Research on hydration-caused thermal cracking risk of steel-concrete composite bridge pylons

Abstract

Due to the large volume and different material of composite bridge pylons, a significant cracking risk has not yet been verified during concrete hydration. To clarify the hydration-caused temperature characteristics of concrete in composite pylons, based on an actual cable-stayed bridge, a 3D thermal-mechanical coupling model was established, demonstrating a good agreement between the FEM and measurements. On this basis, the temperature field and effects of pylon segments were analyzed. The key parameters influencing the temperature field, including the pouring sequences, hydration heat release, cement content, initial temperature, and convective coefficient，were analyzed. Results indicate that the temperature evolution can be divided into three stages: rapid warming, sharp cooling, and fluctuation. The temperature distributions exhibit high inside, low outside, and single-peak along the thickness direction. During the hydration process, the growth rate of the concrete elastic modulus is higher than its tensile strength. The maximum stress of concrete is 5 MPa, considerably higher than its tensile strength, leading to a significant cracking risk. Additionally, the maximum stress of the steel shell reaches 50 MPa. Adjusting the constructional parameters and environmental effects are the most effective improvement measure. The cracking risk of concrete can be reduced by 20% and 25% for every 20 kg/m3 and 50 kJ/kg reduction in the cement content and the cement heat release, respectively. Furthermore, reasonable methods for reducing unfavorable thermal effects are provided, which can facilitate the rational design and construction of composite bridge pylons.