By:Ar. Vikas Kumar Nirmal

A Reinforced Concrete Slab is the one of the most important component in a building. It is a structural element of modern buildings. Slabs are supported onColumnsandBeams.RCC Slabs whose thickness ranges from 10 to 50 centimetres are most often used for the construction of floors and ceilings.Thin concrete slabs are also used for exterior paving purpose.

Construction ProcessA concrete slab can be cast in two ways: It could either be prefabricated or cast in situ.Prefabricated concrete slabsare cast in a factory and then transported to the site ready to be lowered into place between steel or concrete beams.They may be pre-stressed (in the factory), post-stressed (on site), or unstressed. Care should be taken to see that the supporting structure is built to the correct dimensions to avoid trouble with the fitting of slabs over the supporting structure.In situ concrete slabsare built on the building site using formwork. Formwork is a box-like setup in which concrete is poured for the construction of slabs.For reinforced concrete slabs, reinforcing steel bars are placed within the formwork and then the concrete is poured.Plastic tipped metal, or plastic bar chairs are used to hold the reinforcing steel bars away from the bottom and sides of the form-work, so that when the concrete sets it completely envelops the reinforcement.

Types of SlabsFlat Slab: A flat slab is a one-way or two-way system with thickenings in the slab at the columns and load bearing walls called drop panelsAdvantages:Simple formworkNo beamsMinimum structural depthDoesnt require shear reinforcement

Disadvantages:Medium spansGenerally not suitable for supporting brittle (masonry) partitionsDrop panels may interfere with larger mechanical ductingVertical penetrationsneed to avoid area around columnsFor reinforced flat slabs, deflection at the middle strip may be critical.

Types of SlabsRibbed and waffle slabsRibbed and waffle slabs provide a lighter and stiffer slab than an equivalent flat slab, reducing the extend of foundations. They provide a very good form where slab vibration is an issue, such as laboratories and hospitals.BenefitsFlexibleRelatively light, therefore less foundation costs and longer spans are economic speed of constructionFairly slim floor depthsRobustnessExcellent vibration controlThermal massGood for services integrationDurable finishesFire resistance

Types of SlabsCorrugated, usually where the concrete is poured into a corrugated steel tray. This improves strength and prevents the slab bending under its own weight. The corrugations run across the short dimension, from side to side.

Reinforcement Design in SlabsAone way slabhas structural strength in shortest direction.Main reinforcement should be along slabs short direction.Atwo way slabhas structural strength in two directions.Main reinforcement runs both in short and long direction and stay perpendicularly with one another.