Effect of soft story conditions on the seismic performance of tall concrete structures

Abstract

A soft story is characterized as a level in a building that is either less than 70% stiffer than the one directly overhead it or less than 80% stiffer than the average of the three stories above it. Typically, in construction, a soft story configuration occurs when one story of a building is more flexible or less stiff than the other floors. The reduced stiffness in such stories makes them vulnerable to lateral forces during earthquakes, necessitating the reliance on columns for resistance. Weak columns can result in severe damage or even the collapse of the entire structure. This study investigates the behavior of high-rise buildings with soft stories at various positions, examining the impact of shear walls and bracings at soft story levels. Different structural models at different positions are analyzed to assess the influence of soft stories throughout the building's height. The findings indicate that shear walls are more effective at enhancing structural stiffness. Specifically, a third-floor soft story exhibits lower stiffness than other stories, while a twelfth-floor soft story displays greater stiffness. Consequently, placing a soft story at a higher position in the structure is deemed more suitable.