Evaluation of Rock Bolts for Installation in Existing Concrete Structures

摘要

The purpose of this study was to evaluate the effectiveness of short rock bolts installed in existing concrete at shallow embedment depths and subjected to direct tension loads. It is sometimes desirable to use such devices to mount signs and electroliers on existing bridges, where minimal clearance to edges of concrete and shallow embedment depths are problems commonly encountered. The pullout strengths of 1-inch-diameter hollow core rock bolts having expansion shell head assemblies were determined at four embedment depths (8 to 14 inches) and at small distances to edges of concrete blocks (from 4 to 10 inches). Various bonding materials were used to seal the rock bolts in cored holes and to provide additional pullout strength. Creep under sustained tensile loading was also evaluated. Threaded steel bars bonded in 24-inch-deep core-drilled holes were tested for maximum pullout strength and used as control specimens. Limited group tests of rock bolt pairs were also performed to provide information on the effect of spacing on bolt pullout strengths. The hollow core rock bolts tested in direct tension were found to be effective when installed at a minimum depth of 12 inches and with a minimum edge clearance of 6 inches.