SSC JE Civil Engineering 23-Mar-2021 Shift 1 Paper

Concept:
Design bond stress:
● Bond stress is the result of the bonding between the concrete surface and the reinforcement steel.
● It varies depending upon the type of concrete and type of reinforcement used.
● If plane rounded steel is used as reinforcement then the bond stress will be less, if the same concrete is used with HYSD steel as reinforcement then the bond stress is higher.
● The bond between steel and concrete is mainly due to pure adhesive resistance, frictional resistance, and mechanical resistance.
According to IS 456 ∶ 2000, the design bond stress in limit state method for plain bars in tension shall be as below:

Grade of concrete	M20	M25	M30	M35	M40 and above
Design bond stress$\left(\mathrm{N}∕{\mathrm{mm}}^2\right)$	1.2	1.4	1.5	1.7	1.9

Note:
1. For deformed bars conforming to IS 1786, these values shall be increased by 60 percent.
2. For bars in compression. the values of bond stress for bars in tension shall be increased by 25 percent.Calculation:
Design bond stress for deformed bars (conforming to IS 1786) for M20 concrete
= 1.2 × 1.60 = 1.92 N/ ${\mathrm{mm}}^2$