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LARSA Special Session / Latest Development and Technologies in Bridge Analysis and Design


Speaker:   Ali D Karakaplan, Eng.Sc.D.

Increasing complexity in the design and construction of bridges is driving demand for ever-more sophisticated software.  New technologies implemented in today’s software are making bridge design and construction better, safer and more economical.  Developed for the rigorous needs of segmental post-tensioned and cable-supported bridges, ‘4D’ analysis has become essential for design and construction of almost all bridge types. The ‘4D’, which stands for the fourth dimension, or time, is the basis of staged construction analysis. In a staged analysis, changes to the structure over time due to the construction sequence, loading, and time-dependent material properties (such as concrete creep and shrinkage) are modeled and captured using independent steps. ‘Analysis Scenarios’ For live load, eigenvalue, time-history, pushover, and other analysis types can be performed at the appropriate steps during the staged construction analysis.

Influence surface based live load analysis, which is an extension of the influence line concept to 3D models, is becoming more widely used. Influence surfaces have many advantages over influence lines including the automatic distribution of load across girders, automatic transverse placement of design lanes and use of wheel loads instead of axle loads. Influence surface live load analysis is an important tool when using AASHTO LRFD on curved or skewed bridges.

Finite element analysis has until now been considered a difficult and tedious method for modeling and analysis of entire bridge structures. But  with the tools available, a 3D finite element model can be created automatically based on parameters entered. These models can be edited prior to analysis, followed by code check and load rating. Since the code check and load rating are based on a fully 4D analysis using FE based model, these results are superior to a grillage analysis or other simplified method for curved and skewed bridges.

Other advanced methods used by today’s bridge engineers include nonlinear dynamic analysis and nonlinear plastic pushover, which model the inelastic behavior that bridges experience during earthquakes, and vehicle-track-structure-interaction (VTSI) analysis for bridges supporting high-speed rail.

About Ali D Karakaplan, Eng.Sc.D.

Ali Karakaplan has been developing analysis software since the 1980s. He founded New York-based LARSA, Inc. in 1995 and continues to lead the company and develop the analysis engine. The pioneer of ‘4D’, LARSA, Inc. has created a single platform for post-tension concrete, cable-supported and curved steel girder bridge design and construction.  Within a decade of its introduction, LARSA 4D Bridge Series became a standard in leading U.S. firms and for major projects for bridge design and construction.

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