Cyclic loading test of lightly reinforced concrete wall piers with slit dampers in RC frames

摘要

Lightly reinforced concrete (LRC) walls have been widely used in reinforced concrete (RC) buildings in Japan as partitions and enclosure walls. Despite their contributions of considerable strength and stiffness to the structural system, they are generally classified as nonstructural elements and are not considered in seismic design. In recent decades, the use of slits around LRC walls to separate them from primary structures has become a common practice in Japan to avoid premature cracking and to minimize their detrimental effects on the seismic performance of buildings. However, this complete separation has also been thought to weaken the seismic resistance of the building, especially in terms of strength. In this study, we propose to install miniature steel dampers in the slits to form a controlled semirigid connection between the LRC wall piers and RC frames in residential buildings. The connection is hypothesized to provide additional lateral strength and energy dissipation capacity to the primary structure while mitigating the cracking of the LRC wall piers. We conducted quasi-static cyclic loading tests on four half-scaled specimens of a single-span RC frame and an LRC wall pier. In the different specimens, the wall piers were separated by a slit, rigidly connected to the frame or equipped with slit dampers to compare their seismic performance. While the rigidly connected LRC wall pier lost its strength and sustained successive damage prior to achieving a 1/200 story drift ratio, the use of miniature steel dampers enabled the wall piers to contribute moderate strength to the RC frame in a ductile manner and to remain essentially intact prior to a 1/ 200 story drift ratio. At the same story drift, the damper deformation was approximately 60% greater when it was placed at the mid-height than when it was at the bottom of the wall pier. However, the stud connection for the mid-height damper sustained severe damage and concrete cone failure. Thus, correctly designing the stud group under combined shear and bending actions is challenging. Component tests on individual dampers were also conducted to show that the overstrength due to strain hardening could exceed two. Better control of the damage to the LRC wall piers requires full consideration of the significant strain hardening effect of the dampers.