Why is the main reinforcement provided on the longer side of raft footing?
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Why is the main reinforcement provided on the longer side of raft footing?
aviratdhodare
The raft foundation is designed as a flat slab and reinforcement is to be provided in both the directions. The total moment in each direction is equal to w(lx)*(ly)*(ln)/8, where lx and ly are the lengths in x & y-direction and ln is the direction in which the moment is being calculated. This moment is further divided between the column and middle strip and then between positive and negative moments.
Based on this formula, there will be a greater moment in the direction where ln is maximum (larger dimension). To economize, reinforcement in longer direction is provided in the outermost layer as this will give maximum depth.
To state that main reinforcement is provided in a longer direction is wrong— in both directions, main reinforcement is provided.
Kuldeep Singh
You mean to say longer span. The main reinforcement is provided on the longer span because the longest span is in a more critical situation and has to bear a higher bending moment. This is because the uplift pressure from the soil below will be equal in all locations, but the moment developed at the longer span will be higher because of a long arm. It’s a uniformly distributed load, and so it produces a larger moment on a longer beam. Hence, the main reinforcement is put in a longer span.
Komal Bhandakkar
The main reinforcement should be provided on a longer span because of the following reason:
Thank You.
nikeetasharma
The longest span is in more critical section due to which main reinforcement is provided on the longer span. The longest span has to bear a higher bending moment. This is because the uplift pressure from the soil below will be equal in all locations, but the moment developed at the longer span will be higher because of a long arm. Its a uniformly distributed load and so it produces a larger moment on a longer beam. Thus, the main reinforcement is provided in longer span.