Seismic-Response Analysis of RC C-Shaped Core Walls Subjected to Combined Flexure, Shear, and Torsion

Abstract

Although dynamic torsional responses are often regarded as secondary effects in the seismic design of symmetric-plan buildings, torsional effects arising from plan asymmetry can be substantial in some cases. In RC wall buildings, a combination of flexural, shear, and torsion dictates the type of failure, which needs to be addressed in the design of RC walls. This study investigates two aspects of building structures with C-shaped RC walls: (1) evaluation of seismic force demand at different levels of torsional sensitivity, and (2) effectiveness of using the dual plastic hinge method in controlling the seismic shear force demand. A macroscale modeling approach using the wide column analogy captures the inelastic response of C-shaped RC wall buildings, including torsional effects. The numerical model of the wall is validated against available experimental data. Nonlinear time history analyses of typical multistory buildings located in eastern North America (8-, 12-, and 16-story) are performed. Four different levels of torsional sensitivity (B=1.3, 1.7, 2., and 2.5) are considered for each building configuration. Although the studied range of torsional sensitivity has no substantial effect on the bending moment envelope of the building, it significantly increases the story shear force demand during an earthquake. The shear force envelopes in torsionally sensitive buildings (B>1.7) exceed the capacity design envelope predicted by the response spectrum analysis of a large number of selected ground motions. The dual plastic hinge design method recently proposed by other researchers is adopted and is found to be an efficient method, resulting in lower shear force demand along the height of the structure, especially when high torsional flexibility is expected.