Why are RCC plinth beams required?

Protecting the building starts with the foundation and plinth. In fact, over-protecting also begins here…

Building with nature is often termed as temporary, ridiculed as kutcha (raw) and warned as one that would fall apart if anything small goes wrong.

The typical rural housing made up of small foundations, no good plinth, soft mud walls and thatch roof has led professionals to believe so. If nature is not temporary, the natural building too need not be temporary. If protecting the nature becomes important, protecting the building too becomes important.

Of course, protecting the building starts with the foundation and plinth. Incidentally, over-protecting also begins here!

The plinth needs to be strong, but need not be made up of reinforced cement concrete (RCC) all the time. However, irrespective of the specific contexts, RCC plinths are increasingly being cast in most constructions today.

Normal justification

The normal justification is to strengthen the building, where the owners dare take a stand against it, yet end up paying for it!

If argued against it, the team at site would mention how small an addition it is to the budget; not mentioning that many such small additions finally escalate the overall cost.

Most soil conditions and building loads can be managed with normal 1:2:4 plain concrete (PCC), which is good in taking compression. Steel, specially reinforced, is best to tackle tension, which does not prevail much at the wall bottom.

It’s the sheer wall load that needs to be transferred to the foundation; as such, 4” thick plinth concrete is adequate. As a cost-effective measure, reducing plinth concrete width to the wall thickness, say 9” only instead of it being twice the width at 1’6” is feasible, if appropriate conditions prevail.

Uneven settlement

If so, why are the RCC plinth beams required? In soft and water-logged soils, if the earth settles downwards, the plinth may face uneven settlement.

In RCC frame structure, plinth acts as a tie, as a beam at ground level itself. More recently, after few disasters we have faced, RCC plinth beams are being recommended for their earthquake-resistant properties.  In case of boulder-packed foundation in loose soil, RCC plinth is advised to ensure proper load transfers. It is obvious then that we should not question RCC plinths, but question their wasteful application where not necessary.

Before we start with the wall, at the ground level itself, we need to think about anti-termite treatment, borewell, open well, basement room and such others.

Let us look at their cost and climatic implications next week.


Posted on June 26, 2010, in designs, fundamentals. Bookmark the permalink. Leave a comment.

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