Finite element study on bridge details susceptible to distortion-induced fatigue

Some bridges designed prior to the mid 1980s have experienced problems in the web-gap region, above plates connecting intermediate stiffeners to the girder web and below girder top flanges, due to differential deflections of adjacent girders. The effects from cross frames attached to girders subjected to these differential deflections are the cause of out-of-plane deformations or distortions, which are the driving force for fatigue cracks in the web-gap region. A few retrofits exist that focus on reducing or eliminating the magnitude of web-gap stress these include lengthening the web-gap with a slot repair or fixing the connection plate to the top flange creating a positive attachment. Both of these retrofits have been used with mixed results. Because of this, new retrofitting schemes were studied which utilized carbon fiber reinforced polymers (CFRP) to reduce the stress demand and achieve a more even distribution of stresses in web-gap regions by providing an alternative load path for secondary stresses. Finite element (FE) models were used to study the effectiveness of the new retrofit methods in comparison with the slot and positive attachment repair methods. The results of the FE models showed that the CFRP materials repair technique was more effective in reducing the magnitude of web-gap stress and web distortion than the other two aforementioned specimens.