Security Bollards and Post Covers
The aftermaths of the 1995 Oklahoma City bombing and also the September 11, 2001, attacks saw a sharp rise in the installation of bollards for security reasons. Anti-ram installations include not just posts, but other objects created to resist impact without presenting the look of a protective barrier, including large planters or benches that plastic safety bollards. Once the design threat is determined the resistance needed to stop it can be calculated. (See ‘Security Design Concepts’ – below). Specification of anti-ram perimeter takes under consideration both the mass and the speed of an approaching attack vehicle, with the latter being regarded the more significant.
In accordance with Weidlinger Associates principal, Peter DiMaggio – a specialist in security design – careful assessment of the surrounding website is required. “Street and site architecture will determine the highest possible approach speed,” he explained. “If there are no strategies to the building using a long haul-up, an attack vehicle cannot develop high speed, and also the resistance in the anti-ram barriers may be adjusted accordingly.”
Anti-ram resistance is normally measured employing a standard developed by the Department of State, called the K-rating. K-4, K-8 and K-12 each make reference to the cabability to stop a truck of any specific weight and speed and prevent penetration of the payload more than 1 m (3 ft) past the anti-ram barrier. Resistance depends not only on the size and strength from the bollard itself, but in addition on the way it is actually anchored as well as the substrate it’s anchored into.
Videos of bollard crash tests are featured on a number of manufacturer’s Websites. The truck impacts 2 or 3 bollards at high-speed, and also the front in the vehicle often crumples, wrapping completely round the centermost post. Part of the cab may disappear the truck, the front side or rear end could rise several feet within the air, and front or rear axles might detach. The bollards along with their footings are sometimes lifted several feet upward. In every successful tests, the payload on the back in the truck fails to penetrate more than 1 meter past the line of bollards, thus satisfying the conventional.
The most basic security bollard is a piece of 203-mm (8-in.), 254-mm (10-in.), or 305-mm (12 in.) carbon steel structural pipe. Some impact resistance is achieved despite a 102-mm (4-in.) pipe, depending on the engineering of its foundation. It is often filled with concrete to increase stiffness, although unfilled pipe with plate stiffeners inside could possibly produce better resistance in the same diameter pipe. Without any form of internal stiffening, the pipe’s wall-thickness needs to be significantly greater. For fixed-type security bollards, simple pipe bollards may be functionally sufficient, if properly mounted. Undecorated pipe-type bollards can also be specially manufactured.
The largest disadvantage of a plain pipe is aesthetics. A bit of painted pipe fails to truly blend into – a lot less enhance – most architectural schemes. However, this could be overcome with a decorative bollard cover. Many standalone bollards which do not have impact-resistance of their own are made with alternative mounting capability to slip over standard pipe sizes, forming a beautiful and architecturally appropriate impact-resistance system. These decorative covers can also be available to enhance specially engineered (but non-decorative) pipe-type bollards.
Security Design Concepts
A lot of modern security design focuses on the threat of bomb attacks. The most significant element in protecting against explosions is the distance involving the detonation and the target. The force from the blast shockwave diminishes as being a function of the square from the distance. The greater distance which can be placed in between the detonation and also the protected structure – called standoff distance – the greater the threat resistance or, conversely, the less blast resistance must be that are part of the dwelling. Therefore, creation of secure perimeter is the initial step in the overall form of blast resistance.
Standoff is valuable architecturally because it allows a building to become protected without having to look like a bunker. In addition, it has economic impact, since it is frequently less expensive to produce standoff than to bomb-proof the dwelling itself. Security bollards and other anti-ram installations are designed and positioned to create standoff by thwarting the delivery of explosives close to the target with a vehicle.
Any security design is dependent upon a quote of the size of threat to become resisted – the ‘design threat.’ The force of the explosion that may be expected is directly related to the weight- and volume-carrying capabilities of the delivery vehicle. Explosives are measured with regards to tonnes of trinitrotoluene (TNT). Probably the most potent molecular explosives such, as Composition 4 (i.e. C-4), are approximately a third more robust than TNT, whereas a fuel and fertilizer bomb – like was utilized in Oklahoma City – is much less powerful than TNT. Reasonable approximations can be created regarding how much explosive power may be delivered by a person carrying a backpack, a passenger vehicle, a pickup truck, a flatbed truck, etc. according to its weight-and volume-carrying capacity.
You will find three basic types of bollard mountings: fixed, removable, and operable (retractable or fold-down). Fixed bollards could be mounted into existing concrete, or set up in new foundations. Manufactured bollards are usually created with their very own mounting systems. Standalone mountings can be as non-invasive as drilling into existing concrete and anchoring with epoxy or concrete inserts. Such surface-mounted bollards can be used as purely aesthetic installations and substantial visual deterrence and direction, but provide only minimal impact resistance.
Bollards designed to control impact are generally baked into concrete several feet deep, if site conditions permit. Engineering in the mounting depends upon design threat, soil conditions along with other site-specific factors. Strip footings that mount several bollards have better resistance, spreading the impact load more than a wider area. For sites where deep excavation is not desirable or possible (e.g. an urban location using a basement or subway under the pavement), stainless steel bollard made with shallow-depth installation systems are available for both individual posts and groups of bollards. Generally speaking, the shallower the mounting, the broader it ought to be to face up to impact loading.
A removable bollard typically features a permanently installed mount or sleeve below grade, while the sleeve’s top is flush using the pavement. The mating bollard can be manually lifted out from the mount to permit access. This etxxdy is meant for locations where the change of access is occasionally needed. It can include a locking mechanism, either exposed or concealed, to avoid unauthorized removal. Both plain and decorative bollards are accessible for this kind of application. Most removable bollards are certainly not designed for high-impact resistance and are not often found in anti-ram applications.
Retractable bollards telescope down below pavement level, and could be either manual or automatically operated. Manual systems sometimes have lift-assistance mechanisms to help ease and speed deployment. Automatic systems could be electric or hydraulic and sometimes add a dedicated backup power installation therefore the bollard remains functional during emergencies. Retractable systems tend to be unornamented.
Bollards are as ubiquitous since they are overlooked. They speak with the need for defining space, among the basic tasks in the built environment. Decorative bollards and bollard covers offer a versatile solution for bringing pleasing form to a variety of functions. All the different options is vast in terms of both visual style and satisfaction properties. For security applications, a design professional with security expertise should be contained in the planning team.