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# Variable girder spacing

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

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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.

# 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".

# 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.

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.

## 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.

## "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.

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