Gondolas – or cradles – are working platforms attached to a Building Maintenance Unit (BMU). They descent along a facade, transporting window cleaners or maintenance staff. Some cradles are unrestrained and hang in front of the facade, while others are secured to the facade with a cradle restraint system.
No detailed explanation is needed regarding the ‘why’ of cradle restraint systems – just combine the terms ‘window cleaning’ and ‘wind’ in a Youtube search. The top videos will make it pretty clear: an unrestrained cradle that is gripped by wind results in the most frightening and dangerous situations. Also, a cradle that smashes into the facade can cause major damage.
In an interview with Healthday, the late Jim Willingham (a legend in the American window cleaning industry) once said that wind is a major problem for window cleaners working on high-rise buildings.
Each of these options has its own benefits and possibilities. Which one of these restraint systems is best suited for a specific project depends on your preferences or requirements, as well as on the contour of the building. Below we’ll discuss three ways to secure a gondola to the facade.
A Wire Rope Restraint system in action, Collins Arch – Melbourne, Australia
Three ways to restrain a cradle
Each of these options has its own benefits and possibilities. Which one of these restraint systems is best suited for a specific project depends on your preferences or requirements, as well as on the contour of the building. Below we’ll discuss three ways to secure a cradle to the facade.
With wire ropes attached to the facade
Users attach multiple wire ropes to these pins (or stick pins in attachment points) as they work their way down the facade. In this case, the cable(s) of the cradle are secured to the facade at several points. Albeit effective, this method requires manual effort every time the cradle moves up or down.
Wire Rope Restraint
With a so-called mullion guide
In this case, the cradle moves over rails that can be integrated in the building’s facade.
On top of the facade, the cradle is fixed in the rails and is then secured for as long as it moves up and down the building. A mullion guide rail provides maximum stability and requires minimal manual effort.
Mullion Guide Rail
With pins to a soft rope system
A soft rope system effectively prevents a cradle from swinging, but it serves another purpose as well: uniquely, it ensures that a cradle can get close to a sloping facade.
In contrast to the other two systems, a soft rope restraint system can secure a cradle which moves horizontally along a facade.
Soft rope system
Why a cradle restraint system?
With an unrestrained cradle, working in winds over 14 m/s (wind force 6 on the scale of Beaufort) is not advised. Cradles which are continuously restrained to the facade, however, are designed for use in winds up to 20 m/s (wind force 8 on the scale of Beaufort). Winds are stronger and more abrupt at great heights, especially around tall objects such as skyscrapers. Nobody wants to be involved in an incident with a swinging cradle, let alone be responsible for the physical and psychological damage.
A restraint system stabilizes a cradle by keeping it at a fixed distance from the facade. In other words: it secures the position of a cradle in relation to the building. Anyone who’s even been inside a cradle at great heights knows that a stable cradle makes a working at height a lot easier, and therefore a lot quicker.
For advice about the restraint system that is best suited for your project, it’s best to contact us directly.
A cradle descends using a Soft rope system on Crown Sydney, Australia