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Seismic Rehabilitation of Welded Steel Beam-to-Box Column Connections Utilizing Internal Flange Stiffeners
(2010-11-01)
Chou, Chung-Che
;
Jao, Chih-Kai
;
土木工程學系
;
Department of Civil Engineering
This work investigates the seismic performance of rehabilitated steel moment connections using internal flange stiffeners (IFSs) welded to the face of a built-up box column and a beam flange inner side. The objective is to provide a rehabilitation scheme that excludes interference from the composite slab and story height limitation in an existing steel building. Five rehabilitated moment connections with different IFSs were tested according to AISC (2005) loading protocol to validate their cyclic performance. Two rehabilitated moment connections had excellent performance; no welded joint fractures were found in the connections with a drift in excess of 4%. The specimens were modeled using the computer program ABAQUS to further verify the effectiveness of the IFSs in transferring beam moments to a column and to investigate potential sources of connection failure. Design guidelines for the rehabilitation scheme are provided based on test and analytical results. [DOI: 10.1193/1.3480275]
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.
Internal flange stiffened moment connections with low-damage capability under seismic loading
(2013-08-01)
Chou, Chung-Che
;
Lo, Sheng-Wei
;
Liou, Gin-Show
;
土木工程學系
;
Department of Civil Engineering
This study presents the seismic performance of steel moment connections using internal flange stiffeners (IFSs) welded at the face of the wide-flange column and inner side of the beam flange. The objective is to develop a steel moment connection that can achieve good seismic performance with low-damage capability during a large earthquake loading and minimize the repair cost. Four large-scale moment connections were tested to validate the cyclic performance. One connection which represented a welded-unreinforced flange-bolted web connection failed before finishing cyclic tests at a drift of 4%. Three IFS moment connections showed excellent performance and low damage after experiencing the AISC seismic load twice up to the target drift of 4%, without strength reduction. The specimens were also modeled using the computer program ABAQUS to further verify the effectiveness of the IFS in transferring beam moment to the column and to investigate potential sources of connection failure. (C) 2013 Elsevier Ltd. All rights reserved.
Two-plastic-hinge and two dimensional finite element models for post-tensioned precast concrete segmental bridge columns
(2013-01-01)
Chou, Chung-Che
;
Chang, Hao-Jan
;
Hewes, Joshua T.
;
土木工程學系
;
Department of Civil Engineering
Recent studies have confirmed that unbonded post-tensioned (PT) precast concrete segmental bridge columns are capable of undergoing large lateral deformation with negligible residual drift. To provide a clear guideline for the modeling of the columns for practicing engineers as well as researchers, this paper presents two types of numerical models: (i) a two-plastic-hinge model using the sectional moment-curvature analysis procedure at two segment interfaces and (ii) a two-dimensional (2D) finite element model using truss and beam-column elements in the computer program PISA. Three unbonded PT precast concrete-filled tube segmental bridge column specimens are cyclically tested. Two specimens have mild steel bars crossing to different column heights for studying the effects of anchorage position on the hysteretic energy dissipation (ED) capacity. The test results show that (1) the mild steel bars ("ED bars") can increase hysteretic energy dissipation, and Specimens 1-3 have equivalent viscous damping of 6.5-8.8%, (2) a plastic hinge length in the first or second segment varies with anchorage position of ED bars and lateral displacement, and (3) an equivalent unbonded length along which the strain in the ED bar is assumed uniformly distributed on each of the two sides is 5-6 bar diameter. A 2D finite-element model is utilized to predict the cyclic behavior of the specimens. Parametric studies using finite-element models are also conducted to investigate the effects of ED bar area, initial strand force, and aspect ratio on the cyclic behavior. (c) 2012 Elsevier Ltd. All rights reserved.
Seismic design and shake table tests of a steel post-tensioned self-centering moment frame with a slab accommodating frame expansion
(2011-09-01)
Chou, Chung-Che
;
Chen, Jun-Hen
;
土木工程學系
;
Department of Civil Engineering
Post-tensioned (PT) self-centering moment frames were developed as an alternative to welded moment-resisting frames (MRFs). Lateral deformation of a PT frame opens gaps between beams and columns. The use of a composite slab in welded MRFs limits the opening of gaps at the beam-to-column interfaces but cannot be adopted in PT self-centering frames. In this study, a sliding slab is used to minimize restraints to the expansion of the PT frame. A composite slab is rigidly connected to the beams in a single bay of the PT frame. A sliding device is installed between the floor beams and the beams in other bays, wherever the slab is allowed to slide. Many shaking table tests were conducted on a reduced-scale, two-by-two bay one-story specimen, which comprised one PT frame and two gravitational frames (GFs). The PT frame and GFs were self-centering throughout the tests, responding in phase with only minor differences in peak drifts that were caused by the expansion of the PT frame. When the specimen was excited by the 1999 Chi-Chi earthquake with a peak ground acceleration of 1.87g, the maximum interstory drift was 7.2% and the maximum lateral force was 270 kN, equal to 2.2 times the yield force of the specimen. Buckling of the beam bottom flange was observed near the column face, and the initial post-tensioning force in the columns and beams decreased by 50 and 22%, respectively. However, the specimen remained self-centering and its residual drift was 0.01%. Copyright (C) 2011 John Wiley & Sons, Ltd.
Compressive behavior of dual-gusset-plate connections for buckling-restrained braced frames
(2012-09-01)
Chou, Chung-Che
;
Liou, Gin-Show
;
Yu, Jiun-Chi
;
土木工程學系
;
Department of Civil Engineering
This work conducts compression tests and finite element analyses for steel dual-gusset-plate connections used for buckling-restrained braced frames (BRBFs). Compared to a single-gusset-plate connection, dual gusset plates sandwiching a BRB core reduce gusset plate size, eliminate the need for splice plates, and enhance connection stability under compression. The experimental program investigated ultimate compression load by testing ten large dual-gusset-plate connections. Out-of-plane deformation of the gusset plate in the test resembled that of a buckled gusset plate with low bending rigidity provided by the BRB end. The general-purpose nonlinear finite element analysis program ABAQUS was applied for correlation analysis. A parametric study of the dual-gusset-plate connection was performed to study the effects of plate size, presence of centerline stiffeners, and beam and column boundaries on ultimate compression load. The ultimate compression load of the dual-gusset-plate connection could not be predicted based on the AISC-LRFD approach due to beam flange out-of-plane deformation. The ultimate compression load of the dual-gusset-plate connection was reasonably predicted using a column strip length from the Whitmore section to the workpoint of the beam and column centerlines and a buckling coefficient of K = 2. (C) 2012 Elsevier Ltd. All rights reserved.
Evaluating performance of post-tensioned steel connections with strands and reduced flange plates
(2006-07-25)
Chou, Chung-Che
;
Chen, Jun-Hen
;
Chen, Yu-Chih
;
Tsai, Keh-Chyuan
;
土木工程學系
The seismic performance of post-tensioned steel connections for moment-resisting frames was examined experimentally and analytically. Cyclic tests were conducted on three full-scale subassemblies, which had two steel beams post-tensioned to a concrete-filled tube (CFT) column with high-strength strands to provide recentring response. Reduced flange plates (RFPs) welded to the column and bolted to the beam flange were used to increase the dissipation of energy. Test results indicated that (1) the proposed buckling-restrained RFP could dissipate energy in axial tension and compression, (2) the subassemblies could reach an interstorey drift of 4% without strength degradation, and (3) buckling of the beam occurred towards an interstorey drift of 5%, causing a loss of the strand force, the recentring response, and the moment capacity. A general-purpose non-linear finite element analysis program (ABAQUS) was used to perform a correlation study. The behaviour of the steel beam under both post-tensioning and flexural loadings was compared to the test results and predictions. Copyright (C) 2006 John Wiley & Sons, Ltd.
Effects of continuity plate and transverse reinforcement on cyclic behavior of SRC moment connections
(2007-01-01)
Chou, Chung-Che
;
Uang, Chia-Ming
;
土木工程學系
;
Department of Civil Engineering
Two exterior moment connections with a steel-encased reinforced concrete (SRC) column and a steel beam were tested to evaluate the cyclic performance. Continuity plates were eliminated in the first specimen, and about 60% of the transverse reinforcement as specified in the ACI 318 was used in the connection region. Two steel doubler plates offsetting from the column web were used to enhance the shear resistance of the connection. The second specimen used a steel jacket to confine the concrete in the connection region and continuity plates were extended from the steel column to the steel jacket to mobilize the shear resistance of the latter; no transverse reinforcement was used. Full-scale test results showed that both specimens were able to reach an interstory drift ratio in excess of 4%. An analytical model was developed for the concrete shear force transfer mechanism in the connection of the second specimen. This study showed that: (1) using either doubler plates or jacket plates was effective to enhance the shear capacity in the connection, (2) concrete shear resistance degraded before the maximum applied load was reached in the first specimen, (3) the concrete was mobilized to resist shear in the second specimen, and (4) transverse reinforcement as required by the ACI 318 (1995) can be relaxed as long as another shear-resisting mechanism such as doubler plates or jacket plates is provided.
Performance evaluation of steel reduced flange plate moment connections
(2007-11-01)
Chou, Chung-Che
;
Wu, Chia-Ching
;
土木工程學系
;
Department of Civil Engineering
This study details a new moment connection that overcomes difficulties in achieving field-weld quality and eliminates steel beam buckling encountered in steel moment connections. This study presents cyclic test and finite element analysis results of full-scale subassemblies using steel reduced flange plates (RFPs) to connect steel beam flanges and the column without any other direct connection. Since the RFP connection is designed as strong column-strong beam-weak RFPs, the RFP functions as a structural fuse that eliminates weld fractures and beam buckling. Test and analytical results show that (1) the connections transferred the entire beam flexural strength to the column and reached an interstorey drift of 4% with minor strength degradation, (2) failure of the connections was owing to buckling or fracturing of the RFP and not of the beam, and (3) the RFP connection subassembly, modelled using the nonlinear finite element computer program ABAQUS, exhibited hysteretic behaviour similar to that of the flange plate (FP) moment connection subassembly. The inelastic buckling force of the RFP was also evaluated by nonlinear regression analyses performed on a nonlinear model that relates buckling force to RFP geometries. Copyright (C) 2007 John Wiley & Sons, Ltd.

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