Wednesday, September 26, 2007

Structural choices

Contemporary trends show preferences for large uninterrupted spaces indicating a paradigm shift from the old thinking. Structural options play a vital role in these `Flow of spaces.'
LONG AGO in the ages of the kings and pharaohs, the infrastructure and construction industry saw a glorious time. Some structural marvels like the pyramids and pantheons were built using the various structural systems like the stone piers, buttresses, vaults, arches, domes and stone or wood lintels. Considerable research was done to improve the structural systems in these buildings. With time, the structural systems got further improved to suit the modern day requirements.
Contemporary trends show the requirement for large uninterrupted spaces. Also, the new space typically indicates a paradigm shift. Unlike the 19th century houses where each space needed a separate distinct structural enclosure, in the new-age houses, the "Flow of space" concept has a high priority. That is where the choice of structural system has its role.
The structural systems can be of two main types — a load bearing wall structure and the skeleton system or column and beam structure. There is a possibility for using both the systems together as well. The choice of the structural system depends on some factors listed below. The choice also depends on the style of the building decided by the architect.
In a load-bearing wall that protects or creates the room structure, the walls themselves act as the structural members, transferring the load of the floor slabs and walls above, along with the other load to the foundation. Since the walls act as the structural members, all the main walls have to be aligned one above the other, for proper load distribution. This structural system would be preferred where there is a cost constraint and also the soil is a good sandy one.
The choice of finishes is many in the walled structure. Choices are in the form of plastered and painted walls, reddish exposed brickwork like in the old classical British buildings and stonewalls like buildings in Bangalore and Kodaikanal. Especially when going in for an exposed brick work, it is necessary to go in for a load bearing structure, because, the column would be breaking the continuity of the lines of the brick work.
In a skeletal structural system or a column structure, the load is transferred only through the column and beam. The walls in between have no structural importance. They only act as weather shields and space dividers.
A column structure would be preferred in large span spaces and bad clayey soil conditions. Also in cases where additions and alterations have to be done to the existing building, a column structure ensures minimum settling and easier foundation work. The flexibility of column beam structure not only allows for minimum area of walls to be constructed, but also large glazings that could be accommodated.
In special cases where the cost is a constraint but structural requirement like a cantilevered slab have to be provided, a combination of a load-bearing wall structure and a column structure can be tried. Both the load bearing wall structure and the column beam structure can be designed for earthquake resistance but the detailing has to be properly handled. A structural consultant has to be appointed for the same.
Modern day buildings have seen the expression of the structural elements as a bold statement rather than just concealing them inside the walls. The column shape can be rectangular, circular or geometric or a combination of these. But it has to be planned and executed right at the foundation stage. The beams and pergolas also add to the drama. Choosing the right colours to highlight the elements should be given due care.
Many a times, we see buildings in Chennai have false or pseudo column with decorative motifs and capitals that do not symbolise our tradition and are just a statement of falsehood which could be avoided. The expression of the structure is seen in some heritage buildings like the office of the Director General of Police near Marina Beach and the Parliament House in Delhi that show enormous character and are never outdated.
The author is the chief architect of Murali Architects, Chennai.

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