The most typical bollard applications are traffic direction and control, along with safety and security. The first function is achieved from the visual presence of the bollards, and to some degree 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 distinction between the 2 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 the two, 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 often seen in front of the parking lot entrance to a store, as well as at the mouths of streets changed into outdoor malls or ‘walk streets’. In designing bollard installations to get a site, care has to be come 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 do not require impact resistance. A collection of bollards linked with a chain presents a visual cue to not cross the boundary, even though it could be easy enough to get a pedestrian to travel over or underneath 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 as opposed to merely suggesting them. Plain pipe bollards are often 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 from accidental contact. A where to buy bollards at the side of a roadway prevents cars from over-running sidewalks and harming pedestrians. Bell-shaped bollards can actually redirect an automobile back on the roadway when its wheels hit the bollard’s sloped sides.
They are employed where U-turns and tight-radius turns are frequent. This type of usage is extremely common at corners where vehicle drivers often misestimate turns, and pedestrians are particularly close 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 effectiveness of even a low post at stopping cars.
Security Bollards and Post Covers
The aftermaths from the 1995 Oklahoma City bombing as well as the September 11, 2001, attacks saw a sharp increase 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, such as 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 into account both mass and also the speed of the 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 from the surrounding website is required. “Street and site architecture will determine the maximum possible approach speed,” he stated. “If you can find no approaches to your building using a long run-up, an attack vehicle cannot build up high speed, and also the resistance from the anti-ram barriers could be adjusted accordingly.”
Anti-ram resistance is commonly measured employing a standard created by the Department of State, called the K-rating. K-4, K-8 and K-12 each refer to the opportunity to stop a truck of the specific weight and speed and prevent penetration from the payload more than 1 m (3 ft) beyond the anti-ram barrier. Resistance depends not only on the size and strength in the bollard itself, but also on the way it is anchored and also the substrate it’s anchored into.
Videos of bollard crash tests are featured on several manufacturer’s Web sites. The truck impacts several bollards at high-speed, and also the front in the vehicle often crumples, wrapping completely across 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 and their footings are often lifted several feet upward. In every successful tests, the payload on the back in the truck does not penetrate more than 1 meter past the type of bollards, thus satisfying the standard.
The most basic 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 having a 102-mm (4-in.) pipe, depending on the engineering of its foundation. It is often full of concrete to improve stiffness, although unfilled pipe with plate stiffeners inside could possibly produce better resistance within 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 may be functionally sufficient, if properly mounted. Undecorated pipe-type bollards will also be specially manufactured.
The biggest downside of a plain pipe is aesthetics. Some painted pipe does 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 which do not have impact-resistance that belongs to them are created with alternative mounting ability 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 designed (but non-decorative) pipe-type bollards.
Security Design Concepts
Most 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 also the target. The force in the blast shockwave diminishes as being a function of the square of the distance. The greater distance that may be placed in between the detonation and the protected structure – called standoff distance – the higher the threat resistance or, conversely, the less blast resistance must be that are part of the dwelling. Therefore, development of secure perimeter is the initial step within the overall design of blast resistance.
Standoff is valuable architecturally since it allows a building to be protected without having to look like a bunker. It also has economic impact, since it is frequently less expensive to produce standoff 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 near the target by a vehicle.
Any security design depends upon an estimate of the dimensions of threat to get resisted – the ‘design threat.’ The force in the explosion that can be expected is directly related to the body weight- and volume-carrying capabilities of the delivery vehicle. Explosives are measured with regards to tonnes of trinitrotoluene (TNT). By far the most potent molecular explosives such, as Composition 4 (i.e. C-4), are approximately one third 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 about how exactly much explosive power can be delivered by 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 types of bollard mountings: fixed, removable, and operable (retractable or fold-down). Fixed bollards may be mounted into existing concrete, or placed in new foundations. Manufactured bollards are often made 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 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 from the mounting depends upon design threat, soil conditions and other site-specific factors. Strip footings that mount several bollards provide 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 using a basement or subway underneath the pavement), bollards made out of shallow-depth installation systems are available for both individual posts and sets of bollards. Generally speaking, the shallower the mounting, the broader it ought to be to resist impact loading.
A removable bollard typically has a permanently installed mount or sleeve below grade, whilst the sleeve’s top is flush with all the pavement. The mating bollard may be manually lifted from the mount to allow access. This method is meant for locations in which the change of access is occasionally needed. It may include 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 created for high-impact resistance and therefore 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 ease and speed deployment. Automatic systems may be electric or hydraulic and sometimes add 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 the basic tasks of the built environment. Decorative bollards and bollard covers provide a versatile solution for bringing pleasing form to a number of functions. All the different options is vast in terms of both visual style and satisfaction properties. For security applications, a design professional with security expertise needs to be included in the planning team.