Foam Jackets for Steel Columns
Sports stadiums, skyscrapers and airport terminals – structures of this size must meet higher-than-normal levels of fire safety. Especially if they have a steel frame that could rapidly lose its stability in a catastrophic event. VINNAPAS® EZ 3112 is a new binder from WACKER that helps to boost the heat resistance of such structures.
Come 2014 when Brazil hosts the World Cup and then the Olympics in 2016, entire nations will be glued to their screens. They will see tens of thousands of fans flocking to gigantic, futuristic stadiums where sporting rivalries will be fought out against a striking backdrop of steel frames and steel roofs designed to convey an impression of lightness and airiness. Steel skeletons have a low dead load, but a high load-bearing capacity and are therefore usually quick and easy to assemble thanks to prefabrication of parts. This makes steel constructions statically ideal as skeletal structures for exhibition halls and airport terminals. It's a construction method that is especially popular for office tower blocks in the booming cities of the Far East. But wherever so many people come together, safety plays a central role alongside construction efficiency and aesthetics.
Ever More Intricate Architecture
Dr. Wilfried Huster, technical service head of Dispersions and Resins at WACKER POLYMERS, in a meeting with Stefanie Werkstetter at the application technology lab’s storage area.
“Architecture is becoming increasingly more intricate and delicate. At the same time, buildings still need to meet all specified safety standards,” says Dr. Wilfried Huster, head of Application Technology for Dispersions in Europe at WACKER POLYMERS. This applies especially to those relating to fire. True, the steel columns themselves are not flammable, but this otherwise highly stable material has an Achilles heel – intense heat. When the temperature reaches 500 °C, steel frames soften rapidly, and the buildings are in danger of collapse. “Basically, the steel just 'floats' away,” says Dr. Niels Friede, process engineer and head of Emergency Services/Fire Safety at WACKER in Burghausen. Not only that, steel expands extensively in heat. “Unlike stone and even wooden walls, which undergo little dimensional change, steel columns lengthen and widen. In doing so, they force other components apart, thereby further weakening the structural stability,” adds Friede.
Fire protection coating in a laboratory test at Clariant: As of a temperature of 200 to 250 °C, ammonium polyphosphate (the main component of the coating) begins to decompose and reacts with the pentaerythritol to form phosphoric acid esters. At higher temperatures, the melamine content decomposes – generating gaseous ammonia and oxygen which expand the carbon- and phosphorus-containing residues of the esters.
That is why fire safety is so crucial in steel-frame structures. One solution here is to boost the resistance of the columns by painting them with so-called intumescent coatings, which swell in the event of a fire and confer greater “staying power” to the metal columns. The coatings are applied like paints in thicknesses ranging from just 300 micrometers to several millimeters, the precise thickness depending on the application. Even though these heat shields are fairly thin, they nonetheless afford substantial protection. “When a fire breaks out, the coating swells by 10 to 100 times their original thickness to form a thermally insulating foam jacket around the steel column,” says Huster. The thermal insulation properties stem from the foam's high density and very fine pores. The foam slows the rate at which the steel heats up, greatly delaying the time taken to reach the critical 500 °C. “The buildings can thus resist a fire for much longer, and that gives the rescue teams more precious time to save lives,” adds Friede, a fire expert.