Early-age Cracking Risk and Prevention of Concrete Small Box Girder
The precast concrete small box girder produces significant temperature differences during pouring under hydration heat effect,causing cracking risk at early-age and affecting its safety and durability.To clarify the early-age cracking risk of precast concrete small box girder bridge,the concrete small box girder bridge in Ankang area of Shaanxi province was taken as the basis to study its early-age temperature action,thermal effect and cracking risk.The main factors affecting early-age cracking risk of precast small concrete box girder were obtained with orthogonal test analysis.The result shows that the precast small concrete box girder exhibits the rapid hydration reaction after pouring with the temperature peaking at 54.9℃after 12-16 hours.The highest temperatures are localized at the upper axis and bottom plate;while under the influence of environment,the hydration exothermic time at bottom plate is the longest.The temperature distribution of concrete small box girder is symmetric within 72 hours after pouring.Throughout the hydration period,the resistance levels at various locations increase uniformly;however,the stress levels at wing edge,axis and center of web plate are higher,thereby elevating the cracking risk.The maximum thermal stress is 2.71 MPa,and the cracking index is 1.2.The hydration heat temperatures of precast concrete small concrete box girder are influenced by the material properties,structural parameters and environmental factors.The material properties exert the most significant influence,including the cement heat release and cement content.By adjusting the material properties and initial temperature,the early-age cracking risk of precast concrete small box girder can be effectively mitigated.This study provides the valuable insights for the design and construction of precast concrete small box girders,aiming to reduce the early-age cracking risk and improve the safety and durability.
bridge engineeringearly-age cracking riskthermal-mechanical coupling analysisprecast concrete small box girderthermal effect of hydration heat
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