The most typical bollard applications are traffic direction and control, along 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, within these applications visual deterrence is the primary function. Security and safety applications depend on higher levels of impact resistance. The main difference between the two 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 them, for example, allows easy passage for humans and human-powered vehicles – like wheelchairs or shopping carts – but prevents the passage of cars. Such installations tend to be seen while watching car park entrance to a store, and at the mouths of streets changed into outdoor malls or ‘walk streets’. In designing bollard installations for any site, care has to be taken to avoid locating them where they will be 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 line of bollards linked with a chain presents a visual cue not to cross the boundary, though it could be easy enough for any pedestrian to go over or beneath the chain when they choose. Bollards designed to direct traffic are often made 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 on the corners of buildings, or flanking lamp-posts, public phones, fire hydrants, gas pipes and other installations that should be shielded from accidental contact. A removable bollards for sale on the edge of a roadway prevents cars from over-running sidewalks and harming pedestrians. Bell-shaped bollards can certainly redirect a car 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 extremely common at corners where vehicle drivers often misestimate turns, and pedestrians are particularly near the roadbed waiting to cross. In a few 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 even a low post at stopping cars.
Security Bollards and Post Covers
The aftermaths of 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 designed to resist impact without presenting the look of a protective barrier, including large planters or benches that conceal bollards. When the design threat is set, the resistance needed to stop it can be calculated. (See ‘Security Design Concepts’ – below). Specification of anti-ram perimeter takes under consideration the mass as well as the speed of an approaching attack vehicle, with all the latter being considered the more significant.
According to Weidlinger Associates principal, Peter DiMaggio – a specialist in security design – careful assessment of the surrounding site is required. “Street and site architecture determines the utmost possible approach speed,” he stated. “If you will find no strategies to your building having a long term-up, an attack vehicle cannot build up high-speed, as well as the resistance of the anti-ram barriers may be adjusted accordingly.”
Anti-ram resistance is normally measured utilizing a standard designed 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 any specific weight and speed and prevent penetration from the payload greater than 1 m (3 ft) beyond the anti-ram barrier. Resistance depends not just on the size and strength from the bollard itself, but in addition 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 Internet sites. The truck impacts several bollards at high speed, and also the front from the vehicle often crumples, wrapping completely across the centermost post. Portion 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 sometimes lifted several feet upward. In all successful tests, the payload on the back in the truck fails to penetrate a lot more than 1 meter beyond the collection of bollards, thus satisfying the typical.
The easiest 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 a 102-mm (4-in.) pipe, depending on the engineering of the foundation. It is often full of concrete to increase stiffness, although unfilled pipe with plate stiffeners inside could possibly produce better resistance in 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 can also be specially manufactured.
The biggest 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 of their own are made with alternative mounting capability to slip over standard pipe sizes, forming an attractive and architecturally appropriate impact-resistance system. These decorative covers can also be available to enhance specially engineered (but non-decorative) pipe-type bollards.
Security Design Concepts
Much of modern security design focuses on the threat of bomb attacks. The most important element in protecting against explosions is definitely the distance involving the detonation and the target. The force of the blast shockwave diminishes as being a purpose of the square from the distance. The greater distance that may be placed 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 must be that are part of the structure. Therefore, creation of secure perimeter is the first step within the overall form of blast resistance.
Standoff is valuable architecturally because it allows a building to get protected without needing to look like a bunker. It also has economic impact, as it is frequently less expensive to generate standoff rather than to bomb-proof the structure itself. Security bollards and similar anti-ram installations are made and positioned to generate standoff by thwarting the delivery of explosives close to the target with a vehicle.
Any security design depends upon a bid of how big threat to be resisted – the ‘design threat.’ The force in the explosion that can be expected is directly associated with the weight- 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 powerful 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 regarding how much explosive power may be delivered by way of a person carrying a backpack, a passenger vehicle, a pickup truck, a flatbed truck, etc. based upon the 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 placed in new foundations. Manufactured bollards are usually created with their very 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 as purely aesthetic installations and substantial visual deterrence and direction, but provide only minimal impact resistance.
Bollards designed to control impact are usually embedded in concrete several feet deep, if site conditions permit. Engineering in the mounting depends upon design threat, soil conditions along with 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 having a basement or subway under the pavement), bollards made with shallow-depth installation systems are for sale to both individual posts and sets of bollards. Generally, 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, while the sleeve’s top is flush using the pavement. The mating bollard may be manually lifted from the mount to allow access. This technique is intended for locations where 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 intended for high-impact resistance and 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 help ease and speed deployment. Automatic systems may be electric or hydraulic and sometimes incorporate 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 requirement for defining space, one of many basic tasks in the built environment. Decorative bollards and bollard covers provide a versatile solution for bringing pleasing form to a variety of functions. The range of available options is vast with regards to both visual style and satisfaction properties. For security applications, a design professional with security expertise should be included in the planning team.