Required Reinforcement for Mat Foundation

[JoeH78]

Dear All,

In one of design sheets, I've seen that original designer used a below described formula to calculate the reinforcement required for the mat foundation, where M(ULS- kNm) moment and axial (ULS-kN) force exist in section, but nowhere I can see from where that formula is originated, I really will appreciate if someone can point out to me the reference for that formula,

K = M*1000 / (b_w*d²) ; [N/mm²]

w = { 1-(1-2,36*K/fcd) }^1/2/ 1,18 ;

As__required = w*f_cd*b_w*d/ f_yd + N/(2*f_yd/10) ; [ cm² ]

Regards

 

[JedClampett]

I'm getting a little confused because of the units, but it has the look of working stress design. Any concrete reference that's more than 40 years old should explain it. My old 2nd edition Gaylord and Gaylord "Structural Engineering Handbook" goes through it. I think PCA "Design Notes on ACI 318" still has an a chapter on it, but it's a little difficult to get through.
But it's the kind of approach that lends itself to personal instruction rather than book learning. Are there any old timers there that can help you?

 

[KootK]

This looks like a flexural reinforcement method that I've seen where the "w" was something that was looked up from a graph of the function. I imagine that "N" has to do with axial load. The version that I saw was in a concrete text by Kirk & Pilai.

The greatest trick that bond stress ever pulled was convincing the world it didn't exist.

 

[JoeH78]

thank you both for answers,

I just found the design for mat foundation from vulcanhammer.net

http://www.vulcanhammer.net/utc/ence461/s2002/461-sl8.pdf

it refers to something as ENCE 461 which exactly match the A_{s_required}, and having establishing the relations with simple stress-strain relations and extracting the As is quite conceivable.

But the confusing thing is I really don't get whether that ENCE 461 is international standart code or simply stands for acronym of some sort of short courseware for that vulcanhammer company?

Regards,

 

[KootK]

I vote coursework. The document references ACI directly.

The greatest trick that bond stress ever pulled was convincing the world it didn't exist.