Masonry is among the oldest arts and crafts and it was used by all the old civilizations.

We can describe it as a construction system used in building structures (walls, columns, ceilings, pavements, etc) by aligning / overlaying individual units (brick, concrete block, stone…), joined together with or without a bonding mortar.

Today, it is still highly used with a big variety of selected masonry units: clay, concrete, calcium silicate, stone, etc

Masonry works can be found in almost all type of structures and buildings:

And anchoring applications in masonry are required for rehabilitation or new construction:

Until a few years ago there was no official guideline for design of fastening applications on masonry, so engineers would normally adopt recommended loads from anchor suppliers technical tables and apply a “reasonable” safety factor, backed up by engineering judgment, tests on base materials performed on-site and accumulated experience.

The release of ETAG029 guideline brought a new and eagerly awaited concept for

Qualification (Annex A), On-site testing (Annex B) and Design (Annex C) of metal injection anchors for use in masonry.

Fig. 1 Masonry product systems require an European Technical Approval (ETA) to allow Design according to the new ETAG029 guideline,

Professional and accredited design through the usage of ETAG029 Edition April 2013 will be the focus of this article.

First question to be asked, do you know your base material?

European Technical Approvals of Masonry Product usually provide technical data for anchors on several bricks / brick types of different materials and configurations:

Fig. 2 Example – brick types patent on HILTI HIT-HY270 system ETA

So before starting the Design, the Engineer must know the geometry and properties of the bricks on which the anchors will be installed and use the following decision tree:

Fig. 3 Decision tree – two sources of technical data: ETA or On-site tests (OST)

So either the brick in the application is covered by the ETA and this way the respective data (resistances, edge & spacing, embedment depths, installation properties) can be taken directly for Design, or On-site tests (OST) have to be performed to assess the brick’s resistance.

Then the second question would be, When On-site Tests have to be performed?

ETAG029 – Annex B provides recommendations for the execution and evaluation of OST. The thorough analysis of this topic is out of the scope of this article, but a few main aspects should be referred:

• Only tension tests have to be performed – shear can be derived from tensile resistance
• Two types of tests: Pull-out tests (destructive, ultimate load) and Proof-load tests (non-destructive, for a specific design action load)
• A reference brick from the ETA must be chosen, of the same type and material as the brick in the application. This ETA brick sets the maximum loads (Nrk ETA, Vrk ETA) to be taken from the evaluation and will serves as a basis for the parameters to be used in the anchor Design.
• ETAG029 – Annex B defines the number of tests to be executed (5 to 15) and different statistical equations / methods for the evaluation depending of the number and type of tests. In most of these equations there is an influence of a β factor, a variable that considers the different influences of the product, given in the ETA for each reference brick.

Now the brick’s resistance is known - how to proceed with Design?

The ETAG029 – Annex C establishes the concept for Design of metal injection anchors for use in masonry. It provides a detailed definition of the calculation procedure for 8 possible failure modes:

Fig. 4 Tension and shear failures modes to be verified and combined

Failure of the metal part (tension / shear)

• Evaluation for the highest loaded anchor
• Similar to verification for anchors in concrete
• γMs , Nrk,s , Vrk,s and Mrk,s to be taken from ETA

Fig. 5 Failure of metal part: tension and shear

Pull-out of the anchor and brick breakout (tension)

• Evaluation for highest loaded anchor + group of anchors
• Similar to pull-out and concrete cone failure for anchors in concrete
• NRk,p, NRk,b, γM values to be taken from ETA
• ETA provides just one value for both failure modes, considering NRk,p= NRk,b (load for failure, whichever mode happens first)

Fig. 6 Pull-out of and brick breakout failure modes (tension)

There are many factors that will influence the Design resistance for the Pull-out and Brick-breakout failure modes.

These factors can be divided in two categories:

Factors will influence the choice of value from ETA Load tables:

• Positioning and spacing of the anchors on wall
• Orientation of brick on wall
• Cleaning method
• Use category: dry or wet structure
• In-service temperature range

Factors that will multiply the value chosen from the ETA Load tables

• Group factors
• Influence of vertical joints (filled/unfilled; visible/not visible)

Fig. 7 Examples of some parameters that will influence the Design resistance

Pull out of one brick (tension)

• Evaluation for total load - anchor or group of anchors
• No similarity to any failure more in concrete

Fig. 8 Calculation of “pull out of one brick” depends on mortar strength and brick layout

Local brick failure and Brick edge failure (shear)

• Evaluation for effective anchors
• Similar to concrete pryout and concrete edge failure modes
• VRk,b, VRk,c, γM values to be taken from ETA
• Similar influence factors as in pull-out and breakout tension modes

Fig. 9  Local brick failure and Brick edge failure (shear)

Pushing out of one brick (shear)

• Evaluation for total load - anchor or group of anchor
• No similarity to any failure more in concrete

Fig. 10 Calculation of “pushing out of one brick” depends on mortar strength and brick layout

Load Combination N + V

Summary

Demanding applications on Masonry can now have a professional and accredited design using Product Systems with ETA in accordance to ETAG029.

ETA technical data can be used directly for design or serve as a reference for On-site tests evaluation in case the base material resistance is not known / covered.

Need a support?

• If you have any question related to the article or related to anchor design in masonry, please post your question on ask Hilti platform
• If you need an onsite anchor testing to evaluate your brick resistance for anchor design kindly contact your local Hilti engineer.
• For design, you can download our Profis Anchor software with the Masonry module through your local Hilti website