In the proposed precast concrete substructure
system, the grouted anchor bars carry tensile stress across the joint between the column and cap beam. This joint
is the yielding element in the structural system, and it is crucial to the performance of the structure that the
bars yield before other failure mechanisms, including bond failure, occur.
The utilization of a few large-diameter reinforcing anchor bars for the operation of precast concrete bridge
bents make construction simple for operating by reducing the number of alignments to be made in the field. These
bars are grouted into ducts in a precast concrete cap beam.
However, the cap beam is
typically insufficient to anchor the bar, as the depth of the beam is substantially less than the American
Association of State Highway and Transportation Officials (AASHTO) bridge code allows.
For this project, 17 pullout tests were conducted to determine the bond characteristics and
development length of large-diameter bars grouted into ducts.
The bars tested ranged in size from 8 to
18. Pull out tests conducted with embedment lengths of at least six bar diameters yielded the reinforcing
bar, while the test conducted with an embedment length of 14 bar diameters resulted in bar fracture.
The tests and subsequent analysis showed that the bond of these grouted connections is
significantly better than the bond of bars cast directly into concrete. The development lengths needed to
fully anchor the bar are therefore within the depth available in the cap beam.
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