Question

In the case of designing a water tank with Limit State Method, to control the cracking, the maximum stress in HYSD steel bars should not exceed:
1. 115 MPa
2. 125 MPa
3. 130 MPa
4. 150 MPa

Answer 1

Correct Answer - Option 3 : 130 MPa

Explanation

As per codal provisions of IS 3370:​

• Part of structure retaining liquid and enclosing space above liquid should be taken under server exposure condition.
• Maximum cement content is 400 kg/m3 to take care of shrinkage effect.
• Minimum cement content is 320 kg/m3.
• Minimum grade of concrete is M30.
• Maximum allowed crack width is 0.2 mm in LSM design.
• To reduce cracking due to temperature, shrinkage and moisture loss at an early stage of concrete, curing should be done for at least 14 days.
• All the structures to be designed shall be designed for both empty and full condition.
• Cracking of concrete can be controlled to some extent by maintaining slope filling rate of 1 m in 24 hours at the first time of filling.

Permissible stress of the material is as follows:

a) Mild Steel - 115 N/mm2 and HYSD bar – 130 N/mm2

b) Concrete

Grade	Direct tension	Bending Tension
M25	1.3 N/mm2	1.8 N/mm2
M30	1.5 N/mm2	2.0 N/mm2

 

• If the thickness is more than 200 mm, the reinforcement is provided in 2 layers, one on each face
• Minimum steel is 0.64% and 0.4% of the surface zone for mild steel and HYSD respectively
• The above percentage values can be reduced to 0.35% and 0.24% for tank with no dimension more than 15 m