钢桥表面相对湿度的边界条件计算方法

Calculation methods for boundary conditions of relative humidity on steel bridge surface

表面相对湿度是决定钢桥腐蚀速度的重要因素,精确计算表面相对湿度的关键在于选取合适的温度场边界条件,因此进行了拱肋模型相对湿度测试试验,利用有限元分析软件ABAQUS的DFLUX与UVARM子程序实现了钢桥表面相对湿度计算,并对比分析了不同太阳辐射、辐射换热及对流换热的计算方法对钢桥表面相对湿度模拟结果的影响。结果表明:太阳辐射强度对表面相对湿度的影响主要集中在日出、日落时段,采用Hottle模型计算的日总太阳辐射偏大,导致表面相对湿度偏低,建议使用实测太阳辐射数据计算太阳辐射热流密度;天空及地面的辐射换热对表面相对湿度的影响不容忽视,利用简单的大气辐射换热替代天空、地面辐射换热,会导致结构吸收热量增加,表面相对湿度显著减小,建议在计算辐射换热热流密度时考虑天空温度、地面温度的影响;白天对流换热对结构有降温作用,促使表面相对湿度升高,夜晚对流换热作用对结构有升温作用,促使表面相对湿度降低,目前对流换热系数计算方法多基于混凝土结构开展,后续可进行适用于计算钢桥表面相对湿度的对流换热系数研究。

The surface relative humidity is an important factor determining the corrosion rate of steel bridges,and the key to accurately calculate surface relative humidity is selecting appropriate boundary conditions of temperature field.Therefore,the relative humidity tests on the arch rib model was conducted,the finite element analysis software ABAQUS with the DFLUX and UVARM subroutines was used to calculate the surface relative humidity of the steel bridge.A comparative analysis was conducted on the effects of different solar radiation,radiative heat transfer,and convective heat transfer calculation methods on the surface relative humidity of the steel bridge.The results show that the influence of solar radiation intensity on surface relative humidity is mainly concentrated during sunrise and sunset periods.The daily total solar radiation tends to overestimate using the calculation method of Hottle model,leading to lower surface relative humidity.It is recommended to calculate the solar radiation heat flux density based on the measured solar radiation data.The effects of radiation heat transfer with sky and ground on the surface relative humidity should not be ignored.Substituting simple radiation heat transfer with atmospheric for radiation heat transfer with sky and ground will lead to an increase in heat absorption by the structure and a significant decrease in surface relative humidity.It is recommended to consider the effects of sky temperature and ground temperature when calculating the heat flux density of radiative heat transfer.During the day,convective heat transfer has a cooling effect on the structure,causing the surface relative humidity to increase.At night,convective heat transfer has a warming effect on the structure,causing the surface relative humidity to decrease.Currently,the studies on calculation methods of convective heat transfer coefficient are mostly based on concrete structures.It is suggested to conduct research on convective heat transfer coefficients suitable for calculating the surface relative humidity of steel bridges in the future.