Dynamic characteristics and seismic performance evaluation of low rise existing RC moment resisting frame using microtremor technique and standard code of practice

Most of existing multi-storey reinforced concrete (RC) buildings in Malaysia was designed to BS 8110 without considering seismic load. Tremors generated from previous distant earthquakes occurred from Sumatran faults zone had shaken many low-rise to high-rise buildings in Peninsular Malaysia and emerged panic. Worst scenario when the conventional practice of unreinforced masonry like brick wall is weak in lateral resistance and ease to damage. Poor soil condition may also have a crucial modifying influence occasionally acted as a resonator and amplifies the seismic wave when reached to ground surface. A microtremor study was conducted in order to evaluate the dynamic characteristics of site-structure, resonance potential and seismic capacity of an existing 4-storey RC primary school building and its site in SK Sri Molek which located in Batu Pahat-Johor. From the findings, it was expected that the building is prone to resonate since both site and building have only a slight different between their natural frequencies. The predominant building frequencies were predicted at 4.20 Hz and 4.35 Hz in transverse and longitudinal directions whereas for site fundamental frequencies were between 2.69 to 3.20 Hz in North-South (NS) direction and 2.79 to 2.98 Hz in East-West (EW) direction. By using the site response spectra for Kuala Lumpur region based on the consideration of large magnitude of distant earthquake scenario at 9.3 and 530 km of the closest to site distance produced by previous researcher, the design response spectrum (RSA) has given 0.32 m/s2 at natural period between 0.15 to 0.40 s. From this RSA value, an equivalent static analysis (ESA) for base shear force estimation was performed according to EC 8 [2]. The analysis shows that, the design ultimate horizontal load described in BS 8110 [3] based on conventional load combination has been exceeded more than 1.5% as recommended by the code.