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exposed length; concrete anchor; shear; stand-off; finite element analysis; nonlinear analysis
This report describes a study of stand-off anchors in shear with various exposed lengths. Anchor bolts embedded in concrete are commonly used in construction, and often leveling nuts are used to adjust the position of attached steel components. In this case, a portion of anchor bolts may be exposed as in a typical column footing connection without grouting. Such anchor bolts in shear are subjected to combined bending, shear and tension depending upon the stand-off heights, concrete compressive strength, and anchor diameter. The shear capacity of exposed anchors is critically related to the total exposed length, including the stand-off height and the depth of crushed concrete, because the bending moment applied to anchor shaft is directly related to the applied shear by the the exposed length. This is the focus of this study.
A group of shear tests of anchors made of ASTM F1554 Grade 55 threaded rods were conducted to simulate the behavior of exposed anchors in shear. Finite element analyses using TNO DIANA® were conducted to explore key parameters, including the concrete and anchor materials, the anchor diameters, and the stand-off heights. The study indicated that the exposed length reduces with an increase in concrete compressive strength and the stand-off heights while increases with an increase in anchor diameter and strength. Equations were proposed for estimation of total exposed length based on the experimental and numerical results. Design equations were proposed for the shear capacity of stand-off/exposed anchors and the equations are verified by 90 tests collected from four sources in the literature.
Luo, Da and Zhao, Jian, "Calculation of Exposed Length of Anchor Bolts in Shear I: Monotonic Loading" (2020). Civil and Environmental Engineering Faculty Articles. 16.