ارزیابی عمر خستگی اتصالات جوشی در پل فولادی
Abstract
1- Introduction
2- Development of fatigue life model
3- Validation of fatigue life predication model
4- Case study
5- Conclusions
References
Abstract
Welded joints are widely used to connect structural components in steel truss bridges. Weld residual stresses (WRS) and weld residual stresses relaxation (WRSR) have notable influences on fatigue crack propagation in welded joints, and therefore affect the fatigue life of welded joints. Failing to properly consider the effect of WRS and WRSR in fatigue evaluation may lead to inaccurate results. This study presents a fatigue life prediction model based on the elastic fracture mechanics, with consideration of the WRS and WRSR. The solution for stress intensity factor caused by cyclic loading and WRS is derived. The WRS-induced stress intensity factor is calculated using a weight function technique. Fatigue tests of eight welded joint specimens are implemented, and the fatigue failure analysis of specimens is conducted. The proposed fatigue life prediction model is validated against fatigue test results of welded joints. By considering both WRS and WRSR, the model provides a prediction of fatigue life with a maximum error of 14%. Finally, the validated model is employed to investigate the fatigue life of a real bridge. The fatigue life is underestimated by 17% by considering WRS but not considering WRSR; the fatigue life is overestimated by 49% by neglecting WRS and WRSR.
Introduction
Steel trusses are extensively used in highway and railway bridges. Fig. 1 shows the cross section of a typical steel truss girder [1–3].Welded joints and high-strength bolts have been used to connect different bridge components, such as the top and bottom chords, verticals, diagonals, bracings, etc. In Fig. 1, an I-shape steel beam is welded on a gusset plate that connects the bottom chords, vertical and diagonals. It has been found that the fatigue resistance of welded joint, especially the connection of gusset and flange plates (named as T-shape welded joint), is susceptible to traffic loads, weld residual stresses (WRS), weld defects, and stress concentration, etc. [3–5]. However, methods for predicting the fatigue life of the welded joint with consideration of WRS and WRSR are still under development. A lot of research efforts have been devoted to understanding the effect of WRS on fatigue failure. Sumi et al. [6] investigated the effect of WRS on fatigue life and failure paths through fatigue tests of butt welded plates. Galatolo and Lanciotti [7] reported that the WRS increased the growth rate of fatigue crack perpendicular to the weld line, reducing the fatigue life. Gerhard [8] established a formula to relate the WRS and crack growth threshold. Cui et al. [9] found that the WRS highly reduced the fatigue resistance of a steel bridge. Ultrasonic impact treatment was used to increase the threshold of stress intensity factor and enhance the fatigue resistance [10,11]. In addition to the experimental studies, finite element analysis has been carried out to study the effect of WRS on the fatigue life of welded joints under cyclic loading [12]. Although the effect of WRS on the fatigue resistance of welded joints has been studied, there are limited studies on the relaxation of WRS, namely WRSR, which is a phenomenon that the WRS is partially released at the welded joints under cyclic loading [13–17]. WRSR is a complicated procedure governed by the interaction of the amplitude and range of stresses, loading scenario, loading cycles, material properties, etc. [14]. A reasonable estimation of WRSR is the perquisite of predicting fatigue life of welded joints.