How to calculate bending capacity M for a reinforcement concrete wall?

[Akeee]

Hello guys and thank you for your time,

Can you tell me a book or where to search how the bending moment of a RC wall is calculated ? I only got the capable moment from sotftware like Extract but i want to learn how the program does it ? I know how to calculate for a beam, but a wall..

 

[CELinOttawa]

Just like a beam, but on a chosen strip width. Normally per metre length, or foot in the US and old records.

 

[Akeee]

Yea but i read somewhere that i have to split the section of the wall in number of steps of width "x" calculate the capable moment and sum them, i think. that;s why i asking. and how extract/respons does it ?

 

[KootK]

Are you interested in the in plane (strong axis) or out of plane (weak axis) moment capacity? Your last post makes me think that it might be the latter.

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

 

[KootK]

I mean... the former.

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

 

[Akeee]

I want to calculate reinforcement in this was and then bearing capacity.

 

[Akeee]

http://files.engineering.com/getfile.aspx?folder=28d564d2-4ade-451b-ae08-08da038655c3&file=wall.jpg

 

[KootK]

I think that's in plane although I'm not sure what Q1 is. James MacGregor's book on reinforced concert design has the best examples that I know of. The main difference between this and beam design is the presence of axial load and distributed rebar that may not fully yield. In that, the design more closely resembles concrete column design.

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

 

[CELinOttawa]

Kootk understood you correctly... I would have recommended Park and Paulay, but any good concrete text will give you the step by step approach.

Effectively only your extreme bars will yield, but the whole of the far third will take loop road and play games with your traditional computation. Including the (low end factored - ie: 0.6G or similar) dead load couldn't be simpler - You add in the returning moment as additional capacity.

 

[IDS]

Including the (low end factored - ie: 0.6G or similar) dead load couldn't be simpler - You add in the returning moment as additional capacity.

But the axial load affects the neutral axis position, so how can you just add it in as though it was linear?

For any given neutral axis position and specified ultimate concrete strain you can calculate the force in the concrete and the force in all the bars, taking account of the yield stress.

Find the total reaction force, and adjust the neutral axis position so that the reaction is equal to the applied load, then take moments about the centre of the section.

It is fairly straightforward to set up a spreadsheet to do that, or this blog post has links to a paper with a closed form solution and a spreadsheet that will do the job (for a rectangular section, or any section made up of trapezoidal layers).

Doug Jenkins
Interactive Design Services

http://newtonexcelbach.wordpress.com/

 

[mike20793]

Any concrete design book should have a step by step solution for this problem. For in plane moments, you will need to do what is described above: create an axial load-moment interaction diagram, similar to columns, and plot the actual axial load and moment on the wall.