Introduction

In this chapter, the design of structural elements that provide lateral stability or act as diaphragms to transfer lateral actions through the structure is addressed.

There are several ways in which stability or lateral bracing can be provided to a structure and those most commonly used in timber structures are as follows:

(a) Provision of lateral bracing members;

(b) The use of roof or floor diaphragms;

(c) The use of wall diaphragms.

When an element in a structure is subjected to compression due to a direct force or by a bending moment and is insufficiently stiff to prevent lateral instability or excessive lateral deflection, lateral bracing of the member is likely to be required. This is particularly relevant to the design of columns and beams acting as individual members or as members in a braced system, and the methodology used in such cases is given in 9.2.5, EC5 [1].

Examples of the types of situations where lateral stability bracing is commonly required in timber structures are shown in Figure 9.1.

When lateral forces at floor or roof level in timber-framed buildings have to be resisted, this is commonly achieved by the use of the floor and/or roof structure functioning as diaphragms and the end reaction forces are typically provided by wall diaphragms as illustrated in Figure 9.2. The wall forces are then transferred to the foundation structure through the racking resistance of the diaphragms. For clarity, diaphragms or equivalent bracing structures to resist lateral forces when they act along the length of the building, i.e. at right angles to those shown in Figure 9.2, have not been shown. The design procedures for these elements are covered in 9.2.3 and 9.2.4 of EC5.

In this chapter, the design of structural elements that provide stability or act as diaphragms to transfer actions through the structure is addressed.

The general information in 4.3 is relevant to the content of this chapter.

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