TORSIONAL RESPONSE OF SHORT SPAN TRUSS TYPE DECK SUSPENSION BRIDGES UNDER CLOSED FORM APPROXIMATION OF PULSE TYPE GROUND MOTIONS

Near-field ground motions recorded in vicinity of fault cause more and intense damages of structures. The main reason of these damages is the existence of a long period and large amplitude velocity pulse that abruptly transfers the kinetic energy of ground motions to the structures. So, simulation of the mentioned pulse can help the engineers to produce artificial pulse type ground motions. In this paper, the response of suspension bridges under pulse type ground motions and their fitted model is addressed. The Vincent Thomas suspension bridge as a relatively short span suspension bridge is chosen for case study, also six strong records from the three major world-wide earthquakes that have wide range of pulse periods and peak velocity amplitudes were selected to fit by closed form approximation. The results indicate that the suitable overlap between fitted model and its real record cannot sure the precise response. Also, by increasing or decreasing the ratio of the real pulse period to fitted pulse period, the accuracy of the response will be declined, and placement of the period ratio in the certain range and appropriate overlap of the energy spectra will provide the most accurate responses.

Keywords:

Suspension bridge , Near-field , Pulse type ground motion , Closed form approximation , Energy spectra