«European Technical Approvals for Anchors used in Construction 1. Introduction In 1997 the European Organisation for Technical Approvals (EOTA) ...»
European Technical Approvals for Anchors used in
In 1997 the European Organisation for Technical Approvals (EOTA) published the first
European Technical Approval Guideline (ETAG 001) for Metal Anchors for use in Concrete.
The CEO has actively participated in the relevant EOTA Working Group and has strongly
supported the process. Based on this guideline many companies have since gained European
Technical Approvals (ETAs) for their products.
This guidance note is intended to help the users of ETAs, ie the specifiers and installers of anchors, to understand how to select a product with an ETA to the most appropriate ETAG Part and to ensure that installation is carried out to the requirements of the ETA.
The full benefits to specifiers and users are summarised in section 8.
2. Legal background One of the main aims of the European Union is to avoid barriers to trade between Member States. These barriers may be created by different national technical specifications. The intention of the EU was to harmonise the specifications for products in several Directives, which had to be transferred into national law in the Member States. Anchors are covered by the [1,2] Construction Products Directive (CPD). This Directive describes in a general way how to demonstrate fitness of a construction product for its intended use. This can be done by following a harmonised standard or – if a product standard does not exist - by gaining an ETA based on a harmonised European Technical Approval Guideline (eg ETAG 001 Metal Anchors for use in Concrete).
No national regulations shall contradict these technical specifications. During a transitional period of almost three years after endorsement of the ETAG, either existing national regulations or ETAs may be used. After that only ETAs are valid in the Member States. For most of the Parts of ETAG 001 the transitional period has already expired.
3. ETAGs issued to date and under development At the time of publication the following ETAGs have been published.
ETAG 001 Part Comments End of coexistence period Requirements common Part 1 Anchors, general 31 07 02 to all types Part 2 Torque controlled expansion 31 07 02 anchors Requirements specific Part 3 Undercut anchors 31 07 02 to each type Part 4
* Separate Technical Reports cover Torque controlled bonded anchors and Rebar anchoring.
3.2 ETAGs are being developed for Plastic anchors and Injection anchors for masonry.
The EOTA website www.eota.be lists ETAGs endorsed by the Commission (downloadable), along with Technical Reports and details of revisions to ETAGs contained in History/Progress Files and a list of ETAs awarded to date.
4. Terminology EOTA European Organisation for Technical Approvals The organisation responsible for developing ETAGs in line with mandates issued by the European Commission. Includes Approval Bodies from member states. CEO represents European manufacturers as listed on page 8.
ETAG Guideline for European Technical Approval The key document for manufacturers, approval bodies and test laboratories. The framework for test procedures, assessments and design methods against which anchors are tested and assessed. Products not covered by the exact scope of a particular ETAG may be handled via a special procedure by agreement among the Approval Bodies of EOTA. ETAG 001 Annex C Design methods for anchorages is a key document for specifiers.
ETA European Technical Approval
The key document for specifiers. It confirms fitness for the intended use and contains details of the anchor specification, performance characteristics, design method and application limits. It indicates which ETAG the anchor is approved to and which option is covered for the category of use (see section 5).
Attestation of Conformity
The attestation of conformity procedure requires initial type testing of the anchor product by an independent body. It also requires factory production control and its supervision by an independent laboratory. This ensures that both the product and its performance remain unchanged in regular production from that tested in the approval procedure. The ETAG 001 Metal Anchors for use in Concrete requires attestation to high levels as safety critical applications are covered.
An anchor product must have an ETA and have achieved the Attestation of Conformity before the manufacturer may affix CE marking. It allows the construction works to meet the relevant essential requirements of the Construction Products Directive. CE marking enables products to be offered for sale throughout the EU. It is not intended as a quality mark but effectively the requirements are sufficiently strict that, in this case, it may be regarded as one. At present CE marking is already mandatory in most member states of the EU.
5. ETAG 001 Metal Anchors for use in Concrete This ETAG and its various parts covers applications for which failure of the anchor would involve risk to life and/or serious economic consequences.
There are significant differences between the scope of applications, and the methods of assessment and test, covered by Parts 1 – 5, see section 5.1 and Part 6, see section 5.2.
This ETAG covers anchors for single and multiple use in structural and non-structural applications. The full scope of the limitations are discussed in section 6.
5.1.2 Types of anchor covered The main types of anchor are covered, as shown below, other types may be covered later.
These illustrations are general examples only, other configurations of anchors also fall within these categories.
5.1.3 Options There are 12 options covering the various application parameters including concrete strength and condition (ie cracked or non-cracked); loading direction and edge/spacing criteria. Options 1 (valid for cracked and non-cracked concrete) and 7 (valid for non-cracked concrete only) are the most comprehensive, options 6 and 12 are the least - involving severe application limitations.
When selecting an anchor for a particular application, care will be needed to check that the option of a particular ETA covers the application parameters.
Application parameters for options are tabulated below along with the relevant Design Method see 5.1.6.
5.1.4 Test regimes Comprehensive tests with demanding requirements mean specifiers have full confidence.
Requirements are laid down for three key aspects: Suitability, Admissible Service Conditions and Durability.
Suitability These tests investigate the sensitivity of anchors to various influencing factors, where appropriate, such as low and high concrete strength, repeated loads, location in cracks, repeated crack openings, sustained loads, elevated temperatures and aspects of installation such as hole cleaning, drill diameter tolerance, installation torque, humidity and temperature.
Tests are only required in cracked concrete when the approval covers use in cracked concrete.
Admissible Service Conditions These tests determine the characteristic resistances as well as appropriate edge and spacing distances dependent on the option chosen by the manufacturer.
Durability Various environmental conditions are considered. Generally no tests are required if zinc plated anchors are restricted to dry indoor conditions and stainless steel anchors are used for normal external atmospheric exposure or permanently damp internal conditions. For harsh environments different materials or coatings may be approved following special tests. Bonded anchor materials are subject to special accelerated ageing tests.
5.1.5 Assessment criteria applied to test results
Comprehensive requirements for all suitability tests include:
Load/displacement curves are assessed to ensure smooth curves with no uncontrolled slip.
Products must show a limited scatter of results.
Comparison of ultimate values from tests with various influencing factors against results from a reference test.
Special requirements are also set for individual tests.
Characteristic resistances for some anchors may be higher or lower than for previously published values due to the harmonised safety approach of the ETAG. Resistances for cracked concrete are lower than for non-cracked concrete.
5.1.6 Design methods Three design approaches are elaborated in ETAG 001 Annex C as indicated in the table on page 3 – section 5.1.3. These are related to the options. Some terminology is new and will need to be understood to avoid confusion with previous publications from different manufacturers.
In addition to the parameters which differentiate the 12 options such as concrete strength and condition (ie cracked or non-cracked), loading direction, spacing centres and edge distances, there are many other parameters which need to be considered in arriving at a design that will satisfy all the necessary criteria and assumptions on which the ETA has been based. These are detailed in ETAG 001 Annex C “Design Methods for Anchorages.” Some of these parameters include:- concrete member thickness, plate stiffness of the fixture, diameter of clearance holes in the fixture and eccentricity of loading in tension, shear or bending.
Design (selection) of the anchor is intended to be carried out by a suitably qualified engineer.
Most manufacturers provide software to assist in the selection of fixings for these safety critical applications. This is undoubtedly the most efficient way to ensure that all the necessary criteria have been taken into account although selection using Technical Data sheets will still, in theory, be possible. Manufacturers sometimes publish performance characteristics based on criteria other than ETA. The basis of data used in the design (selection) process should therefore be checked.
188.8.131.52 Cracked and non-cracked concrete The responsibility for the decision as to whether the concrete in the area of an anchorage is cracked or not rests solely with the specifying engineer.
Concrete may be cracked as a result of a variety of causes. ETAG 001 Annex C allows each Member State to give guidance on the distinction between cracked and non-cracked concrete.
[See National Annex on page 9, notes on UK Guidance.] In the absence of such guidance a method is given for determining whether a particular part of the structure is cracked or not, by calculating the stress condition. If no such consideration is made then cracked concrete should be assumed.
This means it is possible to solve the problem as there are numerous qualified products on the market. However, the qualification class of the product makes the application more expensive.
Verifying that concrete is not cracked can be required when the amount of the load occurring and the geometrical conditions (small structures, close spacing and edge distances of the anchors) require detailed calculation by exploring all possibilities. The capacity of anchors suitable for cracks given in the ETA can be at least 40% greater when they are anchored in concrete which is not cracked. The extra effort in the calculation can thus be justified.
184.108.40.206 Safety concept The safety concept is based on the Partial Safety Factor approach as required by new standards and approval guidelines rather than the Global Safety Factor approach previously adopted by most standards.
Ultimate limit state
The characteristic resistances and partial safety factors are given in the ETA.
Serviceability limit state Displacements at service loads are quoted in the ETA for use in the serviceability limit state design.
220.127.116.11 Design approach ETAG 001, Annex C provides a sophisticated design concept. In order to gain optimum performance of the anchors and at the same time an economical design. The method distinguishes between different load directions (tension, shear, combined tension and shear)
and the following different failure modes:
The design resistance Rd is calculated for every mode of failure considering all influencing parameters, such as embedment depth, cross-sectional area and steel strength of the anchor, axial and edge spacings, thickness of concrete member, concrete strength, reinforcement, eccentricity of load and condition of concrete (cracked or uncracked). The design resistance is compared with the corresponding design action Sd. The most unfavourable mode of failure is decisive for each load direction.
Subsequent to the proof for separate tension and shear loads an interaction requirement has to be fulfilled for combined tension and shear loads.
5.2 ETAG 001 Part 6 Anchors for multiple use for non-structural applications ETAG 001 Part 6 is sufficiently different in scope to be regarded as a different ETAG although, for convenience, it is designated part of ETAG 001 and many aspects of test methods, assessment criteria and design methods are common.
The basic idea of this guideline is to take benefit of the fact that in case of excessive slip or failure of one anchor the load is transferred to neighbouring anchors.
ETAG Part 6 covers anchors for multiple use in non-structural applications.
The definition of Multiple Use is the responsibility of each member state. [See National Annex on page 9 for details of UK definition.]
A framework definition is included as follows:
“For example the design of the fixture may specify the number n 1 of fixing points to fasten the fixture and the number n2 of anchors per fixing point. Furthermore by specifying the design value of actions NSd on a fixing point to a value ≤ n3 (kN) up to which the strength and stiffness of the fixture are fulfilled and the load transfer in the case of excessive slip or failure of one anchor need not to be taken into account in the design of the fixture.”
The definitions of the member states are included in an Annex to the ETAG Part 6.
Where a member state has not adopted their own definition the following default value applies.
n1 ≥ 4; n2 ≥ 1 and n3 ≤ 3.0 kN or n1 ≥ 3; n2 ≥ 1 and n3 ≤ 2.0 kN.