On the Repair of Impact Damaged Prestressed Concrete Bridge Girders

摘要

Prestressed concrete (PC) bridges are susceptible to catastrophic damage (often from over-height vehicle impact); the extent of which is often difficult to assess until it has progressed to the point of collapse. Impact damage occurs when a vehicle’s height is greater than the vertical clearance between the roadway and overpass and the vehicle strikes the overpass. Impact damage ranges in severity, but generally does not cause immediate collapse of the structure. However, when untreated, impact damage can result in further or accelerated deterioration often resulting in significant prestressing steel corrosion. udPerforming a structural repair requires confidence that the member in need of repair is behaving as anticipated. In doing so, the member should be viewed from a perspective different than conventional engineering assessment practices. For example, the contribution to section capacity of strands which have been exposed or severed due to over-height vehicle impact are neglected in conventional member assessment. This assessment practice has been found to be overly conservative because strands ‘redevelop’ their prestressing force upon entering sound concrete. Furthermore, due to the unanticipated composite action occurring between an AB girder and the barrier wall/curb slab assembly, many AB members that conventionally behave uniaxially are behaving asymmetrically and biaxial bending effects must be considered when determining flexural capacity. Additionally, few (often one) girders are damaged due to the localized nature of impact-damage. Therefore, a rating factor expression was developed to quantify damage to individual girders. udOverall, this dissertation presents new approaches to the assessment, analysis and repair of PC girders. Employment of these assessment and analysis techniques allows for more accurate quantification of in-service member behavior, thus allowing for the most appropriate solution (member/bridge repair or replacement) to be selected. This approach is demonstrated through a case study analysis of a previous experimentally tested girder. Lastly, an approach to determining repair technology limitations (based on geometric and mechanical constraints) through an impact-damaged AB girder repair example is provided.ud