```{live-template:Tutorial} {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. *On this page:* {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|Variable girder spacing^SAP2000 models.zip]```