Pull-down test and numerical validation of multi-story steel moment frame using pulley-based loading system

Abstract

Regarding the structural robustness against progressive collapse, recent studies have revealed that the catenary effect is the critical resisting mechanism for the frame structures under large vertical displacement. The previous studies of the single floor beam-column subassemblies suggest that the catenary effect is greatly affected by the connection performance as well as the horizontal restraint. However, the conventional push-down testing might not appropriately represent the horizontal constraint from the surrounding bays and the vertical loading condition under the uniformly distributed gravity loads. Therefore, the static pull-down test is performed on the multi-story steel moment frame equipped with straight-reduced-section splice plates (SRSP). It is used for high deformability of beam-to-column connection. In addition, a vertical loading system using the fixed pulleys for load transferring is newly proposed for a feasible and safe loading procedure. The experimental results show that the growth of vertical resistance can be mainly attributed to the plastic hardening and the consecutive catenary effect. The maximum resistance is governed by the first rupture of SRSP at the overall chord rotation of 0.178 rad, indicating high deformability of bolted connection with SRSP. Based on the failure sequence of connections and the internal force as well as deformation response, the floor dependency of catenary effect can be significantly observed. It is characterized by the earliest failure emerging at the 1st floor, followed by the consecutive ruptures observed at the upper floors. In terms of the internal force, the vertical contribution derived from the tensile force will be gradually rising for the connection at the 1st floor, in contrast to the negligible catenary effect at the 2nd and 3rd floors. Eventually, the numerical simulation is performed based on the previously proposed material model. The simulated full-range force-displacement curve with the low percentage error of 0.8% for the first rupture displacement demonstrates the validity of the numerical model in terms of the full-range behaviors of multi-story frame structure.