Seismic Design of Low-Rise RC Wall-Frame Buildings for Preferred Performance

Abstract

Hospital buildings are expected to remain Occupiable after earthquakes to cater to the post-disaster response and rescue efforts. This requires a stiffer and stronger structural system compared to the commonly adopted moment frames in normal buildings; wallframe systems are recommended in these buildings. But, in addition to merely providing the wall-frame structural system, it is also essential to adequately design the wall-frames to meet the desirable Occupiable seismic performance. Appropriate seismic structural configuration, Structural Plan Density (SPD) of structural walls, and seismic design parameters are presented of typical hospital building located in Seismic Zone IV, that helped meet the preferred performance. A displacement-based limit state of structural damage in line with classic displacement demand estimation is proposed, to confirm the performance. Fiber inelasticity in walls and moment frames in study frames and buildings are defined, for performing displacement controlled nonlinear static pushover analyses and nonlinear time history analyses in commercial software PERFORM3D. Alongside, limit states of structural damages, namely yielding of longitudinal reinforcement in beams or columns in tension, yielding of vertical longitudinal reinforcement in structural walls in tension, crushing of confined concrete in compression in beams, crushing of confined concrete in compression in columns, and spalling of unconfined concrete in compression in structural walls are also monitored to grade the damages, and in turn the seismic performance of wall-frames. Results suggest, numerical models with fiber inelasticity help predict nonlinear behaviour reasonably well. Moment frames do not provide preferred seismic performance, but wall-frames with plan-aspect ratio more than 4 enhances lateral stiffness, strength, and ductility of wall-frames, thereby meeting the preferred performance. The major findings of the study are at least 3% SPD of structural walls is essential in typical wall-frame hospital buildings to ensure Occupiability performance after earthquakes. Furthermore, Column-to-Beam Strength Ratio of minimum 2 is also required in hospital buildings to remain Occupiable.