Strength and Behavior of Bolt Installations Anchored in Concrete Piers

J. O. Jirsa, H. T. Cichy, M. R. Calzadilla, W. H. Smart, M. P. Pavluvcik, and J. E. Breen


In this study, the primary objective was to investigate the strength and behavior of anchor bolt installations. In one phase, high strength anchor bolt groups embedded in reinforced concrete piers were investigated. Bolts with a 1-3/4-in. diameter and a yield stress of 105 ksi were used. The anchorage length was 20 bar diameters and a nut and two or three standard washers provided bearing at the end. From the tests, the effects of bolt spacing and clear cover on the strength of the anchor bolt groups were determined. Center-to-center bolt spacing ranged from 4.0 in. to 13.5 in.; clear cover ranged from 2.4 in. to 7.4 in. In general, it was confirmed that as bolt spacing, clear cover, or the combination of both, is increased, the group capacity is also increased. Also, groups with shallow clear cover failed very abruptly, while groups with large cover underwent a significant amount of slip while maintaining their load capacity before and after ultimate was reached.

In the second phase, six single bolt tests were performed. The clear concrete cover to each bolt was maintained at 5-5/8 in. Two different steel grades were used in manufacturing the bolts (55 and 1-5 ksi). Anchorage for the bolts consisted of a 90° bend plus steel strap, or a nut and steel strap combination. In this series of tests, the effects of the bolt material and the type of anchorage on the tensile capacity of the installations were determined. A post-tensioned test was performed on a two-bolt group as part of the single bolt tests series.

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