混凝土桥塔早龄期时变对流影响分析及主动控制

Analysis and Active Control of Time-Varying Convection Influences of Concrete Pylon in Early Age Phase

为研究混凝土桥塔早龄期表面温度与受力的真实状态,开展时变对流对其早龄期表面温度应力的影响分析。温度效应计算针对各施工环节选取相应的对流参数,采用模板拆除阶段12h内的风速均值作为边界施加到结构表面。以芜湖长江公路二桥为背景,采用ANSYS分析频遇风速、防护工艺以及冷却工艺对桥塔早龄期表面温度应力的影响,结果表明:在频遇风速影响下,桥塔表面拉应力水平较高是大量开裂产生的主要原因;防护工艺优化及增加冷却工艺可以降低结构表面的累计应力与瞬时应力。在此基础上提出一种基于冷却工艺,通过加速桥塔施工前期的对流效应以提高结构抗裂安全性的对流参数主动控制方法,该方法主动控制阶段的表面降温速率取为6~13℃/d。将所提出的对流参数主动控制方法应用在芜湖长江公路二桥桥塔上取得了很好的控制效果。

In order to study the actual situations of the surface temperatures and forces of concrete pylon in the early age phase,the influences of the time-varying convection on the surface temperature stresses were analyzed.In the calculation of the temperature effects,the corresponding convection parameters should be selected for each construction process and the 12 hours average wind speed should be applied as a boundary to the surface of the structure after the removal of formwork.Based on the Second Wuhu Yangtze River Highway Bridge,the influences of the frequent wind speeds,protection techniques and cooling process on the temperature stresses of the pylon in the early age phase were analyzed,using the ANSYS.The results show that under the influences of the frequent wind speeds,the high tensile stress on the surface of the pylon is the main reason for a large number of the cracks.The optimization of the protection techniques and the adopting of the cooling can both reduce the cumulative stress and the instantaneous stress of the structure surface.A method of the active control of the convective parameters based on the cooling process is proposed,which accelerates the convection effects in the early stage phase to improve the anti-crack safety of the structure.By the calculation,the surface cooling rate in the active control stage is determined to be 6~13°C/d.The proposed method for the active control of the convective parameters has achieved good control effect on the application of the pylon of the bridge.