It is a general rule for all structural fastenings that they must be designed by engineers. Deciding how to design them at the execution stage is not enough. So anchor plates with headed studs must be designed in an engineering-like manner also. This includes providing analytical verification that they have sufficient structural strength and serviceability and producing detailed drawings concerned, such as anchoring and formwork drawings.

Within the scope of general engineering construction and for non-safety-related anchorings, verification of the load-bearing capacity is based on the General Technical Approvals. Such approvals contain all the details required of specific product strengths, permitted edge and centreline distances and instructions and cross-references to the calculation methods to be used.

According to the current status of the General Technical Approvals, anchor plates with headed studs are designed in the same way as anchors based on Annexe C to European Guidelines ETAG 001 [65]. Design includes verification of headed studs against steel failure and verification of the anchor base against concrete failure. In terms of concrete failure, there are a number of failure modes to be considered, depending on the effects of actions involved, such as concrete cone failure, concrete edge fracturing and pry-out failure. The individual failure modes and calculation procedures are described in detail in [76].

In addition to the provisions of ETAG 001, General Technical Approvals for anchor plates with headed studs include additional reinforcement for anchoring the headed studs within the background bending compression area. Particularly where anchorings are close to edges, in new buildings, specifying such additional reinforcement can avoid broken edges and improve structural strength. Further studies on the effectiveness of back-tying reinforcement are described in [77].

During the construction period of the first nuclear power plants there were not yet any rules on using back-tying reinforcement for anchorings with headed studs. For post­calculating anchor plates as part of repairs and retrofits, more recent rules in DIN SPEC 1021-4-2:2009 [75] govern the co-function of existing structural component reinforcement. The existing reinforcement must meet certain design principles such as a sufficient anchoring length inside and outside the fracture cone and should be in the influence area up to 0.75 hef by the headed studs. If these conditions for use are satisfied, anchorings close to edges in existing structures can often be shown to have a greater structural strength. The more extensive rules in DIN SPEC 1021-4-2:2009 are expected to be incorporated in individual approvals for headed studs by the end of 2010.

General Technical Approvals do not cover the verification of the structural strength of anchorings for safety-related components; this must therefore be approved on a case — by-case basis (see section 7.2.5.1).

The notice of consent given by the authorities concerned and the associated expert opinion lay down the calculation methods to be used and the rules to be followed. In exceptional cases, they also include details of the materials to be used, the number and size of the studs to be used for the anchor groups concerned and additional provisions on partial safety factors, if required.

One essential feature here is the data on the structural strength of headed studs in cracked reinforced concrete structural components under accidental actions. This data is based on additional tests and assessments in line with DIBt Guidelines [63], and provides the design basis for fastenings in requirement category A3 to DIN 25449:2008 [15].

The notice of approval also contains additional general rules on accounting for existing reinforcement.

The serviceability of anchor plates with headed studs is less important with non-safety — related fastenings. The loads to be induced are generally relatively small, and the components to be attached are not sensitive to the low levels of deformation to be expected. Reference values for the deformations to be expected in the headed studs are included in the General Technical Approvals.

With safety-related fastenings, the deformation and the sensitivity to deformation of the components to be attached facing accidental actions must be matched to one another. The resilience of the fastenings must be taken into account in calculations when dimensioning components which are vulnerable to deformations, such as pipes.

Reference values for the deformations to be expected in the headed studs under accidental actions are included in the notices of consent and the associated opinions.