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The IUP Journal of Structural Engineering :
Estimation of Period of Vibration of Symmetrical Reinforced Concrete Buildings in Seismic Analysis
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Seismic design codes provide empirical expressions to evaluate fundamental period of vibration of Reinforced Concrete (RC) buildings to derive design base shear. Empirical expression prescribed in the Indian seismic code is a function of the height of the building only and does not consider the effects of other structural parameters of the building. Fundamental period predicted by these expressions is widely used in the practice. It is therefore very important to use realistic values of time period in the seismic design of the structures. This paper deals with the evaluation of fundamental period of vibration of symmetrical RC buildings, which incorporates parameters like number of bays in either direction, base width/plan area of the building and stiffness of the structure, in addition to the height of the structure. Period equations were developed by performing nonlinear regression analysis on the results obtained by dynamic analysis of 132 various structural configurations, and another 36 results were obtained to compare the results of dynamic analysis with the proposed equation.

 
 

The fundamental period of vibration depends upon the distribution of mass and stiffness along the height of the building, and estimation of seismic base shear requires the fundamental natural period of vibration T of the building. Seismic-induced dynamic forces and its directions vary substantially with time and cause considerable inertia forces on the buildings. However, for the building configuration adopted and the construction material chosen, it is not always possible to exactly determine from theoretical considerations, that is, through detailed dynamic analysis. Hence, empirical formulae obtained through experimentally observed behavior of buildings are utilized (Oliveria and Navarro, 2010; Panzera et al., 2013; and Sha et al., 2013). The stiffness contribution of many non-structural elements, such as in-fill masonry panels (Vance, 1995; and Anil and Altin, 2007), is also considered to derive period formula in different countries. For this reason, the empirical expression for T may be specific to each country. The approximate fundamental natural period of vibration (Ta) in second of a moment resisting frames building without brick infill panels may be estimated by empirical expression given in Indian seismic code IS1893 (Part-1)-2002 (Anil and Altin, 2002).

 
 

Structural Engineering Journal, Fundamental period, Nonlinear regression analysis, Number of bays, Dynamic analysis, Stiffness of the structure