A. FIXING SYSTEM CLASSIFICATION
A.1. WHAT IS A FIXING SYSTEM?
The term FIXING SYSTEM indicates the way in which an element is fixed to a load bearing structure defined as BASE MATERIAL.
Precise knowledge of the base material is of primary importance as the different characteristics of the materials influence the choice of the most suitable fixing system.
The fixing systems can be classified according to the type of installation: either cast-in place installation or post-installed installation.
In the latter case, there are two additional types: drill-in systems (ANCHORS) and direct fixing systems (power actuated fixing).
A.2. HOW ARE DRILL IN FIXING SYSTEMS CLASSIFIED?
The classification of drill-in fixing systems is based on the way in which the load is transferred from the anchor to the base material:
- mechanical interlock (undercut fig. 1 , 2 , 3)
- friction (expansion fig. 4 , 5)
- bonding ( fig. 6)
Metal and plastic anchors can work both by mechanical interlocking and by friction.
Chemical anchors work by bonding to the hole walls in solid base materials and by mechanical interlocking in perforated base materials.
A.3. HOW DO UNDERCUT ANCHORS WORK?
In UNDERCUT anchors, the load transfer occurs due to the anchor geometry, which during installation expands beyond the size of the hole in order to «attach itself» to the base material.
This is typical of anchors used on base materials containing hollow parts (in this case the anchor takes advantage of the base material cavities) or concrete selftapping screws.
A.4. HOW DO EXPANSION ANCHORS WORK?
A.5. HOW DO BONDING ANCHORS WORK?
In BONDING anchors, the load transfer occurs due to the bonding of a bar that is fixed to the base material by a chemical adhesive.
The adhesive, normally a resin, which adheres to the anchor on one side and the hole walls on the other, transfers the load through micro keying.
For the fixing to work correctly, the anchor must have a rough surface (e.g. a threaded bar) and the hole must be cleaned properly so that the resin can penetrate the micro-craters formed on the hole walls during the drilling phase.
B. CHOICE OF FIXING SYSTEM AND INSTALLATION METHOD
B.1. WHAT ARE THE ANCHOR INSTALLATION METHODS?
Anchors can fix the element to the base material in the following ways:
- Pre-positioned fixings (fig.8): the anchor is inserted in the base material before positioning the object to be fixed and then is tightened with a screw. The hole in the object to be fixed is normally smaller than the hole in the base material.
- Through fixings (fig.9): the anchor is inserted in the base material through the fixture. The size of the hole of the object to be fixed is either bigger than or equal to the size of the hole in the base material. This hole is drilled either simultaneously with the hole in the base material or if already drilled is used as an outline to drill the hole in the base material.
- Stand-off fixing (fig.10): the object to be fixed is mounted at a distance from the base material. An anchor with a prolonged threaded part is used and the element is fixed with a nut and a lock-nut. The part of the anchor which protrudes from the base material is subject to bending (fixing with lever arm) as well as shear loads.
B.2. WHAT IS A PRE-POSITIONED FIXING?
The PRE-POSITIONED anchor is inserted before positioning the object to be fixed, as it does not go through it.
The installation steps are greater than the THROUGH anchor and include:
- Marking of holes
- Drilling and hole cleaning
- Inserting the anchor into the hole (without the screw)
- Positioning of the object to be fixed
- Final tightening
Installation steps of a PRE-POSITIONED fixing:
B.3. WHAT IS A THROUGH FIXING?
The THROUGH anchor is inserted through the object to be fixed.
The installation steps are very quick compared to the PRE-POSITIONED anchor and include:
- Drilling and hole cleaning of the base material through the object to be fixed
- Inserting the whole anchor through the object to be fixed
- Final tightening
Installation steps of a THROUGH fixing:
B.4. WHICH ANCHORS SHOULD BE USED ON SOLID BRICK?
The solid brick is the oldest type of “industrial” modular element for the construction of buildings.
Bricks which contain a maximum of 15% hollow parts are defined as “solid bricks”.
The standard EN 772-1 determines the compressive strength, where values ranging between 10 and 80 N/mm2 are taken into consideration (generally the resistance is between 20 to 40 N/mm2).
Metallic anchors are suitable for use in this type of base material however it must be taken into consideration that there is discontinuity where the elements are joined together.
The fixing resistance will also depend on the type of mortar used and the position of the holes in regards to the joining lines.
B.5. WHICH ANCHORS SHOULD BE USED ON HONEYCOMB BRICK?
The brick is classified as a honeycomb brick when it has 15% - 45% hollow parts of the transverse surface.
The holes are always kept at a right angle to the laying surface.
Load bearing or curtain walls are made using this material.
Bricks can also be made with porous lightened material for improved heat insulation and sound proofing properties.
Important fixings are not suitable for this type of base material, despite its good compressive strength value, due to the large amount of hollow parts.
The metallic anchors needed for this type of fixing would cause too much tension during the expansion phase.
Chemical anchors are more commonly used as the tension can be distributed between several ribs.
There are no contraindications for plastic anchors.
B.6. WHICH ANCHORS SHOULD BE USED ON SOLID STONE?
Stone is found commonly in the construction of older buildings and despite its variable nature, is a good construction material.
Nowadays, it is used for façade or paving work and rarely as a load bearing material.
A fixing with a high resistance can be carried out if the material is compact and as long as the installer has the foresight to drill the hole in the solid part avoiding the joining lines.
Important fixings cannot be carried out on porous base materials such as tuff and it is therefore recommended to avoid the use of metallic anchors.
Plastic and chemical anchors however are both suitable for use on this material.
Stonework is regulated according to the standard EN 771-6.
B.7. WHICH ANCHORS SHOULD BE USED ON CONCRETE?
CONCRETE is a unique base material as it has good mechanical features and is characterised by the particularity that in certain defined zones of the structure it can present micro-cracks, caused for example by local stress (in fact, in reinforced concrete, metal reinforcement is used to cope with the tensile stress that is not supported by the concrete).
For this reason, there are anchors which are tested and certified only for non-cracked concrete and others that are also for cracked concrete.
C. TECHNICAL DOCUMENTATION
C.1. WHAT TECHNICAL DOCUMENTS ARE AVAILABLE FOR AN ANCHOR?
There are several technical documents available for fixings, the main ones are:
- Certifications (ETA certifications according to ETAG/EAD standards, certifications according to EN standards or according to other country standards such as USA standards ICC ES, …)
- DoP (Declaration of Performance, for CE marked products)
- Third party laboratory test reports (Polimi, Catas, Giordano Institute, …)
- Manufacturer's test report (internal laboratory, on-site tests, …)
- Technical sheets
- Safety data sheets (for chemical products)
C.2. WHAT IS AN ETA CERTIFICATION?
The acronym ETA stands for European Technical Assessment.
As reported in the European framework standard for construction products, “In order to allow a manufacturer of a construction product to draw up a declaration of performance for a construction product which is not covered or not fully covered by a harmonised standard, it is necessary to provide for a European Technical Assessment.” (par 20 CPR EU/ 305 2011 Construction Products Regulation).
The manufacturer of a construction product can obtain the ETA by applying to the EOTA (European Organization for Technical Assessment), the European institution to which all the relevant bodies belong
- to issue the standard according to which the products are evaluated (ETAG / EAD)
- for the evaluation of the product itself, which consists in LABORATORY TESTS and processing their results as required by the ETAG / EAD.
C.3. WHAT ARE THE CONTENTS OF AN ETA CERTIFICATION?
The structure of the anchor ETA is standard, and contains the following information:
- Product name, European guideline reference, manufacturer
- Technical description
- Intended use (design reference standard, installation procedure)
- Working life
- Performance (the characteristic resistance values and the coefficients to be used with the standard calculation are shown)
- AVCP system (factory production control system to maintain consistency of performance)
There are two types of standards that regulate ETA certified fixings: ASSESSMENT standards and DESIGN standards.
The first ones are used to attain the ETA, while the latter are used to apply the data contained in the ETA when designing the specific applications in which the construction product is used.
C.4. WHAT ARE THE CONTENTS OF A DOP (DECLARATION OF PERFORMANCE)?
Each CE marked product must be accompanied by a DoP, which is the acronym for Declaration of Performance.
- Contains all the data relating to the product performance (derived from the ETA / EN certification)
- Constitutes the manufacturer's responsibility for maintaining the performance declared in the manufactured products.
C.5. WHAT ARE THE CONTENTS OF A PRODUCT TECHNICAL SHEET?
Each FRIULSIDER product is supplied with a Technical Sheet.
The structure of the FRIULSIDER TECHNICAL SHEET, for each anchor, always follows the same sequence:
- Quoted product technical drawing and technical data table
- Suitable base materials for the anchor
- Installation instructions
- Technical / mechanical characteristics and component materials
- Characteristic and minimum distances (spacing and edge distances)
C.6. HOW TO CORRECTLY READ A TECHNICAL SHEET?
To determine the suitability of an anchor for a specific application, the following must be verified:
- If the anchor in question is suitable for the base material
- If the type of corrosion protection is suitable for the environment
- Geometric aspects of the anchor (diameter, fixture thickness, hole depth and minimum base material thickness, ...)
- If the required loads are met (tension N, shear V)
- If the application geometry permits the use of the anchor (spacing and edge distances)
How are the loads interpreted in the Friulsider technical sheets?
Num, Vum = mean ultimate loads: arithmetic mean of the failure values.
Nrk, Vrk = characteristic loads: they are the 5% fractile of the measurements. In other words, there is a 5% probability that the effective result is lower than the characteristic load. This evaluation takes also in consideration the dispersion of the results.
The characteristic load is calculated using the following formula:
F5% = Frk = F - ks · σ
- F = mean measurement
- σ = measurement standard deviation
- ks = factor depending on number n measurements
Nrd, Vrd = ultimate limit state loads (or design loads): resistance loads derived from the characteristic loads divided by partial safety factors.
N, V = recommended loads: loads obtained by dividing the design loads by an action factor equal to 1.4 (for certified anchors) or by dividing the mean ultimate load by an appropriate global safety factor.
How are distances interpreted?
Ccr, Scr = characteristic distances: distances below which the load resistance must be suitably reduced.
Cmin, Smin = minimum distances: distances under which the anchor cannot be used.