Empirical formulas and Artificial Neural Networks to estimate the fundamental periods of existing and instrumented RC buildings in Thailand

Even though Bangkok is situated away from known active faults (about 150 km), due to the soft alluvial basin in and around the capital city of Thailand, several of these high-rise buildings experienced noticeable structural and non-structural responses caused by recent long-distance and moderate earthquakes from M w > 7.5 in the Sumatra subduction zone and M w > 6 in Myanmar, Northern Thailand, and Laos. This raises the awareness to assess the dynamic characteristics of buildings in Bangkok and other provinces in Thailand. In the current study, ambient vibration measurements have been performed on 98 reinforced concrete (RC) buildings to determine relationships between the building fundamental period and height of existing structures built prior and after seismic design code issued in 2009. The measured buildings’ height ranges of 7–142 m (2–35 stories) e.g., hospitals, condominiums, offices, etc. Different techniques are adopted to determine the two main translational fundamental periods in orthogonal directions of considered structures including Horizontal-to-vertical spectral ratio, Fourier spectrum analysis, and Half-power bandwidth method, and all considered methods show comparable results, and the empirical formulas are proposed. In order to validate this finding, the estimated fundamental periods of two instrumented hospitals from local and regional earthquakes give similar results to the proposed empirical formulas. In addition, artificial neural networks (ANNs) have been adopted to train and predict the fundamental period using the newly compiled database. For the same RC structures, the soil-structure interaction in Bangkok leading to a longer fundamental period than those reported in published literatures. • The current study measured and analysed ambient vibration of 98 reinforced concrete buildings in Bangkok and Northern Thailand built before and after the issue of DPT1302-09 seismic design code in order to determine the relationship between building height and fundamental period. • Different analysis including HVSR, FFT, and HBW methods have been adopted to obtain building first and second fundamental periods. • Different empirical formulas are computed with regression analysis for both translational fundamental periods and for soil type D and E. For Bangkok, the result reveal that the measured fundamental periods seem to correlate well with those estimates from the current seismic design code (DPT1302-09). This result has been reviewed by additional measurement for buildings built after the issue of the DPT1302-09. • The estimated fundamental periods of two instrumented hospitals in Chiang Mai and Chiang Rai from four local and regional earthquakes have been used to compared with the ones estimated from the proposed formula. The maximum difference is found to be lower than 12 %. • The ANNs was adopted to examine its applicability in estimating the building fundamental periods in the current database with building basic database, and it shows promising results as the MSE value is lower than those obtained from the one estimated by the code provision formula.