Concrete is very weak in tension, and direct tensile strength is only about 8 to 11% of the compressive strength for concrete of grade M25 and above. The use of pozzolanic materials increases the tensile strength of the materials. The strength of concrete is generally not taken into account during design of concrete elements. Knowledge of its values is required when designing for transverse shear, torsion and shrinkage and temperature effects. It is also used in the design process of prestressed concrete structures, liquid retaining structures, roadways and runway slabs.
Direct tensile strength of concrete is difficult to determine. The splitting tensile test on 150mm x 300mm cylinders is often used to find the tensile strength.
The theoretical maximum flexural tensile stresses occurring in the extreme fibres of RC beams, which causes cracking is known as modulus of rupture, fcr.
fcr = 0.7√fck
Shear strength: A combination of flexural and shear stresses exists resulting in a diagonal tension failure. The design shear strength of concrete is given in Table 19 of IS 456, the same has been given below. The maximum shear stress in concrete with shear reinforcement is restricted in Clause 40.2.3, which is given by τc,max = 0.63*√fck.