The most typical bollard applications are traffic direction and control, in addition to safety and security. The initial function is achieved through 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 rely on higher levels of impact resistance. The major difference between the two 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, 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, and at the mouths of streets changed into outdoor malls or ‘walk streets’. In designing bollard installations for any site, care should 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 never require impact resistance. A type of bollards linked with a chain presents a visual cue not to cross the boundary, though it may be easy enough for a pedestrian to travel over or underneath the chain should they choose. Bollards made to direct traffic are often created 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 in 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 removable steel bollards at the edge of a roadway prevents cars from over-running sidewalks and harming pedestrians. Bell-shaped bollards can in fact redirect a vehicle back to 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 kind of usage is extremely common at corners where vehicle drivers often misestimate turns, and pedestrians are particularly near to the roadbed waiting to cross. In certain 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 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 installing 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 set, the resistance needed to stop it could be calculated. (See ‘Security Design Concepts’ – below). Specification of anti-ram perimeter takes under consideration both mass and also the speed of your approaching attack vehicle, with all the latter being considered the better significant.
According to Weidlinger Associates principal, Peter DiMaggio – an expert in security design – careful assessment of the surrounding website is required. “Street and site architecture determines the maximum possible approach speed,” he explained. “If you will find no strategies to your building having a long haul-up, an attack vehicle cannot build-up high-speed, and also the resistance in the anti-ram barriers can be adjusted accordingly.”
Anti-ram resistance is commonly measured utilizing a standard created 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 the specific weight and speed and prevent penetration of the payload more than 1 m (3 ft) past the anti-ram barrier. Resistance depends not only on the size and strength of the bollard itself, but also 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 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. Area of the cab may fly off the truck, the top or rear end could rise several feet within the air, and front or rear axles might detach. The bollards along with their footings are often lifted several feet upward. In all successful tests, the payload on the back of the truck does not penetrate a lot more than 1 meter beyond the type of bollards, thus satisfying the standard.
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 despite having a 102-mm (4-in.) pipe, depending on the engineering of their foundation. It is usually 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 form of internal stiffening, the pipe’s wall-thickness needs to be significantly greater. For fixed-type security bollards, simple pipe bollards could be functionally sufficient, if properly mounted. Undecorated pipe-type bollards will also be specially manufactured.
The biggest disadvantage of a plain pipe is aesthetics. A bit of painted pipe fails to truly blend into – much less enhance – most architectural schemes. However, this is often overcome by way of a decorative bollard cover. Many standalone bollards that do not have impact-resistance of their very own are created with alternative mounting ability to slip over standard pipe sizes, forming a beautiful and architecturally appropriate impact-resistance system. These decorative covers can be offered to enhance specially designed (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 factor in protecting against explosions is definitely the distance between the detonation as well as the target. The force of the blast shockwave diminishes as a function of the square from the distance. The better distance which can be placed involving the detonation and the protected structure – known as standoff distance – the higher the threat resistance or, conversely, the less blast resistance must be included in the structure. Therefore, development of secure perimeter is step one in the overall style of blast resistance.
Standoff is valuable architecturally as it allows a building to become protected without having to resemble a bunker. In addition, it has economic impact, as it is frequently cheaper 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 by a vehicle.
Any security design depends on a bid of how big threat to be resisted – the ‘design threat.’ The force from the explosion which can be expected is directly associated with the body weight- and volume-carrying capabilities of 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 a third more powerful than TNT, whereas a fuel and fertilizer bomb – such as was used in Oklahoma City – is much less powerful than TNT. Reasonable approximations can be made about how exactly much explosive power may be delivered by way of 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 kinds of bollard mountings: fixed, removable, and operable (retractable or fold-down). Fixed bollards can be mounted into existing concrete, or placed 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 as purely aesthetic installations and substantial visual deterrence and direction, but provide only minimal impact resistance.
Bollards designed to protect against impact are usually a part of concrete several feet deep, if site conditions permit. Engineering from the mounting depends upon 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 for sale to both individual posts and sets of bollards. Generally speaking, the shallower the mounting, the broader it ought to be to face up to impact loading.
A removable bollard typically features a permanently installed mount or sleeve below grade, whilst the sleeve’s top is flush with the pavement. The mating bollard could be manually lifted from the mount to enable access. This method is intended for locations in which the change of access is occasionally needed. It could 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 therefore are not often 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 relieve and speed deployment. Automatic systems may be electric or hydraulic and often incorporate a dedicated backup power installation and so the bollard remains functional during emergencies. Retractable systems tend to be unornamented.
Bollards are as ubiquitous since they are overlooked. They talk to the requirement for defining space, among the basic tasks from 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 satisfaction properties. For security applications, a design professional with security expertise ought to be contained in the planning team.