Introduction Corrosion is the leading cause of deterioration of steel bridges in the United States. According to the National Association of Corrosion Engineers (NACE), the costs associated with maintenance and replacement of highway bridges was estimated to be over $13 billion per year in 2002. While this statistic includes both steel and concrete bridges, it is also quite old. Even if one were to assume that 1/5th of this estimate applies to steel bridges, it is still a staggering expenditure, especially when one considers inflation to 2018 dollars. A specific form of corrosion that is of particular concern is that related to crevice or “pack-out” corrosion. The photograph below illustrates the effects of typical pack-out corrosion commonly observed in riveted built-up members. As a result of the accumulation of corrosion product, individual plate components are pushed apart. The forces generated can be excessive and in extreme cases, fastener heads have been known to “pop” off. In some cases, as shown below, individual plates have cracked due to the signification prying forces generated. A literature review has confirmed that there are no codified procedures available to assist owners with the assessment of the effects of pack-out corrosion in built-up steel members. As a result, decisions regarding the need for repair, load posting, or other potential actions must be made almost entirely based on engineering judgement coupled with basic engineering calculations and many assumptions. Finally, while there are various means which have been used to repair members which have been damaged by this form of corrosion, little guidance exists on what approaches are most appropriate.

Objectives and Impact The objectives of the proposed pooled-fund study are as follows: 1) To develop AASHTO ready specifications for the evaluation of the effects of pack-out corrosion in built-up steel tension, compression, and flexural members. 2) Provide guidance on the need for repairs and corrosion rates that can be expected in various environments in order to assist owners in programming when repairs may need to be made. 3) Identify the most effective methods of repairs and provide suggesting verbiage that could be used when preparing special provisions for repairs. 4) Develop several case-study examples, including calculations that will be used for training users on the methodologies to be developed. It is anticipated that the research team will host a number of webinars or on-site training sessions to ensure technology transfer and implementation. 5) The impact of this study is obvious considering there is no such quantitative guidance available at present. The results of the work will allow owners to accurately assess the effects of this form of corrosion on various limits states (e.g., strength, fatigue, buckling, etc.) in built-up steel members. Both flexural and truss-type members will be studied. The ability to program repairs based on data-driven models allows for the best possible use of limited maintenance funds and safely extend the life of the existing inventory.

Research Tasks To achieve the proposed objectives, the following tasks are proposed: Task I – Perform a thorough literature review of both domestic and international research on pack-out corrosion, how various owners have addressed this problem, repair strategies, and collect data on corrosion processes and rates. Task II – Develop a laboratory experimental program that will include large-scale testing of members which contain damage due to pack-out. At present, the research team will explore the use of both simulated pack-out (i.e., newly fabricated components with induced local distortions that simulate pack-out) and “natural” pack-out by obtaining members from various bridge being removed from service. The effects of temperature on the performance of damaged members will also be included in the laboratory testing as the fracture toughness of some older steels is minimal at low temperatures. In this regard, testing of tension and flexural members will be completed at cold temperatures. The benefits of internal redundancy will also be examined. Finally, various mitigation strategies will also be investigated. While there are a number of anti-corrosion products currently available on the market, it is not clear how to evaluate the effectiveness of these products. Therefore, a portion of the work will focus on the evaluation of such products and to subsequently develop methods to assess the short- and long-term effectives of such products. Task III – As data become available from Task II, the research team will conduct numerical (FEA) parametric studies to allow a wider range of damage to be evaluated under various geometries and loading conditions which are not possible to include in the laboratory studies. It is noted the research team at Purdue University has gained extensive experience in the laboratory testing and calibrated non-linear FEA of built-up steel members during the development of the recently published AASHTO Guide Specifications for Internal Redundancy of Mechanically-fastened Built-up Steel Members. Task IV – Based on the results of Tasks I through III, proposed guide specifications for the evaluation of the effects of pack-out corrosion will be developed for consideration by AASHTO COBS. The research team has considerable experience in the development of AASHTO Specifications and has worked very closely with various AASHTO subcommittees to ensure all stakeholders, including FHWA, are involved and have input. Task V - In addition to developing the Guide Specifications, a methodology to estimate the interval from when “non-critical” pack-out becomes “critical” pack-out corrosion will be developed. This information will be particularly useful to owners when programing funding for future repairs. Finally, guidance on the best practices for the repair of pack-out corrosion, when deemed required, will also be compiled. Task VI – Develop training materials to ensure the results are disseminated and the research is moved into practice. Task VII – Summarize the results of the research in a detailed Final Project Report.

Funding and General Information The Indiana Department of Transportation (INDOT) is leading this Pooled Fund Effort and has already committed funding for the project. Several other states have indicated their interest in joining the study. The funding level requested per partner is $40k per year for three years to facilitate Tasks I through Task VII. While this may be a larger commitment than is typically associated with a TPF project, there is considerable large-scale testing associated with this research. As stated, the research team anticipates obtaining full-scale members from existing bridges which include pack-out corrosion. While this greatly improves the laboratory test matrix, this will also require some unique fixtures to load some specimens and shipping of specimens, which will add cost. The total estimated minimum funding level, including approximately $120,000 from INDOT is $600,000. Thus, it is assumed that at least four (4) additional sponsors will join this study. Facilities at Purdue The team at Purdue University is uniquely equipped to perform the proposed research due to the existence of the Bowen Laboratory for Large-scale Civil Engineering. The photographs below show just an overview of this unique facility available to the research. Capabilities include axial loading frames and jacks capable of testing up to 60 foot long members at loads of over 2,000 kips in tension or compression. Flexural and fatigue testing capabilities are also significant and girders as long as 40 can easily be fit into existing load frames. Further, several members presently located at the S-BRITE Center, which contain various levels of pack-out corrosion, are already available to the project for evaluating repair strategies on full-scale members and possibly even laboratory testing. Research Team Purdue University Research Team • Robert J. Connor, Professor of Civil Engineering and Director of the Steel Bridge Research, Inspection, Training, and