COVER STORY - Simulating Bomb Blasts
A 12,000 pound concrete column crumbled and its six steel reinforcing bars buckled as JacobsSchool structural engineers put UCSD's new bomb blast simulator through its paces. In a splitsecond, hydraulically-powered velocity generators punched the 14-inch-thick column at 18meters per second, simulating the powerful force equivalent of 1,100 pounds of TNT detonated atcurbside. Had this and other columns been the key vertical-load bearing elements to a building, theblast would have led to progressive collapse.
The test was part of the commissioning exercises for a new $8.6 million bomb blast simulatorlocated at the school's new Englekirk Structural Engineering Center. Through a series of 40 teststhat will begin this summer, Jacobs School structural engineers, together with a team of industry anduniversity partners will develop and evaluate blast mitigation technologies to harden buildings andbridges against terrorist bomb attacks.
The program is supported by the Technical Support Working Group (TSWG), which has awardedUCSD a total of $16.1 million for its blast mitigation program.The UCSD blast simulator is the world'sfirst full-scale laboratory to simulate the effects of bombs without theuse of explosive materials.The project is led by Jacobs School structuralengineering professors Gil Hegemier and Frieder Seible.Some 60 delegates from the U.S., U.K., Israel, Canada, Singapore,and Italy were on hand to view the blast test May 17 during TSWG'sInternational Blast Computational Physics Workshop hosted by theJacobs School.
"When was the last time you stood 13 feet from an 1,100pound TNT blast?," Seible, Dean of the Jacobs School, jokedwith the group of blast mitigation experts.
Traditionally, researchers need to position themselves oneto two miles away during explosive field tests, and the blastgeneratedfireball obscures much of the resulting data.Andalthough the fireball is dangerous to humans; it is the airblast that causes serious damage to structures
"Today, hardening buildings and bridges against terroristbomb attacks is more of an art than a science," said Seible."Now for the first time, we will be able to create fullycontrolled and repeatable blast simulations; and we will beable to easily view the results."
"We were doing explosive tests in the field well before 9/11,"says Hegemier."But there is so much work to do that we justcan't test everything. Much of what we will be doing with theblast simulator is validating computer models of these eventsthat can be used to design and assess blast mitigation strategies."
The UCSD blast simulator generates the speed and force ofexplosions through a servo-controlled hydraulic system thatimpact test specimens at speeds of up to 26 meters per secondduring a 1-2 millisecond pulse. In the accumulator bank, nitrogencharges hydraulic fluid and builds up pressure.This pressureis released through velocity generators which propel steel platescarrying elastomeric pads precisely shaped to impart specificpressure distributions on the test specimen.
UCSD structural engineers will test a variety ofbuilding components, such as structural columns,which are most vulnerable to blast loads, as well asload-bearing and infill walls, and bridge elements suchas towers.They will simulate a range of blast scenariosincluding the equivalent of 50 pounds of TNT detonatedwithin a few feet of a structure to 5,000 pounds ofTNT detonated from more than 100 feet away.
Throughout the program, the team will evaluatehow the structural components perform before andafter retrofitting with blast mitigation technologies.
Partners in the UCSD blast mitigation testing programinclude Karagozian and Case (K&C) and Science ApplicationsInternational Corporation (SAIC), who will aid in computationalanalysis for design of tests and predictive computer tools basedon testing results. MTS Systems Corporation, the companywhich originally built the UCSD blast simulator, will continueto enhance the equipment.The Energetic Materials Researchand Testing Center at the New Mexico Institute of Mining andTechnology will oversee a series of explosive field tests whichwill help validate UCSD's laboratory results. Structural Groupis providing blast mitigation technologies for the test specimens.
View videos from the bomb blast test at www.jacobsschool.ucsd.edu/news/news_releases/release.sfe?id=377.