Extending Bridge Service Life Through Field Welded Repairs and Retrofits (2016)

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5 NCHRP in the 1970s to study the effect of cyclic loading on the fatigue performance of welded connections (Fenves et al. 2005). As a result, design requirements were revised to include consideration for fatigue in welded connections for shop and field welding. Field welding on bridges began to occur more frequently in the early 1960s and into the 1970s. During this time, steel bridges were designed with a goal of assembling bridges in the field without the use of permanent bolts. Girders were prefabri- cated in a shop and delivered to the construction site for erection. In many cases, the only bolts needed were the erection bolts to help secure in place the various components such as girders and bracing. Once erected, the girders were temporarily sup- ported so that field splices on the girders could be field welded in the erected position. In general, these were intended to be complete joint penetration (CJP) groove welds that included the webs, top flanges, and bottom flanges. The bracing sys- tems, both vertical and lateral bracing, were connected with field welds, often fillet welds. Field welding differs from shop welding for two main reasons: (1) the welding environment is not as controlled, and (2) the steel to be welded cannot be manipulated into position as easily as in the shop. Some of the in-service issues of field weld cracking and field weld failure could possibly be attributed to a lack of welding knowledge, inadequate knowledge of fatigue details, poor quality work, lack of nondestructive testing (NDT) to identify initial defects, and a lack of quality oversight. At this time, CJP welds were not often ground smooth, and there was no type of weld-access holes between the web and flange of the girders. Because of the field conditions, there was often a significant misalignment of members and, as mentioned previously, the erection bolt holes were often plug welded with poor quality welds. 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 varied 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 (both substanti- ated and unsubstantiated) regarding long-term performance, cost, or a lack of knowledge and experience. Agencies that allow field welding find that it is an effective tool for completing repairs within a short time. A design can BACKGROUND Prior to World War II, individual components of bridges in the United States were connected using mechanical fasteners, primarily rivets. During the war, welding became more pro- nounced in the fabrication of members owing to improvements in welding equipment, knowledge regarding the process, and welding applications to support the war effort. The significant transition to welded bridge structures took place post-World War II. Welding on bridges was introduced as early as 1934, when the first all-welded bridge was built in Middlesbrough, England (Sapp 2015). In 1936, the first specification for Design, Construction, Alteration and Repair of Highway and Railway Bridges was issued by the American Welding Society (AWS) (Sapp 2015). Welding on bridges in the United States was implemented in the late 1940s and 1950s, but was primarily limited to highway structures. During this time, bridge design and con- struction transitioned from members comprised of multiple components joined using mechanically fastened members (rivets or bolts) to fewer 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 required that mechan- ical fasteners be used when members were joined together in the field, whereas others allowed field welding in lieu of mechanical fasteners. Field welding included, for example, welding bridge girders at field splices, welding bracing in place, and attaching bearings. The transition from built-up, mechanical fastened mem- bers and connections to all welded members and connections led to issues with fatigue and fracture. Often, the same types of connection details were used, except that welds were substituted for mechanical fasteners. Because of the increased stiffness associated with welded joints, typically lower fatigue resistance, and general lack of understanding regarding fatigue of welded joints, unexpected cracking was observed. With construction of the Interstate Highway System in the 1960s, numerous steel bridges were built containing welded fatigue-prone details, with limited consideration for fatigue compared with current standards. As a result of the observed cracking during the AASHO Road Test and on sev- eral in-service bridges, considerable research was funded by chapter one INTRODUCTION

6 be developed quickly along with a simple set of specifications, and base material can be ordered to the required size. Concur- rently, welding procedures, required welder qualifications, acquisition appropriate weld metal, and access equipment needs can all be identified. When properly executed, a high- quality repair can be undertaken in a minimal amount of time with less disruption to the traveling public. SYNTHESIS OBJECTIVES The objective of this synthesis is to document planned field welded repair and retrofit solutions and practices that owners have used on existing steel bridges. The information contained in this document is intended to help bridge owners evaluate and implement solutions for successfully extending the service life of their bridges. SYNTHESIS SCOPE AND APPROACH This synthesis addresses various aspects of projects where field welding is being considered. The emphasis of this synthesis is planned field welded repairs and retrofits where consideration was given to design, specifications, procedures, qualifications, and inspection requirements before performing work. Infor- mation has been collected regarding when to implement this technique; current related manuals, codes, and specifications; quality assurance and quality control practices; performance of field welded repairs and retrofits; and effective practices for field welding. This synthesis presents current practice in the following specific areas: • General information on field welding internal policies and practices of each agency surveyed; whether they allow field welding currently, allowed it previously, or will not allow field welded repairs and retrofits on their bridges. • The agencies that have standard field welding plans, specifications, procedures, or details and the frequency of field welded projects that have plans or specifications prepared before field welding is performed. • The typical requirements for characterizing the chemistry and grade of the base metal, as well as the typical tech- niques used to verify weldability of the base material. • How often governing specifications and welding codes are specified for field welded projects and the typical welding codes used for field welding. • Types of field welded repairs and retrofits and the fre- quency of each type. • Information on the typical field welding design and welding staff, including whether the welders are from internal staff or outside contractors and whether the welders are certified according to the requirements of the applicable welding code. • The typical quality assurance and quality control prac- tices including welder qualifications and qualification programs, welding procedure development and quali- fication, inspection requirements and procedures, and inspector qualifications. • The in-service performance of field welded repairs and retrofits including the number of agencies that have had projects with major problems and the typical prob- lems that occur. • The effective practices and lessons learned by agencies that have performed field welded repairs and retrofits. Information for this synthesis was obtained from three sources. 1. A literature review was performed to provide back- ground information on the state of practice of field welding for repair and retrofit and 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) for each of the 50 states and the District of Columbia requesting information on their field welding practices. A total of 43 states (86%) responded to the survey. 3. Finally, telephone interviews with representatives from six departments of transportation (DOTs) were con- ducted to acquire additional information on effective practices and lessons learned, along with information on specific field welding projects, which are used as case examples. These six DOTs 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 location. SYNTHESIS ORGANIZATION This synthesis is organized into five chapters: • Chapter one introduces the synthesis, providing back- ground information and summarizing the scope and organization of the document. • Chapter two presents and summarizes the findings from the literature review. • Chapter three presents the results of the survey of the state of the practice. The results are presented in the following topic areas: – Extent of field welding, – Current manual and specifications,

7 – Quality assurance and quality control, and – Performance of repairs and retrofits. • Chapter four summarizes the information provided by the six agencies that were interviewed for the case exam- ples. The results are presented in the following topic areas: – Extent of field welding, – Current manual and specifications, – Quality assurance and quality control, – Performance of repairs and retrofits, and – Effective practices and lessons learned. • Chapter five concludes the reports with a summary of key observations from the findings and suggestions for further research and outreach in field welding. • Three appendices are included: Appendix A provides links to the responding DOT agencies, Appendix B provides a copy of the questionnaire that was dis- tributed electronically to the state participants, and Appendix C presents the responses by state for each of the questions posed to the survey participants. All appendices are available in the online version of the report.