Analyses of seismic performance of a code designed reinforced concrete building

Abstract

This paper studies the inelastic seismic performance of a 12-story reinforced concrete (RC) building. The building utilizes a structural system with moment-resisting frames in the longitudinal direction and a dual structural system consisting of coupled shearwalls and moment-resisting frames in the transverse direction. The frame elements, the shearwalls and the coupling beams are sized and detailed on the basis of the 1994 edition of the Uniform Building Code for seismic Zone 4 (regions of high seismicity). The global and local inelastic behavior of the building in the two orthogonal directions is studied under several earthquake ground motions. Nonlinear concrete behavior, including stiffness degradation and strength loss caused by cracking, crushing of concrete and yielding of steel, is simulated by using the fiber beam-column element of the DRAIN-2D program. Pushover analysis is used to determine the global ductility of the structure. The study indicates that the design strength may be inadequate for some critical earthquakes which tend to induce biased response in the structure. The global response of the building is not much altered when the effect of vertical accelerations is also included. Weak coupling between walls induces large ductility demands in them, which can be directly reduced by increasing the wall strength. Well designed coupled walls are more efficient and economical than isolated walls or weakly coupled walls. Optimum values of beam and wall stiffness and strength can be chosen to minimize ductility demands on the walls of a coupled wall system. The coupling between walls appears to become ineffective, due to the simultaneous yielding of coupling beams and walls when a structure is subjected to an early and large displacement pulse, such as that produced by the Northridge earthquake in the near-field. Although the increasing of wall strength decreases the ductility demand, the real challenge, in this case, is to reduce the peak displacement, which is not particularly sensitive to the strength values.