Water ?
Creep Toughness
Adhesion o
Easy to x
Curing o o
Good, than currcnt
o to currcnt adhesives.
Inferior to currcnt adhesives.
variations between brands.
The use
of structuralwood adhesives
Three ways of bonding wood be distinguished.
- initiative EU
the glue must match the shear strength parallel and the tensile strength to the direction of timber. Approved adhesives
requirements without problems. Swelling and shrinking stresses be small, since all the members are in with each other.
this the adhesive should the tensile strength of the in the direction. Structural butt end jointing of timber, which that the adhesive
the tensile of the is not possible current techniques. Instead, the jointing is out in such a way tensile stresses in the are transformed to stresses in gluelines. This be done in various ways, used is fingerjointing. In this joint the shear strength of' all finger areas should ideally match the tensile of cross-section of' member. Since the shear strength is only 1/10 the tensile strength, the area should be 10 tirnes
area. Again members are line with each other, swelling and shrinking problems.
In case the adhesive must the shear strength and transverse tensile the wood, which is not a problem. jointed will,
-
restrained members like plywood and board are glued to solid wood which are fairly narrow in box beams, joints.In such products lengthwise of the solid wood
match approximately with restrained of woodbased panel.
Stresses along the are therefore small, but they be high across the if the are wide, or the moisture fluctuations great. This may produce fatigue failure in joint with time.
This consists of the following steps:
- conditioning the timber to a moisture content corresponding to the average content which is likely to apply in service,
- machining of the surfaces to be bonded, preferably just before bonding, because freshly cut dust free give the best This be done sharp tools, to prevent the surfaces,
- mixing and application adhesive,
- application of sufficient to tlie members in contact with each other until adhesive got sufficient handling strength,
- in some cases: application of heat during the pressing period in order lo
-
an under Aspeed up curing,
- conditioning of the bonded members to obtain postcuring and temperature-
-
and moisture-equilibrium.
treated wood
treatment may used to protect wood against decay, or to it fire- resistant or If the members are used in production afterwards, they will to be before gluing. This requires a certain penetration of chemical, or of it will be removed by the planing.
Such treatment of may affect the gluing properties, dependant on the type
of treatment. As a the should be tried out
beforehand. The following guidelines may be applied:
- creosote treatments. Gluing is difficult but possible with PRF and polyurethane-adhesives. Gluing and impregnating afterwards is recornmended.
-
salts. The salts usually give nodifficulties. Salts containing free acid boric or compounds able to with formaldehyde ammonium salts) give problems. Some of the decay protecting and most of the fire protecting salts are of this type.
References
CIB 71-PSL of life of building
CIB-publication
(1987). of glued laminated for windows (in Swedish).
rapport
Selbo, M.L. (1965). of melamine in various exposures. Forest Prod. 15 (12).
1965, p.475.
(1986). durability of water-based polymer-isocyanate adhesives for wood. (Japanese with English summary), J. Wood (6) 1986, p.432.
an initiative under EU Comctr
Behaviour of timber and wood-based
natural properties of timber affecting its behaviour when exposed fire, that is theand physical changes under the influence of fire, are explained.
Introduction
There is no simple way of expressing behaviour of a with respect to fire. There are two phases a fire, the developing phase and the fully developed phase and a materials performance to be categorised in respect of those two conditions. The developing incorporates a number of separate phenomena, the combustibility of the material, the ease of ignition, speed of
of across its surface and the rate at which heat is released.
The fully developed phase represents post over conditions where all combustible materials become involved in the fire. desirable properties are the ability to continue to carry load to contain fire within the zone of' without the escape of flames or hot gases and without conducting excessive heat to the unexposed lead indirectly to fire being transmitted to adjacent areas.
The ability to resist fully developed fire is universally as the fire resistance but in general can relate to an element of construction rather than to a material. The performance of even a such a column or a beam is dependent upon such as end conditions and the
magnitude and distribution of any loading.
Considering the behaviour of wood-based materials and solid timber when subjected to developing fire, wood-based will burn and are rated
combustible. Whilst the may be by use of coatings
or impregnation with retarding salts, none of these can render timber, or its related products, albeit higher levels of energy be needed to cause it to bum. Solid timber is not readily ignited and there are very few represent an unacceptable ignition risk in most environments. The actual values are related to the density, species, moisture content and factor.
Timber, being combustible will spread fire across its surface, phenomena being a number of ignitions each triggering an adjacent ignition. As is not readily