The response of Karnali Bridge, Nepal to near-fault earthquakes

Seismic records during recent destructive earthquakes such as Northridge (1994), Kobe (1995), Duzce (1999) and Chi-Chi (1999) revealed peculiarities of ground motion near active faults. Those earthquakes indicated that the vertical acceleration can reach values comparable to horizontal acceleration or may even exceed these accelerations. The unique high amplitude and short to medium duration pulse caused due to the forward directivity was another typical feature of near-field ground motion, which caused significant damage to transportation structure. In this study the relative importance of the vertical ground motion on the response of Karnali cable-stayed bridge, which is situated near an active fault in Nepal, is investigated. This study also tries to identify the effect of the velocity pulses on the response of a steel tower of the cable-stayed bridge. The results indicate that the vertical ground motion will have a minor effect on the axial response of the cable and tower of the cable-stayed bridge. The study identified that forward directivity ground motion could have a damaging effect when velocity pulses are tuned with the natural period of the steel tower of the bridge.