Cyclic loading tests on RC moment frames retrofitted by PC frames with mild press joints through RC slabs for connection

Abstract

In external retrofitting where a new structure is attached to the façade of an existing building, the connection between the two structures is critical for the seismic performance of the retrofitted building. Following a previous study that introduced a precast prestressed concrete frame system with mild press joints (PC-MPJ) for external seismic retrofitting of existing reinforced concrete (RC) frames, this paper presents an experiment of assessing the hysteretic behavior of RC frames combined with PC-MPJ frames through cast-in-situ RC slabs for connection. Two 1/2-scale specimens of different concrete strengths for the existing RC frames were subjected to in-plane cyclic loading with a story drift ratio of up to 1/33. The concrete compressive strength of the existing RC frame in one of the specimens was lower than 10 MPa. The results show that the connection slabs exhibited adequate strength for the force transfer between the existing and retrofitting frames. The deformation of the connection is predominated by the deformation at the slab-to-beam interfaces. The shear stiffness of the connecting RC slabs in both specimens decreased as the interstory drifts increased, and the equivalent stiffness at an interstory drift of 1/150 to 1/100 corresponded well to that estimated by the empirical equations in the current Japanese manual for external seismic retrofitting. The out-of-plane and in-plane bending of the connection slab was also evident from the test results.