The most frequent bollard applications are traffic direction and control, along with safety and security. The initial 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. Safety and security applications depend on higher amounts of impact resistance. The main distinction 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, 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 parking area entrance to a store, and also at the mouths of streets changed into outdoor malls or ‘walk streets’. In designing bollard installations for a site, care must be taken 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 never require impact resistance. A collection of bollards linked by way of a chain presents a visual cue never to cross the boundary, though it could be easy enough to get a pedestrian to visit over or beneath the chain if 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 usually placed at the corners of buildings, or flanking lamp-posts, public phones, fire hydrants, gas pipes and other installations that ought to be shielded 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 actually redirect a vehicle 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 especially 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 potency of even a low post at stopping cars.
Security Bollards and Post Covers
The aftermaths of the 1995 Oklahoma City bombing as well as the September 11, 2001, attacks saw a sharp rise in setting up bollards for security purposes. Anti-ram installations include not just posts, but other objects created to resist impact without presenting the look of a protective barrier, including large planters or benches that conceal bollards. When the design threat is decided, the resistance required to stop it can be calculated. (See ‘Security Design Concepts’ – below). Specification of anti-ram perimeter takes into account both mass and the speed of an approaching attack vehicle, using the latter being considered the better significant.
According to Weidlinger Associates principal, Peter DiMaggio – a specialist in security design – careful assessment of the surrounding website is required. “Street and site architecture determines the maximum possible approach speed,” he said. “If you can find no approaches to the property using a long run-up, an attack vehicle cannot build-up high speed, as well as the resistance in the anti-ram barriers may be adjusted accordingly.”
Anti-ram resistance is commonly measured utilizing a standard created by the Department of State, referred to as K-rating. K-4, K-8 and K-12 each refer to the cabability to stop a truck of the specific weight and speed and prevent penetration in the payload more than 1 m (3 ft) past the anti-ram barrier. Resistance depends not only on the size and strength from the bollard itself, but also on the way it is anchored as well as the substrate it’s anchored into.
Videos of bollard crash tests are featured on a number of 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 round the centermost post. Part of the cab may disappear 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 sometimes lifted several feet upward. In most successful tests, the payload on the back from the truck does not penetrate a lot more than 1 meter beyond the line of bollards, thus satisfying the typical.
The most basic 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 despite a 102-mm (4-in.) pipe, depending on the engineering of the foundation. It is usually filled with concrete to boost stiffness, although unfilled pipe with plate stiffeners inside may actually produce better resistance in the same diameter pipe. Without any type of internal stiffening, the pipe’s wall-thickness has to be significantly greater. For fixed-type security bollards, simple pipe bollards may 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 – 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 that belongs to them are made with alternative mounting capacity to slip over standard pipe sizes, forming a beautiful 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
Most of modern security design focuses on the threat of bomb attacks. The most significant element in protecting against explosions is definitely the distance in between the detonation as well as the target. The force of the blast shockwave diminishes as being a function of the square of the distance. The more distance which can be placed between the detonation and also the protected structure – called standoff distance – the higher the threat resistance or, conversely, the less blast resistance must be built into the structure. Therefore, introduction of secure perimeter is the first step in the overall form of blast resistance.
Standoff is valuable architecturally since it allows a building to get protected without needing to look like a bunker. Additionally, it has economic impact, since it is frequently less costly to produce standoff rather than bomb-proof the structure 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 a vehicle.
Any security design is dependent upon an estimate of the size of threat to be resisted – the ‘design threat.’ The force in the explosion which can be expected is directly linked to the load- and volume-carrying capabilities of the delivery vehicle. Explosives are measured in relation to tonnes of trinitrotoluene (TNT). Probably the most potent molecular explosives such, as Composition 4 (i.e. C-4), are approximately another more robust than TNT, whereas a fuel and fertilizer bomb – including was utilized in Oklahoma City – is much less powerful than TNT. Reasonable approximations can be produced about how exactly much explosive power can be delivered with a person carrying a backpack, a passenger vehicle, a pickup truck, a flatbed truck, etc. based upon the weight-and volume-carrying capacity.
You can find three basic kinds of bollard mountings: fixed, removable, and operable (retractable or fold-down). Fixed bollards can be mounted into existing concrete, or installed in new foundations. Manufactured bollards are often created with their own 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 for 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 in the mounting is dependent upon design threat, soil conditions and other site-specific factors. Strip footings that mount several bollards provide 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 underneath 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 should be to face up to impact loading.
A removable bollard typically has a permanently installed mount or sleeve below grade, while the sleeve’s top is flush using the pavement. The mating bollard may be manually lifted out from the mount to enable access. This method is supposed for locations where the change of access is occasionally needed. It could include a locking mechanism, either exposed or concealed, to avoid unauthorized removal. Both plain and decorative bollards are available for this kind of application. Most removable bollards zuhjvq not created for high-impact resistance and they are not often 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 relieve and speed deployment. Automatic systems could be electric or hydraulic and quite often add a dedicated backup power installation and so the bollard remains functional during emergencies. Retractable systems tend to be unornamented.
Bollards are as ubiquitous as they are overlooked. They speak with the necessity 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. The range of options is vast in terms of both visual style and gratification properties. For security applications, a design professional with security expertise should be included in the planning team.