Design Of Glued Composite Sections

7.3.1 Glued thin webbed beams

Because these sections are designed to function as solid units, the strain is taken to vary linearly over their depth. However, as the value of the modulus of elasticity, E, of each material in the section will normally be different, the theory of bending cannot be directly applied. To analyse these sections the equivalent section approach (sometimes referred to as the modular ratio approach) can be is adopted and has been incorporated into the design procedure used in this chapter.

In this method, one of the materials in the composite section is selected and the others replaced by equivalent areas of the selected material such that when subjected to bending the force in the replaced materials at any distance from the neutral axis will be the same as that taken by the original materials at the same position. By this method, an equivalent homogeneous section is formed and the theory of bending can

(a) I-beams floor joists (b) I-beams in sloped roofs (photo courtesy of

APA, The Engineered Wood Association)

(a) I-beams floor joists (b) I-beams in sloped roofs (photo courtesy of

APA, The Engineered Wood Association)

(c) I-beams (photo courtesy of APA, The (d) Curved box beam (photo courtesy of Fred Bosveld Engineered Wood Association) and Peter Yttrup)

K"1111

(e) Large span box beam and I-joists using LVL (photo courtesy of Engineered Wood products Association of Australia (EWPAA))

(f) Large span box portal frames using LVL (photo courtesy of Engineered Wood products Association of Australia (EWPAA))

(e) Large span box beam and I-joists using LVL (photo courtesy of Engineered Wood products Association of Australia (EWPAA))

(f) Large span box portal frames using LVL (photo courtesy of Engineered Wood products Association of Australia (EWPAA))

Fig. 7.2. Examples of uses of composite timber and wood-based sections.

be applied. The bending stress in the material selected for the section will be found directly from the stress analysis. For the material that has been replaced, the stress is obtained by multiplying the bending stress in the equivalent homogeneous section by the ratio of the modulus of elasticity of the actual material used in the composite section to the modulus of elasticity of the selected material. This ratio is referred to as

Compression

0 0

Post a comment