Flexural members are those elements in a structure that are subjected to bending, and several types and forms of such members are used in timber construction. Typical examples are solid section rectangular beams, floor joists, rafters and purlins. Other examples include glulam beams and composites (thin webbed beams and thin flanged beams), and the design requirements of these types of members are covered in Chapters 6 and 7 respectively. Typical examples of timber beams, floor joists and purlins are shown in Figure 4.1.

Although the design principles used for the design of timber members in bending are essentially the same as those used for members constructed from other materials, e.g. concrete or steel, material characteristics peculiar to timber and wood-based structural products dictate that additional design checks are undertaken. With timber, the material properties are different in the two main directions, i.e. parallel and perpendicular to the grain and, unlike steel and concrete, they are affected by changes in moisture content and duration of load.

This chapter deals in detail with the general requirements that are necessary for the design of flexural members made from straight solid timber or wood-based structural products of uniform cross-section in which the grain runs essentially parallel to the member lengths. The design of tapered, curved and pitched cambered beams is covered in Chapter 6.

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