Evaluation of Code Accidental‐Torsion Provisions from Building Records

A procedure is presented for evaluating building‐code provisions for accidental torsion from analysis of earthquake‐induced motions of nominally symmetric‐plan buildings. This procedure is used to analyze the motions of three buildings recorded during recent California earthquakes. Two alternative approaches to evaluate the code accidental torsion provisions are developed. The first One considers the response histories of base shear and base torque in the building, and the second, the “actual” forces in the structural elements during the earthquake. The results show that base rotational motions cause between 25% and 45% of the total accidental torsion in the buildings. They also demonstrate that the accidental torsional moments specified by the Uniform Building Code are sufficient in representing the torsion in the recorded motions of the three buildings. Further, it is shown that accidental torsion need not be considered in the design of two of the three buildings studied. This observation, however, may not necessarily apply to other structures, such as buildings with torsional vibration periods much longer than their lateral vibration periods.