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.
A.6. WHAT IS AN INJECTION CHEMICAL ANCHOR?
A.7. WHAT TIMINGS INFLUENCE A CHEMICAL ANCHOR?
Two timings need to be respected when installing a chemical fixing:
GEL TIME or working /hardening time, is the time in which the resin hardens and corresponds to the maximum time that the installer has to carry out the installation;
CURING TIME or load application time, is the time required for a complete resin crosslinking in order to apply the final load.
A.8. SCREWS: WHAT ARE THE MAIN ELEMENTS OF A THREAD?
A.9. HOW ARE THE MECHANICAL CHARACTERISTICS OF SCREWS AND THREADED BARS ESTABLISHED?
The mechanical characteristics of screws and threaded bars are identified using abbreviations such as 8.8, which indicates the RESISTANCE CLASS.
This classification is regulated by the ISO 898-1 standard.
For example class 5.8: 5 signifies that failure occurs at a stress equal to 500 N/mm², while 8 indicates that yielding occurs at 80% of the breaking value, therefore at 400 N/mm² .
The resistance class depends on:
- Mechanical and chemical characteristics of the raw material
- Mechanical machining
- Heat treatment
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.
B.8. HOW TO CHOOSE A SUITABLE ANCHOR BASED ON THE LOADS?
THE anchor LOADS can be of different entities and types: such as high stresses (heavy duty fixings, structural ... ) or low stresses. They can also be purely static and quasi static or even dynamic (earthquake, impact, typical cyclic load eg. industrial machinary). A careful analysis of the loads and the subsequent comparison with the technical data sheets or verification using the calculation programs must be carried out to identify the most suitable anchor.
B.9. HOW TO CHOOSE A SUITABLE ANCHOR BASED ON THE GEOMETRY?
The anchor behaviour depends not only on the base material mechanical characteristics but also on the GEOMETRY involved. The installation of an object using more than one anchor can generate a "group effect" due to the proximity between the anchors and result in a reduction in performance; similarly if one or more anchors are positioned very close to the base material edge.
B.10. WHEN CAN AN ANCHOR GENERATE THE MAXIMUM RESISTANCE?
When installing on concrete, the base material is able to absorb the maximum stress that the fixing can reach when it is installed at a edge distance greater than or equal to the characteristic distance Ccr and when, in the case of several anchors, the spacing distance is greater than or equal to the characteristic value Scr.
Ccr and Scr are values that vary from one anchor to another and are indicated in the relevant technical documentation. Every anchor generates a stress transmission CONE in the base material, in this specific case each anchor can fully develop one without interfering with other cones or with the base material edges.
C ≥ Ccr
S ≥ Sc
B.11. DOES THE BASE MATERIAL EDGE DISTANCE INFLUENCE THE ANCHOR RESISTANCE?
When one or more anchors are positioned near the concrete EDGE, there can be three different scenarios depending on the C distance:
- The distance is greater than the characteristic distance Ccr: the anchor can generate the maximum resistance (the stress cone is completely contained in the base material);
- The distance is between the characteristic value Ccr and the minimum value Cmin: the anchor resistance is lower than the maximum and must be reduced (part of the stress cone protrudes from the base material);
- The distance is less than the minimum value Cmin: the anchor is not suitable for the application (an excessive part of the stress cone protrudes from the base material).
The Ccr and Cmin values vary according to the type of anchor and are indicated in the relevant technical documentation.
Cmin < C < Ccr reduction in resistance
C < Cmin unsuitable anchor
B.12. DOES THE ANCHOR SPACING DISTANCE INFLUENCE THE OVERALL FIXING RESISTANCE?
When two or more anchors are positioned NEAR each other, there can be three different scenarios depending on the S distance:
- The spacing distance is greater than the characteristic distance Scr: the anchors can generate the maximum resistance (the stress cones do not interfere with each other);
- The spacing distance is between the characteristic value Scr and the minimum value Smin: each anchor resistance is lower than the maximum and must be reduced (part of the cones interfere with each other);
- The spacing distance is less than the minimum value Smin: the anchors are not suitable for the application (an excessive part of the cones is overlapping).
The Scr and Smin values vary according to the type of anchor and are indicated in the relevant technical documentation.
Smin < S < Scr reduction in resistance
S < Smin unsuitable anchors
B.13. DOES THE BASE MATERIAL THICKNESS INFLUENCE THE CHOICE OF ANCHOR?
Base materials must always have a minimum thickness Hmin, based on the type of anchor and indicated in the relative technical documentation, which not only depends on the fact that the entire length of the fixing must be contained in it, but also on a mechanical factor to avoid cracking due to the stress exerted by the anchor.
H < Hmin unsuitable anchor
B.14. DOES THE EMBEDMENT DEPTH INFLUENCE THE ANCHOR RESISTANCE?
If the anchor embedment in the base material is insufficient, eg. it does not correspond to the h nom value indicated on the technical documentation, the resistance will be lower than the expected nominal value. This can happen when using a through anchor to install a plate with a greater thickness than the max anchor fixture thickness.
h < hnom incorrect installation
B.15. CAN ENVIRONMENTAL CONDITIONS INFLUENCE THE BEHAVIOUR OF THE ANCHOR?
B.16. WHAT METHODS CAN BE ADOPTED TO COUNTERACT ANCHOR CORROSION?
Over time corrosion can affect the functioning of the anchor leading to failure. Anchor protection can be implemented in different ways through:
- PROTECTIVE COATINGS (ZINC PLATING)
- GALVANIC ZINC PLATING: cold electrolytic process which involves a thickness deposit ranging from 5 to 25 µm
- HOT DIP GALVANIZING: immersion process in molten zinc at 450° which involves a minimum thickness deposit of 45 µm
- MATERIAL CHOICE
- STAINLESS STEEL: stainless steel anchors resist corrosion without the need for a protective coating. Various classes of steel for the anchor can be used: A2, A4, A5, HCR.
- PROTECTIVE COATINGS (ZINC PLATING)
B.17. CAN ANCHORS BE FIRE RESISTANT?
Fire resistance is increasingly in demand in various sectors:
- Plant engineering (electrical, thermo-sanitary, oil & gas, ...);
- Safety-critical applications (false ceilings, ...);
- Fire systems
There are different levels of fire resistance for anchors (metal anchors perform the best):
- Anchors are increasingly accompanied by certifications for applications in case of fire;
- The fire resistance can be evaluated by laboratory tests or by calculations, in the first case the resistance values will be higher as they correspond to the actual behaviour of the anchor, in the second case the values will be more conservative;
- The fire resistance values for many metal anchors are already included in the ETA certification.
B.18. HOW IS AN ANCHOR INSTALLED?
There are different types of anchor installation depending on the type of fixing and base material. Some require only a few steps while others multiple steps or even special tools. There are three very important steps which if performed incorrectly can compromise the fixing outcome:
- BASE MATERIAL DRILLING
- HOLE CLEANING
- TORQUE APPLICATION
B.19. HOW DO YOU DRILL A HOLE IN THE BASE MATERIAL?
The base material must be drilled using the most appropriate method in order to avoid damage that could compromise the fixing outcome:
Attention must be paid to the perpendicularity of the hole and the presence of any reinforcements.
B.20. HOW DO YOU CLEAN THE HOLE CORRECTLY?
Different levels of hole cleaning may be required depending on the anchor type and base material characteristics.
- For the correct installation of an anchor, the MAXIMUM HOLE CLEANING LEVEL may be required, which can include several blows with compressed air and cleaning with a brush (e.g. resin fixings with large diameter bars in concrete).
- Or COMPLETE ABSENCE OF HOLE CLEANING, (e.g. various fixings on hollow bricks).
The following are examples from technical data sheets of several products:
B.21. WHAT TYPE OF ANCHORS NEED TIGHTENING TORQUE?
There is a category of anchors where the TIGHTENING TORQUE must be applied during installation: torque controlled expansion anchors. The fixing during this phase generates the frictional force necessary to develop its resistance through the expansion of a component inside the hole. The tightening torque must be applied with a torque wrench.
There are also other types of anchors where, to avoid damage, a maximum torque must not be exceeded during tightening (e.g. chemical fixings or concrete screws).
The reference torque is always indicated in the technical documentation.
B.22. HOW DO INSTALLATION TIMES OF A CHEMICAL ANCHOR VARY ACCORDING TO THE ENVIRONMENTAL TEMPERATURE?
The gel and curing times vary according to the environmental temperature and consequently base material temperature: the higher the TEMPERATURE, the shorter the time. In this respect, chemical fixings are usually divided into two distinct groups: the first group consisting of polyester, vinylester and hybrid resins, characterised by similar and rather short times, and the second group consisting of pure epoxies, which have significantly higher gel and curing times.
B.23. HOW DO YOU INSTALL CHEMICAL ANCHORS IN SOLID BASE MATERIALS?
B.24. HOW DO YOU INSTALL CHEMICAL ANCHORS IN HOLLOW BASE MATERIALS?
B.25. HOW DOES HOLE CLEANING INFLUENCE A CHEMICAL ANCHOR?
Hole cleaning is of fundamental importance for chemical anchors: the below results are from tests carried out in the FRIULSIDER LABORATORY, where it can clearly be seen that when passing from installations with complete cleaning to installations with only a quick hole cleaning the loads obtained in the extraction tests are halved:
B.26. WHEN DOES A RESIN EXPIRE?
The SHELF LIFE of a resin depends on:
- Resin type
- Cartridge type
FRIULSIDER hybrid and vinylester resins have a shelf life of 18 months for a 420 ml coaxial cartridge, 12 months for a 300 ml foiltube cartridge (with internal bag), while pure epoxy for 585 ml or 440 ml shuttle cartridge ml has a duration of 24 months.
Each cartridge clearly states:
- Production lot
- Expiry date
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.
C.7. WHAT ARE THE CERTIFICATION LEVELS FOR A METALLIC OR CHEMICAL STRUCTURAL ANCHOR ON CONCRETE?
The anchors on concrete are certified according to the following standards: EAD 330232-01-0601 for mechanical anchors, EAD 330499-01-0601 for chemical anchors, Technical Report 049 for seismic actions - standards which have replaced the long-standing ETAG 001. THE CERTIFICATION LEVELS are as follows:
- OPTIONS 7 to 12 – non-cracked concrete (op.7 is the most complete)
- OPTIONS 1 to 6 – cracked concrete (op.1 is most complete, max crack 0,3 mm)
- SEISMIC C1 – moderate risk (test with dynamic loads and max crack 0,5 mm)
- SEISMIC C2 – high risk (test with dynamic loads, max crack 0,8 mm and crack cycling)
The certification levels range from the least onerous (uncracked concrete) to the most onerous (seismic C2), forming a hierarchy: to certify an anchor in seismic category C1, you have to pass all the tests for non-cracked concrete, for cracked concrete and for the C1.
C.8. WHAT IS THE EC2-4 PROCEDURE FOR THE CALCULATION OF METALLIC AND CHEMICAL ANCHORS ON CONCRETE?
The calculation of a certified mechanical or chemical anchor on concrete according to the EC2-4 requires the verification of all the possible FAILURE MODES, where the one with the lowest final strength is taken into account, and if both tension and shear are present, two components with the lowest final strength will be combined:
… + failure of any additional reinforcement
C.9. WHAT LEVEL OF PERFORMANCE IS REQUIRED FROM THE ANCHOR IN THE EVENT OF SEISMIC ACTIONS?
The following table, from the Eurocode 2 part 4, indicates the required CERTIFICATION LEVEL in the event of seismic actions. It is based on the building importance class and the seismicity level of the area, using the formula ag × S, and can range from the maximum required performance (seismic C2) to no required seismic performance (for which a certified anchor on cracked or non-cracked concrete is sufficient). In Italy, however, the NTC2018 guidelines must be taken into consideration, where in the event of seismic action a C2 category for structural fixings is required regardless of the building importance class.
C.10. CAN PRODUCTS BE EQUIVALENT TO EACH OTHER?
ATTENTION: there are no perfectly equivalent products!
Products can have the same general characteristics (e.g. the same certification level as for two certified anchors both for cracked concrete, or the same chemical base as in the case of two vinylester resins), however there will always be differences which mean that for a given application even though they are two "equivalent" anchors, one may be suitable and the other not.
Therefore, a specific suitability VERIFCATION must always be carried out when choosing an anchor.
C.11. WHICH TECHNICAL DOCUMENTS CAN BE FOUND ON THE FRIULSIDER WEBSITE?
On the FRIULSIDER website, you can consult the following product documents:
- Technical sheet
- Safety data sheets
- Certifications (ETA, EN)
- Declarations of performance (DoP)
- TOP anchors videos
By registering (username + password) you will also have access to:
The following are also available:
C.12. ARE THERE ENGINEERING SOFTWARE PROGRAMS FOR FRIULSIDER PRODUCTS?
The engineering SOFTWARE can be downloaded free of charge directly from the FRIULSIDER website:
FIXCALC SUITE (anchor and post-installed rebar calculation)
- Seismic design of anchors
- Personalised chemical anchor embedment depth
- Personalised plate geometry
- Personalised number of anchors
- Personalised calculation report
- 3D graphics
- Post installed rebars
Calculation of wood connections
Download them here:
C.13. WHAT TO DO IF YOU NEED ADVICE FOR CHOOSING A FRIULSIDER FIXING OR FOR CARRYING OUT TESTS ON SITE?
FRIULSIDER offers a complete TECHNICAL ASSISTANCE service:
- Identification of the suitable fixing for each application type
- Calculation assistance
- Site inspection and testing
- Designer and installer technical training
- Analysis assistance of technical documentation and certifications
tel. +39 0432 747944