International Concrete Abstracts Portal

SP-228CD This CD-ROM of Special Publication 228 contains the papers presented at the Seventh International Symposium on the Utilization of High-Strength/High- Performance Concrete that was held in Washington, D.C., USA, June 20-24, 2005. The symposium continued the success of previous symposia held in Stavanger, Norway, (1987); Berkeley, California (1990); Lillehammer, Norway, (1993); Paris, France, (1996); Sandefjord, Norway, (1999); and Leipzig, Germany, (2002). The symposium brought together engineers and material scientists from around the world to discuss topics ranging from the latest applications to the most recent research on high-strength and high-performance concrete. In the years since the first symposium was held in Stavanger, there has been worldwide growth in the use of both high-strength and high-performance concrete. In addition to more research and applications of traditional types of high-performance concrete, the use of self-consolidating concrete and ultra-high-performance concrete has moved from the laboratory to practical applications. This publication offers the opportunity to learn the latest about these developments.

Prestress loss estimation is required for properly assessing concrete stresses and member deformation. Earlier methods of prestress loss prediction were based on relatively low concrete strength. Their use for high strength concrete can produce significant errors due to their inability to accommodate varying material properties. Another source of error for earlier methods is that they do not adequately address the interaction between precast concrete members and cast-in-place composite topping. This paper presents the results of the research work conducted by Tadros et al.1 in the National Cooperative Highway Research Program (NCHRP) 18-07 study on prestress losses in high strength concrete which have been adopted by the American Association of State Highway and Transportation Officials, Load and Resistance Factor Design, AASHTO LRFD Specifications2 for inclusion in the 2005 Edition. This paper consists of two parts. Part I describes the development of the new methods that are applicable to conventional and high strength concrete ranging from 4 to 15 ksi (28 to 103 MPa). Part II deals with the experimental program and comparison of measured versus estimated prestress losses.

Prestress loss estimation is required for properly assessing concrete stresses and member deformation. Earlier methods of prestress loss prediction were based on relatively low concrete strength. Their use for high strength concrete can produce significant errors due to their inability to accommodate varying material properties. Another source of error for earlier methods is that they do not adequately address the interaction between precast concrete members and cast-in-place composite topping. This paper presents the results of the research work conducted by Tadros et al.1 in the National Cooperative Highway Research Program (NCHRP) 18-07 study on prestress losses in high strength concrete which have been adopted by the American Association of State Highway and Transportation Officials, Load and Resistance Factor Design, AASHTO LRFD Specifications2 for inclusion in the 2005 Edition. This is the second part of a two parts paper. Part I described the development of the new methods that were applicable to conventional and high strength concrete ranging from 4 to 15 ksi (28 to 103 MPa). This Part II deals with the experimental program of prestress losses in seven full-scale bridge girders. These girders are in four different states; Nebraska, New Hampshire, Texas and Washington that represent four different regions. Previously reported measurements of thirty-one pretensioned girders in seven different states are also examined.

Three 29 m (96 ft.) long, 1.8 m (72 in.) deep bulb-tee girders were fabricatedand tested as part of an ongoing investigation. The girders were designed using a 56-day compressive strength of 69 MPa (10,000 psi). A 3 m (10 ft.) wide, 200 mm (8 in.)thick deck slab was cast on each girder. One girder, designated BT6, was designedusing AASHTO Standard Specifications, 16th Edition, 1996 and the remaining two, BT7and BT8, were designed using AASHTO LRFD Specifications, 2nd Edition, 1998.Each girder was tested under fatigue loading up to 5 million cycles or fatigue failure.BT6 was tested at a maximum extreme fiber tensile stress of MPafc'5.0 (psifc'0.6)of the design concrete compressive strength and successfully completed 5 millioncycles. The maximum tensile stress for BT7 was determined from the measured concrete compressive strength of 90.0 MPa (13,050 psi) and the expression 0 (psifc'5.7). The maximum tensile stress for BT8 was determined fromthe design concrete compressive strength and the expression MPafc'62.0(psifc'5.7). Girders BT7 and BT8 experienced fatigue failure at approximately 1.6million and 2.25 million cycles, respectively.

This paper identifies the fundamental design issues related to the behavior of high-strength concrete (HSC) members with compressive strengths up to 124 MPa (18 ksi) subjected to axial compression loads. The findings are based on critical assessment and synthesis of available data, the experiences of bridge owners, concrete fabricators, and current bridge design codes from North America, Europe, Australia, and Asia. The paper discusses the various factors believed to affect the design and behavior of HSC compression members, including the fundamental properties of concrete, member geometry, support conditions, main and lateral reinforcement, and type of construction. The significance of modeling of the stress-block, potential early spalling of concrete and reliability issues of HSC columns is also discussed. This paper represents the current efforts by the authors to recommend revisions to the AASHTO-LRFD Bridge Design Specifications, which currently limits the compressive strength of concrete to 69 MPa (10 ksi).