The most common bollard applications are traffic direction and control, together with security and safety. The very 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. Safety and security applications depend upon higher degrees of impact resistance. The major distinction between the 2 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, as an example, allows easy passage for humans and human-powered vehicles – like wheelchairs or shopping carts – but prevents the passage of cars. Such installations are often seen before the car park entrance to your store, and also at the mouths of streets converted to outdoor malls or ‘walk streets’. In designing bollard installations for any site, care should be delivered to avoid locating them where they will 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 line of bollards linked by way of a chain presents a visual cue to not cross the boundary, though it might be easy enough for a pedestrian to go over or underneath the chain when they choose. Bollards created to direct traffic are often designed 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 in the corners of buildings, or flanking lamp-posts, public phones, fire hydrants, gas pipes and other installations that should be protected against accidental contact. A buy steel bollards in the fringe 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 may be employed where U-turns and tight-radius turns are frequent. This type of usage is particularly common at corners where vehicle drivers often misestimate turns, and pedestrians are particularly near to the roadbed waiting to cross. In some cities, automatically retractable impact-resistant bollards are installed to manage the flow of traffic into an intersection. Internet videos of ‘bollard runners’ graphically demonstrate the strength of even a low post at stopping cars.
Security Bollards and Post Covers
The aftermaths from the 1995 Oklahoma City bombing and the September 11, 2001, attacks saw a sharp rise in setting up bollards for security purposes. Anti-ram installations include not only posts, but other objects made 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 could be calculated. (See ‘Security Design Concepts’ – below). Specification of anti-ram perimeter takes under consideration the mass and the speed of an approaching attack vehicle, with the latter being considered the greater significant.
In accordance with Weidlinger Associates principal, Peter DiMaggio – a specialist in security design – careful assessment in the surrounding site is required. “Street and site architecture will determine the highest possible approach speed,” he explained. “If there are no approaches to your building using a long term-up, an attack vehicle cannot build up high speed, and also the resistance of the anti-ram barriers can be adjusted accordingly.”
Anti-ram resistance is commonly measured utilizing a standard created by the Department of State, called the K-rating. K-4, K-8 and K-12 each reference the cabability to stop a truck of the specific weight and speed preventing penetration from the payload 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 actually anchored and the substrate it’s anchored into.
Videos of bollard crash tests are featured on several manufacturer’s Web sites. The truck impacts 2 or 3 bollards at high speed, and also the front from the vehicle often crumples, wrapping completely around the centermost post. Area of the cab may fly off the truck, the front side or rear end could rise several feet inside 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 fails to penetrate a lot more than 1 meter past the collection of bollards, thus satisfying the typical.
The most basic security bollard is a piece 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 full of concrete to improve stiffness, although unfilled pipe with plate stiffeners inside might actually produce better resistance inside the same diameter pipe. Without any kind 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 will also be specially manufactured.
The largest drawback to a plain pipe is aesthetics. A bit of painted pipe will not truly blend into – a lot less enhance – most architectural schemes. However, this can be overcome by way of 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 a stylish and architecturally appropriate impact-resistance system. These decorative covers may also be available 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 significant aspect in protecting against explosions is the distance between the detonation as well as the target. The force in the blast shockwave diminishes as a purpose of the square from the distance. The better distance that may be placed in between the detonation and the protected structure – referred to as standoff distance – the greater the threat resistance or, conversely, the less blast resistance needs to be included in the dwelling. Therefore, introduction of secure perimeter is step one in the overall style of blast resistance.
Standoff is valuable architecturally as it allows a building to get protected without having to resemble a bunker. In addition, it has economic impact, because it is frequently cheaper to create 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 to the target by way of a vehicle.
Any security design depends on a quote of the size of threat to be resisted – the ‘design threat.’ The force of the explosion that may be expected is directly related to the weight- and volume-carrying capabilities of 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 a third more powerful than TNT, whereas a fuel and fertilizer bomb – like was utilized in Oklahoma City – is much less powerful than TNT. Reasonable approximations can be produced about how much explosive power may be delivered by 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 types of bollard mountings: fixed, removable, and operable (retractable or fold-down). Fixed bollards may be mounted into existing concrete, or placed in new foundations. Manufactured bollards are frequently made 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 as purely aesthetic installations and substantial visual deterrence and direction, but provide only minimal impact resistance.
Bollards designed to protect against impact are generally embedded in concrete several feet deep, if site conditions permit. Engineering from the mounting depends on design threat, soil conditions as well as other site-specific factors. Strip footings that mount several bollards have better resistance, spreading the impact load spanning a wider area. For sites where deep excavation is not really desirable or possible (e.g. an urban location with a basement or subway under the pavement), bollards created using shallow-depth installation systems are for sale to both individual posts and groups of bollards. Generally, 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, as the sleeve’s top is flush using the pavement. The mating bollard could be manually lifted from the mount to permit access. This system is meant for locations where change of access is occasionally needed. It could 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 intended for high-impact resistance and they are not often used in anti-ram applications.
Retractable bollards telescope down below pavement level, and may 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 often include a dedicated backup power installation and so the bollard remains functional during emergencies. Retractable systems are usually unornamented.
Bollards are as ubiquitous as they are overlooked. They speak with the necessity for defining space, one of many basic tasks from the built environment. Decorative bollards and bollard covers give you a versatile solution for bringing pleasing form to a variety of functions. All the different options 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.