Civil Engineering Reference
In-Depth Information
are drilled, wrap the U-bolt around the stump and insert the threaded ends through the
two holes in the brace. Place nuts and washers onto the U-bolt and then tighten to secure
the brace to the stump. Care must be taken to tighten the nuts so that the brace is held
securely but not so tight so as to crack the stump. I suggested earlier that timber stumps
are more costly than concrete, however if the job requires many sub-floor braces the cost
of the U-bolts and the additional time required fitting them should be entered into the
equation.
Installation of bearers
Check stump heights before fitting the bearers
Before starting the installation of the bearers, double check that the tops of the stumps
are all level. Any that are slightly low can easily be packed up. Those that are too high can
be cut down in the case of timber stumps. Alternatively, for concrete stumps, it may be
possible to take a checkout of the bearer thereby dropping it over the stump so that the
top of the bearer is in the correct position. Check with your consultant or engineer first
to ensure that this is permissible with the timber you are using.
Moisture barriers
Prior to fitting the bearers to the top of the stumps it will be necessary to provide a
moisture barrier between the stumps and the sub-floor timbers. This moisture barrier
might be metal, plastic or malthoid: malthoid is a bitumen product sold in rolls at any
good hardware store. You could use metal ant caps or for the plastic barrier, plastic
window flashing would suffice. The termite barrier Kordon will also meet the moisture
barrier requirements.
When concrete stumps are used the pin that protrudes from the top of the stump is
inserted through the bearer and bent over to secure the bearer in position. More often
than not, bearers are fitted to timber stumps with skew nails through the bearer into the
top of the stump. Bearers can also be fitted to timber stumps with bolts, spikes, vertical
nails or metal strapping.
Legal requirements for nail fixings
When nailing the components of a house together there are
stipulations set down in the building code for nail penetration,
nail size, and the quantity of nails to be used. Furthermore,
there are specific requirements for the application of skew
nails.
Where skew nailing is required the angle of the nail
penetrating the timber shall be no less than 30 degrees but no
greater than 45 degrees. The nail shall be driven into the first
piece of timber not more than 38 mm from the junction of
the timber that it is being joined to, but not less than 25 mm
from that junction (see Figure 3.5).
Figure 3.5
The application of skew nailing
