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roofing bubbled up spaces: vaults and domes

vaultsVaults and domes are fascinating inventions in construction, which have been enthralling many. Aesthetically they intrigue as they bubble up the spaces like baloons. They have started as techniques in spanning large volumes economically ( like arches), but have aquired meanings and connotations over a period. Various techniques of vaulting and doming have evolved, but the basic idea of bubbling remains. As a geometry these forms excite. As methods of construction and possibilities with new materials they intrigingly tantalising.

Vaults are curved in one dimension, whilst domes are two dimensional curves. Vault is like a vertically part of a cylindrical tube and that way it is geometrically simpler. That is why they are called ‘barell vaults’. The domes are like part of a sphere, a ball,or an egg shell.

Vaulting is a known techniques for a long time. Since Roman times. It is also said that the first vaults were built by Nubians in africa. ( http://en.wikipedia.org/wiki/Nubian_vault ). They used to build it with out centering or supports and with bricks. Romans built some very large vaults using bricks and concrete.  The vaults and domes are geometrically stable shapes and get their strength from the shapes itself.

Vaults and domes can be built with bricks and in concrete. With the invention of reinforced cement concrete, the idea of vaults and domes lost their appeal some what. And new possibilities opened up. Yet they continue to offer interesting formal possibilites at comparatively lower cost.  The interest in them is not just in creating large span roofs, but in adding quality to the spaces beneath them. And sometimes offering newer interpretations and connotative meanings externally too.

 

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Prof. K.S. Jagadish, Indian Institute of Sciences, Bangalore has completed a project on “Structural and Architectural Study of Domes and Vaults of South India.” This deals with the structural roof forms before and after 1370 A.D. in the States of Karnataka, Tamil Nadu and Andhra Pradesh. Twenty nine sites in Karnataka, sixteen in Tamil Nadu and three sites in Andhra have been so far covered in the study. He has visited the above sites. It is interesting to note that in ancient times the roofs were either of the post and lintel type or corbelled.  However, Hoysala period artisans had developed arcuate construction of domes, which is different from corbelled construction. After 1370 AD the influence of Islamic architecture can be traced in the roofs.  The Bahamani and Vijayanagar kingdoms contributed to the development of very impressive buildings. After the fall of Vijayanagar the above roof systems could be seen in Tamil Nadu, even in residential buildings.  Local masons shifted to making brick vaults even in villages.  The village of Tiruvaiyaru had many vaulted houses, including the one where the famous saint composer Tyagaraja lived.  The forts in Gingi, the Virabhadra temple in Darashuram and the Tirumala Nayak palace in Madurai are fine examples of later day domes and vaults. The style seems to have reentered Mysore region during the time of Tipu Sultan. He built vaults

 

of various spans in Srirangapatna, Bellary, Chitradurga and other places. The one with a large span was in Bangalore. A monograph on the study so far carried out is under preparation. (http://inae.org/projects.htm)

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Vaults are like extended arches. Semicircular and segmental (parts of a circle) vaults are easier shapes to build. The semicircle tends to bulge at just above the springing base and therefore segmental is better. Ideally, 0.4 span as height offers very stable shape. A catenary vault is considered the very best. To get the catenary shape one could fill a hose pipe with water, hold two ends at the ends of span and allow the hose to sag as much as you reach the required height. Once you invert the shape upside down, you get the shape to build a inverted catenary vault. It is a natural shape defined by the forces.

One cannot build the vault too long either without intermediate supports. When the length of vaults reaches more than twice the span in cross section, they tend to sag longitudinally. One needs to h

bk vault

ave a firm support of a wall or a curved beam, in between.

The most important aspect to take care is the outward thrust at the base of the vaults as the weight of the vault itself tries to make it go flat. The effect will be in pushing the supporting walls outward. And walls may collapse. To counter this buttress walls were used to be built. But an economic alternative is to provide steel ties intermittently with a stiff base like a concrete or steel beam.

First vaults by us were built for a low cost housing demonstration project for the Mysore Urban Development Authority, with ordinary bricks and without centering and  steel reinforcement in 1987. The vaults were of 10’span segmental vaults and were only 3” thick and had a water poof cement plaster on top. Two steel L angles were kept embedded on thin RCC lintels over the end walls and were tied by 12mm rods bolted to the steel angles at intervals.  Making a centering will turn out costly. We used a mobile centering of 3’ width. It was kept over a springing base and the bricks laid seeing that the center of the segment is a brick not a joint. The mobile centering could be lowered next day and moved to the next 3’. It has to be seen that the brick joints are broken across the vaults. The edge of the day’s work will thus will leave jagged edge for the next day’s vaulting to key in.  vault house

The technology was developed by Astra of IISc, Bangalore, and  then director Prof. KS Jagadish was specially involved. We could build 12 demonstration units of low income houses with great difficulty in convincing the engineers and taking up the work ourselves. However, the establishment did not get convinced or felt confident of this simple technique and the idea was shelved for the main project.  To our dismay, the allottes also  did not take it well, as the roof prevented further constructions and use of a terrace. Fair enough.

We tried to use this idea of brick vaulting on industrial buildings. The Prabhu Foods Mushroom cultivation Plant , Mysore (see under  and The Shrishyla Speciality Papers, Mysore. ThePrabhu foood was a group of three small buildings and had been roofed with 12′ span brick vaults. The mobile form work we fabricated came to use here.

prabu food

The  brick vault provided excellent reduction in thermal radiation through the roof .  The idea could not find many takers for some more time.

It was only in after 2000, we could further explore the possibilityof vaulting. First at a residence of Bobby and Srinivasan, Bangalore ( See; http://bsb-architects.com/?p=71/ ) . Only a part of the roof was semi vaulted and used a prefab system with steel sections and hollow clay block infill and a screed concrete.

sunita

srini vault

 

This idea of prefabrication opened up the possibility to experiment with many different kinds of vaults; segments of cirle, ellipse and other conic sections , economically.

We did a number of variations with fluid spaces underneath these vaults. Prof SN Hegde’s house used vaults, exposed bricks and brick dome in a combination.

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In Mahesh and Padmavathi’s residence and in Gayatri and Vijayaraghavan’s residence ( 2007) elliptical sections were used to develop the vaulted form. In Mallikarjun’s residence in Bangalore (2007) only segmental vaults were used in combination with skylights and perforation.vaults123

roof bSo was the central skylight of Govindarju residence at Coimbatore. (2007) GR Reddy Bungalow at Jubilee hills, Hyderabad (2009) has large cascading vaults made completely with steel and hollow clay and screed concrete.

roof a(See: http://www.wienerberger.in/servlet/Satellite? pagename=Wienerberger/WBArticle/ArticleText05&cid=1186564363855&sl=wb_in_home_en/ )

 Domes:

Domes are of different types; by shape or material. The oldest domes , we know are compression type made of bricks or concrete or even mud. The geometry of the dome is evolved by rotating a curve on an axis which bisects it. If one rotates part an ellipse   one gets an elliptical dome  if an arc (part of circle) is revolved, then a spherical or hemispherical dome.  And so on with other curves too. The base of  the domes are genearally circluar.; but there could be exceptions too.

dome

BS Bhooshan and associates built many brick domes since 2000. The JW Golf Club at Mysore used 12 feet and  25 feet domes using ordinary bricks with both sides plastered with cement plaster. Domes were segmental one’s with height = 2/3 base diameter. The thickness was 9″ and was easy to build with half a day’s training (instruction on job) to masons. The center was fixed ( suitably below the base to get the required segment) with a hook and radius was marked with steel road or wire and one end tied to the centre. It was then easy for the mason to lay a full circle on along the thread direction and the bricks touching the radius. When one layer (full circle)  is built completely, the next layer could begin over it. With every layer the bricks get further tilted to the horizontal and the tilt was to be adjusted by the thread to centre and mortar thickness. Towards the top the bricks come too close to vertical and are likely to slide down. This can be prevented by tying the bricks temporally down to the outside of  the dome with a nail. One a layer of circle is complete the bricks support each other from sliding down even if the mortar is not set. The central part is left for a skylight as this part will be tricky and structurally unsound to be covered as part of the dome.

In some later domes in the golf club as well in other projects (Hegde House, Govindraj house) we used wire cut bricks. Inclined arrangements of bricks in layers makes the building easy as the slipping down in prevented. Then we could make patterns of this arragements and exposed them internally. A combination of vaults and domes provide a very enjoyable variation in internal volumes. With the patterning of bricks they can provide a scaling down of surfaces to that of an ornamentation adding to the richness and a revelation of the skills that made them.

(to be continued)

The biggest dome, 40 ft in dia, was of corbelled space frame made up of  welded steel tubes and a skin made of Ferro-cement and waterproofing membrane. The construction detail gave an economic structure and a visually interesting interior.