Instability of beams with reduced beam section moment connections emphasizing the effect of column panel zone ductility

Column panel zone (PZ) ductility significantly affects the failure mode of beams with reduced beam section (RBS) moment connections. Even though good hysteretic behaviour is expected in connections with strong PZs, their flexural strength considerably deteriorates due to beam instability. In contrast, weak PZs are prone to high shear deformation, resulting in brittle fracture of connections. This study aims to question the provisions specified in the codes for the design of PZs. To this end, a numerical analysis was conducted on a series of subassemblies with various PZ properties. Use of lower deep sections is another major concern. It is indicated in this study that partial shear yielding in PZs can improve the hysteretic response of specimens by avoiding premature instability in beams. The results show that the PZ ultimate shear strength commonly prescribed in the design codes does not extend to an adequate safety margin. Furthermore, a new parameter is expressed for controlling an RBS beam as regards instability. This parameter is able to appropriately model the behaviour of RBS beams. The results are generally in good agreement with the existing experimental data.