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

Abstract

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

Twenty Years of Advances in Disproportionate Collapse Research and Best Practices since 9/11/2001

“…Steel structures are the focus of four papers (Kong et al 2021;Qian et al 2021;Song 2022;Kong et al 2022). Kong et al (2021) report their experimental and numerical findings on the progressive collapse behavior of scaled six-column subframe composite floor systems subjected to the removal of a side column.…”

“…The connection between beams and columns is found to be the governing factor of the collapse mechanism. Qian et al (2021) fabricated and tested six multistory steel moment-resisting subframes (three bare frames and three braced frames) aiming to shed light on the effects of the existence of steel braces in the progressive collapse of moment-resisting frames. It is found that the braces can indeed increase the load-resisting progressive collapse capacity and this can be attributed to tensile braces mostly.…”

Survey on the Role of Beam-Column Connections in the Progressive Collapse Resistance of Steel Frame Buildings

“…The presence of steel bracing members in structural bays above the missing column could also influence progressive collapse resistance, as demonstrated by recent experimental and numerical studies. This, however, depends on the type of bracing system since X-bracing, for instance, may ensure increased resistance while V-bracing could have a detrimental effect on performance [43]. Concentric diagonal bracing can affect performance in very different ways depending on whether the bracing members are subject to tension or compression following column loss [44].…”

Effect of tie column on the progressive collapse performance of infilled reinforced concrete frames

“…Recently, the investigation on the contribution of infill walls to structural resistance against progressive collapse has been extended to post-tensioned RC frames (Shan and Li, 2022) and steel frames (Qian et al, 2023). The results indicated that the infill walls significantly improve progressive collapse resistance of the frames at small deformation.…”