Early-Age Behavior of Large-Scale Concrete-Filled Steel Tubular Members: Field Measurement, Simulation, and Neural Network Prediction
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摘要: 对于大直径钢管混凝土(Concrete⁃Filled Steel Tube, CFST)构件,其内部大体积混凝土因早期水化热引起的开裂问题亟待研究。对一座高385 m输电塔的塔腿(直径为2.1 m的CFST构件)浇筑后的混凝土温度及应变进行了实测。结果表明:由于混凝土早期水化作用,其核心区域温度可达到97.0 ℃,与钢壁表面的最大温差可达到30.6 ℃;浇筑30 h后,混凝土中心的拉伸应变达到400×10-6,从而引起混凝土早期开裂。此外,为了研究尺寸对CFST构件早期行为的影响,浇筑并测量了8个不同直径的CFST试件的温度及应变。基于“水化-温度-力”本构模型,开发了CFST构件精细化有限元模型,与试验结果进行对比验证。最后,建立了考虑CFST构件直径、环境温度和混凝土配合比的早期水化热数据库,基于BP神经网络预测了CFST构件的早期行为,表明BP神经网路可实现CFST构件早期水化热的精准预测,有助于降低早期开裂风险。Abstract: 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.
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Key words:
- CFST /
- large diameter /
- hydration /
- multi-field coupling /
- neural network
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