The early fatigue cracking of orthotropic steel decks has been a long-standing problem for heavy traffic regions of China’s long-span bridges. However, the actual fatigue life is much lower than the fatigue life calculated by fatigue design codes. In this study, a modified full range S-N curve, the M-S-N method, is proposed to evaluate welded joint fatigue life, considering mean stress, which is based on metal fatigue theory. As an example, a combined shell-solid finite-element model of a segmental bridge is first built for the Jiangyin Bridge to obtain the real stress, integrating welding residual stress and vehicle load stress. The fatigue life is then calculated and compared in order to consider the influence of different vehicle loads and deck-plate thicknesses. The calculation results show that the fatigue life of the deck-rib welded joint in the Jiangyin Yangtze River Bridge decreases nonlinear at a staggering rate with the increase in vehicle load. Under the condition of severe overload heavy vehicles, the Jiangyin Bridge fatigue life is only 2.17 years according to the M-S-N method, which matches practical situations. Deck-rib fatigue life obviously increases with the increase in deck thickness. The current steel bridge deck design with a 16-mm-thick plate is not safe under heavy traffic conditions.

Fatigue cracking is crucial issue for welded steel bridges that endure repeated vehicle loads. With typical fatigue-life evaluation methods, it is difficult to consider the influence of low stress amplitude. Based on existing full-range S-N curves and their formulas for base metal, a unified fatigue-life evaluation method is recommended for welded joints. The basis for construction of full-range S-N curves is to obtain the welding residual stress and stress concentration factor. In this paper, rib-to-deck welded joints are introduced as examples to demonstrate the detailed steps of a fatigue-life evaluation procedure. From the analysis of welding residual stress, it can be concluded that residual stress is influenced by the geometric dimensions of the composite members. With an increase in the geometric dimensions, the level of residual stress is increased. In addition, static-load experiments were conducted to obtain the stress concentration factor. A hot-spot full-range S-N curve was then obtain...

An orthotropic steel deck (OSD) has a complicated structure, and its fatigue life is mainly determined by various welding details. Fatigue assessment of deck-to-rib welded joints under long-term train loads is an important concern for engineers. Using the stress range–number of cycles (S-N) curves that are recommended by existing specifications, it is difficult to consider welding residual stress. As a type of initial stress, welding residual stress reduces structural fatigue life by influencing the mean stress of the external cyclic load. However, the effect of mean stress is often overlooked by traditional welding fatigue theory. In this paper, a full-range S-N curve model of steel fatigue resistance integrating welding residual stress is proposed by adopting the Soderberg formula to equivalently transform the stress amplitude and mean stress. The Nanjing Dashengguan Bridge, a six-line railway steel arch bridge and the longest steel arch bridge in the world, is used as an example to demonstrate the fatigue life evaluation procedure of the proposed model in detail. First, the distribution of the welding residual stress of deck-to-rib welded details is obtained based on a refined finite-element model (FEM), and its accuracy is verified experimentally. Second, the partial welded joint model is embedded into the whole multiscale FEM of the steel deck. The structural/real stress spectrum of the welded details under a passenger/freight train is obtained by integrating the coupling effect of the train load stress and residual stress. Finally, fatigue life evaluation of the deck-to-rib welded details of the Dashengguan Bridge is carried out based on the proposed S-N curve model, integrating the residual stress and annual train volume. The results show that (1) the longitudinal residual stress (${\sigma }_Z$ ) on the top and bottom surfaces of the deck vary with its welding direction respectively (perpendicular or parallel); (2) the maximum value of the real stress under the coupling effect of train load stress and residual stress is less than the yield strength ($f_y$ ), so the influence of mean stress on the fatigue life of welded joints should still be considered; and (3) the fatigue life calculated by the proposed model is more accurate and conservative than a common standard. In summary, the proposed model provides a basis for determining whether the Dashengguan Bridge can allow freight trains to pass.

The driving security of trains at high speeds is among the pivotal issues significantly affected by the smoothness of rail lines. For high-speed railway steel bridges, the fatigue cracking of typical positions under the rail lines will reduce the stiffness of the deck plate, inducing the smoothing of the rail lines. In this paper, a new theoretical approach is proposed that integrates the fatigue assessment of a typical welded joint for high-speed railway steel bridges in service. Based on the strain history data recorded by a structural health monitoring system, the theoretical approach includes various factors, including stress concentration, environmental corrosion, and train flow. Upon application in an actual high-speed railway bridge with an orthotropic steel deck, the approach was used to conduct determinative and reliable fatigue-life evaluation of the bridge. A static-load experiment was conducted to obtain the stress distribution around the weld and the difference in stress between the p...

In this study, the seismic performances of a 14-storey office building in Nanjing, China, due to its plan and vertical irregularities in the structural system, were evaluated using the response spectrum method, elastic time history analysis and elastic–plastic time history analysis. In combination of these three methods, the storey drifts and elastic–plastic states of typical structural members under three levels of earthquakes were determined to verify the robustness of the structural design program. The damage states of typical structural members at some sensitive positions were estimated and evaluated under rare earthquakes. Consequently, all structural members were within the scope of elastic performances under the actions of frequent earthquakes. The maximum displacements and storey drifts satisfied the requirements of the design codes within the scope of elastic or elastic–plastic deformations. The induced damages could reach “moderate damage” states, satisfying the requirements for the expected performances by the codes. The consequences indicated that the design scheme and critical parameters for the building structure satisfied the requirements of seismic performances from the codes.

The steel truss arch is an important structural type for high-speed railway bridges with long spans. The fatigue assessment of rigid hangers under long-term train loads is an important concern. In this study, the Nanjing Dashengguan Bridge, a six-line railway steel arch bridge with three planes of truss arches and the largest span in the world, was taken as a case study. First, a fatigue assessment of one short hanger was carried out based on dynamic strain monitoring data in 2015. The influence of bending behavior, train lane, number of carriages, and train speed on the fatigue performance of the short hanger were investigated. Second, the fatigue damage distribution of full-field hangers induced by a single train was analyzed based on a calibrated finite-element model. The influence of driving direction on the fatigue performance of rigid hangers was discussed. Finally, an engineering approach for fatigue performance assessment of full-field hangers was proposed based on annual train volume. Consequently, it was shown that the bending behavior has considerable influence on the fatigue effects of short hangers. In addition, train lane and driving direction also have a significant influence on the fatigue performance of hangers. The fatigue damage of short hangers in the middle truss arch was the most remarkable, followed by the side truss arch on the downstream side (the Beijing–Shanghai High Speed Railway) and then by the side truss arch on the upstream side (the Shanghai–Wuhan–Chengdu Railway), which should be paid greater attention to in daily maintenance.