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This paper aims to present a mathematical model of predicting the residual moment capacity of fire-damaged reinforced concrete (RC) elements after cooling to ambient temperature which also reflects the role of bond between steel rebar and surrounding concrete.

The prediction of residual moment capacity of fire-damaged RC element has been carried out for two scenarios: by assuming perfect bond between surrounding concrete and steel rebar after fire exposure and by incorporating a relative slip between surrounding concrete and steel rebar and hence assuming partial bond between them after fire scenario. The predicted results are then compared with the experimental results available in different literatures.

It is found that on comparison between the predicted results and the experimental results, the proposed mathematical prediction model, when bond-characteristics are considered, shows better agreement with the experimental results as compared with those by conventional method with perfect bond assumption.

The constitutive relationship for thermal residual properties of steel rebar and concrete has been used in the proposed prediction model along with relative slip approach between surrounding concrete and steel rebar after fire scenario and consequently to predict the residual moment capacity of the fire-damaged RC element after cooling.

This study attempts to investigate the post-fire residual stress-strain behaviour of unconfined plain and fibrous concretes under axial compression. The experimental variables of the study were concrete strength levels, volume fractions of flat crimped steel fibres and polypropylene fibres, inclusion of hybrid fibres and temperature of exposure. A total of 147 cylindrical specimens (150 x 450 mm) were cast and tested under this study. The specimens were first exposed to temperatures ranging from room temperature to 800°C and then tested under uni-axial compression after cooling to obtain complete residual stress-strain response. Based on the test data obtained, a simple empirical model is proposed to describe the complete residual stress-strain relationships of plain and fibre reinforced concrete after exposure at elevated temperatures. Important observations have been made in the paper about the influence of temperature on various mechanical properties namely strength, stress-strain curves, compressive toughness and modulus of elasticity of both plain and fibrous concretes.