THE INFLUENCE OF CASTING POSITION ON DEVELOPMENT AND SPLICE LENGTH OF REINFORCING BARS

The objective of this study was to reexamine the development and splice length requirements for top cast bars based on a comparison of stresses developed at ultimate rather than at a specified value of loaded end slip. To understand the historical development of design provisions for the influence of casting position, an extensive survey of the literature was undertaken. An experimental investigation of the magnitude of bond strength reduction as a function of (1) the location and orientation of the reinforcement and (2) the properties (slump) of the fresh concrete was undertaken. Specimens were designed and constructed with bars cast at different heights above the bottom of the form and oriented horizontally or vertically. The bond strength of each of these bars was compared to that of a bottom bar at ultimate. The specimens consisted of large blocks of concrete with a number of bars or splices cast in each block. The spacing of adjacent bars along the specimen height was varied to minimize the interaction of splitting cracks. Four trial specimens were designed and tested to define the dimensions of the primary test specimens. A total of six specimens containing from 8 to 16 anchored or spliced bars was tested. Slip of the bar relative to the concrete was measured and comparisons between bars were made using load-slip curves. Based on the test results, suggestions are made for revision specifications for "top reinforcement" development and splice length as a function of casting position and concrete slump characteristics. The tests discussed in this report are part of a larger project which includes tests to investigate the effect of casting position and shear on the bond strength of lapped splices. (FHWA)