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{live-template:Tutorial}

{info}While this tutorial was developed for the [SAP2000|sap2000:home] bridge modeler, the concept also applies to [CSiBridge|csibridge:Home].{info}


h1. Key modeling steps

* Create a parametric variation through the Bridge > Parametric Variations option.

* Assign the parametric variation through the Bridge > Bridge Objects > Modify/Show Bridge Object > Spans > Modify/Show > Modify/Show Section Variation Along Selected Span option.


h1. Example

Consider a two-span bridge with two 15m long spans. The deck superstructure consists of four steel girders supporting a cast-in-place slab. Total superstructure width is 12m, girder spacing is 3m, and the overhang on each side is 1.5m.

These specifications may be defined as shown in Figure 1:

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!Variable_girder_spacing_-_bridge_deck_section_definition.png|align=center,border=1!

{center-text}Figure 1 - Bridge deck section definition{center-text}

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For the second span, the width linearly increases from 12m to 15m. Uniform flare and one-sided flare will be considered.

h2. Uniform flare

Girder spacing increases from 3m to 4m. The structure is symmetric about the [layout line|tutorials:Layout-line geometry]. This may be modeled as follows:

* For all girders in the second span, assign linear parametric variation (from 0m to 1m) to girder spacing.

* For the second span, assign linear parametric variation (from 0m to 3m) to the total deck width.

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!Variable_girder_spacing_-_uniform_flare_screenshot.png|align=center,border=1!

{center-text}Figure 2 - Variable girder spacing for uniform flare{center-text}


h2. One-sided flare

Girder spacing increases from 3m to 4m, while for both spans, the right edge of the bridge is straight. This may be modeled by assigning, in addition to the parametric variations for uniform flare, the following:

* Linear parametric variation (from 0m to 1.5m) to X offset from the reference point to the insertion point.

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!Variable_girder_spacing_-_one_way_flare.png|align=center,border=1!

{center-text}Figure 3 - Variable girder spacing for one-sided flare{center-text}


h1. Attachments

* [Relevant SAP2000 models |Variable girder spacing^SAP2000 models.zip] (zipped SDB file)