Two-way Slab Design - Column Strip vs Band width

[fracture_point]

Hi,

I have some confusion regarding the strip method that is used and general convention that is used within my company.

The company uses finite element analysis to determine forces with column strips defined as L/4 of the minimum bay dimension to average the moment over and design the steel for. Within this column strip, it is required that a certain amount of the steel must be concentrated within a 'band width' of H_slab/2 from the column face.

I want to understand better why it is required to keep a certain amount of steel within this width if we are already defining a column strip of L/4, but can't find it directly referred to in any books. Does anyone have an explanation or can anyone provide a book recommendation?

Thanks

 

[JAE]

Look at ACI 318-11 section 13.5.3



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[JAE]

For ACI 318-14 it is 8.4.2.3


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[Retrograde]

If you look at the moment plot from your FE software you will see that the moment is concentrated over the columns. That is why the code wants you to concentrate the reinforcement over the column otherwise you can get excess cracking.

 

[fracture_point]

Thanks JAE and Retrogade.

Section 13.5 cleared it up perfectly, and tying this in with page 436 in Nilson's 15th edition of concrete design explained the theory behind this design requirement!

Cheers