Optimum Design of Welded Steel Plate Girder Bridges Using a Genetic Algorithm with Elitism

The genetic algorithm (GA) is a general optimization technique that has some unique features that are especially suitable for structural engineering problems. This work uses a simple GA with elitism to find the optimum design of welded steel plate girder bridges. The objectives are to minimize the weight and the cost of the girders. Two types of plate-girder bridges are studied: a single-span bridge and a two-equal-span continuous bridge. Bridges with various span lengths, in increments of 20?ft, are investigated; results are tabulated, parametric studies are made, and meaningful conclusions are drawn.     

GB/T3323.1-2019标准解析

介绍新版焊缝射线检测标准的主要内容,分析新旧标准的差异,阐述新版标准与其他标准的关联性,为正确理解和使用该系列标准提供了参考.     

正面角焊缝断裂原因分析

对正面角焊缝断裂原因进行了分析，在角焊缝处对最大剪应力面进行了探讨，试验证明断裂面位置与最大剪应力面是吻合的，同时运用图解等方法，进一步验证加大沿载荷方向的焊脚尺寸，可提高接头强度。     

Predicting weld creep strength reduction for 9% Cr steels

In design standards and in post-service life assessment, the cross-weld (CW) creep strength of ferritic steels is nearly universally assumed to be 80% of the corresponding value for the parent material (PH). However, CW data assessment of some 9% Cr steels such as E911 and P91 suggests that this would not hold at least at the high temperature end of the testing range. The resulting weld creep strength factor (WSF) is then attaining values well below 0.8 when extrapolated to typical design life of 100 000 h or more. Under such conditions the conventional value of 0.8 would result in non-conservative (too long) predicted life for structures subjected to CW loading in the creep regime.To accommodate the CW strength data for realistic values of WSF requires appropriate correction based on actual data. For this purpose, an alternative assessment approach, rigidity parameter correction (RPC), is proposed. This approach can be used to predict CW rupture strength from the PM master curves, with any PM rupture model optimized to correspond to the welded materials data.     

Finite element computation of fatigue growth rates for mode I cracks subjected to welding residual stresses

This paper presents a finite element modeling procedure for predicting fatigue crack growth rate in butt welds subject to mode I loading condition. Sequentially coupled three-dimensional thermal–mechanical finite element model to simulate welding residual stress was first developed. The weld-induced residual stress effect on the fatigue crack growth rate was then modeled by calculating the stress intensity factor due to the residual stress field based on the superposition rule of the linear elastic fracture mechanics. The results demonstrated the significance of the residual stresses in assessment of the fatigue crack growth rate in the welds.     

Minimization of stress concentration factors in fatigue crack repairs

A numerical study is reported of a repair by flaw removal on a conventional welded joint. The repair profile is optimized with respect to the flaw and joint dimensions in order to minimize the resulting stress concentration factor (SCF). Two dimensional (edge repair) and three dimensional (surface repair) finite element analyses were made for the determination of SCF values and a graphical representation of results is presented. A relation between edge repair and surface repair is obtained and short and long repairs are defined. The weld geometry and repair orientation effects on SCF values are discussed. Finally, implications on using short and long repairs on fatigue initiation and inspection are presented.     

Weld defect detection using PPM EMAT generated shear horizontal ultrasound

Austenitic welds are inspected using PPM EMAT generated shear horizontal (SH) waves. Results are compared to measurements taken using a 1D piezoelectric phased array using the total focusing method (TFM). For the first time there is clear experimental evidence of the SH wave method demonstrating higher sensitivity to defect detection. SH waves suffer less beam steering in a weld than either compression or SV waves, which can miss defects due to weld microstructure anisotropy and attenuation. All defects were identified from every side of the weld/plate using the SH waves, but this was not possible using the piezoelectric transducer.     

Effects of the Process Parameters on Austenitic Stainless Steel by TIG-Flux Welding

The effects of the process parameters of TIG （tungsten inset gas）-flux welding on the welds morphology, angular distortion, ferrite content and hot cracking in austenitic stainless steel were investigated. Autogenous TIG welding process was applied to the type 304 stainless steel through a thin layer of activating flux to produce a bead on plate welded joint. TiO2, SiO2, Fe2O3, Cr2O3, ZnO and MnO2 were used as the activating fluxes. The experimental results indicated that the TIG-flux welding can increase the weld depth/width ratio and reduce the HAZ （heat affected zone） range, and therefore the angular distortion of the weldment can be reduced. It was also found that the retained ferrite content within the TIG-flux welds is increased, and has a beneficial effect in reducing hot cracking tendency for stainless steels of the austenitic type weld metals. A plasma column constriction increases the current density at the anode spot and then a substantial increase in penetration of the TIG-flux welds can be obtained.     

Investigation of Large Web Fractures of Welded Steel Plate Girder Bridge

Constructed in 1972 with ASTM A36 (250 MPa) steel, a highway bridge in Maryland is comprised of seven welded steel plate girders of a constant web depth of 2,286 mm (90 in.). In March 2003, the web fractures of two steel girders were discovered in a three-span continuous superstructure unit. A full-height web fracture occurred in an interior girder at a cross frame connection plate; and a partial-height web fracture occurred in an exterior girder at an intermediate transverse stiffener next to a cross frame. The investigation of the girder fractures involved fracture surface examination, material testing, fracture mechanics analysis, and comprehensive finite-element modeling for fracture driving forces. The fracture mechanics analysis indicated that a brittle web fracture could occur at a high stress level with either a surface crack or a through-thickness crack of certain dimensions. Finite-element analysis using a global model and submodels investigated three possible causes: (1) localized distortion of the unsupported web gap due to the lateral forces of cross frame members; (2) fabrication induced out-of-flatness of the web plate under in-plane loading; and (3) residual stresses at the fracture origin area due to the stiffener-to-web welds. The investigation concluded that one or a combination of these can result in the high local tensile stresses triggering a brittle web fracture with certain crack dimensions at the fracture origin area. Several retrofit concepts were investigated for their effectiveness in reducing stresses in the fracture origin area. Bridge inspections in the subsequent 6 years after the web fractures have not reported any other cracks in the bridge.     

铜铝线焊接工艺探讨

介绍了铝线电机中铝线焊接工艺,从铝线脱漆、铝线焊锡、焊接点密封三个步骤对该工艺进行升级,降低了铜铝电化学腐蚀带来的负面影响,从而确保焊接接头的可靠性和使用寿命。