Determination of t8/5 cooling times for underwater local dry welding of steel

Knowledge of thermal history is the basic condition for studying the structure - properties of welded joints. The determinant of thermal history is the thermal cycle, whose in-situ measurements are still a big challenge. Water as the welding environment complicates this issue even more. The article presents a method to determine an equation for calculating t_8/5 cooling times for underwater gas metal arc welding of unalloyed steels using the local dry cavity method. The work uses the contact method of temperature measurements with the use of thermocouples to obtain the temperature changes of the points of welded joints covered by the thermal field. On this basis, the values of the t_8/5 cooling times were determined. A regression analysis of the Response Surface Method was used to determine the equation, which resulted in a second-order model with interactions. Statistically significant factors were determined (thickness of welded elements and heat input value) and the model veracity was confirmed as the assumptions of normality and homogeneity of variance (homoscedasticity) of the residuals were met. The t_8/5 cooling time values depend on the thickness of the welded elements and heat input value in a nonlinear way. In terms of the test conditions, the cooling times ranged from 3.0 to 7.7 s. The equation allowed for the calculation of t_8/5 cooling times during underwater welding of unalloyed steels using the local dry cavity method based on the variability of the experimental conditions with satisfactory accuracy.     

宽幅钢箱梁若干设计要点研究

随着经济建设的发展，桥梁宽度日益增加，宽幅钢箱梁被广泛的应用于各类工程实践，为探究此类结构的受力模式，以2×40 m跨径的宽幅钢箱梁为研究对象，建立三维数值分析模型。以典型工况为荷载条件，验证单梁法、梁格法及板壳单元法的设计精度，在此基础上，分析、归纳及总结了宽幅钢箱梁的受力特性，结合有限元分析成果及中外规范着重论述了宽幅钢箱梁横梁的受力模式及简化计算方法，提出了宽幅钢箱梁的设计建议，以期为类似结构的设计提供参考。