End Zone Reinforcement for Pretensioned Concrete Girders
In this study, a literature review was conducted to establish the background of current specifications and to evaluate the applicability of various theories and methods for design of end zone reinforcement. Analytical methods reviewed in this paper include finite element analysis, strut- and-tie modeling, and the Gergely-Sozen equivalent beam method. Previous experimental work combined with work conducted as part of this study were used to correlate between various theoretical and experimental results. This paper illustrates that no single theoretical method adequately represents the complex behavior at the end of a pretensioned concrete member. A general semi-empirical design procedure is proposed here. It is based on theoretical behavior and experimental observation. Standard reinforcement details are given. The proposed procedure could result in reduction in the congestion of reinforcement while maintaining acceptable crack control at the member end. Application of the proposed procedure to highly pretensioned bridge girders is demonstrated.
Release methodology of strands to reduce end cracking in pretensioned concrete girders
Results of numerical and experimental investigations concerning the causes of prestressed concrete girder end cracks are reported in this paper. The cracks, which developed during the flame-cutting release process, resulted from the restraining effect of unreleased strands as the girders shortened from the partially transferred prestress and from shear stresses generated by the cutting order of the strands. Several methods were examined to eliminate the cracks, including changes to the strand cutting pattern, debonding some of the strands in the end regions, and increasing the slope of the top surface of the bottom flange. The first two of these methods were implemented in the field and found to be successful.
Cooperative Collection Development
The author discusses cooperative collection development from an historical perspective and examines some of the projects conceived and implemented during the past forty years. In many cases the projects failed even after years of concentrated effort. However, more important than these failures are new efforts that are being made. The major focus of this article is on both current regional projects and the more broadly based ARL-sponsored North American Collections Inventory Project. The author discusses these efforts and offers some specific judgments regarding the possibility that these projects will lead to a truly successful coordinated collection development project on a national basis.