MARC CASPE

Security perimeter standards and physical-barrier technologies have rapidly developed in recent years due to increasing threats to buildings and human lives. Security perimeter technologies require assessing all risks and vulnerabilities. Based on crash-validation test standards, innovative technologies are available using analytic simulation tools followed by prototype validations. Attractive antiterrorism designs now can provide landscaping of city streets without deep excavations.

Photo: Courtesy of KKCS

Simulations and actual crashes fine-tune design process.

“The Specification for Vehicle Crash Test of Perimeter Barriers and Gates” was first published in 1985 by the U.S. Dept. of State and then revised in 2003. The State Dept. standard is being replaced with “ASTM F 2656-07 Standard Test Method for Vehicle Crash Testing of Perimeter Barriers.” State Dept. K-ratings and ASTM M-designations both specify an impact of a 15,000-lb vehicle (perpendicular to a crash barrier’s front face) at speeds of 30, 40 or 50 mph. The well-known K-ratings are based on the kinetic energy of the vehicle during impact.

JUN JI

A number of crash-barrier systems have been developed, from bollards and so-called Jersey barriers to planters and benches. These systems have been crash-validated to different levels of performances. Most traditional barriers follow the concept of providing rigid structures to stop the truck bed and relying on truck-body deformations to dissipate kinetic energy.

Recently, some new energy-dissipation concepts provide crash barriers with a shop-calibrated deceleration force to stop the truck gradually over time. This stategy controls impact forces transferred to the base, thereby significantly reducing barrier strength and foundation requirements.

LIN SHEN

Picking one barrier system may not provide the best solution for all security perimeter protection. Comprehensive comparisons and evaluations of crash-barrier systems have to be made to achieve optimal objectives. Research has shown that specific site conditions could significantly impact performance.

Barrier systems can be designed based on special requirements such as shallow foundation, combined anticrash and antiblast functions, and temporary/operable barriers. Analyses of truck-borne explosives catapulted into a secured area recently have attracted attention because protection against it has not yet been fully evaluated. Gradual deceleration performs better against catapulting than sudden impact, in addition to reducing blast over-pressure.

Consideration of crash barriers in the planning stage of a new construction project is important, especially achieving a maximum possible blast stand-off distance from the facility. While there are always strict security and functional requirements for any barrier system, architects and landscape planners should work closely with security professionals in the design and implementation of crash-barrier systems to attain aesthetically pleasing results that camouflage barriers placed on city streets.

QIAN WANG

Prototype perimeter crash-barrier testing standards are based on right-angle impact scenarios. Owners and design professionals also should consider site conditions such as foundation soil properties and truck-crash penetration distance, as a detonation’s blast over-pressure is reduced by a power of three with distance. High-fidelity physics-based finite-element simulations can accurately predict the dynamic behavior of barriers.

The use of high-tech finite element crash simulations provides useful information for fine-tuning and optimization, before and after a prototype crash test is performed. Confidence is built when actual crash observations and analytic results match one another closely, enabling modifications without additional prototype crashes.

To provide reliable and effective security solutions for owners, security professionals should utilize multidisciplinary expertise to perform complete risk assessment, scientific structural analyses and barrier evaluations. Highly resilient protection systems should always be calibrated as a key feature in the solution.

Marc Caspe is manager of engineering at KKCS, Oakland, Calif. He can be reached at 415-299-9914 or caspeco@juno.com. Jun Ji is KKCS senior engineer and can be reached at 217-721-2501 or junji999@gmail.com. Lin Shen, KKCS engineer, can be reached at 217-493-3418 or shenlin9@gmail.com. Qian Wang, KKCS engineer can be reached at 319-331-5734 or ceqwang@gmail.com.