Fabrication procedure effects on fatigue resistance of rib-to-deck welded joints of steel orthotropic bridge decks.

摘要

Orthotropic steel bridge decks have been widely used for long- and medium-span bridges due to excellent structural characteristics. However, orthotropic decks have experienced various fatigue problems, resulting from high cyclic stresses in conjunction with inadequate welding details. In particular, crack at rib-to-deck welded joints due to wheel load is a concern because inspection and repair of the back side of this weld for closed ribs is not practical due to lack of access. Fatigue resistance of rib-to-deck joints can be significantly influenced by fabrication effects including weld melt-through and distortion control measures (for example, precambering and heat-straightening). Current design practice is to use empirical approach for fatigue safety assessments by conforming to the detailing requirements [for example, at least 80% partial-joint-penetration (PJP) weld at the rib-to-deck joint]. However, little experimental and analytical research has been done as to the codespecified requirements and fabrication procedure effects on the fatigue resistance of the PJP joint.;Six 2-span, full-scale orthotropic steel deck specimens (10 m long by 3 m wide) were fabricated and subjected to 8 million loading cycles to study the effects of both weld melt-through and distortion control measures on the fatigue resistance of the PJP joint. Test results showed that six cracks initiated from the weld toe outside the closed rib. Only one crack developed at the weld root inside the rib; this crack initiated from a location transitioning from the 80% PJP to 100% penetration. Weld melt-through appeared to be detrimental in fatigue resistance. Precambering was beneficial as two effectively precambered specimens did not experience cracking in the PJP welds.;Finite element analysis using effective notch stress method showed a good correlation with the observed crack pattern in testing. Bending stresses were dominant at the PJP joint; shear and membrane stresses were very small. Parametric study showed that the fatigue resistance of the PJP joint can be significantly influenced by transverse loading location, deck plate thickness, and weld penetration ratio. Increasing the deck plate thickness was efficient in reducing the stresses, while the rib plate thickness had a little effect. Shallower weld penetration at the PJP joint appeared to have a positive effect in enhancing the fatigue resistance.