APPLICATION OF ANGLES-WITH-PLATE RETROFIT IN REPAIRING DISTORTION-INDUCED FATIGUE DAMAGES IN STRINGER TO FLOORBEAM CONNECTIONS AND SKEWED GIRDER TO CROSS-FRAME CONNECTIONS

Abstract

Caused by secondary stresses, distortion-induced fatigue is a serious problem faced by many aging bridges. The angles-with-plates retrofit developed at the University of Kansas has shown its potential to effectively and cost-efficiently repair distortion-induced fatigue damage in straight girder to cross-frame connections (Bennett et al. 2014). The performance of the retrofit in this application motivated the researchers to investigate its performance in other types of connections susceptible to distortion-induced fatigue. This thesis consists of two parts. Each part includes a description of two physical tests and a series of computer simulations. Part I describes an investigation on single-plate and double-angle stringer to floorbeam connection subassemblies. Part II describes a study conducted on 20-degree and 40-degree skewed girder to cross-frame connection subassemblies. Both studies were aimed at evaluating the efficacy of the angles-with-plate retrofit in repairing distortion-induced fatigue damage. The efficacy of the angles-with-plate retrofit in stopping fatigue crack propagation was evaluated through physical tests. Cyclic loads were applied on the connection subassemblies to initiate and propagate fatigue cracks. The angles-with-plate retrofit was then applied to repair the damaged connections. Computer simulations of the tested specimens were used to quantitatively analyze effectiveness of the retrofit in reducing stress demands at damaged regions. The results indicated that the angles-with-plate retrofit can efficiently mitigate distortion-induced fatigue damage in these connections. In the tests of the single-plate connection and the skewed girder to cross-frame connections, the retrofit successfully stopped the development of fatigue cracks. The computer simulation results indicated that in the single-plate connection subassembly, the retrofit was able to reduce the peak stress at cracks in the floorbeam web by 80% and by 90% for cracks at the floorbeam web-to-flange weld; in the skewed girder to cross-frame connection subassemblies, the retrofit reduced the peak stress in the 20-degree connection and 40-degree connection by 56% and 66%, respectively (Chen 2015). The double-angle connection subassembly did not show any sign of fatigue damage, therefore, the retrofit was not tested on it.