Fundamental period of vibration for reinforced concrete buildings.

The fundamental period of vibration of buildings is one of the parameters that has a significant influence on the earthquake induced lateral forces. The fundamental period of vibration of reinforced concrete buildings measured during major earthquakes are collected and then compared with the empirical values given in the Uniform Building Code (UBC-97) and the National Building Code of Canada (NBCC-95). Comparisons between measured periods and the current code estimations have shown that the code estimation is inadequate for most of the buildings. Although few researches have been conducted, still there is room left to improve the code formulas. For shear wall buildings, the codes overestimate or underestimate the period of the building considerably. A new formula is proposed in this study to calculate the fundamental period of shear wall buildings. A very good correlation between computed and measured values is obtained. For the moment-resisting frame buildings, the current codes estimation of the fundamental period translate into a conservative values of the design base shear forces. However, when the non-structural elements contribute to the overall stiffness of the building, the code estimation deviates from the measured values substantially. In this research, a study is conducted to evaluate the effect of non-structural elements on the fundamental period of the moment-resisting frame buildings. It is concluded that the fundamental period of the infilled frame is about 25% to 65% of the bare frame's period