ABSTRACT
Two USA-based AASHTO Guide Specifications were published in 2018, with 2022 interims. They offer the analytical framework needed to revisit the way we evaluate redundancy in steel bridges considering system-level and member-level redundancy for new or existing bridges. For the last four decades, the steel bridge industry in the United States has become accustomed to determining redundancy through engineering judgement married to a single approach, namely load path redundancy (referring to the number of primary girder lines). Publication of these new AASHTO Guide Specifications enables designers and owners to design outside the box that we put ourselves in 40 years ago. In addition, the Guide Specifications also include a methodology to establish an inspection interval for a special inspection of internally redundant members (IRMs) that is of sufficient depth to reliably detect a severed component. This is a major departure from the calendar-based approach to setting inspection intervals and is a big step toward developing an integrated fractur control plan. This paper discusses the development of the AASHTO Guide Specifications for internal redundancy, exploring the historical context and providing a working example of how the evaluation of an existing structure could demonstrate inherent redundancy previously not considered within the US bridge industry.
