Journal of Seismology and Earthquake Engineering
Volume:2 Issue: 2, Spring 2000

This paper extends a rational seismological modeling approach for earthquake response spectra in a moderate seismicity region, using the Coastal Region of South China as the example, by incorporating into the model the regional crustal effects on bedrock earthquake ground motions. Such crustal effects cause significant modifications to peak ground motion predictions and hence have an important influence on the amplitudes of spectral responses (accelerations, velocities and displacements) developed in the form of design response spectra associated with a range of return periods from 500 to 2,500 years. The concept of the Characteristic Response Spectrum (CRS) is introduced. The CRS, which is solely a function of the crustal properties and the assumed Maximum Credible Earthquake (MCE) magnitude, has been found to dictate the seismic hazard of the subject region. The adopted approach emphasizes the importance of studying the composition and the structure of the earth''s crust in modelling the seismic hazard in regions of moderate seismicity. It is found that the predictions made by the seismological model based on characteristic agnitude-Distance (M-R) combinations are very consistent with current code provisions in the velocity-controlled period range. However, significant discrepancies have been identified in other period ranges. In addition, the empirical modelling methodology based on adapting the properties of western United States (primarily Californian) seismic data, as used by some previous researchers to predict peak ground motions (for engineering purposes) for the South China region, appears to give overly conservative results when extrapolated to large magnitude chatacteristic events.

An investigation is carried out with an actual 13-story building to assess the viability and effectiveness of a recently proposed roof isolation system that aims at reducing the response of buildings to earthquakes. The roof isolation system entails the insertion of flexible laminated rubber bearings between a building''s roof and the columns that support it, and the addition of viscous dampers connected between the roof and the rest of the building. It is based on the concept of a vibration absorber and on the idea of making the roof, flexible bearings, and viscous dampers respectively constitute the mass, spring, and dashpot of such an absorber. The investigation includes a comparison of the building''s response under a severe ground motion when it is considered with and without the isolation system, as well as the determination of the properties and size of the required isolation system components. It is found that the proposed isolation system is effective, is constructable, and has the potential to become an attractive way to reduce structural and nonstructural earthquake damage in low and medium-rise buildings.

In this paper a damage assessment procedure has been proposed based on backpropagating feedforward neural network simulators and a genetic algorithm identifier. Damage assessment is performed in two steps. First, neural networks are utilized to locate possible damage states associated with the changes in vibration signature. Second, genetic based identification procedure has been applied to evaluate the dynamic parameters of the structure at damaged locations. The stiffness of the damaged parts of the structure has been identified by the genetic algorithm such that the difference between analytically predicted and experimentally observed response is minimized throughout the response time history. The amount of stiffness reduction is assumed as the degree of damage. To verify the performance of the proposed scheme, the location and degree of damage in computer-simulated linear and nonlinear structures has been detected. Also to investigate the performacne of the proposed method in conjunction with real data, experiments on a 12 scale model of a four-story steel structure has been performed.

Seismic response of structures supported on the sliding systems to bi-directional (i.e. two horizontal components) earthquake ground motion is investigated. The frictional forces of sliding system are assumed to be dependent on the relative velocity at the sliding interface with bi-directional interaction. Coupled differential equations of motion of the structure with sliding system in two orthogonal directions are derived and solved in the incremental form using step-by step method with iterations. The iterations are required due to dependence of the frictional forces on the response of the system. The response of the isolated system is analyzed to investigate the effects of velocity dependence and bi-directional interaction of frictional forces of sliding system. Thest effects are investigated under important patametric variations such as the fundamental time period of superstructure, period, damping and friction coefficient of the sliding system. It is ovserved that the dependence of friction coefficient on relative velocity of system does not have noticeable effects on the peak response of the isolated system. However, if the effects of bi-directional interaction of frictional forces are neglected then the sliding base displacement will be underestimated which is crucial from the design point of view. Further, the bi-directional interaction effects are found to be more severe for the sliding systems without restoring force (i.e. purefriction) in comparison to the systems with restoring force.