Duncan Paterson

Cover plates are often added to existing (loaded) steel columns as an effective retrofit method for increasing their compressive design strength. Current bridge design specifications provide equations for calculating the compressive design strength of steel columns. However, these equations cannot be extended to calculate the design strength of retrofitted columns because they do not account for the effects of cover plates added to the existing loaded members. The authors previously investigated the fundamental behavior of retrofitted built-up steel double-box columns using the finite-element analysis approach and also developed and benchmarked a nonlinear inelastic column buckling (NICB) analysis approach that accounts for the mechanics of existing (loaded) built-up steel columns retrofitted by added cover plates. This paper presents the results of comprehensive parametric studies conducted using the benchmarked NICB analysis approach to evaluate the behavior and strength of retrofitted steel col...

The movable bridge crossing the Cumberland River in Nashville, TN has an overall length of 695ft with a center swing span that is 275ft out-to-out. Two fixed-position spans on each side of the swing span are 206ft from center-to-center of bearings. It was found that during routine operations the swing span would not completely close. Inspections noted that the adjacent ‘fixed’ span had started moving toward the swing span and creating points of interference. Additionally, it was concluded that the reason for the encroachment was deterioration of the pier’s core caused by scour. Since the location is subject to both heavy river and heavy rail traffic, there is effectively no downtime for the structure. Thus, all construction work was required to be performed within two 12-hour outages. Included herein are an overview of the bridge history, the sources of the span movement, the pier repairs, and the integrated geotechnical and structural collaboration used to reposition the span.

The 740ft Swing Bridge in Katharyn, KY was originally constructed in 1905 with a 338ft center-pinned swing truss carrying a single track. The swing truss was fixed in place in the 1940’s. The bridge was selected for replacement due to significant deterioration of the bridge, the pin connections, and the members. The selected alternate was four deck-girder spans, which adds two concrete piers in the Salt River waterway. While attempting to install the northern pier pile foundation, a debris field consisting of stones, concrete, and other materials was discovered. After evaluating the results of a preliminary investigation and excavation, it is believed that the original pivot pier had collapsed during a flood event shortly after construction and was abandoned to the river. A new pier was then simply built on top of the remains. A reassessment of the alternates and additional geotechnical exploration indicated that the traditional pile foundation should be replaced with a micro-pile system that penetrates the debris field. Thus, the original pier location and superstructure layout were maintained. The presentation includes a project overview and then focusses on the debris field discovery, the foundation redesign including impacts of obstructions, and final construction of the bridge. All analysis and design were completed according to the current applicable edition of the American Railway Engineering and Maintenance-of-Way Association, Chapters 8 - Concrete Structures, and Chapter 15 - Steel Structures.

The orthotropic steel deck bridge is a structural system that has the potential to provide an extended service life and standardized modular design as compared to more conventional bridge construction. This paper summarizes proposed changes to the fifth edition of the AASHTO LRFD Bridge Design Specifications related to orthotropic deck bridges. The current version of AASHTO-LRFD contains provisions that provide limited guidance to complete the fatigue design. Contained within these proposed changes is a new framework for design verification, which may be based on different levels of design or physical testing. Criteria related to loads, load factors, limit states including fatigue in particular, resistance, and analysis requirements are covered in detail. Designs made according to these new provisions can be expected to perform very well and meet the design service life as per AASHTO-LRFD.