Composite Beam Design Procedure

Following is a typical composite beam design process for a new building. Note that the sequence of steps taken in any particular design may vary but the basic process will probably be essentially the same.

  1. Use the Design menu > Composite Beam Design > View/Revise Preferences command to choose the composite beam design code. In addition, this command allows review of and changes to other composite beam design preferences. ETABS provides default values for all composite beam design preferences so this command can be used to review the values and to make changes when necessary.

  2. Review the lists of sections in the various Auto-Select section properties those are section properties which define lists of section properties. When designing a structure, ETABS only chooses sections for members which have been assigned an Auto-Select section property, choosing for each member the most efficient section in the Auto-Select list. This approach is aimed at preventing ETABS from choosing sections which may be standard but are not readily available. The ETABS A-CompBm Auto-Select section includes widely available sections, but section availability varies regionally, and you should review the contents of the A-CompBm section and add all missing potentially useful sections. Note that only I-shaped and channel sections can be used for composite beam design, and all other types of sections are designed as non-composite.

  3. Create the building model. Again, unless you are modelling an existing building, the composite beams and girders should be assigned Auto-Select section properties. Be sure you create a construction load pattern and assign construction loads as design codes require them; ETABS does not automatically create them. Run the building analysis using the Analyze menu > Run Analysis command.

  4. If needed, assign composite beam overwrites by first selecting the beam(s) to be assigned overwrites and then using the Design menu > Composite Beam Design > View/Revise Overwrites command. ETABS provides default values for all composite beam design overwrites. Use this command to review the values and make appropriate changes.

  5. If needed, designate design groups using the Design menu > Composite Beam Design > Select Design Group command. Note that at least one design group must have been created using the Assign menu > Group Names command before the Select Design Group command can be used. Adding beams to a group ensures that when the group is specified for design, all beams in that group are given the same section. This step is optional. Another approach is to let ETABS choose the most efficient designs for each beam, review those, and then use the Copy Design and Paste Design commands to make the designs uniform. Unlike the Design Group method, the Design Painter yields similar cambers and similar minimum percentages of composite action.

  6. ETABS automatically creates default design load combinations based on the active design code. For composite beam design, separate design load combinations are specified for construction loading, final loading considering strength, and final loading considering deflection. These default load combinations are named DCmpC1, DCmpC2, etc., for the construction loading combinations. DCmpS1, DCmpS2, etc. for the load combinations used to check strength under final loads, and DcmpD1, DCmpD2, etc. for the combinations used to check deflections. You can replace those combinations with your own load combinations by clicking the Design menu > Composite Beam Design > Select Design Combinations command. Note that at least one design combo must have been created using the Define menu > Load Combinations command before the Select Design Combinations command can be used. Design load combinations for each of these three conditions are specified using the Design menu > Composite Beam Design > Select Design Combo command.

  7. Click the Design menu > Composite Beam Design > Start Design/Check command to run the composite beam design. ETABS designs the beams and then displays the design results. If you switch to another type of view, or exit ETABS and re-open the model, you can view the design results again by clicking Design menu > Composite Beam Design > Display Design Info.

  8. Run the building analysis using the Analyze menu > Run Analysis command. Note that the beam section properties used for the analysis are the last specified design section properties. Internal forces and deflections are now computed based on the actual self-weight of the newly designed beams.

  9. Click the Design menu > Composite Beam Design > Start Design/Check command to run the composite beam design based on the latest analysis results.

  10. Use Model Explorer > Tables to select design data for on-screen display in tabular format.

  11. Use the File menu > Report command to print composite beam design data. If a beam(s) is selected before this command is used, data is printed for the selected beam(s) only.

  12. Right click on a beam while the design results are displayed to enter the interactive design mode and interactively design the beam. If design results are not currently displayed, click the Design menu > Composite Beam Design > Interactive Design command and then right click a beam to enter the interactive design mode for that beam. Note that while the interactive design mode is active, you can also view diagrams (load, moment, shear and deflection) and design details on the screen.

  13. Select a beam(s) and use the Design menu > Composite Beam Design > Change Design Section command to change the beam design section property for the selected beam(s).

  14. Select a beam and click the Design menu > Composite Beam Design > Copy Design command then select more beams and click the Design menu > Composite Beam Design > Paste Design command to assign the design section, camber and minimum percentage of composite action of the first beam to the other beams.

  15. Run the building analysis again using the Analyze menu > Run Analysis command.

  16. Click the Design menu > Composite Beam Design > Verify all Members Passed command to verify that no members are overstressed or otherwise unacceptable. If you later change the Composite Beam Design Preferences, or make changes to the model that require re-running the Analysis, you can again click the Design menu > Composite Beam Design > Verify all Members Passed.

  17. If any beams do not pass, ETABS prompts you to select them. Choose Yes and click the Design menu > Composite Beam Design > Start Design/Check command to re-design these beams.

  18. Repeat the process in steps 15, 16, and 17 as many times as necessary to complete design. Design is an iterative process. The sections that are used to run the original analysis typically are not the same sections used at the end of the design process. The Design menu > Composite Beam Design > Verify Analysis vs Design Section command is useful for checking that the design sections are the same as the analysis sections.

  19. When the project has reached a stage where you no longer wish to change design sections, select all beams and click the Design menu > Composite Beam Design > Make Auto Select Section Null command. This removes any auto select section assignments from the selected beams.

  20. Run the building analysis again using the Analyze menu > Run Analysis command. This ensures that the analysis results reflect the final design.

  21. Click the Design menu > Composite Beam Design > Verify Analysis all Members Passed command.

  22. Use the File menu > Report > Show Project Report command to print selected composite beam design results if desired.