Measurement of Natural Frequency of Residential Buildings in Earthquake Prone Areas

Abstract

Northern Thailand is the highest seismicity area of the country. Past major earthquakes caused damages to buildings and infrastructures in different degree. Most of the affected buildings were small structures such as residential buildings which were not earthquake resistant design. The dynamic characteristics of these buildings have not been investigated. Therefore, this research aims to identify the natural period of small residential buildings by ambient vibration measurement. Altogether 36 buildings in Chiang Rai were studied. Among them, 14 buildings are concrete, 22 buildings are concrete-wooden structures, 4 buildings are one-story, 30 buildings are two-story and 2 buildings are three-story. The measurement was conducted using two sets of sensitive velocity meters to record microtremor vibrations of the buildings. The natural periods were identified for the translational modes. Structural characteristics of buildings such as the number of columns and amount of infill wall in each direction were considered to investigate their contribution to the lateral stiffness. The study found that the natural frequency of most buildings ranges between 3 and 5 Hz. However, there is variability in the natural frequency values found in other buildings. Some buildings have a dominant natural frequency range of 5 to 10 Hz. This demonstrates the diversity in the design of small-scale buildings, which varies based on the structural design and materials used in construction. Furthermore, it was also observed that in buildings that use mixed materials, such as wood-concrete structures, there is variation in the natural frequencies in different parts that use different materials.