Characterization and Sensitivity Analysis of Concrete Damage Evaluation Indices in Bridge Structures under Fire Environments

ABSTRACT The degradation mechanisms of concrete in bridge structures under prolonged fire exposure represent a critical safety challenge in addressing multihazard environmental interactions. Although existing research predominantly employs single-index assessment systems, these approaches fail to meet the technical requirements for post-fire rehabilitation decision-making. This study proposes a multivariate assessment framework to quantify thermal damage in bridge concrete through systematic experimental investigations. Through in-depth research, the characteristics, causal mechanisms, and degree of sensitivity of damage evaluation indicators with temperature changes were derived. The results of the study indicate that the characteristics of various damage evaluation indices are not only closely related to the absence, decomposition, and interaction of the internal components of concrete at high temperatures, but are also significantly affected by the intrinsic properties of the indices themselves; dynamic elastic modulus (measured by dynamic testing methods that reflect the response of materials to alternating loads or vibrations) and compressive elastic modulus (obtained by uniaxial compression tests that reflect the stress–strain relationship of the material under quasistatic loading) show superior sensitivity, with damage variables reaching 96.80 % and 92.86 %, respectively. at 700°C, demonstrating monotonic degradation patterns; considering the limitations of on-site sampling or testing conditions in practical engineering applications, nondestructive testing (NDT) indicators such as ultrasonic pulse velocity, impact-echo stress wave velocity, and infrared thermal image average temperature rise (69.81 %, 81.47 %, and 62.07 % of damage variables at 700°C, respectively) can be used as alternatives. There may be limitations in the use of these NDT indicators when applied individually, and it is recommended that they be combined with compressive modulus testing results for comprehensive analysis to ensure the accuracy and reliability of damage evaluation outcomes.