February 2, 2018
by Scott Espenson
Vehicle ramming attacks are on the rise in the United States and abroad. Therefore, many government agencies—at the federal, state, and local levels—are assessing vulnerabilities in their facilities and public spaces.
Passive bollards have long served as a successful preventive method to stop vehicles from encroaching areas with unrestricted walking access (e.g. sidewalks, tourist attractions, and parks). They are manufactured in a wide array of architectural shapes, finishes, and sizes. This allows them to blend in or even complement the surrounding environment.
However, bollards are not an efficient option for spaces requiring longer runs. Anti-ram fencing, which is more cost-effective and practical than bollards, is ideal for restricting unauthorized vehicle access to a facility and for protecting office buildings, critical infrastructure, hazardous materials, and people who are in high-risk areas or adjacent to roadways or parking lots where free access is not required.
How crash test standards and ratings apply to anti-ram fencing
When selecting anti-ram vehicle fencing, consideration should be given to how a system was designed and tested to ensure it meets the applicable threat conditions. Additionally, understanding the various testing standards simplifies the process of comparing crash ratings between products. It is important to note the standards referenced in this article are designed for testing vehicle barriers against head-on attacks, as opposed to testing conducted for highway barriers, which often measure the effects of a glancing blow.
U.S. crash test standards for vehicle barriers have evolved a great deal over the years. In 1985, the U.S. Department of State (DOS) published a rating system and test standard, which was subsequently revised in 2003. While the initial rating system—SD-STD-02.01, Certification Standard–Test Method for Vehicle Crash Testing of Perimeter Barriers and Gates—allowed for different penetration distances occurring from a medium-duty truck, the 2003 revision (SD-STD-02.01 Rev A) required all barriers receiving a DOS certification allow no more than 1 m (3.3 ft) of vehicle test bed penetration beyond the inside of the barrier. The DOS test method utilized a 6804-kg (15,000-lb) medium-duty truck as the test vehicle.
In 2009, the DOS retired SD-STD-02.01 Rev A and stated all new barriers to be considered for embassy projects should be tested to ASTM International standards. ASTM F2656-15, Standard Test Method for Crash Testing of Vehicle Security Barriers, is the most recent standard to which anti-ram vehicle barriers are tested. A corresponding performance rating is also assigned based on the test vehicle type, speed, and penetration distance.
Test vehicles span six style and weight categories, from a small passenger car (1102 kg [2430 lb]) to a heavy goods vehicle (29,483 kg [65,000 lb]). Vehicles are impacted into the barrier at speeds ranging from 48 to 96 km/h (30 to 60 mph). Finally, the penetration distance of the vehicle into the barrier falls into one of three categories—from less than 1 m (3.3 ft) (P1) up to 30 m (98 ft) (P3).
The DOS SD-STD 02.01 Rev A ratings are still used frequently in project specifications. These ratings were assigned based on impact speed, similar to ASTM ratings. Products successfully tested with vehicles traveling at 48 km/h (30 mph) were assigned a K4 rating, a K8 rating at 64 km/h (40 mph), and a K12 rating at 80 km/h (50 mph).
Property owners should first seek to understand the threat conditions for the particular site they want to secure, and then determine the performance level. For reference, the DOS typically requires barriers used on embassy projects be tested with a medium-duty truck (6804 kg [15,000 lb]) traveling 80 km/h and have less than a 1-m penetration distance, which is equivalent to the ASTM F2656 M50-P1 rating.
Separately, the Department of Defense (DOD) maintains an approved list of vehicle barriers and fencing. While the DOD does not have its own unique crash testing standard, the U.S. Army Corps of Engineers (USACE) reviews crash test reports and independently validates the barriers. It is important to note not every product obtaining a crash test performance rating is placed on the DOD Anti-ram Vehicle Barrier List.
Differentiating the various types of anti-ram fencing
Choosing an anti-ram fence largely comes down to two options—post and beam or cable-based—and the differences lie right in the name.
Post and beam anti-ram fencing systems rely on a single steel, horizontal beam mounted between two anchor posts. These are typically spaced around 9 m (30 ft) apart, depending on the crash rating and manufacturer. Post and beam systems utilizing tubular steel offer a clean, aesthetically appealing look and simple connection points with minimal hardware.
Cable-based fences utilize anchor and intermediate posts spaced as close as 2.4 m (8 ft) apart, to which a tensioned cable is attached. The cable is relied upon to stop all vehicular threats, and is either exposed, or often, ornamentally hidden in the fence. Multiple runs of cable line the posts, and the amount of cable needed largely depends on the desired level of crash test certification. Cable-based fence may include tall pickets, which act as anti-pedestrian security and also add another level of protection.
However, the real difference between the two types of fence lies in the installation.
Purchase price vs. total cost
Purchasing an anti-ram perimeter security fence system is only half the financial battle to securing a property’s border against vehicle-borne attacks—cost of installation also needs to be dealt with. Contractors, architects, and owners can realize significant savings by looking beyond the initial purchase price of the fence system and exploring the steps, materials, and equipment necessary to complete the project.
Traditional cable-based fence systems require extensive amounts of hardware, intermediate posts, wire rope, and concrete. These drive up the total project cost and lengthen the construction schedule. Post and beam perimeter fences eliminate these components and cut installation costs nearly in half while still providing crash-tested certification to ASTM F2656 standards.
Over a 1000-m (3281-ft) span, a DOS K12 or ASTM F2656 M50-P1 cable-based fence system can include up to 20 anchor posts and 380 line posts, while supporting multiple runs of cable. With up to 400 post holes in just a 1000-m stretch, the cost of materials and labor hours begins to add up quickly when one considers each hole requires auguring, concrete fill, and a rebar cage.
To effectively prevent vehicles from penetrating the fence, spools of cable must be run in multiple lines—sometimes up to eight—through line and anchor posts in time-consuming fashion. The whole system also requires a significant amount of hardware—clamps and nuts to tension each cable—to maintain its safety standards.
Further, the maintenance and work is not finished when the cable-based fence install is complete. Cables must be checked periodically to adjust tensioning and maintain the fence’s ability to prevent vehicle penetration.
All of this work is above and beyond what is needed to install a post and beam anti-ram fence, which has a simple design.
In the case of M50-P1 systems, vertical anchor posts are spaced approximately 9 m apart and rely on a single tubular beam—connected by one nut and bolt on each post—to absorb the energy of a crash, as opposed to multiple runs of wire rope and the line posts supporting them. The result is 110 posts in a 1000-m span, vs. the 400 posts used with a cable-based fence system. This is nearly 75 percent fewer holes to dig, even before factoring in the different-sized holes and the time it takes to switch back and forth between auger bit sizes.
Post hole foundations are shallower than with cable-based anchor posts, and require less concrete. While the rebar cage must always be priced and built separately with a cable-based fence system, rebar sticks are included with some post and beam fence designs. To install, contractors simply insert the rebar into predrilled holes in the anchor posts. No extra expenses or labor are required to build elaborate cages. Additionally, post and beam fences are engineered to be extremely simple and efficient in terms of the hardware used and the effort required for construction. All of this ultimately leads to abundant savings.
This simplicity in installation, coupled with high crash test standards, led to the installation of a post and beam fence in a Navy base in California, a Department of Energy (DOE) facility in Colorado, and a utility facility in Missouri.
One must focus on requirements (crash test ratings), financial considerations (differing installation costs), and preferences (aesthetics of post and beam vs. cable-based) while selecting the proper anti-ram fence for the project.
Scott Espenson has worked at Ross Technology for more than 20 years. His responsibilities as perimeter security product manager for the past decade have included the oversight of new product development, product testing, sales, project management, and fulfillment. With a strong background in controls technology with the United States Air Force, he has been active in creating and sourcing advanced control systems for Ross perimeter security products. Espenson’s international experience includes overseeing numerous security projects in the Middle East. He can be contacted at ScottE@rosstechnology.com.
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