Understanding RCC – structural footing drawings
The mat is lifted off the ground by placing small concrete cover blocks or big jalli stones. This is to ensure that concrete when poured in fully surrounds the mat. A minimum of 1 inch lift is recommended. This prevents the rebars from being exposed to outside and rust in the open. So concrete should fully cover the mat. [Cover blocks: cover refers to the concrete that covers a reinforcement steel. A minimum of 1 inch cover is required for all RCC structures to full cover the steel from getting exposed to air and outside conditions. This is ensured using a cover block which lifts the mat from ground by few inches depending on size of the cover block]
Notice how the mat is bent upward towards the edges of the mat. This allows a firmer grip into the poured concrete of around 1 to 2 feet.
It is important that all intersections of the mat rebars is bound using steel binding wires. This holds the mat rebars in place when pouring concrete and also adds to strength. [ binding wire is to be procured from the same steel supplier – tata steel/jindal/ or any other good brand suitable for your geographic area/seismic zone]
The column rebars emanate from the mat. Notice the column overlap onto the mat in L shape. This is normally captured in the structural drawing. It is around 1.5 to 2 feet. In effect the footing acts as a strong hold for the RCC column structure.
It is a normal practice that sometimes an anti-termite solution is poured around it and allowed to soak into the walls of this dig up.
Concrete of nearly 1.5 to 2 feet depth is poured into these footings depending on the load the column takes. A vibrator is a must to ensure that the concrete compaction is achieved and there are no air bubbles.
Next day after concrete is poured in ensure that sufficient water is covered on the mat for curing. Curing is a very important step and only curing ensures the concrete achieves the desired strength. Do not underestimate the importance of curing.
Hope the information presented clears some aspects. Here is a more complete list of articles. Do read about them
- Understanding RCC – structural RCC columns
- Understanding RCC – structural Beam aspects
- Understanding RCC – Reinforcement steel bar or rebar
hi there,
please could you show me picture of how they ensure all rebars are placed all in lone for example do do you use string line
Manythanks
Yes, the verticality of column is ensured using plumb line or string line. I would at night time use laser lines to cross verify. Please check laser line level article. Hope this answers the query.
If you are referring to how the 8 rebars that are tied as column, the column is built horizontally on the road. Rods are straightened, cut into equal lengths. Now the rods are placed into the box shaped binding rebar(ring). Now rods are tied to the inside of the rings using binding wires all while still on the ground. Once the entire column is ready it’s erected on the mat .