Curved roofs without limits

Does anyone wish to have a dome shape, without any limitations? The answer lies in shell roofs, says Sathya Prakash Varanashi

How is the Taj Mahal roofed? It is a question that need not be asked because all of us know it is roofed by a dome. The commoners may not know of the technical details about the bulbous shape atop, but the technical experts can analyse its form and behaviour from different perspectives. Domes have dominated the historic skyline for centuries and continue to have a prominent role even today.

However, most buildings that we build today cannot take a dome for reasons like upper floors are ruled out, they effect the possible terrace, the rise of the dome may create unwanted interior volume, expert skills are required to do a stable dome or that they are possible mainly on circular plans. Does anyone wish to have a dome shape, without any of the above limitations? The answer lies in shell roofs.

Technically, shell roofs are not the same as the domes, but share a few common factors like arch action for transferring the building loads. Among the viewers, of course, they evoke similar feelings as domes due to the curved form. The shell roofs can be in thin concrete or masonry, curved in form, spanning short distances. Unlike the domes, they are not hemispherical in form and do not rise high, as such enable useable floors above them.

In India, many well-known institutions like Structural Engineering Research Centre, Auroville or Anangapur Building Centre have explored shell roofs for application towards cost-effective, fast track constructions with an alternative aesthetics. The former ones worked with varied materials including concrete roofs, while the last one worked mainly with natural masonry materials. The building centre worked with what is technically termed as funicular shells based on the catenary curve principle, which suggests the curved shell roof would transfer loads to the edges in an axial or perpendicular manner, creating least of deflection and turning moments.

For a flat roof

Shell roofs normally enable a normal flat roof, create beautiful patterns in ceilings, speed up the work, save much of concrete and reduce steel consumption by more than half. While the funicular roof best suits square profiles, it can be constructed atop rectangular plans also.

Of course, the profile needs to be evolved carefully and the formwork done to the specific curves. For all the advantages of funicular shell roofs, it demands expert advice and masonry skills. Once trained, the team may venture into even complex roofing solutions.