Early-Age Behavior of Large-Scale Concrete-Filled Steel Tubular Members： Field Measurement， Simulation， and Neural Network Prediction

For concrete-filled steel tube （CFST） columns with a large diameter， the cracking problems caused by the early-age hydration heat in the internal mass concrete urgently need to be studied. The temperature and strain in the concrete of the tower leg （a 2.1 m diameter CFST member） after pouring were measured. The tower leg is part of the world’s highest transmission tower， which stands 385 meters tall.The results showed that due to the early-age hydration of concrete， the temperature in its core region reached 97.0 ℃， with a maximum temperature difference of up to 30.6 ℃ compared to the steel wall surface. The tensile strain at the core region of the concrete reached 400×10^-6 after 30 hours of pouring， leading to early-age cracking in the concrete. Additionally， to investigate the impact of size on the early-age behavior of CFST members， eight CFST specimens with different diameters were manufactured and measured for temperature and strain. Based on the “hydration-thermal-mechanical” constitutive model， a refined finite element model for CFST members was developed and validated against experimental results. Finally， an early-age hydration heat database considering the diameter of CFST members， ambient temperature， and concrete mix proportions was established. Based on a BP neural network， the early-age behavior of CFST members was predicted. The BP neural network enables accurate prediction of early-age hydration heat in CFST members， thereby helping to reduce the risk of early-age cracking.