Tension stiffening in reinforced concrete - instantaneous and time-dependent behaviour

The research presented in this thesis is concerned with the time-dependent behaviour of reinforced concrete and the mechanisms of tension stiffening. The research programcomprises both experimental investigation and numerical modeling. The aims are to provide a comprehensive understanding about tension stiffening under short-term and long-term loading.Of particular interests are the effects of concrete creep and shrinkage on the change of tension stiffening with time.The experimental program involved testing axially loaded reinforced concrete prisms and simply-supported reinforced concrete beams and slabs under short-term and long-term loadings. The experimental results have demonstrated that tension stiffening is greatly influenced by the drying shrinkage of concrete, the extent of cracking and the deterioration with time of the bond between the reinforcement and the concrete.A two-dimensional continuum-based finite element model has been developed. The model incorporates instantaneous and time-dependent constitutive laws for concrete, steel and importantly the bond interface between them. A shrinkage-related bond model has been proposed to accurately model the loss of tension stiffening under long-term loading.The finite element model has been used to simulate the response of the test specimens and the numerical results are in close agreement with the experimental results. A parametric study has also been undertaken using the finite element model; the effects of different parameters (concrete cover, reinforcing ratio, etc.) on time-dependent tension stiffening have been examined. The significance of each parameter has been discussed