UC San Diego

The primary objective of this thesis is to evaluate the effects of torsion on the nonlinear seismic response of a thirteen-story reinforced concrete frame-wall structure with an asymmetric stiffness in plan. The NEHRP building structure, located in Berkeley, CA and previously designed by André Barbosa, was modeled in ETABS and SAP2000 to perform several analyses. The models accounted for realistic cracked concrete section stiffnesses, expected material properties, and nonlinear plastic hinges. Due to limitations of ETABS in performing nonlinear dynamic time history analysis, the model was exported to SAP2000. An asymmetric lateral stiffness model was created by moving one of the shear walls from the center of the building toward the outside of the building. OpenSees was used to find the nonlinear hinge moment-rotation relationships. Using a suite of seven ground motion record pairs, an essentially linear dynamic time history analysis was performed on the symmetric and asymmetric ETABS models. The SAP2000 models were used to perform a series of nonlinear static (pushover) analyses. Fully nonlinear, including material and geometric nonlinearity, time history analyses were performed on the SAP2000 models using the seven ground motion pairs, appropriately cut to shorter lengths to reduce the analysis run-time. In each analysis case, the results of the symmetric and asymmetric models were compared. Overall, the asymmetric model typically experienced torsional effects and larger displacement responses than the symmetric model. The more nonlinear the structure behaved, the more influence torsion had on the response of the model with asymmetrically-placed shear walls