This tutorial describes how to model a composite bridge, with a concrete slab over steel girders for which the girder height varies between the pier sections and midspan sections.

Modeling Steps

The key idea is to assign nonprismatic girder section to the bridge deck section to obtain the desired variation.

Create New Model from Template

• Use "File > New Model", select "KN, m, C" units and Quick BrIM template.
• Set span lengths to "30; 30" and select bridge deck section type "Steel Girder"

Define Nonprismatic Steel Girder Sections

• "Define > Section Properties > Frame Sections"
  • rename the default girder section "FSEC1" to "GRD 1.22m"
  • create copy of "GRD 1.22m" section, change the overall height to 2.22m and save the section as "GRD 2.22m"
  • create nonprismatic sections "GRD span1" and "GRD span2" (via "Add New Property" button, frame section property Other and [nonprismatic section]) to specify 1.22m deep girder for the first 15m of the length and variation from 1.22m deep girder to 2.22 deep girder for the remaining 15m of the girder length using the previously defined sections "GRD 1.22m" and "GRD 2.22m". For "GRD span1" section, the depth will increase, while for "GRD span2 section, the depth will decrease:

Create Bridge Deck Sections

• Use "BrIM > Deck Section > Add Copy of Section" menu command to create bridge sections to be assigned to the first and the second spans of the bridge object. These sections will be named "SPAN1" and "SPAN2" and will utilize the previously defined nonprismatic girder sections "GRD span1" and GRD span2" as shown below:

Assign Bridge Deck Sections to the Bridge Object

• Use "Bridge > Bridge Objects > Modify/Show Bridge Object > Modify/Show Assignments, Spans" menu command to assign the previously defined bridge deck sections "SPAN1" and "SPAN2" to the bridge object spans 1 and 2:

• Go to "View > Set Display Options > Show Extruded Shape" to display the extruded shape of the bridge: