Vol.39/No.2 (152) (2024)
Title | Experimental Study on Reinforced Concrete Box Girder Strengthened in Shear With Carbon Fiber Reinforced Polymer (CFRP) Patches |
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Author | Hsiao-Hui Hung, Chi-Rung Jiang, Chun-Chung Chen, Fang-Yao Yeh, Kuo-Long Chen, Tsair-Yi Luo, Yi-Ting Lee, Kang-Yu Peng, Ming-Shing Wu, Chien-Hung Chen |
Keywords | CFRP patch, shear strength, RC box girder |
Abstract | The purpose of this research is to investigate the shear strengthening effect of carbon fiber reinforced polymer (CFRP) patched on reinforced concrete (RC) box girder with concrete shear cracks through specimen tests. Therefore, Two RC box girder specimens with insufficient shear strength were designed and fabricated, and the loading tests were carried out after strengthening of girders by CFRP was applied. The CFRP shear reinforcement was designed according to the guide specification published by American Association of State Highway and Transportation Officials (AASHTO). In order to simulate the state of RC box girder after shear cracks already occurred, one of the box girder specimens was loaded at first until shear cracks occurred and then strengthened with CFRP patches, while the other box girder specimen was directly strengthened with CFRP patches. Then, both strengthened specimens were respectively subjected to loading tests. Through the comparison of the loading test results of the specimens before and after strengthening with CFRP patches, the shear strengthening effect of the CFRP patch was confirmed. In addition, through the comparison of the test results of two strengthened specimens performed under different conditions, the benefits of shear strengthening with CFRP patch on RC box girder with existed damage can also be confirmed. |
Title | Shear Behavior of Prestressed Concrete Girders With High-Strength Transverse Reinforcement |
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Author | Yu-Chen Ou, Dwi Prasetya, Jhen-Wei Wu |
Keywords | bridges, prestressed concrete, girder, shear strength, high-strength steel reinforcement, SD790 |
Abstract | This study investigated the influence of high-strength shear reinforcement on the shear behavior of prestressed concrete girders. Six I-girders, with a cross-sectional height of 600 mm and a total length of 5 m, were constructed and tested in the laboratory using two types of rebar as shear reinforcement: high-strength steel (SD790) and normal-strength steel (SD420W). The test parameters included the transverse reinforcement ratio and prestressing level. Monotonic-static loading was applied in all girders using two loading points. The test results indicated that a direct replacement of normal-strength shear reinforcement with high-strength shear reinforcement increased the shear capacity of the girder. The equivalent shear strength replacement of normalstrength shear reinforcement with high-strength shear reinforcement based on the specified yield strength showed a decrease in the ultimate shear strength. Thus, the use of fy = 790 MPa in shear design calculation is not recommended. In addition, the equivalent shear strength replacement based on a yield strength limit of fy = 600 MPa resulted in similar ultimate shear strengths between the specimen with the normal-strength shear reinforcement and that with the high-strength shear reinforcement. Furthermore, the experimental results were evaluated using the ACI 318-19 and AASHTO LRFD 2020 shear strength models. The findings showed that the yield strength limitation for shear strength design in the ACI 318 could be increased up to 600 MPa. Using 690 MPa as the yield strength limit with the AASHTO LRFD shear strength model still provided a high degree of conservatism. |
Title | Hybrid Simulation of a Steel Seven-Story Dual System With Measured Buckling-Induced First-Story Box Column Shortening in Subassemblage Tests |
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Author | Cheng-Wei Huang, Kung-Juin Wang, Chung-Che Chou, Hou-Kuan Shen, Claudio Sepulveda, Gilberto Mosqueda, Chia-Ming Uang |
Keywords | hybrid simulation, moderately ductile built up box column, buckling, forced control, displacement compatibility |
Abstract | This paper presents a series of hybrid simulation (HS) conducted on full-scale steel beam-column connection subassemblages to study the seismic responses of a two-dimensional steel dual frame, considering first-story steel column shortening caused by local or global buckling during the seismic events. A seven-story two-bay dual frame system is composed of a special moment frame (SMF) and a buckling-restrained braced frame (BRBF) using built-up box columns. The experimental substructure consists of a full-scale interior column and beam cruciform subassemblage, including a moderately ductile first-story built-up box column and two I-shaped beams. Under combined axial and lateral loads, local buckling can occur near the column base, resulting in column shortening. The specimen is loaded through a four degree of freedom (DOF) mixed-mode control (three displacement- and one forcecontrol) actuation system that simplifies the laboratory loading conditions given the complex boundary conditions of the frame structure. To account for column shortening in the HS, a new approach is applied to enforce compatible displacements between the experiment and numerical model. With the column axial load in force control and column shortening, a set of fictitious equivalent forces is applied to columns in the numerical model to achieve compatible displacements. Shortening of two exterior columns in the model is simulated through finite element analysis using the computer program ABAQUS. The test results confirm that the proposed modeling and control methods could successfully integrate the information available in the laboratory and ABAQUS simulation into the HS, resulting in a more realistic frame response that captures the effect of column shortening in the analysis. The moderately ductile built-up box column is also verified to perform well in near-fault earthquake loadings. |
Title | A Simplified Seismic Design Method for Steel-Timber Hybrid Buildings Considering Shear Force Modification |
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Author | Kai-Jun Huang, Pei-Ching Chen |
Keywords | steel-timber hybrid building, structural dynamic interaction, design seismic force, incremental dynamic analysis |
Abstract | A steel-timber hybrid building consists of a conventional steel moment-resisting frame in its lower section, while the upper part is constructed with timber. In this study, a simplified method for structural design of steel-timber hybrid buildings has been proposed. It incorporates the dynamic interaction between the superstructure and the substructure into the existing Seismic Design Specifications and Commentary of Buildings in Taiwan. First a steel-timber hybrid building is simplified into a two degrees-of-freedom (2DOF) linear model. Parameter analysis is conducted to investigate the effects of the mass ratio and the frequency ratio of the superstructure to the substructure on the dynamic response of the 2DOF model. Accordingly, a seismic force modification factor can be defined, and the design seismic force for the upper timber structure can be calculated directly by using this modification factor. Meanwhile, the design seismic force for the lower steel structure can be determined individually by considering the base shear of the upper timber structure transmitted to the top of the lower steel structure. Four steel-timber hybrid buildings with different elevation have been designed based on the proposed method. OpenSees is used to build the nonlinear numerical model of the steel-timber hybrid buildings to perform nonlinear pushover analysis and incremental dynamic analysis (IDA). A total number of 44 earthquakes recommended in FEMA P695 are used for IDA. Based on FEMA P695 and relevant literature recommendations, the limit states of the steel-timber hybrid buildings can be assessed. The IDA results indicate that the Collapse Margin Ratios suggested in FEMA P695 is satisfied which demonstrates the applicability of the proposed simplified design method for design of steeltimber hybrid buildings in Taiwan. |
Title | Application and GUI Program Development of Empirical and Statistical Green’s Function Method in Earthquake Motion Simulation |
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Author | Wen-I Liao, Yuan-Ting Chen |
Keywords | empirical Green’s function method, statistical Green’s function method, MATLAB, strong ground motion simulation |
Abstract | This study primarily utilizes the empirical Green’s function method for seismic motion simulation graphical user interface (GUI) program development. The main theoretical concept involves the superposition of observed small earthquake event acceleration time histories to simulate the strong earthquake time history that occurs at the same site during a large earthquake. This method can effectively simulate acceleration time history of large earthquakes. To address the issue of the empirical Green’s function method being unable to simulate strong ground motion for locations without records of small earthquake events, this study proposes the statistical Green’s function method to simulate the strong ground motion acceleration time history at such sites. The main theory behind this approach is to use the recorded acceleration time histories of small earthquakes from surrounding monitoring stations to statistically analyze the relationship between ground acceleration amplitude spectra, phase spectra, and source-toreceiver distance. Subsequently, by calculating the results, the source-to-receiver distance for the desired simulation site can be used to calculate the amplitude spectra and phase spectra at that site. Then, by performing a Fourier inverse transform on the amplitude spectra and phase spectra, the acceleration time history of small earthquakes at that site can be obtained. Finally, this small earthquake event acceleration time history is used in place of actual small earthquake records in the empirical Green’s function method to simulate the strong ground motion at that site. Additionally, the developed GUI interface program includes functions for generating response spectrum-compatible acceleration time histories and amplifying acceleration time histories at specified period range. |