Shell Structures

R. Sundaram, B.E.SM (MIT.USA) B.L., FIE. M.ASCE, M.ACI. M.IASS.
Chairman & Managing Director, Sundaram Architects Pvt. Ltd., Bangalore, India.
President, Structural Engineers World Congress Inc. [SEWC Inc.] Worldwide.

Environmental issues are drawing worldwide attention. Manufacturing of cement results in emission of carbon dioxide gas into atmosphere and that is most polluting. Therefore we must use less of cement. Concrete thin shell roofs require minimum concrete and steel when compared to other concrete structural systems. Consequently minimum of cement is used and so in this way concrete shells are environmental friendly. The shells have other features like they can span large areas efficiently and they are aesthetically pleasing. Of course cost of form work has to be controlled by intelligent reuse of form work. Moldability of concrete to any shape has resulted in immense variety of structural forms which are extremely aesthetically pleasing. Concrete shell roofs are of different kinds and for many uses. Cylindrical, hyperbolic paraboloid and folded plates have been used. The roofs cover convention centres, food courts, industrial buildings, sports halls, wedding reception halls, multipurpose halls and the like. Shells built as early as in 1963 are behaving extremely well. This paper includes photographs and drawings of the shells built in India from 1963 until the present.

Many outstanding concrete shell structures have been designed and built in different parts of the world. Of late, there is a great demand for large span buildings due to various functional requirements like sports stadia, convention centres, theatres, exhibition halls etc. An analytical and rational approach is needed to select an appropriate span keeping the future needs into consideration.

Concrete shell roofs are one of the best alternatives to cover large spans.

The analysis and design of large span concrete roofs is indeed a challenging and interesting job compared to conventional roofs. In addition to a careful consideration of all critical load combination on the structure, analysis of the structural behaviour, during different stages of construction and final design are all essential steps for the successful realization of concrete shell structures.

As far as choice of the material is concerned, in recent times, the material is not just limited to structural steel. In this context, it is worth mentioning that concrete is a very versatile construction material which can take any desired shape and form for the structure. With the growing need for large span concrete roofs, precast, prestressed concrete structures can be adopted in order to minimise the dead weight of the structure and also to reduce the material consumption and shorten the construction time.

Different Geometrical Patterns
Different geometrical patterns

Large span concrete shell roofs are an ideal solution and is a result of a unique synthesis between architecture and structural engineering.

The unique combination of concrete and steel can be used in innumerable number situations resulting in awesome structures and it is a source of inspiration for many designers who have created innovative shapes and forms spanning large areas in different parts of the world. Such structures are immensely pleasing to the eye while satisfying functional requirements.

No structural form perhaps does greater justice to the special attributes of concrete than thin shell construction. They derive strength through form rather than through mass.

The transition from pure sculpture to utilitarian architecture includes a great spectrum of variations.

Thin shells are probably the best morphological structures to express this range through their inherent plasticity of form which lends them to diverse expressions. Thin shells come in an immense variety of structural forms.

The paper presents details of several concrete shell roofs designed and built by the author's office. The details contain important features like construction methods and design issues.

NBMCW February 2016