Dimensioning concrete beams

[JohanCh]

Hello.

I have been searching and looking for information on the sizing of concrete beams. I am designing a somewhat larger deck, and since I need to get up a bit and live in a stone house, I thought it could be a fun project to cast my own footings and beams.

I would like to make a couple of beams with a span of 3500mm. I got the recommendation that if I make it 230*60 with 2*10mm reinforcement at the top and bottom, about 30mm from the outer edges, it will hold.

But I would like to understand more about how this is actually calculated. Does anyone have tips on where to find information about this?

Best regards, Johan Ch

 

[calzonespecial]

Hello.

I have searched and looked for information about the sizing of concrete beams. I am designing a slightly larger patio, and since I need to elevate it and live in a stone house, I thought it could be a fun project to cast my own pillars and beams.

I would like to make a couple of beams with a span of 3500mm. I received the recommendation that if I make it 230*60 with 2*10mm reinforcement at the top and bottom, about 30mm from the outer edges, it will hold.

But I would like to understand more about how to actually calculate this. Does anyone have tips on where to find information about this?

Best regards, Johan Ch

Hi,

I can't calculate concrete very well, but you should be able to do an overlay on the bending by thinking that the reinforcement takes the moment, i.e. It's on the safe side since the concrete itself can take some of at least the compression at the bottom.

Mmax = 2*Aarm*fyd*(230mm - 2*30mm) = ... Nm

and compare it with the moment you have, e.g., M = 1.35*g*L^2/8 (distributed load, like the self-weight of the beam and other loads you apply)

Since you have a slender cross-section (h / b = large), you should consider lateral stability. Someone knowledgeable can surely help you with that.

 

[fsn]

Hello,

I can't calculate concrete that well but you should be able to overlay the bending by thinking that the reinforcement takes the moment, i.e., it will be on the safe side since the concrete itself can take part of at least the compression on the underside.

Mmax = 2*Aarm*fyd*(230mm - 2*30mm) = ... Nm

and compare it with the moment you have, e.g. M = 1.35*g*L^2/8 (distributed load, such as the self-weight of the beam and other things you load on)

Since you have a slender cross-section (h / b = large) you should consider lateral stability. Someone knowledgeable can surely help you with that.

It is rather tension on the underside, i.e. the reinforcement (which I believe is under-dimensioned) and compression on the top side.

 

[calzonespecial]

It's tension rather than compression at the bottom, i.e., the reinforcement (which I believe is undersized) and compression at the top.

Exactly right I got it mixed up.