Unreinforced Concrete Section Analysis 1

[Aytacoglu]

Hi Everyone,

I am currently trying to analyse a section which is unreinforced concrete. I have attached below a sketch of the thing I am trying to analyse.

I am not sure how to go with this. I've got a load at the top which will create a bending moment at the interface of the section, which I need to check whether it is sufficient to take the load. I am not sure what strength value to use for the concrete to do this check (maybe 8 N/mm2 bending strength?). I calculate the bending moment due to the self weight of concrete and the live load from above, but I need to compare with strength.

Can someone please help me to show how I can check this?

Many Thanks!

 

[BAretired]

You don't dimension the vertical column, which carries the greatest moment. And you don't show the thickness of the entire shape. But most of all, the building code does not permit plain concrete to be used in a structure such as this.

I suggest you omit the jog (saves form work) and reinforce the column and the horizontal cantilever for a moment of 5/2 (900+b/2)^2 N-mm.

 

[GeorgeTheCivilEngineer]

Presumably it's an assessment rather than a design.

12.3.1(2) of Eurocode 2... But basically don't do it. Plain concrete has a brittle failure mode and even if what it is resisting is unimportant, you don't want a lump of concrete snapping off and failing. The only uses should be in foundations, slabs and walls.

 

[BAretired]

You don't dimension the vertical column, which carries the greatest moment. And you don't show the thickness of the entire shape. But most of all, the building code does not permit plain concrete to be used in a structure such as this.

I suggest you omit the jog (saves form work) and reinforce the column and the horizontal cantilever for a moment of 5/2 (900+b/2)^2 N-mm.

The concrete strength value will certainly be greater than 8MPa...that would be ridiculously low. I recommend 30MPa as a minimum.

 

[dik]

Can you do a P/A and M/S to see what the level of stress is? For plain concrete, the stresses have to be very low and regular elastic analysis is generally OK.

 

[Aytacoglu]

Thank you for your responses. Apologies for not being more clearer on this. This is for an assessment of an existing structure. Currently we do not have any archive information or any surveys so I just wanted to do a quick check for the section assuming it to be plain concrete (worst case), where if it passes than for sure the section will pass. As there are some rebars inside that section for sure.

 

[BAretired]

Your approach to date has been disingenuous, to say the least.

 

[KootK]

Sure, do some P/A & M/Sx stuff as Dick suggested using whatever your code directs you to use for the tensile strength of concrete as your allowable stress.