Thursday, December 26, 2013

RAMPS as Transfer Systems in Buildings


Ramps are inclined pedestrian passages without vertical risers and have a pitch lower than stairs. Ramps are easier to ascend or descend than stairs, but occupy more floor space. 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 %. For short run such as 5mts. Some labour laws allow 25 % pitch for very short runs (2mts) such as for ware house and factory entrances, but only for ascent. 10 % pitch is a very common provision in building design. Ramps for wheel chair users should not be steeper than 5 % (1:20). Length must not be more than 6 mts in passage length, and landings or rests should be at least 1650 long. Casual ramps or slopes in parks and landscaped areas nominally follow the angle of repose of the soil, but if these are to be used as passage ways, the pitch must not be greater than 8 %.

Width requirements: for single lane traffic 750mm, furniture passage 900mm, for cinema hall interior mid seat aisles minimum 1200mm, increasing 70mm in width for every 1mt of passage run.

Straight line layout of multiple ramps
must be avoided. If inevitable it should for 2 passage laps only. Secondary units of the ramp at right angle or U turn are advisable. For normal users ramp lengths of maximum 25 mts or 2 mts climb per lap are ideal.

Ramps are used in place of stairs or steps. Ramps provide a very smooth transfer between elevations. Wheeled items like trolleys, perambulators, chairs, vehicles are easy to move on ramps than stairs. Ramps require the least energy amongst all movement systems between different elevations. Ramps due to their design, take up a lot of space and require a large structure. Continuous ramps tend to accelerate the movement speed in descent and become hazardous. Circular ramps generate concentric force during rapid descents. Multi-directional ramps require additional elements to cutoff the accelerated speed of descent at the change junctions.

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 (small width -under 800mm, ramps allow holding of both side rails), configuration of the ramp structure, pitch, 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 head load (railway coolies), as the weight on head raises the 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. All ramps in a consecutive usage must be of one consistent pitch. Parabolic, concave or convex curvature pitches are not favoured in buildings.

Ramps have been used for moving materials to construct structures like Pyramids, Ziggurats and Inca temples. Ramps have been used to move heavy guns to fortification tops, to negotiate hills and mountains and to draw water from wells. Ramps have been used as entrance way in many buildings, such as the Ziggurat, Egyptian temple of Queen Hatshepsut, etc. Ramps have been used by Le Corbusier as an indicative of democracy and ceremony (Cultural Centre, Textile mill owners building, Shodhan Villa at  Ahmedabad, India and at the Secretariat building, Chandigarh, India.)

Ramp and stair combination: Ramps are also used along with steps to provide a dual system. However to match the gradient of the ramp, such steps have very 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. 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. Roller coaster rides make extensive use of ramps structures to create very intensive centripetal and centrifugal forces with high accelerated speeds that almost defy the gravity. Cycling stadiums use double curvature ramps. Channelled ramps of water parks use and inward as well as outward curves (clockwise and anti clockwise movements), variety of pitches and parabolic curves (mainly in the end section) to generate sideways thrusts, acceleration and de-acceleration.

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