Seismic protection of the road bridge span structure in zones of highseismic hazard

摘要

The conception of multi-level seismic protection for road girder bridges is presented.Protection of span structure is reached by installing antifrictional sliding bearings and presencetwo-side ties between abutments and span, such as expansion joints, limiters and special cable system.In the paper are shown the structures of expansion joints and limiter for seismic protection ofsectional and continuos spans. For proposal structures are presented some results of calculationsand tests, which are, confirmed their efficiency.For seismic protection of road bridges, which are strategic for relief and economic there, isgrowing interest in the performance of bridges that should remain open to traffic at all times. In thecase of girder bridges, which are widely spread, the way of their protection by the isolation of spanstructure from bearings (horizontal seismic motion) has the most practical interest (Maffy 1973,Medeot & Albajar 1992). Such seismic isolation has proved very effective in similar applications,for example, in nuclear power stations. It’s worth noting also that in zones of high seismic risk andhigh probability of recurrences of seismic impact in particular the seismic isolation is apparent themost effective but expensive way of protection. However, taking into account all consequences ofstrong earthquakes it will be noted that the use of seismic isolation is recommended, because therisk of structure damaging in earthquakes gets hardly probable. Here the high level of security ofthe isolated unit, which is able to operate completely even after the earthquake of design forced,should be noted.The objects of our investigation are continuous beam bridges in which the seismic isolation isreached by installing antifrictional sliding bearings. These bridges are considered to be the mostpreferable ones for seismic construction and simultaneously they insure uniformity of roadway,comfortable and safety traffic, easier maintenance, etc.Besides, being generated the long temperature lashes demand allowance for large displacements,the mass of the isolated structure increases, the construction of the expansive joins becomescomplicated, etc. And above-mentioned problems rise with the lengthening of the span structureand therefore performance of the structure in longitudinal direction represents the greater interest.The design of structural protection is easily regulated when tie systems are provided, such asspecial cable systems, expansive joints, limiters, passive members (for example, uncontucted stoppers).Definite types of ties are required on bridges anyway, while other ones may be used therepartly or may not be used at all.Figure 1 shows the version of the super structure protection system, practical implementation ofwhich may has greatly various configurations.