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 Reinf

University dissertation from Luleå tekniska universitet

Abstract: To meet the future traffic demands there is a constant need of making the infrastructure more effective. This can be achieved by increasing the capacity and/or life length of traffic lines. A part of the efforts to do this is increasing the load carrying capacity of the railway bridges so that 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 trough railway bridge, The Övik Bridge, with two spans in Örnsköldsvik, in northern Sweden, is treated. To investigate the ultimate behavior of the bridge a full scale load test up to failure was performed in 2006. At the loading test in Örnsköldsvik a steel beam was placed in the mid of one of the spans of the bridge. The failure was caused by pulling the steel beam downwards with cables which were 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, the structural models for the shear failure are still the object of intense research. The bottom sides of the edge beams of the Örnsköldsvik Bridge were strengthened with Near Surface Mounted reinforcement (NSM) consisting of Carbon Fibre Reinforced Polymers (CFRP) to increase the bending 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. Concrete properties were determined by testing drilled core samples. Displacements and deflections of the bridge, strains in concrete, steel and carbon fibre reinforcement were measured during the test as a function of the increasing load. In this thesis the analysis of the failure of the bridge, structural models describing the behavior and load carrying capacity are evaluated according to different design codes. Advanced finite element analysis is applied with both geometrical and material non-linearities included. To verify the models used in codes and computer calculations the response of the bridge during the test is compared with the calculation results. The refined and calibrated FEM model is used to predict how high axle loads of a train the Övik Bridge could have sustained. The Övik Bridge was designed in 1950’s for axle loads of 20 ton. The calculations methods developed in this thesis show that the axle loads in the failure state could have been increased at least up to 154 tons without strengthening and to 215 ton with strengthening of the bridge slab with carbon fibre reinforcement bars with Af = 100 mm2 c 150 mm using statistical mean values of loads and material properties in the calculations.

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