flexural rigidity of a composite section 1

[HanStrulo]

Good morning,

Could you advise me on how to calculate the flexural rigidity of the following section?

I usually use the stiffness of the steel I beam alone but my deflections are really high and i was wondering if i could make use of of the concrete too.

diameter of the circles is 1m and the concrete fc=7MPa. The I beam is W610.

Thanks alot.

 

[JoshPlumSE]

What are you using this for? A secant wall?

 

[HanStrulo]

yes. trying to reduce the settlement without increasing the W section.

 

[Agent666]

Is the concrete reinforced?

https://engineervsheep.com

 

[HanStrulo]

No. just lean mix concrete.

 

[centondollar]

I assume that the cantilever length of these secant wall "mini-columns" is large, and that bending moment is thus large. How do you expect those unreinforced concrete columns to resist any bending at all? My spontaneous first thought is that they will crack immediately throughout the entire section (assuming that they are analyzed locally as an overhanging beam with soil pressure, and not as some sort of "ring-diaphragm") and provide only very little - if any - stiffness.

 

[mikealpha88]

For deflection you will need moment of inertia for the steel including reinforcement and concrete. Usually for composite structure steel Ix will be dominant.

 

[HanStrulo]

@ centondollar

Thanks for the insight.

I am trying to manually verify that the max moment on the concrete will not induce any cracking. i do it usually by considering a 1 m width beam from the interlock of the concrete only piles and apply max earth pressure and the beam formulas to get the stress on the extreme fibres and then just make sure it's less than the fc of the concrete.

 

[jayrod12]

If you want no cracking, you'd want to ensure that the extreme fibre stress doesn't exceed the modulus of rupture fr. Which would be a borderline impossible task while still keeping things economical.

 

[BAretired]

It seems to me that bond stress would be an important factor to consider. If the bond strength is gone, the section is no longer composite.

BA