The most common 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 at some level by impact resistance, although, in these applications visual deterrence is the primary function. Safety and security applications depend upon higher levels of impact resistance. The key difference between the 2 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 often seen before the parking area entrance to your store, as well as 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 likely become a navigational hazard to authorized vehicles or cyclists.
Some applications for traffic guidance depend on the cooperation of drivers and pedestrians and do not require impact resistance. A collection of bollards linked by a chain presents a visual cue to not cross the boundary, though it could be easy enough for a pedestrian to travel over or under the chain should they choose. Bollards made to direct traffic are occasionally 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 along with other installations that should be protected against accidental contact. A removable bollards for sale at the fringe of a roadway prevents cars from over-running sidewalks and harming pedestrians. Bell-shaped bollards can actually redirect an automobile 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 type 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 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 strength of also a low post at stopping cars.
Security Bollards and Post Covers
The aftermaths of the 1995 Oklahoma City bombing and the September 11, 2001, attacks saw a sharp surge in setting up bollards for security purposes. Anti-ram installations include not only 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. Once the design threat is decided, the resistance required to stop it could be calculated. (See ‘Security Design Concepts’ – below). Specification of anti-ram perimeter takes into consideration the mass and also the speed of an approaching attack vehicle, using the latter being considered the better significant.
In accordance with Weidlinger Associates principal, Peter DiMaggio – a professional in security design – careful assessment from the surrounding site is required. “Street and site architecture will determine the utmost possible approach speed,” he explained. “If you will find no methods to your building with a long run-up, an attack vehicle cannot develop high speed, and the resistance from the anti-ram barriers can be adjusted accordingly.”
Anti-ram resistance is often measured employing a standard developed 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 a specific weight and speed preventing penetration from the payload greater than 1 m (3 ft) beyond the anti-ram barrier. Resistance depends not just on the size and strength of the bollard itself, but also on the way it really is anchored and also the substrate it’s anchored into.
Videos of bollard crash tests are featured on numerous manufacturer’s Internet sites. The truck impacts two or three bollards at high-speed, as well as the front from the vehicle often crumples, wrapping completely around 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 and their footings are often lifted several feet upward. In all successful tests, the payload on the back from the truck does not penetrate more than 1 meter beyond the line 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 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 might actually produce better resistance within 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 may 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 – much less enhance – most architectural schemes. However, this can be overcome by a decorative bollard cover. Many standalone bollards which do not have impact-resistance that belongs to them are designed 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 accessible to enhance specially designed (but non-decorative) pipe-type bollards.
Security Design Concepts
Much of modern security design focuses on the threat of bomb attacks. The most important factor in protecting against explosions will be the distance in between the detonation and the target. The force from the blast shockwave diminishes as a function of the square in the distance. The greater distance that may be placed involving the detonation and the protected structure – referred to as standoff distance – the higher the threat resistance or, conversely, the less blast resistance must be built into the dwelling. Therefore, introduction of secure perimeter is the initial step in the overall form of blast resistance.
Standoff is valuable architecturally as it allows a building to get protected with out to look like 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 close to the target by way of a vehicle.
Any security design depends upon a quote of how big threat to be resisted – the ‘design threat.’ The force from the explosion that can be expected is directly related to the body weight- and volume-carrying capabilities in the delivery vehicle. Explosives are measured in terms of tonnes of trinitrotoluene (TNT). The most potent molecular explosives such, as Composition 4 (i.e. C-4), are approximately one third stronger than TNT, whereas a fuel and fertilizer bomb – like was applied in Oklahoma City – is considerably less powerful than TNT. Reasonable approximations can be produced regarding how much explosive power can 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 can find three basic varieties of bollard mountings: fixed, removable, and operable (retractable or fold-down). Fixed bollards could be mounted into existing concrete, or installed in new foundations. Manufactured bollards are frequently designed with their particular 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 for purely aesthetic installations and substantial visual deterrence and direction, but provide only minimal impact resistance.
Bollards designed to protect against impact are often a part of concrete several feet deep, if site conditions permit. Engineering in the mounting is dependent upon 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 will not be desirable or possible (e.g. an urban location with a basement or subway underneath the pavement), bollards created using shallow-depth installation systems are accessible for both individual posts and teams of bollards. In general, the shallower the mounting, the broader it must be to resist impact loading.
A removable bollard typically features a permanently installed mount or sleeve below grade, while the sleeve’s top is flush with the pavement. The mating bollard can be manually lifted out from the mount to enable access. This method is intended for locations where the change of access is occasionally needed. It could add a locking mechanism, either exposed or concealed, to stop unauthorized removal. Both plain and decorative bollards are available for this type of application. Most removable bollards zuhjvq not intended for high-impact resistance and they are usually not found 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 ease and speed deployment. Automatic systems might be electric or hydraulic and quite often incorporate 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 to the requirement for defining space, among the basic tasks from the built environment. Decorative bollards and bollard covers offer a versatile solution for bringing pleasing form to many different functions. The plethora of available options is vast with regards to both visual style and satisfaction properties. For security applications, a design professional with security expertise needs to be within the planning team.