Rocking Response of Taller Reinforced Concrete Walls

Abstract eng:
The study of seismic response of taller reinforced concrete shear walls with rocking foundations is carried out on the example of a 20-storey building. The building is framed by simple ductile concrete shear and located in Montreal, Canada. The location is representative of Eastern North American seismic conditions characterized by high-frequency ground motions that can exemplify the impact of higher modes on the response. The walls are designed and detailed according to the Canadian design provisions for ductile shear walls. Different options for the foundation design are considered to examine the effect of foundation size on the type of structural response. Two-dimensional nonlinear time history analyses of the wallfoundation system were performed using the OpenSees program for simulated ground motions compatible with the design spectrum. Wall inelastic behaviour and the nonlinear soil response were both represented in the model. Soil-structure interaction and uplift due to overturning are modeled using the beam-on-nonlinear-Winkler-foundation concept. The overturning moments, base shears and roof displacements are compared to those obtained assuming a fixed-base condition to quantify the impact of rocking on the superstructure. The usefulness of rocking to mitigate higher-mode effects is also evaluated. The foundation displacements and stresses in the soil are examined to assess the consequences of the rocking behaviour on the global structural response. The analyses show that the code compliant design exhibited yielding at the wall base and rocking. Reduction of foundation size increased the rocking response and eliminated the inelastic response in the superstructure. Rocking reduced the force demand on the superstructure without significantly increasing the displacements, but some permanent deformations and high bearing pressures developed in the soil under the foundation edges. Rocking did not reduce the impact of higher modes on the response.

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