The most typical bollard applications are traffic direction and control, in addition to security and safety. The first function is achieved from the visual presence of the bollards, and to some extent 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 key difference between both is safety designs are concerned with stopping accidental breach of a defined space, whereas security is 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 example, 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 while watching parking area entrance to your store, as well as at the mouths of streets changed into outdoor malls or ‘walk streets’. In designing bollard installations for a site, care must be come to avoid locating them where they are going to be 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 with a chain presents a visual cue to not cross the boundary, even though it could be easy enough to get a pedestrian to go over or under the chain should they choose. Bollards created 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 instead of 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 need to be protected from accidental contact. A buy steel bollards at the side of a roadway prevents cars from over-running sidewalks and harming pedestrians. Bell-shaped bollards can actually redirect a car back onto 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 especially common at corners where vehicle drivers often misestimate turns, and pedestrians are especially close 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 potency of also a low post at stopping cars.
Security Bollards and Post Covers
The aftermaths from the 1995 Oklahoma City bombing as well as the September 11, 2001, attacks saw a sharp rise in installing bollards for security purposes. Anti-ram installations include not just posts, but other objects made to resist impact without presenting the appearance of a protective barrier, like large planters or benches that conceal bollards. When the design threat is determined, the resistance needed to stop it may be calculated. (See ‘Security Design Concepts’ – below). Specification of anti-ram perimeter takes under consideration both the mass and also the speed of your approaching attack vehicle, with the latter being considered the more significant.
According to Weidlinger Associates principal, Peter DiMaggio – a professional in security design – careful assessment of the surrounding site is required. “Street and site architecture determines the utmost possible approach speed,” he stated. “If you can find no strategies to your building using a long haul-up, an attack vehicle cannot develop high-speed, as well as the resistance from the anti-ram barriers may be adjusted accordingly.”
Anti-ram resistance is commonly measured using a standard created by the Department of State, known as the K-rating. K-4, K-8 and K-12 each make reference to the opportunity to stop a truck of the specific weight and speed preventing penetration from the payload a lot more than 1 m (3 ft) beyond the anti-ram barrier. Resistance depends not only on the size and strength in the bollard itself, but in addition on the way it really is anchored as well as the substrate it’s anchored into.
Videos of bollard crash tests are featured on numerous manufacturer’s Internet sites. The truck impacts two or three bollards at high-speed, and also the front in the vehicle often crumples, wrapping completely across the centermost post. Area of the cab may disappear the truck, the top or rear end could rise several feet in the air, and front or rear axles might detach. The bollards as well as their footings are occasionally lifted several feet upward. In most successful tests, the payload on the back from the truck will not penetrate greater than 1 meter beyond the collection of bollards, thus satisfying the standard.
The easiest 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 improve 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 needs to be significantly greater. For fixed-type security bollards, simple pipe bollards could 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 does not truly blend into – a lot less enhance – most architectural schemes. However, this can be overcome by a decorative bollard cover. Many standalone bollards that do not have impact-resistance of their very own are created 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 offered to enhance specially designed (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 between the detonation as well as the target. The force in the blast shockwave diminishes being a function of the square of the distance. The more distance which can be placed between the detonation as well as the protected structure – referred to as standoff distance – the higher the threat resistance or, conversely, the less blast resistance needs to be that are part of the structure. Therefore, development 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 without needing to resemble a bunker. Additionally, it has economic impact, as it is frequently cheaper to produce standoff rather than to bomb-proof the dwelling itself. Security bollards and other anti-ram installations are created and positioned to generate standoff by thwarting the delivery of explosives near to the target by way of a vehicle.
Any security design depends on a bid of how big threat to become resisted – the ‘design threat.’ The force from the explosion that can be expected is directly related to the load- and volume-carrying capabilities of the delivery vehicle. Explosives are measured in relation to tonnes of trinitrotoluene (TNT). 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 used in Oklahoma City – is considerably less powerful than TNT. Reasonable approximations can be created about how much explosive power could be delivered with a person carrying a backpack, a passenger vehicle, a pickup truck, a flatbed truck, etc. according to its weight-and volume-carrying capacity.
There are three basic types 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 frequently created 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 purely aesthetic installations and substantial visual deterrence and direction, but provide only minimal impact resistance.
Bollards made to control impact are generally embedded in concrete several feet deep, if site conditions permit. Engineering in the mounting is dependent upon design threat, soil conditions as well as 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 will not be desirable or possible (e.g. an urban location having a basement or subway beneath the pavement), bollards made with shallow-depth installation systems are available for both individual posts and teams of bollards. In general, the shallower the mounting, the broader it ought to be to face up to 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 can be manually lifted out of the mount to permit access. This technique is supposed for locations in which the change of access is occasionally needed. It may incorporate a locking mechanism, either exposed or concealed, to stop unauthorized removal. Both plain and decorative bollards are available for this type of application. Most removable bollards zuhjvq not created for high-impact resistance and they are usually not utilized 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 could be electric or hydraulic and sometimes include 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, among the basic tasks of the built environment. Decorative bollards and bollard covers provide a versatile solution for bringing pleasing form to a number of functions. The plethora of available choices is vast with regards to both visual style and gratification properties. For security applications, a design professional with security expertise should be included in the planning team.