Inconsistent Formulae for Required Steel in BS8110 based textbooks 2

[nicolas77]

Hi,

I have note that to calculate required steel according to BS 8110-1:1997 we used the formula As = M / 0.95 fy z, This is followed by J. B. Higgins, B. R. Rogers, Design and Detail (BS 8110:1997), p. 8 and W.M.C.McKenzie, Design of Structural Elements, Third Edition, p. 235 among other.

However we find the formula As - M / 0.87 fy z even As - M / 0.87 fy 0.8d in other book.

I will be most grateful to get some clarification as I am studying this in calculating steel required in the context of a two-way restrained solid slab.

 

[Bogusbogedi]

It all depends on the limitations of the stress block diagram and how it was derived.
Look at the following link for more guidance

https://jonochshorn.com/structuralelements/book/5.07-beams.html

 

[nicolas77]

Thank you. I will go through it. So far I found that it is based on different factors of safety that has evolved with time through the different version of the BS8110 code and perhaps with EN code mingling with it. The reciprocals of those safety factors accounts for the different constant 0.87 and 0.95 in the steel required.

 

[Bogusbogedi]

@nicola77 you are right, I got confused with the derivations, check out mosley pg 58. The most plausible answer i could search for