Browsing by Author "Chou, Chung-Che"

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Column restraint in post-tensioned self-centering moment frames
(2010-06-01)
Chou, Chung-Che
;
Chen, Jun-Hen
;
土木工程學系
;
Department of Civil Engineering
Gaps between beam-to-column interfaces in a post-tensioned (PT) self-centering frame with more than one column are constrained by columns, which causes beam compression force different from the applied PT force. This study proposes an analytical method for evaluating column bending stiffness and beam compression force by modeling column deformation according to gap-openings at all stories. The predicted compression forces in the beams are validated by a cyclic analysis of a three-story PT frame and by cyclic tests of a full-scale, two-bay by first-story PT frame, which represents a substructure of the three-story PT frame. The proposed method shows that compared with the strand tensile force, the beam compression force is increased at the 1st story but is decreased at the 2nd and 3rd stories due to column deformation compatibility. The PT frame tests show that the proposed method reasonably predicts beam compression force and strand force and that the beam compression force is 2 and 60% larger than the strand force with respect to a minor restraint and a pin-supported boundary condition, respectively, at the tops of the columns. Therefore, the earlier method using a pin-supported boundary condition at upper story columns represents an upper bound of the effect and is shown to be overly conservative for cases where a structure responds primarily in its first mode. The proposed method allows for more accurate prediction of the column restraint effects for structures that respond in a pre-determined mode shape which is more typical of low and mid-rise structures. Copyright (C) 2009 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.
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.
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.
Hysteretic model development and seismic response of unbonded post-tensioned precast CFT segmental bridge columns
(2008-05-01)
Chou, Chung-Che
;
Hsu, Chih-Po
;
土木工程學系
;
Department of Civil Engineering
The study investigated the cyclic behavior of unbonded, post-tensioned, precast concrete-filled tube segmental bridge columns by loading each specimen twice. Moreover, a stiffness -degrading flag-shaped (SDFS) hysteretic model was developed based on self-centering and stiffness-degrading behaviors. The proposed model overcomes the deficiency of cyclic behavior prediction using a FS model, which self-centers with fixed elastic and inelastic stiffnesses. Experimental and analytical results showed that (1) deformation capabilities of the column under the first and second cyclic tests were similar; however, energy dissipation capacities significantly differed from each other, and (2) the SDFS model predicted the cyclic response of the column better than the FS model. Inelastic time-history analyses were performed to demonstrate the dynamic response variability of a single-degree-of-freedom (SDOF) system using both models. A parametric study, performed on SDOF systems subjected to eight historical earthquakes, showed that increased displacement ductility demand was significant for structures with a low period and low-to-medium yield strength ratio and reduced displacement ductility demand in these systems was effectively attained by increasing energy dissipation capacity. Copyright (C) 2008 John Wiley & Sons, Ltd.
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.
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.
Post-tensioned self-centering moment connections with beam bottom flange energy dissipators
(2009-10-01)
Chou, Chung-Che
;
Lai, Yu-Jen
;
土木工程學系
;
Department of Civil Engineering
This work presents results of experimental and analytical studies of self-centering moment connections. The connection subassembly consists of post-tensioned steel beams, a reinforced concrete column, and energy dissipators placed only below the beam bottom flange for simplicity of construction, ease of replacement, and no interference with the composite slab. Two types of steel energy dissipators are proposed: one includes a reduced section plate restrained by two flat plates, and the other uses cross-shaped steel plates. Cyclic tests are conducted on three full-scale post-tensioned connection subassemblies and six energy dissipators. Finite element analysis is performed to investigate the cyclic performance and likelihood of fracture at critical regions in the energy dissipators. Cyclic test results show that (1) energy dissipation, moment, and flexural stiffness of the beam in positive bending are larger than those of the beam in negative bending, (2) the location of the compression toe at the end of the beam stabilizes at the junction between the beam flange and web after an interstory drift of 1.5%, in which the gap opening angles of the beams are similar in both bending directions, and (3) the shoulder radius equal to 2.5 times plate thickness results in a premature fracture along the shape transition of the reduced section plate. This study also develops an iterative analytical procedure for predicting un-symmetrical cyclic responses of post-tensioned connection subassemblies.(c) 2009 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.
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.
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]
Seismic rehabilitation performance of steel side plate moment connections
(2010-01-01)
Chou, Chung-Che
;
Tsai, Keh-Chyuan
;
Wang, Yuang-Yu
;
Jao, Chih-Kai
;
土木工程學系
Moment connections in all existing steel building located in Kaohsiung, Taiwan were rehabilitated to satisfy seismic requirements based oil the 2005 AISC seismic provisions. Construction of the building was ceased in 1996 due to financial difficulties and was recommenced in 2007 with enhanced connection performance. Steel moment connections in the existing building were Constructed by groove welding the beam flanges and boiling the beam web to the column. Four moment connections, two from the existing steel building were cyclically tested. A non-rehabilitated moment connection with bolted web-welded flanges was tested as a benchmark. Three moment connections rehabilitated by welding full-depth side plates between file column Face and beam flange inner side were tested to validate the rehabilitation performance. Test results revealed that (1) the non-rehabilitated existing moment connection made by in situ welding process prior to 1996 had similar deformation capacity its contemporary connection specimens made by laboratory welding process, (2) all rehabilitated moment connections exhibited excellent performance, exceeding a 4% drift Without fractures of beam flange groove-welded joints, and (3) presence of file full-depth side plates effectively reduced beam flange tensile strain near the column face by almost half compared With the non-rehabilitated moment connection. The connection specimens were also modeled Using the non-linear finite element computer program ABAQUS 10 further confirm the effectiveness of the side plate in transferring beam moments to the column and to investigate potential Sources of connection failure. A design procedure was made based oil experimental and analytical Studies. Copyright (C) 2009 John Wiley & Sons, Ltd.
Seismic self-centering steel beam-to-column moment connections using bolted friction devices
(2008-04-10)
Tsai, Keh-Chyuan
;
Chou, Chung-Che
;
Lin, Chi-Lon
;
Chen, Pei-Ching
;
Jhang, Sheng-Jhih
This paper first presents the force-deformation relationship of a post-tensioned (PT) steel beam-to-column connection constructed with bolted web friction devices (FDs). This paper then describes the test program conducted in the National Center for Research on Earthquake Engineering, Taiwan, on four bolted FDs and four full-scale PT beam-to-column moment connection subassemblies using the FDs. Tests confirm that (1) the hysteretic behavior of four bolted FDs is very stable, (2) the friction coefficient between the steel plate and the brass shim is about 0.34, (3) the proposed force-deformation relationships reasonably predict the experimental responses of the PT connections under cyclically increasing deformations up to a beam peak rotation of 0.05 rad, and (4) the decompression moments do not degrade as beam cyclic deformations increase. Copyright (C) 2007 John Wiley & Sons, Ltd.
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.
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.
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
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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.