Data Utilization Report California Strong Motion Instrumentation Program, Report No. CP/SEAM-09/01, December 1, 2009.
This investigation focused on developing an improved understanding of challenges associated with computation of nonlinear response of three-dimensional building to recorded ground motions, and if the base shear estimated from recorded motions, denoted as “estimated base shear” in this report, is an accurate indicator of the true base shear. For this purpose, three-dimensional models of two buildings – one reinforced-concrete building and one steel building – are developed in OpenSees and Perform3D¬. The analysis of these models included pushover analysis for lateral force distribution proportional to the first mode in each of the two principle directions, and nonlinear response history analysis (RHA) to compute response for 30 ground motions recorded during past earthquakes. It was found that modeling assumptions as well as different software may lead to significantly different pushover curves: concentrated plasticity model leads to lower strength, early initiation of yielding, and post yielding strength loss in pushover curves compared to spread plasticity model, strength loss model for beams/columns leads to significant post yielding strength loss in the pushover curve, and differences in solution schemes and convergence criteria available in different software programs also affect the pushover curves. It was also found that there prediction of median peak response from different software can differ from 10% to 40%. Finally, the median estimated base shear exceeds the true base shear by 10% to 20% with the value exceeding by as much as 50% for individual earthquake. Therefore, estimated base shear should be used with caution as an estimate of the true base shear.
Civil and Environmental Engineering