Dynamic loaded reinforced concrete Influence of bond-slip behaviour

Sammanfattning

Reinforced concrete is one of the most widely used materials of the 20th century.Concrete, which exhibits good abilities in resisting compressive forces, is combinedwith steel, which can resist tensile forces. The transfer of the forces between thematerials is guaranteed by the phenomenon of bond. In a section, where strainin concrete and steel is different, a relative displacement occurs which is calledbond-slip behaviour. Structures are subjected to a static load and sometimes alsoa dynamic load. A static load is a load that remains constant throughout the lifespanof a structure. In contrast, a dynamic impact load occurs when two bodiescollide. The force grows rapidly in a short time interval until a peak and thendrops again to the initial value. In this thesis, bond-slip behaviour of concreteand reinforcement under static and impact loading, as well as various numericalsimulation methods, are investigated.The first aim of the thesis was to design and conduct a series of pull-out experiments.The results were considered erroneous and therefore unsuitable to be abase for numerical investigations. Therefore, experimental data were obtainedfrom the literature. The static pull-out model was created and calibrated to fit theexperimental curve. In the next step, the impact loading experiment conductedin Chalmers University was utilized to create and calibrate a new model, with theparameters determined during previous calibration. Different bond coefficientsand two simulation methods (Cohesive method, Connector method) were studiedregarding deflection over time and plastic strain. Computational time study is alsoa part of this thesis.The results of the two methods are different but comparable. The Cohesive methodexhibits reduced stiffness under static loading, which correlates with experimentalresults, but when the non-linear behaviour initiates, it underestimates the experimentalresponse and at that moment the Connector method is a better representation.Under impact loading, the Connector method is more effective indemonstrating the failure mode and is more time-efficient. The Cohesive methodgives results that are closer to the experiment in regards to deflection over time. Itwas also discovered that lower bond strength primarily results in bending failure,which is a positive effect as this failure is less brittle than shear failure.Keywords: Bond, Bond-slip, Slip, Reinforced concrete, Impact loading, Repeatedloading, Finite element method, FEM, Cohesive method, Connector method.