Vol.39/No.1 (151) (2024)
Special Issue:
Guest Editor: Professor Chien-Kuo Chiu, Professor Pei-Ching Chen
| Title | Analysis and Validation of Isolation Systems With Multi-Functional Friction Damper |
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| Author | Chia-Shang Chang Chien, Shan-Ru Chen, Mei-Ting Guo |
| Keywords | performance test, conical friction pendulum isolators, multi-functional friction damper, seismic isolation system, shaking table test |
| Abstract | In recent years, earthquake disasters have gradually attracted global attention. Due to the unpredictability of earthquakes, whenever strong earthquakes occur, they often cause losses of people’s lives and property. In serious cases, they even affect the overall economic development of the country. The conical friction pendulum isolators (CFPI) is a seismic isolation system with the characteristic of extended structural period, which can improve the resonance effect produced by long-period velocity pulses of near-field seismic waves and fixed-period seismic isolation structures. Nevertheless, although the CFPI has an excellent seismic isolation effect in reducing acceleration of the superstructure, its base sliding displacement will amplify with the peak surface acceleration. The multi-functional friction dampers provide multi-stage activation mechanisms, and studies have shown that they have great shock absorption effects under different earthquake intensities when configured to structures. Therefore, the study in turn installed them in seismic base isolation layers to form a supplementary damping isolation system, improving the safety of the seismic isolator system under the effect of near-field seismic waves. According to the results of numerical simulation, the seismic isolation system with supplementary damping isolation has satisfactory vibration isolation effects regardless of affected by far- or near-field seismic waves. Additionally, to verify the theoretical formulas, the study also conducted the seismic performance test of the multifunctional supplementary damping system by shaking table and fit the results of the shaking table test and numerical simulation analysis. The results showed a fairly good fitting effect, which validates the accuracy of the theoretical formulas in this study. |
| Title | Bridge Scour Depth Prediction Using Phase Space Attractor and Deep Learning |
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| Author | Chang-Yi Lee, Zu-yi Chen, Yen-Yu Yang, Shu-Wei Chang, Chang-Wei Huang |
| Keywords | bridge scouring, deep learning, embedding theorem, convolutional neural network |
| Abstract | Cross-river bridges often suffer attacks of the foundation scour. Scour can significantly reduce the stiffness and strength of a bridge foundation, resulting in damage or even collapse of the bridge. To ensure the safety of a soured bridge, it is important to develop a real-time scour monitoring system to measure the scour depth of the bridge. In this study, a data-driven method is proposed to measure the scour depth using time series data from accelerometers. The concept of attractor in the phase space is used to describe the dynamic characteristics of scoured bridges. High-dimensional attractors for scoured bridges are reconstructed by a single sensor based on Takens’ embedding theorem. The reconstructed attractors are converted into two-dimensional grayscale images, which are then identified by the convolutional neural network (CNN) to obtain the scour depth. The accuracy of the proposed method is verified by the dynamic responses of bridges with different scour depths subjected to ambient vibrations from numerical simulations. The results demonstrate that the proposed data-driven method can determine the scour depth more accurately than conventional vibration-based methods in the case when the scour is not severe. |
| Title | Study of Aspect Ratios for Base Isolated Buildings With Lead-Rubber Bearings |
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| Author | Yi-Chian Wu, Chia-Ming Chang, Cho-Yen Yang |
| Keywords | base isolation, elastomeric bearing, stability, aspect ratios, nonlinear time history analysis |
| Abstract | Seismic isolation shifts the fundamental frequency of structures away from the dominant frequencies of earthquakes by employing bearings with low horizontal stiffness, resulting in reduced responses of superstructures. However, an isolated building with a higher aspect ratio may introduce excessive overturning moments that can further cause tensile failure to bearings. Moreover, the elastomeric bearings, which are familiar and common in Taiwan, consist of laminated rubber layers with in-between steel shims, yielding complicated and coupled mechanics. Thus, the stability of the isolation bearings and the overall structural system should be concurrently considered. Such complicated behavior for an isolated building with elastomeric bearings as mentioned above may not be simulated or presented by conventional analysis in practical application. Therefore, this research studies the coupling effect for base isolated buildings with lead-rubber bearings, and then the relationship between aspect ratios and selected isolation bearings is constructed. In this research, the superstructure is simplified to be single-degreeof-freedom and mounted on an isolation system consisting of a rigid floor and two bearings. Each bearing is modeled by a simple mechanical model proposed by Koh and Kelly to consider the coupling effect. Based on the tension prevention of bearings, an aspect ratio criterion is also derived and proposed. This aspect ratio criterion is further verified by time history analyses which consider various factors, such as the period of superstructure, isolation period, fault effect, and layout of bearings. As found in the parametric study, an isolated building designed by the proposed aspect ratio formula has a pretty low probability of tensile failures on bearings, as compared to the recommendation in the Japanese design code. Thus, the proposed aspect ratio criterion is more conservative and can be consequently a reference for engineers in the preliminary design phases of base isolated buildings with lead-rubber bearings. |
| Title | Application of Hybrid Testing in a RC Structure With Seismic Retrofitting |
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| Author | Fu-Pei Hsiao, Lyan-Ywan Lu, Hung Cheng, Bo-Tse Hsu, Shih-Wei Yeh |
| Keywords | hybrid testing, RC structure, seismic retrofitting, open framework, OpenSees, OpenFresco |
| Abstract | The most realistic experimental method for evaluating the behavior of reinforced concrete (RC) structures under ground motion is a shaking table test (STT). However, the construction of RC shaking table test specimens is costly, and the shaking table equipment usually has limited capabilities; therefore, conducting a large-scale structure test using a STT is difficult. To this end, this paper aims to develop a cost-effective hybrid testing (HT) technique that combines numerical simulation with large-scale structural experiments to test the nonlinear response of large-scale RC structures under strong ground motions. To make the result more applicable, this paper adopts the framework of an open-source hybrid testing technology. The technique used the OpenSees (Open System for Earthquake Engineering Simulation) as an open-source finite-element analysis software to build the RC nonlinear numerical substructure (NS) and the OpenFresco (Open source Framework for Experimental Setup and Control) as an open-source middle software to connect the physical substructure (PS) and a controller, which was connected to the hydraulic facility in Tainan Laboratory of the National Center for Research on Earthquake Engineering (NCREE). In the HT of this study, the target structure was a seven-story RC structure. The PS was taken to be the first-floor middle span retrofitted by an embedded RC portal frame, while the remaining structure, treated as the NS, was simulated by an OpenSees nonlinear numerical model with plastic hinges. The HT result demonstrates that the seismic responses of the retrofitted RC structure predicted by the HT experimental result match very well with the theoretical values predicted by a nonlinear finite-element model. The average difference between the experimental and theoretical first-floor displacements is merely 5%. The nonlinear behavior contributed by the plastic hinge was also observed in the test. This study confirms that by cooperating with the existing hydraulic facility in Tainan Laboratory of the NCREE, the established open-framework HT technique with a nonlinear numerical substructure is a feasible means for the experimental study of a large-scale RC structure. |
| Title | New Seismic Attenuation Technology: Resonator-Type Metamaterial |
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| Author | Yuan-Yu Lo, Tung-Yu Wu, Shiang-Jung Wang |
| Keywords | seismic metamaterial, finite element analysis, local resonance, bandgap |
| Abstract | Seismic metamaterials represent a novel earthquake-resistance technology. By manipulating wave propagation through artificial structures, they create regions where waves of specific frequencies cannot pass, preventing seismic waves of primary frequencies from reaching structures. Currently, seismic metamaterials face two major challenges: (1) the band gap frequency of the metamaterial is relatively higher than the primary frequency of earthquakes, and (2) there is a lack of metamaterials specifically designed for body waves. In light of this, our study designs a new low-frequency (0.35–1.5 Hz) seismic metamaterial unit targeting body waves based on duallayer tube-type resonators. Row and ordering analyses were conducted to determine the optimal arrangement of metamaterial units for reduction effects. The influence of the soil layer outside the metamaterial on its reduction effect was also investigated. Simulation results show that a group of four consecutive metamaterial units is the most economical arrangement, and the reduction effect of the metamaterial on SH waves was sensitive to the thickness of the soil layer. A subsequent ground response analysis demonstrated that when excited by actual seismic waves, the designed metamaterial units can reduce the spectral acceleration at the corresponding metamaterial band gap period to half, indicating the promising potential of the dual-layer tube-type resonators. |