Load-carrying capacity of a strengthened reinforced concrete bridge : Non-linear finite element modeling of a test to failure. Assessment of train load capacity of a two span railway trough bridge in Örnsköldsvik strengthened with bars of Carbon Fibre Re

Sammanfattning: To meet the future traffic demands there is a constant need of making the infrastructure moreeffective. This can be achieved by increasing the capacity and/or life length of traffic lines. Apart of the efforts to do this is increasing the load carrying capacity of the railway bridges sothat it is possible to allow heavier freight trains to pass the bridges.In this thesis the assessment of the load carrying capacity of a strengthened concrete troughrailway bridge, The Övik Bridge, with two spans in Örnsköldsvik, in northern Sweden, istreated. To investigate the ultimate behavior of the bridge a full scale load test up to failure wasperformed in 2006.At the loading test in Örnsköldsvik a steel beam was placed in the mid of one of the spans ofthe bridge. The failure was caused by pulling the steel beam downwards with cables whichwere anchored with injection into the drilled holes in the bedrock beneath the bridge.While the mechanism of a bending failure is commonly considered to be well investigated, thestructural models for the shear failure are still the object of intense research. The bottom sidesof the edge beams of the Örnsköldsvik Bridge were strengthened with Near Surface Mountedreinforcement (NSM) consisting of Carbon Fibre Reinforced Polymers (CFRP) to increase thebending capacity and in that way steer the bridge to failure in shear instead of bending.The material properties of the reinforcement were determined in tension tests. Concreteproperties were determined by testing drilled core samples. Displacements and deflections ofthe bridge, strains in concrete, steel and carbon fibre reinforcement were measured during thetest as a function of the increasing load.In this thesis the analysis of the failure of the bridge, structural models describing the behaviorand load carrying capacity are evaluated according to different design codes. Advanced finiteelement analysis is applied with both geometrical and material non-linearities included. Toverify the models used in codes and computer calculations the response of the bridge duringthe test is compared with the calculation results.The refined and calibrated FEM model is used to predict how high axle loads of a train theÖvik Bridge could have sustained. The Övik Bridge was designed in 1950’s for axle loads of20 ton. The calculations methods developed in this thesis show that the axle loads in the failurestate could have been increased at least up to 154 tons without strengthening and to 215 tonwith strengthening of the bridge slab with carbon fibre reinforcement bars with Af = 100 mm2c 150 mm using statistical mean values of loads and material properties in the calculations.