Bridge Analysis, Design and Repair
339203 - Repair of Steel Bridge Girder Subjected to Distortion-Induced Fatigue Using both Steel Retrofit and CFRP Composites
Saturday, April 21
8:00 AM - 9:30 AM
Fatigue damage in steel bridges can result in localized cracking in the structure, causing frequent inspections and costly maintenance and repairs. As highway demands increase and economic constraints further tighten, the need for cost-effective, practical retrofits becomes evermore urgent. One of the most common types of fatigue damage is distortion-induced fatigue. Distortion-induced fatigue commonly occurs at connections of transverse structural members and is thought to be responsible for up to 90% of fatigue cracking in steel bridges. Due to the lack of connection between the girder flanges and the connection stiffeners in steel bridges constructed before 1985, many of these structures have experienced distortion-induced fatigue in web gap regions.
While many methods have been developed for mitigating distortion-induced fatigue cracking, the majority are invasive and disruptive to traffic. Therefore, repair techniques that can effectively repair distortion-induced fatigue damage in steel bridges with minimal disruption to the traveling public are needed. A new retrofit for distortion-induced fatigue, the ‘angles-with-plate’ retrofit, does not produce interference with the concrete deck and can be installed while traffic is maintained. This retrofit consists of two steel angles that are bolted to the transverse connection plate and the web of the steel girder, and a steel plate which is bolted to the opposite side of the web.
On the other hand, strengthening steel structures using externally bonded Carbon Fiber Reinforced Polymers (CFRP) has received much attention over the last decades; however, little research on strengthening steel bridges subjected to distortion-induced fatigue with CFRP materials has been carried out. Unlike many traditional repair methods for distortion-induced fatigue, CFRP is less intrusive during the repair process since it can be glued in place, rather than requiring bolting or welding. Moreover, repairs made by bonding CFRP contribute minimal additional weight to the structure and introduce less stress concentrations as compared to mechanical fastening.
The objective of this study aims to study the fatigue behavior of steel bridge girders repaired with a combination of the ‘angles and plate’ retrofit and CFRP composites. A CFRP layer was added to the previously-developed retrofit to engage the girder flange without requiring bolting or welding. The scope of this study includes experimental fatigue testing of a 9-ft long steel plate girder to investigate the performance of the combined retrofit in reducing distortion-induced fatigue crack susceptibility. Additionally, computational simulations were performed using the commercially-available software Abaqus to model the retrofitted girder. The models were used to characterize the efficiency of the combined retrofit and the expected failure mechanism of the CFRP portion of the retrofit.
This presentation is expected to be of interest to designers and academicians, and aims to further expand the available ‘toolkit’ of repair technologies for distortion-induced fatigue that are implementable with minimal disruption to the traveling public.