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 reasons. Anti-ram installations include not only posts, but other objects created to resist impact without presenting the look of a protective barrier, including large planters or benches that steel bollards. Once the design threat is established 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 and also the speed of an approaching attack vehicle, with the latter being considered the more significant.
Based on Weidlinger Associates principal, Peter DiMaggio – a specialist in security design – careful assessment in the surrounding site is required. “Street and site architecture will determine the maximum possible approach speed,” he stated. “If you will find no strategies to your building using a long haul-up, an attack vehicle cannot build up high speed, as well as the resistance of the anti-ram barriers can be adjusted accordingly.”
Anti-ram resistance is commonly measured utilizing a standard developed by the Department of State, referred to as K-rating. K-4, K-8 and K-12 each reference the ability to stop a truck of the specific weight and speed preventing penetration in the payload more than 1 m (3 ft) past the anti-ram barrier. Resistance depends not merely on the size and strength in the bollard itself, but additionally on the way it is anchored and also the substrate it’s anchored into.
Videos of bollard crash tests are featured on a number of manufacturer’s Websites. The truck impacts several bollards at high speed, and the front from the vehicle often crumples, wrapping completely around the centermost post. Part of the cab may fly off the truck, the front 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 occasionally lifted several feet upward. In every successful tests, the payload on the back from the truck fails to penetrate greater than 1 meter beyond the type of bollards, thus satisfying the conventional.
The most basic 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 the foundation. It is usually full of concrete to improve stiffness, although unfilled pipe with plate stiffeners inside could possibly produce better resistance in the same diameter pipe. Without any type of internal stiffening, the pipe’s wall-thickness must 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 greatest downside of a plain pipe is aesthetics. A bit of painted pipe fails to truly blend into – significantly less enhance – most architectural schemes. However, this could be overcome by a decorative bollard cover. Many standalone bollards that do not have impact-resistance that belongs to them are created with alternative mounting capacity to slip over standard pipe sizes, forming a beautiful and architecturally appropriate impact-resistance system. These decorative covers can also be available to enhance specifically created (but non-decorative) pipe-type bollards.
Security Design Concepts
Much of modern security design focuses on the threat of bomb attacks. The most important factor in protecting against explosions is the distance in between the detonation and also the target. The force in the blast shockwave diminishes as being a function of the square from the distance. The greater distance which can be placed involving the detonation and the protected structure – called standoff distance – the higher the threat resistance or, conversely, the less blast resistance has to be included in the structure. Therefore, development of secure perimeter is the initial step inside the overall form of blast resistance.
Standoff is valuable architecturally since it allows a building to get protected without needing to resemble a bunker. It also has economic impact, as it is frequently less costly to produce standoff than to bomb-proof the structure itself. Security bollards and other anti-ram installations are designed and positioned to generate standoff by thwarting the delivery of explosives near to the target by a vehicle.
Any security design depends upon a bid of the dimensions of threat to get resisted – the ‘design threat.’ The force from the explosion that can be expected is directly related to the weight- and volume-carrying capabilities in the delivery vehicle. Explosives are measured in relation to tonnes of trinitrotoluene (TNT). By far the most potent molecular explosives such, as Composition 4 (i.e. C-4), are approximately one third stronger than TNT, whereas a fuel and fertilizer bomb – including was utilized in Oklahoma City – is much less powerful than TNT. Reasonable approximations can be made about how much explosive power can be delivered by 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 varieties 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 often made 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 as purely aesthetic installations and substantial visual deterrence and direction, but provide only minimal impact resistance.
Bollards made to protect against impact are usually a part of concrete several feet deep, if site conditions permit. Engineering from the mounting depends on 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 really desirable or possible (e.g. an urban location with a basement or subway under the pavement), stainless bollards made out of shallow-depth installation systems are for sale to both individual posts and groups of bollards. In general, the shallower the mounting, the broader it must 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 with all the pavement. The mating bollard can be manually lifted out of the mount to permit access. This etxxdy is meant for locations in which the change of access is occasionally needed. It can add a locking mechanism, either exposed or concealed, to stop unauthorized removal. Both plain and decorative bollards are available for this kind of application. Most removable bollards usually are not designed for high-impact resistance and they are not often found in anti-ram applications.
Retractable bollards telescope down below pavement level, and might 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 quite often incorporate a dedicated backup power installation therefore the bollard remains functional during emergencies. Retractable systems are usually unornamented.
Bollards are as ubiquitous as they are overlooked. They talk to the requirement for defining space, one of 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. The range of available options is vast when it comes to both visual style and performance properties. For security applications, a design professional with security expertise ought to be included in the planning team.