The most typical bollard applications are traffic direction and control, in addition to safety and security. The initial function is achieved from 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 main difference between the 2 is safety designs are concerned with stopping accidental breach of the 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 example, allows easy passage for humans and human-powered vehicles – like wheelchairs or shopping carts – but prevents the passage of cars. Such installations tend to be seen while watching parking area 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 taken to avoid locating them where they will likely turn into a navigational hazard to authorized vehicles or cyclists.
Some applications for traffic guidance depend on the cooperation of drivers and pedestrians and you should not require impact resistance. A collection of bollards linked by a chain presents a visual cue to not cross the boundary, although it could be easy enough for a pedestrian to visit over or beneath the chain if they choose. Bollards created to direct traffic are sometimes 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 usually placed in the corners of buildings, or flanking lamp-posts, public phones, fire hydrants, gas pipes as well as other installations that ought to be protected against accidental contact. A steel bollard post at the side of a roadway prevents cars from over-running sidewalks and harming pedestrians. Bell-shaped bollards can actually 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 to the roadbed waiting to cross. In certain 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 strength of even a low post at stopping cars.
Security Bollards and Post Covers
The aftermaths of the 1995 Oklahoma City bombing and also the September 11, 2001, attacks saw a sharp increase in setting up bollards for security purposes. Anti-ram installations include not only 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. Once the design threat is determined, the resistance necessary to stop it can be calculated. (See ‘Security Design Concepts’ – below). Specification of anti-ram perimeter takes under consideration both the mass as well as the speed of your 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 of the surrounding website is required. “Street and site architecture determines the utmost possible approach speed,” he explained. “If there are no approaches to your building with a long term-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 normally measured using a standard developed by the Department of State, referred to as K-rating. K-4, K-8 and K-12 each refer to the ability to stop a truck of any specific weight and speed and prevent penetration in the payload greater than 1 m (3 ft) beyond the anti-ram barrier. Resistance depends not just on the size and strength from the bollard itself, but also on the way it is actually anchored and the substrate it’s anchored into.
Videos of bollard crash tests are featured on several manufacturer’s Internet sites. The truck impacts several bollards at high speed, and the front of the vehicle often crumples, wrapping completely across the centermost post. Part of the cab may fly off the truck, the front side or rear end could rise several feet in the air, and front or rear axles might detach. The bollards as well as their footings are often lifted several feet upward. In all successful tests, the payload on the back in the truck will not penetrate more than 1 meter beyond the type of bollards, thus satisfying the standard.
The simplest security bollard is a bit 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 filled with concrete to boost stiffness, although unfilled pipe with plate stiffeners inside could possibly produce better resistance within the same diameter pipe. Without any kind of internal stiffening, the pipe’s wall-thickness needs to be significantly greater. For fixed-type security bollards, simple pipe bollards may be functionally sufficient, if properly mounted. Undecorated pipe-type bollards can also be specially manufactured.
The largest drawback to 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 a decorative bollard cover. Many standalone bollards which do not have impact-resistance of their own are created with alternative mounting capacity 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 aspect in protecting against explosions will be the distance in between the detonation and the target. The force in the blast shockwave diminishes as a function of the square in the distance. The more 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 needs to be that are part of the structure. Therefore, introduction of secure perimeter is the first step inside the overall design of blast resistance.
Standoff is valuable architecturally since it allows a building to get protected with out to look like a bunker. It also has economic impact, since it is frequently less costly to produce standoff than to bomb-proof the dwelling itself. Security bollards and similar anti-ram installations are created and positioned to generate standoff by thwarting the delivery of explosives near to the target by way of a vehicle.
Any security design depends on a quote of the dimensions of threat to be resisted – the ‘design threat.’ The force of the explosion that may be expected is directly associated with the body weight- and volume-carrying capabilities from the delivery vehicle. Explosives are measured with regards to tonnes of trinitrotoluene (TNT). Probably 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 – including was applied 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 on the weight-and volume-carrying capacity.
You can find three basic kinds 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 usually created with their very own 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 purely aesthetic installations and substantial visual deterrence and direction, but provide only minimal impact resistance.
Bollards created to protect against impact are usually embedded in concrete several feet deep, if site conditions permit. Engineering of the mounting depends on design threat, soil conditions as well as 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 is not really desirable or possible (e.g. an urban location using a basement or subway under 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 must 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 could be manually lifted out from the mount to allow access. This system is meant for locations where the change of access is occasionally needed. It could include a locking mechanism, either exposed or concealed, to avoid unauthorized removal. Both plain and decorative bollards are accessible for this sort of application. Most removable bollards zuhjvq not intended 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 ease and speed deployment. Automatic systems may be electric or hydraulic and sometimes include a dedicated backup power installation and so the bollard remains functional during emergencies. Retractable systems are generally unornamented.
Bollards are as ubiquitous as they are overlooked. They talk to the necessity for defining space, one of many basic tasks in the built environment. Decorative bollards and bollard covers offer a versatile solution for bringing pleasing form to a number of functions. The plethora of available choices is vast with regards to both visual style and satisfaction properties. For security applications, a design professional with security expertise needs to be included in the planning team.