The most frequent bollard applications are traffic direction and control, together with safety and security. The very first function is achieved through the visual presence of the bollards, and to some degree by impact resistance, although, in these applications visual deterrence is the primary function. Security and safety applications depend upon higher amounts of impact resistance. The key distinction between the two 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, as an 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 while watching parking area entrance to some store, as well as at the mouths of streets changed into outdoor malls or ‘walk streets’. In designing bollard installations for a site, care has to be delivered to avoid locating them where they will 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 line of bollards linked by way of a chain presents a visual cue not to cross the boundary, although it might be easy enough to get a pedestrian to go over or underneath the chain when they choose. Bollards designed to direct traffic are sometimes made 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 at the corners of buildings, or flanking lamp-posts, public phones, fire hydrants, gas pipes as well as other installations that ought to be shielded from accidental contact. A removable bollards for sale in the side of a roadway prevents cars from over-running sidewalks and harming pedestrians. Bell-shaped bollards can certainly redirect a vehicle back on 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 sort of usage is extremely common at corners where vehicle drivers often misestimate turns, and pedestrians are specifically near to the roadbed waiting to cross. In some 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 potency of a low post at stopping cars.
Security Bollards and Post Covers
The aftermaths from 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 merely posts, but other objects made to resist impact without presenting the look of a protective barrier, such as large planters or benches that conceal bollards. When the design threat is set, the resistance required 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 an approaching attack vehicle, using the latter being considered the greater significant.
Based on Weidlinger Associates principal, Peter DiMaggio – a professional in security design – careful assessment in the surrounding site is required. “Street and site architecture determines the highest possible approach speed,” he explained. “If you will find no approaches to the property with a long run-up, an attack vehicle cannot build up high-speed, and the resistance from the anti-ram barriers may be adjusted accordingly.”
Anti-ram resistance is normally measured employing a standard created by the Department of State, called 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 and prevent penetration in the payload more than 1 m (3 ft) past the anti-ram barrier. Resistance depends not merely on the size and strength in the bollard itself, but in addition on the way it is anchored and the substrate it’s anchored into.
Videos of bollard crash tests are featured on several manufacturer’s Internet sites. The truck impacts two or three bollards at high speed, and the front from the vehicle often crumples, wrapping completely around the centermost post. Portion of the cab may disappear the truck, the front 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 all successful tests, the payload on the back from the truck fails to penetrate more than 1 meter past the collection of bollards, thus satisfying the typical.
The most basic 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 despite having a 102-mm (4-in.) pipe, depending on the engineering of the foundation. It is usually loaded with concrete to improve stiffness, although unfilled pipe with plate stiffeners inside might actually produce better resistance inside the same diameter pipe. Without any type 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 can also be specially manufactured.
The greatest downside of a plain pipe is aesthetics. Some painted pipe does not truly blend into – significantly 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 very 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
A lot 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 and the target. The force of the blast shockwave diminishes being a purpose of the square in the distance. The better distance that may be placed in between the detonation as well as the protected structure – known as standoff distance – the higher the threat resistance or, conversely, the less blast resistance needs to be built into the structure. Therefore, creation of secure perimeter is the first step inside the overall design of blast resistance.
Standoff is valuable architecturally because it allows a building to be protected without having to resemble a bunker. It also has economic impact, since it is frequently cheaper to create standoff rather than to bomb-proof the dwelling itself. Security bollards and similar anti-ram installations are made and positioned to produce standoff by thwarting the delivery of explosives near to the target by way of a vehicle.
Any security design depends on a quote of how big threat to get resisted – the ‘design threat.’ The force of the explosion which can be expected is directly associated with the body weight- and volume-carrying capabilities of 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 another more robust than TNT, whereas a fuel and fertilizer bomb – such as was used in Oklahoma City – is considerably less powerful than TNT. Reasonable approximations can be produced about how exactly much explosive power can be delivered by way of a person carrying a backpack, a passenger vehicle, a pickup truck, a flatbed truck, etc. according to its weight-and volume-carrying capacity.
You will find three basic kinds of bollard mountings: fixed, removable, and operable (retractable or fold-down). Fixed bollards could be mounted into existing concrete, or set up in new foundations. Manufactured bollards are frequently 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 designed to control impact are generally embedded in concrete several feet deep, if site conditions permit. Engineering of the mounting is dependent upon design threat, soil conditions along with 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 using a basement or subway underneath 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 should 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 using the pavement. The mating bollard may be manually lifted out from the mount to allow access. This system is meant for locations where the change of access is occasionally needed. It can add a locking mechanism, either exposed or concealed, to stop unauthorized removal. Both plain and decorative bollards are for sale to this sort of application. Most removable bollards zuhjvq not created for high-impact resistance and are usually not found 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 relieve and speed deployment. Automatic systems might 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 speak with the requirement for defining space, one of the basic tasks of the built environment. Decorative bollards and bollard covers offer a versatile solution for bringing pleasing form to a number of functions. The plethora of options is vast when it comes to both visual style and satisfaction properties. For security applications, a design professional with security expertise needs to be contained in the planning team.