AU09 SpeakerHandout SE204-2

Concrete Reinforcement with Autodesk Revit Structure and Robot Structural Analysis Brian Johnson Autodesk, Inc.

SE204-2 Learn how to model, analyze, and design concrete reinforcement using Autodesk Revit Structure and Autodesk Robot Structural Analysis Professional. This in-depth discussion will show you how to model rebar in Revit Structure using manual tools and Extensions and how to analyze or design rebar using the reinforcing link to Robot. Explore the many reinforced concrete analysis and design tools in Robot for the entire structure or for specific elements. Improve your production and reduce errors using Revit/Robot interoperability. Finally, learn some approaches to scheduling rebar on construction documents.

About the Speaker: Brian is a Structural Technical Specialist for Autodesk. He is an expert in structural modeling and design using Revit Structure. Brian is a licensed structural engineer with over ten years of building design and consulting experience. During that time he worked as a Project Engineer/Manager and Principal on a variety of structures. He earned a B.S. in Civil Engineering from the University of Texas at Austin.

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Concrete Reinforcement with Autodesk Revit Structure and Robot Structural Analysis

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Introduction The scope of this course will encompass modeling and design of concrete elements in Revit Structure and Robot Structural Analysis Professional. There are many ways to approach modeling, designing, and documenting reinforced concrete (RC) elements in the Autodesk Structural Engineering portfolio. We will start with modeling reinforcement in Revit Structure using manual techniques and by leveraging the Extensions for Revit Structure. Next, well look at analysis and design of RC structures and individual components using Robot Structural Analysis. Finally, we will review detailing and documentation ideas for RC elements.

Modeling Rebar in Revit Structure There are a variety of ways to model and document concrete reinforcement in Revit Structure. One common approach is to add text parameters to concrete framing elements to specify reinforcement. This methodology is great for documentation schedules; however, you lose the other benefits of BIM such as access to quantities, visualization, and in some cases interoperability with analysis and design software.

The second approach is to model concrete reinforcement. Most concrete elements in Revit Structure can host Area & Path Reinforcement and Structural Rebar. Concrete cover settings can be created and used to facilitate modeling Rebar and to maintain consistency throughout the structural model.

All reinforcement elements are System families and as such cannot be created or nested in Component families. One additional caveat is that reinforcement can only be modeled in planar elements that is to say not in warped or twisted shapes.

Manual Modeling

Area & Path Reinforcement Area and Path Reinforcement elements are primarily used for Structural Walls, Structural Floors, and Foundation Slabs. You define Area and Path Reinforcement in Sketch mode allowing you to easily articulate the reinforcement boundaries.

The tags used for these two objects are common for representing slab and wall reinforcement. Graphically, the actual bars are only visible in Section views. In Elevation and Plan views


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only the boundaries have visibility, and generally you do not want to see the boundary lines in Construction Documents.

Revit Structure does not quantify Area and Path Reinforcement by number of bars; you will only get an Estimated Reinforcement Volume when selecting the reinforcement itself or the host element. Additionally, you cannot create a schedule of Area & Path Reinforcement. You can only grab the Estimate from the Wall or Floor schedules.

Revit Structure will trim Area Reinforcement around hosted Openings and Windows (not Doors at least not out of the box). The Estimated Reinforcement Volume is adjusted accordingly. Revit Structure makes no attempt to trim Path Reinforcement at similar openings.

Structural Rebar Structural Rebar provides more versatility than Area & Path Reinforcement since you can model it in most any concrete element. Structural Rebar has a variety of parameters to control hook lengths (e.g. 6db),

bend radii (e.g. 90, 135, 180), profile (e.g. S1, T2), and layout rules most of these settings are provided out of the box per ACI standards. Additionally, Structural

Rebar can be scheduled with all quantities and bend lengths, and you are able to control visibility in each view.

Manually modeling Structural Rebar is best done in a Section View using typical Rebar profiles and leveraging the concrete cover guides. However, you can also Sketch custom profiles as needed. As with Path Reinforcement, Structural Rebar is not aware of hosted Openings and will span right through them. As such you will want to model separate Rebar elements each side of the opening.

Extensions for Revit Structure The Reinforcement Extensions for Revit Structure provide a faster way to model Rebar for common elements such as beams, columns, walls, and footings. Most of these Extensions model with Structural Rebar; however, the Walls Extension gives you the option to model as Area Reinforcement instead.

The typical procedure is to select a single element or multiple identical elements, execute the appropriate Extension, and define the rebar parameters. The Extension will then model the reinforcement per your criteria.


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The Extension will pull in the host elements layout and cross-sectional properties. The reinforcement parameters are set up for that elements common rebar types columns have Ties and Vertical bars while Beams have Stirrups, Bottom bars, and Top bars. If you selected multiple items, the rebar will be generated for each host element.

Most Extensions have a check box to Save data without reinforcement generation. Checking this will generate and preserve the rebar information as hidden data in the Revit file. The graphic elements are not created, and the data is not accessible by the schedules. This is primarily beneficial for maintaining good model performance.

You can modify or delete rebar created with the Extensions by selecting the element(s) and clicking Modify or Delete from the Ribbon panel. Any Rebar that you modeled manually will not be altered when running the Reinforcement Extensions. It will actually appear in a User-defined reinforcement tab for review (but not modification) in the Extension dialog.


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The Interferences of reinforcing bars Extension is a special Extension that will check for interferences between one rebar and another. This can be performed for the entire model or for selected elements. A list of clashes is presented graphically and in a report for review and correction as needed.

Extensions for Robot Structural Analysis

Reinforcement Design Instead of just modeling Rebar, the Reinforcement Design Robot Extension will also facilitate structural analysis and design of reinforced concrete Beams, Columns, and Spread Footings. There are two workflows for this Extension. The first is to design new rebar for the element. The second is to verify the design of rebar previously modeled with a Revit Reinforcement Extension.

The process is to select an element for design, execute the Extension, perform the new design or verification in Robot Structural Analysis, and finally, update the Revit model. Once executed the Extension should spawn a new session of Robot Structural Analysis if not already opened.


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Note that while this is a bi-directional link between Robot Structural Analysis and Revit Structure, the link becomes asymmetrical after the first round-trip exchange. Subsequent exchanges for the same element can only be updated from Robot Structural Analysis provided no layout or cross-section revisions were made in Revit Structure.

Integration with Robot Structural Analysis The Integration link between Revit Structure and Robot Structural Analysis will optionally transfer reinforcement for beams, columns, and spread footings. In this case the entire structural model (or selected portion) is transferred rather than just the concrete element and existing reinforcement.

Similar reinforcement transfer caveats apply for the Integration Extension as for the Reinforcement Design Extension.

Reinforced Concrete Design in Robot Structural Analysis Robot Structural Analysis Professional has a robust set of reinforced concrete design tools. There are two points of entry for RC design through component design modules and via a whole-structure approach.

For either approach I recommend customizing your Job Preferences based on the project location and design requirements. These settings can be saved and reused for future projects. They generally include selecting units, material and section databases, and design codes. During the installation process Robot localizes your settings appropriately, so minor tweaking is probably all that is needed. For RC design in North America, Robot has databases and design codes for recent versions of ACI 318 and CSA A23.


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In terms of analysis and design capabilities, Robot Structural Analysis performs mild steel design in member/bar elements and panel elements such as slabs and walls. It is not possible to directly design pre-stressed and post-tension concrete elements, however, there are methods for equivalent loading. Furthermore, while two-way analysis and design are possible, Robot Structural Analysis does not allocate steel for column and middle strips. The focus of this discussion is one-way mild steel design.

RC Member Design After running analysis calculations for an entire structure, you can quickly design concrete reinforcement for all or select RC elements based on theoretical required areas of steel. The design criteria are fairly general allowing definition of typical cover and bar size to use for longitudinal and transverse bars. Different criteria can be established and used for different elements. After running the calculations, you can review but not edit the results. A similar design review can be performed for panel elements as well.

This design approach, while limited in design criteria, provides a birds eye review of all the RC elements to help you quickly determine elements that are failing versus those that are

grossly over-capacity. As such you are able to optimize the structure at a global scale.

Additionally, you can select RC elements for a more detailed and interactive design process using the RC Design modules.


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RC Design Modules The RC design modules are used for design of individual elements within a 3D structure model or as separate files independent of any 3D structure model. Furthermore, the column, beam, and spread footing modules are also used directly by the Reinforcement Design Extension in Revit Structure.

The design process is as expected. Define geometry, loads, and design criteria. Run analysis and design calculations. Evaluate results & modify design as needed. Finally, generate calculation notes and design documentation. The interface and design criteria will indeed differ


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between modules; however, the process is generally the same.

The RC Column and RC Beam modules have Reinforcement Editing (Edition) views that provide a more direct graphical way to modify the provided reinforcement. Graphical design results are shown and automatic design verification is available to instantly see the impact of a modification on elements capacity. In addition to direct modification of the design this view can also be exported in DWG or DWF format for use in AutoCAD.

Documentation

Results Output in Robot Design results for RC elements are easily produced from Calculation Notes which include, per your selection, material & section properties, loads, tabular & graphical results, required/provided reinforcement, and a schedule of quantities. Any Limit State failures and other warnings are also denoted in the note as well.

You can also create a drawing in Robot Structural Analysis showing the designed concrete reinforcement in elevation and section. The created drawing or drawings have a level of detail like that of shop and fabrication drawings. These drawings may be a useful design record to accompany the Calculation Note.

For whole-structure analysis and design, you can create customized printouts leveraging tabular data and graphical screen captures. Note that the screen captures can be created with the option to update upon printing. Finally, print or export to Word or Excel for any post-processing you might fancy.

Detailing and Schedules in Revit Structure Two common approaches for detailing and documentation of concrete reinforcement for Construction Documents are to 1) consolidate design information into tabular schedules used in conjunction with typical details (North America) or 2) to graphically represent actual conditions for elements (most other locales).


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The graphical approach is fairly simple to produce in Revit Structure. Simply create Framing Elevation Views and Sections where needed. Tag rebar to track revisions during the design process. This method requires well-defined visibility and graphic standards and no doubt, highly customized Tags. The main drawback relates to graphical representation of overlapping bars such as splices or horizontal beam bars lying in the same plane. As such, AutoCAD Structural Detailing may be a great tool to better graphically define the structure (see last section).

The scheduling approach is viable; however, many rebar schedules typically include element cross-sectional geometry mixed with the actual rebar specification. In Revit Structure these two types of data are listed in separate tables host element table and Structural Rebar table. As such the two can have relational parameters; however, they cannot be combined into a joined table. Thus, more creative methodologies are needed to produce Construction Document schedules similar to current methods.

Every firm has their own preferences and standards for how to group and schedule data. Thus, there is no one right way to accomplish this. Here are some general ideas to get you started.

Leverage Family and Shared Parameters There are a bevy of useful parameters out of the box, but they may not be enough for scheduling rebar. Enter Shared Parameters. For example, a shared Bar Section Location parameter may indicate TOP, MID, BOT, VERT, HORIZ, and Bar Span Location may have values of LEFT, CENTER, RIGHT.

Some firms chose to schedule bars with generic span properties instead of actual lengths like an A bar that extends from the mid-span of one beam to the mid-span of the adjacent beam (Top-Left or Top Right bar). A shared parameter called Bar Type may indicate A, B, or whatever code is appropriate.

Since there is no visible parameter in either the hosting concrete element or the hosted rebar element to relate one to the other, I suggest relating the Mark (or Type Mark) parameter in the concrete element to the Schedule Mark parameter in Structural Rebar. For example, I Mark a column C12 and adjust all the Schedule Marks of the appropriate rebar to C12. Note that Revit Structure and the Extensions will create all the rebar in an element with the same Schedule Mark.


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In some cases the Revit Extensions may create a new Rebar Shape type if it cannot find a match currently in the project. An example is the creation of Ties in the Column Reinforcement Extension. Instead of using the T2 Rebar Shape, Revit Structure generates a new type called Rebar Shape 1. They are nearly identical with exception of the Rebar Hook parameter (Standard v. Stirrup/Tie). So, on a schedule the Rebar Shape field will have values like 00, 17, S1, T2, and then Rebar Shape 1. Instead of trying to revise each instance of Rebar Shape 1 to T2, just create a new parameter called Shape with the value of T2 for both Rebar Shape Types. (Note: the difference between a Standard Bend and Stirrup/Tie bend definition is probably too detailed for Construction Documents, hence this methodology.)

Tweak Tags Consider your approach to tagging both concrete elements and rebar. Instead of only showing a concrete beam size (Type) or only the beam Mark, create a tag with both. This way the cross-section geometry is indicated on plan (rather than the schedule) and the Mark will correlate to the rebar Schedule Mark in the schedule.

Schedules The Structural Rebar schedules created out of the box will look more like a shop list. You could even schedule all the ACI bend dimensions if you so desired. However, leveraging the aforementioned parameter techniques you will be able to represent the information used in your current schedules. It will more than likely have a different format.

Use Filtering criteria to create schedules for just beams or just columns. Sort and group by the rebars Schedule Mark. Furthermore, consider using a Key Schedule to possibly improve the layout.

Data Export Lastly, consider using External applications to create schedules. Consider this workflow:


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1. Export the Revit data to a data-store like Excel, Access, or MySQL. 2. Create the relationships between hosting concrete elements (Mark) and hosted Structural Rebar

elements (Schedule Mark) using Primary/Foreign Keys. 3. Add custom fields not used in Revit, as needed. 4. Merge the related data and custom fields using custom Queries, for example. 5. Link this external table to an AutoCAD file. 6. Link the AutoCAD table into a Drafting View in Revit Structure.

Detailing and Schedules in ASD Concrete reinforcement created via Extensions in Revit Structure or in Robot Structural Analysis can be exported to AutoCAD Structural Detailing to create shop drawings. Design engineers in North America typically do not perform this level of detail for Construction Documents; however, it might prove useful in some cases to quickly generate concrete reinforcement details for inclusion in Construction Documents, design calculation notes, or presentation drawings.

Summary Remember that goals for the Building Information Modeling process is to stream line our design efforts, leverage data for more than just documents, and ultimately produce a better structure. This course looked at various ways to accomplish those goals by modeling concrete reinforcement in Revit Structure, analyzing and designing reinforcement in Robot Structural Analysis, and documenting the modeled rebar in Revit Structure.

IntroductionModeling Rebar in Revit StructureManual ModelingArea & Path ReinforcementStructural Rebar

Extensions for Revit StructureExtensions for Robot Structural AnalysisReinforcement DesignIntegration with Robot Structural Analysis

Reinforced Concrete Design in Robot Structural AnalysisRC Member Design/RC Design Modules

DocumentationResults Output in RobotDetailing and Schedules in Revit StructureLeverage Family and Shared ParametersTweak TagsSchedulesData Export

Detailing and Schedules in ASD

Summary

AU09 SpeakerHandout SE204-2

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