Office of Special Funded Projects
Anchorage to Concrete
Recently some designers have been specifying the size of the hole used for drill and bond rebar. These projects called out a diameter only slightly larger than the diameter of the dowel bar, for example if the bar was a #16, the hole diameter being called out was only 19mm. The drilled hole must be large enough to ensure an adequate bond. Caltrans has performed pull-out tests of drill and bond/grout bars and the results are summarized in Tables A.4 and A.5 on page 5-87 of the Bridge Design Aids. These tests used certain hole diameters as shown in the tables: bar diameter + 1/4"(6mm) for grout and bar diameter + 1/2"(13mm) for bond. These diameters are specified in Standard Specifications 51-1.13 and 83-2.02(D)1and therefore designers should NOT specify the diameter of the hole used for drill and bond/grout rebar.
In addition, the diameter of the hole should not be called out for either the drill and bond (epoxy cartridge) or the resin capsule anchors since the hole diameter is controlled by the manufacturer of those products.
For further information, refer to "Anchorage to Concrete" in Bridge Design Aids pages 5-81 to 5-92.