Spatiotemporal Thermal Analysis of Large-Volume Concrete Girders: Distributed Fiber Sensing and Hydration Heat Simulation

To investigate the spatiotemporal distribution of early-age hydration heat-induced temperature fields, this study integrates distributed fiber optic sensing (DFOS) technology with a thermal parameter finite element model (FEM). First, a high-precision DFOS system and traditional point-type semiconductor sensors were deployed to continuously monitor the temperature of a 50 m large-volume concrete box girder (LVBG) over 100 h. Experimental results show that full-field LVBG temperature changes can be measured by DFOS compared to traditional point sensors. DFOS, leveraging its full-scale spatial coverage capability, revealed a three-stage temperature evolution: rapid heating (peak temperature of 79.4 °C at 40 h), sustained high temperatures (>75 °C for 20 h), and gradual cooling (rate: 0.45 °C/h). In contrast, conventional point sensors may miss localized hotspots due to insufficient spatial coverage. Second, a FEM was developed on the ABAQUS 2021 (finite element analysis software) platform, incorporating a UMATHT (user material thermal) subroutine to update temperature-dependent thermal conductivity and specific heat in real time during hydration heat transfer simulations. The proposed model significantly improved prediction accuracy by integrating parameter mechanisms (equivalent age), and it improved prediction accuracy by about 40% compared to static-parameter models. The FEM results exhibited strong consistency with DFOS-measured data, validating the model’s reliability in capturing thermal gradients in geometrically complex structures. This validated framework offers a robust tool for optimizing thermal management strategies in large-scale infrastructure projects. The research results of this paper can serve as a reference for the temperature measurement and prediction of large-volume concrete.