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Chung L.-L.,Center for Research on Earthquake Engineering | Wu L.-Y.,University of Taipei | Huang H.-H.,University of Taipei | Chang C.-H.,University of Taipei | Lien K.-H.,University of Taipei
Earthquake Engineering and Engineering Vibration | Year: 2010

Optimal design theory for linear tuned mass dampers (TMD) has been thoroughly investigated, but is still under development for nonlinear TMDs. In this paper, optimization procedures in the time domain are proposed for design of a TMD with nonlinear viscous damping. A dynamic analysis of a structure implemented with a nonlinear TMD is conducted first. Optimum design parameters for the nonlinear TMD are searched using an optimization method to minimize the performance index. The feasibility of the proposed optimization method is illustrated numerically by using the Taipei 101 structure implemented with TMD. The sensitivity analysis shows that the performance index is less sensitive to the damping coefficient than to the frequency ratio. Time history analysis is conducted using the Taipei 101 structure implemented with different TMDs under wind excitation. For both linear and nonlinear TMDs, the comfort requirements for building occupants are satisfied as long as the TMD is properly designed. It was found that as the damping exponent increases, the relative displacement of the TMD decreases but the damping force increases. © Institute of Engineering Mechanics, China Earthquake Administration and Springer Berlin Heidelberg 2009.

Lin T.-K.,Center for Research on Earthquake Engineering | Chen C.-C.,University of Taipei | Chang K.-C.,University of Taipei | Lin C.-C.J.,Center for Research on Earthquake Engineering | Hwang J.-S.,University of Taipei
Earthquake Engineering and Engineering Vibration | Year: 2010

This study proposes a micro vibration mitigation system using viscous dampers to solve the problem of vibration in a high-tech building. Due to the operating frequency of the air conditioners and fundamental mode of the floors, a resonant phenomenon is occasionally experienced at the upper levels of the structure. Several strategies were considered, and viscous dampers combined with a suspension system were chosen to mitigate this annoying situation. A theoretical analysis was first executed to determine the optimal design value of the damper and the suspension spring. An efficient reduction in floor velocity of approximately 50 % was achieved by the proposed system. Practical verifications including a performance test of the micro-vibration-oriented dampers, the pragmatic application result, and a comparison in one-third octave spectrum was then carried out. The performance of the system was demonstrated by the data measured. It alleviated more trembling than was numerically expected. The energy absorbed by the viscous dampers is illustrated by the hysteresis loops and the one-third octave spectrum. It is found that with the proposed system, the vibration can be effectively captured by the viscous damper and converted to lower frequency-content tremors. The success of this project greatly supports the proposed standard two-stage analysis procedure for mitigating micro-vibration problems in practice. This research extends the use of viscous dampers to a new field. © Institute of Engineering Mechanics, China Earthquake Administration and Springer Berlin Heidelberg 2009.

Hung H.-H.,Center for Research on Earthquake Engineering | Yang Y.B.,Sudan University of Science and Technology
Earthquake Engineering and Engineering Vibration | Year: 2010

The 2.5D finite/infinite element approach is adopted to study wave propagation problems caused by underground moving trains. The irregularities of the near field, including the tunnel structure and parts of the soil, are modeled by the finite elements, and the wave propagation properties of the far field extending to infinity are modeled by the infinite elements. One particular feature of the 2.5D approach is that it enables the computation of the three-dimensional response of the half-space, taking into account the load-moving effect, using only a two-dimensional profile. Although the 2.5D finite/infinite element approach shows a great advantage in studying the wave propagation caused by moving trains, attention should be given to the calculation aspects, such as the rules for mesh establishment, in order to avoid producing inaccurate or erroneous results. In this paper, some essential points for consideration in analysis are highlighted, along with techniques to enhance the speed of the calculations. All these observations should prove useful in making the 2.5D finite/infinite element approach an effective one. © 2010 Institute of Engineering Mechanics, China Earthquake Administration and Springer Berlin Heidelberg.

Chang H.-Y.,National University of Kaohsiung | Lin K.-C.,Center for Research on Earthquake Engineering
Natural Hazards | Year: 2013

On March 4, 2010, at 08:18 local time, an earthquake with a magnitude of ML 6.4 hits southern Taiwan. The earthquake occurred in the mountainous area of Kaohsiung County at a depth of 22.64 km. The epicenter was located in the area struck by the 2009 Morakot Typhoon, which destroyed nearly 2,000 houses, leaving 461 people dead and 192 missing. Trapped residents were moved from the affected regions, and the earthquake did not cause any deaths, but injured 96 people. Damage reports were also issued on low-rise and mid-rise reinforced concrete (RC) buildings located 30 km or more from the epicenter. This paper presents the main results of a damage investigation on the largest seismic disaster in a century in the county of Kaohsiung. The focus was on the damage incurred by different types of building structures, including governmental, religious, commercial, and residential buildings. Detailed descriptions are given of the structural configurations as well as the types of damage sustained by five selected buildings. Suggestions are also made to prevent similar damage to low-rise RC buildings in a future disaster. © 2013 Springer Science+Business Media Dordrecht.

Chang K.-C.,University of Taipei | Sung Y.-C.,University of Taipei | Liu K.-Y.,Center for Research on Earthquake Engineering | Wang P.-H.,Center for Research on Earthquake Engineering | And 3 more authors.
Earthquake Engineering and Engineering Vibration | Year: 2014

This paper presents in-situ seismic performance tests of a bridge before its demolition due to accumulated scouring problem. The tests were conducted on three single columns and one caisson-type foundation. The three single columns were 1.8 m in diameter, reinforced by 30-D32 longitudinal reinforcements and laterally hooped by D16 reinforcements with spacing of 20 cm. The column height is 9.54 m, 10.59 m and 10.37 m for Column P2, P3, and P4, respectively. Column P2 had no exposed foundation and was subjected to pseudo-dynamic tests with peak ground acceleration of 0.32 g first, followed by one cyclic loading test. Column P3 was the benchmark specimen with exposed length of 1.2 m on its foundation. The exposed length for Column P4 was excavated to 4 m, approximately 1/3 of the foundation length, to study the effect of the scouring problem to the column performance. Both Column P3 and Column P4 were subjected to cyclic loading tests. Based on the test results, due to the large dimension of the caisson foundation and the well graded gravel soil type that provided large lateral resistance, the seismic performance among the three columns had only minor differences. Lateral push tests were also conducted on the caisson foundation at Column P5. The caisson was 12 m long and had circular cross-sections whose diameters were 5 m in the upper portion and 4 m in the lower portion. An analytical model to simulate the test results was developed in the OpenSees platform. The analytical model comprised nonlinear flexural elements as well as nonlinear soil springs. The analytical results closely followed the experimental test results. A parametric study to predict the behavior of the bridge column with different ground motions and different levels of scouring on the foundation are also discussed. © 2014, Institute of Engineering Mechanics, China Earthquake Administration and Springer-Verlag Berlin Heidelberg.

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