The most common bollard applications are traffic direction and control, along with security and safety. The initial function is achieved by the visual presence of the bollards, and to some extent 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 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 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 are often seen before the parking lot entrance to some store, and also at the mouths of streets transformed into outdoor malls or ‘walk streets’. In designing bollard installations to get a site, care has to be taken to avoid locating them where they are going to turn into 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 collection of bollards linked by way of a chain presents a visual cue never to cross the boundary, although it might be easy enough to get a pedestrian to travel over or beneath the chain should they choose. Bollards made to direct traffic are often designed 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 frequently placed at 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 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 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 even a low post at stopping cars.
Security Bollards and Post Covers
The aftermaths in the 1995 Oklahoma City bombing and the September 11, 2001, attacks saw a sharp increase in the installation of bollards for security purposes. Anti-ram installations include not only posts, but other objects designed to resist impact without presenting the appearance of a protective barrier, including large planters or benches that conceal bollards. After the design threat is set, the resistance required to stop it can be calculated. (See ‘Security Design Concepts’ – below). Specification of anti-ram perimeter takes into account the mass as well as the speed of the approaching attack vehicle, with the latter being considered the greater significant.
In accordance with Weidlinger Associates principal, Peter DiMaggio – an expert in security design – careful assessment in the surrounding website is required. “Street and site architecture will determine the highest possible approach speed,” he explained. “If you can find no approaches to the property using a long haul-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 normally measured employing a standard designed by the Department of State, known as the K-rating. K-4, K-8 and K-12 each make reference to the opportunity to stop a truck of a specific weight and speed and stop penetration from the payload greater than 1 m (3 ft) beyond the anti-ram barrier. Resistance depends not merely on the size and strength in the bollard itself, but additionally on the way it really is anchored and also 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, and also the front of the vehicle often crumples, wrapping completely across the centermost post. Area of the cab may disappear the truck, the front side or rear end could rise several feet in the air, and front or rear axles might detach. The bollards and their footings are sometimes lifted several feet upward. In every successful tests, the payload on the back in the truck does not penetrate more than 1 meter beyond the collection of bollards, thus satisfying the typical.
The simplest security bollard is some 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 their foundation. It is usually loaded with concrete to improve stiffness, although unfilled pipe with plate stiffeners inside might actually produce better resistance in the same diameter pipe. Without any form 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 greatest downside of a plain pipe is aesthetics. A piece of painted pipe fails to truly blend into – a lot less enhance – most architectural schemes. However, this is often overcome with a decorative bollard cover. Many standalone bollards which do not have impact-resistance of their own are created with alternative mounting capability to slip over standard pipe sizes, forming a beautiful and architecturally appropriate impact-resistance system. These decorative covers can 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 important element in protecting against explosions will be the distance involving the detonation as well as the target. The force of the blast shockwave diminishes as a purpose of the square in the distance. The greater distance that may be placed in between the detonation and also the protected structure – referred to as standoff distance – the greater the threat resistance or, conversely, the less blast resistance must be that are part of the dwelling. Therefore, creation of secure perimeter is the initial step within the overall form of blast resistance.
Standoff is valuable architecturally since it allows a building to become protected with out to resemble a bunker. It also has economic impact, as it is frequently less expensive to generate standoff rather than bomb-proof the structure itself. Security bollards and similar anti-ram installations are designed and positioned to create standoff by thwarting the delivery of explosives near the target with a vehicle.
Any security design depends on a quote of the size of threat to get resisted – the ‘design threat.’ The force of the explosion that may be expected is directly associated with the load- and volume-carrying capabilities of the delivery vehicle. Explosives are measured in relation to tonnes of trinitrotoluene (TNT). By far 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 – including was utilized 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 its weight-and volume-carrying capacity.
You will 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 created with their 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 for 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 on design threat, soil conditions along with other site-specific factors. Strip footings that mount several bollards provide 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 using a basement or subway underneath the pavement), bollards made with shallow-depth installation systems are accessible for both individual posts and sets of bollards. Generally, the shallower the mounting, the broader it ought to be to face up to impact loading.
A removable bollard typically includes a permanently installed mount or sleeve below grade, whilst the sleeve’s top is flush using the pavement. The mating bollard can be manually lifted out of the mount to permit access. This technique is meant for locations in which the change of access is occasionally needed. It may incorporate a locking mechanism, either exposed or concealed, to stop 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 might 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 talk to the need for defining space, one of the basic tasks from the built environment. Decorative bollards and bollard covers offer a versatile solution for bringing pleasing form to a variety of functions. The plethora of options is vast in terms of both visual style and satisfaction properties. For security applications, a design professional with security expertise should be within the planning team.