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This tutorial describes how to model a composite bridge, with a concrete slab over steel girders that have variable flange thickness.

*On this page:*


h1. Modeling Steps

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

h2. Create New Model from Template

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

h2. Define Nonprismatic Steel Girder Sections

* "Define > Section Properties > Frame Sections"
** rename the default girder section "FSEC1" to "GRD 50mm FLANGE"
** create copy of "GRD 50mm FLANGE" section, change the thickness for the top and bottom flanges to 75mm and section depth to 1.27m (to keep the web depth the same as for the previous section) and save the section as "GRD 75mm FLANGE"
** create nonprismatic sections "GRD span1" and "GRD span2" (via "Add New Property" button, frame section property Other and [nonprismatic section|kb:nonprismatic section]) as follows: (1) for "GRD span1" specify the "GRD 50mm FLANGE" section for the first 20m length of the section and "GRD 75mm FLANGE" section for the next 10m length of the section; (2) for "GRD span2" specify the "GRD 75mm FLANGE" section for the first 10m length of the section and "GRD 50mm FLANGE" section for the next 20m length of the section:


h2. Create Bridge Deck Sections

* Use "Bridge > 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:


h2. 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:


* Set OpenGL graphics via "Option > Graphics Mode > OpenGL" menu command
* Go to "View > Set Display Options > Show Extruded Shape" to display the extruded shape of the bridge (there is a slight graphical display issue, but the frame elements are inserted such that the locations at the top of the web form a continuous line; this can be checked by reviewing insertion point, which is top center, and offsets):

!Extruded view.png|width=1000pxpx!