Anchorage of Large-Diameter Reinforcing Bars in Ducts

In precast concrete systems, connections are often made by grouting bars that project from one member into ducts embedded in another. For bridge bents, bar-duct systems can be assembled rapidly if a few large bars and ducts are used to connect the column and cap beam. In some cases, the required anchorage lengths for the large bars exceed the length available. To evaluate the anchorage requirements for this situation, 14 pullout tests were performed on bars with sizes up to No. 18. The tests and a nonlinear finite element model showed that, under conditions similar to those tested, large bars can develop their yield and fracture strengths in as few as six and 10 bar diameters, respectively. The effects of the bar size were found to be small compared to the scatter among the test results. Parallel tests with polypropylene fibers showed that fibers generally decreased pullout resistance, although this is likely the result of reduced grout strength.