Evaluation of torsional component of ground motion by different methods using dense array data

Abstract

In addition to the structural torsional effects coming from the horizontal asymmetry of the building structure one can also meet with the direct torsional ground excitations of the building. The dynamic analyses of structures have been carried out by neglecting the excitation by the rotational ground motions in engineering practice largely caused by the lack of recorded torsional ground motions. Using dense array data is one of the approaches has been developed to produce torsional component of ground motion. In this paper, by using the data of Chiba dense array and applying three methods of Time Derivation, Finite Difference and Geodetic, torsional motion are estimated and compared. In this array, accelerometers are placed densely with separation distances between 5 and 300 m. The results showed that the peak torsional ground motion which was computed by Time Derivation method is larger than which was computed by Geodetic method. Peak torsional ground motion values that are estimated by Finite Difference method show smaller values than those computed by Time Derivation for long separation distances (>20 m). However, the values estimated from the Finite Difference and Time Derivation methods are relatively close for short separation distances. Also, the effects of peak ground acceleration and magnitude of events on the torsional motions have been investigated and the relationship between PGA and the maximum torsional motion for different methods has been proposed.