Comparing seismic performances of single-span RC frames with and without wing wall retrofitting by shaking table tests

Abstract

It is necessary to retrofit existing single-span reinforced concrete (RC) frames which could not meet the current seismic codes due to lack of multiple seismic lines of defence. Adding wing wall is one of the retrofit method that can improve the redundancy of single-span RC frames. To study the effectiveness of single-span frames retrofitted by wing walls, shaking table tests were conducted on two 1:5 specimens to compare the seismic behaviour of single-span RC frames with and without wing wall retrofitting. First, a retrofit scheme for the frame using wing walls was selected. Two specimens—a single-span RC frame and an identical frame with a wing wall retrofit—were placed on the same shaking table board and tested simultaneously. Contrast tests were conducted for 20 earthquake cases. The main conclusions are as follows: (1) Adding wing walls to a single-span frame in bi-direction is a reasonable strengthening scheme. (2) For the single-span frame without retrofitting, cracks appeared in the early stages and rapidly developed, forming plastic hinges at the ends of the beams and columns. For the single-span frame with retrofitting, cracks first appeared in the construction joints between the wing walls and beams, and then extended to wing walls and beams. The test phenomena indicate that adding wing walls to a single-span frame can increase system redundancy, and act as the first anti-seismic line of defence. (3) From the measured data, it is shown that adding wing walls to a single-span frame can improve its seismic capacity and control the lateral deformation. The peak floor displacement response of the retrofitted frame reduced by 30%–40% compare with that of the frame without retrofitting. (4) When input PGA was 0.15g (design based earthquake), slight damage occurred to the frame retrofitted by wing wall, while damage of the frame without retrofitting was moderate. When input PGA was 0.30g (rare earthquake), moderate damage occurred to the frame retrofitted by wing wall, while damage of frame without retrofitting was severe. Therefore, adding wing walls is an effective method for retrofitting single-span RC frame structures.