The I-435 Bridge over the Missouri River at Kansas City, Missouri, consists of twin twogirder structures. Inspections by the Missouri Department of Transportation (MoDOT) in 2003 detected numerous cracks at the floor beam and lateral member connections throughout the 30-year-old bridge. An initial evaluation suggested that many of the cracks were the result of distortion-induced stresses. No evidence of unstable crack extension was observed. A comprehensive fatigue study was subsequently carried out to investigate the extent and cause of cracking and to evaluate possible long-term retrofit solutions. Based on the study findings, a retrofit plan was implemented that addressed details susceptible to distortion-induced cracking, end restraint cracking, and crack growth from embedded defects. Large-hole and loosening type retrofits were utilized to reduce the possibility of crack extension. The installed retrofits will significantly extend the remaining fatigue life and facilitate ease of inspection of this critical infrastructure link.

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<p>The Abraham Lincoln Bridge is a 3-tower cable-stayed bridge connecting Louisville, Kentucky to Jeffersonville, Indiana. The design included an innovative foundation layout, cable-stayed detailing that simplified construction, and probabilistic 100 year service life design. The design contemplated the construction approach preferred by the Design Build contractor. This collaborative approach between the designer and contractor was critical to achieving efficient design elements such as the anchor box, anchorages at the deck level, and tie downs. Yet, despite careful planning, challenges presented themselves during construction, such as deficiencies of concrete materials and difficulties during shaft construction. This paper takes an in depth look at these challenges that arose during construction as we endeavour to share the knowledge gained, not from what went well, but rather from our collective failures.</p>

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<p>KYTC's project requirements and the design/build team's drive to reduce cost and shorten construction schedule led to the development of a three-tower cable-stayed bridge with a flexible foundation system in the longitudinal direction. Working through the site specific challenges and external constraints the design team was able to deliver an affordable solution that could be built in a short period of time.</p> <p>The key measures taken by the design build team to address these unique challenges included the following:</p><ul> <li><p>The design/build team worked effectively with the owner's engineer to develop project specific design criteria to address the unique behaviour of the flexible system and to provide overall safety margin for the structural system consistent with the project requirements specified in the RFP;</p></li> <li><p>At the start of the final design, the designer identified the key system behaviour that needed to be properly captured not only for the completed structure but also for the critical erection stages. Appropriate computer models were developed to ensure such behaviour was properly modelled. Sensitivity of the key behaviour to the design assumptions including construction tolerances were also properly incorporated;</p></li> <li><p>At the early design stages, the designer and the contractor had extensive discussions and reached a consensus on the appropriate restrictions that are required in placement of superstructure steelwork and precast deck panels to limit the erection loads on the flexible foundations;</p></li> <li><p>To comply with the contractor's very aggressive construction schedule, the designer had to complete the design of the first tower before all studies and investigations (such as wind tunnel and technique shat load tests) had been completed. The designer made some reasonably conservative assumptions in design of the first tower based on the available information and prior experience. The first tower design was then confirmed, and design of the other towers, anchor piers and superstructure was progressively optimized when findings from the studies and investigations became available.</p></li></ul><p>The end result is a durable structure that will grace the Louisville Skyline for years to come.</p>