In flat slab system, say that the total length is 48m x 24m, column with drop panel with spacing of 6m... In this case , main bar outermost top bar (T1) and outermost bottom bar (B1) should be parallel to the 24m , right?

I came across an example that main bar T1 & B1 is parallel to 48m... Which one is correct ?

Or it doesnt matter that whether mian bar is parallel to shorter / longer dimension of the overall flat slab system ?

  • $\begingroup$ You are correct if there is no other complications. $\endgroup$
    – r13
    Commented Feb 13, 2023 at 16:38

1 Answer 1


The direction of the main bars (T1 and B1) in a flat slab system depends on various design factors such as the span length, load distribution, structural efficiency, and code requirements.

In general, the main bars are usually placed parallel to the shorter dimension of the slab to reduce the slab's overall span length and provide better structural efficiency. This is because longer spans tend to produce higher bending moments, which can increase the size and number of reinforcement bars required to resist the loads.

However, there may be cases where the main bars are placed parallel to the longer dimension of the slab due to specific design requirements or to minimize the number of drop panels. In these cases, the design must account for the increased span length and ensure that the slab is adequately reinforced to resist the loads.

In summary, the direction of the main bars in a flat slab system depends on the specific design requirements and considerations, and it can be parallel to either the shorter or the longer dimension of the slab.


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