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t2/5he where t1 and t2 are as defined in Figure 11.2 and he is the tooth penetration depth (in mm). The strength of the connection will reduce to 75% of its full value if the minimum permitted values of t1 and t2 are used. Also, when t1 and t2 exceed 3he and 5he respectively, there will be no increase in joint strength due to this factor. k2 is the modification factor for the loaded end distance, a3jt, and, for a member with a sloping end, based on the requirements of BS5268-2 [4], the distance can be taken to be that shown in Figure 11.3. The factor only applies to members having a loaded end and is dependent on the type of toothed-plate connector being used as follows.

For types C1-C9, the minimum loaded end distance is given as 2.0dc in Table 11.2; however, a smaller distance is permitted in the strength equation provided it is not less than 1.1dc or the minimum loaded end distance criteria

End distance

End distance

Edge distance

End distance

End distance

Edge distance

a - must not be less than / a - must not be less than the appropriate edge distance the appropriate edge distance

Circular connector Rectangular connector

Fig. 11.3. End and edge distance for connectors (based on BS 5268-2).

a - must not be less than / a - must not be less than the appropriate edge distance the appropriate edge distance

Circular connector Rectangular connector

Fig. 11.3. End and edge distance for connectors (based on BS 5268-2).

allowed for bolts (see Table 10.9), whichever is the greater. If a loaded end distance less than 2.0dc is used, the value of k2 will be:

I a3jt/1.5dc where dc is as previously defined and:

a3jt = max

1.1dc

80 mm

Here d is the bolt diameter and both d and dc are in mm.

Provided the minimum loaded end distance required for the connector bolt is greater than the minimum loaded end distance required for the connector, k2 will remain equal to 1 for a connector loaded end distance greater than 1.5dc. It will only be less than 1 when the distance is smaller than 1.5dc, reducing to a value of 0.73 at the minimum permitted end distance of 1.1dc. In other words, the connector will continue to exhibit ductile behaviour when its loaded end distance is less than the 2dc minimum value given in Table 11.2. However, its characteristic strength will be reduced when the distance is less than 1.5dc, reaching a minimum value at 1.1dc.

With types C10 and C11, a similar situation applies but for these connectors the loaded end distance, a3 t, may only be reduced to 1.5dc, i.e.:

80 mm where dc and d are as previously defined.

With these connectors, provided the minimum loaded end distance required for the connector bolt is less than the loaded end distance required for the toothed-plate connector, k2 will equal 1 when the connector loaded end distance is 2.0dc (or greater) and will be smaller than 1 when the distance is less than 2.0dc. It will reduce to a value of 0.75 at the minimum permitted loaded end distance of 1.5dc.

k3 is a modification factor for timber density, and:

where pk is the characteristic density of the timber in the connection (in kg/m3).

The reference strength equations (11.4) are based on a connection where the timber has a characteristic density of 350 kg/m3, i.e. strength class C14 in BS EN 338:2003 [5]. Factor k3 will increase the strength of the connector when higher strength class timber is used, achieving a maximum increase of 50% when the characteristic density is 525 kg/m3. This will cover all of the strength classes for softwood in BS EN 338 as well as hardwood strength class D30. Although it is likely that strength classes D35 and D40 will be able to be used with this type of connector, D50 to D70 will not because of the resistance offered by the timber to the penetration of the connector teeth.

As stated previously, the minimum spacings, edge and end distances are given in Table 11.2 for the different types of connector and the symbols are the same as those shown in Figures 10.11 and 11.3.

Where types C1, C2, C6 and C7 connectors are being used and they are staggered, as shown in Figure 11.4, the minimum spacings a1 and a2 in Table 11.2 may be reduced by the use of reduction factors ka1 and ka2, respectively, so that:

• the minimum spacing parallel to the grain = ka1a1

• the minimum spacing perpendicular to the grain = ka2a2

provided the reduction factors ka1 and ka2 comply with the following criteria:

Where the connection contains a row of connectors parallel to the grain, EC5 allows the full strength of each toothed-plate connector in the row to be used when loaded

¿yka2a2

Connector position

Fig. 11.4. Reduced distances for staggered toothed-plate connectors (based on EC5 Figure 8.13).

in this direction. For connections in single or double shear, irrespective of the type of connector being used, when determining the strength of a connection the number of connectors per shear plane shall be taken to equal the number of connector bolts. This will apply when the connectors are loaded parallel or perpendicular to the grain. When determining the strength of the connector bolts, however, the effective number of bolts as described in 10.4.1.3 shall be used when loaded parallel to the grain and the actual number of connector bolts when loaded perpendicular to the grain.

The requirements of bolts and washers shall fully comply with criteria given in Section 10.4.3 in EC5.

See Example 11.12.1.

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