and software development for over 30 years. He is co-founder and CEO

of SOFiSTiK AG, a leading German supplier of software for analysis, design, and detailing. He is on the

board of the German section of buildingSMART®, and chairs the working group “innovations” of the

Bavarian chamber of building engineers. Whenever time allows, he loves to fly balloons and to sail.

E-Mail: [email protected]

Workflows for Analysis and Design Using Autodesk® Revit® Structure and Add-ons

Overview about this Lecture

How can structural engineers benefit from Building Information Modeling (BIM)? This lecture

will discuss several areas and demonstrate the workflow using the current product portfolio of

Autodesk® and SOFiSTiK®.

Autodesk® Revit® Structure integrates the analytical model of a building structure with

the real geometry in the form of the architectural or coordination model. Engineers use this

model for structural analysis and design. However, it will never be possible to include all

analytical data, or perform all necessary design tasks with this model. As in the past, there

will always be a need for partial and finer models, as well as particular design tasks such as

footing design.


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Step 1: Description of the Project

General For this Lecture a typical small fabrication hall with office or storage rooms included is

used. However, all relevant topics can be discussed and demonstrated, even with this small

and simple project.

The Project Figure 1 shows the hall in both a physical and analytical view. The structure consists of

prefabricated concrete units. The lecture starts with the concrete hall already defined in

Autodesk® Revit® Structure. Basic knowledge about this software is beyond the scope for

this lecture.

Figure 1: Physical and analytical view of the sample project

What should be considered in creating such a model? The appropriate level of detailing should be used. In this case the physical model

will also be used for the formwork drawings.

Support conditions

Loading (selected loads only in our sample)

What should be considered when adapting and completing the analytical

model? Insignificant eccentricities should be ignored. The analytical model can be adjusted

independently to the physical model.


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Materials and Cross Sections should be checked. (As shown in Figure 2, it is very

easy to assign SOFiSTiK materials and cross sections with the mapping tables in

SOFiSTiK Extensions for Revit)

Working with SOFiSTiK load distribution areas, it is necessary to define element

groups using their respective parameter (see Figure 3)

Figure 2: Mapping tables

Step 2: Export to SOFiSTiK Analysis Software

“SOFiSTiK Extensions for Revit” provides a seamless integration of FE analysis and design

into Autodesk® Revit® Structure. Automatic FE meshing, using one of the most powerful

3D mesh generators can be started directly to allow quick changes of the calculation model.

Figure 3 shows the ribbon tab with all commands. There are three new Parameters defined

by SOFiSTiK that are necessary to control the further workflow.

SOFiSTiK_Group Controls the group which generated elements will belong to. Groups

are used to control the distribution of loads, and are also used in

many design and post processing tasks.

SOFiSTiK_UseExcentricity Controls whether members within the analytical model that are

placed eccentrically from their center of gravity will be exported

with this eccentricity or not.

SOFiSTiK_EffectiveWidth Beams integrated into slabs must be designed as T-Beams. The

parameter controls the effective width of the T-Beam.


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Figure 3: SOFiSTiK Extensions for Revit Structure

After pushing the Export Button the user is prompted to create a new project and a new

database (see figure 4). A country-specific standard and other global project settings can be

chosen within the export dialog. After creating a SOFiSTiK project different export

properties may also be selected. For example, it can be selected whether the entire system

shall be exported or only a subsystem. To check the overall behavior of the building the

entire model is first exported. This is also needed for earthquake dynamic design.

Figure 4: SSD - SOFiSTiK Structural Desktop

Once we have exported the model, we switch to the SOFiSTiK Structural Desktop (SSD) to

verify the exported data. Figure 5 shows a screen print of SOFiSTiK Animator, a perfect tool

to visually check what the software is doing. We see the 3 element groups defined in Revit


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in different colors. It is also very useful for checking the load distribution areas. For

instance, we will see, that the free area load over the structure requires information about

which element groups will actually be loaded. These groups can be displayed in different

colors.

Figure 5: System check in SOFiSTiK Animator

Step 3: Completion in SOFiPLUS

Since not everything that is possible within SOFiSTiK can be specified in Autodesk®

Revit® Structure, all missing information can be added either with SOFiSTiK’s powerful

macro language or with SOFiSTiK’s graphical preprocessor SOFiPLUS. The possibility to

reuse those definitions for later runs with a modified model is essential for the overall

performance and acceptance of BIM.

SOFiPLUS is based on AutoCAD® and is SOFiSTiK's standard pre-processor. SOFiPLUS

enables the engineer to generate almost any FE-structure, from simple slabs to arbitrary

freeform-surfaces. The program takes full advantage of the enhanced AutoCAD® modeling-


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technology. It is available as an add-on application running on a standard AutoCAD®

installation, or as a standalone version based on AutoCAD® technology. This approach of

using AutoCAD® as a pre-processor for FEA is most likely unique in the AEC-world.

Figure 6: Defining additional properties in SOFiPLUS

As a small sample, we will use SOFiPLUS to adjust the properties of two load distribution

areas. The snow load which is defined above our structure shall have a “depth” of two

meters and will load the members in groups 2 and 3 only. We can, of course, modify almost

everything else in SOFiPLUS, e.g. geometry, cross sections, loading, boundary conditions

etc. However it is recommended to do as much as possible within Autodesk® Revit®

Structure. All modifications done in SOFiPLUS must be repeated each time the Revit Model

is changed and exported. As BIM becomes increasingly popular, it is very likely that this

problem will be eliminated in the future.

Step 4: Calculation of the entire system

Now we can go back to the SSD and proceed with the analysis. All features of SOFiSTiK

software are available here without any restrictions. In our case we will add the task

“Eigenvalues” to determine the first 10 eigenforms.


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shows the deformation behavior

of the structure for eigenvalue 3.

Additionally, the 4 load cases are

analyzed and superpositioning of

the results is performed, as well

as an initial design of beams,

columns, slabs and walls.

Figure 7: Deformation due to eigenvalue 3

After the analysis of the entire system, in practice it is necessary to perform many other

design tasks. For instance we need a finer 2-D subsystem for the analysis of the slab in

order to exclude membrane forces and obtain realistic shear forces.

Step 5: Export and Analysis of the Slab as Subsystem

As previously discussed, it may be necessary to perform a more refined analysis of the slab

as a 2D system. There exist three major obstacles to this which are addressed perfectly

with SOFiSTiK Version 2012.

First, there is just one area load over the whole slab. For superpositioning it is necessary to

divide this into many smaller areas defined in different load cases. The command “Area

Load Division” allows you to divide the existing load into appropriately smaller ones in

seconds. Figure 8 shows the result.


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Figure 8: SOFiSTiK Area Load Division

Secondly, the appropriate support conditions must be defined. The “Partial support into

sub system” function not only creates a new separate database containing the subsystem,

but also detects all supporting elements and creates rigid or elastic support conditions in

their place.

Figure 9: Deformation resulting from a partial area load

Thirdly, there is a rectangular beam supporting the slab. For the concrete beam design a T-

section beam is required. The parameter “SOFiSTiK_EffectiveWidth” allows the user to


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define a theoretical flange from the slab for use in the design task; however this T-beam

section will not be used in the analysis because it will result in a localized area of increased

stiffness. Instead, a complex algorithm in SOFiSTiK calculates an appropriate stiffness in

these locations, resulting in realistic design results.

Figure 10: Bending Moment of the T-Beam

Step 6: Code Checking - Design of footings

This step demonstrates how to leverage the BIM model to perform code checking tasks on

a sample of single pad footings. Currently, a software prototype is used to integrate existing

SOFiSTiK software for design and detailing of footings into Autodesk® Revit® Structure.

Figure 11: Sleeve foundation example


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The Software uses the support forces stored in the SOFiSTiK database. You can define all

the required information such as maximum soil pressure, type of foundation etc. The size

and material of the columns is transferred from the model automatically.

After design, the foundation is added into the model automatically. The program makes a

proposal for the required rebars, which can also be added to the model.

Step 7: Detailing the slab

Finally the detailing tasks should be done. In this sample we create a reinforcement plan

based on the results of the slab analysis and on the geometry defined before. Because the

Rebar objects in Autodesk® Revit® Structure do not currently have the functionality

needed in Europe, we use the program SOFiCAD, the quasi-standard tool used in Germany

for RC detailing based on AutoCAD®. This software is well connected with the SOFiSTiK

FEA Software and can make use of any drawing sheets defined in Autodesk® Revit®

Structure.

Figure 12: Export to SOFiCAD

We first export a Revit formwork drawing as a base to create the reinforcement plan in

SOFiCAD. There is a function which creates a master dwg-file for a sheet and an external

reference (XREF) for each view on this sheet. Reinforcement bars and meshes will be

drawn on the master dwg-file. This allows easy handling of modifications in the geometry


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by performing another export of the views. Any existing reinforcement will not be deleted

by this process; it needs only to be adjusted to suit the changed geometry.

Figure 13: Required floor reinforcement

Secondly, we import the required reinforcement into the drawing. This information is

shown in a raster with numbers colored according to their value. It is possible to obtain

automatic reinforcement layouts with loose bars, prefabricated meshes or BAMTEC®

carpets. Another approach is to define a basic reinforcement layout. The software is then

able to display the amount of reinforcement which is still required, as demonstrated in

Figure 13 with meshes. A popular workflow is to cover the basic reinforcement with

meshes and to then add further loose bars to cover the peaks.

Conclusion

This lecture has demonstrated how structural engineers can benefit from the idea of BIM.

Many processes work very well with today’s software solutions; however, there are still

some gaps which software developers need to close. As the idea of BIM becomes more

popular in the world, there is no doubt that this will happen in the near future.

Documents

Workflows for Analysis and Design Using Autodesk® …aucache.autodesk.com/au2011/sessions/4166/class... · Workflows for Analysis and Design Using Autodesk® Revit® Structure and