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30 A general reference published by VSL International, a large warping can generally be ignored. Sophisticated elastic prestresser with international experience, is discussed below. analysis techniques such as finite element methods have been shown to produce excellent results that compare well with Rogowsky, D. M. and Marti, P. (1991) Detailing for Post- physical testing. It is therefore not necessary to do any more Tensioning, VSL International Ltd., Bern, Switzerland. sophisticated research on this subject. It is necessary for our project to explore the accuracy of less sophisticated methods Detailing for Post-Tensioning includes discussions and such as grillage analysis. If grillage analysis methods can be examples demonstrating the forces that are produced by shown to produce reliable results, than they can be used both post-tensioning, in particular, those in anchorage zones and in design and as a verification tool for even less sophisticated regions of tendon curvature. Emphasis is placed on the use of analysis methods. The goal is to identify the simplest meth- strut-and-tie models to determine the tensile reinforcement ods that can be used safely. requirements. Article 4.4, "Tendon Curvature Effects," deals It also seems that several potential configurations of curved with special issues associated with curved tendons, including box-girder bridges need further study from the designer's in-plane deviation forces, out-of-plane bundle flattening point of view. Although some research work has been per- forces, minimum radius requirements, and minimum tangent formed on skewed bridges, bearings, and interior diaphragms, length requirements. The radial force generated by a curved most of it has not found its way into design specifications. tendon is given as P/R where P is the tendon force and R is the Part of our goal is to develop design procedures to handle radius of curvature of the tendon. Methods for preventing these issues. tendon breakout in thin curved webs include adequate lateral Conventional reinforced and prestressed concrete design methods can be used for curved concrete box-girder design, shear capacity of the concrete cover (adequate cover) or pro- provided accurate global demands can be established. Con- viding tieback reinforcement. siderable work has been performed over the years in these areas. Torsion design, particularly as it applies to box-girders Summary is well established, and further refinement of these methods is beyond the scope of this project. A considerable body of research has been conducted on The local behavior of prestressed tendons in curved con- box-girder bridges. Much of this is useful to this project. crete box-girder bridges is an issue to be addressed by this With respect to global response analysis, research can be project. Although excellent research has been conducted at broadly divided between steel and concrete bridges. Concrete the University of Texas (Van Landuyt, 1991) this needs to be bridges have been found to be stiff enough so that torsion studied further using available analytical techniques.