Strengthening of a railway bridge with NSMR and CFRP tubes

Strengthening of structures with CFRP is today considered an accepted method to upgrade concrete structures. In this paper two different CFRP strengthening systems are combined to give extended service life to a Swedish double-trough-double-track railway bridge, constructed in concrete with a 10 meter span. One system is the reliable NSMR (Near Surface Mounted Reinforcement) system while the other one is new; intended to strengthen the interior of a concrete structure, and the other system uses CFRP tubes integrated in drilled holes in the bridge. Both systems are used to increase tensile flexural strength of the slab transverse to the tracks. NSMR bars are positioned in the concrete cover on the underside of the bridge, while the new system is inserted in holes drilled through the bridge, in the cross direction and located in the upper part of the bridge slab. In connection with the strengthening monitoring has been carried out; this to obtain an understanding of the bridge behavior before and after strengthening, and to demonstrate any effects of the extra CFRP reinforcement. Results from these measurements are presented together with how the strengthening work has been carried out. Sensors on bars and tubes display proofs of utilization of the CFRP while displacement sensors and strain gauges on the steel reinforcement due to the small loads in the service limit state show minor effect.