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PRECAST LINTELS

It has been attempted in the past and the recent endeavour by an architect in Mysuru has further improved the earlier ideas.

28bgp-greensens_26_2637392eWe are now living in an age of innovation where the old order is continuously being replaced by the new. Should this sound like a great time, let us remind ourselves the fact that such an age will also be a time of both gains and losses. Large number of time-tested ideas like courtyards and hot air ventilation are rarely found today, despite them being valid even now. However, there is hope in many other items of works, which are still popular, despite being practised in an improvised version.

In many ways, improvisation is also a part of innovation, yet by retaining the original at a conceptual mode, we see our past flowing into the present. The change is more gradual when we effect better finished and more efficiently managed products and services. Many such improvisations happen during construction at site mostly thought out by the project team; as such do not get documented for wider dissemination. Lack of professional efforts to collate the best practices within us compounds this lacuna, hence the potential to upgrade our methods and skill sets gets largely lost.

Lintels can be a good case to illustrate. In the past, the support above any opening like a door, called as lintel, was achieved by stone, wood, door frame itself or totally avoided by having an arch. With RCC lintels being the order of the day even in small villages now, it is time to relook at it.

Options

One option is to revive the past with stone lintels and another could be to avoid them except where needed absolutely, choosing to do cut lintels. In many cases due to site conditions or earthquake considerations, we may need them to run all around the walls at 7 ft. height.

roviding the necessary shuttering, casting, curing and de-shuttering means slowing down the project; letting cement water flow down defacing the wall below and face tricky situations in some cases on the external side of the wall. If the lintel could be precast on ground to be placed on wall top, the task gets much easier.

Each piece has to be cast to the exact wall length needed; junctions between two pieces has be resolved to provide continuity; placement of all the pieces needs to be secure and aligned.

What if we can go one step further in improvising the idea? Let us pre-cast the U-shaped lintel channels on ground, cut them to fit wall lengths, lift and place them on wall tops securely with rich mortar base.

The channel itself acts like the lintel; hence reinforcement rods can be considered only where required. Once the channels are filled with the required mortar mix and cured, further wall work can resume without much delay.

Pre-casting the lintel has been attempted in the past and the recent attempts by architect Rajesh Jain in Mysuru has improved the earlier ideas. There will be further scope too, as long as we wish to better a product.

Lintels and ‘overdesigning’

How to minimise the design to save money and materials?

lintelHow often do we try discussing with the elderly people at home about getting a building done? The general experience is about the difficulties in forging a dialogue, due to differing construction practices from their time to our contexts. We feel there are advances made in these years and many of them feel we are wasting money by ‘over-designing.’

One simple example could be the case of lintels, which are the horizontal monolith members above any opening to support the wall above doors and windows. In the past, these could be with wood or stone, but often we notice there were no members at all – the wall sits directly on the wood frame! The frame takes the load, so why lintels?

Traditionally, carpenters would prepare the door and window frames in advance, before the walls start, such that the requisite seasoning of the wood is complete. As the mason builds the walls, these frames are placed in the centre of wall thickness and the wall continues without any extra lintel member. Even today, we can see such houses standing for centuries. If so, why are we adding the lintel beam, that too in thick and strong concrete?

Horizontal rigidity

Lintels help in tying the building laterally and if continuously placed around all the walls provide a horizontal rigidity to the building, which is a compulsory measure in earthquake-prone zones. However, do we need them all the time in all kinds of buildings, including small houses, in places like Bangalore with least risk of earthquakes? Even expert answers may differ, but reducing the lintels as per context and upon structural engineer’s advice is possible. Every concrete lintels need support by shuttering, time for bar bending and concreting, curing with water and such others, demanding time, money and materials. Can we save on this, even if it’s partly?

Once the walls have reached the lintel level, we can place a wood plank as support, place two M.S. reinforcement rods of required diameter across the opening, pour nominal thin screed concrete, place the bricks vertically with the central three bricks forming a wedge narrowing downwards.

This method uses two concepts – that of reinforced brick beam in terms of steel and principles of flat arch in the brick work. On the top of this flat masonry, two more rods can be placed if heavy loading is expected. For opening up to 5 feet wide, this method can be applied with specifications as advised by engineers. As one sees, there are no concrete beams, delay due to formwork or curing and such others.

Today we design with very high factor of safety, a precautionary approach where nothing may go wrong.  Understandably, this method very often leads to over designing, as the example of lintels may prove. We can think appropriately, minimise the design to save money and materials. To that end, all the three stakeholders, namely the designers, owners and builders, should think alike towards a cost-effective and eco-friendly building.