Final answer:
The minimum recommended grade of structural concrete for a 20-meter high building in Seismic Zone V according to IS 13920:2016 is M25. This ensures the structure can withstand the higher seismic forces expected in this zone.
Step-by-step explanation:
According to IS 13920:2016, which deals with the ductile detailing of reinforced concrete structures subject to seismic forces, the grade of concrete is an important consideration. For a 20-meter high building located in Seismic Zone V, which faces the highest level of seismicity in India, the standard recommends a higher grade of concrete due to the expected seismic forces.
The minimum grade of structural concrete recommended for this scenario is M25.
It's important to note the significance of using the proper grade of concrete. Concrete has a high ultimate compressive strength, which means it can withstand significant vertical forces without failing. However, its ultimate shear strength is comparatively lower, which is why a higher grade is required in areas with high seismic activity to prevent failure due to shearing forces.
Calculating Thermal Stress
When calculating thermal stress on concrete blocks, the temperature difference between the time of laying the blocks and the expected maximum temperature is considered. Using the formula for thermal stress, σ = Α * E * ΔT, where σ is the stress, Α is the coefficient of thermal expansion (approximately 12 x 10⁻⁶ / °C for concrete), E is the Young's modulus of elasticity, and ΔT is the temperature change, we can assess the stress on a hot day when the temperature increases to 38 °C from the initial 5 °C.