The current provisions for the design of posttensioned concrete anchorage zones in AASHTO's bridge design specification state only that designers should limit the average bearing pressure ahead of the anchorage device to less than 3,000 lb/in. 2 or 0.9 f;;(f;; is the initial concrete compressive strength), whichever is smaller. The specification does not give any guidance for other forces in the anchorage zone, which in many cases are critical. A research project funded by NCHRP and conducted at the University of Texas at Austin was initiated in 1984 with the primary objective of developing a rational and systematic approach to anchorage zone design that could be implemented in the AASHTO bridge specification. The project is completed, and the process of submitting provisions to AASHTO is under way. The proposed provisions provide guidelines for both ultimate and service limit states. It is proposed to divide the anchorage zone into a local zone and a general zone, to require an acceptance test for anchorage devices with high bearing stresses, and to implement design procedures for the general zone that can use a strut-and-tie model, finite element analysis, or approximate equations, or all of these. An introduction into the project and those provisions that are being proposed to AASHTO are presented.

In the 1950s and 1960s extensive research on anchorage zones for posttensioned concrete members was conducted (1-6). Most researchers used theory-of-elasticity-type analysis and small anchor block tests to investigate anchorage zone forces and stresses. These studies gave a basic understanding of the forces in simple anchorage zone configurations. The theories and charts developed by Guyon (7) in the 1950s are still often used in the design of concentric, multiple, and eccentric anchorage zones. However, when anchorage zone configurations are more complex, engineers have difficulty extrapolating from these basic results. In the 1970s the situation improved somewhat as the use of finite element analysis (FEA) became more common. Yet, many times, this type of analysis is too time consuming, expensive, or difficult to translate into reinforcement patterns. In the late 1970s and early 1980s, a study by Stone and Breen (8, 9) provided empirical equations for the design of single anchorages in thin members but did not provide a generalized approach. In 1987 an article by Schlaich et al.(JO) helped to focus attention on the importance of a consistent and rational approach to design. The article introduced the concept of D-and B-regions within a structural system and utilized the strutand-tie model (STM). B-STM regions are zones in which Bernoulli's theory of plane strain is valid. D-regions (discontinuity, disturbed, or detailed) are zones in which the strain