Principal Investigator: Salam Rahmatalla
About this Project
Brief Project Description & Background
Thousands of old multiple-steel-girder bridges were built in the U.S., and are vulnerable to fatigue cracking (Connor and Fisher 2006; Fisher, 1997; Al-Emrani and Kliger, 2009; Lu et al., 2010). Fatigue cracking normally occurs due to poor detailing and out of plane relative displacement, mostly in the web area of the girder-floor beam connections. The implementation of retrofits to stop fatigue crack growth in steel girder bridges has shown variable success. The “stop-holes” (Grondin and Kulak, 2010) retrofit, where holes are drilled at the tips of existing cracks, has been customarily adopted by many DOTs across the U.S. as a common repair practice for highway bridges. While stop-holes are an effective method to stop fatigue crack growth, the choice of stop hole sizes and locations relative to the crack tips may still contribute to a short solution to the problem (Cousins et al., 1998). Indeed, field studies (Wipf et al., 1998; Tarries et al., 2002) have shown the tendency of some of these cracks to reinitiate and grow around the holes, which can potentially cause a real danger to the integrity and safety of a bridge. Therefore, there is a critical and urgent need for a comprehensive research project with a methodology that can detect crack reinitiation and growth in these critical regions of bridges, and predict the loading capacity and expected fatigue life of the connections so that repair planners can take the right repair steps for bridges with long life service.
The objective of this comprehensive research project is to develop a damage detection methodology that can detect crack reinitiation and growth in the critical regions of bridges, and predict the loading capacity and the expected fatigue life of the connections, so that repair planners can take the right repair steps for bridges with long life service.
The proposed research addresses a major safety issue in the U.S. highway system with a proactive repair action and modification plan that can be decided based upon the conditions of the retrofit fatigue cracks on a bridge. As a result of the proposed research, the repair plans of highway bridges can be stayed within the improved state of good repair, and will contribute to road safety and improve the economic competitiveness of the U.S. transportation system.
The deteriorated condition of retrofitted fatigue cracks on old multiple-steel-girder bridge connections can cause catastrophic consequences if the crack sizes go beyond acceptable limits, and therefore may require immediate action by bridge repair planners and emergency responders. Extensive efforts have been devoted to investigating the causes behind fatigue crack initiation and growth in girder-steel bridges, and several retrofit repair schemes have been suggested and implemented in the field, with varying levels of success. One effective way to stop fatigue crack growth involves drilling holes near the crack tips; however, due to uncertainties in operational loading conditions and optimal hole size, cracks can grow around these holes and cause potentially dangerous scenarios. Fatigue cracks can grow quickly and cause unexpected damage before the traditional biennial inspection can take place. Therefore, it is critical to remotely detect fatigue crack reinitiation and growth at retrofit connections to help emergency responders and repair planners determine the action that has to be taken. In the proposed project, an experimental-numerical vibration-based damage detection methodology will be evaluated with respect to its effectiveness in capturing and predicting fatigue crack reinitiation and propagation of retrofit connections. Extended finite element (X-FEM) models of the retrofit connections will be developed in which fatigue crack growth around circular holes can be modeled and investigated. The goal of this work is to help highway bridge repair and maintenance teams develop more cost-effective repair plans and safer infrastructures. Preliminary results of a current vibration-based damage-detection methodology are very promising when it comes to the methods ability to detect fatigue cracks in field applications.