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12.5.2 Connection design procedure

Consider a single or double shear connection with the generalised fastener configuration shown in Figure 12.2, in which there are n fasteners of the same size in aregular pattern.

At the ULS design condition each shear plane of the connection is subjected to a combination of moment, Md, and lateral forces, Hd and Vd.

The fastener at the greatest distance from the centroid will have the maximum movement (and hence force) under the action of the moment, and when including for the additional effect of the lateral forces Hd and Vd, fastener A in Figure 12.2a will be subjected to the greatest combined force.

Consider the connection subjected to a moment per shear plane, Md, causing a rotation fr and a lateral displacement of 5max in fastener A, as shown in Figures 12.2b-12.2c.

At the ULS, assuming that the slip modulus of each fastener is, say, K, for this loading configuration the maximum force, Fm d max, will be in fastener A and can be written as

where fr is the rotation of the connection under the action of Md and rmax is the radial distance from the centroid to fastener A.

Similarly, from the relationship in equation (12.2), the force in any intermediate fastener, i, will be:

Tmax where Si is the lateral movement of fastener i, ri is the radial distance of fastener i from the centroid, and the moment taken by fastener i will be:

Tmax Tmax

The moment taken by the n fasteners per shear plane in the connection will be:

J7 n

From the above equation, it is to be noted that, as stated in 12.5.1, the moment in the connection is independent of the stiffness of the fastener and from this relationship the maximum force per shear plane, Fm d max, under the action of the moment will be:

If the lateral horizontal and vertical forces per shear plane in each fastener are now considered,

Hd Vd

When Md, Hd and Vd are acting on the connection, the largest force will be in fastener A, and will be obtained from the vector sum of the forces calculated from equations (12.7) and (12.8). The vector forces are shown in Figure 12.3 and the maximum force in this fastener per shear plane, Fd, will be:

Fd = y (Fv,d + Fm d,max cos 0)2 + (Fh>d + Fm>d,max sin 0)2 (12.9)

and the angle, a, of Fd from the horizontal axis will be:

When a circular pattern is used for the fasteners, which is common practice for moment resisting connections, the above equations can be simplified. If there are fasteners lying on the horizontal axis through the group centroid, as shown in Figure 12.4, the fastener with the greatest load will be fastener A and the force per shear plane in that fastener, Fd, and the angle of inclination of this force to the horizontal, a, will be:

Fastener A

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