The most common bollard applications are traffic direction and control, together with security and safety. The first function is achieved by the visual presence of the bollards, and to some degree by impact resistance, although, in these applications visual deterrence is the primary function. Security and safety applications rely on higher degrees of impact resistance. The major difference between the two is safety designs are concerned with stopping accidental breach of a 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 them, for instance, allows easy passage for humans and human-powered vehicles – such as wheelchairs or shopping carts – but prevents the passage of cars. Such installations tend to be seen before the parking area entrance to a store, and at the mouths of streets transformed into outdoor malls or ‘walk streets’. In designing bollard installations to get a site, care must be taken to avoid locating them where they will likely turn into a navigational hazard to authorized vehicles or cyclists.
Some applications for traffic guidance depend on the cooperation of drivers and pedestrians and do not require impact resistance. A type of bollards linked by way of a chain presents a visual cue to not cross the boundary, though it could be easy enough to get a pedestrian to visit over or under the chain when they choose. Bollards designed to direct traffic are occasionally created to fold, deflect, or break away on impact.
Adding greater collision resistance allows a bollard to enforce traffic restrictions rather than merely suggesting them. Plain pipe bollards are often placed on the corners of buildings, or flanking lamp-posts, public phones, fire hydrants, gas pipes and other installations that ought to be protected from accidental contact. A plastic safety bollards in the edge of a roadway prevents cars from over-running sidewalks and harming pedestrians. Bell-shaped bollards can certainly redirect a vehicle back to the roadway when its wheels hit the bollard’s sloped sides.
They are employed where U-turns and tight-radius turns are frequent. This sort of usage is particularly common at corners where vehicle drivers often misestimate turns, and pedestrians are specifically near 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 a low post at stopping cars.
Security Bollards and Post Covers
The aftermaths in the 1995 Oklahoma City bombing as well as the September 11, 2001, attacks saw a sharp increase in setting up bollards for security purposes. Anti-ram installations include not only posts, but other objects designed to resist impact without presenting the look of a protective barrier, including large planters or benches that conceal bollards. Once 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 both the mass and also 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 from the surrounding website is required. “Street and site architecture determines the maximum possible approach speed,” he stated. “If there are no approaches to the building with a long term-up, an attack vehicle cannot develop high-speed, and the resistance of the anti-ram barriers could be adjusted accordingly.”
Anti-ram resistance is often measured using a standard created 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 the specific weight and speed preventing penetration of the payload greater than 1 m (3 ft) beyond the anti-ram barrier. Resistance depends not only on the size and strength of the bollard itself, but also on the way it is anchored and also the substrate it’s anchored into.
Videos of bollard crash tests are featured on several manufacturer’s Internet sites. The truck impacts two or three bollards at high-speed, and also the front of the vehicle often crumples, wrapping completely around the centermost post. Portion of the cab may fly off the truck, the front side or rear end could rise several feet within the air, and front or rear axles might detach. The bollards and their footings are occasionally lifted several feet upward. In every successful tests, the payload on the back in the truck fails to penetrate a lot more than 1 meter past the collection of bollards, thus satisfying the conventional.
The simplest 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 despite having a 102-mm (4-in.) pipe, depending on the engineering of their foundation. It is often loaded with concrete to improve stiffness, although unfilled pipe with plate stiffeners inside might actually produce better resistance inside the same diameter pipe. Without any type 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 greatest drawback to a plain pipe is aesthetics. A bit of painted pipe fails to truly blend into – a lot 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 made with alternative mounting capacity to slip over standard pipe sizes, forming an attractive 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
A lot of modern security design focuses on the threat of bomb attacks. The most significant element in protecting against explosions will be the distance involving the detonation and also the target. The force of the blast shockwave diminishes being a purpose of the square in the distance. The more distance that may be placed in between the detonation and 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 because it allows a building to be protected with out to resemble a bunker. Additionally, it has economic impact, because it is frequently less costly to create standoff rather than bomb-proof the structure itself. Security bollards and similar anti-ram installations are made and positioned to generate standoff by thwarting the delivery of explosives close to the target with a vehicle.
Any security design depends upon a bid of the dimensions of threat to become resisted – the ‘design threat.’ The force in the explosion that can be expected is directly associated with the body 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 a third more powerful 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 regarding how much explosive power could 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 can find three basic types 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 designed with their particular mounting systems. Standalone mountings may 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 designed to control impact are generally a part of concrete several feet deep, if site conditions permit. Engineering from the mounting is dependent upon design threat, soil conditions and 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 desirable or possible (e.g. an urban location with a basement or subway under the pavement), 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 must 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 can be manually lifted out from the mount to enable access. This system is supposed for locations in which the change of access is occasionally needed. It can incorporate a locking mechanism, either exposed or concealed, to avoid unauthorized removal. Both plain and decorative bollards are available for this sort of application. Most removable bollards zuhjvq not created for high-impact resistance and they are usually not 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 might be electric or hydraulic and sometimes add a dedicated backup power installation and so the bollard remains functional during emergencies. Retractable systems are generally unornamented.
Bollards are as ubiquitous as they are overlooked. They speak with the necessity for defining space, among the basic tasks of the built environment. Decorative bollards and bollard covers provide a versatile solution for bringing pleasing form to many different 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 included in the planning team.