A time and cost-effective strengthening of RC half joint bridges exposed to brittle failure: application to a case study

This paper addresses the strengthening of a reinforced concrete (RC) road bridge with Gerber-type beams, prompted by the recent collapses of some Italian bridges. The study discusses the characteristics of half-joint bridges, also known as Gerber beam types. These designs, originating in the late 1800s and commonly utilized from the 1950s to the 1970s, exhibit an isostatic structure. While they are easy to design, typically featuring pairs of piers with symmetrical cantilevers and two or more suspended spans, they often suffer from weakening of the half joints (saddles), necessitating structural consolidation. Designers have proposed several solutions to strengthen this type of bridges and the approach presented in this paper focuses on cost-effectiveness and efficiency. It involves a gradual demolition of longitudinal strips on the RC slab of suspended beams, followed by the installation of new steel beams to create a mixed RC-steel system. The application of this method is illustrated in a double-pier bridge spanning the Arno River, Italy. The bridge’s rehabilitation required a complete closure of the traffic road for twelve weeks, followed by alternating traffic for twenty-four weeks. The paper discusses both the design and construction aspects of the proposed intervention, considering costs and implementation time. Furthermore, a low-cost health monitoring procedure is briefly introduced.