Civil Engineering Reference
In-Depth Information
To overcome both of these problems the 'wind beam' or 'collar' was introduced. Whether
the collar acts as a tie or a strut for the couples will depend upon the stiffness of the sup-
porting wall below. Assuming however, that the wall is so substantial that it will not be
pushed outward by the bottom section of the couples, then the collar will act as a strut. If
however, as is more likely with early timber framed buildings, the wall is relatively flex-
ible then in that case the collar would act as a tie holding the couples together. There
would still be some outward thrust but this would be limited by the collar to the degree of
bending in the lower part of the couple only. Figure 1.2 illustrates this condition. It can
readily be appreciated that in larger roofs, where the walls are relatively flexible, there is a
considerable tying effect in the collar demanding a more sophisticated joint between collar
and couple than could be achieved with simple iron nails. The collar was therefore fre-
quently jointed to the couple with a halved dovetail shaped joint, often secured with hard-
wood pegs.
