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 purposes. Anti-ram installations include not only posts, but other objects created to resist impact without presenting the look of a protective barrier, such as large planters or benches that buy steel 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 into consideration both the mass and the speed of an approaching attack vehicle, with the latter being considered the more significant.
In accordance with Weidlinger Associates principal, Peter DiMaggio – a professional in security design – careful assessment of the surrounding site is required. “Street and site architecture will determine the maximum possible approach speed,” he explained. “If you will find no approaches to the building having a long haul-up, an attack vehicle cannot develop high-speed, and the resistance in the anti-ram barriers may be adjusted accordingly.”
Anti-ram resistance is commonly measured employing a standard designed by the Department of State, called the K-rating. K-4, K-8 and K-12 each refer to the cabability to stop a truck of a specific weight and speed and prevent penetration in the payload a lot 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 in addition on the way it is 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 of 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 in the air, and front or rear axles might detach. The bollards as well as their footings are often lifted several feet upward. In all successful tests, the payload on the back from the truck fails to penetrate greater than 1 meter past the line of bollards, thus satisfying the conventional.
The simplest 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 even with a 102-mm (4-in.) pipe, depending on the engineering of its foundation. It is usually loaded with concrete to increase stiffness, although unfilled pipe with plate stiffeners inside might actually produce better resistance within the same diameter pipe. Without any kind of internal stiffening, the pipe’s wall-thickness needs to be significantly greater. For fixed-type security bollards, simple pipe bollards might be functionally sufficient, if properly mounted. Undecorated pipe-type bollards will also be specially manufactured.
The largest downside of a plain pipe is aesthetics. A bit of painted pipe fails to truly blend into – much less enhance – most architectural schemes. However, this can be overcome by a decorative bollard cover. Many standalone bollards which do not have impact-resistance of their very own are created with alternative mounting capacity to slip over standard pipe sizes, forming a stylish and architecturally appropriate impact-resistance system. These decorative covers may also be available to enhance specifically created (but non-decorative) pipe-type bollards.
Security Design Concepts
Most of modern security design focuses on the threat of bomb attacks. The most significant element in protecting against explosions will be the distance between the detonation as well as the target. The force in the blast shockwave diminishes as a function of the square of the distance. The better distance that may be placed in between the detonation and also the protected structure – referred to as standoff distance – the higher the threat resistance or, conversely, the less blast resistance must be that are part of the structure. Therefore, creation of secure perimeter is the first step within the overall style of blast resistance.
Standoff is valuable architecturally as it allows a building to be protected without having to look like a bunker. In addition, it has economic impact, since it is frequently less expensive to produce standoff rather than bomb-proof the dwelling itself. Security bollards and other anti-ram installations are designed and positioned to generate standoff by thwarting the delivery of explosives close to the target by a vehicle.
Any security design depends on a quote of the dimensions of threat to get resisted – the ‘design threat.’ The force of the explosion which can be expected is directly associated with the load- and volume-carrying capabilities of the delivery vehicle. Explosives are measured in terms of tonnes of trinitrotoluene (TNT). By far the most potent molecular explosives such, as Composition 4 (i.e. C-4), are approximately another more powerful than TNT, whereas a fuel and fertilizer bomb – including was used in Oklahoma City – is much less powerful than TNT. Reasonable approximations can be created about 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. based on 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 may be mounted into existing concrete, or placed 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 protect against impact are often a part of concrete several feet deep, if site conditions permit. Engineering from the mounting depends upon design threat, soil conditions and other site-specific factors. Strip footings that mount several bollards have better resistance, spreading the impact load spanning a wider area. For sites where deep excavation is not desirable or possible (e.g. an urban location with a basement or subway under the pavement), stainless bollards made with shallow-depth installation systems are available for both individual posts and sets of bollards. Generally speaking, the shallower the mounting, the broader it ought to 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 the pavement. The mating bollard may be manually lifted out of the mount to permit access. This etxxdy is supposed for locations where the change of access is occasionally needed. It could add a locking mechanism, either exposed or concealed, to stop unauthorized removal. Both plain and decorative bollards are available for this type of application. Most removable bollards are certainly not created 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 might be electric or hydraulic and sometimes incorporate a dedicated backup power installation and so the bollard remains functional during emergencies. Retractable systems are generally unornamented.
Bollards are as ubiquitous since they are overlooked. They speak with the requirement for defining space, among 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 options is vast with regards to both visual style and satisfaction properties. For security applications, a design professional with security expertise needs to be within the planning team.