Most large buildings are constructed to withstand high winds and moderate seismic activity, but not explosive blasts. One solution may be at hand.
Using a material previously applied to concrete buildings in California and elsewhere for earthquake retrofitting, a university researcher, with the help of the U.S. Army, is now testing the material to help protect buildings in case of a terrorist bomb attack.
To do this, Sarah Orton, assistant professor of civil engineering at the University of Missouri, uses sheets of carbon fiber reinforced polymer, a fabric that can carry 143,000 pounds of force per square inch.
“CFRP enables structures to be retrofitted to withstand extreme loads, which prolongs the useful life of the structure and makes it safer for the occupants,” Orton told Homeland1.
Once CFRP is applied to existing structures using a special anchor previously invented by Orton, the CFRP increases the bending capacity of walls or columns under duress from an explosive blast.
In earlier research, Orton found that her CFRP anchors enable fuller utilization of the tensile capacity of a CFRP sheet and thereby further increase the capacity of a CFRP-strengthened reinforced-concrete beam.
The reinforcing process goes like this. Holes are drilled in the concrete, then CFRP fabric is saturated with epoxy. The flat CFRP sheet is laid on top of the concrete. The anchors, which are also made of CFRP, are then pushed through the fabric into the pre-drilled holes.
“Since everything is still ‘wet’ and the epoxy not cured, they will bond together when the epoxy does cure to make one strong continuous CFRP that is anchored into the concrete,” Orton said.
The Army Engineer Research and Development Center worked with Orton to study the effectiveness of applying CFRP in different ways. Tests explosions were detonated near various CFRP-reinforced concrete slabs.
It was found that CFRP, when layered and anchored, provided a significant amount of protection. Moreover, Orton said, applying additional protection to the front of the concrete slab, such as a steel plate, further enhances the slab’s performance.
While buildings can now be clad in blast-proofing sheets of CFRP, they can’t be protected from the realities of finance. Orton says the high costs of about $30 per square foot are keeping CFRP from being widely implemented in non-earthquake prone areas.