The assessment of the residual strength of post-heated concrete structural members in a professional way is a prime factor to take a decision about the restoration or destruction of fire-damaged structure. This Paper explores the numerical modelling of RC square columns damaged by exposure to heat at 5000C, unjacketed. Software ABAQUS was used for numerical modelling of fire damaged compression member i-e column. The main objective of this study is prediction of axial load and axial deformation of fire damaged concrete using finite element studies. Moreover, a parametric nonlinear finite element (FE) research is carried out to check the effect of viscosity parameters on numerical simulation of fire damaged concrete columns. For the said objectives, numerical simulation of existing experimental study of fire damaged RC columns is conducted with varied values of viscosity parameters. The numerical analysis (Finite Element Modeling) indicated that axial load capacity decreases and axial deformation increases after exposure to fire. The experimental and numerical studies are compared in terms of load displacement analysis. The use of optimum viscosity parameter and its definition to FEM improves significantly the performance of convergence and reduces analysis time of numerical simulations of RC square columns. Moreover, a good agreement was found between the experimental and the finite model results.

In this study, the effect of post-fire prolonged air-recuring on the recovery of strength of reinforced concrete was investigated after exposing to elevated temperature levels varying from 300 ºC to 900 ºC. The main objective of the paper is to find the effectiveness of prolonged air-recuring on strength of fire damaged RC columns. In order to achieve this, a total of 24 reinforced concrete circular columns having size 200 1200 mm were casted and tested under compressive loading. Eighteen specimens were heated in an electric furnace such that six specimens at each temperature level i.e. 300ºC, 500 ºC and 900 ºC. After heating, specimens were allowed to cool down naturally at ambient temperature and then specimens were air-recured in open environment (high humidity) following by repairing of respective specimens with various confinement techniques. After post fire prolonged air-recuring, test results showed that decrease in axial compressive at all temperature levels was less compared to values reported in literature for corresponding temperatures. This confirms the recovery of microstructure and thus increase in strength of post heated reinforced concrete circular columns due to prolonged air-recuring. It has been observed that both the confinement techniques i.e. single layer of CFRP only and epoxy injection, steel wire mesh filled with epoxy resin mortar along with CFRP wrapping restored the original strength or even more of air-recured post heated reinforced concrete circular columns compared to that of un-heated control specimens or even more.