Design Strength Of A Laterally Loaded Metal Dowel Connection

The strength equations given in the following sub-sections assume that in the connection the design shear strength of the fasteners will always exceed the design capacity derived from the timber/panel strength equations for the relevant fastener type. Where the shear strength of the fastener is required, it must be determined in accordance with the requirements of EN 1993-1-1, Eurocode 3, Design of Steel Structures, General Rules and Rules for Buildings.

10.5.1 Loaded parallel to the grain

The design strength of a laterally loaded single fastener, Fv,Rd, is obtained from the characteristic load-carrying capacity of the laterally loaded fastener as follows:

Km where:

• kmod is the modification factor referred to in 2.2.20, and where the connection comprises two timber elements kmod,1 and kmod,2 the value used in the equation will be kmod = v/kmod,1kmod,2, as required by EC5, equation (2.6).

• KMis the partial factor for connections given in Table 2.6. Except when determining the plate strength of punched metal plate fasteners, the factor value will be 1.3.

• Fv Rk is the characteristic load-carrying capacity of the fastener per shear plane when loaded laterally, i.e. the lowest value determined from the relevant equations given in Tables 10.2 and 10.3.

For a connection containing rpl rows of fasteners laterally loaded parallel to the grain, with each row containing n equally spaced fasteners of the same size, each with a design strength per shear plane, Fv Rd, the effective lateral load design capacity of the connection parallel to the grain, Fv ef Rd, will be:

where nef is the effective number of fasteners in the connection in each row parallel to the grain and nsp is the number of shear planes in the connection.

10.5.2 Loaded perpendicular to the grain

Where loads are imposed on the timber by fasteners loaded perpendicular to the grain, there are two possible forms of failure:

(a) By the timber splitting in tension and this condition is covered in 10.3.6.1.

(b) By ductile yielding of the fastener and for this condition, where there are rpr lines of fasteners with each line containing n fasteners, all of the same size:

where:

• Fv efjRd is the effective design strength of the fastener per shear plane when loaded laterally and perpendicular to the grain.

• nsp is the number of shear planes in the connection.

• n is the number of fasteners in each line of fasteners perpendicular to the grain. If overlapping nails are being used, n will be the number of overlapping nails as defined in equation (10.44).

• Fv Rd is the design load-carrying capacity of a laterally loaded single fastener per shear plane when loaded perpendicular to the grain. For nails and staples <8 mm in diameter, as well as smooth shank screws with a diameter <6 mm, the capacity will be the same as for the fastener loaded parallel to the grain. For bolts and dowels as well as smooth shank screws with a diameter >6 mm and nails >8 mm in diameter in connections using timber or LVL, the capacity derived from the strength equations in Tables 10.2 and 10.3 will have to take account of the requirements of equation (10.34) where the characteristic embedment strength of the timber or LVL in the connection will become:

From the above, the design load-carrying capacity of a connection loaded perpendicular to the grain will be:

Design capacity of connection = min(F90,Rd, Fv>efjRd) (10.53)

where F90,Rd is the design splitting capacity of the timber, and for softwood is obtained from equation (10.41c).

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