Influence of dynamic characteristics of earthquakes to structural response

Zeceva Draga is bridge constructed in Croatia few years ago. It is 940,8 m long, and is situated on a horizontal curve. Bridge spans are 2x40+16x50+40 m. The difference in height of left and right abutment is approximately 23m. The superstructure is a box girder 12,5 m wide and 4 m high. The bridge has 18 piers, the highest being approximately 53 m high. The bridge was calculated using 8 accelograms with magnitudes of 5.5, 6, 6.5 and 7, with epicenter distances of 0 and 15 km. The accelograms were created based on two earthquakes that took place in 1979 in the Adriatic region; in Petrovac, with the magnitude M=6.8, and Ulcinj with magnitude M=5.3. Time history analysis was preformed for past period of 1000 years. Calculation was made for synthetic time sequence of accelerations which, correspond to earthquakes with magnitudes 5.5, 6.5 and 7.0 with epicenter distances of 0 and 15 km. The greatest seismic forces are obtained for magnitude of 7 but for epicenter distance of 15 km. Maximum ground acceleration is about 40% greater in case when distance was 0 km from epicenter to distance 15 km from epicenter. From accelograms (acceleration-time) spectrum curves (acceleration-frequency) were obtained and analyzed. To determine frequency content of accelograms, Fourier amplitude spectrum is calculated. The whole frequency range was analyzed. Conclusion about influence of dynamic characteristics of earthquakes to structural response is given.