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name = Steel girder bridge with variable flange thickness

description = Simple tutorial to create steel girder bridge with variable flange thickness.

keyword = bridge; steel bridge; bridge modeler

program = SAP2000

version = V14.0.0

status = done

id = ok/bridge - variable flange thickness i girder steel bridge}}

This tutorial describes how to model a composite bridge, with

Live Template


This tutorial was initially developed for bridge modeler in SAP2000, but the concept applies also to CSiBridge.

This tutorial describes the modeling process for a composite bridge composed of a concrete slab over steel girders that have with variable flange thickness.

Modeling Steps

The key idea is to assign nonprismatic girder section

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Modeling steps

To obtain the variable flange thickness desired, users should assign non-prismatic girder sections to the bridge deck section to obtain the desired variation of flange thickness.



new model from



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

Define Nonprismatic Steel Girder Sections

  • ".

Define non-prismatic steel girder sections

  • Select Define > Section Properties > Frame Sections "

    • rename Rename the default girder section " FSEC1 " to "'GRD 50mm FLANGE"create copy of "GRD 50mm FLANGE" Flange'.
    • Copy the 'GRD 50mm Flange' section, change the thickness for the top and bottom flanges to 75mm and , change the section depth to 1.27m (to keep the maintaining consistency with previous web depth the same as for the previous section), and then 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) Flange'.
    • Select Add New Property > Frame Section Property (other) > Non-prismatic Section to create non-prismatic sections 'GRD span1' and 'GRD span2' as follows: (1) for "'GRD span1" ', specify the "'GRD 50mm FLANGE" Flange' section for the first 20m of length of the section and ", and the 'GRD 75mm FLANGE" Flange' section for the next 10m of length of the section; (2) for "'GRD span2" ', specify the "'GRD 75mm FLANGE" Flange' section for the first 10m of length of the section and ", and the 'GRD 50mm FLANGE" Flange' section for the next 20m length of the sectionof length. This process is shown in Figure 1:

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Figure 1 - Section definition

Create bridge deck sections

  • Use "the 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 Name these sections SPAN1 and SPAN2, and utilize the previously-defined nonprismatic non-prismatic girder sections "'GRD span1" ' and 'GRD span2" ', as shown belowin Figure 2:

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Assign Bridge Deck Sections to the Bridge Object


Figure 2 - Bridge section data

Assign bridge deck sections to the bridge object

  • Use the 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 2first and second spans of the bridge object, as shown in Figure 3:

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Figure 3 - Span assignments

  • Set OpenGL graphics via "using the Option > Graphics Mode > OpenGL " menu command
  • Go to "Use View > Set Display Options > Show Extruded Shape " to display the extruded shape of the bridge (. Please note that there is a slight graphical display issuediscontinuity, but though the frame elements are inserted such that the locations at the top-of the -web locations form a continuous line; this can . This may be checked by reviewing the insertion point , which is (top center, ) and offsets). The extruded view is shown in Figure 4:

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Figure 4 - Extruded view

See Also


  • File | filename = Variable flange thickness steel girder bridge SAP2000 V14.0.0 | title = SAP2000 V14.0.0 model (Zipped SDB file)

Bridge Modeler