Finite-Element Analysis of Flexural Strengthening Performance of Fire-Damaged RC Beams

Abstract In this study, a simplified cross-sectional approach based on finite-element analysis was developed to evaluate the flexural strengthening performance of fire-damaged RC beams using externally bonded steel plates and CFRP strips. The strength degradation of the simplified concrete cross section and reinforcing bars was determined based on the temperature field calculation results from FE software. The strength degradation models proposed in previous literature were adopted and applied based on the obtained temperature distribution. The finite-element model was validated with the previous experimental test to evaluate the accuracy of the model in predicting the residual flexural capacity of RC beams after fire exposure. It is shown that the finite-element model (FEM) was able to predict the flexural behavior of fire-damaged RC members reasonably well. The ISO-834 standard fire curve was applied to the reference flexure beam for 60 min, 90 min, and 120 min of heating before strengthening by employing the proposed methodology. The parametric study in this investigation includes the thickness and width of the strengthening materials for the comparison of the flexural capacity recovery of both retrofitting methods. The analysis results showed that the ultimate load and stiffness of fire-damaged beams strengthened with both materials improved significantly compared to the heated beams without strengthening. The damaged beams group retrofitted with externally bonded steel plates exhibited a greater increase in both ultimate load and stiffness compared to the damaged beams group retrofitted with externally bonded CFRP strips.