Structural Assessment of a Concrete Bridge : Probabilistic analysis of the Shear Resistance of the Kiruna Mine Bridge Using In-Situ Material Properties

The demolition of an old structure and replacement with a new one is a very complex, time consuming and expensive task, especially if it needs to be conducted without interruption of its functioning (e.g. carrying traffic). In the case of bridges, closing one of them due to such an action can paralyze the infrastructure net and influence the life of thousands of people. This is why the proper assessment of bridge capacity, and the decision regarding possible strengthening or limiting of loads is crucial for the existing transportation system.In this thesis the basis of reliability, assessment of structures and calculations of safety are explained. As an example the shear capacity of a road bridge girder in Kiruna, northern Sweden, is discussed.First, on basis of samples of concrete and reinforcement, the in-situ properties of the materials are found by laboratory tests (concrete compressive and tensile strength fcc.and fct and yielding strength of stirrups fy). Next, models in three structural codes are described and used: (1) Eurocode 2, which is used in the European Union, (2) the performance-based international Model code 2010 and (3) the Swedish standard BBK 04. The influence of the prestress forces has been partially taken into account.Three different approaches are used to obtain the shear capacity/resistance of one of the girders in the bridge: (I) The design resistance, computed using material properties taken from standards - in same way as during design of the structure. (II) The resistance based on characteristic properties found by testing of the build-in materials. (III) Finally using the outcome from the laboratory tests a probabilistic approach is used to find the different levels of safety of the structure.Although the theories behind codes varies, all the results obtained with use of simplified methods are similar.With proper assessment of material properties it can be shown that the structure has bigger carrying capacity than what it was originally designed for. This would allow an increased traffic volume without any physical intervention. Thanks to this, large amount of money and time can be saved by avoiding structural strengthening or replacement. It also has a positive environmental impact.During the final test of the Kiruna Bridge a total load of 13,4 MN could be applied to the studied span. If it’s assumed that one third of the force is carried by each girder and the shear force in midspan is half of the force on the girder, then we get a shear resistance of ca. VR ≈ 13,4/6 = 2,23 MN – about twice the values obtained by the simplified models used, mostly due to neglecting influence of the prestress force on the concrete behaviour and simplifications of strength calculation.Validerat; 20150205 (global_studentproject_submitter