Strengthening of masonry–unreinforced concrete railway bridges with PBO-FRCM materials

Many existing railway bridges have been designed for live loads significantly lower than those produced by the present day train traffic. The most part of them are masonry arch bridges whose load carrying capacity needs to be verified with respect to the current traffic loads in order to define the necessary strengthening interventions. In the last two decades innovative strengthening techniques based on the use of polymeric and, more recently, cementitious fiber reinforced composite materials have been adopted. The design criteria adopted for the strengthening intervention with a poliparafenilenbenzobisoxazole (PBO) fiber reinforced cementitious matrix (FRCM) material of a railway bridge on the ancient Rome–Naples railway line are presented in the paper. The structure is constituted by unreinforced concrete barrel vaults supported by masonry piers. The bridge is analyzed both in its original and in its strengthened configuration following the approach of the collapse mechanisms. This approach allows to capture the strengthening effect of the PBO-FRCM material in terms of modification of the collapse mechanism and increase of the load collapse multiplier. The analyses evidence a lack of load carrying capacity of about 40% with respect to that required by current codes. The proposed strengthening intervention allows to overcome this lack.