26 November 2010

Large glass installation: miracles of vacuum lifting

The cladding world has gone mad. Facade units get bigger and bigger every year. Glass and panel dimensions are exceeding any reasonable measure. Who are to be blamed for it? Architects are partly responsible, for sure. The last gossip says Foster + Partners are designing a big company HQ in the Pacific coast with 15m long insulated glass units. Seismic movements in the region don't seem to refrain the architects from trying the impossible once again...
Henze-Glas DGU in the factory, before shipping to Glasstec 2010.  35 chaps are sitting on top of the 18m long glass unit
The monster DGU unit as shown at Glasstec 2010
But industry has also entered the race with pleasure. The 'jumbo size' glass, that is, the maximum dimensions of a glass sheet, was 6,000 x 3,210mm up to 2007. Since then a new jumbo size appeared: 9,000 x 3,210mm. Double glass units of 7,500 x 3,200mm or even 9,000 x 3200mm are now commercially avilable. Visitors at the last Glasstec Düsseldorf in October 2010 could see a huge insulated glass panel of 18,000 x 3,300mm! It had three layers of 10mm and weighed 4,5 tons. The producer was the large-dimensions glass specialist Henze-Glas from Hörden, Germany.

The Henze-Glas guys usually take care of the fabrication and supply of their glass units to jobsite, all in one, since large dimensions are not easy to handle. But the tricky question is: how can a facade contractor install glass or metal panel units around 10m long in a facade? This is the issue we are going to discuss in this post.

Mankind has been aware of the power of air pressure since Otto von Guericke’s demonstration of the Magdeburg hemisferes in 1656, when 16 horses were unable to separate two hemispheres which had been pumped free of oxygen. Boyle and Hooke, two good old names of physics, worked together to design and build an improved air pump. Their work was the origin of the Boyle's law: the volume of a gas body is inversely proportional to its pressure.

Early Wood's Powr Grip cups, beginning of 1960's

It wasn’t until the 1960s that air pressure power started to be used with vacuum lifting equipment for transporting and installing glass panels at construction sites. One of the founders of the guild was Howard Wood, who in 1961 designed and built the first Wood's Powr-Grip Valve Grinder. The tool consisted of a small, spring-action vacuum pump mounted in a wooden handle, opposite a rubber suction cup which attached to the flat surface of an engine valve. The demand for the unique little lifting tool grew, and a glazier friend from Wood's suggested that he develop a vacuum cup for handling glass. With support from friends, Howard began manufacturing vacuum cups for glass handling in 1963, and obtained a patent for his design in March 1966.

Hydraulica 2000 vacuum lifter
Vacuum cups were soon attached to cranes or lifting devices, and soon a new machine came into play: vacuum lifters. The generally smooth and gas-tight surface of glass means vacuum lifting devices are just right for the job. That is also the case with metal panels. These days even stone and prefab concrete panels are lifted and moved using air suckers.

Vacuum lift atached to a crane from Anver
Wirth GmbH is a German company that builds applications for vacuum lifting. The first version of their Oktopus lifter appeared in 1992. With devices like that installing large-format roofing, ceiling and facade panels made of sandwich, profiled sheets and glass has become much easier. Today's vacuum lifting equipment is based on individual suction cups attached to thin structural elements hung from a crane. These systems allow for the installation of vertical wall panels up to 12m long, or even horizontal roof panels up to 22m long.

The lifting devices can be hung from a crane, attached to a forklift, to a truck-mounted crane or to an elevated working platform - also known as cherry picker. Several hydraulic functions integrated into the vacuum lifters allow panels to swing up and down, be raised and lowered, twist left and right, or move forward and backward horizontally.

One of the best options is to use a vacuum lifter attached to a minicrane, also called a spider crane. Two European companies are well-known builders of minicranes: Unic Cranes from Scotland and Riebsamen from Germany, the latter being better known for their brand Glasboy. These minicranes can be used for mounting curtain wall units from the floor above, or for mounting glass in a skylight from the atrium below. The dimensions of a minicrane when its legs and arm are folded are really minimal, allowing the smallest minicranes to be lifted inside an elevator.

Minicrane Glasboy Frey 860 from Riebsamen
Some special devices can solve typical installation problems. One of them is the presence of overhangs in high level installation works. If a cantilevered slab prevents cranes from lowering their load flush with the envelope, an overhang beam provides an ingenious way of overcoming the problem. The  Libro 500 overhang beam for example provides a reach from suspension point to pad extension that allows glazing under overhangs up to a depth of 1,750mm.

All the options of cranes, minicranes and vacuum lifting devices can be checked (and hired, if you need them) at the UK webpage of GGR Group, a must see for those with a lifting problem to solve. If your site is in the US, then go visit the founding fathers, the guys of Wood's Powr Grip. If your doubts are more general or you want to have an overview of the crane and lifting world, have a look at Vertikal magazine.

Now, let us enter a slightly tougher issue. Which lifting device do I need for my load? How many suction cups are required considering the glass dimensions? Is suction lifting really safe? Depending on the application and the device, the load bearing capacity of a vacuum lifter varies between 250 kg and 1,000 kg. Vacuum lifting devices suitable for construction sites must be battery powered and therefore completely self-sufficient. A safety system inside the device constantly monitors the condition of the vacuum circuit and the batteries. Optical and acoustic warning signals give early indication of deviations from the normal conditions. A reserve vacuum system maintains load bearing capacities even in the event of a loss of power, so that there is enough time to safely deposit the load once an alarm goes off.

Robotic (left) and Libro 500 overhang crane lifts
European norm EN 13155 defines how to verify the load bearing capacity of vacuum lifting equipment. Load bearing parts are to be checked at three times the nominal load bearing capacity of the device. Vacuum lifters must be able to hold a load, in all positions at the end of the vacuum range, of at least two times the nominal load bearing capacity of the device. The combination of vacuum lifting device and suctioned load must, obviously, not exceed the load bearing capacity of the lifting equipment (crane / forklift / working platform). If you are interested in the same topic from the US, your document should be ASME Standard B30.20, addressing vacuum lifting and general materials handling products.

The load bearing capacity of the suction cups depends mainly on the following four factors: a) Size of the suction cups; b) Pressure difference between the level of vacuum in the suction cup and the ambient pressure; c) Load direction (vertical, parallel or sloped to the suction cup surface); and d) Surface properties and porosity of the suctioned material.

As a rule of thumb, a vacuum lifter used at a height of 1000m admits 10% less weight than the same device at sea level. The load direction is even more critical. If the load to be lifted is picked and released in a horizontal position, the maximum load capacity will be two times higher than if the load has be hold in vertical. Finally, the suction cup diametre defines the load bearing capacity of the system. The chart below, taken from Wirth Webpage, shows the relationship between suction cup diametre and load bearing at sea level for both horizontal (blue line) and vertical (red line) load directions.

We started this post talking about large glass units. The vacuum lifters you can find in the market have a maximum load bearing capacity of 1 metric ton at best. What if your glass is really large - and heavy? No problem, there is always a German wizard with a solution for that - regardless the names they give to their inventions. Bystronic Glass has built the world's largest glass vacuum lifter up to now: the Glasmaxilift 5000 is able to handle glass lites up to 15 meters in length and 5 metric tons using just air pressure. You got it. And Foster + Partners will have their huge glass installed as well.


Ha Nguyen said...

The master, thank you very much.

Tie down straps said...

A mechanical kerb lifter can also be made to fit mechanical lifters like forklifts or crane-trucks so that larger stones can be placed.

www.stahlindo.co.id said...

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urmileshkumar said...

glass weighs 2.5 kgms/m2 per mm thickness and handlinglapses can be very dangerous. still you can find 15 meter long 19 mm thick glass facade in frankfurt airport. producing glass in any length is not a problem, but its transportation and handling is!!!

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A to Z Glazing said...
This comment has been removed by the author.
A to Z Glazing said...

A to Z Glazing said...
A very interesting article, would be interesting to see how the unit glass weight would be supported/distributed in the base of the frame as a glass unit of 9m x 3m would weigh in at at least 1700kg.
Recently we were ask to look at some units that seem to be breaking under their own weight, they are only 3.8 M high x 1.5m wide (390kg). They were manufactured in Germany an installed in London with vertically structural joints, the problem is possibly due to the way they have been set on blocks in the frame - it's possible the blocks are not of the correct density or just ill placed.
I guess for units of 9m x 3m they would be a modular unit pre-set into a frame. The problem is often once the work is complete, getting a company to replace just a one-off unit.
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