Fatigue and Fracture Research Group
 

Parametric Analysis of Cross-Frame Layout on Distortion-Induced Fatigue in Skewed Steel Bridges

Pooled-Fund Study: CA, FHWA, IA, IL, KS, NJ, NY, OR, PA, WA, WisDOT, WY participating

 
Cross-frame layouts studied: (a) Skewed-parallel; (b) Skewed-staggered; (c) Skewed-unstaggered
 

Drs. Bennett, Matamoros, Rolfe, and Barrett-Gonzalez are working on a project to investigate the effectiveness of different treatments on the fatigue performance of bridge details under distortion-induced fatigue loading.

The effect of skew angle, cross-frame spacing, cross-frame layout, cross-frame stiffness, and load placement on the potential for distortion-induced fatigue damage in steel bridges was investigated by performing a suite of more than 1,000 analysis jobs of high-resolution 3D finite element models. Bridge configurations with different cross-frame layouts were evaluated, including configurations with cross-frames placed parallel to skew angle (skewed-parallel) and perpendicular to the girder line, both staggered (skewed-staggered) and unstaggered (skewed-unstaggered). Skew angles of configurations evaluated ranged between 0 and 50 degrees, and cross-frame spacing ranged from 7.5 ft to 30 ft.

Finite Element Model - View of the overall skewed bridge layout with staggered cross-frames.


FInite Element Model - Deformed shape of bridge with skewed-parallel cross-frame placement

FInite Element Model - Deformed shape of bridge with staggered cross-frame placement

Influence and envelope surfaces were constructed to show the relationship between load placement, location of the maximum web gap stress, and the magnitude of the maximum web gap stress. It was found that the maximum web gap stress always occurred when loads were positioned directly above the intersection of a cross-frame and girder web. The parametric study showed that cross-frames stiffness and spacing had a significant effect on the susceptibility to distortion-induced fatigue damage; greater cross-frame stiffness resulted in higher web gap stresses, and increased cross-frame spacing resulted in increased web gap stresses.

It was also found that bridge configuration was key to determining the location of web gaps where damage is most likely to occur. In skewed-parallel and skewed-unstaggered layouts, maximum web gap stresses were identified in top web gaps, while in skewed-staggered configurations maximum stresses occurred in bottom web gaps.


More information concerning this study, including quarterly progress reports, can be found on the Transportation Pooled Fund  website.