Fatigue behavior of welded coverplates treated with Ultrasonic Impact Treatment and bolting Brian Vilhauer a , Caroline R. Bennett b,⇑ , Adolfo B. Matamoros b,1 , Stanley T. Rolfe b a 910 Par Ln., Dell Rapids, SD 57022, United States b University of Kansas, Civil, Environmental, and Architectural Engineering Department, 1530 W. 15th St., 2150 Learned Hall, Lawrence, KS 66045, United States article info Article history: Received 6 April 2010 Revised 23 February 2011 Accepted 4 September 2011 Available online 4 November 2011 Keywords: Fatigue Bolts Welds Cracking Rehabilitation Retrofit Ultrasonic Impact Treatment Cover plate Steel bridge abstract Damage due to traffic-induced fatigue is a common problem in welded steel girder bridges. Engineers tasked with the duty of repairing fatigue-damaged bridges face difficult decisions about the choice of repair method to implement. In some instances different repair methods are used in combination, under the assumption that the combined effects of two techniques that have been shown separately to improve fatigue life will result in greater improvement. This study evaluated the interaction that may take place between different repair methods for a particular type of fatigue vulnerable detail. The detail that was chosen for the study was a welded connection between a plate and a coverplate, often used in older bridges. Specifically, this study investigated the fatigue life enhancement afforded by three retrofit meth- ods: post-installation of tensioned bolts behind the weld, application of Ultrasonic Impact Treatment (UIT) to the weld, and a combination of the two techniques. Results of 15 fatigue tests showed that UIT was a highly effective technique to enhance the fatigue life of coverplate end details. Weld treatment with UIT resulted in an improvement in fatigue life over control specimens by a factor of 25. This translated into an improvement in fatigue life from that of an AASTHO fatigue Category E detail to that of an AASHTO fatigue Category A detail. The bolting procedure, as imple- mented in this study, had a negligible effect on fatigue life. The combination of the two methods was found to be less effective than using UIT alone due to stresses induced by the bolt on the untreated por- tion of the weld. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction Numerous aging steel highway bridges are currently developing cracks due to traffic-induced fatigue. Many of these bridges were designed at a time when little was known about the causes of fati- gue crack initiation and propagation in steel structures. As a result, structural connection details having fatigue–vulnerable combina- tions of geometric discontinuities and large stress ranges were used in these structures. Many of these details are now recognized as undesirable and are no longer constructed. However, state Departments of Transportation (DOTs) must repair existing fatigue cracks and retrofit susceptible connection details. Due to the escalating costs of bridge replacement coupled with the large num- ber of aging steel bridges with fatigue-susceptible details across the United States, means to efficiently extend the useable life of fatigue–prone steel bridges are critically needed. Welded connections in steel bridge girders account for a large percentage of fatigue critical details in the national inventory. Welds are particularly susceptible to fatigue cracking because of planar or volumetric discontinuities often present in the weld or base metal, such as porosity, slag inclusions, lack of fusion, and undercut [1]. Additional factors such as geometry-induced stress concentrations, residual stresses, and distortion tend to decrease the fatigue strength of welded connections. This is particularly worthy of consideration given that many common steel bridge gir- der connections utilize welded connections in a wide range of applications, including cover plates, transverse and longitudinal stiffeners, connection plates, flange transitions, and web-to-flange connections. Welded cover plates are of especial concern because this is a common detail particularly vulnerable to fatigue damage. Although welded coverplates are no longer commonly used to increase bending resistance of bridges, this was not the case 40 years ago. Many existing bridges were retrofitted with welded coverplates to increase their capacity as traffic loads intensified over time. It has since been found that welded cover plates tend to be particularly susceptible to fatigue crack initiation in the welds at cover plate terminations, and for this reason have been 0141-0296/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.engstruct.2011.09.009 ⇑ Corresponding author. Tel.: +1 (785) 864 3235; fax: +1 (785) 864 5631. E-mail addresses: crb@ku.edu (C.R. Bennett), abm@ku.edu (A.B. Matamoros), srolfe@ku.edu (S.T. Rolfe). 1 Tel.: +1 (785) 864 3235; fax: +1 (785) 864 5631. Engineering Structures 34 (2012) 163–172 Contents lists available at SciVerse ScienceDirect Engineering Structures journal homepage: www.elsevier.com/locate/engstruct