The most typical bollard applications are traffic direction and control, together with safety and security. 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 depend upon higher amounts of impact resistance. The key difference between both is safety designs are concerned with stopping accidental breach of a 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 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 frequently seen in front of the parking area entrance to your store, and also at the mouths of streets changed into outdoor malls or ‘walk streets’. In designing bollard installations to get a site, care should 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 do not require impact resistance. A type of bollards linked by way of a chain presents a visual cue to not cross the boundary, though it could be easy enough for a pedestrian to visit over or under 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 as opposed to 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 ought to 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 in fact 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 especially common at corners where vehicle drivers often misestimate turns, and pedestrians are specifically 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 from the 1995 Oklahoma City bombing as well as the September 11, 2001, attacks saw a sharp surge in installing bollards for security purposes. Anti-ram installations include not merely posts, but other objects made to resist impact without presenting the look of a protective barrier, like large planters or benches that conceal bollards. Once the design threat is set, the resistance needed to stop it could be calculated. (See ‘Security Design Concepts’ – below). Specification of anti-ram perimeter takes into consideration both the mass and also the speed of the approaching attack vehicle, using the latter being considered the better 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 determines the maximum possible approach speed,” he stated. “If there are no approaches to your building with a long run-up, an attack vehicle cannot build-up high-speed, as well as the resistance in the anti-ram barriers can be adjusted accordingly.”
Anti-ram resistance is commonly measured utilizing a standard developed by the Department of State, referred to as K-rating. K-4, K-8 and K-12 each make reference to the cabability to stop a truck of a specific weight and speed and prevent penetration of the payload a lot more than 1 m (3 ft) past the anti-ram barrier. Resistance depends not merely on the size and strength in the bollard itself, but also on the way it is actually anchored and also the substrate it’s anchored into.
Videos of bollard crash tests are featured on numerous manufacturer’s Websites. The truck impacts several bollards at high-speed, as well as the front of the vehicle often crumples, wrapping completely across the centermost post. Part of the cab may fly off the truck, the top or rear end could rise several feet in the air, and front or rear axles might detach. The bollards and their footings are occasionally lifted several feet upward. In all successful tests, the payload on the back from the truck fails to penetrate a lot more than 1 meter beyond the type of bollards, thus satisfying the conventional.
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 often full of concrete to increase stiffness, although unfilled pipe with plate stiffeners inside may actually produce better resistance within the same diameter pipe. Without any form of internal stiffening, the pipe’s wall-thickness has to 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 largest downside of a plain pipe is aesthetics. A bit of painted pipe does not truly blend into – significantly less enhance – most architectural schemes. However, this is often overcome with a decorative bollard cover. Many standalone bollards which do not have impact-resistance that belongs to them 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 be available 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 important factor in protecting against explosions will be the distance involving the detonation as well as the target. The force from the blast shockwave diminishes being a purpose of the square in the distance. The greater distance that can be placed between the detonation as well as the protected structure – known as standoff distance – the higher the threat resistance or, conversely, the less blast resistance must be built into the structure. Therefore, development of secure perimeter is the first step in the overall form of blast resistance.
Standoff is valuable architecturally because it allows a building to be protected without needing to look like a bunker. It also has economic impact, since it is frequently less expensive to produce standoff rather than to bomb-proof the structure itself. Security bollards and other anti-ram installations are created and positioned to produce standoff by thwarting the delivery of explosives near to the target by a vehicle.
Any security design is dependent upon an estimate of how big threat to become resisted – the ‘design threat.’ The force from the explosion that may be expected is directly related to the body weight- and volume-carrying capabilities in the delivery vehicle. Explosives are measured with regards to tonnes of trinitrotoluene (TNT). The most potent molecular explosives such, as Composition 4 (i.e. C-4), are approximately a third more robust than TNT, whereas a fuel and fertilizer bomb – like was used in Oklahoma City – is much less powerful than TNT. Reasonable approximations can be produced about how exactly much explosive power can be delivered by way of a person carrying a backpack, a passenger vehicle, a pickup truck, a flatbed truck, etc. according to its 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 set up in new foundations. Manufactured bollards are usually 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 created to control impact are usually 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 is not really desirable or possible (e.g. an urban location using a basement or subway under the pavement), bollards created using shallow-depth installation systems are available for both individual posts and groups of bollards. Generally, the shallower the mounting, the broader it should be to face up to impact loading.
A removable bollard typically features 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 permit access. This system 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 accessible for this type of application. Most removable bollards zuhjvq not designed for high-impact resistance and they are usually not used 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 relieve and speed deployment. Automatic systems could be electric or hydraulic and often add a dedicated backup power installation and so the bollard remains functional during emergencies. Retractable systems tend to be unornamented.
Bollards are as ubiquitous because they are overlooked. They speak with the necessity for defining space, one of many 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 range of options is vast in terms of both visual style and performance properties. For security applications, a design professional with security expertise needs to be contained in the planning team.