Q

where all veneers are parallel to the beam axis and V0 is the reference volume against which the function exponent has been derived, and equals 0.01 m3; V is the stressed volume (in m3) of the apex zone with a maximum value of 2Vbeam/3, where Vbeam is the volume of the beam.

From the geometry of the apex zone, for the beam types shown in Figure 6.7, all having a thickness b, the stressed volume, V, is given in Table 6.6.

6.4.2.5 Criterion for bending stress -for double tapered beams, curved beams and pitched cambered beams

To achieve an acceptable design, the design bending stress in the apex zone of the beam section must be no greater than its reduced design bending strength, i.e.:

where am,o,d is the design tensile bending stress in the apex zone and is obtained from 6.4.2.1.1 for double tapered beams and pitched cambered beams, and 6.4.2.2.1 for curved beams; kr fm,0,d is the reduced design bending strength of the apex zone of the beam and is obtained from 6.4.2.3 for double tapered beams, pitched cambered beams and curved beams.

6.4.2.6 Criterion for radial tension stress - for double tapered beams, curved beams and pitched cambered beams

To achieve an acceptable design, the design tensile stress perpendicular to the grain in the apex zone of the beam section for the relevant beam type must be no greater than its reduced design tension strength, i.e.:

where at,9o,d is the design tension stress in the apex zone and is obtained from 6.4.2.1.2 for double tapered beams and pitched cambered beams, and 6.4.2.2.2 for curved beams; kdis^oi f,t,90,d is the reduced design tensile strength of the apex zone of the beam and is obtained from 6.4.2.4 for double tapered beams, pitched cambered beams and curved beams.

See Example 6.7.4.

6.4.3 Design of double tapered beams, curved and pitched cambered beams subjected to combined shear and tension perpendicular to the grain

When double tapered beams, curved beams and pitched cambered beams of breadth b and depth hap at the apex are subjected to combined shear stresses and tension stresses perpendicular to the grain, these stresses will interact and in EC5 the criterion to be met at the design condition is:

Td 90 d

fv,d kdiskvol /t,90,d where

• Td is the design shear stress at the apex section. When the design shear force at the apex is Fd, the design shear stress can be assumed to be Td = 3Fd/2bhap;

• /v,d is the design shear strength of the beam and for a glulam beam it will be kmodksys/v,g,k/KM, where the functions are as previously defined;

• ^t,90,dis the design tension stress on the beam at the apex and, for the relevant beam type, is obtained from 6.4.2.1.2 and 6.4.2.2.2;

• kdiskvol/t,90,d is the reduced tensile strength of the beam perpendicular to the grain and is obtained from 6.4.2.4.

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