Connection overstrength in steel-braced RC frames

Steel bracing systems can be used effectively for seismic retrofitting of existing RC buildings as well as for seismic design of new buildings. Although adaptation of bracing to upgrade the lateral load capacity of existing RC frames has been the subject of a number of successful studies, guidelines for its use in newly constructed RC frames need to be further developed. An important consideration in the design of steel-braced RC frames is the level of interaction between the strength capacities of the RC frame and the bracing system. In this paper, results of experimental and numerical investigations aimed at evaluating the level of capacity interaction between the two systems are discussed. For these investigations, cyclic loading tests are conducted on scaled moment resisting frames with and without bracing. It is found that the capacity interaction is primarily due to the connections overstrength. The experimental results are also used to calibrate full-scale numerical models. A parametric numerical investigation on the effects of the main problem variables is then conducted and the influence of each parameter on the level of the overstrength is determined. Based on these findings, guidelines for the seismic design of the internally cross-braced RC frames with direct connections are provided.