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# Page History

## Key

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{info}This tutorial was initially developed for the Bridge Modeler in SAP2000, but the concept applies also to [CSiBridge|csibridge:Home].{info}.

As of SAP2000 V14.1.0, it is possible to assign parametric variation to girder spacing and to offsets from reference point to the insertion points.

{toc}

h1. Key modeling steps

The key modeling steps involve:

* Creating parametric variations via "Bridge > Parametric Variations".
* Assigning the parametric variation via "Bridge > Bridge Objects > Modify/Show Bridge Object > Spans > Modify/Show > Modify/Show Section Variation Along Selected Span".

h1. Examples

Consider a 2-span bridge with two 15m long spans. The deck superstructure consists of 4 steel girders supporting a cast in place slab. The total superstructure width is 12m, the spacing of the girders is 3m and the overhangs on each side are 1.5m long.

!Variable_girder_spacing_-_bridge_deck_section_definition.png!

The width of the second span linearly increases from 12m to 15m. Let's consider the following two cases: uniform flare and "one-sided" flare.

h2. Uniform Flare

The girder spacing increases from 3m to 4m, while the structure is symmetric about the layout line. This can be modeled as follows:

* Assign linear parametric variation (from 0m to 1m) to girder spacing for all girders in the second span.
* Assign linear parametric variation (from 0m to 3m) to the total deck width for second span.

!Variable_girder_spacing_-_uniform_flare_screenshot.png!

h2. "One-Sided" Flare

The girder spacing increases from 3m to 4m, but the right edge of the bridge for both spans is a straight line. This can be modeled by assigning the following parametric variation in addition to the parametric variations assigned for uniform flare:

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

!Variable_girder_spacing_-_one_way_flare.png!

h1. Attachments

* [Relevant SAP2000 models|^SAP2000Variable girder spacing^SAP2000 models.zip]```