Temperature field data from the steel truss arch girder and longitudinal displacement data from six groups of rubber bearings were collected by the structural health monitoring system for the Dashengguan Yangtze Bridge. By using long-term monitoring data, two correlations are investigated: the linear correlation between the longitudinal displacement and the temperature field (including uniform temperature and temperature gradient); and the linear correlation of the longitudinal displacements in different locations. A multivariate linear regression equation is used to model the first correlation, and a Lagrange polynomial interpolation is used to model the second correlation. The final mathematical models, representing the healthy state of the bearings, can be applied to simulate the longitudinal displacements of the main girder. Furthermore, the change regularity of longitudinal displacements for the degraded rubber bearings is revealed taking advantage of a hysteretic model and presumed envelope ...

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...

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...

Taking advantage of the structural health monitoring system installed on the steel truss arch girder of the Dashengguan Yangtze Bridge, the monitoring correlation between strain and uniform temperature at night is obtained, and then the correlation analysis of wavelet packet decomposition is carried out, which can effectively decrease the discreteness of the monitoring correlation. After that, the whole finite-element model of the Dashengguan Yangtze Bridge is simplified into one top chord member, one diagonal web member, and one bottom chord member with imposed displacement movements on the supports. The simulated correlation between static strain and temperature is calculated using the flexibility equation of force method from the simplified finite-element model, which is close to the monitoring correlation, and the first-order derivative of flexibility equation is used to remove the influence of temperature action. Furthermore, the influence of degrading axial flexibility is analyzed, showing that the linear slopes $k_A\sim k_H$ are primarily affected by the degradation of chord members $\{T{C}_{a,-2},T{C}_{a,-1},T{C}_{a,0},T{C}_{a,1},T{C}_{a,2},T{C}_{a,3}\}$ , $\{T{C}_{b,-2},T{C}_{b,-1},T{C}_{b,0},T{C}_{b,1},T{C}_{b,2},T{C}_{b,3}\}$ , $\{B{C}_{a,-2},B{C}_{a,-1},B{C}_{a,0},B{C}_{a,1},B{C}_{a,2},B{C}_{a,3}\}$ , and $\{C{V}_{a,1}\}$ , and using the monitoring data, the method of detecting and locating the aging truss members is finally put forward.

The temperature differences in bridge structures have been one primary concern for bridge engineers and researchers. In the traditional view, the temperature differences between steel truss members are treated as uniform because of the good heat transfer characteristic of steel material and the shading effect of deck coverage. However, for some steel truss bridges, some truss members are directly exposed to solar radiation, while some other truss members are totally shaded by steel decks, which may cause obvious temperature differences between them, so it is reasonable to doubt the correctness of uniform temperature existing between steel truss members. In this research, the temperature differences between steel truss members in two long-span truss bridges are analyzed using long-term temperature field data, and after analysis, the temperature differences which contain obvious positive or negative values are made clear. Furthermore, the evaluation method of temperature differences in bridge service life for thermal action design is put forward together with the determination method of probability density function, and the evaluated temperature differences are further obtained after probability statistics analysis. Finally, the evaluated temperature differences are classified by sun radiation and steel deck coverage, and then compared with the specified values in the three specifications. The research results can provide important reference for current specifications and structural design, especially for steel truss bridges.