This report documents research performed to develop recommended revisions to the AASHTO LRFD Bridge Design Specifications to extend the applicability of the transfer, development, and splice length provisions for prestressed and non-prestressed concrete members to concrete strengths greater than 10 ksi. The report details the research performed and includes recommended revisions to the AASHTO LRFD Bridge Design Specifications. The material in this report will be of immediate interest to bridge designers. The AASHTO LRFD Bridge Design Specifications contain barriers to the use of highstrength concrete. These barriers restrict the application of existing and new technology to bridges. The AASHTO LRFD Bridge Design Specifications state that design concrete compressive strengths above 10 ksi shall be used only when allowed by specific articles or when physical tests are made to establish the relationships between the concrete strength and other properties. When the AASHTO LRFD Bridge Design Specifications were written, there was a lack of data to demonstrate that the provisions were applicable to concrete compressive strengths above 10 ksi. Recent research has started to address design issues with higher strength concretes. FHWA Showcase Projects encourage the use of highperformance concretes—including high-strength concrete—in bridge structures. As the industry moves toward the use of high-strength concrete, the need to revise the AASHTO LRFD Bridge Design Specifications is more urgent. There is, therefore, a need to expand the AASHTO LRFD Bridge Design Specifications to allow greater use of high-strength concrete. Two recent NCHRP reports complement the work accomplished in NCHRP Project 12-60 http://onlinepubs.trb.org/onlinepubs/nchrp/nchrp_rpt_603.pdfin removing barriers to the use of high-strength concrete. NCHRP Report 579: Application of LRFD Bridge Design Specifications to High-Strength Structural Concrete: Shear Provisions identifies all barriers in the AASHTO LRFD Bridge Design Specifications to the use of high-strength concrete and provides research findings to remove the barriers related to shear. NCHRP Report 595: Application of the LRFD Bridge Design Specifications to High-Strength Structural Concrete: Flexure and Compression Provisions addresses flexural and compression issues. Recommendations from these reports have already been adopted into the AASHTO LRFD Bridge Design Specifications. The objective of NCHRP Project 12-60 was to develop recommended revisions to the AASHTO LRFD Bridge Design Specifications for normal-weight concrete having compressive strengths up to 15 ksi, relating to transfer and development length of prestressing strand with diameters up to 0.62 in. and development and splice length in tension and compression of individual bars, bundled bars, and welded wire reinforcement and development length of standard hooks. This research was performed by Purdue University and Oklahoma State University. The report fully documents the research leading to the recommended revisions to Section 5 of the AASHTO LRFD Bridge Design Specifications. AASHTO is expected This report may be accessed by Internet users at to consider these recommendations for adoption in 2008. (Author/publisher)
Samenvatting