Period Formulas for Concrete Shear

Most seismic codes specify empirical fonnulas to estimate the fundamental vibration period of buildings. Evaluated first in this paper are the fonnulas specified in present U.S. codes using the available data on the fundamental period of buildings "measured" from their motions recorded during eight California e~­ quakes, starting with the 1971 San Fernando earthquake and ending w.ith the 1994 Northridge earth~u~e. It 1S shown that current code fonnulas for estimating the fundamental penod of concrete shear wall bUi1dmgs are grossly inadequate. Subsequently, an improved fonnula is developed by calibr~ting a the.oretical fonnula, deriv~ using Dunkerley's method, against the measured period data through regress10n analys1s. A]so recommended IS a factor to limit the period calculated by a "rational" analysis. such as Rayleigh's method.