Security Bollards and Post Covers
The aftermaths of the 1995 Oklahoma City bombing as well as the September 11, 2001, attacks saw a sharp rise 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 look of a protective barrier, like large planters or benches that traffic bollards. Once the design threat is determined the resistance required to stop it can be calculated. (See ‘Security Design Concepts’ – below). Specification of anti-ram perimeter takes under consideration both the mass as well as the speed of an approaching attack vehicle, with the latter being considered the more significant.
According to Weidlinger Associates principal, Peter DiMaggio – an expert in security design – careful assessment from the surrounding site is required. “Street and site architecture determines the maximum possible approach speed,” he stated. “If you will find no methods to the building having a long term-up, an attack vehicle cannot develop high speed, and the resistance from the anti-ram barriers could be adjusted accordingly.”
Anti-ram resistance is commonly measured using a standard created by the Department of State, known as the K-rating. K-4, K-8 and K-12 each reference the opportunity to stop a truck of a specific weight and speed and stop penetration from the payload a lot more than 1 m (3 ft) beyond the anti-ram barrier. Resistance depends not just on the size and strength in the bollard itself, but in addition on the way it really is anchored and the substrate it’s anchored into.
Videos of bollard crash tests are featured on several manufacturer’s Internet sites. The truck impacts several bollards at high-speed, and also the front from the vehicle often crumples, wrapping completely around the centermost post. Portion of the cab may disappear the truck, the top or rear end could rise several feet within the air, and front or rear axles might detach. The bollards and their footings are often lifted several feet upward. In all successful tests, the payload on the back from the truck does not penetrate a lot more than 1 meter beyond the collection of bollards, thus satisfying the standard.
The easiest security bollard is some 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 in the same diameter pipe. Without any form of internal stiffening, the pipe’s wall-thickness must be significantly greater. For fixed-type security bollards, simple pipe bollards might be functionally sufficient, if properly mounted. Undecorated pipe-type bollards are also specially manufactured.
The greatest disadvantage of a plain pipe is aesthetics. Some painted pipe fails to truly blend into – a lot 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 that belongs to them are created with alternative mounting capability to slip over standard pipe sizes, forming a stylish and architecturally appropriate impact-resistance system. These decorative covers can also be available to enhance specially designed (but non-decorative) pipe-type bollards.
Security Design Concepts
Much of modern security design focuses on the threat of bomb attacks. The most important element in protecting against explosions will be the distance in between the detonation and the target. The force in the blast shockwave diminishes being a function of the square of the distance. The better distance which can be placed involving the detonation as well as 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 the initial step inside the overall form of blast resistance.
Standoff is valuable architecturally since it allows a building to become protected with out to resemble a bunker. Additionally, it has economic impact, because it is frequently cheaper to generate standoff rather than bomb-proof the dwelling itself. Security bollards and similar anti-ram installations are made and positioned to generate standoff by thwarting the delivery of explosives near to the target by a vehicle.
Any security design depends on a quote of the dimensions of threat to be resisted – the ‘design threat.’ The force in the explosion that may be expected is directly linked to the body weight- and volume-carrying capabilities of the delivery vehicle. Explosives are measured in terms of tonnes of trinitrotoluene (TNT). Probably the most potent molecular explosives such, as Composition 4 (i.e. C-4), are approximately another more robust than TNT, whereas a fuel and fertilizer bomb – like was used in Oklahoma City – is much less powerful than TNT. Reasonable approximations can be made regarding how much explosive power may be delivered by way of 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 kinds 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 designed with their 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 for purely aesthetic installations and substantial visual deterrence and direction, but provide only minimal impact resistance.
Bollards made 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 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 desirable or possible (e.g. an urban location having a basement or subway beneath the pavement), pipe bollard covers made with shallow-depth installation systems are available for both individual posts and teams of bollards. Generally speaking, the shallower the mounting, the broader it must be to resist impact loading.
A removable bollard typically features a permanently installed mount or sleeve below grade, whilst the sleeve’s top is flush with all the pavement. The mating bollard could be manually lifted from the mount to allow access. This etxxdy is intended for locations where the change of access is occasionally needed. It could include a locking mechanism, either exposed or concealed, to prevent unauthorized removal. Both plain and decorative bollards are available for this kind of application. Most removable bollards are certainly not intended for high-impact resistance and they are usually not 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 relieve and speed deployment. Automatic systems might be electric or hydraulic and sometimes include a dedicated backup power installation so the bollard remains functional during emergencies. Retractable systems tend to be unornamented.
Bollards are as ubiquitous as they are overlooked. They speak to the requirement for defining space, one of the basic tasks from the built environment. Decorative bollards and bollard covers offer a versatile solution for bringing pleasing form to many different functions. The plethora of available choices is vast when it comes to both visual style and gratification properties. For security applications, a design professional with security expertise should be contained in the planning team.