Seismic behaviour factor, R, for steel X-braced and knee-braced RC buildings

The seismic behaviour factor (R) is evaluated for steel X-braced and knee-braced RC buildings. The R factor components including ductility reduction factor and overstrength factor are extracted from inelastic pushover analyses of brace-frame systems of different heights and configurations. The effects of some parameters influencing the value of R factor, including the height of the frame, share of bracing system from the applied load and the type of bracing system are investigated. It is found that the two latter parameters have a more localised effect on the R values and their influence does not warrant generalisation at this stage. However, the height of this type of lateral load-resisting system has a profound effect on the R factor, as it directly affects the ductility capacity of the dual system. Finally, based on the findings presented in the article, tentative R values are proposed for steel-braced moment-resisting RC frame dual systems for different ductility demands.