Eurocode 2 - Part 4 (I.S. EN 1992-4:2018)

Background

The regulatory framework for construction products started with the Construction Products Directive (CPD) in 1989. This was replaced by the Construction Products Regulation in 2011. 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 are CEN (European Committee for Standardisation). They are responsible for the development of the European standards (ENs) for construction and other areas.

Another organisation which plays an important role is EOTA (European Organisation for Technical Assessments). Their role is to develop the EAD’s (European Assessment documents) which define the criteria to assess product performances.

The TABs (Technical Assessment Bodies) e.g. DIBt, CSTB issue the ETA’s (European Technical Assessments) 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 ETAG (European Technical Approval Guideline). 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. The recommended values should be used for all the Nationally Determined Parameters (NDPs) described within Eurocode part I.S. EN 1992-4:2018.

 

What are the Main Technical Differences

Although there are differences between ETAG 0001 and EC2-4 there are more similarities 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:

Terminology

• EC2-4 covers a wider range of fasteners with a change in terminology
• Post installed fasteners – mechanical and chemical
• Cast in Fasteners
• Anchor channels

Design Source

• 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.).

Fastening Configurations

• There will be a wider range of configurations covered by EC2-4. It is now possible to have 7 different fastening configurations, assuming the annular gap is filled between the fixture and the fastener.

Concrete Grades

EC2-4 allows the consideration of low/ high strength concrete grades

ETAG 001:     C 20/25 to C 50/60.

EC2-4:            C 12/15 to C 90/105

Concrete Strength

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.

The main changes to the resistance determination are highlighted below:

Tension Verifications:

Concrete Cone Failure:

Compression forces resultant from a bending moment is taken into account in EC2-4. This will result in a new factor  being included which has the potential to increase this resistance by a maximum of 2. 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  is introduced to the combined concrete cone and pull out failure equation. It is based on a product performance dependent 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% reduction in capacity. However with products that have performed well under the test criteria (with a high product performance dependent 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.
• or
• 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 2 times hef (the effective embedment depth).

Shear verifications:

 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 meet

• At least 2 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 2 cases where existing reinforcement can increase the concrete edge failure resistance.

1. Where dense reinforcement is present, a 40% increase in resistance is possible.
2. Where there is some edge reinforcement, a 20% increase in resistance is possible.

Case 2 is no longer valid under EC2-4.

Combined resistance verification:

A better resistance is possible when the governing failure mode type is different in tension and shear.

Summary

• 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