An assessment method to ensure applicability of concrete capacity method for design of anchorages: Linear force distribution approach

Abstract

AbstractThe concrete capacity design (CCD) method for the design of anchorages comes with a pre‐requisite that the base plate connecting the anchors of a group should be “sufficiently stiff.” This article addresses a frequently and vastly discussed topic in fastening technology, namely “What a sufficiently stiff base plate actually means?” The qualitative definition used by the codes requires that the deformation of the base plate should be small compared to the anchor displacements, in addition to the requirement that the base plate should remain linear elastic. This requirement indirectly ensures that the forces among the anchors of the group are distributed in a linear manner, which is the primary requirement to apply the CCD method for design of anchorages. Such a qualitative definition has raised more questions than answers and haunts the fastening technology community. Perhaps the possible solution to this problem requires asking the question differently, that addresses the problem directly: How can it be ensured that the tension forces among the anchors of a group are distributed in a linear manner? This paper first discusses the problem in detail highlighting several issues in the current approach and later provides an overview of an assessment method in form of a set of criteria that can be used to evaluate whether the tension force distribution is linear for an anchorage with a given anchor pattern, baseplate, attachment, and load case. The principle of the approach is based on a combination of simple mathematical formulations and the evaluation of finite element calculations performed on anchorages modeled with base plate, attachment, and anchors. The proposed formulations are described, and it is explained why they are adequate to find practical and safe general solutions to the problems. The application of the set of criteria allows the calculation of an optimum base plate thickness, sufficient to distribute the forces linearly among the anchors, without being overly conservative.