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Loaded end

Loaded end a3,c

(b) Edge and end distances Fig. 10.11. Fastener spacings and distances.

180o < a< 360o Unloaded edge to allow fixings to be formed in dense timber and this is a requirement for nails driven in timber with a characteristic density greater than 500 kg/m3 (EC5,8.3.1.1) and for all screws in hardwood (EC5,10.4.5). The above and other related requirements in EC5 are summarised in the notes accompanying Tables 10.8 and 10.9. EC5 rules for spacing, edge and end distances for joints formed with nails and/or staples are summarised in Table 10.8 and the following requirements also apply.

Additional requirements in EC5 (a) Laterally loaded nailed connections

General

8.3.1.1(2) - the timber should be pre-drilled when

• its characteristic density >500 kg/m3;

• the nail diameter exceeds 8d (Note that this should be 6d and is one of the proposed draft amendments to be made to EC5, referred to in Appendix C).

Nailed timber-to-timber connections

8.3.1.2(6) - when the thickness of the timber members is smaller than tderived from EC5, equation (8.18), given below, the members should be pre-drilled:

Table 10.8 Minimum spacings and edge and end distances using nails and/or staples of diameter d for timber-to-timber connections*

Minimum spacing or distance

Nails (see Figure 10.11)

Without pre-drilled holes With pre-drilled holes d > 6 mm and/or p^ > Staples (see Figures 10.11 and

Spacing or distance and af < 420 kg/m3 420 kg/m3 < < 500 kg/m3 500 kg/m3 10.17)

Spacing parallel to the d < 5 mm : (5 + 5| cosa|)<i (7 + 8| cosa|)<i (4 + | cosa|)<i for 9 > 30° : (10 + 5| cosa|)<i grain - a\

0° < a < 360° d > 5 mm : (5 + 7| cosa|)<i for 9 < 30° : (15 + 5| cosa|)d

Spacing perpendicular to 5d Id (3 + |sina|)<i 15d the grain - a2 0° < a < 360°

Loaded end distance a3 t (10 + 5cosa)<i (15 + 5cosa)<i (7 + 5 cos a)d (15 + 5| cosa|)<i

Unloaded end a3tC 10d 15d Id 15d -90° < a < 270°

Loaded edge distance a^ d < 5 mm : (5 + 2 sin a)d d < 5 mm : (7 + 2 sin a)d d < 5 mm : (3 + 2 sin a)d (15 + 51 sin a \)d

0° < a < 180° d > 5 mm : (5 + 5 sin a)d d > 5 mm : (7 + 5 sin a)d d > 5 mm : (3 + 4 sin a)d

Unloaded edge 5d Id 3d 10d distance 180° < a < 360°

'a is the angle between the direction of the nail force and the grain.

Table 10.9 Minimum spacings and edge and end distances for bolts and/or dowels in timber-to-timber, panel-to-timber and steel-to-timber connections*

Spacing or distance (see Figure 10.11) and at

Minimum spacing or distance

Bolts

Dowels

Spacing parallel to the grain: a1 0° < a < 360°

(4 + I cosa|)d

(3 + 2| cosa\)d

Spacing perpendicular to the grain: a2

0° < a < 360°

4d

3d

Loaded end distance: a3 t -90° < a < 90° '

max (7d; 8O mm)

max (7d; 80 mm)

Unloaded end distance: a3 c 90° < a < 150° 150° < a < 210° 210° < a < 270°

max [(1 + 6 sin a)d; 4d] 4d max [(1 + 6 sin a)d; 4d]

max (a3,t |sin a|)d; 3d) 3d max (a3,t |sin a|)d; 3d)

Loaded edge distance: a4 t

0° < a < 180°

max [(2 + 2 sin a)d; 3d]

max [(2 + 2 sin a)d; 3d]

Unloaded edge distance: a4 c 180° < a < 360°

3d

3d

ta is the angle between the direction of the nail force and the grain.

ta is the angle between the direction of the nail force and the grain.

where t is the thickness of timber member to avoid pre-drilling (in mm), pk is the characteristic timber density (in kg/m3), and d is the nail diameter (in mm). 8.3.1.2(7) - the requirement of NA.2.8 in the UKNA to EC5 [10] is that this rule should not be applied to nailed joints.

(b) Nailed panel-to-timber connections

8.3.1.3(1) - minimum nail spacings for all nailed panel-to-timber connections are those given in Table 10.8 multiplied by a factor of 0.85. The end/edge distances remain unchanged unless specifically defined in EC5.

8.3.1.3(2) - minimum edge distances and end distances in plywood members should be taken as 3d for an unloaded edge (or end) and (3 + 4 sin a)d for a loaded edge (or end).

(c) Nailed steel-to-timber connections

8.4.1.4(1) - minimum nail spacings are those given in Table 10.8 multiplied by a factor of 0.7. The minimum edge and end distances remain unchanged.

EC5 rules for spacing, edge and end distances for joints formed with bolts and/or dowels are summarised in Table 10.9.

EC5 rules for spacing, edge and end distances for joints formed with screws (EC5, 8.7.1) are as follows:

Tension split in the timber

Tension split in the timber

FEd force components

Fig. 10.12. Member loaded in tension at an angle to the grain.

FEd force components

Fig. 10.12. Member loaded in tension at an angle to the grain.

• For smooth shank screws with a diameter greater than 6 mm, the rules for bolts will apply.

• For smooth shank screws with a diameter d of 6 mm or less, the rules for nails given in Table 10.8 will apply.

In the above, the diameter, d, will be the shank diameter of the screw.

Where multiple dowel-type connections near the end of the timber member in a steel-to-timber connection are loaded parallel to the grain, there is a risk of a brittle-type failure due to block shear and plug shear. This type of failure is referred to in EC5, 8.2.3(5), and in Annex A (informative), and the guidance in NA.3.1 of the UKNA to EC5 is that the annex should only be used in connections where:

• there are ten or more metal dowel type fasteners with a diameter <6 mm in a row parallel to the grain;

• there are five or more metal dowel type fasteners with a diameter >6 mm in a row parallel to the grain.

10.3.6.1 Brittle failure due to connection forces at an angle to the grain

This form of brittle failure can arise when fasteners apply a force at an angle to the timber grain resulting in the possibility of splitting caused by the force component perpendicular to the grain, as shown in Figure 10.12. This failure can occur at a load less than the design capacity of the fasteners.

Preliminary issues of Eurocode 5 were written on the premise that by using the minimum spacings, end and edge distances given in the code, splitting would be prevented and joint failure would always be by ductile failure of the fasteners. The strength of the timber was based solely on a check of the shear strength of the member. Prior to the final publication of EC5 this was revised to incorporate a design check on the splitting resistance of the connection members where the forces in the fasteners were able to induce a tension component perpendicular to the grain in the connection members.

The strength equation in EC5 is developed from the application of linear elastic fracture mechanics, and the requirements are covered in EC5, 8.1.4, as follows.

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