Errors and New Trends in Widening the Deck of a Road Bridge

Maintenance and upgrading are the urging needs of the European infrastructural network that, for masonry bridges, mainly mean: (i) widening of the deck; (ii) installation of the safety barriers; (iii) seismic safety, for seismic-prone areas. The common approach to the first two issues makes use of r.c. slabs, often lied down on the spandrels, and some other procedure somehow derived from r.c. construction. The outcomes may be serious damages to the bridges: the load distribution on the bridge is completely changed from the original design and damage may be induced in the arch barrel. In this paper, a case study is discussed to introduce a new technique for widening the bridge deck and setting the safety barriers is discussed: a r.c. slab, lied down onto the fill and separate from the spandrels, with lateral cantilevers, is used to widen the deck and so restrain the safety barriers. Large concrete blocks connected to the bedrock by means of piles have been built behind the skewbacks as horizontal restraints to the slab in case of seismic actions. In this way horizontal actions on the slab and the impact load of vehicles on the barriers are directly sustained by new structures and not by the old bridge. Such an approach is also cheap and does not necessarily ask for interrupting the bridge service.