ALTERNATIVE TECHNOLOGIES                


FUNICULAR SHELLS

Environmental degradation witnessed today is a result of an irresponsible use of materials. Materials are being made to perform contrary to their natural qualities.

Most materials behave best in compression but the over reliance on RCC has resulted in tensile structures which are made to perform contrary to the natural qualities of the materials. For example, a conventional beam upon loading tends to bend at the centre. The upper region of the beam is in compression while the lower part is in tension, . To counter the tensile stresses steel reinforcements are required in the lower portion against its natural capabilities. Upon inverting the structure, it is converted into a compression structure, with a considerable reduction in the amount of steel and cement. In this case, a nominal ring beam is capable of taking the lateral thrust developed in the structure.

Compression structures provide an alternate appropriate construction technology which optimises the use of material and natural resources. Traditionally compression structures in the form arches, vaults, domes, catenaries and doubly curved structures also called funicular shells have been used extensively in the temples / forts. These structures are a standing proof of the durable performance of such structures that have stood the test of time.

The funicular shell roof is one such compression structure, which ensures conservation of natural resources by utilising waste materials effectively and optimising the use of expensive steel and cement. Further, the arch distributes the point load in all direction equally thus, is able to withstand impact loading at any point.
Advantages
  1. A simple yet splendid roofing system using natural materials and technology as against the monotonous and complex conventional practices.
  2. Funicular shells can take any Shape- Square, rectangle, trapezium, triangular or any other shape. The trick lies in casting the mould.
  3. The upper half of the edge beam is required to hold the stirrups only. It is cast along with the funicular shell; therefore, it can be a triangular section also.
  4. The funicular shell can carry various conduits, toilet pipes in the area above the brick - bat layer. These can run along the periphery where the maximum depth is available.
  5. Funicular shell roof facilitates in the installment of fixtures likes- ceiling fans, light fixtures etc.
  6. Skylight can be introduced in the roof. This can be achieved by leaving a hollow in the fibreglass mould while casting. Since the circle is itself very strong when used in compression, so as a hollow also it becomes very strong.
  7. The edge beam can be given a slight camber or lift in the centre, about 1"-3". This way the beam also acts as an arch, comes under compression, further increasing its load bearing capacity. This also reduces the amount of steel and cement being consumed in the beam.
  8. The funicular shell allows ample flexibility in design. Since the funicular shell acts as an arch, it takes load in compression and distributes the load equally in all direction. Thus, on the first floor, the wall can be placed anywhere since it will always rest on the arch.
Salient Features
  • A doubly curved structure on edge beam.
  • Compression structure able to span square, rectangular, triangular or orthogonal spaces.
  • An attractive alternative to RCC slab for small to medium span.
  • Ensures optimal utilisation of steel and cement.
  • Can be demoulded every 48 hours.

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