Characterization of Site Effect and Natural Frequency of Railway Bridges

Resonance could occur as a wave propagates through the soil resulting from seismic vulnerability activities. The resonance impact resulting from the local site effects may cause civil infrastructures failure such as railway bridge collapse. This study presented possibilities of the resonance in the BH77 railway bridge in Lampung, Indonesia. Characteristics of the site effect around the bridge were evaluated using microtremor data. Measurements were made at nine locations, with two points were on the bridge, and seven other points were scattered around the bridge. Microtremor data were analyzed using the Horizontal to Vertical Spectral Ratio (HVSR) method to find natural frequencies and amplification factors. Furthermore, the site effect around the bridge was analyzed using the natural frequency, the amplification factor, and the seismic vulnerability index (Kg) to have site effect characteristics. Results of the study indicated that the research area showed amplification factors (A0) ranging from 5.15 to 12.19. The site natural frequency obtained from the study was about 4.01-7.27 Hz. The seismic vulnerability index in the study area was 4.2-19.4. The obtained natural frequency (F0) on the bridge had a value between 5.20 and 6.19 Hz, and the natural frequency value at the site was 4.01-7.27 Hz, respectively. This phenomenon indicated that there would be a possibility of resonance on the railway bridge. It is interesting to note that this case study might be beneficial to practicing engineers and researchers.