Performance assessment of typical buildings in Singapore to long-distance earthquakes
Goh, Key Seng
Date of Issue2014
School of Civil and Environmental Engineering
Although Singapore is located in a low seismicity area, the country is exposed to long-distance earthquakes originated from Sumatra. As part of the effort to assess the seismic performance of buildings in Singapore, relationships between the natural vibration period and the height of high-rise residential buildings in Singapore are derived empirically by conducting regression analysis on ambient vibration test (AVT) results of 116 buildings. It is found that the vibration periods estimated from the proposed period-height relationship for buildings located at soft-soil site are about 40% longer than the vibration periods estimated for buildings located at firm-soil site. Measurements are also conducted to study the influence of buildings on the measured frequency of the surrounding soil. The results show that the distance of building influence on the measured frequency of the surrounding soil may reach up to one building height for a firm-soil site and two building heights for a soft-soil site. Two generic building models of 15 and 30 stories representing typical high-rise residential buildings in Singapore are constructed using OpenSEEs. A methodology is proposed for estimating the level of perception to tremors of occupants living in high-rise residential buildings, which is based on statistical analysis of analytical results of seismic response of generic building models to recorded ground motions. The results estimated using the proposed methodology are found to match well with the reports from the local newspapers and the authorities. Pushover analyses are conducted to determine the seismic capacity of the generic building models. The overstrength ratios of the 15-storey and 30-storey generic models are found to be 5.47 and 6.90, respectively. The ground motions at rock site due to the maximum credible earthquakes (MCE) in Sumatran strike-slip fault and subduction zone are generated using spectrum-matching method in frequency domain. The MCE ground motions at a typical soft-soil site in Singapore are subsequently generated using equivalent linear model of the horizontally-layered soil deposit, which is implemented in the widely-used computer program SHAKE91. Time history analyses are conducted for the generic building models subjected to the simulated ground motions. It is found that shear failure is unlikely to occur at the beam-column joints of the generic building models due to the MCE ground motions. However, torsional effects, which may amplify the displacement responses of the generic models, are not considered in these analyses. Torsional response of nonductile structures with soft-first-storey subjected to bidirectional ground motions is subsequently studied using a simplified two-storey model with two-way eccentricities. The stiffness and strength ratios, stiffness and strength eccentricities, ductility capacity, and overstrength ratio are varied to examine the effects of these parameters on the torsional responses. Ductility demand-capacity curves are then constructed, which can be used to approximately assess the seismic performance of existing structures, and as guidelines for designing new structures in Singapore to withstand the MCE ground motions considering the coupling of torsional and soft-first-storey effects. It is concluded that nonductile structure with overstrength ratio above 5.0 is less likely to fail during the MCE event. As the overstrength ratios of the two generic building models are larger than 5.0, the generic building models are thus unlikely to fail when subjected to the MCE ground motions at the soft-soil site considering torsional effects.
DRNTU::Engineering::Civil engineering::Structures and design