Vol.38/No.1 (147) (2023)
| Title | Discussion on Influence of Reinforced Concrete Beam Reinforcement Detail with Flush Outside Faces of Beams and Columns on Seismic Performance |
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| Author | Tai-Kuang Lee, Cheng-Cheng Chen |
| Keywords | reinforced concrete beams, columns, flush outside faces of beams and columns, seismic performance |
| Abstract | In domestic buildings, the eccentric beam-column connections with the flush outside faces of beams and columns are common, and the ductility of RC beams with eccentric connections has not been experimentally verified. In view of such domestic engineering practice problems, this study plans four large-scale reinforced concrete beam specimens, and conducts experimental verification at the Materials Experiment Center of the Architecture and Building Research Institute, Ministry of the Interior, Taiwan. In this study, the R specimen (the main reinforcement of the beam is not offset, and the stirrups are of normal size), the RH/SU specimen (the main reinforcement of the beam is offset inward and the stirrups are reduced in size, the side is equipped with U-shaped transverse auxiliary reinforcement and two longitudinal auxiliary reinforcements are fixed), the RH specimen (beam main reinforcement is shifted inward and stirrups are reduced in size), and the SH/SLB specimen (beam main reinforcement is shifted inward and the stirrups are normal size, and two longitudinal auxiliary reinforcements are arranged at the corners of the stirrup) are fabricated. The research results show that: (1) All specimens (including 3 beam reinforcement details with flush outside faces) can develop beam end rotation angle of 4% radian, which can meet the seismic requirement of the specification. For the seismic performance in the negative direction, the RH/SU specimen is the best, the RH specimen is the second, the R specimen is the third, and the SH/SLB specimen is the worst. There is only one top and bottom main reinforcement of the SH/SLB specimen, which is surrounded by the corner of the stirrup. The longitudinal auxiliary reinforcement is arranged at the corner of the stirrup of the beam, which may have an adverse effect on the seismic performance of the RC beam. Therefore, it is recommended that the corners of the stirrups should be equipped with the main beam reinforcement. (2) The concrete cover on one side of the RH specimen is 85 mm, but the results of this study show that the lateral strength and seismic performance of the RH specimen are not inferior to the R specimen. It is acceptable to use the type of the RH specimen in practice. (3) The seismic performance of the RH/SU and RH specimens is better than that of the R specimen, but the RH specimen has wider crack width and the degree of spalling of the concrete cover is obviously more serious than that of the RH/SU specimen. Therefore, it is recommended to use the type of the RH/SU specimen in practice. |
| Title | Analyses and designs of the connections jointing the new steel structure and the existing RC structure in NCREE’s office building extension |
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| Author | Yu-Cheng Lin, Ming‐Chieh Chuang, Guan-Hong Lin, Pin-Pin Deng, Keh-Chyuan Tsai, Ching-Yi Tsai, An-Chien Wu, Jui-Liang Lin |
| Keywords | seismic design, strengthened connection, chemical anchor, finite element analysis, nonlinear response history analysis |
| Abstract | The existing six-story office building of the National Center for Research on Earthquake Engineering (NCREE) was extended to thirteen-story from October 2019 to November 2020. This study presents the analysis and design of the connections jointing the existing RC structure and the new steel service core from the second to seventh floors. A steel bracket, which is welded to the steel beam bottom flange and connected to the RC column using chemical anchors, was considered as the basic design of the connection to transfer the gravity shear from the steel beam. This shear connection detail could avoid the congested reinforcing bars inside the RC beam-to-column joint, however, three alternative designs using strengthened schemes are investigated in this study. Nonlinear response history analyses (NRHAs) using PISA3D program for the NCREE’s 13-story composite building were conducted in order to gain insight into the possible maximum seismic force and deformational demands on the connections. The features of dual mass centroids and dual rigid diaphragms for the second to seventh floors are incorporated into the PISA3D model. The 6DOF joint elements are utilized to represent the aforementioned bracketed connections on the interface. The axial push-pull stiffness of 100 tf/mm, computed from an Abaqus finite element model (FEM) analysis for the connections, is utilized for all the 6DOF joint elements. A total of sixteen sets of ground accelerations are utilized. NRHA results indicate that the maximum axial force and maximum in-plane rotation of the connection at the steel beam end are about 165 tf and 0.01 radian, respectively. The Abaqus FEM analyses were conducted for investigation of four connection types including the basic design and three improved designs. The FEM analysis results indicate that the beam bracket of the basic design exhibits obvious shear yielding. The uneven anchor bolt forces developed are very evident. The improved load-carry capacity and a more uniform bolt forces developed are found in the strengthened designs, such as the stiffened steel angles at the beam web and bracket with cover plate. In addition, an approximately 200×200 mm triangular region on the cover plate corner with a low stress demand is observed. Based on these connections’ FEM analysis results, this study confirms that the strengthened scheme adopts double-sided stiffened steel angles at the beam web, the straight bracket with the angular cuts on the cover plates is suitable. The strengthened scheme adopted in the project not only meets the seismic demands but also allows the inspections of the anchor bolts in the future, if necessary. |
| Title | Mechanical Characteristics and Testing Device Development of Headed Reinforcements for Uniaxial Tension Test |
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| Author | Ker-Chun Lin, Chen-Yu Ou, Kai-Ning Chi, Sheng-Jhih Jhuang, Wen-I Liao |
| Keywords | headed reinforcement, testing device to test single headed reinforcement in tension, slip of head part, elongation, tensile strength |
| Abstract | This paper mainly investigates mechanical characteristics of headed reinforcements in tension popular used in Taiwan and develops a fixture for testing to effectively shorten test time. A total of 41 headed reinforcement specimens that include four types of steel grade, SD 420W、SD 490W、SD 550W and SD 690, and three main types of head part, welded head, threaded head, grouted sleeve head. Test results related to head part slip showed that upper loading bounds of 0.7Py and 0.95Py to assess head part slip can acquire the same identified results those are qualified or not. The slip results for the various head parts indicated that the slip of welded head by friction was very limit. The slips of head part with the other heads from small to large in sequence were threaded head and grouted sleeve head. For the threaded heads of the headed reinforcements, all the slips were smaller than 0.2 mm. For the grouted sleeve heads of them, the slips of head part without a restraining-slip nut were more significant than 0.3 mm, but the slips of head part with a restraining-slip nut enable to be reduced under 0.3 mm as long as using proper fabricated process. Test results also presented that the maximum tensile strengths of each specimen exceeded its minimum specified ultimate strength and 1.25 times its minimum specified yield strength. The testing device developed in this study can install measure instruments quick and visually and get reliable measure results of head part slip. It also significantly reduces 78% of testing time per piece compared with the existed testing fixture. The load capacity of the fixture is for #12 reinforcement of SD 690. |
| Title | A Study on Nonlinear Dynamic Behavior of Reinforced Concrete Structures using Concentrated Plasticity Model |
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| Author | Fu-Pei Hsiao, Lyan-Ywan Lu, Hsuan-Wen Huang, Hung Cheng |
| Keywords | concentrated plasticity model, nonlinear RC, shaking table test, TEASDA, ASCE 41, ETABS, OpenSees, ModIMK |
| Abstract | In recent years, some strong earthquakes, including the 921 Chi-Chi Earthquake, the 0206 Meinong Earthquake, and the 0206 Hualien Earthquake, have caused the collapse of med-to-high rise reinforced concrete (RC) buildings, and resulted in heavy casualties and severe property losses. Because of this, it is crucial to perform accurate numerical simulation for the nonlinear structural response of med-to-high rise RC buildings. This paper establishes a 7-story RC frame model with different plastic hinges using the commercial software ETABS and the open-source finite element software OpenSees developed by the University of California at Berkeley, USA. The effect of different plastic hinge settings on nonlinear time history analysis of the RC building is explored in this study. Then, based on the shaking table test results of the 7-story RC building, it is judged which plastic hinge analysis results are closer to the experimental structural response. Furthermore, since ETABS is a commercial software, its extensibility is relatively limited. In other words, users cannot add newly developed materials and elements to ETABS, nor connect ETABS with the experimental control system to conduct experiments. Therefore, this paper proposes a method to convert an ETABS model to a OpenSees model. This method will enable researchers to establish the plastic hinges for an equivalent OpenSees model with the help of ETABS, and to take the openness advantage of OpenSees software for analysis. |
| Title | Regional evaluation of resilience based on FEMA P58: a case study for nonductile reinforced concrete frames in Los Angeles |
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| Author | Peng-Yu Chen, Ertugrul Taciroglu |
| Keywords | Probabilistic seismic assessment, regional evaluation, FEMA P58, nonductile reinforced concrete frames, incremental dynamic analysis, resilient index |
| Abstract | Seismic damage and loss assessment are highly related to buildings’ performance. However, the current nonlinear static analysis for performance evaluation is a deterministic methodology, where the uncertainties and variation of ground motion and numerical modeling cannot be considered. Furthermore, the outcome of engineering parameters is difficult to be utilized by decision-makers who may not have engineering backgrounds. While the world is toward developing resilient city, it is still not clear to structural engineers how to quantify the seismic resilience and evaluate it for large-scale regions. Hence, this research proposes a framework for regional resilience evaluation, which is based on probabilistic seismic assessment (i.e., FEMA P58) to incorporate incremental dynamic analysis and Monte Carlo simulation for damage and loss assessment. Moreover, the outcome of the regional evaluation is used to quantify the resilience index to illustrate the ability of a city for recovering from an earthquake. To demonstrate the application of the proposed framework, 1,452 nonductile reinforced concrete frames in Los Angeles are simulated by developing an automatic modeling program. Around 950,000 nonlinear time history analyses are conducted through a supercomputer, and the outcomes are used for loss estimation and resilience quantification. The results show that the mean loss ratio for nonductile frames under maximum-considered earthquake is 37.3%, and the resilience index indicates that the city needs at least 3 years to recover. While the presented work is a US-based case study, the authors hope the framework can be extended and localized for Taiwan’s development of resilient city. |