Abstract
In the thermal analysis of concrete box girder bridges, the high thermal conductivity of steel bars is often oversimplified, leading to deviations in temperature field prediction results. At high temperatures, the thermal conductivity of steel significantly alters the temperature gradient distribution within the section, thereby affecting thermal stress and the resistance to cracking. The box girder is widely used in long-span bridges due to its excellent torsional stiffness and economic benefits. However, the complex temperature field may cause cracking, warping, and durability problems. The significant thermal conductivity difference between steel and concrete will produce a localized temperature gradient in the area with dense reinforcement (which will induce thermal stress concentration and endanger the stability of the structure). Existing studies often overlook the thermal conductivity of steel bars, assuming a purely thermal conductivity process, which deviates from the actual situation. This study combines theoretical analysis, refined finite element modeling, parametric research (reinforcement diameter and stirrup spacing), and related stress analysis to propose the thermal siphon effect. The study shows that increasing the reinforcement diameter from 16 mm to 26 mm can significantly reduce the homogenization time of the structural temperature. When the stirrup spacing along the heat conduction direction is reduced from 170 mm to 30 mm, the reinforcement is dense, and the diameter is large. The structure can reach thermal equilibrium faster, and the temperature gradient is smaller. The temperature gradient causes the surface concrete to be under tension and the internal concrete to be under pressure, which may lead to surface cracking. In areas with dense reinforcement, accelerated heat transfer results in a significant increase in temperature, which can induce local stress concentration.
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