Post 388 ⇒ by Gautam Shah →
Guardrails are, both, protective barriers and rails for guidance. These are placed against a drop in terrain (of more than 750mm), against the edges of exclusive passage, or rights of ways. Guardrails, mark a visually recognizable guide line. Such guide lines are recognizable in inclement weather (heavy rains, fog, smog and darkness). A guard rail often is designed to bear heavier impact of side thrusts in comparison to a hand rail. A hand rail, as per most of the building standards cannot have a gap larger than 100 mm, whereas for Guardrails can have a gap slightly smaller than the front wheel dia of the vehicles, or at least 220mm.
Guardrails are placed in buildings, terrains and roads. Many of the edge side structures such as, hand rails, parapets or fences can be called guard rails. Guardrails are both man-made structures or contoured natural features. Guardrails on any type of passage ways should be minimal. Modern roads are designed in a manner to eliminate the need for a guard rail. These means include provisions of apron spaces, contoured ends and landscaped features to indicate presence of zones of dangers. Road barricades work as guardrails. Many are installed as temporary (demountable) or permanent structures to prevent surprise or forced entry of terrorists or demonstrators.
Guardrails are essentially of two types: 1. Rigid ones bear an impact to an extent, but mainly help bounce back of the object in certain direction, and possibly retard the movement of the object; 2. Flexible ones bear the impact substantially within the body and yet redirect the object to a safer zone. In both the cases an objective is to keep the vehicle upright while being deflected along the guardrail.
Road guardrails are designed with the roads or installed as retrofit when certain sections show such a need. Former types of guardrails are fairly long whereas the later types are zone-specific and comparatively shorter. Specific types of guide rails are placed to prevent accidents due to the road elements or fixed objects. These elements include bridge supports, piers, road signages, culverts, trees, etc.
Guardrails on roads and other sites have the inner edge (use or the movement side face) completely free of obstructions. The rails are so constructed that they form a continuous visual and functional surface. The joints formed with a backing element rather than by lapping. The colour and surface texture are consistent.
Guardrails function as an integrated system where the guardrail, posts, post foundation structure and support braces, all share the impact load. In spite of a rigid design, guardrails do deflect. The amount of deflection depends on such factors as: straight or curved formation of the guardrail layout, height of the guardrail, shape or section of the rail, direction of the impact (parallel, head-on, angular), weight of impacting objects (mass-inertia), height of the impacting object, nature of support posts, and distance between the supports.
Road and other guard rails are universal structures, serving variety of vehicles (cars, trucks, motorcycles, cycles), people (adults, infirm, children, rowdy crowds), climatic conditions (rains, fog, smog, snow), and varying terrain conditions (floods, landslides, dumping, oil leaks). An optimum height for a car may not prevent a truck from toppling over the rail and a motorbike or human being sliding under it.