Minimum Reinforcement Ratio of Block Foundation (EN 1992-1-1, 7.3.2 & 9.2.1.1)

[Gnoowij]

Dear alls

Regarding the eurocode EN 1992-1-1, Minimum reinforcement ratio is given with eq 7.1, cl 7.3.2 and eq 9.1N, cl 9.2

As,min x σs = kc x k x fct,eff x Act (7.1)

As,min = 0.26 x fctm/fyk x bt x d (9.1N)

1. There is no tension force on the block foundation. (Such a small weigh is loadded on the block foundation (5m x 4m x D 1.5m)
2. If there is a tension force, there would be stress by 'Shirnkage and Temperature' on the surface.
3. All(most of) the foundations should be concerned in terms of Shrinkage and Temperature. If so, it should follow As,min from (7.1) always.
4. If it follows 7.1 to calculate minimum reinforcement ratio, it always would be higher than the result from calculating with 9.1N. (like two times)

According to the explanation on cl 7.3.2 (2), it says that

'Unless a more rigorous calculation shows lesser areas to be adequate, the required minimum areas of reinforcement may be calculated as follows. In profiled cross sections like T-beams and box girders, minimum reinforcement should be determined for the individual parts of the section (webs, flanges).'

I don't usally calculate the stress due to shrinkage and Temperature to design a foundation since I normally follow the As,min described on 9.1N. And I'm not sure that 7.3.4 (Calculation of crack widths) can be used for the stress by Shrinkage and Temperature.
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FYI, the stress by Shrinkage + Temperature would be as the following
ε = 0.0005 (0.00025 + 0.00025)
Ec = 10000MPa
σ = 5MPa (> fctm (=2.9Mpa, C30)) -> so the crack occurs

Crack by Shrinkage and Temperature would occur at the most of foundations.
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Which case or situation should I use eq 7.1? or should I consider eq 7.1 and 9.1N to calculate the minimum reinforcement ratio?

 

[GeorgeTheCivilEngineer]

Those provisions don't relate to foundations. Have you considered Section 12 in the eurocode?

 

[Gnoowij]

Rep to GeorgeTheCivilEnineer
Thank you for your reply.

However, the small pump (ingnorable dynamic load exist) is laid on the foundation. Regardless of whether the dynamic load is large or small, if there is dynamic load, chapter 12 cannot be concerned.
(I might have mentioned on the question, sorry)

I don't understand that cl 7.3 is not related to foundation.

When we design foundation, we treat as a Beam to design. (That's why I followed minimum reinforcement ratio given in cl. 9.2.

Accoring to the cl.9.2, Eurocode gives minimum reinforcement ratio, but there is also saying that 'see the cl 7.3.2 if crack control is required.'

What sort of situation could be without controlling crack as designing Foundaiton.