The most common bollard applications are traffic direction and control, along with security and safety. The 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. Security and safety applications rely on higher amounts of impact resistance. The major distinction between both 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 them, for instance, allows easy passage for humans and human-powered vehicles – like wheelchairs or shopping carts – but prevents the passage of cars. Such installations are frequently seen before the parking lot entrance to your 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 taken 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 type of bollards linked by a chain presents a visual cue to not cross the boundary, even though it might be easy enough for any pedestrian to travel over or underneath the chain if 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 usually placed on the corners of buildings, or flanking lamp-posts, public phones, fire hydrants, gas pipes and other installations that need to be protected from accidental contact. A steel bollards in the edge of a roadway prevents cars from over-running sidewalks and harming pedestrians. Bell-shaped bollards can in fact redirect an automobile 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 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 a few cities, automatically retractable impact-resistant bollards are installed to regulate 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 from the 1995 Oklahoma City bombing as well as the September 11, 2001, attacks saw a sharp rise in setting up bollards for security purposes. Anti-ram installations include not merely posts, but other objects designed to resist impact without presenting the appearance of a protective barrier, including large planters or benches that conceal bollards. Once the design threat is decided, the resistance needed to stop it may be calculated. (See ‘Security Design Concepts’ – below). Specification of anti-ram perimeter takes into consideration the mass as well as the speed of your approaching attack vehicle, with all the latter being considered the better significant.
According to Weidlinger Associates principal, Peter DiMaggio – a professional in security design – careful assessment from the surrounding site is required. “Street and site architecture determines the utmost possible approach speed,” he explained. “If you can find no methods to the building using a long term-up, an attack vehicle cannot develop high speed, and the resistance from the anti-ram barriers can be adjusted accordingly.”
Anti-ram resistance is normally measured employing a standard created by the Department of State, referred to as K-rating. K-4, K-8 and K-12 each reference the ability to stop a truck of any specific weight and speed and stop penetration from the payload greater than 1 m (3 ft) beyond the anti-ram barrier. Resistance depends not just on the size and strength in 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 Websites. The truck impacts several bollards at high speed, and the front in 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 inside the air, and front or rear axles might detach. The bollards along with their footings are occasionally lifted several feet upward. In every successful tests, the payload on the back of the truck does not penetrate more than 1 meter beyond the line of bollards, thus satisfying the standard.
The most basic 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 despite having a 102-mm (4-in.) pipe, depending on the engineering of their foundation. It is usually filled with concrete to boost stiffness, although unfilled pipe with plate stiffeners inside might actually produce better resistance inside the same diameter pipe. Without any form 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 greatest drawback to a plain pipe is aesthetics. A piece of painted pipe does not truly blend into – much less enhance – most architectural schemes. However, this could be overcome by way of 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 accessible to enhance specifically created (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 aspect in protecting against explosions is definitely the distance involving the detonation and the target. The force in the blast shockwave diminishes as a function of the square in the distance. The greater distance which can be placed in between the detonation and also the protected structure – known as standoff distance – the higher the threat resistance or, conversely, the less blast resistance must be that are part of the dwelling. Therefore, introduction of secure perimeter is the first step within the overall style of blast resistance.
Standoff is valuable architecturally as it allows a building to become protected without needing to resemble a bunker. It also has economic impact, because it is frequently less costly to generate standoff rather than to bomb-proof the dwelling itself. Security bollards and similar anti-ram installations are designed and positioned to generate standoff by thwarting the delivery of explosives near to the target by way of a vehicle.
Any security design is dependent upon a bid of how big threat to be resisted – the ‘design threat.’ The force from the explosion that may be expected is directly related to the body weight- and volume-carrying capabilities from the delivery vehicle. Explosives are measured in terms of tonnes of trinitrotoluene (TNT). Probably the most potent molecular explosives such, as Composition 4 (i.e. C-4), are approximately another stronger than TNT, whereas a fuel and fertilizer bomb – including was applied in Oklahoma City – is considerably less powerful than TNT. Reasonable approximations can be produced about how exactly much explosive power could be delivered with a person carrying a backpack, a passenger vehicle, a pickup truck, a flatbed truck, etc. according to the weight-and volume-carrying capacity.
You will find three basic types 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 made 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 as purely aesthetic installations and substantial visual deterrence and direction, but provide only minimal impact resistance.
Bollards created to protect against impact are usually baked into concrete several feet deep, if site conditions permit. Engineering in the mounting depends on design threat, soil conditions and 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 beneath the pavement), bollards made out of shallow-depth installation systems are available for both individual posts and groups of bollards. Generally speaking, the shallower the mounting, the broader it ought to be to face up to impact loading.
A removable bollard typically has a permanently installed mount or sleeve below grade, as the sleeve’s top is flush with the pavement. The mating bollard may be manually lifted out from the mount to allow access. This technique is supposed for locations where the change of access is occasionally needed. It can add a locking mechanism, either exposed or concealed, to avoid unauthorized removal. Both plain and decorative bollards are for sale to this kind of application. Most removable bollards zuhjvq not intended for high-impact resistance and are usually not utilized 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 may be electric or hydraulic and often incorporate a dedicated backup power installation therefore the bollard remains functional during emergencies. Retractable systems are generally unornamented.
Bollards are as ubiquitous as 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 options is vast with regards to both visual style and gratification properties. For security applications, a design professional with security expertise needs to be contained in the planning team.