Research and numerical simulation on the impact compressive mechanical properties of concrete after high-temperature exposure

Under increasing tunnel construction-related hazards such as fire and impact, this study investigates the dynamic mechanical response of tunnel lining concrete after high-temperature damage. Using C35 concrete and modifying the Holmquist-Johnson-Cook (HJC) constitutive model, a refined finite element model of the Split Hopkinson Pressure Bar (SHPB) test was established on the ABAQUS platform with CT-scan-based 3D reconstructed specimens. Results show that the model accurately characterizes concrete’s dynamic behavior after high-temperature exposure. High-temperature damage significantly deteriorates dynamic properties: after 20 minutes of fire exposure, the dynamic compressive strength reduction coefficient tends to 0.5-0.6, and failure mode shifts from brittle to ductile. At impact velocities of 5.4-11.3 m/s, peak stress increases by 40% (room temperature) and 33% (after 30 min heating), indicating a significant strain rate strengthening effect. Macroscopic failure follows a progressive mechanism: stress wave triggering, damage domination, displacement response, plastic accumulation, and global failure. A multiple regression model for peak stress and a staged damage variable prediction model are developed, accurately quantifying concrete’s response under coupled effects of high-temperature exposure (0-120 min) and impact velocity (≤40 m/s). This work provides a reliable numerical method and theoretical basis for post-fire dynamic performance assessment of tunnel lining concrete.