Journal of Seismology and Earthquake Engineering
Volume:2 Issue: 1, Autumn 1998

The objective of this paper is to describe and illustrate a rational seismological modelling approach for developing design earthquake response spectra for application in a moderate seismicity region. In the first stage a seismicity model is developed, using the Coastal Region of South China (CRSC) as an example. Combining this with a generic source model and an assumed generic crustal model, the ground motion parameters (representing acceleration,velocity and displacement properties) have been determined. Importantly, the generic crustal model is assumed to have properties which are identical to the continental shield region of Eastern North America (ENA). Subsequently, response spectrum modelling procedures are described and applied to the example region, to determine design-level spectral for rock sites. The response spectra predicted by theseismological model were found to be very consistent with current code provisions, and with design spectra proposed by other researchers, in the velocity-controlled medium period range. However, significant discrepancies have been identified in other period ranges. The ground motion parameters and response spectra derived in this study were based on the generic ENA crustal conditions. The effects which the regional crustal properties and the crustal thickness have upon the ground motion parameters have been described in the second part of the paper.

An analysis is given for the mechanical characteristics of multilayer elastomeric isolation bearings where the reinforcing elements-normally steel plates-are replaced by a fiber reinforcement. The fiber-reinforced isolator, in contrast to the steel-reinforced isolator (which is assumed to be rigid both in extension and flexure), is assumed to be flexible in extension, but completely without flexural rigidity. The influence of fiber flexibility on the mechanical properties of the fiber-rein-forced isolator, such as vertical and horizontal stiffness, is studied, and it is shown that it should be possible to produce a fiber- reinforced isolator that matches the behavior of steel-reinforced isolator. The fiber-reinforced isolator will be significantly lighter and could lead to a much less labor intensive manufacturing process.

Dynamic analysis of a secondary system mounted on a torsionally coupled non-linear primary system is presented for bi-directional random earthquake excitation, which is idealized as a broad band stationary random process. The hysteretic force deformation behavior of the non-linear primary system is modelled by a set of coupled non-linear differential equations. The responses are obtained by the linearized frequency domain spectral analysis and are compared with those obtained by the time domain simulation procedure. The response quantities of interest are the relative displacement between the primary and the secondary structural systems and the absolute acceleration of the secondary system itself. The response behavior of the secondary system is examined under a set of parametric variations. These parameters include the uncoupled lateral frequencies of the primary and the secondary structural systems; the ratio of the uncoupled lateral to rotational frequencies of the primary system; the hysteretic parameters of the primary system; eccentricity ratios of the primary and the secondary structural systems in x and y directions; damping ratios of the primary and the secondary structural systems; and the mass ratio of the two sub-systems. Some of the results of the study show that the responses of the secondary system increase with the increase in normalized eccentricities of the primary system under the tuned condition. However, an opposite trend is observed under the untuned condition. Responses of the secondary system is found to be more if the interaction between the primary and the secondary structural systems is considered. Further, responses of the secondary system decrease with the increase in the mass ratio between the secondary and the primary systems.

As a part of a project sponsored by Strong Motion Instru- mentation Program of state of California [4], twenty extensively instrumented buildings were inspected, their damage state documented, and the level of forces and deformations that they experienced were compared to design code levels at the time of design as well as more modern code provisions. Among these twenty buildings, there were several buildings from which significant amount of information, including photos and valuable response characteristics were gathered in relation to performance of nonstructural systems and components. Six of these buildings, as follows, are selected for presentation in this paper.The Olive View Hospital Building in Sylmar, A 13 story office building in Sherman Oaks, A 10 story residential building in Burbank, A 6 story commercial building in Burbank, A 3 story department store in Century City, A 20 story hotel in north Hollywood. The imposed seismic demands and the extent of nonstructural damage in each building is compared and contrasted with force demands as interpreted by model codes and guidelines such as UBC-97, NEHRP-97, and FEMA-273 documents.