Paul Brown & Associates
GN Construction
Sitting atop an elevated position in St. Mary's Bay, XXXII is a boutique apartment complex with views of downtown Auckland and the Waitakere Ranges.
Occupant privacy and thermal gain is provided by Azimuth Sliding Screens. The 42 screens used in the design are manufactured from aluminium grating, each panel using 40x3mm flat bars and a 60x6 angle perimeter. The screens are able to be manipulated into the optimal position by occupants.
As the screens are not for weather tightness or security, it was easy to foresee a situation whereby they would not be secured into position. This would leave the free to slide if subjected to reasonable wind gusts, which was a dead-man latch, requiring the occupant to release the latch in order to the move the screen, the latch automatically re-engaging afterwards.
The question then becomes one of which dead-man latch. After investigating and looking all over the world for a suitable option, we found nothing that would give us the confidence needed that it could be used without risk. There was nothing available with test reports showing the latch was robust and durable enough to cope and hold under pressure from wind gusts.
With no products to incorporate into the installation of the screens, we decided to take the best available product and modify it ourselves. To make sure it met our demands for risk mitigation, we then tested it to failure.
Wind speeds vary in and around Auckland, but we do know gusts are generally both more frequent and faster by any section of coastline. Greater speed is also encountered higher up, with localised acceleration possible due to factors such as nearby buildings, or even the wind gaining strength as it moves around the corner of the building.
Gusts exceeding 63km/h are not uncommon (you can expect this for around 55 days per year at Auckland Airport) and gusts of over 96km/h will be encountered a few times per year. For reference, the highest Auckland gust recorded (defined as a 10-minute average) is 204km/h at Manukau Heads, on 21/2/1992. Note that Cyclone Gabrielle recorded wind speeds of 150 to 160km/h when it made landfall in NZ.
To test our modified latch design, a full 1:1 scale mock-up was manufactured and then placed on the turntable in front of the wind tunnel. This mock-up was rotated to simulate the varying angle of wind direction, with all angles tested at every speed increment.
A maximum force was encountered at a 30-degree angle of incidence. This was the angle at which the most load was placed on the latch by the wind.
The next step was to increase the speed until the latch failed. The first tests had the latch failing when the wind tunnel was running at 15m/s (54km/h). That would be enough for significant issues to likely occur multiple times per year, and we should note this was the first iteration of a modified latch. The unmodified latch would have failed at a lower wind speed.
Further modifications to the latch were made and the testing regime was repeated until we again reached the point of failure.
Multiple tests to the point of failure allowed us to identify the weakest point in the original latch design of the product we had selected as the best option. We found this to be the bolt used to secure the latch, which would break with a relatively low amount of force.
Our modified design used a protective metal encasing which would add the robustness needed and protect the weak point, without compromising the easy operation of the screen itself. We tested our solution up to 45m/s (162km/h), a peed which has only been exceeded by wind gusts in Auckland by that record breaking Manukau gust in 1992.
You can view some of the testing footage in the video below. We should note, the testing rig was built to simulate the actual environment and not to look pretty (the finished version on the actual apartments was much more attractive).
We took the best latch we could source, and it failed at what we would consider to be a low and frequently experienced wind speed, not just in the location of intended use but in multiple other Cities and towns across New Zealand.
For sliding screens to be used in medium density apartments and/or buildings or multiple storeys, there is significant risk from wind-induced damage (noting the potential for wind noise is also a concern). The currently available latches are unable to offer the safety required and require significant modification to meet anything approaching an acceptable level.
For prudent risk mitigation, we'd recommend the use of wind tunnel testing for similar projects or speaking with us about our now tried and tested design that we know already works.
Sitting atop an elevated position in St. Mary's Bay, XXXII is a boutique apartment complex with views of downtown Auckland and the Waitakere Ranges.
Occupant privacy and thermal gain is provided by Azimuth Sliding Screens. The 42 screens used in the design are manufactured from aluminium grating, each panel using 40x3mm flat bars and a 60x6mm angle perimeter. The screens are able to be manipulated into the optimal position by occupants.
As the screens are not for weather tightness or security, it was easy to foresee a situation whereby they would not be secured into position. This would leave them free to slide if subjected to reasonable wind gusts, which was considered likely given their elevated position. The obvious solution was a dead-man latch, requiring the occupant to release the latch in order to move the screen, the latch automatically re-engaging afterwards.
The question then becomes one of which dead-man latch. After investigating and looking all over the world for a suitable option, we found nothing that would give us the confidence needed that it could be used without risk. There was nothing available with test reports showing the latch was robust and durable enough to cope and hold under pressure from wind gusts.
With no products to incorporate into the installation of the screens, we decided to take the best available product and modify it ourselves. To make sure it met our demands for risk mitigation, we then tested it to failure.
Wind speeds vary in and around Auckland, but we do know gusts are generally both more frequent and faster by any section of coastline. Greater speed is also encountered higher up, with localised acceleration possible due to factors such as nearby buildings, or even the wind gaining strength as it moves around the corner of the building.
Gusts exceeding 63km/h are not uncommon (you can expect this for round 55 days per year at the Auckland Airport) and gusts of over 96km/h will be encountered a few times per year. For reference, the highest Auckland gust recorded (defined as a 10-minute average) is 204km/h at Manukau Heads, on 21/2/1992. Note that Cyclone Gabrielle recorded wind speeds of 150 to 160km/h when it made landfall in NZ.
To test our modified latch design, a full 1:1 scale mock-up was manufactured and then paced on the turntable in front of the wind tunnel. This mock-up was rotated to simulate the varying angle of wind direction, with all angles tested at every speed increment.
A maximum force was encountered at a 30-degree angle of incidence. This was the angle at which the most load was placed on the latch by the wind.
The next step was to increase the speed until the latch failed. The first tests had the latch failing when the wind tunnel was running at 15m/s (54km/h). That would be enough for significant issues to likely occur multiple times per year, and we should note this was the first iteration of a modified latch. The unmodified latch would have failed at a lower wind speed.
Further modifications to the latch were made and the testing regime was repeated until we again reached the point of failure.
Multiple tests to the point of failure allowed us to identify the weakest point in the original latch design of the product we had selected as the best option. We found this to be the bolt used to secure the latch, which would break with a relatively low amount of force.
Our modified design used a protective metal encasing which would add the robustness needed and protect the weak point, without compromising the easy operation of the screen itself. We tested our solution up to 45m/s (162km/h), a speed which has only been exceeded by the wind gusts in Auckland by that record breaking Manukau gust in 1992.
You can view some of the testing footage in the video below. We should note, the testing rig was built to simulate the actual environment and not to look pretty (the finished version on the actual apartments was much more attractive).
We took the best latch we could source and it failed at what we would consider to be a low and frequently experienced wind speed, not just in the location of intended use but in multiple other Cities and towns across New Zealand.
For sliding screens to be used in medium density apartments and/or buildings of multiple storeys, there is significant risk from wind-induced damage (noting the potential for wind noise is also a concern). The currently available latches are unable to offer the safety required and require a significant modification to meet anything approaching an acceptable level.
For prudent risk mitigation, we'd recommend the use of wind tunnel testing for similar projects or speaking with us about our now tried and tested design that we know already works.
Invercargill
Auckland
