Look around in almost any urban setting and you’ll spot bollards: short, adaptable posts that guide traffic away from pedestrians and property, often adding architectural flair to the landscape. When made of concrete-filled steel pipe, and installed securely, these guideposts also stand guard, catching the impact of vehicles that have left the roadway. When planning the perimeter around a building, architects and engineers will consider bollards as part of their security plans.
Depending on the site, this plan may include a variety of types of security bollard. High-impact or safety bollards are relatively inexpensive ways to provide perimeter protection against recklessness or accident. For sites that are protecting against concerted criminal attack, a planner might include crash- or k-rated bollards, which are also commonly known as anti-ram bollards.
Safety or high-impact bollards are the antecedent of anti-terrorist bollards. They’ve been part of the urban landscape for traffic guidance and asset protection for centuries. Early forms of security bollards were simple posts placed in front of stonework to prevent carriage wheels from rubbing and damaging the building, but as vehicles became more highly powered, the engineering behind bollards developed as well. Today, most high-impact installations consist of steel posts filled with concrete, installed to help mitigate damage to people or property in the event of an accident. Depending on average traffic conditions around these bollards, they are available in different diameters, providing different levels of impact resistance.
Traditionally, bollards act as a guide to law-abiding traffic. Weighty versions are a deterrent to reckless drivers, as collision will cause vehicle damage. In the event of an accident, steel pipe bollards act as a safety barrier, absorbing some of the impact forces of an out-of-control car and making the repercussions to people and property much less severe.
Development of K-ratings
These hardy high-impact bollards were such pervasive elements of urban safety that they became an increasing area of research and interest after 9/11. How much support could they provide against a concerted attack, rather than just standing guard against misadventure?
In criminal or terrorist scenarios, the driver of an incoming vehicle may not care about damage to the vehicle or driver and so be unaffected by standard security bollards. What would the stopping power be of a bollard under a concerted charge? To evaluate bollards and other perimeter components, the Department of State revived the K-Rating—a system for evaluating structural resistance to assault, developed by the Defense Department in the 1980s.
K-rated bollards are tested barriers proven to stop a 15,000 lb diesel truck impacting at 30, 40, or 50 mph, depending on the rating.
K-rated bollards, as well as fences, medians, and other forms of perimeter security installation, are tested barriers proven to stop a 15,000-pound diesel truck impacting at 30, 40, or 50 mph. The Department of State was particularly interested in preventing bombs or other explosive payloads from being delivered to structures, so by 2003, DoS K-ratings came to focus on devices that would prevent a truck’s flatbed from penetrating farther than 3.3 feet through a structure. If bollards or other perimeter obstacles are shown to stop a concerted attack within a meter, they are useful in the site planning of safe zones around targeted installations.
|K-rating for Crash-Rated Obstacles|
After widespread interest in K-rated installations, the American Society for Testing and Materials (ASTM) introduced a rigorously stepped system of crash ratings for measuring vehicle penetration through security barriers. The ASTM standard measures the vehicle penetration of cars, pickup trucks, medium-duty trucks, and heavy goods vehicles each at 30, 40, and 50 mph. Although this precisely defined system has replaced the DoS K-rating in testing facilities, “K-rating” is still often used as industry shorthand to talk about barriers crash-rated for medium-duty trucks. It is mostly a historical designation at this point.
Crash rated bollards are designed to protect high-target buildings from concerted vehicular attack. If a security bollard is unrated, it does not mean it has no stopping power, but rather that its stopping power is unknown.
The site placement of crash-rated bollards requires extra consideration: unlike standard safety bollards, a crash rated bollard should be set at enough of a distance to ensure that a vehicle carrying a bomb is stopped before it is close enough to the structure for explosives to do damage. Therefore, crash-rated bollards are often placed to ensure a wide safe zone around a vulnerable area. Sometimes, staggered or unpredictable patterns of placement make them more effective.
Crash-rated bollards are becoming an increasing element of city and security planning documents, and are mandated for many government or military installations. In 2009, the NYPD released an Engineering Security document outlining how to do risk assessment for buildings in the city, recommending anti-terrorist crash-rated bollards for “High and Medium Tier” buildings. These are defined as buildings that “present exceptional threat, vulnerability and impact characteristics.” Although these represent only a small fraction of all buildings in New York, their protection helps create a feeling of security throughout the city.
An ongoing area of research is in properly categorizing threat to new site developments, and balancing security approaches with likeliest threats and cost efficiency.
Differences in installation
Both crash-rated and high-impact bollards are commonly made of steel pipes filled with concrete. Crash-rated bollards are often quite a bit more expensive and require specialized installation teams and methods.
If the steel pipes used are plain, either type of security bollard can be covered to fit its architectural surroundings. Bollard covers can be made of many materials depending on the location and the look: ductile iron, cast iron, steel, concrete, and plastic are all commonly used in creating decorative covers. However, when installing a crash-rated bollard, the behavior of that cover in all scenarios need to be considered. Plastic or steel are most often used in crash-rated covers, as other covers are more likely to produce shrapnel: this would be especially dangerous in situations with explosives onboard.
Both types of security bollard are usually buried several feet below grade and fixed in place with concrete. Consultation with an engineer is important, since elements of the substrate influence how secure the bollard is within in its placement. Crash-rated bollards often come with additional subgrade footings made of steel.
If there are underground utilities or structures that prevent deep mounting, shallow mounted crash-rated bollards are an option. These are usually installed with a beam system that connects many bollards in an underground lattice, spreading widely, like the roots of a tree, to provide impact stability.
Safety and crash-rated bollards applied together
Bollards that are crash-rated against bombardment are often used in conjunction with high-impact safety bollards. In these situations, safety bollards are deployed in a “soft perimeter,” often alongside trees and other landscape features, to create obstacles in the longer approach to a building. These may include parking lot bollards, lane delimiters, and bollards defining pedestrian zones. Although these may not be crash-rated, they provide impediment and if an incoming vehicle behaves erratically through this soft perimeter, security forces are warned.
Closer to the site being secured, anti-ram or crash-rated bollards are used, in conjunction with other techniques, to create a “hard perimeter,” far enough from the building entrance to prevent delivery of a payload.
Creating a secure perimeter
Most safety applications will need only standard security bollards to protect against accident or recklessness, and provide a guide to drivers who have no criminal intent. Safety bollards of this type are most appropriate as parking posts and around utility meters; around the perimeter of storefronts, playgrounds, parks and patios; and lining roadways or medians.
However, for those places that are more likely to be targeted by criminal or terrorist intent, creation of a security site plan might include crash-rated bollards. Vendors of such bollards specialize in both design and the oversight of proper installation. If crash-rated bollards are appropriate for your site, the American Department of Defense provides a list of anti-ram bollard vendors.