Pillars of strength

Pillars of strength

Do the pillars and columns in your home bother you? Are you thinking of adding a few in your new house?  K R Srikanta Prasad discusses why the addition of pillars is a necessity.

The term “pillars of strength” refers to any object or person who provides great support to something or someone. Likewise, in a building or structure, pillars and columns form a very important framework.

Pillars can be defined as vertical load-bearing members in a structural system. Like legs bear the load of bodies, pillars bear the load of a superstructure and transfer it to the footings and the ground below.

The fact that the slender vertical pillars in high-rise building withstand carrying a load weighing thousands of tonnes amazes me.

In modern-day construction, the architect and the structural designer work in tandem to decide on the size, shape, location, spacing and material for the pillars.

While an architect finds the columns obtrusive, a structural engineer feels that they are a necessity!

The architect designs column free spaces and the engineer places pillars everywhere...the tussle continues!

But with the advent of advanced high strength material and design process, pillars are getting sleeker and spaces are getting bigger.
But all said and done, pillars are essential load-bearing structures in a building.

Before we understand the intricacies of pillars, we need to learn its basic structural aspects. All buildings can be categorised as either framed structures or load-bearing wall structures when we look at it from a structural aspect.

Framed structures are the ones which have columns and beams as their skeleton which are load bearing.  In masonry structures, it is essentially the walls that bear the weight of the superstructure.

So, pillars are given relevance in framed structures. Usually, multi-storeyed structures and huge complexes are ‘framed structures’. They have a network of beams and columns. The walls are usually made of thin light-weight material and are non-load bearing.

These days, framed structures are more used than the load-bearing wall structures because of the various benefits and flexibility offered.

The location of columns in a structure depends on the following aspects: the architectural layout and aesthetics, critical pressure points of the structure, structural feasibility, material used and future expansion of the present structure.

The material used plays a major role in the design of the frame. They can be of wood, brick or stone masonry, structural steel sections, reinforced cement concrete (RCC) or composite.

In the Indian construction scenario, structural steel is used mostly for industrial structures and RCC pillars are the most common and widely used for homes.

Design flexibility

Even though providing RCC pillars proves more expensive ( by 20 per cent) compared to wall structures, they have advantages such as design flexibility, easy execution and are coherent and non-obtrusive.

While casting RCC pillars, the following technical requirements have to be observed: cover to the reinforcement, appropriate ties and lap lengths for steel, concrete quality, accurate form work and compaction of concrete using vibrators and curing.

Typically,these elements are designed by a structural engineer based on the load that is to be carried. These include dead weight, live loads, wind, seismic and dynamic loads.

The different important aspects are the shape, size, orientation, grade of concrete and the amount of steel. With rigorous methods of analysis and design available, the details are prepared keeping the codal provision in view.

Normally, the most optimum and practically viable details are implemented. The challenge before a structural engineer is to optimise the quantity of steel and cement concrete for economical as well as strong columns. The strength of concrete and steel hold the key.

Load bearing walls

Under normal circumstances, buildings up to two storeys can be built with load-bearing walls. But under specific conditions such as weak soil, large spans, etc, pillars are essential even for small structures.

There is also a practice wherein pillars are introduced only at a few critical points where necessary and load bearing walls take care of the rest.

The composite sections such as reinforced masonry or masonry+concrete are also used in specific cases where architecture demands. Another huge advantage is that a well designed pillar system offers is the provision for future additions or alterations.

But for the presence of pillars, my friend could not have converted his two adjacent two bed room flats into one large three bed room luxury apartment!

For anybody in general and design freaks in particular, these elements look monotonous and boring. For a structure, it is essential for strength and stability. Like an unseen and unrecognized skeleton, people prefer it hidden!

But even a small fracture makes a structure shaky and worthless! Whether to provide columns or not depends on architectural design, structural feasibility, site conditions, purpose of construction and its future needs.

For an engineer, the identification of high stress nodal points of a proposed structure and offering a strong, stable and durable structural system that holds the visible system together is interesting.

(The writer is a civil engineer.)

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