A FINITE-ELEMENT-BASED APPROACH TO MODELING CRACKING & REPAIRS FOR DISTORTION-INDUCED FATIGUE IN STEEL BRIDGES

Distortion-induced fatigue damage is a common problem in steel girder bridges built prior to the mid-1980s.The University of Kansas has studied and developed several retrofit techniques with an aim to determine the efficacy of different retrofit measures to mitigate the effects of distortion-induced fatigue and stop fatigue crack growth or slow the rate of crack propagation. One simple and commonly-used retrofit technique is the practice of drilling crack-arrest holes at the tips of cracks to smooth out the sharp crack tip, reducing the stress concentration and halting fatigue crack propagation. The practice of hole-drilling has existed for decades, but its application to distortion-induced fatigue cracking has not been adequately studied. Another technique discussed in this thesis, called the angles-with-plate retrofit, requires two angles providing attachment between the connection plate and girder web with a plate placed on the other side of the web to distribute out-of-plane forces. An appealing aspect of the angles-with-plate retrofit is the minimal traffic disruption required during retrofit application. Girder subassemblies were chosen for study to evaluate for the effectiveness of various retrofits using both analytical approach and experimental testing. This dissertation is divided into five parts and appendices. The first part is the introduction for the dissertation. The second part is analytical and experimental investigations of repairing fatigue damage in steel plate with adhesively bonded carbon fiber reinforced polymer (CFRP) overlays under tension loading. Parts 3 and 4 are analytical and experimental investigations of evaluating the uses of crack-arrest holes and angles-with-plate retrofit to effectively repair distortion-induced fatigue cracking on 3-m (9-ft) steel girder specimens under fatigue loading. Part 5 is the recommendations and synthesis. Part 2, Part 3 and Part 4 within the document contain particular formatting associated with published or expected publishing requirements. Part 1: Introduction Part 2: Use of CFRP Overlays to Repair Fatigue Damage in Steel Plates under Tension Loading Part 3: Effectiveness of Crack-Arrest Holes under Distortion-Induced Fatigue Loading Part 4: Evaluation of Three Computational Techniques for Quantifying Distortion-Induced Fatigue Crack Propensity Using Finite Element Analysis Part 5: Recommendations and Synthesis Part 2 was published in the Journal of Composites for Construction, American Society of Civil Engineers (ASCE), 2014.18. Part 3 was presented at the ASCE 2014 Structures Congress in April 2014 in Boston, Massachusetts. This research has been accepted for presentation and potential proceedings publication for the 16th European Bridge Conference in June 2015 in Edinburgh, United Kingdom. Part4is intended for future publication