Numerical assessment of lateral distortional buckling in steel-concrete composite beams

Abstract

Steel-concrete composite beams, when requested by negative moment, can fail due to Lateral Distortional Buckling (LDB), local buckling, or by the combination of these stability modes. LDB is a mode of stability in which the web must distort in order for the compression flange to displace and twist during buckling. The standard procedures that address this phenomenon use the conventional lateral-torsional buckling theories for the buckling of partially restrained beams or the U-frame model. This study investigates, through the development of refined physical and geometrical nonlinear numerical analyzes with the ABAQUS software, the strength of steel-concrete composite beams under the action of negative moment. The influences of several parameters are analyzed, such as: steel profile cross section, longitudinal reinforcement rate, unrestrained length, presence of the web stiffeners and the distribution of negative moment along the span. The results are compared with standard procedures and analytical methods. It can be concluded that the cross section and the presence of web stiffeners are the parameters that most influence the LDB strength. Regarding the standard procedures, it was found that both those who adopt the conventional lateral-torsional buckling theories and those who use the U-frame model provide conservative results. Therefore, further investigations are necessary to better understand the behavior of these elements under the action of negative moment.