Defense Technology International - January/February 2008 - (Page 12) SCIENCE WATCH MICHAEL DUMIAK LOOKS THAT WON’T KILL enough to pancake two-thirds of the building from the 10th floor to Researchers are working on ma- but the rebar can’t be more than the ground. Barney says security terials and engineering techniques 2% of the cross-sectional area of requirements are now based on for government structures like em- a piece of concrete, otherwise the whether the building system can bassies and consulates that com- concrete will be crushed before the resist the removal of a major strucbine aesthetics with improved blast steel yields. If the concrete’s inter- tural member in the facade, and not nal porous structure is crushed, the on the strength of a bomb. It’s a difresistance. In an era of car bombs and securi- material undergoes a catastrophic ficult challenge. “You can make the building roty alerts, architects must figure out failure, which means walls collapse bust and redundant, or flexible,” how to combine security and pub- and columns fall. Another material Mayrhofer be- she says. Both are expensive, and lic access in building design without sacrificing one for the other. At the lieves to be effective is Sifcon, or point to another challenge. “It’s supposed to be bomb-proof new U.S. embassy in Berlin, and an open expression of for example, concrete, guns American government,” she and cameras are everywhere. says. “Those two don’t go toGuards demand that bicyclists gether.” dismount before riding past Barney’s design for the new the $170-million building. The federal building in Oklahoma perceived tension surrounding City, which opened in 2004 the structure makes the nearby just north of where the MurNorth Korean embassy seem rah Federal Building stood, almost inviting. features changes that are deConstruction options are signed to enhance security: It being developed to overcome has only three stories; there this. are setback barriers around In Freiburg, Germany, rethe building; most of the glass searchers test polymer confaces an inner courtyard; encrete and other materials at Security concerns at new U.S. Embassy tranceways connect in a pasthe Ernst-Mach-Institut (EMI) in Berlin favor fortress-like architecture. sageway lined with concrete— of the Fraunhofer Institute for Developments in building materials a requirement, in case a bomb High-Speed Dynamics. Polymer could soften the look of government gets in the building—but the concrete uses resin instead of structures without sacrificing safety. passageway doesn’t look like cement to bind stone aggregate. Researchers are getting good slurry-infiltrated concrete. This has a tunnel; and the building core is results by adding a damping layer been around for some time and is dispersed, so exit stairs are at the of polymer concrete—made by mix- costly, but he advocates its use in perimeter. All in all, it’s a good-looking epoxy resin with corn cobs and columns or connecting joints and ing building. One important design feature is flax fibers—to the side of reinforced connection points between walls, walls. The resin blend makes the ceilings and columns. Sifcon is a anchoring silicone-laminated blastconcrete more porous and thus ideal mix of steel fibers and concrete. resistant glass in steel tubes. This is for use as a hard but tensile cush- Mayrhofer says it enhances rein- intended to keep the plates in place ion. The material acts as a damping forced concrete by a factor of two and relatively intact rather than layer, absorbing a blast wave and because the steel fibers make it exploding into millions of deadly shards in a blast. distributing and weakening blast more ductile. “There’s no such thing as shatter“We don’t need bunkers. We can pressure before it hits the brittle construct standard buildings with proof glazing,” says Steve Norville, reinforced concrete underneath. When a bomb explodes, a shock security if we use columns with a glass expert and civil engineering wave rolls from the blast point and Sifcon,” Mayrhofer says, and engi- professor at Texas Tech University. directs energy at anything in its neer the weak points in the building “You want to make sure the frame holds the glass, but while holding it, path, says Christoph Mayrhofer, a with precision. When Timothy McVeigh bombed the glass also absorbs a lot of the materials scientist and blast-resistance expert at EMI. The resulting the Alfred P. Murrah Federal Build- blast energy.” Polycarbonate and glass-clad polyhazards to a building include struc- ing in Oklahoma City in 1995, only tural damage or collapse, and frag- one column collapsed in the initial carbonate laminates are options, blast, says Chicago architect Carol although expensive. Researchers mentation of glass. The strategy for resisting blasts Ross Barney, whose firm designed at Lucent and DuPont are bringing works on two levels: what hap- the replacement building. But it glass infused by layers of polymer pens before materials fail and was enough. Because Murrah was to market as an alternative. Experts what happens after. Concrete is built with cast-in-place concrete, say windows laminated with nano brittle, with little tensile strength. everything interlocked. When one materials for reinforcement may be It can be reinforced by steel rebar, concrete floor fell, the weight was an option in the future. I MICHAEL DUMIAK/DEFENSE TECHNOLOGY INTERNATIONAL 12 DEFENSE TECHNOLOGY INTERNATIONAL JANUARY/FEBRUARY 2008 www.aviationweek.com/dti http://www.aviationweek.com/dti
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