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EXTENDING BRIDGE SERVICE LIFE THROUGH FIELD WELDED REPAIR AND RETROFITS The objective of this synthesis is to document practices and solutions associated with field welded repairs on existing steel bridges used by owners. The report is intended to help bridge owners evaluate and implement solutions for successfully extending the service life of their bridges. The information gathered for this synthesis included, but was not limited to, the extent to which field welding is performed on existing steel bridges, the common types of field welded repairs and retrofits, and manuals or specifications for field welded repairs and retrofits. Quality assurance and quality control practices are also investigated including welder qualifications and testing, material identification, welding procedure development and qualification, and verification inspection. Finally, the in-service performance of repairs and retrofits and effective practices are presented. In the United States, welding on bridge structures was first implemented in the late 1940s and 1950s, but was primarily limited to highway bridge structures, not other bridge structures such as railroad bridges. During this time, bridge design and construction transitioned from members comprised of multiple components joined using mechanically fastened members (rivets or bolts) to a few elements joined using welds. Welding took place in fabrication shops and sometimes in the field, depending on how the bridge member and/or structure was designed and fabricated. Some agencies chose mechanical fasteners when members were joined together in the field, whereas others allowed field welding in lieu of mechanical fasteners. Field welding consisted of welding bridge girders at field splices, welding bracing in place, attaching bearings, etc. With construction of the Interstate Highway System in the 1960s, numerous steel bridges were built that contained welded fatigue-prone details with limited consideration for fatigue compared with current standards. Field welding for the purposes of repair and retrofit is often performed as a repair strategy to mitigate cracks that occurred as a result of these various conditions. Repair and retrofit field welding has also been used to mitigate distortion-induced and out-of-plane fatigue cracking and to strengthen areas of section loss or a limited capacity rating. Although field welding has been used successfully by some agencies, it is still not widely implemented because of concerns regarding long-term performance, cost, or lack of knowledge and experience. Information for this synthesis was obtained from three sources: 1. A literature review was performed to provide background information on the state of practice of field welding for repair and retrofit and to uncover previous research that was performed on this topic. 2. A survey was distributed to voting members of the AASHTO Subcommittee on Bridges and Structures (SCOBS) requesting information on their field welding practices. A total of 43 state departments of transportation (DOTs) responded to the survey, an 86% response rate. 3. Telephone interviews with representatives from six DOTs were conducted to acquire additional information on effective practices and specific field welding projects, which are used as case examples. SUMMARY
2 The six DOTs that were selected for the phone interviews were chosen based on several factors, including an expressed willingness to provide additional information; details on their specific field welded project(s) including type of damage, type of bridge, and type of bridge member; and varied geographic locations. The literature review found that field welding presents special challenges when compared with original shop fabrication. Concerns regarding overhead positioning of many field welding repairs were raised in multiple sources. Another of these challenges is the weldability of the steel, because it may be of unknown composition. The American National Standards Institute (ANSI)/American Welding Society (AWS) defines weldability as the capacity of material to be welded under the imposed fabrication conditions into a specific, suitably designed structure performing satisfactorily in the intended service. Any adverse fabrication conditions present in the field must be accounted for during a determination of the weldability of a material for field welding. Field welded repairs and retrofits will also likely involve welding of steels that have ASTM specifications that are out of date compared with current specified bridge steels. Of the 43 state DOT survey respondents, 32 (74%) noted that their agency allows for planned field welded repairs and retrofits to be performed. Of the 11 agencies (26.6%) that do not allow planned field welded repairs and retrofits, two have previously done field welding. The remaining nine agencies have never done field welding and do not currently allow it. States as far north as Alaska, North Dakota, Minnesota, and Maine allow field welding, and overall, there does not appear to be a correlation between lowest anticipated temperatures and general geographic location and the propensity for field welding. The survey results determined that two primary welding codes are used for the structural welding of steel structures in the United States: AWS Bridge Welding Code D1.5 and AWS Structural Welding Code D1.1. AASHTO/AWS Bridge Welding Code D1.5 is the welding code required for new fabrication of bridges by the AASHTO bridge design specification. AWS Structural Welding Code D1.1 is the welding code that is required for fabrication of buildings and other structures. The specific welding code to be applied to bridge field welding may vary from state to state. Various state DOT manuals that cover field welding were reviewed to determine any aspects that are typically included in these manuals. In general, welder qualification programs are instituted by each state DOT in which the welder qualification tests are conducted or witnessed by state representatives. Records of field welders who have successfully passed the qualification test are entered into the departmentâs database. The literature review revealed that one of the greatest concerns of field welding is the quality. Field welding requires the same quality control measures as shop welding; however, quality control is more difficult to maintain under field conditions. As discovered during the literature review, this concern was expressed in multiple references. One report stated that the inspection of repair welds is to be at least as thorough as when the bridge was orig- inally fabricated. This includes matching the current requirements for the methods and extent of the inspection compared with current bridge fabrication practices. According to the same report, visual welding inspection is the most important inspection method and is used on all repair welds, independent of the utilization of any other inspection methods. Welding inspectors are typically provided with the repair procedure and details, drawings or sketches, and acceptance criteria. Visual inspection is performed before, during, and after welding. The agencies surveyed for the case examples stress the importance of good inspection by qualified people. Each of these agencies perform visual inspection in-house by a Certified Weld Inspector or an experienced individual. Nondestructive testing (NDT) varied; some agencies contracted all testing out, whereas others performed a portion of the testing in-house and/or contracted the remainder out.
3 Agencies surveyed emphasized the importance of quality welders. The ability of a welder to produce a weld of acceptable quality can be verified through the use of welder performance qualification tests specified in the applicable welding code. The qualification is typically indefinite provided that the welder carries out similar work within a certain time period. However, this may vary depending on specific agency requirements. The agencies interviewed for the case examples often require additional welder qualification tests. The agencies surveyed for the case examples all stressed the importance of good procedures and proper qualifications. They required field procedures, welder qualifications, inspection procedures, visual and NDT inspector qualifications, and emphasized the importance of following the inspection requirements. Most of the agencies surveyed reported good results from field welded repairs. Agencies were asked whether there have been any major problems associated with the field welded repairs and retrofits. This question was put to all agencies that answered that they either allow planned field welded repairs and retrofits or have performed them previously, a total of 34 agencies. Twenty-four of the 34 agencies responded that there have been no major problems associated with repairs and retrofits specifically because they were field welds. Six agencies reported that it was not known whether there have been any major problems specifically because they were field welds and agencies that they have had major problems specifically because they were field welds. The most common issue with field welding among the small number of agencies that reported having major problems was premature cracking, which was selected by three of the four agencies. Improper welding and quality workmanship issues were the next most common, selected by two of the four agencies. Installation not in accordance with the plans and speci- fications was selected by one agency. All six agencies surveyed for the case examples reported good results from the welded repairs. Each of these agencies endorses the use of field repair welding and plan on continuing to do such repairs. They also reported that field welding is an economical repair method. The synthesis revealed that many agencies identified a lack of experienced inspectors and/or a lack of qualified agency supervisors or administrators to allow field welded repairs and retrofits in their program. The results of the synthesis identified the following gaps in current knowledge that could be addressed by further research activities: ⢠Identifying the effective practices performed by the states that have used field welding successfully; ⢠The second activity is monitoring actual field welded repairs; and ⢠Recording data on how the fatigue life of the repair is influenced by the environment, vibration, dead load and live load stresses, and quality.
