The northern coastlines of Australia are frequently battered by high winds and cyclones during the mid to late summer season.
In these conditions, the most vulnerable part of any structure to failure is the roof.
This is caused by the suction forces created on the downwind side of the roof which rise and fall as the wind gusts and then lulls. This places fatigue stresses on the roof connection. If insufficient retention of the roof exists, fatigue failures occur and the roof will begin to separate. Once the roof is gone there is little chance the rest of the building will survive.
Roof Retention:
The
greatest influence on the retention of any roof are effective reinforcing plates
under the heads of the roofing screws.
Current corrugated Cyclone Plates are an effective proven solution offering reasonable pullover resistance during high winds. They however suffer a number of negative aspects which could be detrimental to the roofs security:
1. If the screws are installed off-centre, the plate tends to bear more heavily on side of the roofing profile. In heavy winds the roofing sheet will move causing a non-uniform loading and the cyclone plate will have little influence on the pullover load. Fatigue failure of the roofing profile can then occur.
2. They are bulky to handle and awkward to install
3. Tend to trap swarf and debris under the plate, leading to corrosion
4. Prone to leakage
