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 made to resist impact without presenting the look of a protective barrier, including large planters or benches that safety 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 into account both the mass and also the speed of an approaching attack vehicle, with the latter being regarded the more significant.
According to Weidlinger Associates principal, Peter DiMaggio – an expert in security design – careful assessment in the surrounding website is required. “Street and site architecture will determine the highest possible approach speed,” he said. “If you can find no approaches to your building having a long haul-up, an attack vehicle cannot develop high-speed, and also the resistance in the anti-ram barriers may be adjusted accordingly.”
Anti-ram resistance is normally measured employing a standard developed by the Department of State, called the K-rating. K-4, K-8 and K-12 each make reference to the cabability to stop a truck of any 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 merely on the size and strength of the bollard itself, but additionally on the way it is anchored and the substrate it’s anchored into.
Videos of bollard crash tests are featured on a number of manufacturer’s Web sites. The truck impacts 2 or 3 bollards at high-speed, and the front from the vehicle often crumples, wrapping completely across the centermost post. Part of the cab may fly off 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 in the truck will not penetrate greater than 1 meter beyond the collection of bollards, thus satisfying the typical.
The most basic 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 even with a 102-mm (4-in.) pipe, depending on the engineering of its foundation. It is often loaded with concrete to increase stiffness, although unfilled pipe with plate stiffeners inside may actually produce better resistance within 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 could be functionally sufficient, if properly mounted. Undecorated pipe-type bollards are also specially manufactured.
The largest drawback to a plain pipe is aesthetics. A bit of painted pipe will not truly blend into – much less enhance – most architectural schemes. However, this could be overcome with a decorative bollard cover. Many standalone bollards that do not have impact-resistance that belongs to them are made with alternative mounting ability to slip over standard pipe sizes, forming a stylish and architecturally appropriate impact-resistance system. These decorative covers may also be available to enhance specially engineered (but non-decorative) pipe-type bollards.
Security Design Concepts
Much of modern security design focuses on the threat of bomb attacks. The most significant element in protecting against explosions is the distance in between the detonation as well as the target. The force of the blast shockwave diminishes as being a function of the square from the distance. The more distance that may be placed involving the detonation as well as the protected structure – known 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 inside the overall style of blast resistance.
Standoff is valuable architecturally because it allows a building to become protected without having to resemble a bunker. Additionally, it has economic impact, since it is frequently less costly to produce standoff rather than bomb-proof the structure itself. Security bollards and other anti-ram installations are made and positioned to create standoff by thwarting the delivery of explosives close to the target by way of 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 linked to the body weight- and volume-carrying capabilities from the delivery vehicle. Explosives are measured with regards to tonnes of trinitrotoluene (TNT). Probably 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 – such as was utilized in Oklahoma City – is considerably less powerful than TNT. Reasonable approximations can be produced about how much explosive power can be delivered with a person carrying a backpack, a passenger vehicle, a pickup truck, a flatbed truck, etc. based upon the weight-and volume-carrying capacity.
You can find three basic types of bollard mountings: fixed, removable, and operable (retractable or fold-down). Fixed bollards can be mounted into existing concrete, or installed in new foundations. Manufactured bollards are frequently created with their very 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 purely aesthetic installations and substantial visual deterrence and direction, but provide only minimal impact resistance.
Bollards made to control impact are usually baked into concrete several feet deep, if site conditions permit. Engineering of the mounting depends on design threat, soil conditions along with other site-specific factors. Strip footings that mount several bollards provide 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 underneath the pavement), steel bollard covers created using shallow-depth installation systems are available for both individual posts and groups of bollards. Generally speaking, the shallower the mounting, the broader it ought to be to resist impact loading.
A removable bollard typically includes a permanently installed mount or sleeve below grade, while the sleeve’s top is flush with the pavement. The mating bollard could be manually lifted out from the mount to permit access. This etxxdy is meant for locations where the change of access is occasionally needed. It may incorporate a locking mechanism, either exposed or concealed, to avoid unauthorized removal. Both plain and decorative bollards are for sale to this type of application. Most removable bollards are not intended for high-impact resistance and therefore 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 may be electric or hydraulic and sometimes add a dedicated backup power installation so the bollard remains functional during emergencies. Retractable systems are usually unornamented.
Bollards are as ubiquitous because they are overlooked. They talk to the requirement for defining space, among the basic tasks of the built environment. Decorative bollards and bollard covers offer a versatile solution for bringing pleasing form to a variety of functions. The plethora of options is vast with regards to both visual style and satisfaction properties. For security applications, a design professional with security expertise needs to be contained in the planning team.