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This tutorial describes the modeling process for a composite bridge composed of a concrete slab over steel girders with variable height between pier sections and midspan sections.


  • Select Define > Section Properties > Frame Sections

    • Rename the default girder section FSEC1 to 'GRD 1.22m'.

    • Copy the 'GRD 1.22m' section, change the overall height to 2.22m, and save the section as 'GRD 2.22m'.

    • Select Add New Property > Frame Section Property (other) > Nonprismatic Section to create nonprismatic sections 'GRD span1' and 'GRD span2'.

    • Use the previously defined sections 'GRD 1.22m' and 'GRD 2.22m' to specify a 1.22m girder depth for the first 15m of length, and a variation from 1.22m to 2.22 for the remaining 15m of the girder length. Depth increases for the 'GRD span1' section, and decrease for the 'GRD span2'. This procedure is shown in Figure 1:

Figure 1 - Haunched steel-girder bridge

Create bridge deck sections

  • Use the BrIM > Deck Section > Add Copy of Section command to create bridge sections to be assigned to the first and the second spans of the bridge object. Name these sections SPAN1 and SPAN2. Specify the previously-defined non-prismatic girder sections 'GRD span1' and 'GRD span2', as shown in Figure 2:

Figure 2 - Deck section definition

Assign bridge deck sections to the bridge object

  • Use the Bridge > Bridge Objects > Modify/Show Bridge Object > Modify/Show Assignments, Spans command to assign the previously-defined bridge deck sections SPAN1 and SPAN2 to the bridge object spans 1 and 2, as shown in Figure 3:

Figure 3 - Deck section assignment

  • Select the View > Set Display Options > Show Extruded Shape option to display the extruded shape of the bridge, as shown in Figure 4:

Figure 4 - Steel girder bridge

See Also