LARSA 4D Introductory Training Manual for Bridge ... - LARSA, Inc.

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LARSA 4D Introductory Training Manual for Bridge Projects 22
LARSA 4D Introductory Training Manual for Bridge Projects Influence Line Live Load Analysis Influence line and surface analysis is an extension of the moving load analysis which uses the effects of a unit load to rapidly compute the effects of arbitrary complex load patterns on design lanes. Influence-based results are often necessary to comply with bridge design codes, such as the AASHTO LRFD, which requires finding the worst case scenario out of more possibilities than can be analyzed individually. LARSA 4D supports both influence lines and influence surfaces. Influence lines is used on models where girders are represented by linear elements, whereas influence surfaces is used on models with a deck surface modeled as plate elements. In this section we will use influence line analysis to find the worst-case truck positioning according to AASHTO LRFD. There are two parts to influence analysis. The first part determines how the influence coefficients (i.e. unit loads) are computed on a lane on the bridge. The second part specifies vehicle and uniform load options according to a design code. Preparing the Influence Coefficients: The Lane A “lane” in LARSA 4D is a linear path in the model along which a vehicle pattern or unit load will march in a moving load or live load analysis. A lane can take any path through 3D space. If it falls off of a girder, the loading will cause moments. For an influence line analysis, we must place a lane on the structure where a traffic lane will fall. Because our cross-section is 24 ft wide, two 12 ft lanes will fit: one 6 ft offset to the left (+y side) and one 6 ft offset to the right (-y side). We will start by creating the right lane. Create a new lane using Draw → From Selected Members → Lane . A new lane is created riding on the top of the cross-section surface. It appears as a line above the member elements. If you cannot see the lane, open Graphics → Show and ensure Lanes/Surfaces is checked. Graphics > Show 23
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LARSA 4D Introductory Training Manual for Bridge ... - LARSA, Inc.

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