The most common bollard applications are traffic direction and control, together with 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 depend upon higher levels of impact resistance. The major difference between both is safety designs are concerned with stopping accidental breach of the 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 the two, 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 are frequently seen in front of the car park entrance to some store, and also at the mouths of streets changed into outdoor malls or ‘walk streets’. In designing bollard installations to get a site, care should be taken 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 you should not require impact resistance. A type of bollards linked with a chain presents a visual cue to not cross the boundary, although it could be easy enough to get a pedestrian to visit over or under the chain when they choose. Bollards made 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 frequently placed at the corners of buildings, or flanking lamp-posts, public phones, fire hydrants, gas pipes and other installations that ought to be protected against accidental contact. A removable security bollards at the fringe of a roadway prevents cars from over-running sidewalks and harming pedestrians. Bell-shaped bollards can certainly redirect a vehicle 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 particularly common at corners where vehicle drivers often misestimate turns, and pedestrians are particularly close to the roadbed waiting to cross. In certain 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 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. After the design threat is determined, the resistance needed to stop it could be calculated. (See ‘Security Design Concepts’ – below). Specification of anti-ram perimeter takes into account both mass and also the speed of your approaching attack vehicle, with the latter being considered the more significant.
In accordance with Weidlinger Associates principal, Peter DiMaggio – a specialist in security design – careful assessment of the surrounding website is required. “Street and site architecture determines the utmost possible approach speed,” he said. “If you will find no approaches to the property using a long run-up, an attack vehicle cannot build-up high-speed, as well as the resistance of the anti-ram barriers could be adjusted accordingly.”
Anti-ram resistance is normally measured utilizing a standard created by the Department of State, known as the K-rating. K-4, K-8 and K-12 each refer to the opportunity 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 just on the size and strength of the bollard itself, but in addition on the way it is anchored and also the substrate it’s anchored into.
Videos of bollard crash tests are featured on numerous manufacturer’s Web sites. The truck impacts several bollards at high-speed, and the front of the vehicle often crumples, wrapping completely across the centermost post. Portion of the cab may fly off the truck, the front 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 most successful tests, the payload on the back in the truck does not penetrate more than 1 meter past the collection of bollards, thus satisfying the standard.
The easiest 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 even with a 102-mm (4-in.) pipe, depending on the engineering of its foundation. It is often loaded with concrete to boost stiffness, although unfilled pipe with plate stiffeners inside might actually produce better resistance within 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 largest disadvantage of a plain pipe is aesthetics. A piece of painted pipe does not truly blend into – much less enhance – most architectural schemes. However, this is often overcome with a decorative bollard cover. Many standalone bollards that do not have impact-resistance of their very own are created with alternative mounting ability to slip over standard pipe sizes, forming an attractive and architecturally appropriate impact-resistance system. These decorative covers can also be offered to enhance specifically created (but non-decorative) pipe-type bollards.
Security Design Concepts
A lot of modern security design focuses on the threat of bomb attacks. The most important element in protecting against explosions is the distance in between the detonation as well as the target. The force from the blast shockwave diminishes as a function of the square of the distance. The better distance that may be placed in between 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 dwelling. Therefore, creation of secure perimeter is step one inside the overall form of blast resistance.
Standoff is valuable architecturally as it allows a building to be protected without needing to resemble a bunker. Additionally, it has economic impact, as it is frequently less expensive to generate standoff rather than bomb-proof the structure itself. Security bollards and similar anti-ram installations are made and positioned to create standoff by thwarting the delivery of explosives close to the target by a vehicle.
Any security design depends upon a quote of the size of threat to be resisted – the ‘design threat.’ The force from the explosion that may be expected is directly related to the body weight- and volume-carrying capabilities in 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 – such as was utilized in Oklahoma City – is considerably less powerful than TNT. Reasonable approximations can be created regarding how much explosive power could be delivered with a person carrying a backpack, a passenger vehicle, a pickup truck, a flatbed truck, etc. based on 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 set up in new foundations. Manufactured bollards are frequently made with their particular 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 as purely aesthetic installations and substantial visual deterrence and direction, but provide only minimal impact resistance.
Bollards made to control impact are generally baked into concrete several feet deep, if site conditions permit. Engineering of the mounting depends upon design threat, soil conditions and 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 with a basement or subway under the pavement), bollards made out of shallow-depth installation systems are available for both individual posts and groups of bollards. Generally speaking, the shallower the mounting, the broader it must be to face up to impact loading.
A removable bollard typically has a permanently installed mount or sleeve below grade, whilst the sleeve’s top is flush with the pavement. The mating bollard could be manually lifted out of the mount to allow access. This system 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 available for this sort of application. Most removable bollards zuhjvq not created for high-impact resistance and therefore are not often utilized in anti-ram applications.
Retractable bollards telescope down below pavement level, and might 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 because they are overlooked. They speak with the need for defining space, one of the 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. All the different available options is vast with regards to both visual style and gratification properties. For security applications, a design professional with security expertise should be within the planning team.