RESPONSE OF A CONCRETE BRIDGE CONSIDERING THE USE OF PASSIVE OR ACTIVE SEISMIC PROTECTION DEVICES

The last seismic events produced worldwide (Chile, Haiti, Turkey) have shown the vulnerability of a large number of bridge structures on the seismic action. Many of these structures have collapsed, the main cause being the unseating of the spans on the substructures elements. This was the case especially for bridges having simply supported decks, where the in plane dimensions of the supporting saddles have had inappropriate dimensions with respect to the horizontal movements caused by the seismic action. Analyzing the mode of failure of these bridges an important conclusion came out: the spatial displacements induced by the seismic action should be more carefully considered even in the early design stage of new bridges. Usually, in the design stage, the use of active seismic devices to limit the effects of the earthquake action is not considered. But, especially for long bridges, without expansion joints and having piers with different heights, the induced motion can produce severe damages if special measures for dissipating energy are not taken. The different response in frequency of the piers can lead to high values of the stresses at their base. Moreover, using inappropriate types of bearings can lead to displacements having as consequence the damaging of bearings and expansion joints. In this paper, the response of a concrete bridge on the new motorway "Transylvania" considering the use of passive or active seismic devices is investigated and a comparison of the obtained results is made. The bridge has 24 spans of about 40 m, a total length of 980 m and a number of six expansion joints. The dynamic response of the bridge is investigated through nonlinear time -history analyses based on different input functions for the ground motion.