Seismic Code Improvements Based on Recorded Motions of Buildings During Earthquake

Summarized in this paper are the results of two recent investigations utilizing recorded motions of buildings to develop improvements in two aspects of seismic code provisions for buildings: (1) fundamental vibration period formulas, and (2) accidental torsion. INTRODUCTION The recorded motions of buildings during earthquakes are the basic data against which methods of earthquake-resistant design and techniques for calculating earthquake response must be judged. Perhaps the most common research use of these data has been in refining and improving structural modelling and response analysis techniques to match the calculated responses with data. Our interest has been quite different in recent years. We have utilized responses to investigate issues in building design that are not amenable to traditional analytical approaches. In particular, we have investigated two aspects of seismic code provisions for buildings: (1) fundamental vibration period formulas, and (2) accidental torsion. The code formulas for estimating building period must be related to the actual periods of buildings, not to calculated values. The actual periods of interest are those measured from recorded motions of buildings shaken strongly during earthquakes. We have developed a comprehensive database of measured periods of buildings and proposed new formulas suitable for code application to estimate building period. The subject of accidental torsion is not amenable to investigations by traditional analytical approaches because standard dynamic analyses do not predict torsion in symmetric-plan buildings. Analysis of recorded motions of nominally-symmetric-plan buildings provides the most direct means of developing an understanding of the torsional response of such buildings and for evaluating building code provisions for accidental torsion. We have utilized recorded motions of seven nominally­ symmetric-plan buildings to evaluate a recent procedure for considering accidental torsion in building design.