Cyclic Testing of Welded HSS-to-HSS Moment Connections for Seismic Applications

Abstract

Hollow structural sections (HSS) are currently underutilized in seismic moment frame systems as possible alternatives to typical wide-flange members. To explore the potential use of HSS moment connections in seismic moment frame systems and evaluate connection detailing requirements, experimental tests of welded unreinforced and reinforced HSS-to-HSS connections are conducted under increasing cyclic rotations to failure. The behavior of the unreinforced connections is limited by their inability to isolate inelasticity to the beam member and panel zone region leading to eventual fracture at lower than anticipated drift levels. However, through plate and external diaphragm plate reinforced HSS-to-HSS moment connections are able to move the location of inelasticity into the HSS beam member resulting in desired beam plastic hinging. Although the unreinforced connections have limited ductility, the reinforced connection detailing leads to stable degradation of the moment capacity at increasing drift levels with fracture initiating only at very large rotations attributable to eventual onset of local buckling in the plastic hinge region. The through and diaphragm plates are found to have an important effect in ensuring that the sources of inelastic rotation are limited to the beam and panel zone region. Additionally, the use of reinforcement improves the connection stiffness. Overall, the study shows that fully welded HSS-to-HSS seismic moment connections are viable provided proper detailing of the connection is performed.