Sls

Depending on the connector type, the toothed plate will be made from cold rolled uncoated low-carbon steel, continuous hot dipped galvanised mild steel or malleable cast iron. With steel connectors, the edges of the connector plate are bent over to form triangular projecting teeth, and with cast iron connectors, conical spikes having a blunted point project from one or both faces. An example of a circular toothed-plate connector formed from steel plate having projecting teeth on one or both sides is shown in Figure 11.1.

Single-sided toothed-plate connectors can be used to connect timber to steel or, if connections are required to be demountable in timber-to-timber joints, they can be used in pairs back to back. Double-sided toothed plates are suitable where non-demountable timber-to-timber connections are required.

To assemble, the bolt hole is formed in the members, the connector is located in position, and the connection is pressed together mechanically or, if relatively low-density timber is being used, by the use of a high-strength bolt fitted with large washers. After pressing into position, the connector bolt and its washers are fitted. The connector must be pressed fully into the timber to develop its design capacity. Because the resistance offered by the timber to the penetration of the connector teeth will increase as the

(a) Single-sided toothed plate Fig. 11.1. Toothed-plate connectors.

Connector bolt

Toothed-plate connector

(b) Double-sided toothed plate

Connector bolt

Toothed-plate connector

(b) Double-sided toothed plate density of the timber increases, toothed-plate connectors are not suitable for use with timber having a characteristic density greater than about 500 kg/m3.

The design requirements for toothed-plate connectors are covered in EC5,8.10. In a connection formed with a double-sided toothed plate, the load is passed by embedment stresses from one of the members to the teeth of the connector and from there by shear stresses within the connector plate to the teeth on the opposite side and into the other member through embedment stresses. Embedment slip at the connector teeth also results in the timber members bearing onto the bolt and the joint strength is taken to be a combination of the force carried by the toothed-plate connector and the bolt. The bolt also holds the members together to ensure that the connector(s) remain fully embedded in the timber. Because the shear strength of the bolt considerably exceeds the embedment strength or the strength of any brittle failure mechanism in the timber, shear failure of the bolt is not considered in the strength assessment equations given in

Where a single-sided toothed-plate connector is used, the load transfer mechanism from the toothed side of the connector will be the same as for the double-sided connector but thereafter the load is passed directly to the bolt by bearing stresses between the connector and the bolt and also by bearing of the member onto the bolt due to embedment slip at the connector teeth. From there the bolt functions as a normal dow-elled connection. Again, with this connection, the joint strength is a combination of the strength of the toothed-plate connector and the bolt.

Ductile failure mechanisms as described above will only arise if brittle failure is prevented and, as with metal dowel type fasteners referred to in Chapter 10, this is achieved in EC5 by specifying minimum spacings, end and edge distances as well as minimum member thicknesses. The minimum spacings etc., for the toothed-plate connector, are given in Table 11.2 and the minimum spacing requirements for the connector bolts are as given in Table 10.9. With regard to member thicknesses, the minimum requirements are:

The thickness is as shown in Figure 11.2 and t1 is the thickness of the outer timber member(s) in the connection. t2 is the thickness of the inner timber member in the connection, and he is the embedment depth of the toothed-plate connector teeth (in mm) in the member being considered, i.e. = (hc - t)/2 for a double-sided connector and (hc - t) for a single-sided connector, where hc is the connector height and t is the thickness of the metal used for the connector.

The characteristic strength of a connection formed using a toothed-plate connector is:

where FvjRk,connection is the characteristic strength of the toothed-plate connection (in N), Fv,Rk is the characteristic load-carrying capacity of the toothed-plate connector (in N), and Fv Rk,b0it is the characteristic strength of the connector bolt (in N).

Type C2, C4, C7, C9 and C11 toothed-plate connectors are single sided, type C1, C3, C5, C6, C8 and C10 are double sided and different strength equations apply for each type. The strength of a laterally loaded toothed-plate connector is independent of

0 0

Post a comment