A numerical assignment on local pressure capacity of the concrete under the head of straight anchor bolts

Abstract

High-strength straight anchor bolts materials require longer embedment lengths in the concrete so the headed bars are employed to significantly reduce the required embedment length of these bars. But they impose concentrated stress on a small concrete surface under the head. In this study, behavior of headed bolts was numerically studied using 3D finite element method (FEM). First, an experimental program consists of four concrete specimens with variations only in head diameter was conducted. Second, FEM program consists of 22 concrete specimens was conducted. The effect of concrete cover thickness around the head was ranging from 85 mm to 510 mm. This variation resulted in a broad range of concrete cover-to-stud diameter ratios from 5 to 30. Additionally, studying the impact of head geometry (hexagonal, square, circular, and pentagonal) was performed. The effect of head diameter from 12 mm up to 50 mm was examined. This study also assessed the effect of using high strength concrete under the head region. The results showed that all specimens exhibited localized compressive failure of the concrete beneath the headed bars. Due to its increased number of sides, the hexagonal head performed better than the square head. When compared to a headed bar with a diameter of 12 mm, the ultimate local pressure of headed bars with diameters of 15, 17, 20, 25, 30, 40, and 50 mm dropped by 53, 60, 68, 76, 78, 87, and 90%, respectively. When the concrete cover-to-stud diameter increased from 5 to 30, there was a noticeable improvement in the final local pressure and the related slip under the rebar head. Overall performance of the bars improved with increase of the members number of the head. When high strength concrete was used under the head, the ultimate local pressure of headed bars increased by 29-152%. Many new formulas were proposed for estimating ultimate local pressure of headed bars.