Vol.31/No.4 (124) (2016)
| Title | A Computer Program for Axial Load-moment Interaction Diagram for New High-strength Reinforced Concrete Columns- New RC-PM |
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| Author | Yu-Chen Ou, Tung-Chun Tsai |
| Keywords | reinforced concrete, high strength, columns, axial load-moment interaction diagram, New RC, computer program |
| Abstract | To address the need for high-rise reinforced concrete buildings in Taiwan, Taiwan New High-Strength Reinforced Concrete (Taiwan New RC) project was initiated. The project integrates the resources of academia and industry of Taiwan to develop the New RC structures for use in Taiwan. The longitudinal and transverse reinforcement used in the project are SD690 (yield strength of 685 MPa) and SD790 (yield strength of 785 MPa), respectively. The concrete compressive strength is typically ≧ 70 MPa. To support the Taiwan New RC project, a computer program, referred to as New RC-PM, was developed in this research to calculate the axial load-moment (PM) interaction diagram for New RC columns as well as for conventional RC columns. The theoretical background and verification of the New RC-PM are presented and discussed in this paper. Moreover, a test database with 18 New RC columns were established. The New RC-PM was used to analyze the PM interaction diagrams of the columns, which were then compared with the test results. The comparison showed that the New RC-PM could conservatively estimate the axial-bending strengths of the columns. The New RC-PM was further used to evaluate the methods for calculating the maximum probable moment strength (Mpr) of the current building and bridge codes. Evaluation results showed that the Mpr calculated by the current building code was unconservative for all the columns. The method of the current bridge code significantly improved the degree of unconservatism of the method of the building code. However, the Mpr was still unconservative for most compression-controlled columns. To address the issue, a new method to calculate the Mpr was proposed in this research. Comparison with the test results showed that the Mpr calculated by the proposed method was reasonably conservative for most of the columns. |
| Title | Seismic Retrofit by External Reinforced Concrete Frames – Using School Building of HOU-JIA Junior High School as Example |
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| Author | Sheng-Hsueh Lin, Yu-Chih Lai, Tao Lai, Lap-Loi Chung, Guo-Luen Huang, Chien-Chuang Tseng |
| Keywords | retrofit by external frames, seismic retrofit, pushover analysis, shear capacity of slab |
| Abstract | In Chi-Chi earthquake, the school buildings in Taiwan were damaged seriously. Because rebuilding school buildings will be uneconomical and that will be a tremendous amount of work, seismic retrofit methods are usually adopted to raise seismic performance of buildings. The typical retrofit methods of school buildings in Taiwan include RC jacketing, wing wall and shear wall etc. However, those methods above will affect the function of the existing building during the construction. In this paper, retrofit method with adding external frames, seldom seen in Taiwan, is proposed. The advantage of this method is that the function of the existing building will not be affectedduring the construction. We first use a school building to discuss the feasibility of the method. And it is suggested that the method can be used on the buildings whose functioncannot be affected during construction, such as hospitals. We use a school building of HOU-JIA junior high school to apply a retrofit design of this seismic retrofit method using slabs to connect existing building and external frames. After the retrofit design, we do pushover analysis to make sure the seismic capacity of the retrofitted school building is enough. Finally, we check the shear capacities of slabs to make sure they can completely transfer the earthquake load from the existing building to external frames. By the design example, we prove that the retrofit method of RC external frame is fit to the common squat school buildings. |
| Title | Seismic Performance of Large BCR Steel Columns |
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| Author | Cheng-Cheng Chen, Shu-Hao Lin, Pin-Da Wu |
| Keywords | cold formed structural tube, steel structure, steel column, earthquake-resistant structures |
| Abstract | This study examined the ductility development of large cold-formed square tube columns through cyclic loading test of five full-sized specimens. Specimens included crack-sensitive and local-buckling-sensitive specimens. In addition, specimens using internal diaphragm and external diaphragm were employed to weld the columns to the beams. Based on the test results, the following conclusions can be drawn: (1) The cold-forming process caused considerable plastic strain on the cross sections of the steel columns, however, by controlling the heat input in the welding passes, premature cracks can then be suppressed. (2) For the specimens with a column wall width-to-thickness ratio equals to 10.9, a story drifty ratio capacity no less than 7% and a plastic hinge rotation capacity no lower than 4.5% can be reached. (3) For the specimens with a column wall width-to-thickness ratio of 23.9, which is much larger the code limitation of 15.6, a story drift ratio capacity between 4.2%–4.4% and a plastic hinge rotation capacity between 2.1%–2.2% can be reached; generally, the specimens satisfied the requirements for seismic structures. (4) Although a more restrict with-to-thickness ratio for cold-formed square section than for box column is specified by the code, the ductility of the structural tube and the box column with the same section width and wall thickness is similar. |
| Title | Optimal Design of Viscous Dampers for Two and Three-Dimensional Building Structures |
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| Author | Peng-Tai Chan, Chih-Shen Cheng, Liang-Jenq Leu |
| Keywords | Viscous dampers, optimal placement of dampers, shear type buildings, three-dimensional asymmetric buildings |
| Abstract | Nowadays, passive energy dissipation devices are widely used in building structures. Design codes such as FEMA273/274 suggested that the equivalent damping ratio of supplemental viscous dampers be used. However, how to place viscous dampers optimally was not addressed. Several optimal damper placement methods have been proposed to improve the seismic performance of structures but they usually involve complicated procedure and therefore are not suitable for practical applications. The goal of this study is aimed at finding the optimal placement of viscous dampers using proposed simple methods. The proposed methods and other optimal damper placement methods are applied to different shear type buildings and a three-dimensional asymmetric building. Their performance and applicability are compared using statistical methods under a series of spectrum-compatible ground motions. |
| Title | Effect of Vibration Reduction of Bidirectional Suspension-type Tuned Mass Damper |
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| Author | Jing Jhang, Wei-Ru Liao, Yong-An Lai, Kuan-Hua Lien, Lap-Loi Chung, Chien-Chuang Tseng |
| Keywords | Tuned Mass Damper, bidirectional analysis, wind-induced vibration control, high-rise building |
| Abstract | The tuned mass damper (TMD) is widely utilized for civil engineering to control wind-induced vibration in high-rise building. In this research, the design and analysis procedures of the bidirectional suspension-type tuned mass damper are proposed and demonstrated. The main structure is simplified as a shear building model to install the suspension-type tuned mass damper for simulation by the dynamic time history analysis. For common pendulum tuned mass damper, the suspension position and viscous damper implement location are located at different floors. Therefore the reaction force and damping force of the tuned mass damper are acting on different degrees of freedom of the main structure. Although the damping force of a damper is acting in both the two horizontal directions because the damper is implemented with an angle to the floor plane, the damping force is independent in the two horizontal directions if the dampers are allocated in symmetric layout. Therefore, the damping matrix can be decoupled. The feasibility of the bidirectional suspension-type tuned mass damper is illustrated by the high-rise building subjected to the design wind force with return periods of 1 year and 50 years, respectively. Following numerical verification, the effects of vibration reduction for the high-rise building subjected to the design wind forces are demonstrated. |
| Title | Selection of modal frequencies adopted in ambient vibration method for determination of stay cable force |
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| Author | Wen-Hwa Wu, Chien-Chou Chen, Yi-Ren Wang |
| Keywords | stay cable, cable force, ambient vibration method, modal frequency, anchorage system |
| Abstract | The ambient vibration method is typically employed in engineering practice to determine the tension of a stay cable and its precision strongly depends on the appropriate selection of cable frequencies. In general, the modal frequencies of a stay cable are close to an arithmetic sequence and these well separated frequency values are not difficult to be identified. From recent measurements on different stay cables by this research group, however, it is found that the identification of cable frequencies is possibly disturbed by the frequencies of bridge deck, the biased constraint of anchorage system, and the coupled interaction for the cable with its anchorage system. This study is consequently aimed to systematically explore these three types of difficulties such that the goal of clarified cable frequency identification and accurate cable force estimation can be attained. For the confusion caused by the frequencies of bridge deck, it is suggested to conduct the cable frequency identification over a wider frequency range and then exclude the interference of the deck frequencies in the lower frequency range based on the equally spaced relationship of cable frequencies conveniently observed in the higher frequency range. Regarding the biased constraint of anchorage system to induce a pair of frequencies for each vibration mode, it is recommended to consistently adopt the higher or lower frequency value in each pair for the computation of cable force established on a basis of common boundary constraints. Finally, the phenomenon that a particularcable frequency within a specific frequency range can irregularly splitinto two is confirmed to result from the coupled interaction between the cable and its anchorage system. Under such circumstances, special attention should be paid to choose the cable frequencies not influenced by this coupling for evaluating the cable tension. |