Volume 3, Issue 2 March 2003

2003
2002
2001

Bomb-Resistant Buildings by David Pescovitz Printer-friendly version The cable system designed by Berkeley researchers prevented the floor (shown here) from entirely collapsing after it dropped two feet. Abolhassan Astaneh-Asl photo Berkeley civil engineers are borrowing from suspension bridges to protect buildings from terrorist explosives. Professor Abolhassan Astaneh-Asl and his graduate students recently tested a cable system that successfully keeps a collapsing floor hanging on, even if a support column is blown out. "Cable is the best structural element we have to reduce impact," says Astaneh, who presented his findings at the American Association for the Advancement of Science meeting in February. "By nature, [cable] is very flexible, so it bends rather than breaks under the lateral blast load; yet it can carry large tension forces similar to the way cables work on suspension bridges." At the AAAS meeting, Astaneh conducted a symposium on security technologies ranging from biometrics to new airport security approaches. He discussed the cable system as part of a talk about protecting buildings from terrorist attack and on lessons learned from the World Trade Center catastrophe. The cable-based design was first proposed after the Oklahoma City collapse by Berkeley emeritus professor of civil engineering Joe Penzien. In 1998, Astaneh received a General Services Administration grant to analyze and test the system. Last year, he demonstrated that embedding 1.25-inch diameter steel cables within a typical building's concrete floors and anchoring them to corner support columns or braced spans would keep a floor from collapsing. Just days after a two-week scientific reconnaissance mission to the site of the collapsed World Trade Center, Astaneh-Asl was back on campus testing a new technique to prevent future high-rise disasters. Eliza Haskins photo The latest experiments were part of a National Science Foundation-supported viability study of retrofitting existing buildings with suspension cables. The cable system was designed to protect a building's vulnerable outer support beams. "It is almost impossible to always keep terrorists from getting close to those columns," Astaneh says. "In Oklahoma City, a terrorist was able to park a rental truck 10 feet away from an outer support column. The explosives took out just one column, but that caused the upper floors to bear down in a chain of events that brought down half of the building, killing 168 people." To test the cable system, Astaneh and his students built a full-scale typical building floor with five support columns in Berkeley's civil engineering test bay. The steel cables passed through one-inch holes in the columns and were affixed to the concrete model floor. In one test, a support column was knocked out and a massive hydraulic jack — the largest in the country — applied 240,000 pounds of downward force to simulate the weight of a floor above. The test floor dropped three feet, but stayed connected to the remaining columns that carried the extra weight. Can steel cables strengthen existing buildings? We want to hear from you... "The cable prevents a progressive and catastrophic collapse," Astaneh says. "The floor may slope down two to three feet, but people can still escape to safety from the building. Not only can the system potentially save lives, it can limit the damage to something that can be easily repaired." According to Astaneh, retrofitting existing buildings with the cable system would add $2 per square foot, about one percent of the current cost of building construction. Since the 1995 Oklahoma City bombing that destroyed the Alfred P. Murrah Federal building, Astaneh has focused his research on improving the structural integrity of the nation's buildings, utilities, and other infrastructures during fires, earthquakes, explosions, and other hazards. A week after the September 11 attack on the World Trade Center, Astaneh embarked on a reconnaissance mission to Ground Zero to help determine the precise structural factors that led to the buildings' collapse. Abolhassan Astaneh-Asl's Home Page "Lessons Learned from the Toppled Towers" by David Pescovitz (Lab Notes) "Cables hold promise in protecting existing buildings from bomb, researchers find" by Sarah Yang (UC Berkeley Media Relations) "Report from Ground Zero" by Robert Sanders (UC Berkeley Media Relations) Lab Notes is published online by the Public Affairs Office of the UC Berkeley College of Engineering. The Lab Notes mission is to illuminate groundbreaking research underway today at the College of Engineering that will dramatically change our lives tomorrow. Editor, Director of Public Affairs: Teresa Moore Writer, Researcher: David Pescovitz Designer: Robyn Altman Subscribe or send comments to the Engineering Public Affairs Office: lab-notes@coe.berkeley.edu. © 2003 UC Regents. Updated 2/28/03.