Transversal Post Tensioning of RC Trough Bridges - Laboratory Tests

The Swedish Transport Administration (Trafikverket) is the owner of a large number of railway concrete trough bridges, which were designed according to Swedish design codes in the 1950's. The traffic loads are today higher than the design loads and the horizontal level of ballast is also much higher today, which implies that the contribution from the ballast to the deadload is considerable. The degree of utilization of the bottom slab is very high, which can be confirmed by calculations and visual inspections (flexural cracks are visible). This paper presents the results from a laboratory test on scaled down trough bridge specimens strengthened by transversal post-tensioning of the slab. Calculations according to two design codes where the horizontal prestressing force is considered, gives a theoretical increase of the shear capacity with 5 - 11%, and the test indicated an even larger increase of shear capacity. The main objective for the strengthening was to increase the shear capacity. In addition, adding a prestressing force also increased the theoretical flexural capacity, in this case with 21%.