iii ACKNOWLEDGMENTS iv TABLE OF CONTENTS vii LIST OF FIGURES xvii LIST OF TABLES xxv

Assessing seismic collapse safety of modern reinforced concrete moment frame buildings

Most seismic codes specify empirical formulas to estimate the fundamental vibration period of buildings. Evaluated first in this paper are the formulas specified in present U.S. codes using the available data on the fundamental period of buildings “measured” from their motions recorded during eight California earthquakes, starting with the 1971 San Fernando earthquake and ending with the 1994 Northridge earthquake. It is shown that, although the code formulas provide periods that are generally shorter than measured periods, these formulas can be improved to provide better correlation with the measured data. Subsequently, improved formulas for estimating the fundamental periods of reinforced concrete (R/C) and steel moment-resisting frame buildings are developed by regression analysis of the measured period data. Also recommended are factors to limit the period calculated by a rational analysis, such as Rayleigh’s method.

/pdf/period-formulas-for-moment-resisting-frame-buildings-1tr5d0gs6d.pdf

Period formulas for moment-resisting frame buildings

Damping in structures: its evaluation and treatment of uncertainty

Only when the data base is of sufficient quality can a theoretical model of any process be justified. Such a data base has recently been assembled in the field of damping in tall buildings. It is now possible to specify a damping value appropriate to a particular building vibrating at a specified amplitude which is well correlated with values which are measured in practice. The mechanism on which this predictor is based suggests that the predictor will be applicable to other types of structure as well. As yet the data base for these other structures does not exist, but some circumstantial evidence is encouraging.

Damping in tall buildings—a mechanism and a predictor

Most seismic codes specify empirical formulas to estimate the fundamental vibration period of buildings. Evaluated first in this paper are the formulas specified in present U.S. codes using the available data on the fundamental period of buildings “measured” from their motions recorded during eight California earthquakes, starting with the 1971 San 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. Subsequently, an improved formula is developed by calibrating a theoretical formula, derived using Dunkerley's method, against the measured period data through regression analysis. Also recommended is a factor to limit the period calculated by a “rational” analysis, such as Rayleigh's method.

/pdf/period-formulas-for-concrete-shear-wall-buildings-59cebsdvr2.pdf

Period formulas for concrete shear wall buildings

A Fourier spectra analysis of the recorded February 9, 1971, San Fernando earthquake response of 12 southern California high-rise buildings was conducted and damping in building normal modes of vibration was estimated. Obtained damping values were correlated with building basement 0% damped pseudovelocity response spectrum and empirical equations were derived for damping estimation. A procedure utilizing these equations was developed for the selection of damping values for use in building design.

Ramaswami Vasudevan

Papers

Earthquake Design of Buildings:Damping