PERIOD FORMULAS FOR CONCRETE SHEAR WALL BUILDINGS

Most seismic codes specify empirical formulas to estimate the fundamen tal vibration period of buildings. Evaluated first in this paper are t he formulas specified in present U.S. codes using the available data o n the fundamental period of buildings ''measured'' from their motions recorded during eight California earthquakes, starting with the 1971 S an Fernando earthquake and ending with the 1994 Northridge earthquake. It is shown that current code formulas for estimating the fundamental period of concrete shear wall buildings are grossly inadequate. Subse quently, an improved formula is developed by calibrating a theoretical formula, derived using Dunkerley's method, against the measured perio d data through regression analysis. Also recommended is a factor to li mit the period calculated by a ''rational'' analysis, such as Rayleigh 's method.