A Numerical Approach for Calculating the Mechanical Performance of the Fire-damaged Reinforced Concrete Continuous Beams

To study the mechanical performance of reinforced concrete continuous beams after fire,a theoretical analysis on test results was carried out and a simplified algorithm was proposed for engineering practice.The experiment included standard ISO834 fire test on a two-span beam and subsequent static load tests at ambient temperature on the fire damaged beam and a reference beam. Based on the measured temperature curve,the temperature distribution of the fire exposed beam was computed by the finite element method.According to the stress-strain relationship of fire-damaged concrete and rebar,the moment-curvature relationship of the beam section and the bending stiffness of the beam were obtained. Furthermore, the moment distribution and deformation performance of both the reference beam and fire damaged beam were predicted. The computing results demonstrate that,when the compressive region of beam is subjected to elevated temperatures,bending stiffness and flexural strength will be both decreased and bending stiffness will decline more significantly;however,when the tensile region of the beam is subjected to fire,bending stiffness and flexural strength will decrease much slightly.Compared to the reference beam,the fire damaged beam is found in computing transiting more moment to the mid-span. Additionally,computing result shows the plastic hinge appears firstly at the mid-span point and then near the middle support point of twospan beam, which is totally different from the reference beam.The computing results have excellent agreements with the test observation.Also it is proved the traditional algorithm for continuous beam in ambient is not suitable in predicting the behavior of fire-damaged counterpart.