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

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41 remelt the metal at the weld toe to improve the fatigue resistance. • Capacity strengthening typically involves a retrofit to increase capacity resulting from a poor load rating, such as adding stiffeners to increase shear resistance. These repairs are employed in cases where the members were designed to support a lighter load than required under current specifications and are distinguished from those where damage of some kind exists. • Corrosion and impact damage strengthening include repair or retrofit of damaged members. These members may have corrosion damage that has resulted in signifi- cant section loss and either require additional stiffening or complete replacement of the member. The specific welding code to be applied to bridge field welding may vary from state to state. Two primary welding codes are used for structural welding of steel structures in the United States: • 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 required for fabrication of buildings and other structures. The American Welding Society (AWS) has published a guidance document for the strengthening and repair of existing structures as AWS D1.7 Guide for Strengthening and Repairing Existing Structures. Welder qualification programs are instituted by many state departments of transportation (DOTs) where the welder qual- ification tests are conducted or witnessed by state represen- tatives and a record of field welders who have successfully passed the qualification test are entered into the department’s database. These DOTs require that all personnel performing field welding on their construction project pass the welder qualification process and be documented as qualified welders. Many of the state agencies had field welding inspection guides that included information to aid weld inspectors. The quality of the field welds is a concern that was raised in multiple references. Quality control can be more diffi- cult to maintain under field conditions; however, the qual- ity requirements are the same for both field welds and shop The objective of this synthesis was to document practices and solutions associated with field welded repairs on existing steel bridges that owners have used. The information gathered dur- ing this synthesis included the extent to which field welding is performed on existing steel bridges, the common types of field welded repairs and retrofits, and manuals or speci- fications used for field welded repairs and retrofits. Quality assurance and quality control practices were also investigated, including welder qualifications and testing, material identifi- cation, welding procedure development and qualification, and verification inspection. The in-service performance of repairs and retrofits was also reviewed. Field welding is welding of a material outside of a fabri- cation shop and typically occurs at a bridge site. Welding on bridge structures in the United States was implemented in the late 1940s and 1950s, but was primarily limited to highway structures. Historically, field welding on highway bridges began to occur on a more frequent basis in the early 1960s into the 1970s. During this time, bridge design and construction transitioned from members comprised of multiple components joined using mechanically fastened members (rivets or bolts) to few elements joined using welds. Welding took place pri- marily in fabrication shops and sometimes in the field. Field welding differs from shop welding for the following reasons: the welding ambient environment where field welding occurs is not as controlled as the environment in a bridge fabrication shop and the configuration of the steel to be welded cannot be manipulated into position easily. Protection from wind and moisture can be an issue, although protection can be provided by constructing a temporary enclosure around the repair site. Vibrations from live load traffic and dead load residual stress can also be an issue. Field welding for the purposes of repair and retrofit is often performed as repair strategy to mitigate cracks that occurred as a result of these various conditions. The literature review revealed that field welded repairs are performed on structures for three primary reasons: fatigue improvement, capacity strengthening, and corrosion and impact damage repairs or retrofits. • Fatigue improvement typically includes retrofit of out-of-plane and distortion-induced cracking by weld- ing the connection stiffener to the flange. In most cases, the welding is on the tension flange. Along with field welded retrofits for out-of-plane cracking, gas tungsten arc welding, also known as TIG welding, can be used to chapter five CONCLUSIONS

42 welds. Similar quality control systems and practices are not in place in the field environment as they are in the shop environment. Research on field welding has been performed that utilized experimental testing of fatigue crack weld repair while under tensile stress or dynamic loading. These studies found that it is possible to carry out repair welding under dynamic loading, but that the preferred procedure was to close the bridge to traffic while the root pass and possibly a second pass of weld metal are deposited. Other research performed on the fatigue resistance of field welds has determined that repair welds had at least the fatigue life as the original shop weld, as long as proper procedures were followed to achieve a quality repair. Field welded repairs and retrofits that have been imple- mented on steel bridges and documented in literature have performed well in-service. Only one occasion of problems with a field welded repair or retrofit was found during the literature review and this was attributed to undersized and poor quality welds. To better understand the current field welding practices used by state transportation agencies, a survey of practice was conducted through NCHRP in cooperation with AASHTO. The survey was distributed to AASHTO Subcommittee on Buildings and Structures (SCOBS) voting members, who were encouraged to forward it to the person within the agency who would be most familiar with that agency’s field welding practices. The main findings of the survey are summarized as follows: • Seventy-four present of the agencies surveyed allow planned field welded repairs and retrofits to be performed. • Of the agencies that do not currently allow planned field welded repairs and retrofits, only two have previously performed field welding. • Although a large number of agencies responded that they allow planned field welded repairs and retrofits, only six provided case examples of field welded projects that met the scope of this project. • States as far north as Alaska, North Dakota, Minnesota, and Maine allow field welding. There does not appear to be a correlation between lowest anticipated temperatures and general geographic location and the propensity for field welding. • Quality of work was the most common reason chosen for why agencies do not allow field welding. • Most agencies contract out their field welding projects. • Most agencies require the use of a governing specification or welding code: – Eighty-one percent that require a weld code specify AASHTO/AWS D1.5 Bridge Welding Code. – Thirteen percent that require a weld code specify AWS D1.1 Structural Welding Code even though AASHTO/AWS D1.5 is specifically developed for bridge welding and is specified for bridge fabrication. • Fewer than half of the agencies responded that they “always” require base material property determination before field welding: – The most common method for determining base material properties was by using date built information. – The use of shop drawings was the second most com- mon method to determine base material properties with removal of material samples. – Use of date built information and shop drawings will not provide the actual chemical makeup of the material. • A majority of agencies used welders certified according to the controlling welding code for the field welding on their projects. • Less than one-third of the agencies “always” require welding inspectors, including inspections that may not be done until after the welding process is complete. • Seventy percent of survey respondents reported that there have been no major problems associated with repairs and retrofits specifically because they were field welds. • Only four agencies mentioned that they have had major problems with repairs and retrofits specifically because they were field welds: – The most common issue was premature cracking, which was selected by three of these four agencies. – Improper welding and quality workmanship issues were the next most common, selected by two of the four agencies. The six case examples discussed a variety of types of field welded repairs. Included were repairs for impact damage, corrosion, and out-of-plane bending. All of the agencies inter- viewed reported a positive outcome from the field welded repair and plan to continue to implement field welded repairs on future work. There were no follow-up problems reported with the field welded repairs and these repairs were reported to be cost-effective. • Connecticut DOT does a significant amount of field welding and endorses it as a repair method. • Illinois DOT emphasized that it is important to clearly identify all welding requirements in the contract plans. • Maine DOT reported good success with field welded repairs. • Massachusetts DOT endorses field repair welding and reports the following effective practices: the use of cer- tified welders, the use of approved welding procedures, and having a certified weld inspector on site. • Tennessee DOT has performed multiple field repair welds and endorses the continued use of field welding. The agency has found that the most effective practices for field welding are: good inspections, requiring quali- fied welders with experience in bridge welding, and requiring written weld procedures. • Texas DOT frequently performs field repair welding on existing bridges. The agency has a welder certification program and allows only certified welders to perform

43 field welding. All welders are to be certified. The agency emphasized the importance of having an expert certi- fied weld inspector on site full time while the work is being done. Similar points of emphasis were reported by the agen- cies when asked what was important in achieving a positive outcome to a field welded repair or retrofit. When asked to share some lessons learned, the agencies suggested a variety of items they either corrected, would do differently, or would require on future projects. • Illinois, Connecticut, and Texas DOTs reported that they would not do anything different. • Massachusetts DOT stressed the importance of correct details and specifications. • Maine DOT highlighted the importance of good weld- access holes for the welder. • Tennessee DOT emphasized the importance of hiring a contractor that was experienced in field welding and the importance of qualified inspection. The results of the synthesis identified the following gaps in current knowledge that could be addressed by the research activities: • Identify the effective practices performed by the states that have used field welding correctly. • Monitor actual field welded repairs and record data on how the fatigue life of the repair may be influenced by environment, vibration, dead load and live load stresses, and quality.