The most common bollard applications are traffic direction and control, in addition to security and safety. The initial function is achieved through the visual presence of the bollards, and to some degree by impact resistance, although, in these applications visual deterrence is the primary function. Safety and security applications depend upon higher amounts of impact resistance. The key distinction between both is safety designs are concerned with stopping accidental breach of the defined space, whereas security is all about stopping intentional ramming.
Closely spaced lines of bollards can form a traffic filter, separating motor vehicles from pedestrians and bicycles. Placing the posts with 1 m (3 ft) of clearance between the two, for example, allows easy passage for humans and human-powered vehicles – including wheelchairs or shopping carts – but prevents the passage of cars. Such installations are frequently seen before the car park entrance to some store, as well as at the mouths of streets transformed into outdoor malls or ‘walk streets’. In designing bollard installations for any site, care should be come to avoid locating them where they will likely become a navigational hazard to authorized vehicles or cyclists.
Some applications for traffic guidance depend on the cooperation of drivers and pedestrians and you should not require impact resistance. A collection of bollards linked by a chain presents a visual cue to not cross the boundary, though it could be easy enough for a pedestrian to visit over or under the chain should they choose. Bollards designed to direct traffic are sometimes designed to fold, deflect, or break away on impact.
Adding greater collision resistance allows a bollard to enforce traffic restrictions instead of merely suggesting them. Plain pipe bollards are usually placed in the corners of buildings, or flanking lamp-posts, public phones, fire hydrants, gas pipes along with other installations that should be protected against accidental contact. A steel bollards on the edge of a roadway prevents cars from over-running sidewalks and harming pedestrians. Bell-shaped bollards can actually redirect an automobile back to the roadway when its wheels hit the bollard’s sloped sides.
These are employed where U-turns and tight-radius turns are frequent. This kind of usage is particularly common at corners where vehicle drivers often misestimate turns, and pedestrians are especially near to the roadbed waiting to cross. In some cities, automatically retractable impact-resistant bollards are installed to regulate the flow of traffic into an intersection. Internet videos of ‘bollard runners’ graphically demonstrate the effectiveness of even a low post at stopping cars.
Security Bollards and Post Covers
The aftermaths from the 1995 Oklahoma City bombing and also the September 11, 2001, attacks saw a sharp surge in installing bollards for security purposes. Anti-ram installations include not only posts, but other objects designed to resist impact without presenting the appearance of a protective barrier, including large planters or benches that conceal bollards. When the design threat is decided, the resistance required to stop it may be calculated. (See ‘Security Design Concepts’ – below). Specification of anti-ram perimeter takes into account the mass as well as the speed of your approaching attack vehicle, using the latter being considered the greater significant.
According to Weidlinger Associates principal, Peter DiMaggio – a professional in security design – careful assessment of the surrounding website is required. “Street and site architecture determines the maximum possible approach speed,” he stated. “If you can find no strategies to your building using a long run-up, an attack vehicle cannot build up high speed, and the resistance in the anti-ram barriers may be adjusted accordingly.”
Anti-ram resistance is commonly measured using a standard developed by the Department of State, called the K-rating. K-4, K-8 and K-12 each make reference to the opportunity to stop a truck of any specific weight and speed and prevent penetration in the payload greater 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 actually anchored and also the substrate it’s anchored into.
Videos of bollard crash tests are featured on several manufacturer’s Websites. The truck impacts two or three bollards at high-speed, and the front of the vehicle often crumples, wrapping completely round the centermost post. Part 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 and their footings are occasionally lifted several feet upward. In all successful tests, the payload on the back in the truck fails to penetrate more than 1 meter past the line 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 even with a 102-mm (4-in.) pipe, depending on the engineering of their foundation. It is usually filled with concrete to increase stiffness, although unfilled pipe with plate stiffeners inside could possibly produce better resistance inside 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 might be functionally sufficient, if properly mounted. Undecorated pipe-type bollards can also be specially manufactured.
The largest disadvantage of a plain pipe is aesthetics. A bit of painted pipe fails to truly blend into – significantly less enhance – most architectural schemes. However, this is often overcome by way of a decorative bollard cover. Many standalone bollards that do not have impact-resistance of their own are designed with alternative mounting ability to slip over standard pipe sizes, forming an attractive and architecturally appropriate impact-resistance system. These decorative covers may also be offered 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 element in protecting against explosions will be the distance in between the detonation and also the target. The force of the blast shockwave diminishes being a function of the square from the distance. The more distance that may be placed involving the detonation and also the protected structure – referred to as 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 first step in the overall style of blast resistance.
Standoff is valuable architecturally since it allows a building to be protected with out to look like a bunker. Additionally, it has economic impact, as it is frequently less costly to create standoff rather than to 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 near to the target by way of a vehicle.
Any security design depends upon a quote of the dimensions of threat to get resisted – the ‘design threat.’ The force of the explosion that may be expected is directly linked to the load- 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 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 produced about how much explosive power can be delivered by way of a person carrying a backpack, a passenger vehicle, a pickup truck, a flatbed truck, etc. based upon its weight-and volume-carrying capacity.
There are three basic varieties 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 frequently made with their very 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 as purely aesthetic installations and substantial visual deterrence and direction, but provide only minimal impact resistance.
Bollards designed to protect against impact are often baked into concrete several feet deep, if site conditions permit. Engineering from 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 over a wider area. For sites where deep excavation is not desirable or possible (e.g. an urban location using a basement or subway under the pavement), bollards made with shallow-depth installation systems are for sale to both individual posts and groups of bollards. Generally speaking, 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, while the sleeve’s top is flush with the pavement. The mating bollard can be manually lifted out of the mount to enable access. This system is meant 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 sort of application. Most removable bollards zuhjvq not intended for high-impact resistance and are not often used 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 quite often add a dedicated backup power installation 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, one of many basic tasks of the built environment. Decorative bollards and bollard covers give you a versatile solution for bringing pleasing form to a variety of functions. The range of available options is vast in terms of both visual style and performance properties. For security applications, a design professional with security expertise needs to be contained in the planning team.