Funicular Shells Part-1

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ROOFING SYSTEMS

F

unicular Shell

Most materials behave best in compression but we force materials against their inherent values thus causing more problems than resolving them. The roofing system consists of waste stone masonry funicular shells. A funicular shell is the equivalent of a 3 dimensional catenary, developed on a rectilinear base. Funicular shells have been loaded to ten times the design loads of RCC and have come out winners all the way. Even the weakest of materials when used in compression will surpass RCC used in the flat form. A flat arch rotated around the centre results in a load bearing brick roof without the use of steel. 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. Diagonal g rid of funicular shell gives the illusion of a larger space. Eliminate use of high-energy steel reinforcement used in the conventional RCC roof. ! Allows efficient use of waste materials and provides personality, colour and texture. ! Minimises requirement of internal plasters. ! Provides roofing at a lower cost. ! In these illustrations a square base of size 2.2 m X 2.2 m has been used. However, any size and proportion is possible. Design of Funicular Shell Roof The entire area to be roofed is divided into a grid depending on the size of the funicular shell required or the size / shape of moulds available. The Edge beam / supporting beam is half cast. The reinforcement cage of the edge beam can either be pre welded or made in the conventional manner. The rise to span ratio is 1:6 thus; the optimal span of the shell is 3m though it can span up to 15m. The mould is supported between the edge beams. Timber  planks are used to bridge the gap between the edge of the mould and the edge beam. A thin layer of sand is put on top of the mould with a layer of the finishing materials- brick / stone tiles / mud blocks etc. along the curvature of the mould or  according to individual choice. Interesting patterns may be created by artistically mingling the chosen materials along with waste byproducts e.g.- edging of marble / granite slab or broken tiles etc. Cement slurry in the ratio 1:2 is poured over the assembly and is allowed to settle. It keeps the finishing

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materials in position and facilitates pointing for a finished appearance. A second layer comprising broken stone / bricks is placed on edge so that it acts as a series of wedges resulting in an arch action. Removal of the mould within 48 hours strengthens the arch action. To achieve a flat surface, brickbats or cinder can be used as filler  material over the funicular shell. Advantages: A simple yet splendid roofing system using natural ! materials and technology as opposed to the monotonous and complex conventional system. Funicular shells can take any shape- square, rectangle, ! trapezium, triangular or any other shape. The knack lies in the casting of the mould. The upper half of the edge beam is required to hold the ! stirrups. It is cast along with the funicular shell; therefore, it can also be a triangular section. 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. ! Funicular shell roof facilitates the installment of fixtures like- ceiling fans, light fixtures etc. A skylight can be introduced in the roof. This can be ! achieved by leaving a hollow while casting, using the inherent strength of a ring in compression. ! The edge beam can be given a slight camber or lift in the centre, about 1"-3". Thus, 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 consumed in the beam. ! The funicular shell allows ample flexibility in design. Since it acts as an arch, it takes load in compression and distributes it equally in all directions. Thus, on the first floor, the wall can be placed anywhere since it will always rest on the arch. Salient Features !

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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.