Buckling resistance condition for a spaced column (5.3.1 (EC5, 6.3.2)) Relative slenderness about the y-y

(equation (5.3); EC5, equation (6.21)) — ■ A ——

As relative slenderness ratio is greater than 0.3, conditions in 5.3.1 (EC5, 6.3.2(3)) will apply:

Factor j3c for solid timber j3c — 0.2

Instability factor, ky ky — 0.5 ■ [1 + jc ■ (xrei.y - 0.3) + X^el y\

(equation (5.4a); EC5, equation (6.25)) ky + Jky, - k y krel.y kc.y = 0.54

Instability factor condition (equation (5.11a); EC5, equation (6.23) kcy ' /c-ad - with bending stresses equal to zero)

Strength of the packs:

Shear force across the shafts, Vd (equation (8.14); EC5, equation (C.5)) =

Shear condition:

Design shear force on the pack, Td Td =

Design shear stress across the pack,

Bending condition (critical condition will be the pack and the shaft in tension perpendicular to the grain due to the bending stresses at the glued interface with the shaft):

Bending moment at the junction with the shaft, Md

Design stress on the pack due to the am d = bending moment, am d

Design strength of the pack based on /t.90.d = the tension strength perpendicular to the grain, /t.9o.d

Section is satisfactory as a spaced column in strength class C22 timber.

Example 8.8.3 A lattice column with N lattice bracing is assembled from two shafts of equal cross-section, 63 mm thick by 225 mm deep, as shown in Figure E8.8.3. The column is pin jointed at each end and held laterally in position at these locations. It is fabricated from C22 timber to BS EN 338:2003 and functions under service class 1 conditions. The eccentricity of the diagonal at each connection is 150 mm.

Check the adequacy of the latticed column to support a combined characteristic permanent axial compression action of 45 kN, a characteristic short-duration variable axial compression action of 60 kN and a characteristic bending moment due to self-weight of 1.0 kN/m about the z-z axis. Also calculate the design loads to be taken by the bracing and their connections.

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