by SATHYA PRAKASH
VARANASHI, Architect
Instead of placing a
full surface centering, we can provide part support to erect the roof &
keep moving this support to complete the roofing. A look at the details by Mr. SATHYA PRAKASH VARANASHI
It is an irony to
realise that the problem of modern roofing is often the problem of erecting the
centering too. The more complex the roof with curves and fluid shapes, equally
complex will be the temporary support.
Incidentally, even
with the ordinary flat RCC roofs, the centering cost could be anywhere about 25
per cent of the total cost of roof, excluding the finishing cost.
This happens partly
because the concrete roof has to be cast by pouring the mix on a flat pre-set
surface; hence the surface has to be created before hand.
Traditional buildings
most often had stone slabs, wooden beams, clay tiles, thatch and such
individual components to be lifted up and placed, hence required part support
only. Even today, by reverting to the old practice, we can save on the
centering cost.
Research..!
In this direction,
pioneering research has been done by Jagadish, Reddy and Yogananda, civil
engineers of the Indian Institute of Science, who formed a group called ASTRA.
They suggested alternative roofs using masonry and found curved roofs called
vaults to be strong and economical.
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| Mr. Sathya Prakash Varanashi |
Instead of placing a
full surface centering, they suggested we can provide part support to erect the
roof and keep moving this support to complete the roofing.
Once the walls of the
room, preferably square or rectangular, reach the roof level, a wall beam is
placed in L shape along the lower ends of the vault. This shape houses the two
ends of the specially fabricated steel truss, two of them placed adjacent with
just enough gaps where masonry blocks can be kept on top and the roof built using
rich mortar.
The two pieces are
tied to avoid them falling apart. Once the blocks are placed, the formwork is
moved the next day to repeat the process.
Though stabilised
blocks have been popularly used in Bangalore, clay or / cement blocks can also be used, as long as it
is all done under supervision.
Where the upper floor
has to be useable, vaults can be done fairly flat with the sides filled up to
get another floor. Normally these are used for the last roof and top surface
finished with joint water proofing.
This system does not
immediately suit barrel vaults, but works well with segmental vaults with
catenary curve. Profiling the catenary curve is important to achieve best
results. The wall beams are necessary to balance the side thrusts.
In traditional
buildings, thick walls or side buttressing were used to get the structural
stability, which we can not afford to do today. Up to 12 ft. span, this system
makes ecological and economical sense. For wider spans, thicker base and
thinner top can be provided. The thickness of vault itself can be altered based
on the room sizes.
Building vaults with
moving supports has been around Bangalore for over 20 years now, the early
models still going strong. Unfortunately, such radical ideas are not known to
too many owners and builders, as such continue to be ignored.
About the author...!
The writer Mr. Sathya Prakash Varanashi is an
architect working for eco-friendly designs and can be contacted at
varanashi@gmail.com.
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| Mr. Sathya Prakash Varanashi |
Mr. Sathya Prakash Varanashi studied architecture in Bangalore, urban design in Delhi and heritage conservation in England. A former Professor of Architecture, he is involved in academics, outreach activities, freelance writing, professional associations and NGO initiatives.
Right from his early days, he was attracted to designs ideas rooted in cost, culture, climate and creativity, thanks to the influence of architects such as Laurie Baker, Shankar Kanade, K. Jaisim, A.G.K. Menon and K.T. Ravindran. His consultancy firm, Sathya Consultants, in Bangalore has been professing and practising eco-friendly cost-effective architecture for the last 15 years.
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