The most frequent bollard applications are traffic direction and control, in addition to safety and security. The first function is achieved by the visual presence of the bollards, and at some level by impact resistance, although, within these applications visual deterrence is the primary function. Safety and security applications rely on higher amounts of impact resistance. The major distinction 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 them, for example, allows easy passage for humans and human-powered vehicles – including wheelchairs or shopping carts – but prevents the passage of cars. Such installations are frequently seen in front of the parking lot 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 delivered to avoid locating them where they are going to become 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 by a chain presents a visual cue to not cross the boundary, though it may be easy enough for any pedestrian to visit over or under the chain should they choose. Bollards designed to direct traffic are sometimes 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 usually placed in the corners of buildings, or flanking lamp-posts, public phones, fire hydrants, gas pipes as well as other installations that need to be protected against accidental contact. A metal bollards for sale at the edge of a roadway prevents cars from over-running sidewalks and harming pedestrians. Bell-shaped bollards can in fact 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 sort 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 certain cities, automatically retractable impact-resistant bollards are installed to control 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 and also the September 11, 2001, attacks saw a sharp rise in the installation of 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, such as large planters or benches that conceal bollards. After the design threat is decided, the resistance necessary to stop it could be calculated. (See ‘Security Design Concepts’ – below). Specification of anti-ram perimeter takes into account both mass and the speed of the approaching attack vehicle, with all the latter being considered the greater significant.
Based on Weidlinger Associates principal, Peter DiMaggio – a professional in security design – careful assessment from the surrounding website is required. “Street and site architecture will determine the highest possible approach speed,” he said. “If you can find no approaches to the property using a long term-up, an attack vehicle cannot build-up high-speed, and the resistance in the anti-ram barriers may be adjusted accordingly.”
Anti-ram resistance is often measured utilizing a standard developed by the Department of State, referred to as K-rating. K-4, K-8 and K-12 each refer to the opportunity to stop a truck of any 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 in the bollard itself, but additionally on the way it really is anchored and the substrate it’s anchored into.
Videos of bollard crash tests are featured on a number of manufacturer’s Websites. The truck impacts two or three bollards at high-speed, as well as the front of the vehicle often crumples, wrapping completely across the centermost post. Part 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 along with their footings are occasionally lifted several feet upward. In every successful tests, the payload on the back from the truck does not penetrate greater than 1 meter beyond the collection of bollards, thus satisfying the standard.
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 even with a 102-mm (4-in.) pipe, depending on the engineering of the foundation. It is usually full of concrete to increase stiffness, although unfilled pipe with plate stiffeners inside might actually produce better resistance in 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 disadvantage of a plain pipe is aesthetics. A bit of painted pipe does not truly blend into – much less enhance – most architectural schemes. However, this could be overcome by a decorative bollard cover. Many standalone bollards that do not have impact-resistance of their own are created with alternative mounting capability to slip over standard pipe sizes, forming a stylish 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
Most of modern security design focuses on the threat of bomb attacks. The most significant aspect in protecting against explosions is the distance in between the detonation and the target. The force of the blast shockwave diminishes as a purpose of the square of the distance. The better distance that may be placed in 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 built into the structure. Therefore, development of secure perimeter is the first step within 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, 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 generate standoff by thwarting the delivery of explosives near to the target by a vehicle.
Any security design depends on an estimate of the size of threat to get resisted – the ‘design threat.’ The force of the explosion that may be expected is directly related to the weight- and volume-carrying capabilities from the delivery vehicle. Explosives are measured with regards to tonnes of trinitrotoluene (TNT). The most potent molecular explosives such, as Composition 4 (i.e. C-4), are approximately one third more robust than TNT, whereas a fuel and fertilizer bomb – like was utilized in Oklahoma City – is considerably 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 kinds 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 usually created with their 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 usually embedded in concrete several feet deep, if site conditions permit. Engineering in 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 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 underneath 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 must be to resist impact loading.
A removable bollard typically has a permanently installed mount or sleeve below grade, as the sleeve’s top is flush with the pavement. The mating bollard could be manually lifted out from the mount to enable access. This method is intended for locations where change of access is occasionally needed. It could incorporate a locking mechanism, either exposed or concealed, to prevent unauthorized removal. Both plain and decorative bollards are accessible for this sort of application. Most removable bollards zuhjvq not designed 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 may be electric or hydraulic and quite often incorporate a dedicated backup power installation so the bollard remains functional during emergencies. Retractable systems are usually unornamented.
Bollards are as ubiquitous because they are overlooked. They speak to 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 available options is vast with regards to both visual style and gratification properties. For security applications, a design professional with security expertise needs to be contained in the planning team.