The non-linear resonance vibration method is a promising non-linear acoustic technique that has been used to evaluate contact-type defects of concrete induced by exposure to fire. In this work, an experimental study was performed on thin fire-damaged concrete discs to evaluate residual tensile strength using the non-linear resonance vibration method. Using correlation analysis, an experimental relationship is proposed between splitting tensile strength and a hysteretic non-linearity parameter (HNP), as measured from some 350 fire-damaged concrete discs of different mix proportions. In addition, the thermal gradient damage of concrete was examined to verify the efficiency of the proposed equation. It was found that the tensile strength of fire-damaged concrete could be effectively estimated from the measured HNP without consideration of the mix proportion, peak temperature, period after the fire or thermal gradient damage. Notation d diameter of sample F maximum applied load recorded at failure f measured resonance frequency at increased input amplitudes f 0 measured linear resonance frequency l length of sample M elastic modulus M 0 linear elastic modulus T s splitting tensile strength T s0 splitting tensile strength of undamaged sample T sn splitting tensile strength of damaged sample t time of one-dimensional (1D) dynamic behaviour of solids AE hysteretic non-linearity parameter (HNP) AE h HNP measured by amplitude-dependent resonance frequency shift AE h0 HNP of undamaged sample AE hn HNP of damaged samplẽ å strain amplitude in proportion to input amplitude å strain of 1D dynamic behaviour of solids _ å strain rate (_ å ¼ då=dt)

In this study, the effects of different mix proportions and fire scenarios (exposure temperatures and post-fire-curing periods) on fire-damaged concrete were analyzed using a nonlinear resonance vibration method based on nonlinear acoustics. The hysteretic nonlinearity parameter was obtained, which can sensitively reflect the damage level of fire-damaged concrete. In addition, a splitting tensile strength test was performed on each fire-damaged specimen to evaluate the residual property. Using the results, a prediction model for estimating the residual strength of fire-damaged concrete was proposed on the basis of the correlation between the hysteretic nonlinearity parameter and the ratio of splitting tensile strength.