Security Bollards and Post Covers
The aftermaths of the 1995 Oklahoma City bombing and the September 11, 2001, attacks saw a sharp increase in the installation of bollards for security purposes. Anti-ram installations include not just posts, but other objects designed to resist impact without presenting the appearance of a protective barrier, like large planters or benches that security bollards. Once the design threat is established the resistance necessary to stop it may be calculated. (See ‘Security Design Concepts’ – below). Specification of anti-ram perimeter takes into consideration both the mass as well as the speed of an approaching attack vehicle, with the latter being considered the more significant.
In accordance with Weidlinger Associates principal, Peter DiMaggio – a specialist in security design – careful assessment from the surrounding site is required. “Street and site architecture determines the utmost possible approach speed,” he said. “If you will find no strategies to the building with a long run-up, an attack vehicle cannot build-up high-speed, as well as the resistance in the anti-ram barriers can be adjusted accordingly.”
Anti-ram resistance is often measured using a standard designed by the Department of State, known as the K-rating. K-4, K-8 and K-12 each reference the ability to stop a truck of the specific weight and speed and prevent penetration in the payload more than 1 m (3 ft) beyond the anti-ram barrier. Resistance depends not only on the size and strength in the bollard itself, but also on the way it is anchored as well as the substrate it’s anchored into.
Videos of bollard crash tests are featured on several manufacturer’s Web sites. The truck impacts 2 or 3 bollards at high speed, as well as the front in the vehicle often crumples, wrapping completely round the centermost post. Portion 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 as well as their footings are often lifted several feet upward. In every successful tests, the payload on the back in the truck does not penetrate greater than 1 meter past the collection of bollards, thus satisfying the typical.
The easiest security bollard is a bit of 203-mm (8-in.), 254-mm (10-in.), or 305-mm (12 in.) carbon steel structural pipe. Some impact resistance is achieved despite having a 102-mm (4-in.) pipe, depending on the engineering of its foundation. It is usually filled with concrete to improve stiffness, although unfilled pipe with plate stiffeners inside might actually produce better resistance within the same diameter pipe. Without any type of internal stiffening, the pipe’s wall-thickness has to be significantly greater. For fixed-type security bollards, simple pipe bollards may be functionally sufficient, if properly mounted. Undecorated pipe-type bollards are also specially manufactured.
The biggest drawback to a plain pipe is aesthetics. Some painted pipe does not truly blend into – significantly less enhance – most architectural schemes. However, this could be overcome by way of a decorative bollard cover. Many standalone bollards that do not have impact-resistance of their own are made with alternative mounting ability to slip over standard pipe sizes, forming a beautiful and architecturally appropriate impact-resistance system. These decorative covers may also be available to enhance specially designed (but non-decorative) pipe-type bollards.
Security Design Concepts
Most of modern security design focuses on the threat of bomb attacks. The most important element in protecting against explosions is the distance between the detonation and the target. The force from the blast shockwave diminishes as being a function of the square of the distance. The more distance that may be placed between the detonation and the protected structure – called standoff distance – the greater the threat resistance or, conversely, the less blast resistance needs to be built into the structure. Therefore, creation of secure perimeter is step one within the overall design of blast resistance.
Standoff is valuable architecturally because it allows a building to become protected with out to look like a bunker. It also has economic impact, as it is frequently less costly to create standoff rather than to bomb-proof the dwelling itself. Security bollards and other anti-ram installations are created and positioned to create standoff by thwarting the delivery of explosives close to the target with a vehicle.
Any security design depends on a quote of the dimensions of threat to be resisted – the ‘design threat.’ The force from the explosion that may be expected is directly related to the weight- and volume-carrying capabilities in the delivery vehicle. Explosives are measured with regards to tonnes of trinitrotoluene (TNT). By far 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 produced regarding how much explosive power could be delivered with a person carrying a backpack, a passenger vehicle, a pickup truck, a flatbed truck, etc. based on the weight-and volume-carrying capacity.
You will find three basic types of bollard mountings: fixed, removable, and operable (retractable or fold-down). Fixed bollards can be mounted into existing concrete, or set up in new foundations. Manufactured bollards are frequently designed with their particular mounting systems. Standalone mountings could 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 created to control impact are usually embedded in concrete several feet deep, if site conditions permit. Engineering of the mounting is dependent upon design threat, soil conditions as well as 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 really desirable or possible (e.g. an urban location with a basement or subway under the pavement), stainless steel pipe bollards created using shallow-depth installation systems are accessible for both individual posts and teams of bollards. Generally speaking, the shallower the mounting, the broader it ought to be to resist impact loading.
A removable bollard typically has a permanently installed mount or sleeve below grade, as the sleeve’s top is flush using the pavement. The mating bollard may be manually lifted out of the mount to enable access. This etxxdy is intended for locations where change of access is occasionally needed. It could include a locking mechanism, either exposed or concealed, to avoid unauthorized removal. Both plain and decorative bollards are available for this sort of application. Most removable bollards are not designed for high-impact resistance and are usually not utilized in anti-ram applications.
Retractable bollards telescope down below pavement level, and may be either manual or automatically operated. Manual systems sometimes have lift-assistance mechanisms to help ease and speed deployment. Automatic systems may be electric or hydraulic and quite often incorporate a dedicated backup power installation so the bollard remains functional during emergencies. Retractable systems are generally unornamented.
Bollards are as ubiquitous as they are overlooked. They talk to the need for defining space, one of many basic tasks from the built environment. Decorative bollards and bollard covers provide a versatile solution for bringing pleasing form to a variety of functions. The range of available options is vast in terms of both visual style and performance properties. For security applications, a design professional with security expertise needs to be contained in the planning team.