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D4-011
15:20
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15:35
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TOWARD A 10-SECOND EARTHQUAKE EARLY WARNING SYSTEM IN TAIWAN
Earthquake early warning (EEW) system is one of the most practical tools to mitigate seismic risks. When an earthquake occurred, it can provide warnings before the strong ground shakings strike target areas. People and automatic facilities might take appropriate actions against the shakings. Central Weather Bureau of Taiwan (CWB) has developed and operated the EEW system for about two decades. The earthworm based earthquake alarm reporting (eBEAR) system was developed and has been used to issue warnings to the public via TV broadcasts and mobile phones since 2016.In average, the EEW system can provide warnings about 15 seconds after the occurrences of inland earthquakes. This implies that the blind zone of the EEW system is about 53 km. In order to reduce the processing time of the EEW system, the CWB has improved the density of the CWB seismic network by deploying about 250 real-time strong motion seismic stations. Additionally, a new algorithm for rapidly locating earthquakes has been developed and tested. The new algorithm is directly to use the concept of effective epicenter and effective magnitude for predicting intensities. In this way, the processing time in the procedure of earthquake location can be reduced. Here we simulated historical events for testing the new algorithm. At the same time, we equipped the new algorithms in the online testing system. After testing and modifying, the EEW system is going to issue warnings within 10 s after occurrences of earthquakes.
Da-Yi Chen, Nai-Chi Hsiao
earthquake early warning, Earthworm, Seismic Network
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SE8-014
15:35
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15:50
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HORIZONTAL DISPLACEMENT RESPONSES AND PARAMETRIC STUDY OF SLOPED ROLLING-TYPE SEISMIC ISOLATORS
The sloped rolling-type isolation bearings feature the constant transmitted horizontal acceleration performance (or zero post-elastic stiffness) owing to the fixed-angle sloped rolling surface design. In engineering practice, the constant acceleration level can be simply designed and predicted by the equation of motion. Nevertheless, for the bearings that possess zero post-elastic stiffness, the equivalent lateral force procedure might not be adequate for predicting their maximum horizontal displacement responses under a given seismic demand. To address this problem, several parameters for bearing designs and seismic demands are numerically and statistically studied to discuss the effect on the displacement responses. Such parameters include the sloping angles and friction damping forces for bearing designs, as well as the corner periods and effective peak accelerations (EPA) for characterizing the seismic design response spectra. Therefore, considering a small number to many coefficients, several statistics-based empirical formulas which can approximate the maximum horizontal displacement responses are proposed. Not only the accuracy but the conservative property of the proposed empirical formulas is discussed by comparing their predictions with the nonlinear response history analysis results. To efficiently determine the horizontal displacement capacity of sloped rolling-type seismic isolators during the preliminary design stage, the statistics-based empirical formula considering a reasonable number of coefficients is recommended.
Kuo-Chun Chang, Shiang-Jung Wang, Chung-Han Yu, Wang-Chuen Lin, Jenn-Shin Hwang
constant transmitted acceleration, equipment isolation, isolation displacement, sloped rolling-type isolation bearing, statistics-based empirical formula
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SE8-015
15:50
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16:05
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BEYOND DESIGN PERFORMANCE OF VISCOELASTIC DAMPERS
The actual performance and damage of viscoelastic dampers under maximum considered shaking or greater earthquakes as well as their residual performance under aftershocks was rarely discussed before. In this study, four coefficients of the fraction differential model considering ambient temperature, temperature rising, cyclic soften, and strain hardening effects were firstly characterized from performance test with shear strain levels less than 300%. Secondly, VE dampers were tested with larger shear strain levels, until 1000%, to realize their ultimate performances. In between each large shear strain level, the performance test under 300% shear strain was performed to further understand their residual performance after damage. The fraction differential model was also adopted for characterizing their post-damage behavior. The result shows that the stiffness and damping coefficient of VE dampers decrease proportionally with varying shear strain levels from 600% to 840%, and can still remain half of the original values after 840%. Thirdly, VE dampers were tested subjected to seismic response histories which can be numerically analyzed in an off-line manner. Either before or after damage, the predictions by the fraction differential model have a very good agreement with the test results.
Shiang-Jung Wang, Chung-Han Yu, Kuo Chun Chang
Beyond Design Performance, Empirical Post‐damage Model, Residual Performance, Viscoelastic Damper
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I1-012
16:05
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16:20
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STRUCTURAL HEALTH MONITORING FOR CONTROLLED BUILDINGS WITH ACTIVE MASS DAMPERS
In active control field, active mass damper (AMD) is one of the most popular devices that has been studied and applied in real structures with confirmed vibration control efficiency against wind- and earthquake loadings. Most of the past efforts emphasized the derivation of theories for control gains and the investigation of vibration control effectiveness of AMDs. In practice, an AMD is generally assembled in-situ along with the construction of a building. In such a case, the AMD and the building is coupled as an entire system. After the construction is completed, the dynamic properties of the AMD subsystem and the primary building itself are unknown and cannot be identified individually to verify their design demands. This paper pays attention on the development of structural health monitoring (SHM) procedure of the active mass damper controlled systems. For vibration-based SHM of a real structure, significant external forces, for instance, earthquakes or shakers, have to be available to excite the building to respond to a certain extent. The vibration response measurements of the structure can then be the input data for the followed SHM procedure. The idea of the present study is to utilize the AMD not only for vibration control but also for SHM of the building itself once the AMD can be an exciter of the building at any time. For this purpose, a methodology is developed to uncouple the dynamic properties of the primary building and the AMD system based on the complex eigenparameters of the coupled building-AMD system. The controlled gain can also be identified and can be used as an index of the health condition of the primary building. The protocol of AMD test forces and the relationship between the index and the frequency drop of the structure are also established. Results from numerical verifications show that the procedure can identify the condition of the structure.
Chang-Ching Chang, Jer-Fu Wang
active mass damper, structural control, structural health monitoring, system identification technique
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I1-013
16:20
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16:35
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REVIEW ON PRESTRESS LOSS EVALUATION IN CONCRETE BEAMS
In the last few decades, prestressing techniques have been used to build very important structures, infrastructures, and bridges. Since the serviceability and the safety of prestressed concrete members rely on the effective state of prestressing, development of tools and dynamic procedures capable of estimating the effective prestress loss have been widely carried on. Amongst other techniques, static identi?cation using second-order deflections has proved to be an accurate and reliable method to evaluate prestress loss. This paper represents a review of some important research works on prestress loss evaluation in concrete beams presented in the literature. Comments and recommendations will be made at proper places, while concluding remarks including future research directions will be presented at the end of the paper.
Kuo-Chun Chang, Chun-Chung Chen, Marco Bonopera
concrete beam, identification, inverse problem, prestress loss
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