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Full Scale Nonlinear Seismic Bridge Design Analysis on a Desktop Computer

This paper, written by Peter Barrett of CAE Associates, and Eduardo Salete, Professor at UNED in Spain, was presented at the NAFEMS World Congress in 2011.


With advances in software and desktop computer performance it is now possible to perform automated design calculations using full scale, real time nonlinear simulations.  This paper presents an example of a detailed bridge seismic analysis that simultaneously performs analysis and design calculations automatically.  The model includes nonlinear hysteresis base isolation supports which enable the predictions of local and global deformation histories.  The fidelity of the model is sufficient to capture time-marching stresses in the columns and concrete deck where automated code checking is applied.  The analyses are run using shared memory parallel processing to reduce computational resources.

In most design projects high end analysis and local concrete design are preformed independently with data transfer limited to isolated forces, moments or displacements often imported manually into spreadsheets.  The more complex analyses are limited to a validation role as opposed to being implemented early in the design cycle. If these analyses discover necessary design changes, these modifications can lead to time and cost overruns.

The modeling technique presented herein demonstrates the use of integrated commercial FEA software that automates the design of concrete reinforcement during the analysis simulation meeting the extreme loading conditions of the seismic event.  Bending, shear and torsional reinforcement are designed on an element-by-element basis where the enveloping rebar requirements can be graphically displayed.  Displacement, stress and reaction time history data is also captured.

Nonlinear effects include large deflections and surface-to-surface contact elements used to model expansion joints as well as the hysteretic response of the base isolation supports.   The model includes a combination of beam, shell and 3-d solids, where the post processing of the 3d solid elements is performed using a unique method of transforming these results into design based forces and moments. 

These calculations are done on a desktop computer utilizing parallel processing algorithms that leverage its multiple cores.  Benchmark results on the computational efficiencies are reported.