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Case for glass becomes clearer

Post Time:Aug 04,2009Classify:Industry NewsView:284

We’ve long been accustomed to the wide range of specialty concretes, specialty steels, all sorts of new materials engineered for specific purposes.

They have become so commonplace that we overlook the fact that metallurgists, polymer chemists, nanoscientists and other scientists are constantly devising advanced materials, and that those advanced materials are driving change in the construction industry.
Consider glass.

Once used only in windows, it became a common material in building façades back when we first began to take energy efficiency seriously.

Now, scientists are turning to it for use in load-bearing structures, for super-strong façades designed for hurricane-prone areas, for reflectivity, for all sorts of things.

Ride the elevator to the 103rd floor of the Willis Tower in Chicago, and you’ll be able to view the surrounding city from one of several glass observation rooms — glass floors, glass walls and glass ceilings — that protrude 4 ½ feet from the building façade. The glass is so clear that you feel as though you’re stepping out into space, and not all visitors can convince themselves to do it.

Materials scientists laminated five layers of glass with polymers to make the structures strong and safe. Software engineers wrote programs to analyze every square inch of the panels to ensure that stresses were within precise limits.

Now people are working on glass arches and footbridges. They already have built glass staircases in some of Apple Computer’s stores.

Step by step, those same materials scientists are moving toward materials and methods that could one day lead to glass structures that utilize no metal or other materials at all.

They’ve already found another use for extremely strong glass in the façade of a 35-storey office tower in Miami.

Developer Alan Ojeda said the façades will withstand gusts of 327 miles an hour as well as impacts from all sorts of objects, including roof gravel from nearby buildings. In fact, this new glass as been dubbed “large-missile impact glass” because it will withstand strikes from a 2x4 stud weighing nine pounds.

Florida building codes have been revised to take hurricane-force wind damage into account, but the standard test is to fire pea-sized ball bearings at panes to see if they withstand the impact. Glass that passes the test is required in all new homes, but only for the first 30 feet of taller buildings. That makes Ojeda’s 35-storey project unique.

Ojeda said the new glass will add $30 to $40 a square foot to the price of the curtain wall.

Of course, it’s not just the glass that is stronger. The entire curtain-wall assembly, from aluminum framing to silicon sealant to anchors have all been beefed up.

From glass/polymer laminate and super-strong curtain walls, we move to reflective white paint that contains countless glass “microspheres.”

This one is the brainchild of Ronald Savin, a retired materials scientist who spent most of his career in the military developing coatings for spacecraft and airplanes.

He was familiar with the use of microspheres to lighten airplane parts, but he knew they were also highly reflective. So he decided to use them in a white roof paint to help keep buildings cool.

The paint is applied over a waterproof undercoat made of recycled rubber tires. Tests have shown that the paint deflects about 85 per cent of the heat that strikes it, reducing the surface temperature by as much as 50 degrees Fahrenheit. That means less energy to cool the building’s interior, reduced air-conditioning costs and carbon emissions.

Hilton Hotels spent more than $150,000 to cover Savin’s research costs, and have applied the paint to the roof of their hotel in Anaheim, Calif.

Source: dcnonlAuthor: shangyi

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