SMARTBOOK TIMBER SCREWS

TIMBER SCREWS Smartbook

THEORY

from page 5

The right screw for the correct application

In order to guarantee the expected service life of connections and ensure adequate strength and durability, the screw selection must take into account its resistance to corrosion, the effect of timber shrinkage and swelling on its mechanical strength, its behaviour in fire conditions and the material on which it is installed.

CORROSION

SHRINKAGE and SWELLING

FIRE

APPLICATIONS

and CONNECTORS

MATERIALS

from page 6

from page 24

from page 32

from page 46

from page 55

PRACTICAL

How to install correctly?

from page 57

After choosing the screw, it is necessary to install it correctly, according to the type of joint in which it will be used, taking into account the materials present and using suitable tools for the type of application.

MINIMUM DISTANCES and PRE-DRILL

INSERTION MOMENT

TIMBER-TO-TIMBER

METAL-TO-TIMBER

SCREWDRIVERS

from page 58

from page 60

from page 62

from page 63

from page 70

Therightscrew for the correct application

THEORY

ATMOSPHERIC CORROSIVITY CLASSES

INFLUENCING FACTORS

Corrosion caused by the atmosphere depends on relative humidity, air pollution, chloride content and whether the connection is internal, external protected or external. Exposure is described by the CE category which is based on category C as defined in EN ISO 9223.

Atmospheric corrosivity only affects the exposed part of the connector.

SERVICE CLASSES

INFLUENCING FACTORS

The service classes are related to the thermo-hygrometric conditions of the environment in which a timber structural element is installed. They relate the temperature and humidity of the surroundings to the water content within the material.

presence of chlorides

pollution

exposure

level of humidity

WOOD CORROSIVITY CLASSES

INFLUENCING FACTORS

Corrosion caused by wood depends on the wood species, wood treatment and moisture content. Exposure is defined by the TE category as indicated.

The corrosivity of wood only affects the connector part inserted in the wooden element.

pH of the wood

moisture content of the wood

SERVICE CLASSES - SC

[Defined according to the new generation of Eurocode 5 (prEN 1995-1-1)(6)]

SC1 SC2 SC3 SC4

EXPOSURE

most common cases

elements within insulated and conditioned buildings

sheltered elements (i.e. not directly exposed to rain or precipitation), in uninsulated and unconditioned structures

RELATIVE HUMIDITY AND EQUILIBRIUM MOISTURE CONTENT OF THE WOOD

Annual average(2)

relative atmospheric humidity of the surrounding air

elements directly exposed to the weather and not permanently exposed to water

in contact corresponding wood moisture content(4)(5)

elements immersed in soil or water (e.g. foundation piles and marine structures)

relative atmospheric humidity of the surrounding air

Maximum(1) corresponding wood moisture content(4)(5)

(1) The upper limit of relative humidity must not be exceeded for more than a several consecutive weeks per year.

(2) The average annual relative humidity over a ten-year period is used to assign wood elements to the corrosivity categories for dowel type fasteners.

(3) The moisture content of members in SC4 (primarily fully saturated) is affected by the surrounding element (e.g. soil or water).

(4) The moisture content may not apply to engineered wood products, LVL or wood-based panel products.

(5) Corresponding representative moisture of SWB (Solid Wood Based) elements.

(6) prEN 1995-1-1 (n.d.) Basis of design and materials - Final draft (22.01.2021) - Project team SC5.T3 & SC5/WG10, CEN.

ATMOSPHERIC CORROSIVITY CLASSES - C

[Defined according to EN 14592:2022 based on EN ISO 9223]

occasional condensation frequent condensation permanent condensation

from 10 to 3 km

6.2 to 1.9 mi from the coast

from 3 to 0,25 km 1.9 mi to 820 ft from the coast

< 0,25 km 820 ft from the coast

medium

from 3 to 60 high

from 10 to 100 m 35 to 325 ft from 0 to 10 m 0 to 35 ft from the road with antifreeze salts

from 60 to 300 very high

from 300 to 1500

from 5 to 30 from 30 to 90 from 90 to 250

urban and industrial areas with medium pollution highly polluted urban and industrial area environment with very high industrial pollution

WOOD CORROSIVITY CLASSES - T

[Defined according to EN 14592:2022]

WOOD SPECIES pH VALUE

Wood contains an acetic acid ester that acts as a corrosive agent for various metals in contact with wood. The presence of acetic acid determines the pH of the wood species

WOOD TREATMENT

Wood treatment includes treatment with chlorides, copper and flame retardants.

In the case of heat-treated wood, the pH level is decreased

MOISTURE CONTENT

Each timber exposure category corresponds, for solid wood, to the annual average moisture content in the indicated service class (as defined on page 7)

SERVICE CLASS

Of the environment in which the wooden element is installed

any pH > 4 "standard" timbers low acidity

pH ≤ 4 “aggressive” woods high acidity

WOOD SPECIES and pH for T3 and T4

[Defined according to Wagenführ R; Wagenführ A. 2022. Holzatlas e Coatings for Display and Storage in Museums January 1999

Publisher: Canadian Conservation Institute Jean Tetreault]

The presence of acetic acid is particularly important when wood is directly exposed to weather (SC3). Knowing which wood species is more acidic is therefore crucial when evaluating the corrosion potential of fasteners and connectors.

"standard" timbers low acidity

pH > 4

“aggressive” woods high acidity

pH ≤ 4

Douglas fir Pseudotsuga menziesii

Blue Douglas fir Pseudotsuga taxifolia

Oak or European oak Quercus robur

Jarrah

Eucalyptus marginata

Western red cedar Thuja plicata

European chestnut Castanea sativa

Thermally treated beech

African juniper Juniperus procera

Idigbo Terminalia ivorensis

African Padouk Pterocarpus soyauxii

American black cherry Prunus serotina

Maritime pine Pinus pinaster

Red oak Quercus rubra

White oak Quercus alba

Black oak Quercus nigra

Oak Quercus petraea

Which timbers are the most aggressive? It depends on the pH!

TANNINS and pH

Tannins are a chemical substance found in plant extracts, belonging to the polyphenol family, common in plants and trees. Their biological role is that of defence; they are molecules with antioxidant properties.

Protection or corrosion?

Their effect on metal, however, is contrary to what one would expect. In fact, as soon as the corrosion process begins, tannins adhere to the surface of the connector and form a protective layer that slows the corrosion rate. The more tannins present in wood, the slower the corrosion of a connector once triggered.

EFFECT OF TANNINS

connector: fully threaded screw

coating: zinc plated (≈ 10μm)

wood: green oak

exposure time: 6 months

service class [SC]: SC3

atmospheric corrosivity classes [C]: C2

wood corrosivity class [T]: T4

external no corrosion

below the surface strong corrosion

tannins

inside the wood low corrosion

tannins

Tests carried out by R&D Rothoblaas have shown that, in just two months, the effect of the tannins is evident:

1 On the part of the connector embedded deep into the wooden element, a substantial black protective layer can be seen.

2 Near the wood surface, the connector has corroded (red rust) because the protective layer has been washed away by water.

CORROSION RATE

Corrosion rate of Zn in wood extracts [µm/year] with varying pH and tannin content(1)

The most important factor to consider in the corrosion of embedded fasteners is the wood corrosivity class (T) related to pH and wood moisture.

At the same pH level, the presence of tannins slows down the corrosive phenomenon.

We usually tend to associate tannins with corrosion because so many tannin-rich woods are also acidic (pH < 4). However, there are exceptions, such as Maritime pine and Douglas fir, which are classified T4, although they have relatively low tannin content compared to other acidic wood species.

oak pine acacia elm

EXPERIMENTAL TESTING

An experimental campaign was carried out at our laboratory to evaluate the corrosion trend of connectors over time.

During the tests, the following were analysed:

• about 350 configurations

• obtained by combining 6 different types of screws

• for a period of 1 year

The specimens were placed in environments with different service classes

The screws were extracted on a monthly basis to assess the corrosion rate and the influence of the different variables involved.

SET-UP

wood: oak

exposure time: 12 months

service class [SC]: SC3

atmospheric corrosivity classes [C]: C2

wood corrosivity class [T]: T4

RESULTS:

after 1 month

slight signs of tannins, no presence of rust

after 10 month

strong presence of tannins, strong signs of red rust

no presence of rust

no presence of rust no presence of rust

presence of tannins, no presence of rust

strong presence of tannins, signs of rust

no presence of rust

STEEL AND COATINGS

C5 EVO ANTI-CORROSION COATING

Multi-layer coating capable of withstanding outdoor environments classified C5 according to ISO 9223. SST with exposure time greater than 3000h carried out on screws previously screwed and unscrewed in Douglas fir timber.

C4 EVO ANTI-CORROSION COATING

Inorganic-based multilayer coating with an external functional layer of about 15-20 μm in an epoxy matrix with aluminium flakes. Suitability for atmospheric corrosivity class C4 as proven by RISE.

ORGANIC ANTI-CORROSION COATING

Coloured organic-based coating that provides excellent resistance to atmospheric and wood corrosive agents in outdoor applications.

ELECTROLYTIC GALVANIZING

Coating consisting of a 5 to 12 micron layer of electrolytic galvanizing with Cr passivation; standard for most connectors.

HIGH CORROSION RESISTANT

Austenitic stainless steel. It is characterised by its high molybdenum and low carbon content. It offers very high resistance to general corrosion, stress corrosion cracking, intergranular corrosion and pitting.

STAINLESS STEEL - A4 | AISI316

Austenitic stainless steel. The presence of molybdenum provides high resistance to generalised and crevice corrosion.

STAINLESS STEEL - A2 | AISI304

Austenitic stainless steel. It is the most common of the austenitic steels. It offers an excellent level of protection against generalised corrosion.

STAINLESS STEEL - A2 | AISI305

Austenitic stainless steel similar to A2 | AISI304. This alloy contains slightly more carbon than 304, making it more workable in production.

STAINLESS STEEL - AISI410

Martensitic stainless steel. Characterised by its high carbon content. Suitable for outdoor applications (SC3). This stainless steels offers the highest mechanical performance compared to the other available stainless steels.

The best compromise between corrosion resistance and mechanical strength

Aesthetic and design requirements: all range connectors

DISTANCE FROM THE SEA RESISTANCE TO CHLORIDE EXPOSURE

Comparison of atmospheric corrosion resistance between different types of zinc coatings and different types of stainless steel used in screws for timber, considering only the influence of chlorides (salt) and without a cleaning cycle (based on EN 14592:2022 and EN 1993-1-4:2014).

electrolytic galvanizing(1)

organic anti-corrosion coating

C4 EVO anti-corrosion coating(2)

C5 EVO anti-corrosion coating(2)

HCR (High Corrosion Resistant) stainless steel

stainless steel - A4 | AISI316

stainless steel - A2 | AISI305 (3)

stainless steel AISI410

(1) Only for protected outdoor exposure conditions.

(2) EN 14592:2022 currently limits the service life of alternative coatings to 15 years.

(3) A2 AISI304: considering the metal completely exposed to rain.

C4 EVO is a multilayer coating composed of:

• An external functional layer of epoxy matrix with aluminium flakes of around 1520 μm, which gives the coating optimum resistance to mechanical and thermal stresses. The aluminium flakes also serve, when required, as sacrificial cathodes for the metal base of the screw.

• A central binding layer for the external functional layer.

• A internal layer of around 4 μm zinc microns which acts as an additional layer of corrosion resistance.

Organic matrix

Cohesion layer

Zn - Zinc

Fe - Carbon Steel

What is the best material if I am near the sea?

MATERIAL AND COATING SELECTION

T-C CORROSION RESISTANCE

Assessment of the corrosion behaviour of material and coatings depending on the corrosivity class of the environment(1) and the corrosivity class of the timber (according to EN 14592:2022 and EN 1993-1-4:2014).

Medium corrosion resistance. Recommended for indoor and outdoor applications in joints not directly exposed to water.

The organic-based coating provides high corrosion resistance even in aggressive wood environments.

Rated in the highest corrosion resistance class by EN 1993-1-4:A1 (CRC V), it offers the highest corrosion resistance for the environment (C5) and wood (T5). Only category suitable for use in indoor pools.

Classified CRC III by EN1993-1-4:A1, it offers a level of corrosion protection suitable for outdoor environments including near the sea (C4) and on acid woods.

atmospheric corrosivity classes

Rothoblaas experience

wood corrosivity classes

Rothoblaas experience

The inorganic-based coating with an epoxy matrix layer provides excellent resistance in aggressive outdoor environments.

Classified CRC II by EN19931-4:A1, it offers a level of corrosion protection suitable for many outdoor environments and wood species.

Multilayer coating capable of withstanding outdoor environments classified C5 and very aggressive woods.

Martensitic stainless steel. Suitable for outdoor use (SC3). Possible application on acid wood but away from corrosive agents (chlorides, sulphides, etc.).

(1) For stainless steel, an equivalent atmospheric corrosivity class was determined considering only the influence of chlorides (salt) and without a cleaning cycle.

COMBINATION WITH PLATES

Screws are often used in combination with metal plates. In such cases, it must be ensured that both components of the connection are sufficiently resistant to the atmospheric environment and the corrosiveness of the timber element.

How to make the rightchoice?

determination of the various classes (atmospheric, service and wood corrosivity) according to the environment

3 simple steps to find the right solution

selection of metal plate material and coating

EXAMPLE: timber elements directly exposed to the weather in an environment close to the sea

OUTDOOR CONCEALED HOOK TIMBER-TO-TIMBER CONNECTOR PAN HEAD SCREW

selection of fastener material and coating based on compatibility with the environment and the plate

LEGEND:

use according to regulations

Rothoblaas experience

The combination of dissimilar metals in outdoor environments also requires an assessment of the risk of corrosion by galvanic coupling.

(1)The correspondence of corrosivity classes C and T with service classes SC is an approximate representation of common cases. There may be special cases that are not included in this table.

GALVANIC COUPLING

The combination of dissimilar metals in outdoor or wet environments requires an assessment of the risk of corrosion by galvanic coupling. For galvanic coupling corrosion to occur, the following 3 conditions must be fulfilled simultaneously:

metals of different types (different electrical potential)

plate

presence of an electrolyte

electrical continuity between the two metals

screw

The more dissimilar the metals (greater potential difference), the greater the risk of corrosion. The potential for galvanic corrosion between metals is determined by how far apart they are on the "galvanic series of metals". Approximately, a potential difference greater than 0.4-0.5 V could be considered significant/critical.

Galvanic series of metals: corrosion potential of various metals in salt water

galvanic potential [Volt]

nobler CATODIC protected part

copper

nickel

silver

titanium

magnesium

zinc

aluminium alloy

steel and cast iron

stainless steels - 410, 416, 304, 305, 316

less noble ANODIC corroded part

gold and platinum

In these cases, the less noble metal (Zn) is dissolved (anodic dissolution), while the more noble part (A4) is not attacked by corrosion (acting as a cathode).

The following measures can be taken to prevent or minimise the risk of galvanic corrosion:

Use similar materials or materials with a small potential difference.

Coat the anode or cathode to prevent electrical connection.

Prevent moisture from coming into contact with both metals.

DISSIMILAR METALS

Sometimes we cannot avoid using dissimilar metals. In this case, we must ensure that the fasteners (e.g. screws or nails) are of a more noble material than the connection, as is the case with LOCK connectors (aluminium) when used with KKF screws (stainless steel AISI410) in an outdoor context.

TIMBER AND GALVANIC COUPLING

When we talk about timber and galvanic coupling, we must consider the distinction between free water and bonded water

Potentially, free water could act as an electrolyte, but the associated risk of galvanic coupling is very low and only occurs if the electrolyte touches both dissimilar materials. Free water does not flow abundantly from the timber cells.

Bound water can't act as a electrolyte because it's bound within the cells of the timber.

Since the equilibrium moisture content of timber is close to 12 % and there is no free water in timber with a moisture content of less than 20 %, the timber surrounding the connection can protect the connection from galvanic corrosion by absorbing excess moisture and prevent a build-up of free water.

SHRINKAGE AND SWELLING

The behaviour of timber material

HYGROSCOPIC

Wood is a living, porous and hygroscopic material, which means that by its nature it can acquire or lose moisture depending on the environmental conditions in which it is located.

Δu < 0% reduction in humidity shrinkage

ANISOTROPIC

The mechanical performance and deformations in a timber element are dependent on the direction (longitudinal and radial/tangential).

NOT UNIFORM

There are many different wood species in the world with different and specific characteristics and densities.

longitudinal direction

Δu > 0% increase in humidity swelling

≠transverse direction

depending on the wood species different densities

DIFFERENT DIMENSIONAL VARIATIONS depending on moisture variation, direction relative to the grain and wood species

HYGROSCOPY

RESIDUAL MOISTURE

Wood puts itself in hygroscopic equilibrium with its environment: it releases or absorbs moisture until it finds a balance point. Based on the climatic conditions of the environment (temperature and relative air humidity), it is possible to determine the corresponding moisture content within the wood.

A wooden element placed in an environment with a relative humidity of 65% and a temperature of 20°C (68 °F) will, in equilibrium, have a corresponding humidity value of 12%

As a rule, wood must be supplied with a moisture content as close as possible to that appropriate to the environmental conditions in which it will be in the finished work, so that it is not subject to corresponding moisture variations and consequently to shrinkage or swelling phenomena.

STRENGTH REDUCTION

The presence of moisture in the timber element influences its static performance: for the same stress, an element placed in an environment with high humidity (e.g. SC3) has lower mechanical strength than in SC1. At the design level, appropriate correction coefficients (kmod) must be applied to take this phenomenon into account.

Correction coefficients for load duration and moisture kmod(1)

How moistureinfluences the behaviour of timber

ANISOTROPY AND WOOD SPECIES

The cellular structure of wood influences its mechanical performance and results in a significant difference in strength and stiffness depending on the direction relative to the grain. Two cases are considered in design: parallel or perpendicular (radial/tangential).

Typical stress-strain curves

Cellular structure: how it influences timber behaviour

DEPENDING ON THE DIRECTION

The phenomena of shrinkage and swelling also differ depending on the direction considered in the timber element. The linear dimensional changes of wood are proportional to the change in moisture content:

Lfinal = Linitial [1 + ksh/sw (ufinal − uinitial)]

where:

- Lfinal is the dimension associated with the final moisture content

- Linitial is the dimension associated with initial moisture content

- ksh/sw is the shrinkage/swelling coefficient in the direction considered (see table below)

- uinitial is the initial moisture content of the wood [%]

- ufinal is the final moisture content of the wood [%]

Shrinkage/swelling coefficients ksh/sw(1) for a 1% change in residual moisture content in direction:

Hygroscopic dimensional changes (shrinkage and swelling) occur for moisture content below the Fibre Saturation Point (FSP), which conventionally corresponds to a moisture content of 30%. For moisture content above the FPS, there are changes in mass but not in volume.

SWELLING: DIMENSIONAL CHANGES

The dimensional variations found, while similar in absolute value, are much more pronounced in the

direction than in the longitudinal direction.

Usually, in timber structures, the construction tolerance is in the millimetre range; swelling or shrinkage that is not taken into account and accommodated generates stress increases and localised cracking or splitting phenomena.

Small variations in moisture, deformationslarge

SWELLING: STRESS INCREMENTS

TIMBER-TO-TIMBER

A change in moisture within a timber element causes additional stress on the connector(1)

LATERALLY LOADED SCREWS

The connector restricts on the free deformation of the wood: swelling could cause an increase in the embedment stress on the connector axis, which results in an additional shear load.

AXIALLY LOADED SCREWS

The impeded swelling results in a concentrated load at the screw head, which tends to penetrate into the timber element. The connector is subjected to a load even in the absence of stresses acting on the connection.

STEEL-TO-TIMBER

A metal plate creates a rigid confinement of the wood and prevents its deformation induced by changes in moisture content.

LATERALLY LOADED SCREWS

When used with a metal plate, the connector has less capacity to accommodate material deformations.

The connector is subjected to a load even in the absence of stresses acting on the connection.

AXIALLY LOADED SCREWS

The connector is significantly stressed in the axial direction if it is positioned in such a way that it cannot allow the movement of the wood.

Moisture variations affect the strength of connections

SWELLING: CONFINED ELEMENTS

Steel-to-timber: attention to stresses

The metal element represents a rigid confinement of the timber: in the presence of a change in moisture, the element is not free to swell.

Prevented swelling generates compressive force on timber. The timber element retains its initial geometry and size but not its stress state. When you have a confined element, the connector is subject to a load even in the absence of external loads acting on the connection if there is a change in moisture.

If the element is not confined, it can deform freely.

The connectors inside will still be subject to additional stress.

The constraint is not rigid enough to prevent the timber from swelling; the plate deforms to accommodate the movement but is constrained by the connector.

The metal element does not deform; the dimensional change of the timber occurs unevenly and generates significant additional stresses on the connector.

DESIGN BEST PRACTICES

It must be verified that swelling and shrinkage do not compromise the performance of other structural members by generating unintentional stresses that affect strength or deflection.

The design and installation of partially or fully threaded self-tapping screws must take into account the moisture conditions of the timber elements and the fluctuations that may occur during transport, assembly, construction and operation. The design must consider possible additional stresses related to temporary conditions.

For more information on METAL-TO-TIMBER installation see page 63.

EXPERIMENTAL TESTING

An experimental campaign was carried out in our laboratory to assess the stress increase on connectors as a result of moisture changes in timber.

During the tests, about 20 configurations were analysed by combining 3 different types installation conditions in steel-to-timber connections

The specimens were placed in defined environments in which the moisture content of the timber elements could be varied in a controlled manner.

The screws were extracted on a daily basis to assess the influence of the different variables involved.

wood: glulam (softwood)

exposure time: 6 weeks

screws: HBS PLATE

initial moisture content: 11%

SET-UP RESULTS: thick plate thick plate

0 week 6 weeks

initial configuration

thick plate + XYLOFON 35 thick plate + XYLOFON 35

THEORY | SHRINKAGE AND SWELLING | 31

FIRE

oftimbercomparedtosteel?

Timber structures properly designed ensure high performance also under fire circumstances.

TIMBER

Timber is a combustible material that burns at a predictable rate: when exposed to fire, a portion of the cross section is lost through charring and pyrolysis while the inner, residual section retains its mechanical characteristics (strength and stiffness).

One-dimensional design (effective) charring rate for solid timber and glulam ß0 ≈ 0,65 mm/min (ßeff ≈ 1.8 in/hr)

METAL

Metals, primarily steel used in the construction of timber buildings, are noncombustible materials that are highly heat conductive and can cause structural failures during fire events if not detailed and protected correctly. When exposed to fire and high temperatures, the mechanical properties (strength and stiffness) of metal rapidly decrease.

If not considered, it may cause an unintended collapse of the connection.

WHY DOES TIMBER RESIST FIRE?

charred thickness heat affected (pyrolysis) zone initial cross section charred zone residual cross section 32 | FIRE | THEORY

Timber is a combustible material that can be completely destroyed if exposed to external heat sources for long durations and high intensities. However:

• timber is a hygroscopic material containing water, which considerably slows down the penetration of heat into the section, even at very high outside temperatures;

• The charred layer acts as an insulator against heat penetration into the section, as the hot gases produced during pyrolysis slow down the temperature increase in the layer itself.

Looking at the cross-section of a timber element after it has been exposed to fire, three layers can be identified:

• a charred zone corresponding to the layer of wood completely affected by the combustion process;

• a heat affected (pyrolysis) zone that has not yet been charred but has undergone temperature increases above 100°C (212 °F), which is assumed to have zero residual resistance;

RESIDUAL CAPACITY

light alloys

Instance t=0 both materials have 100 % strength

Instance t=10 min for steel the strength has been reduced to 20% while for timber it is still 85%

Instance t=20 min steel has collapsed and no longer has any strength while timber has 65% strength left

STEEL and LIGHT ALLOYS: development of the strength characteristics of metal elements subjected to normalised fire (irrespective of section size).

TIMBER: development of the strength characteristics of timber elements subjected to normalised fire (the curve varies with the size of the section).

ISO 834 standard fire curve (ASTM E119 similar)

METAL CONNECTORS

Steel has a much higher thermal conductivity than timber: if exposed to the same heat source, it will heat up much faster than timber and will also transmit the heat to the inside of the section, generating an internal charred layer.

What influences the fire behaviour of a connector?

DIAMETER

The larger the diameter of the connector, the more heat it will transmit to the inside of the timber

Ø20 (0.79 in) bolt exposed to a heat source

Ø12 (0.48 in) screw with head exposed to a heat source

LENGTH

The length, as well as the diameter, material and type of screw head also affect heat transmission. The longer the screw, the lower the temperatures because the tip of the connector is away from the heat source and is in a cooler area of timber.

screw tip at 200°C (392°F)

screw tip at 20°C (68°F)

MATERIAL

With the same geometry, stainless steel performs better than carbon steel. Having a lower conductivity coefficient, temperatures along the length of a stainless steel screw are lower and the charred zone around it is smaller.

THE IMPORTANCE OF PROTECTION

Covering the screw head or protecting the metal from direct exposure to fire brings significant benefits in terms of heat propagation and charring depth.

In fact, the charring depth can be reduced by varying the penetration depth of the head into the timber: greater the penetration depth into the wood, less will be the charring depth. By then covering the head with a timber plug, charring along the length of the screw will be zero.

si: thickness of head penetration into timber

sc: charring thickness

si = 0 mm (0 in)

sc = 30 mm (1.18 in)

after exposure to fire

si = 10 mm (0.40 in) sc = 20 mm (0.79 in)

si = 20 mm (0.79 in) sc = 10 mm (0.40 in)

= 0 mm (0 in)

Rif. N. Werther, M. Gräfe, V. Hofmann, S. Winter „Untersuchungen zum Brandverhalten von querkraft- beanspruchten Verbindungen bei Holzbaukonstruktionen, Neuentwicklung und Optimierung von Verbindungssystemen und allgemeinen Konstruktionsregeln, 2015“

FIRE RESISTANCE

Fire resistance indicates the ability of a building element to maintain structural stability during a fire condition for a given period of time, while retaining the ability to compartmentalise smoke and hot gases generated by combustion. The primary purpose of fire resistance is to ensure the load-bearing capacity of the structure under fire conditions. The characteristics that must be maintained during the action of fire are indicated by three letters:

R load bearing ability of the building element to maintain mechanical resistance under the action of fire

Etightness

ability of the assembly to resist the passage of flames, vapour and hot gasses to other areas of the structure

I thermal insulation ability of the assembly to limit heat transmission to other areas of the structure

The fire resistance abbreviation is followed by numbers indicating the minutes of stability in case of fire.

the mechanical strength, smoke tightness and thermal insulation of the element are maintained for 120 minutes (2h) after fire outbreak

the mechanical strength of the element is maintained for 60 minutes after the fire outbreak

Structural frame elements such as columns and beams are only required to maintain load-bearing capacity (R); floors and walls separating building compartments require, all three characteristics (REI).

FULL-SCALE TESTING

In cooperation with RISE - Research Institutes of Sweden, we carried out full-scale tests to determine the EI value of some of the most common joints in timber construction.

RESEARCH PROJECTS

Our next research projects will focus on studying the fire behaviour of the most common nodes in the world of timber construction. Our aim is to study them from every point of view, considering both static and sealing and thermal insulation aspects, in order to understand how the joint response changes during a fire in relation to the elements present.

IT'S NOT TACTICS, IT'S PREVENTION. Play in advance and handle fire problems with passive protection solutions: design your building by incorporating Rothoblaas tapes, sealants and membranes.

FIRE PROTECTION

UNPROTECTED JOINTS(1) TIMBER-TO-TIMBER

We protect timber structures

= 28 + 70 mm

= 28 + 70 mm

For connections with screws or nails, the fire resistance (Rtd) can be increased by up to 60 minutes by increasing the size of the timber elements.

bolts dowels

Fire resistance up to 120 minutes can be implemented by increasing the size of the timber elements (tfi) and the edge distances of the metal elements.

For STEEL-TO-TIMBER joints with exposed plate: the rules valid for steel structures apply (EN 1993-1-2).

PROTECTED JOINTS

Fire resistance can be achieved by designing partial or total fire protection systems. These protection systems can be timber dowels or plugs, timber panels or gypsum board (type A, H or F).

PARTIAL

The partial system selected only protects the connection for part of the required fire resistance time (e.g. 60 minutes resistance required, protection materials will resist fire for 45 minutes, the other 15 minutes must be ensured by the unprotected connection).

TOTAL

The total system protects the connection for the total fire resistance time required (e.g. 60 minutes protection required, protection materials will resist fire for 60 minutes).

CALCULATION EXAMPLE TIMBER CAP THICKNESS - PARTIAL PROTECTION [chap. 6.2.1.2 EN 1995-1-2:2005]

Panel thickness 1 and dowel depth 2 must be calculated according to the desired fire resistance.

afi = ßn · 1,5 · (treq - Rtd)

where:

afi = panel/anchor thickness

Rtd = unprotected connector fire resistance

treq = desired fire resistance

ßn= 0,8 for solid timber, 0,7 in all other cases

Dowel protection with R60 timber plugs:

afi = 0,7 · 1,5 · (60 - 20) = 42 mm

1.65 in

Note: The penetration depth into the timber of protective board fasteners must be ≥ 6 d (≥ 10-d in the case of Type F plasterboard).

LOADS IN CASE OF FIRE

During an extraordinary event such as a fire, the loads acting on structural elements are considered to be lower than the loads used for the design of structural elements at ultimate limit states (which are increased through coefficients)(1)

EXAMPLE

The snow on a roof during a fire tends to melt and therefore the weight on the structure is less; similarly, during a fire, people leave the premises, via the escape routes, decreasing the accidental category live load acting on the structural elements.

snow load at the design stage

Part of the roof not affected by the fire (snow still present)

accidental overload category (live load) at the design stage (estimation of the occupancy or use)

Part of the roof affected by a fire (no snow)

lower snow load under fire conditions

minor category accidental overload (live load) in fire conditions

(1)In fire design, this difference is accounted for by using (statistically determined) smaller load combination coefficients than for SLU design.

AXIALLY LOADED SCREWS

STRENGTH REDUCTION COEFFICIENT

Since they are subject to a lower load than the load used to design the connections under normal conditions, it is acceptable that the strength of the connection under fire conditions is also lower:

ηk,fi = Rk,fi/Rk

ηk,fi strength reduction coefficient under fire conditions

Rk characteristic connection strength under normal conditions

Rk,fi connection strength under fire conditions

a1 minimum distance between screw axis and beam edge

Determination of a1 from the chosen coefficient η and the desired fire resistance.

DETERMINATION OF THE SECTION UNDER FIRE CONDITIONS(1)

After determining a1, the minimum section under fire conditions can be calculated.

CALCULATION EXAMPLE PROJECT DATA

MAIN

SECONDARY BEAM

Angle in vertical plane α=0 ° Angle in horizontal plane β=0 °

FULLY THREADED SCREW WITH CYLINDRICAL HEAD

VERIFICATION

Threaded length on head side: Sg,HT = 135 mm (5 5/16 in);

Threaded length on tip side: Sg,NT=135 mm (5 5/16 in);

STRENGTH REDUCTION COEFFICIENT SELECTION

ηK,FI selected equal to 0,5

CHARACTERISTIC CONNECTOR STRENGTH UNDER STANDARD CONDITIONS:

FV,RK = 26,52 kN

R v = 1,194 lbf

allowable connector strength under standard conditions

CHARACTERISTIC CONNECTOR STRENGTH UNDER FIRE CONDITIONS:

FV,RK,FI = ηk,fi· FV,RK = 0,5 · 26,52 kN = 13,26 kN

Rv,FI=nki·Rv=0.5·1,194 lbf = 597 lbf

allowable connector strength under fire conditions

MINIMUM DISTANCES IN CASE OF FIRE

CROSSED SCREWS INSTALLED AT AN ANGLE Α TO THE GRAIN(1)

WITH AND WITHOUT PRE-DRILLING HOLE

SCREWS IN TENSION INSTALLED AT AN ANGLE Α TO THE GRAIN(1)

Values calculated using ηk,fi = 0,5 | a2,CG = a1 according to EN 1995-1-2

(1) New generation Eurocodes prEN 1995-1-2 (n.a.)

(2) For main beam-secondary beam joints with VGZ screws d = 7 mm (0.28 in) inclined or crossed, inserted at an angle of

to the secondary beam head, with a minimum secondary beam height of 18 d, the minimum distance

ROTHOBLAAS

THE PRACTICAL SCHOOL, USEFUL GUIDEBOOKS

Do you want to build in timber? We can give you the most up-to-date training, the smartest guides, the right products.

www.rothoblaas.com

APPLICATIONS AND SCREWS

PARTIALLY THREADED SCREWS FULLY THREADED SCREWS

STRENGTH

Concentration of stresses at localised areas in the direction of the load. Resistance is dependent on the bearing stress on the hole in the timber and the bending of the screw.

SCREWS FOR SHEAR LOADS

RESISTANCE PROPORTIONAL TO THE DIAMETER

STRENGTH

Stress distributed along the entire surface of the thread. High resistance associated with the surrounding timber engaged by tangential stresses.

CONNECTORS

STRESSED AXIALLY

RESISTANCE PROPORTIONAL TO THE THREADED LENGTH

STIFFNESS

• high slip

• low stiffness

• high ductility

STIFFNESS

• limited slip

• high stiffness

• reduced ductility

COMPARISON OF SCREWS

BEAM-TO-BEAM CONNECTION

Connection of two glulam beams (GL24h characteristic density = 385 kg/m3, Specific Gravity = 0,42) of height

H = 200 mm (7 3/4 in) loaded parallel to the grain. Design according to EN 1995-1-1:2004/A2:2014.

SOLUTION A

TBS partially thread screw

Ø8 x 300 mm (0.32 in x 11 3/4 in)

4 screws

SOLUTION B

VGZ fully threaded screw

Ø9 x 400 mm (0.36 in x 15 3/4 in)

1 screw

STRENGTH STIFFNESS

Rv,k = 14,4 kN

Z = 980 lbf (ASD)

Rv,k = 14,9 kN

Z = 800 lbf (ASD)

4 partially threaded screws are required to equal the sliding resistance of 1 fully threaded screw inclined at 45°.

Kser = 6,1 kN/mm

34.8 kip/in

Kser = 29,4 kN/mm

167.9 kip/in

A joint constructed with fully threaded screws is capable of providing greater stiffness: under the same stress, there will be less deformation than with partially threaded screws.

CONNECTION WITH CROSSED SCREWS

The vertical shear force F is distributed over the screws installed at 45°, stressing them axially.

FULLY THREADED

1 screw under tension

1 screw in compression

PARTIALLY THREAD

The threaded portion provides excellent performance in both tensile and compressive forces and enables a high overall strength to be achieved.

The screw head does not resist compression forces (it pulls out of the timber) and offers limited capacity for tension forces (pull-through < thread withdrawal).

PARTIALLY THREADED SCREWS

Shear-stressed screws: resistance proportional to diameter

LEGEND: installation without pre-drilled hole installation with pre-drilled hole

use not recommended but possible with specific precautions

FULLY THREADED SCREWS

Structural screws are considered to be (Ø ≥ 5 mm-0.20 in)

OUTDOOR SCREWS

CONNECTORS FOR HYBRID CONNECTIONS

WASHER AND METAL-TO-TIMBER

HUS VGU

Certified washers for screws with countersunk heads.

SOFTWOOD-HARDWOOD

HBS HARDWOOD

CONCRETE-TO-TIMBER

CTC Certified connector for concrete-timber composite systems, calculation software available.

SOFTWOOD-HARDWOOD

Certified screw for hybrid connections between softwood and BeechLVL elements.

TIMBER-TO-METAL

SBS-SPP

Self-drilling screw for fastening timber elements and panels to metal substructures up to 10 mm thick.

TIMBER-TO-METAL-TO-TIMBER

SBD - SBD EVO

Self-drilling dowelallows drilling of metal plates up to 10 mm (3/8 in) thick.

Certified screw for hybrid connections between softwood and BeechLVL elements.

TIMBER-INSULATION LAYER-TIMBER

DGZ

Fastening system for rigid or soft insulation installed on roofs or walls.

SBS-SPP

Ideal for fastening timber-to-metal-to-timber composite ceiling systems with trapezoidal sheet metal.

MATERIALS

Until 200 years ago, timber was the most commonly used material for construction; it was later replaced by steel and concrete. Timber as a "building material" has evolved over the last 100 years with the introduction of engineered wood products (GLT, CLT and LVL). Two macro-categories are distinguished: softwoods and hardwoods.

LEGEND: Douglas Fir Fir

Solid timber Monterey pine Pine

GLT

SPF (spruce-pine-fir) Cedar

CLT

Cross Laminated Timber

LVL

Laminated Veneer Lumber

OSB

Oriented Strand Board

Larch average density characteristic density

Birch Iroko

Ash Bangkirai

Oak Beech Ipè

Wenge Bamboo

Massaranduba Teak Eucalyptus

ROTHOBLAAS

DRILL BITS FOR DEEP DRILLING IN SOFT AND EUROPEAN HARDWOODS

TWIST DRILL BITS FOR HARDWOOD, MELAMINE-FACED BOARDS AND OTHER MATERIALS

How to install correctly?

MINIMUM DISTANCES AND PRE-DRILL

MINIMUM SPACING AND DISTANCES

The positioning of the screws within the timber element must take into account the interaction between the two elements.

The use of adequate spacing and minimum spacing between screws avoids splitting of the timber element and brittle connection failure mechanisms.

insufficient spacing between screws

inadequate edge and end distances

MINIMUM DISTANCES AND SPACING REQUIREMENTSfor screws, with and without pre-drilled holes and on different materials, available in the "Screws and connectors for timber" catalogue www.rothoblaas.com

PRE-DRILL AND PILOT HOLE

A pre-drilled hole allows the screw to be installed with less resistance and minimises damage in the timber. Pre-drilling is carried out along the entire length of the screw. Installation with a pre-drilled hole generally allows for reduced spacing and minimum edge and end distances

installation without pre-drilled hole

installation with pre-drilled hole

The portion of timber affected by the insertion of the screw is greater in the case of no pre-drilling.

Screws can be placed at a reduced distance because they are not affected by the interaction with each other.

Pilot holes or guide holes are used to facilitate the insertion of screws. They have limited length (usually 40-80 mm 1.5-3 in) . They are recommended when installing long screws or when a very precise insertion angle is required.

PRE-DRILL HOLE DIAMETER

The size of the pre-drilled hole depends on the geometry of the screw and the type of wood on which it is to be installed (for more specific information on materials, see page 55).

dv,rec the recommended pre-drill hole diameter

dv the pre-drill hole diameter

d2 the internal thread diameter

d1 the nominal diameter

ds the shank diameter

d1 the nominal diameter

d2 the internal thread diameter

THE IMPORTANCE OF CORRECT PRE-DRILL

The force on the screw during insertion exceeds the torsional resistance of the screw.

A portion of the thread is not in contact with the wood; the withdrawal resistance decreases.

(1) ETA-11/0030.

INSERTION MOMENT

To penetrate timber, the screw must overcome its resistance force.

The force during installation (tortional insertion moment - Rtor) is related to the geometry of the fastener and the material of the support. To avoid breakage, the force on the screw must not equal or exceed its intrinsic torsion resistance (ftor). According to the European standard(1), a minimum screwing torsion ratio of 1,50 (ftor,k / Rtor,mean ≥ 1,5) must be ensured.

The graphs below show the development of the insertion moment for screws applied under different conditions, both in terms of the timber used and the type of pre-drill.

insertion type A

WITHOUT pre-drilled hole (LV = 0 mm)

insertion type B

WITH pre-drilled hole of length LV = L/2

insertion type C

WITH pre-drilled hole of length LV = L

SOFTWOOD

The installation of screws in wood with relatively low density can also be achieved without a pre-drilling hole. The force on the screw remains below the torsional limit [A-B-C].

The use of a pilot hole facilitates installation and ensures that the screw is oriented in the right direction and angle.

HARDWOOD

“Standard" screws require a pre-drillied hole [C] in order to be installed in hard wood; otherwise, there is a risk of breakage [A].

Partial length pre-drilled holes [B] reduce the insertion moment on the screw but does not preclude the possibility of breakage.

Screws with specific geometry for hardwood (HARDWOOD screws) can be installed without pre-drilling holes [AH].

IMPULSE and IMPACT : YES or NO?

Rothoblaas carried out an experimental campaign in cooperation with the University of Innsbruck to evaluate the influence of the use of different screwdrivers on the mechanical properties of screws (e.g. tensile strength) and the insertion moment.

partially threaded

HBS Ø6 - Ø8

(0.24 - 0.32 in)

TBS Ø10

(0.40 in)

fully threaded

VGZ Ø7 - Ø9

(0.28 - 0.36 in)

VGS Ø11 - Ø13

L up to 800 mm (31 1/2 in)

(0.44 - 0.52 in)

TENSILE STRENGTH

The steel tensile strengths of new, unused screws (reference samples) were compared with screws installed in timber (inserted and then extracted with different screwdrivers).

The tensile strength is not dependent on the type of driver used during installation: as shown in the graph to the right, the differences, less than 2%, are presumably related to the intrinsic variability of the timber elements used and not to the screwdriver used.

INSERTION MOMENT

The use of an impact screwdriver/pulse screw gun did not cause any substantial change in insertion resistance compared to installation with a “standard” screwdriver. The characteristic torsion ratio (ftor,k / Rtor,MW) remained below the torsional limits of the standard.

ACCREDITED TEST REPORT (202011-0088) “Influence on the tension strength of screws type HBS, TBS, VGS and VGZ by the use of different screw-in devices “available on www.rothoblaas.com

TIMBER-TO-TIMBER CONNECTION

In the case of screws used in timber-to-timber (softwood) structural connections, a pulse screw gun/screwdriver can also be used for installation.

Proper installation ensures structural performance and relative strength of partially or fully threaded self-drilling screws in timber-to-timber and metal-to-timber connections.

Do not hammer the screw tips into the timber.

The screw cannot be reused.

In general, it is recommended to insert the connector in one operation, without making stops and starts that could create overstressing states in the screw.

Select the appropriate size and type of bit. Rothoblaas CATCH or CATCHL screw holder can be used to ensure that the bit remains in the screw head recess during installation.

A pilot hole is recommended to ensure the correct installation direction.

It is recommended to use the JIG VGZ 45° installation template. Respect the insertion angle.

METAL-TO-TIMBER CONNECTION

The screw must not be subjected to extreme stress and therefore must not come into contact with the plate in an abrupt manner which can lead to breakage even after installation.

With an impact screwdriver/pulse screw gun, it is difficult to determine the precise stopping point. The screw is not continuously stressed, which is why the use of the impact screwdriver/pulse screw gun is not recommended.

METAL-TO-TIMBER CONNECTION

INSTALLATION REQUIREMENTS

CONDITIONS OF USE

Avoid dimensional changes in the metal, e.g. due to large temperature fluctuations.

INSERTION

Respect the insertion angle.

TIGHTENING

Avoid accidental stress during installation. Shrinkage or swelling of timber elements due to changes in moisture content must be avoided.

Avoid bending.

The installation of multiple screws must be performed to guarantee that loads are distributed evenly to all fasteners.

Use standard screwdrivers and to ensure correct tightening by using a torque wrench or to use torque-controlled screwdrivers in order to avoid prestressing screw heads.

Recommended tightening torque values:

FINISHES

Ensuring full contact between the underside of the screw head and the metal element.

PARTICULAR CONSIDERATION SHOULD BE GIVEN TO

Due to the installation angle, a large head is critical in metal-to-timber applications.

Limited or incorrect contact between the metal element and the screw head can lead to localized prestressing resulting in reduced connection capacity or localised screw failure.

PLATE HOLES

The diameter of a hole in a metal plate must always be larger than the outer diameter of the screw, in order to prevent the thread from being damaged during installation and the connector from not performing as intended.

Ensure that the screw threads do not come into contact with the metal element during insertion.

CONSTRUCTION PRESCRIPTIONS: DECKING

Attention to detail guarantees the durability, aesthetics and stability of the decking. It also helps prevent of problems related to rot, cracks or deformation.

DISTANCE BETWEEN BOARDS

• allow for the wood to move

• avoid the accumulation of water or rot at the ends of the boards

• avoid accumulation of dirt

FASTENERS CHOICE

• meet appearance requirements

• visible or hidden fastening

• guarantee safety and stability

• plan for an appropriate spacing between the substructure elements 40÷60 cm (16 in-24 in)

• verify that the substructure is level

• use the same material for the decking and substructure

UNDERBOARD VENTILATION

• avoid the accumulation of water and moisture

• allow for the wood to move

• avoid direct contact between the board and supporting structure

POSITIONING OF FASTENINGS

• avoid cracking of the boards

• ensure permanent fixture

• allow for the wood to move

• avoid standing water

• avoid the localised accumulation of moisture in the wood

• avoid accumulation of dirt

Proper selection of a wood species and decking quality on the basis of the design requirements can avoid shrinkage, swelling, various deformations between elements and warping. These problems can compromise the proper functioning of the fastening system.

TIME OF CONSTRUCTION

Terraces: screwchoosingtheright and installation instructions

3 YEARS LATER

ROTHOBLAAS RECOMMENDS

DRILL STOP SET OF DRILL BITS AND COUNTERBORE CUTTER WITH SWIVEL DEPTH STOP

BROAD COUNTERBORE CUTTER FOR KKT, KKZ, KKA

CRAB MAXI BOARD CLAMP

Swivel handle for precise adjustments

To tension from 5 to 7 boards together

Opening from 200 to 770 mm (8 to 30 in)

STAR STAR FOR DISTANCES

The 5 most common dimensions in a single tool

Creation of uniformly sized joints

Thickness from 4 to 8 mm (3/16 to 5/16 in)

OUTDOOR , everything you need to design and build outdoor environments. Discover the outdoor guide on our website or request the catalogue from your agent. www.rothoblaas.com

CONSTRUCTION REQUIREMENTS: WORKSITE

During transport, storage and assembly, wooden elements must be protected to minimise their changes in moisture content.

CONSTRUCTION PHASE: construction in progress

When installed, timber elements have moisture contents compatible with those of the factory in which they were manufactured.

INTERMEDIATE PHASE: construction site is exposed to the weather

If it is not properly protected, in the event of rain, the increase in humidity in the air leads to a considerable increase in moisture content in the wooden elements.

FINISHED WORK: construction completed

Timber elements are in moisture equilibrium with the final environmental conditions. Protecting the structure from weather, especially the joints, during the construction phase ensures structural performance as designed.

ROTHOBLAAS RECOMMENDS

CAP TOP

TARPAULIN

Construction site: best practiceformoisturemanagement

Each size is equipped with a reinforced lifting hook for easier installation.

Thanks to the metal fastening eyelets every metre, it is possible to fix the tarpaulin to the roof.

The large mass per unit area and the type of material guarantee better mechanical resistance and durability over time.

When fixing the tarpaulin to the roof it is important that all eyelets are always anchored so that the wind load is spread over as many eyelets as possible.

TRASPIR ADHESIVE 260

HIGHLY BREATHABLE SELF-ADHESIVE MEMBRANE

SELF-ADHESIVE

Thanks to the new generation glue, the membrane ensures good adhesion even on rough OSB.

SECURE SEALING

The adhesive surface prevents the formation of airflow behind the membrane in case of accidental breakage or failure to seal.

BREATHABLE

Thanks to the patented glue, the membrane remains perfectly breathable even when fully bonded.

SELF-ADHESIVE SLATED BITUMINOUS MEMBRANE

EASY INSTALLATION

The slate finish makes BYTUM SLATE 3500 usable on slopes up to 5° as an under-tile and compatible with mortar and foam.

WIDE RANGE

Available in 4 colours to meet different application areas and aesthetic requirements.

FLEXIBILITY

Flexibility and workability are guaranteed even at low temperatures thanks to the polymer-modified bituminous compound.

SCREWDRIVERS

Whatistheright screwdriverformy screws?

The choice of a screw or drill driver depends on the type and size of the screw, the application and the type of material.

SMALL SCREWS | Ø3,5-Ø10 mm (0.14 - 0.40 in)

• Universal use for multiple applications

• Ideal for construction site use with battery-powered system

• Switchable percussion function and adjustment of maximum torque level for precise work

LARGE SCREWS | Ø8-Ø12 mm (0.32 - 0.48 in)

ASB 18

2-SPEED CORDLESS DRILL DRIVER

• Powerful drill driver for structural screws

• In first gear it allows the installation of connectors, including very long ones

• In second gear (high speed) it allows the drilling of both timber and steel elements

CONNECTORS | Ø11-Ø20 (0.44 - 0.79 in)

B 13 B

2-SPEED DRILL DRIVER

• Powerful and robust 2000W motor with right/left rotation for very high torque output in 1st gear (> 250 Nm-184 lbf-ft)

• With the use of appropriate adaptors, it allows the installation of threaded rods or very long screws in timber

D 38 RLE

4-SPEED DRILL DRIVER

TOOLS AND MACHINES, everything you need to work in best conditions on site. Discover them on our website or ask your trusted agent for the catalogue. www.rothoblaas.com

Rotho Blaas Srl does not guarantee the legal and/or design conformity of data and calculations, as Rotho Blass provides indicative tools such as technical-commercial service within the sales activity.

Rotho Blaas Srl follows a policy of continuous development of its products, thereby reserving the right to modify their characteristics, technical specifications and other documentation without notice.

The user or the designer are responsible to verify, at each use, the conformity of the data to the regulations in force and to the project. The ultimate responsibility for choosing the appropriate product for a specific application lies with the user/designer. The values resulting from "experimental investigations" are based on the actual test results and valid only for the test conditions specified.

Rotho Blaas Srl does not guarantee and in no case can be held responsible for damages, losses and costs or other consequences, for any reason (warranty for defects, warranty for malfunction, product or legal responsibility, etc.) deriving from the use or inability to use the products for any purpose; from non-conforming use of the product;

Rotho Blaas Srl is not liable in any way for any errors in printing and/or typing. In the event of differences between the contents of the catalogue versions in the various languages, the Italian text is binding and takes precedence with respect to the translations.

Pictures are partially completed with accessories not included. Images are for illustration purposes only. Packaged quantities may vary.

This catalogue is private property of Rotho Blaas Srl and may not be copied, reproduced or published, totally or in part, without prior written consent. All violations will be prosecuted according to law.

The general purchase conditions of Rotho Blaas Srl are available on the website www.rothoblaas.com.

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