Assessment of Soil-Building Resonant Effect for DMDP Area in Bangladesh

Abstract

The intention of this study is to estimate the expected soil-building resonance phenomena of the Dhaka Metropolitan Development Plan (DMDP) area of Bangladesh during earthquakes. The target is to identify the effect of the geology of the shallow depth and the buildings situated on the ground above the DMDP area. The predominant frequency of the soil is obtained from the horizontal-to-vertical spectral ratio (HVR) analysis of microtremor observations. Similarly, longitudinal and crosswise principal vibrational frequencies of each building have been ascertained from the fast Fourier transform (FFT) of the observed microtremor measurements. When the principal vibrational period of the structure is near to the period of the nearby ground, building-soil resonance may occur. A rapid visual assessment (RVA) has been carried out for 3,252 educational institutes in the DMDP area and through the prioritization scheme, 611 buildings have been selected for preliminary engineering assessment (PEA). Some of these buildings will be later allowed to be either retrofitted or demolished based on the findings of this study. Out of those prioritized buildings, microtremor measurements have been performed on selected 114 buildings and nearby soil for which standard penetration test and seismic downhole test data are available. Also, microtremor observations at additional 500 free-field locations are available from a previous study. The period-number of story linear relationship, estimated from the 114 microtremor observations, allowed estimating the fundamental frequency for 3,252 buildings. The DMDP area symbolizes a significant example since the principal vibrational period for the majority of the structures is reasonably different from the predominant period of the nearby ground. Only around 4% of the structures demonstrate a significant likelihood that a building-soil resonance effect may take place, while around 96% are at a relatively low resonance stage.