Browsing by Author "Connor, Robert J."

Now showing 1 - 3 of 3
  • Thumbnail Image
    Dynamic Fracture and Crack Arrest Toughness Evaluation of High-Performance Steel Used in Highway Bridges
    Collins, William N.; Yount, Tristan D.; Sherman, Ryan J.; Leon, Roberto T.; Connor, Robert J. (MDPI, 2023-04-26)
    Impact energy tests are an efficient method of verifying adequate toughness of steel prior to it being put into service. Based on a multitude of historical correlations between impact energy and fracture toughness, minimum impact energy requirements that correspond to desired levels of fracture toughness are prescribed by steel bridge design specifications. Research characterizing the fracture behavior of grade 485 and 690 (70 and 100) high-performance steel utilized impact, fracture toughness, and crack arrest testing to verify adequate performance for bridge applications. Fracture toughness results from both quasi-static and dynamic stress intensity rate tests were analyzed using the most recently adopted master curve methodology. Both impact and fracture toughness tests indicated performance significantly greater than the minimum required by material specifications. Even at the AASHTO Zone III service temperature, which is significantly colder than prescribed test temperatures, minimum average impact energy requirements were greatly exceeded. All master curve reference temperatures, both for quasi-static and dynamic loading rates, were found to be colder than the Zone III minimum service temperature. Three correlations between impact energy and fracture toughness were evaluated and found to estimate reference temperatures that are conservative by 12 to 50 °C (22 to 90 °F) on average for the grades and specimen types tested. The evaluation of two reference temperature shifts intended to account for the loading rate was also performed and the results are discussed.
  • Thumbnail Image
    Fracture Resilience and Redundancy of Built-up Steel Girders
    Hebdon, Matthew H.; Connor, Robert J. (American Institute of Steel Construction, 2016-04-15)
    Internal member redundancy provides built-up steel girders with the ability to resist total member failure in the event an individual component fails. Anecdotal evidence of in- service performance has historically shown this to be the case in many bridges. However, due to the lack of experimental data, these members are currently required to be inspected as fracture-critical when deemed non-redundant. The full-scale experimental and analytical research program described in this paper provides needed information on parameters that affect the ability of built-up members to arrest a fracture, as well as describing the length of the remaining fatigue life. The results from this study have been used to develop recommended assessment procedures for built- up flexural members when a component has failed. Proposed evaluation guidelines will permit bridges with built-up steel girders where sufficient capacity exists, and the fracture critical designation can be removed, to be inspected using a rational in-service interval and level of detail. Considering the large number of riveted fracture critical bridges in the inventory, both highway and railroad bridge owners will benefit from this research since it allows for implementation of a more rational inspection strategy without compromising safety and reliability. The strategy provides a more integrated approach to inspection that accounts for the probability of detection capabilities, fatigue life, and fracture resilience. Further, new members utilizing high-strength bolted built-up members have the potential to be used without the penalty of being classified as fracture critical in terms of inspection
  • Thumbnail Image
    Towards a Better Estimation of Inspection Intervals for Cracking Steel Railroad Bridges
    Hebdon, Matthew H.; Connor, Robert J. (American Railway Engineering and Maintenance-of-Way Association, 2015-10-05)
    In order to best prioritize limited funds for railroad bridge capital and maintenance, it is important for the bridge engineer to have an accurate estimate of service life for existing steel bridges. In the context of the paper, “service life” is affected by several damage modes such as corrosion, fatigue and fracture as well as other factures such as redundancy. Use of conservative bridge design loads and conservative computation methods can result in an estimated steel bridge life that is inappropriately short, resulting in less-than- optimal allocation of limited funds. Methods recommended to achieve more appropriate life estimates are based on recent research on riveted steel bridge members, as well as inspection and life estimation procedures used in the aircraft and pipeline industries. Collectively these practices are sometimes referred to as Fitness-for-service (FFS). Implementation of FFS allows consideration of inspection policies and trending of inspection, redundancy, material toughness, and statistical variability of loads and member performance. Considerable efforts underway for highway bridges are providing valuable input to the process. Testing of steel bridges at FAST and in revenue service, as well as laboratory testing at Purdue University, is providing additional data for development of new recommendations for better life assessment of steel railway bridges. The recommended procedures utilize an implementable FFS approach that links inspection, fatigue, and material fracture toughness to perform a risk-based assessment of an individual bridge or an entire inventory.