Security Bollards and Post Covers
The aftermaths of the 1995 Oklahoma City bombing as well as the September 11, 2001, attacks saw a sharp increase in the installation of bollards for security needs. Anti-ram installations include not only posts, but other objects designed to resist impact without presenting the look of a protective barrier, like large planters or benches that metal safety bollards. Once the design threat is established the resistance required to stop it may be calculated. (See ‘Security Design Concepts’ – below). Specification of anti-ram perimeter takes into account 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 website is required. “Street and site architecture determines the highest possible approach speed,” he said. “If there are no approaches to the building with a long haul-up, an attack vehicle cannot build up high-speed, and the resistance in the anti-ram barriers can be adjusted accordingly.”
Anti-ram resistance is normally measured using a standard designed by the Department of State, known as the K-rating. K-4, K-8 and K-12 each make reference to the cabability to stop a truck of a specific weight and speed preventing penetration from the payload greater than 1 m (3 ft) past the anti-ram barrier. Resistance depends not merely on the size and strength of the bollard itself, but additionally on the way it really is anchored and the substrate it’s anchored into.
Videos of bollard crash tests are featured on numerous 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. Area of the cab may disappear 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 all successful tests, the payload on the back in the truck does not penetrate a lot more than 1 meter beyond the collection of bollards, thus satisfying the conventional.
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 a 102-mm (4-in.) pipe, depending on the engineering of its foundation. It is usually filled with concrete to boost stiffness, although unfilled pipe with plate stiffeners inside could possibly produce better resistance within the same diameter pipe. Without any form of internal stiffening, the pipe’s wall-thickness has to be significantly greater. For fixed-type security bollards, simple pipe bollards might be functionally sufficient, if properly mounted. Undecorated pipe-type bollards can also be specially manufactured.
The greatest downside of a plain pipe is aesthetics. Some painted pipe does not 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 which do not have impact-resistance that belongs to them are made with alternative mounting capability to slip over standard pipe sizes, forming an attractive and architecturally appropriate impact-resistance system. These decorative covers may also be accessible 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 is the distance between the detonation and the target. The force of the blast shockwave diminishes as a function of the square in the distance. The better distance that may be placed between the detonation and also the protected structure – known as standoff distance – the higher the threat resistance or, conversely, the less blast resistance needs to be built into the dwelling. Therefore, development of secure perimeter is step one in the overall design of blast resistance.
Standoff is valuable architecturally since it allows a building to be protected with out to resemble a bunker. It also has economic impact, as it is frequently less expensive to generate standoff rather than bomb-proof the dwelling itself. Security bollards and similar anti-ram installations are created and positioned to create standoff by thwarting the delivery of explosives near the target by way of a vehicle.
Any security design depends on an estimate of how big threat to be resisted – the ‘design threat.’ The force of the explosion that can be expected is directly linked to the load- and volume-carrying capabilities in 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 stronger than TNT, whereas a fuel and fertilizer bomb – like was utilized in Oklahoma City – is much less powerful than TNT. Reasonable approximations can be made about how exactly much explosive power could 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 may be mounted into existing concrete, or installed in new foundations. Manufactured bollards are usually made with their own 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 for purely aesthetic installations and substantial visual deterrence and direction, but provide only minimal impact resistance.
Bollards made to control impact are usually a part of concrete several feet deep, if site conditions permit. Engineering in the mounting depends on design threat, soil conditions and other site-specific factors. Strip footings that mount several bollards provide 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 beneath the pavement), stainless bollards made out of shallow-depth installation systems are available for both individual posts and teams of bollards. In general, the shallower the mounting, the broader it should be to resist 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 could be manually lifted out from the mount to allow access. This etxxdy is meant for locations where change of access is occasionally needed. It could add a locking mechanism, either exposed or concealed, to prevent unauthorized removal. Both plain and decorative bollards are accessible for this type of application. Most removable bollards usually are 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 ease and speed deployment. Automatic systems may be electric or hydraulic and sometimes include a dedicated backup power installation and so the bollard remains functional during emergencies. Retractable systems are usually unornamented.
Bollards are as ubiquitous because they are overlooked. They speak to the need for defining space, one of many basic tasks from the built environment. Decorative bollards and bollard covers offer a versatile solution for bringing pleasing form to a variety of functions. All the different available choices is vast with regards to both visual style and satisfaction properties. For security applications, a design professional with security expertise needs to be included in the planning team.