The optimal design of upgrading operations on r.c. bridges in seismic areas

The final results of a research project aimed at optimizing the choice and design of the operations for seismic upgrading of existing r.c. bridges are summarized: this information is still missing from current codes that do not supply either general concepts or special provisions for upgrading. A specific structural type is investigated: namely, multispan r.c. girder bridges made by a simply-supported or continuous horizontal deck and vertical piers of different height. The probabilistic assessment of the seismic safety of these bridges, in their current state and in the states resulting from the use of alternative upgrading technologies, lets it be inferred that the reliability is significantly increased when the existing bearings are replaced by isolating devices, which also permit joining the deck slabs and eliminating the structural joints; the design of this kind of operation is optimized by planning the optimal arrangement of the devices, and by calibrating their mechanical characteristics. The strengthening of the piers by r.c. jacketing or steel encasing appears less effective.