Browsing by Author "Chen, Jun-Hen"

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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.
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.
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.
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.