Effects of Steel Braces on Robustness of Steel Frames against Progressive Collapse

External installation of steel braces is an effective approach to increase the lateral load resistance moment-resisting frames. However, effects existence on robustness frames resist progressive collapse still not clear because little study has been carried out. To fill this gap, in paper, six multistory subframes (three bare and three braced frames) were fabricated tested. Test results indicated that specimen with reduced beam section connection zone performed best among types connections due guaranteed formation plastic hinges at location avoiding brittle fracture weld connection. Experimental proved could load-resisting capacity by 45.1% 83.9% frame end plate connection, respectively. The gusset restricted rotation second story V-shaped bracing, which decreased its deformation degraded catenary action capacity. Actually, ultimate bracing only 87.5% counterpart without any braces. Because compressive severely buckled before displacement reached 0.4% span, it had effect yield but increased initial stiffness Thus, a majority benefits system attributed tensile Moreover, analytical evaluated differences development mechanisms different stories. Furthermore, contribution was decomposed individually analysis.