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Subassemblage tests and finite element analyses of sandwiched buckling-restrained braces
(2010-08-01)
Chou, Chung-Che
;
Chen, Sheng-Yang
;
土木工程學系
;
Department of Civil Engineering
This study presents the experimental and finite element analysis results of a proposed steel buckling-restrained brace (BRB). The proposed BRB has two components: (1) a steel core plate that carries all axial forces during tension and compression, and (2) two identical restraining members that sandwich the core plate with fully tensioned high-strength A490 bolts to prevent core buckling. Instead of using unbonded material, a small air gap is provided between the core plate and the restraining members to allow for lateral expansion of the core plate under compression. Since two restraining members can be disassembled easily by removing the bolts, a damaged steel core can be replaced after a large earthquake. Thus, manufacturing new restraining members is not required. Four BRB subassemblages were tested to investigate the inelastic deformation capabilities and verify the stability predictions for the braces. Test results indicate that three BRBs with sufficient flexural rigidity of the restraining member develop (1) stable hysteretic responses up to core axial strains of 2.1%-2.6%, (2) maximum compressive loads of 1724-1951 kN (1.4-1.6 times the actual yield load), and (3) a cumulative plastic ductility that is much higher than that specified in AISC seismic provisions (2005). One BRB, intentionally designed with inadequate flexural rigidity of the restraining member, experienced global buckling as predicted. Nonlinear finite element analysis was conducted for each BRB for a correlation study. The objective of the analysis was to conduct a parametric study for different BRBs to further verify the effects of restraining member size, number of bolts, core plate length and cross-sectional area on buckling load evaluation. The design procedure for the sandwiched BRB was provided based on test and finite element analysis results. (C) 2010 Elsevier Ltd. All rights reserved.
Tests and analyses of a full-scale post-tensioned RCS frame subassembly
(2010-11-01)
Chou, Chung-Che
;
Chen, Jun-Hen
;
土木工程學系
;
Department of Civil Engineering
A series of cyclic tests of a full-scale one-story two-bay specimen frame, a substructure of a three-story post-tensioned (PT) self-centering (SC) building using reinforced concrete columns and steel beams, were conducted in the Taiwan National Center for Research on Earthquake Engineering. The objectives of the tests were: (1) to examine the connection performance, progress of damage, and strength degradation of the frame, (2) to assess the hysteretic responses of the frame subjected to various loading patterns, and (3) to study the effects of column restraints on the frame expansion. Time-history analyses of the three-story PT building subjected to the design basis earthquake (DBE) and the maximum considered earthquake (MCE) were conducted to investigate seismic demands of the proposed system. These tests confirmed the SC response of the PT frame and explored failure of the beam compression toe, which was never observed in prior tests of beam-column subassemblages. The nonlinear structural analysis computer program PISA could be used to simulate the experimental results well; time-history analyses of the three-story building showed that the proposed frame can meet seismic demands by MCE level ground motions. (C) 2010 Elsevier Ltd. All rights reserved.
Seismic design and behavior of post-tensioned steel connections including effects of a composite slab
(2008-11-01)
Chou, Chung-Che
;
Wang, Yu-Chi
;
Chen, Jun-Hen
;
土木工程學系
;
Department of Civil Engineering
Three series of six full-scale, cyclic tests on post-tensioned (PT) beam-to-column connections were conducted to evaluate the cyclic performance. Each specimen represented an interior connection with steel beams PT to a column; one specimen also incorporated a composite slab. Reduced Flange Plates (RFPs) were added at the beam-to-column interface for energy dissipation, and flange reinforcing plates were provided outside the beam flanges to minimize yielding upon decompression. This paper describes the durability of the proposed connection, the effects of web stiffeners on beam local buckling, and the interaction of a composite slab. The first test series demonstrated that as long as beam yielding could be prevented before an interstory drift of 4%, the PT connection was capable of reaching an interstory drift of 5% or experiencing the AISC seismic loads twice without beam buckling. The second test series showed that beam buckling could be prevented by utilizing web stiffeners instead of increasing the length of the flange reinforcing plate. The third test series included a matched pair of specimens, one bare steel beam and one including a composite slab. Results that emphasize the influence of the composite slab on re-centering behavior and specific comments on the slab response were presented. The presence of a composite slab corresponded to higher-achieved moments due to the tensile capacities of the metal deck flutes, wire mesh, and longitudinal reinforcement, which were placed parallel to the PT beam. However, the re-centering behavior could be maintained after fractures of the wire mesh in the proposed slab details. Estimates of beam moments considering the presence of a composite slab were presented based on the cyclic test results. (C) 2008 Elsevier Ltd. All rights reserved.

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