Tension or compression perpendicular to grain:

Panel shear:

category and all are processed in a similar way. Examples include high-density fibre-board, medium-density fibreboard, tempered hardboard, cement-bonded particleboard, etc. For fibreboards, chips are refined to wood fibres by the aid of steam and then dried and adhesive is added to form a mat of wood particles and pressed until the adhesive is cured. After cooling the boards are cut to the required sizes. Wood chipboard is a particular derivative of this product family, and is made from small particles of wood and binder.

In BS EN 312:2003 [21] seven types of particleboards (chipboards) are classified and are distinguished as follows:

• P1 general purpose boards for use in dry conditions

• P2 boards for interior fitments (including furniture) for use in dry conditions

• P3 non-load-bearing boards for use in humid conditions

• P4 load-bearing boards for use in dry conditions

• P5 load-bearing boards for use in humid conditions

• P6 heavy-duty load-bearing boards for use in dry conditions

• P7 heavy-duty load-bearing boards for use in humid conditions.

Note that dry conditions refer to service class 1 only and humid conditions refer to service classes 1 and 2.

The P1, P2 and P3 grade particleboards (chipboards) are for general applications including furniture manufacturing and kitchen worktops. Boards of type P4-P7 are intended for use in design and construction of load-bearing or stiffening building elements such as walls, flooring, roofing and I-beams. For dry internal applications grade P4 can be used. The P4 grade is adequate where no moisture will be encountered during or after construction. The moisture-resistant grade P5 is the most commonly specified flooring in the United Kingdom. It is used extensively in new build house building and refurbishment projects. Durability is achieved by using advanced moisture-resistant resins. A green identification dye is added to the surface of the P5 grade to visually differentiate it on-site.

BS EN 12369-1:2001 gives the minimum characteristic values for particleboards complying with BS EN 312:2003, which are summarised in Table 1.18.

1.7.8 Thin webbed joists (I-joists)

I-joists are structurally engineered timber joists comprising flanges made from solid timber or LVL and a web made from OSB, plywood or particleboard. The flanges and web are bonded together to form an I-section member, a structurally efficient alterative to conventional solid timber. I-joists are economical and versatile structural elements in which the geometry permits efficient use of material by concentrating the timber in the outermost areas of the cross-section where it is required to resist the stresses. The flanges are commonly designed to provide the moment capacity of the beam and the web to predominantly carry the shear force; see Figure 1.15.

I-joists are lightweight and can easily be handled by one or two persons, they generally possess higher strength and stiffness than comparable-sized solid timber, resist

Table 1.18 Minimum strength, stiffness and density values for particleboards P4 and P5 complying with EN 312: 2003 (based on BS EN 12369-1:2001)
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