Vol.31/No.2 (122) (2016)
| Title | The seismic performance and crosstie unity of reinforced concrete columns using the lap-spliced crosstie under various axial loads |
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| Author | Tai-Kuang Lee, Cheng-Cheng Chen |
| Keywords | lap-spliced crosstie, RC columns, seismic performance |
| Abstract | A lap-spliced crosstie consists of two J-shaped steel bars (rebars) that have a straight end and an end featuring a 180° hook. In this study, a lateral cyclic load test was conducted on four specimens of large-sized reinforced concrete (RC) columns to investigate the seismic resistance capability and crosstie unity of RC columns comprising lap-spliced crossties under various axial loads. The research results are presented as follows: (a) The ductility of the specimens that adopted the lap-spliced crossties was comparable to that of the specimens using crossties featuring a 180° hook on the two ends. (b) Without axial load, the straight end of the J-bars did not slip toward the inside of the column, suggesting that two J-bars were effectively spliced to be a crosstie featuring a 180° hook on its two ends and maintaining good unity. (c) The ductility of RC columns comprising lap-spliced crossties and crossties featuring a 180° hook on the two ends is significantly decayed with increasing axial load ratio. |
| Title | Seismic Behavior of Exterior Beam-Column Joints with Headed Bars |
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| Author | Ker-Chun Lin, Chien-Kuo Chiu, Kai-Ning Chi |
| Keywords | beam-column joint, headed bar anchorage length, shear of the panel zone |
| Abstract | This paper presents the seismic behavior of 12exterior RC beam-column joint specimens that headed bars were adoptedas main bars of their beam members and anchored into theirpanel zone. Two types of net spacing of 2 times and 2.2 times diameter of headed bars were used. All specimens meet the requirements of the strong column-weak beamof the ACI 318-11 Code.Other main parameters included the anchorage lengths of headed bars and the shear demand-to-capacity ratioof the panel zone.The results showed that when the net spacing of headed bars used 2.2 times their diameter and anchorage lengthplaced long enough, the seismic performance of specimen that used headed bars was so well as that of using the standard 90-degree hooked bars.It proved an applicability of the headed bar replacing the hooked bar. Based on seismic assessments of ACI 374.1-05 and proposed by this paper, assessed results indicated that specimens with net spacing of 2 times diameter of headed bar were able to meet their assessed criteria of strength, stiffness and dissipating energy at 4% radian of drift ration as long as the anchored length of headed bar satisfied the development length stipulated in ACI 318-11. However, a specimen with an unexpected failure mode of shear friction slide was excluded. Analysis results of specimen strengths presented that if anchored lengths of headed bar exceeded the development length of headed bar required by the ACI 352-02 Code, the developing average stress of the headed bars was able to reach 1.25 times its nominal yield stress of seismic design requirement. |
| Title | Preliminary Seismic Evaluation of School Buildings Retrofitted with Reinforced Concrete Jacketing |
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| Author | Lap-Loi Chung, Sheng-Hsueh Lin, Yao-Sheng Yang, Shyh-Jiann Hwang, Fu-Pei Hsiao, Tsung-Chih Chiou, Lai-Yun Wu, Yu-Chih Lai |
| Keywords | school building, reinforced concrete jacketing, preliminary evaluation, in-situ test |
| Abstract | Preliminary evaluation is an important screening procedure for the seismic performance of school buildings so that the magnitude of the problem of seismic deficiency of school buildings can be reduced effectively. According to the seismic zone, importance factor and dimension of the vertical members in the first floor, seismic capacity and demand of a school building can be evaluated. Base on the score (capacity to demand ratio), the priority of the school building to enter into the stage of detailed evaluation is determined. However, a simple and quick evaluation method for the school buildings after retrofit has not been proposed yet. In this paper, a preliminary evaluation method is developed for the school buildings retrofitted with reinforced concrete jacketing. First of all, lateral strength of the reinforced concrete jacketing region per unit cross sectional area is established. Experimental results of two structures are adopted to investigate the feasibility of the proposed method including material strength, ultimate base shear strength, allowable ductility ratio, weight of building, fundamental vibration period and basic seismic performance. After comparison, the preliminary seismic evaluation for school buildings retrofitted with reinforced concrete jacketing proposed in this paper is effective and conservative. Before retrofit design, the amount of retrofit can be estimated by this method. After retrofit design, the rationality of the design can be confirmed by this method. |
| Title | Development and Cyclic Tests of Circular RC Columns Confined with a GFRP-Wrapped Spiral Corrugated Tube |
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| Author | Chung-Che Chou, Kai-Yi Wu, Chung-Sheng Lee |
| Keywords | Glass Fiber Reinforced Polymer (GFRP), Spiral Corrugated Tube, Confined Reinforced Concrete Column, Seismic Tests |
| Abstract | This paper presents the cyclic behavior of novel circular reinforced concrete columns confined with a FRP-Wrapped Spiral Corrugated Tube (FWSCT). In order to analyze the behavior of FWSCT concrete columns in axial and lateral loads, a load-displacement analysis program was also developed by the authors. Three specimens that had no transverse hoops were constructed and tested under small and large axial loads to investigate their seismic performances. Specimen FWSCT-0 was confined with only a spiral corrugated tube without Glass Fiber Reinforced Polymer (GFRP); Specimens FWSCT-5 and FWSCT-8that were made in Taiwan were confined with 5 and 8 layers of GFRP, respectively. Test results showed that Specimen FWSCT-0 experienced shear failure, while Specimens FWSCT-5 and FWSCT-8 exhibited rupture of longitudinal steel bars at story drifts of 6% and 8%, respectively. It was also found that the plastic hinge of the new column was developed on both ends of the column gap and extended into the footing. The analytical program reasonably predicts test results by using the observed plastic hinge length. |
| Title | Seismic Design, Tests and Analysis of a Full-scale Two-story Reinforced Concrete Frame with Buckling-restrained Braces – Part I: Specimen Design and Seismic Tests |
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| Author | Hsun-Horng Yang, Jie-Luen Huang, An-Chien Wu, Chao-Hsien Li, Ching-Yi Tsai, Kung-Juin Wang, Keh-Chyuan Tsai |
| Keywords | reinforced concrete frame, buckling-restrained brace, steel embedment, hybrid test, seismic design, softened strut-and-tie model |
| Abstract | Buckling-restrained braces (BRBs) have been widely used nowadays in steel structures as it can provide high stiffness, strength and ductility without compression buckling. Researches on using BRBs for seismic retrofit of existing reinforced concrete (RC) buildings have been reported. It is found the construction of BRB and RC member interfaces are often difficult, mostly due to the tensile and shear strengths of post-installed anchors in concrete are limited. As a result, the size and effectiveness of the BRBs are restricted. Nonetheless, researches on applying BRBs for new RC constructions are rather limited. This research investigates the seismic design and analysis methods of using the proposed I-shape steel embedment as the interface for the BRB and RC members. Steel embedment is designed to transfer the BRB normal and shear forces in order to secure the seismic performance of the RC buildings. In this study, a full-scale two-story RC frame with BRBs (BRB-RCF) is tested using hybrid and cyclic loading test procedures. The BRBs are arranged in zigzag configuration. The design of gussets incorporates the BRB axial and RC frame actions, while the beam and column members comply with ACI 318-14 seismic design provisions. The results are divided into two papers to discuss the design and construction methods of the steel embedment, seismic performance of the BRB-RCF, and seismic responses of the BRBs, gussets and RC members. A typical PISA3D numerical model of the BRB-RCF was constructed to predict the test responses and select the earthquake ground motions for hybrid tests. Analytical results indicate that the seismic responses of the BRB-RCF can be satisfactorily predicted only under the small earthquake. After all tests, a calibrated PISA3D numerical model is validated. It is illustrated with details in the Part II paper that the experimental responses of the BRB-RCF can be accurately simulated using the proposed procedures. |
| Title | Seismic Design, Tests and Analysis of a Full-scale Two-story Reinforced Concrete Frame with Buckling-restrained Braces – Part II: Test Results and Response Analysis |
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| Author | Hsun-Horng Yang, Jie-Luen Huang, An-Chien Wu, Chao-Hsien Li, Ching-Yi Tsai, Kung-Juin Wang, Keh-Chyuan Tsai |
| Keywords | reinforced concrete frame, buckling-restrained brace, steel embedment, hybrid test, gusset buckling, nonlinear analysis |
| Abstract | Seismic design and analytical response predictions of the full-scaled two-story BRB-RCF are introduced in the Part I paper. This Part II paper discusses the experimental observations, test results and analytical simulations using a refined PISA3D model. In the 50/50 earthquake, the ratios of peak BRB and BRB-RCF shear are 52% and 71% for the first and second stories, respectively. Similar ratios can be obtained if a factor 0.7 is applied on the gross moment of inertia for RC members in the ETABS elastic model. In the 10/50 and 2/50 events, the ratios become about 60% and 70% for the first and second stories, respectively. These indicate that BRBs can provide a high lateral stiffness and strength. The hysteresis energy dissipated ratios in the four hybrid tests are ranging from 60% to 94% for the two stories, confirming that BRBs can effectively dissipate seismic input energy. When the 2.75% inter-story drift ratio (IDR) cycles were completed during the cyclic loading test, the cumulative plastic deformations were more than 476 and 680 for the first- and second-story BRBs, respectively. When both two stories reached an IDR of 3.5%, the frame’s lateral force versus deformation response was still very stable. Up to the first IDR=4.5% loading cycle, the first story top gusset buckled, caused the subsequent flexural buckling of the first story BRB to occur. This is consistent with the predicted results as this gusset’s demand-to-capacity ratio DCR is 1.05 for the buckling limit state when the effective length factor Kcr=2.0 is considered. Nonetheless, the buckled BRB have a DCR=0.95 in the steel casing. No failure of the steel embedment is observed in the tests. Test results confirm that the ACI provisions and the simplified softened strut-and-tie model can be effectively applied to prevent the RC discontinuity region failure. This study demonstrates that the proposed design and construction methods for the steel embedment are effective and practical for the real applications. The response analysis of the refined PISA3D model calibrated from using the test results is conducted to demonstrate the accuracy enhancement compared to the typical model. |