RCC Structure : Slabs

by: aayush210789

 A slab is a flat two dimensional planar structural element having thickness small compared to its other two dimensions. It provides a working flat surface or a covering shelter in buildings. It primarily transfer the load by bending in one or two directions. Reinforced concrete slabs are used in floors, roofs and walls of buildings and as the decks of bridges. Slabs may be supported on monolithic concrete beam, steel beams, walls or directly over the columns. Concrete slab behave primarily as flexural members and the design is similar to that of beams. 

IIClassification of Slabs
 Slabs are classified based on many aspects:
  • Based of shape: Square, rectangular, circular and polygonal in shape. 
  • Based on type of support: Slab supported on walls, Slab supported on beams, Slab supported on columns (Flat slabs). 
  • Based on support or boundary condition: Simply supported, Cantilever slab, Overhanging slab, Fixed or Continues slab. 
  • Based on use: Roof slab, Floor slab, Foundation slab, Water tank slab. 
  • Basis of cross section or sectional configuration: Ribbed slab /Grid slab, Solid slab, Filler slab, Folded plate 
  • Basis of spanning directions : One way slab – Spanning in one direction & Two way slab _ Spanning in two direction
IIIMethod of Analysis
The analysis of slabs is extremely complicated because of the influence of number of factors stated above. Thus the exact (close form) solutions are not easily available. The various methods are: 
  • Classical methods – Levy and Naviers solutions(Plate analysis) 
  • Yield line analysis – Used for ultimate /limit analysis 
  • Numerical techniques – Finite element and Finite difference method. 
  • Semi empirical – Prescribed by codes for practical design which uses coefficients. 

IVLoad on slab
The load on slab comprises of Dead load, floor finish and live load. The loads are calculated per unit area (load/m2). 
  • Dead load = D x 25 kN/m2 (Where D is thickness of slab in m) 
  • Floor finish (Assumed as)= 1 to 2 kN/m2 
  •  Live load (Assumed as) = 3 to 5 kN/m2 (depending on the occupancy of the building)