EVALUATION OF CODE ACCIDENTAL-TORSION PROVISIONS FROM BUILDING RECORDS

A procedure is presented for evaluating building-code provisions for a ccidental torsion from analysis of earthquake-induced motions of nomin ally symmetric-plan buildings. This procedure is used to analyze the m otions of three buildings recorded during recent California earthquake s. Two alternative approaches to evaluate the code accidental torsion provisions are developed. The first one considers the response histori es of base shear and base torque in the building, and the second, the ''actual'' forces in the structural elements during the earthquake. Th e results show that base rotational motions cause between 25% and 45% of the total accidental torsion in the buildings. They also demonstrat e that the accidental torsional moments specified by the Uniform Build ing Code are sufficient in representing the torsion in the recorded mo tions of the three buildings. Further, it is shown that accidental tor sion need not be considered in the design of two of the three building s studied. This observation, however, may not necessarily apply to oth er structures, such as buildings with torsional vibration periods much longer than their lateral vibration periods.