DESIGN ASSUMPTIONS FOR THE BEAMS AND THE SLABS SPANNING IN ONE DIRECTION.

DESIGN REQUIREMENTS :-- Concrete is strong in compression and very weak in tension .Its tensile strength ie modulus of rupture is only a fraction of its compressive strength.If a plain concrete beam is loaded , it will fail when the stress on tension side reaches the tensile strength of concrete.The stress on compression side will be much less than the strength of concrete in compression .To make maximum use of strength of concrete, steel reinforcement is used to take up tensile stresses in reinforced concrete beams.In the case of slabs the depth is small as compared to its length and breadth.The simplest form of the slab is on two support and are designed on the assumption that they consist of number of strips of span land breadth one metre though in practice the slab is cast in one piece and it is not composed of the separate strips.The strip can be analysed by the same formulae which are used for the design of the rectangular beams.The bending moments are calculated for a width of a one metre .The load per square metre of the slab will be load per metre run of the assumed beam having width one metre and span l .As the slab spans between two supports the bars in the direction of span are said to be the main and the bars to the direction at right angles to the span are called distribution steel.All slabs must have transverse steel to assist in distribution of stresses.These stresses are caused by the superimposed loading, temperature changes and shrinkage during drying process .As the distribution steel is wired to main steel it keeps main steel in position during the pouring of the wet concrete into the form work.