3D FE Analysis of Anchor Bolts with Large Embedment Depths

In engineering practice, headed anchors are often used to transfer loads into reinforced concrete members. Experience, a large number of experiments as well as numerical studies of anchors of different sizes confirm that fastenings are capable to transfer a tension force into a concrete member without using reinforcement. Provided the steel strength of the stud as well as the load bearing area of the head are large enough, a headed stud subjected to a tensile load normally fails by cone shaped concrete breakout. To better understand the crack growth and to predict the concrete cone pull-out failure load of headed studs for different embedment depths a number of experimental and theoretical studies have been carried out. Due to the fact that the tests with large embedment depths are rather demanding, most of the experiments were carried out for embedment depths that range from hef = 100 to 500 mm. For anchorages with larger embedment depths, which are relatively often used in the engineering practice, there are almost no experiments available. Consequently, for these fastenings the influence of the geometry (edge influence, influence of the anchor spacing, influence of the thickness of the concrete member, etc.) and type of loading (tensile, shear or combined) on the failure load and failure mode is not confirmed by experiments. In last two decades significant work has been done in the development and further improvement of numerical tools. These tools can be employed in the analysis of non-standard anchorages. Unfortunately, the objectivity of the numerical simulation depends very much on the choice of the material model. Therefore, the numerical results should be confirmed by experiments. In the present paper the results of a finite element study of fastenings which were designed for the application in nuclear power plants in Korea are presented. In the three-dimensional finite element analysis the code MASA, which is based on the microplane model for concrete, is performed. The numerical investigations were actually a part of an extensive test program. The results of the study were used to support a test program that had to be carried out for a non-standard fastening systems in which the anchor bolts with embedment depths that varied from 0.5 m to over 1.0 m were employed. Furthermore, the head sizes of the anchor bolts were much larger than that used in the standard pull-out experiments. The analysis was carried out for tensile and shear loads. For both cases the edge influence and the influence of the reinforcement was investigated. The numerical results are compared with test results, which were obtained afterwards. Therefore, the numerical study was a real benchmark test for the finite element code used in the numerical investigations. The calculated failure modes and failure loads shows very good agreement with measured data. It is interesting to observe that for some cases the measured and calculated data shows disagreement with the data obtained using current design code recommendations.