The 30-year journey to Eurocode 2 Part 4: From guideline to European standard
16 December 2019
Today post installed anchor design provisions which were pushed and developed by EOTA are now under the responsibility of CEN.
The regulatory framework for construction products started with the Construction Products Directive (CPD) in 1989, was replaced by the Construction Products Regulation (CPR) in 2011, and both documents sought to ensure free movement of construction products in the EU.
The CPD/ CPR laid the framework and defined the roles and responsibilities of the different organisations involved.
One of the key organisations is European Committee for Standardisation (CEN). It is responsible for the development of the European standards (ENs) for construction and other areas.
Another organisation which plays an important role is European Organisation for Technical Assessments (EOTA). Its role is to develop the European Assessment documents (EADs) which define the criteria to assess product performances.
The Technical Assessment Bodies (TABs), for example, DIBt, CSTB issue the European Technical Assessments (ETAs) for construction products based on the EADs.
When CEN received the mandate to develop the Eurocode standards, post-installed anchor design was not mature enough to be included and it was excluded from the scope of the Eurocode.
EOTA then received the mandate from the European Commission to develop post-installed anchor design provisions.
This was completed under the umbrella of an European Technical Approval Guideline (ETAG). This led to ETAG 001 which was first published in 1997.
Today post-installed anchor design provisions which were pushed and developed by EOTA are now under the responsibility of CEN.
After almost 30 years of anchor design under local guidelines and then ETAG, Eurocode 1992-4 for Design of fastenings for use in concrete is published in Ireland– I.S. EN 1992-4:2018.
Main technical differences
Although there are differences between ETAG 0001 and EC2-4 there are more similarites than differences. The basis of design still refers to a rigid baseplate with the partial safety factor concept and the derivation of the forces still remain the same.
The main changes to the scope are:
EC2-4 covers a wider range of fasteners with a change in terminology:
The design method for fastenings is covered in one single document. Previously the design method was spread between many different documents (seismic, bonded fasteners, fire, fatigue, etc.).
There will be a wider range of configerations covered by EC2-4. It is now possible to have seven different fastening configerations, assuming the annular gap is filled between the fixture and the fastener.
ETAG001 uses the cube strength whereas EC2-4 uses cylindrical strength. This will result in a minor change to the concrete strength relevant formulas.
For example, in the concrete cone failure verification (mechanical fasteners) and Pull-out/ Cone failure verification (chemical fasteners) a slightly lower resistance may be evident with the EC2-4 formulas.
Main changes to resistance determination
Concrete cone failure. Compression forces resultant from a bending moment is taken into account in EC2-4. This will result in a new factor ψ_(M,N) being included which has the potential to increase this resistance by a maximum of two. This will assist where spacings between fasteners are close, deep embedment cases and cases with large bending moments.
Sustained load factor. This is a new factor which takes long term loading into account and the effects of creep.
- ETAG 001: Creep behaviour was included in the qualification criteria (ETAG 001 Part 5). This was a pass/fail type of sustained load test which was based on tension design resistance and was included in the ETA. It did not effect the design resistance of the fastener.
- EC2-4.The factor ψ_sus is introduced to the combined concrete cone and pull out failure equation. It is based on a product performance dependant factor and the ratio of the sustained load to the value of the total actions. For cases with a high ratio of sustained load to total actions this will result in a maximum of 40 per cent reduction in capacity. However with products that have performed well under the test criteria (with a high product performance dependant factor) the reduction will be less.
Splitting failure resistance. Currently in ETAG 001 Annex C if either of the below conditions are fulfilled the splitting failure verification to be omitted:
- Concrete is defined as cracked concrete and the concrete crack width is limited by existing rebar to 0.3mm.
- Concrete is defined as uncracked concrete and the edge distance in all directions c ≥ 1,2 ccr,sp and h ≥ 2 hef, where ccr,sp is the critical edge distance for splitting failure, h is the thickness of the concrete member and hef is the effective embedment depth.
In EC2-4 the splitting failure verification can be omitted also if it meets the same condition for cracked concrete as in ETAG 001 Annex C or in uncracked concrete the condition is less onerous:
- In all directions the edge distance c ≥ 1,0 ccr,sp for single fastener and c ≥ 1,2 ccr,sp for a group of fasteners, and h ≥ hmin
The difference will result in a benefit when designing fasteners in thin slab applications as EC2-4 is limited by hmin (minimum thickness of slab) where previously it was two times heff (the effective embedment depth).
Steel failure of the fastener with a lever arm. Where a grout layer is required under the fixture, it is common that a larger diameter/ higher steel strength fastener is required due to the shear resistance reduction. For some cases in EC2-4 it is possible to have a higher steel resistance where the base plate requires grouting.
To use the higher steel resistance the following conditions must be met:
- At least two anchors in group
- No tension/moment
- Uncracked concrete situation
- Grout thickness is no thicker than 40mm and ≤ 5d
- Grout strength > 30 Mpa and rough surface interface
Concrete edge failure resistance
Existing rebar influence:
ETAG: There are two cases where existing reinforcement can increase the concrete edge failure resistance.
1.) Where dense reinforcement is present, a 40 per cent increase in resistance is possible.
2.) Where there is some edge reinforcement, a 20 per cent increase in resistance is possible.
Case 2 is no longer valid under EC2-4.
- EN1992-4 represents the state of the art for design of fastenings for use in concrete, and is consistent with the rest of Eurocode Series.
- EN1992-4 covers in one design document, all fastener types (mechanical, chemical, cast-in channels, headed studs) and all load conditions (static, fire, seismic, fatigue).
- EN1992-4 introduces few technical changes vs. ETAG 001, but…
- …the most important change is the transition from «guideline» to «standard», that leads to awareness, acceptance and obligation for proper anchor design.
Author: Cathy Flynn is a key project engineer with Hilti Ireland. She holds a bachelor’s degree in mechanical engineering from Trinity College Dublin. She has worked on landmark projects such as Eli Lilly Cork, Intel and other high profile pharma and data centre projects. For further information please contact her directly at: firstname.lastname@example.org or email@example.com://www.engineersjournal.ie/2019/12/16/the-30-year-journey-to-eurocode-2-part-4-from-guideline-to-european-standard/http://www.engineersjournal.ie/wp-content/uploads/2019/12/a1-Steel-Structure-EC2-1.jpghttp://www.engineersjournal.ie/wp-content/uploads/2019/12/a1-Steel-Structure-EC2-1-300x300.jpgCivilconstruction,government,regulations