IS 456 is the Indian Standard Code of Practice for the design of reinforced concrete structures. It outlines the requirements for the cover of concrete in reinforced concrete structures. Cover refers to the distance between the surface of the reinforcement and the outer surface of the concrete. The cover requirements are specified to ensure that the reinforcement is adequately protected from the surrounding environment and is not exposed to the elements. In this blog post, we will discuss the cover requirements as per IS 456.
Nominal cover is the design depth of concrete cover to all steel reinforcements, including links.
General Requirements
The general requirements for cover are specified in Clause 26 of IS 456. It states that the nominal cover to the reinforcement should not be less than the following:
a. For mild exposure conditions: 20 mm
b. For moderate exposure conditions: 30 mm
c. For severe exposure conditions: 45 mm
The exposure conditions refer to the type of environment the structure will be exposed to, such as atmospheric, marine, or chemical exposure.
Cover for Reinforcement in Tension
The cover requirements for reinforcement in tension are specified in Clause 26.4.1 of IS 456. The nominal cover for reinforcement in tension should not be less than the following:
a. For mild exposure conditions: diameter of the bar or 15 mm, whichever is greater
b. For moderate exposure conditions: diameter of the bar or 30 mm, whichever is greater
c. For severe exposure conditions: diameter of the bar or 45 mm, whichever is greater
Cover for Reinforcement in Compression
The cover requirements for reinforcement in compression are specified in Clause 26.4.2 of IS 456. The nominal cover for reinforcement in compression should not be less than the following:
a. For mild exposure conditions: diameter of the bar or 40 mm, whichever is greater
b. For moderate exposure conditions: diameter of the bar or 40 mm, whichever is greater
c. For severe exposure conditions: diameter of the bar or 40 mm, whichever is greater
Cover for Different Types of Structures
The cover requirements for different types of structures are specified in Clause 26.4 of IS 456. The following are the cover requirements for different types of structures:
a. Footings and Rafts: The nominal cover for footings and rafts should not be less than 50 mm or the diameter of the bar, whichever is greater.
b. Beams, Slabs, and Walls: The nominal cover for beams, slabs, and walls should not be less than 20 mm.
c. Columns: The nominal cover for columns should not be less than 40 mm or the diameter of the bar, whichever is greater.
Tolerance
The tolerance for cover is specified in Table 16 of IS 456. The cover should not vary from the nominal cover by more than 10mm positive side only. No negative tolerance is allowed.
Cover is an essential component of reinforced concrete structures and the cover requirements as per IS 456 ensure that the reinforcement is adequately protected from the surrounding environment. The cover requirements vary based on the exposure conditions, the type of structure, and the type of reinforcement.
It is important to ensure that the cover requirements are followed during the design and construction of reinforced concrete structures. In addition, it is important to ensure that the tolerances for cover are also followed to prevent any deviations from the nominal cover.
Special cases may arise where the cover requirements may be different from the general requirements, and it is important to account for these cases during the design and construction process.
Following the cover requirements as per IS 456 is crucial to ensuring the longevity and durability of reinforced concrete structures. By ensuring that the reinforcement is adequately protected, the risk of corrosion and other types of damage can be minimized, ultimately leading to safer and more resilient structures.
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