Fatigue and Fracture Research Group
 

Enhancement of Welded Steel Bridge Girders Susceptible to Distortion-Induced Fatigue, TPF-5(189)

Pooled-Fund Study: KS, CA, FHWA, IA, IL, NJ, NY, OR, PA, WI, WYDOT participating

 
Exterior girder distorted due to relative deflection of an interior, connected girder
 

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.

 It is common for bridge girders to experience different vertical deflections than an adjacent girder at the same location on the bridge span.  Different deflections between girders can arise from skewed bridge supports and low load sharing between adjacent girders.  For example, if a vehicle drives across a bridge deck centered directly over one girder, it is likely that that girder will deflect more than a girder adjacent to it.  This problem is exacerbated with increasing span length and spacing between girders.  Differential deflection between adjacent girders can become a fatigue problem, depending on the configuration of the connecting elements tying the girders together. 

As one girder moves vertically relative to another, the lateral connecting elements can place large forces on the girder(s) and structural elements it is connected to.  These lateral forces result in out-of-plane stresses, which can be severe.  When loaded repeatedly, cracking can occur.  This type of fatigue loading is called distortion-induced fatigue, and it is the largest cause of cracking in steel bridges.

State DOTs are interested in retrofitting steel bridges that are susceptible to distortion-induced fatigue to improve their performance under these conditions.  Different methods of improving fatigue performance are being investigated in a large-scale experimental testing effort.  Techniques such as application of carbon fiber reinforced polymer (CFRP) elements and innovative steel retrofits are being investigated on an assemblage of three-dimensional, half-scale bridge girders connected with lateral cross-frames.  The interior girder of the group is loaded vertically and allowed to deflect relative to the two exterior girders until cracking forms in the exterior girders.  The crack(s) will be treated with one or more of the techniques described, and compared to untreated bridge systems. 

The outcome of this research project will be the development and proving of new retrofit techniques that can be used to extend the fatigue lives of existing steel bridges.

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