Seismic tests of thin-profile buckling-restrained braces
Journal
10th U.S. National Conference on Earthquake Engineering: Frontiers of Earthquake Engineering
Date Issued
2014
Author(s)
Abstract
Tests of 14 thin-profile buckling-restrained braces (Thin-BRB) using the rectangular steel casing were conducted in the Taiwan National Center for Research on Earthquake Engineering. Both the pin-connected (8 specimens) and the welded details (6 specimens) are adopted for the Thin-BRB to gusset connections. A flat steel core plate parallel to the gusset plate is adopted as the energy dissipation segment for the Thin-BRBs. This configuration can minimize the width of the steel casing. However, the high mode core plate buckling waves would form when the flat steel core is compressed. The wave crests would be in contact with the restraining member and create outward normal forces on the steel casing. The local bulging failure may occur if the restraining mortar is too thin to spread the force out, or the steel casing is too weak to sustain such outward normal forces. The purposes of this study are to investigate local bulging failure behavior and provide the recommendations for seismic design of Thin-BRBs. The outward normal force and steel casing capacity are investigated by experiments and finite element model (FEM) analyses. 14 Thin-BRB specimens with yield force capacities range from 337 kN to 3184 kN were tested using cyclic increasing axial displacements. All the specimens¡¦ steel casing widths are smaller than 200mm. Seven BRB specimens bulged out when a compressive core strain exceeds more than 3.0% during the tests. It was found from test results that the high mode buckling wave length is about 10 times the core plate thickness. Based on the experimental and FEM analytical results, it is confirmed that the outward normal forces can be estimated based on the high mode buckling wave length and the gap between the steel core and restraining member. According to FEM analyses, the outward normal force would spread through the mortar and act on the inner surface of steel casing within a rectangular area, which can be computed from the core plate width and the mortar thickness. In order to prevent the local bulging failure, the steel casing must be strong enough to resist the outward normal forces induced by the high mode core plate buckling. In this study, it is found that the capacity of the steel casing can be estimated by using the yield line theory based on the FEM analyses and the experimental observations. The test and FEM analytical results indicate that the proposed method in computing the outward normal force and the steel casing capacity can be adopted to predict the possibility of local bulging failure. This paper concludes with the recommendations for seismic design of Thin-BRBs.
SDGs
Type
conference paper