Post 289 – by Gautam Shah
Ramps are inclined passages for smooth transfer people, vehicles and goods between elevations. Ramps have a pitch lower than stairs, and are physically easier to ascend or descend than stairs. Ramps occupy more floor space compared to any other gravity transfer system.
Ramps require less force than lifting a load straight up though at an increase in the distance moved. An inclined plane allows the same work to be done with a smaller force exerted over a greater distance. A ramp is an inclined plane, one of the six classical simple machines defined by Renaissance scientists. Inclined planes have been used to move up an object along its inclined plane or by for lifting loads straight up from wells and mines. Indian leather water bags (mashaq) were pulled up by bullocks moving down a ramp.
Inclined slopes as simple machines have been used in many different conditions. A wedge is an inclined machine. A screw, is an inclined narrow spiral wrapped around a cylinder. Inclined planes have been used by people since prehistoric times to move heavy objects. Heavy stones used in Stonehenge or Dolmens were set in place with inclined planes made of earth. Egyptian pyramids, Ziggurats and Inca temples were constructed with inclined planes. Greeks constructed Diolkos, a paved ramp 6 km long, to drag ships overland across the Isthmus of Corinth. Ramps have been used to move heavy guns to fortification tops, to negotiate hills and mountains, and to draw water from wells and minerals from deep mines.
Ramps have been used to move a mass of people in public buildings and places. Ramps have been used by Le Corbusier as an indicative of democracy and ceremony. Ramps are used in place of stairs or steps. Wheeled items like trolleys, perambulators, chairs, vehicles are easy to move on ramps than stairs.
Inclined slopes, using the Earth or soil’s capacity to remain stable in inclined form has been used for constructing causeways. The stable angle of friction or angle of repose, is the maximum angle at which a soil mass remains stable and ‘at which loads can rest motionless on an inclined plane due to friction, without sliding down’.
Ramps when steeper than 10 %, require a non slip flooring and a grip-able handrail. Ideal pitch for a ramp is below 8.33 % (1:12), however most codes accept pitches up to 16.66 %, some labour laws allow 25 % pitch for very short runs (2mts). Ramps for wheel chair users and patient trolleys should not be steeper than 5 % (1:20). Length of a ramp must not be more than 6 mts, after which a break in gradient in the form of a level landings or rests should be at least 1650 long. Straight line layout of multiple ramp units (even with adequate provision of mid landings, must be avoided, instead a secondary ramp unit at right angle or U turn is advisable. For physically normal users, a ramp, per lap lengths of maximum 25 mts or 2 mts climb, are ideal. Width requirements: for single lane traffic 750 mm, furniture passage 900 mm, for drama or cinema aisles minimum 900 mm, increasing 35 mm for every 1500 mm of run.
Continuous ramps tend to accelerate the movement speed in descent and so become hazardous. Multi-directional ramps require additional elements to cut-off descent speeds at the change junctions. Circular ramps generate concentric force during rapid descents. Circular ramps of clock-wise or counter-clock movement have relevance (if any) in either the decent or accent.
Factors that define the utility of a ramp are: Texture of the floor, gripping power of the handrail, height of the handrail, distance between two handrails (in narrow ramps), configurations of the ramp structure, angle, movement to ascend/ descend, age profile of the users, orthopaedic functionality of the user, etc. It is very difficult and hazardous to move on a ramp with any type of hand, shoulder or head loads (railway porters), as the weight disturbs the nominal centre of gravity of the body. This is the reason why people stoop forward while climbing up steep slopes, and backward while moving down a ramp slope.
Ramps along with steps provide a dual system, however to match the gradient of the ramp, such steps have a wide tread and very low height riser, making them very difficult to use. In hospital areas such steps between or on one, or both sides of the ramp help the person to push the chair or trolley up or down the slope with better control. The same configuration is used in industrial warehouses to move large barrels or wheeled items. Ramp and stair combination is also used in inclined elevators often called a funicular railway. The slope accommodates the rails or the guides of the inclined elevator and the steps are used by the service personnel. Here the gradient is usually very acute so the tread is very narrow while the riser very tall.
Parabolic ramps are used in places like Amusement parks, water games parks etc. A parabola has two sets of inclinations. The short radius curvature of the parabola, if at the lower end, helps in retarding the speed of descent, while the larger curvature of the parabola, if at the lower part, the initial acceleration gets a sudden boost at the end. This later version is very hazardous, and is used if only sufficient fore space or speed absorption mechanism (sand pit, water pool) is provided for beyond the parabola. Ice-skating tournaments where a skater needs very high speed start to accomplish the required twists, turns, lump before landing, have such slopes. A roller coaster rides makes extensive use of ramps structures to create very intensive centripetal and centrifugal forces with high accelerated speeds that almost defy the gravity. Cycling Velodroma uses double curvature ramps.
Inclined planes are widely used in the form of loading ramps to load and unload goods on trucks, ships, and planes. Wheelchair ramps are used to allow people in wheelchairs to get over vertical obstacles without exceeding their strength. Escalators and slanted conveyor belts are also forms of inclined planes. Aircraft slides and fire evacuation tubes allow people to rapidly and safely reach the ground.