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Trimmer joists C

Tongued and grooved boarding (b) Solid timber tongued and grooved decking

Load-bearing partition wall and spreader beam

Masonry wall

Stairwell

Trimmer joists Joist hanger nailed together

(a) A typical suspended floor arrangement

Trimmer joists Joist hanger nailed together

(c) A typical joist to trimmer joists connection

10-mm bolts staggered at 600-mm centres

10-mm bolts staggered at 600-mm centres

6-10-mm-thick steel plate, 10 mm less in depth than timber joists

Joists

Joists

6-10-mm-thick steel plate, 10 mm less in depth than timber joists

Joists

Joists

Solid blocking between joists

Timber wall plate

Support wall

Solid blocking between joists

Timber wall plate

Support wall

(d) Flitched beam

(e) A typical support arrangement

Fig. 1.18. Suspended timber flooring - typical components.

in the production of EWPs and also in timber construction to manufacture adhesively bonded components and connections (glued joints).

Connections bonded by adhesives can result in a better appearance and are often stiffer, requiring less timber; if formed by thermosetting resins they can perform better in fire than mechanical connectors. Their main disadvantage is the high level of quality control that is required in their manufacture and they can also degrade in conditions of fluctuating moisture content, in particular where dissimilar materials are involved. Examples of uses of adhesives in structural timber connections include finger joints, scarf joints, splice and gusset plates (using high-quality structural plywood plates), in the manufacture of I-beams, box beams, stress skin panels and in composite (sandwich) constructions where OSB or plywood side panels are bonded to a core of polystyrene such as in the manufacture of SIPs.

Structural adhesives should be weather and boil proof to BS EN 301:2006 [24]. Acceptable strength and durability can be achieved by using phenolic and aminoplastic-type adhesives as defined in BS EN 301:2006. The adhesives should meet the requirements for adhesives type I or II as follows:

• Type I adhesives, which will stand full outdoor exposure and temperatures up to and above 50°C.

• Type II adhesives, which may be used in heated and ventilated buildings and exterior protected from weather. They may not be able to stand prolonged exposure to weather or to temperatures above 50°C.

The following adhesives may be considered:

• Resorcinol formaldehyde and phenol resorcinol formaldehyde

Type: phenolic thermoset resin - for exterior use. Uses: finger jointing, laminating, timber jointing, etc.

• Phenol-formaldehyde (PF) hot setting

Type: phenolic thermoset resin - for exterior use. Uses: plywood, laminating, particleboard, etc.

• Melamine urea formaldehyde

Type: aminoplastic thermoset resin - for semi-exterior and humid interior use. Uses: plywood, laminating, particleboard, timber jointing etc.

• Urea formaldehyde

Type: aminoplastic thermoset resin - for interior use. Uses: plywood, laminating, particleboard, timber jointing etc.

• Casein adhesives

Type: milk product - for interior use only. Uses: general purpose timber jointing.

It should be noted that not all adhesives are classified in accordance with BS EN 301:2006. It is therefore important for the designer to ensure that the adhesives selected are suitable for the specified service class and comply with the relevant building regulations. It is also important that timber is conditioned to a moisture content corresponding to the average moisture content likely to be attained in service and that surfaces are properly prepared prior to gluing.

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