CYCLONE TESTING FOR COMMERCIAL FORCESHIELD ROLLER SHUTTERS
The shutter is mounted on the outside of the window frame of a building and can be rolled up onto a drum contained in the eaves space. The shutter consists of a series of hinged slats.
The slats were 30mm high and approximately 18mm wide hollow rectangular sections. They were made from extruded aluminium with a wall thickness of approximately 1.3mm.
The slats had a continuous tongue and groove along their top and bottom edges so that each slat hinges onto the adjoining slat to allow the blind to roll around the mounting drum. The 1.3mm thick tongue was perforated with small trapezoidal holes spaced at 12mm. The hook ended tongue is made longer than necessary so that each slat can be lifted at 12mm. The hook ended tongue is made longer than necessary so that each slat can be lifted 6mm before moving the slat below it.
Each end of the slats, approximately 30mm, slides along vertical aluminium shutter guides attached to the window frame. The shutter guides are a low C-section, 66mm wide with a 24mm high web, and a wall thickness measured at 1.5mm. A strengthening wall is located 25mm in from the web. It divides the channel into a section for the slats and one for the fixings. A plastic clip was inserted in the end of every second slat to secure it in the guide. The clips were fixed in place by a 3mm diameter rivet to the inner face of the slat. Each clip had a tab, 15mm long x 5mm high x 2mm thick, on each side,
TEST SETUP
One shutter was tested. The shutter guides were fixed to the hardwood frame by 12g x 30mm pan head screws, spaced at 300mm centres. A 17mm diameter holes was drilled in the outside flange of the channel to allow the head of the screw to tighten onto the inside flange. The opening of the guides was flush with the inside edge of the frame to give a 1.44m clear span. The shutter was 1.2m high. The frame was rigidly supported at its four corners.
TEST PROCEDURE
For cyclone prone areas, a standard impact has been devised to stimulate the effect of flying debris during a severe tropical cyclone. Clauses 3.4.7. of the Australian Wind Loading Code, AS1170.2-1989, state that in cyclonic regions, windows shall be considered as potential dominant openings, unless capable of resisting impact by a 4kg piece of 100mm x 50mm cross section, travelling at a speed of 15m/s and striking them at any angle.
The missile was dropped down a taut nylon thread from a height above target of thirteen meters. Ignoring the frictional effects of air and nylon thread, the theoretical speed at impact can be calculated as 16m/s. The actual speed would therefore be approximately 15m/s.
RESULTS
The impact location was at the mid-span and mid-height of the panel. The shutter was closed, that is, no gaps between the blades, and held closed by nails at the end of the tracks. The shutter resisted the 4kg falling mass. A permanent deformation of approximately 10mm remained at the impact location. This was due to the tongue section of the slats immediately under the missile being bent at 90º to the slat. Each slat was still attached to its neighbour. On removal of the shutter from the guides, the legs of the clips on the end of the slats were bent outwards.
CONCLUSION
The 1.44m span Forceshield Commercial shutter with channel guides and clips satisfied the impact loading criterior, clause 3.4.7. of AS1170.2-1989, by resisting the 4kg missile travelling at 15m/s. The aluminium channels were fixed to the hardwood frame at 300mm centres by 10-guage x 30mm pan head screws.