Monitored incoherency patterns of seismic ground motion and dynamic response of a long cable-stayed bridge

Abstract

The Evripos bridge in central Greece, connects the island of Evia to the mainland. The cable-stayed section of the bridge is 395 m in length, with a central span of 215 m and side-spans of 90 m each. The deck, 13.5 m in width, is at 40 m above sea-level, suspended by cables from two, 90 m high pylons. A permanent accelerometer special array of 43 sensors was installed on the bridge in 1994 by the Institute of Engineering Seismology and Earthquake Engineering. Two triaxial sensors have been monitoring the free-field (near pier M4) and pier M5 base response on the mainland (Boeotean) coast and two others the respective locations (pier base M6 and free-field near pier M7) on the Euboean coast. Since then the bridge’s behavior to seismic excitations has been continuously monitored and investigated. From various earthquake events recorded at the site, it became obvious that the excitation at each of the aforementioned locations differs, with the lowest peak acceleration values observed at site M7 for all three components, independently of magnitude, azimuth and epicentral distance of the earthquake, a fact that can be attributed to local site conditions. In the present research effort, an investigation of the dynamic response of the Evripos bridge due to the asynchronous base excitations along its supports is carried out. Comparisons are made with the conventional design procedure of assuming a common (synchronous) base excitation at all supports and interesting conclusions are drawn regarding the impact of spatially variable ground motion on the seismic response of the particular bridge.