Connections in Precast Concrete Structures Effects of Restrained Creep and Shrinkage by K. T. Burton, W. G. Corley and E. Hognestad* SYNOPSIS This paper reports an experimental and analytical investigation of the influence of creep and shrinkage deformations on precast-prestressed con- crete T-beams with their ends restrained against horizontal movement. The tests demonstrated that shrinkage and creep of the concrete introduces horizontal forces in such members. Depending upon the degree of restraint, these forces may be of such magnitude that their inclusion in design of beam end details, column supports, and corbels is required. An approximate method for estimating the magnitude of these induced forces is presented. BACKGROUND A series of laboratory projects con- cerning connections in precast con- crete structures has been carried out at the Research and Development Laboratories of the Portland Cement Association. Five previous papers in this series, collectively entitled "Con- nections in Precast Concrete Struc- tures," have been concerned with continuity connections in double-tee floor construction( i t , the bearing strength of column heads supporting precast beams( 2 ), the performance of scarf joints in beams and columns (s), the strength of corbels protruding from columns to support beams14 >, *Former Development Engineer; Manager, Structural Development Section; and Di- rector of Development, respectively, Port- land Cement Association Research and Development Division, Skokie, Illinois. f Numbers refer to references at end of article. and the strength of column base plate connections ( 5 ) . Previous tests have shown that horizontal forces resulting from re- strained creep and shrinkage of beams resting on column heads( 2 > or corbels( 4 ) may seriously reduce the strength of these supports. A few cases of distress have also been ob- served in the field. Effects of such horizontal forces must be included in design of column heads, corbels, and other supports unless special provi- sions are made for free horizontal movement of the beams. Also, hori- zontal forces must be adequately provided for in design of beam end details. The laboratory work reported in this paper deals with the nature and magnitude of deformations and forces caused by shrinkage and creep of prestressed beams re- strained at their supports. Analytical 18 PCI Journal
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