Vol.35/No.3 (137) (2020)
| Title | Effects of SM570M-CHW steel beam flange eccentricity and box-column flange thickness on electro-slag welding failure |
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| Author | Yu-Jun Huang, You-Wei Hu, Chih-Kuang Chin, Ching-Yi Tsai, Chao-Hsien, Li,Sheng-Jhih Jhuang, Ker-Chun Lin, Keh-ChyuanTsai |
| Keywords | steel box column, SM570M-CHW steel, electro-slag welding, circumferentially notched tensile test, steel fracture prediction model, finite element analysis, overlapping distance of beam flange and diaphragm |
| Abstract | Steel box columns are widely used in seismic steel building structures in Taiwan. In order to effectively transfer the beam-end moment to the column, diaphragm plates are welded inside the box column at the same elevations of the welded beam flanges. Electro-slag welding (ESW) procedure is common applied to attach the diaphragm plates to the column. Recently, the SM570M-CHW grade high strength steel is prevailingas it reduces the column sizes. In this study, four full-scaled welded SM570M-CHW steel beam-to-column (BC)joint specimens and eleven ESW component specimens were fabricated and tested. The key design parameters of these specimens include column flange thickness, beam flange eccentricity with respect to the diaphragm plate. This study investigates the applicability of stress modified critical strain and degraded significant plastic strain modelsin predicting the crack initiation fracture of the diaphragm-to-column ESW joint. The ESW component specimens were subjected to monotonic tensile loads, while the welded BC joint specimenswere subjected to cyclically increasing displacement to investigate the effects of beam flange eccentricity and column flange thickness on the ESW fractures. Test results show that when the ESW was subjected to monotonic tension only, it could fracture when the “overlapping distance of beam flange and diaphragm” (OD) was smaller or equal to zero. On the contrary, it remained intact even when the ODwas greater or equal to thickness of beam flange. Cyclic test results of the welded BC joints show that the connection with the 25mm thick column flange failed at the 3% inter-story drift (IDR) cycle, while the specimen with the 45mm column flange went through 5% IDR cycle without failure. The finite element model analysisresults show that when the column flange thickness increases from 25mm to 45mm, the stress concentrations are reduced and the crack tip opening displacement is decreased by 3 times. This study also carried out parametric study, focusing on the effects of the column flange thickness, the beam flange thickness and the OD on ESW fracture. Results show that increasing the column flange thickness, or the OD and decreasing the beam flange thickness reduce the stress concentration near ESW. In order to avoid the ESW fracture, the results of this study suggest that column flange thickness be equal to or larger than diaphragm or beam flange thickness; and the ODbe larger than one quarter of the diaphragm or beam flange thickness. |
| Title | Development of Ground Motion Characteristics Prediction Module and its Application to the Control of Intelligent Isolation System |
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| Author | Chia-En Hsiao, Kuang-Yi Lin, Tzu-Kang Lin, Lyan-Ywan Lu |
| Keywords | Ground motion characteristics, Support vector machine, Structural control, Genetic algorithm, Fuzzy control. |
| Abstract | In recent years, researches on structural control combining earthquake early warning have been widely studied. In the field of seismic engineering, ground motions can be mainly classified into near-fault and far-field ground motions. While the ground motion characteristics have a great influence on control performance; however, the existing earthquake early warning system can only predict the peak ground acceleration, and the optimal control efficiency cannot be promptly achieved. Therefore, a prediction module for ground motion characteristics is proposed in this study. A database of near-fault ground motions and far-field ground motions is first collected, and the six p-wave features and the high-frequency energy accumulations of the ground dynamic spectrum are used to establish the ground motion characteristic prediction module by utilizing support vector machine. In order to develop the intelligent structural control system, the Leverage-type Stiffness Controllable Isolation System (LSCIS) is used as the structural control mechanism. The effective isolation stiffness of the LSCIS can be swiftly changed to control the dynamic response of the structure. The control parameters corresponding to different types of ground motion are optimized by genetic algorithm, and fuzzy control is adopted for the intelligent isolation system. |
| Title | Piezoelectric Tuned Mass Damper for Vertical Vibration Reduction and Energy Harvesting |
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| Author | Yong-An Lai, Wei-Ling Chou, Lap-Loi Chung |
| Keywords | tuned mass damper, piezoelectric material, energy harvesting, vertical vibration reduction, optimal design |
| Abstract | In recent years, the energy consumption has continually grown. However, due to climate change, the use of fossil fuel to generate electrical power forces to be reduced. Therefore, looking for environmental friendly energy sources is one of the current research priorities. Because of the development of civil engineering technology, the design and construction of structures turn into more economical. The weight of the bridge structure is becoming lighter, the appearance is accomplishing slender, and the structural period is therefore prolonged, making the bridge structure more susceptible to external forces such as pedestrian loads. In order to effectively reduce the vibration, civil engineers designed and installed Tuned Mass Damper (TMD). Through the tuning of the natural frequency of TMD to the structure, the vibration energy of the structure was absorbed and then dissipated by dashpot. However, this absorbed energy is a kind of green energy source to waste to be dissipated. In view of this, this article studies “Piezoelectric Tuned Mass Damper (Piezo-TMD)”, which uses piezoelectric materials to convert the mechanical vibration energy into electricity for energy harvesting. This research proposes the model and derives the equation of motion of the Piezo-TMD system. Different from the conventional TMD, Piezo-TMD has a circuit equation in addition to the mechanical equation, and these two equations are mutually coupled. The design goal of the Piezo-TMD in this paper is to maximize the average power for energy harvesting, and the numerical simulations are carried out with a pedestrian bridge structure. The simulation results show that the Piezo-TMD achieves the similar performance of vibration reduction as the conventional TMD and thus the vibration comfort requirement can be satisfied. Moreover, the vibration energy is further transferred to electricity for harvest to verify the feasibility of Piezo-TMD. In addition to tuning the mechanical natural frequency of the Piezo-TMD, the natural frequency of the circuit also needs to be tuned to the structure, so that the vibration energy of the structure can be effectively transferred to the circuit by using the resonance effect. |
| Title | Double-curvature cyclic test of columns with five-spiral reinforcement and discreet computational shear strength model |
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| Author | Yu-Chen Ou and Jhe-Yan Li |
| Keywords | shear strength; five-spiral reinforcement; columns; discreet computational shear strength model; cyclic test |
| Abstract | Five-spiral reinforcement has been proved to have superior confinement capability to conventional rectilinear hoops. The objective of this research is to investigate the shear strength of five-spiral reinforcement. Large-scale columns with five-spiral reinforcement and control columns with conventional rectilinear reinforcement were tested in this research using double-curvature cyclic loading. Test results showed that with the same volume of reinforcement and similar reinforcement yield strength and concrete compressive strength, the shear strength of columns with five-spiral reinforcement was slightly less than that with conventional rectilinear reinforcement. However, the strength degradation after the peak strength for columns with five-spiral reinforcement was slower than that for columns with conventional rectilinear reinforcement. Under high axial load, the failure mode of columns with five-spiral reinforcement was fracture of spirals.In contrast, the failure mode of columns with conventional rectilinear reinforcement was the loosening of hook anchorage of the reinforcement. An improved discreet computational shear strength model is developed in this research and validated by the test results. The model can be conservatively used for estimating the shear strength of five-spiral reinforcement. Moreover, the model shows a conservatism for estimating the shear strength of five-spiral reinforcement similar tothat shown by the code shear strength equations for conventional rectilinear reinforcement. |
| Title | Effect of sensor deploymentonen on the accuracy of ambient vibration method incorporating mode shape functions for cable tension estimation |
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| Author | Chien-Chou Chen, Wen-Hwa Wu, Shin-Yi Chen and Gwolong Lai |
| Keywords | ambient vibration method, cable tension estimation, mode shape, effective vibration length, multiple synchronous measurements, sensor deployment |
| Abstract | The complicated boundary conditions resulted from the anchorage systems at both ends usually deteriorate the accuracy of the ambient method for cable tension estimation. Motivated by tackling such a problem, a novel method incorporating the mode shape functions was recently proposed by this research group. More specifically, the fitting for the sinusoidal components of mode shape functions was adopted to determine the effective vibration length for each mode such that the interference from the complicated boundary conditions can be eliminated. The success of this method is most critically decided by the accurate reproduction of the sinusoidal components of mode shape functions based on multiple synchronous measurements. The current paper first explains the basic concepts of this cable tension estimation method with the theoretically derived mode shape functions and frequency equations. The finite element models are further employed to evaluate the accuracy of this method and establish the guidelines for the preferred sensor deployment in measurement points and spacing with the consideration of practical measurement limitations. Finally, the applicability of the developed guidelines and the corresponding accuracy in tension estimation are verified by demonstrative laboratory experiments with a prestressed strand. |