Stress concentrations at longitudinal-transverse stiffener plate intersections

Abstract

While the NCBRP program has evaluated the fatigue strength for many of the welded details that are typically used in highway bridge construction, only those details which have been the subject of recent research projects are specified in the AASHTO Standard Specifications for Highway Bridges (1992). Many existing details resemble those currently covered by specification, but closer inspection of these details reveals inherent differences. A coped longitudinal attachment intersecting a transverse stiffener is an example of such a detail. In order to measure the severity of different intersection geometries, the finite element stress analysis method was used in order to obtain the SCF for each detail. The SCF for each coped detail was compared to that of a base model with no cope. The non coped model signifies the SCF that correlates to an AASHTO Category E detail. The SCF for a Category C detail was also obtained. The severity of the cope detail was determined by the relationship of its SCF to the SCF of the Category C and E detail. The studied parameters for this investigation were gusset plate width, size of the cope, and the thickness of the gusset and web plate. From this investigation several conclusions could be made. The cope in the longitudinal plate should not be smaller than one inch. Smaller gap sizes can reduce the fatigue strength of the detail when compared to a slightly larger cope size. As the cope size is reduced, the two welds come close together and the SCF for each weld toe superimposed on each other. The close proximity of the weld can also lead to large restraint forces in the weld region, which also reduces the detail's fatigue strength. The best possible category for a detail with a cope is Category D. However, depending on the size of the cope and thickness ratio between the plate and web, this category can be reduced to Category E. An equation was developed that would predict the AASHTO fatigue category for a given plate width, cope size, and thickness ratio.