Civil Engineering Reference
In-Depth Information
The diameter of the nail required could be briefly described as being the thickest nail
that can be driven into the timber without causing the timber to split. It is widely
accepted that a 75 mm nail is acceptable for most applications for the construction of a
residential house frame. It is worth noting that a hammer-driven 75 mm nail is 3.75 mm
thick whereas gun nails are generally 3 mm thick
Pre-drilling to avoid timber splitting
If the engineers' specifications for a particular application call for a nail with a diameter
that causes splitting of the timber, you will have to drill a hole for the nail. The diameter
of the hole drilled shall be 80 per cent of the diameter of the nail. If exactly 80 per cent
cannot be achieved drill a slightly smaller hole.
Nail requirements to laminate structural timber
It may be necessary to laminate two pieces of structural timber together and there are nail
requirements for this. On many occasions it will not be possible to purchase the timber
size required to fulfil the specifications detailed in the timber schedule on the approved
plans. For example, a common bearer specification would be 90 × 70 MGP12 pine.
90 × 70 pine is not a common product therefore it will be necessary to join two pieces of
timber 90 × 35. Always remember that when joining timber that the joint is to be vertical.
The nails to laminate the two pieces of timber together shall not be less than 2.8 mm.
The nails shall be no further apart along the timber, than double the depth of the timbers
being joined. The nails shall be staggered. One nail at the upper edge of the timber, and
the next at the lower edge. If there is no nail over the stump when the bearer is in place,
an additional nail should be inserted.
Lay bearers with any bow in the timber facing up
The ends of the bearers need to be fully supported on the stumps. Where concrete stumps
are used it will be a little more difficult to gain this bearing, as the metal pin of the stump
will prevent the bearer being joined at the centre line of the stump. It is however crucial
that the bearer have a full 20 mm of support on the stump. When timber stumps are used
the bearer should be joined at the centre line of the stump.
Bearers are to be fitted to the top of the stumps with the bow up. That is, the bearer
will rest on the stump at either end of the bearer, and any bow will cause the bearer to be
off the stump or stumps within the length of the bearer.
You will have to cut the bearer to a length to suit the position of the stumps. Cut one
end of the bearer square. In the past the bearers were halved over each other however this
is no longer necessary. This was a method of preventing the bearers from pulling apart,
thereby ensuring constant support of the bearers on the stumps. Sit the bearer in position
on the stumps and then mark the required length that the bearer is to be cut to. In the
case of concrete stumps, you will also mark the position of the steel pins of the stumps to
enable the holes to be drilled in the bearers.
Drill holes for a concrete stump
You will need to drill holes to accommodate the still pin of a concrete stump, so drill
10 mm holes in the bearers for these steel pins to pass through. It should be noted that
