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"Research sponsored by the American Association of State Highway and Transportation Officials in cooperation with the Federal Highway Administration."
The design procedure to calculate the shear capacity of bridge girders that was used forty years ago is very different than those procedures that are recommended in the current AASHTO LRFD Specifications. As a result, many bridge girders that were built forty years ago do not meet current design standards, and in some cases warrant replacement due to insufficient calculated shear capacity. However despite this insufficient calculated capacity, these bridge girders have been found to function adequately in service with minimal signs of distress. The objective of this research was to investigate the actual in service capacity of prestressed concrete girders that have been in service over an extended period of time.
"As the nation's infrastructure continues to age, advanced concrete technologies have been developed to both reduce a structure's costs and increase its life expectancy. Since the early 1990's, self-consolidating concrete (SCC) has been one of these technologies. Many, however, have been reluctant to implement SCC in highway girders due to the mixture constituents. One of these concerns is the reduced content and size of the coarse aggregate. These differences in the concrete potentially hinder SCC's mechanical properties and shear resistance. Additionally, for high strength concretes (HSC) with weaker aggregates, shear cracks tend to propagate through the coarse aggregate, reducing the aggregate interlock component of the shear resistance. This study aimed at assessing the web-shear strength both with and without web reinforcement of two precast-prestressed Nebraska University (NU) 53 girders fabricated with high strength self-consolidating concrete (HS-SCC). The results were compared to the ACI 318 (2011) and AASHTO LRFD (2012) code estimates, and a finite element model (FEM) package, Response 2000. ATENA Engineering, a finite element analysis (FEA) program, was also used to evaluate the qualitative results, specifically crack patterns and the effect of the coarse aggregate content and size. A prestressed concrete database was also constructed to assess the effect of the reduced coarse aggregate content on the shear capacity of HS-SCC in prestressed concrete members. The mechanical properties of the HS-SCC mix were also tested and compared to relevant empirical equations. The HS-SCC mix investigated in this study proves to be a viable cost-saving alternative for bridge superstructure elements"--Abstract, page iii.
This report establishes a user's manual for the acceptance, repair, or rejection of precast/prestressed concrete girders with longitudinal web cracking. The report also proposes revisions to the AASHTO LRFD Bridge Design Specifications and provides recommendations to develop improved crack control reinforcement details for use in new girders. The material in this report will be of immediate interest to bridge engineers.