Preliminary Design of Seismically Isolated R/C Highway Overpasses - Features of Relevant Software and Experimental Testing of Elastomeric Bearings

Abstract eng:
The preliminary design of seismically isolated R/C highway overpasses is the target of a software based on the current design provisions of Eurocode 8 (Part 2) as well as on engineering decisions included in the expert system. The features of this expert system, which is aimed to facilitate the design of a highway overpass by isolating its deck with the inclusion of elastomeric bearings, are presented and discussed. For such an upgrade scheme a number of successive checks is necessary in order to select an optimum geometry of the bearings. The developed software includes a series of checks provided by Eurocode 8 (Part 2), in order to ensure the satisfactory seismic performance of the selected upgrade scheme. In doing so, the software accesses a specially created database of the geometrical and mechanical characteristics of either cylindrical or prismatic elastometallic bearings which are commercially available; this database can be easily enriched by relevant data from laboratory tests on isolation devices. The basic assumptions included in the software are (a) modeling the seismic response of the bridge overpass as a SDOF system, and (b) only the longitudinal direction response is considered; it is common practice for seismically isolated bridge systems to restrain the transverse movement of the deck by stoppers. Moreover, the results form a number of tests performed in the Laboratory of Strength of Materials and Structures of Aristotle University, verified the quality of the production process of a local producer of elastomeric bearings subjecting production samples to the sequence of tests specified by International Standard ISO 22762-1 (2005). Strain amplitudes larger than 250% resulted in the debonding of the elastomer from the steel plating. Artificial aging resulted in a small increase of the axial (vertical) stiffness and a small decrease of the shear (horizontal) stiffness of the tested bearings. More specimens must be tested to validate further these findings.

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