Concrete Column Interaction Diagram, c>d'
Concrete Column Interaction Diagram, c>d'
(OP)
I am designing a concrete column and am trying to calculate the interaction diagrams so I can play with different sizes and amounts of steel and be able to see it visually. I have set up an excel spreasheet to give me values for Mo, Po, Mb, Pb to start my diagram off with.
The problem is not concerning the Blanced Condition, but the condition that solves for where M and P = zero, which follows in the spreadsheet.
The problem is that I end up getting a negative value for f's, which results in a negative value for Cs (boxed in red). I can see that it is caused because my c value is less than my d'.
I was thinking that to solve the problem I would play with my values to get a positive number for f's and Cs, but then I got to wondering whether or not it was necessarily a bad thing that these values came up negative.
I am struggling conceptually. I think that this is saying that the compressive steel is not doing any work and the concrete is taking all of the compressive force.
Can someone please help shed some light on whether or not this is a bad thing, and what excatly is going on conceptually here?
The problem is not concerning the Blanced Condition, but the condition that solves for where M and P = zero, which follows in the spreadsheet.
The problem is that I end up getting a negative value for f's, which results in a negative value for Cs (boxed in red). I can see that it is caused because my c value is less than my d'.
I was thinking that to solve the problem I would play with my values to get a positive number for f's and Cs, but then I got to wondering whether or not it was necessarily a bad thing that these values came up negative.
I am struggling conceptually. I think that this is saying that the compressive steel is not doing any work and the concrete is taking all of the compressive force.
Can someone please help shed some light on whether or not this is a bad thing, and what excatly is going on conceptually here?






RE: Concrete Column Interaction Diagram, c>d'
Treat as a beam with two layers of steel.
RE: Concrete Column Interaction Diagram, c>d'
For Concrete:
RECTBEAM (318-05)_Ver1.2.xls -- Based on ACI 318-05
RECTBEAM_Ver3.2.xls -- Based on ACI 318-99
For either of these used the Uniaxial or Biaxial Tabs to get the Interaction Diagrams.
For Masonry:
Axial_and_Flexure.xls
This is a spreadsheet my Masonry professor gave us to use when I was getting my Master. Use the Allow Stress Interaction or Strength Interaction Tabs. Note: using the Strength Interaction Tab with em=0.003 and fm=f'c will give you a semi-close approximation of the interaction diagram for concrete.
Hope these help.
RE: Concrete Column Interaction Diagram, c>d'
RE: Concrete Column Interaction Diagram, c>d'
Quite curiously, as in the 2 previous cases, these unusual outcomes of analysis seem to have actual counterpart in the physical behaviour of what analyzed; other well known case is that, even when we lay our rebar at the bottom for simply supported beams "to gain mechanical arm" beams having the same amount of steel distributed in the side faces are shown in some cases to attain the same moment strength and superior ductilty (the service level behaviour maybe likely not being as good).
RE: Concrete Column Interaction Diagram, c>d'
Spanky7 - thank you. I will take a look at these.
RE: Concrete Column Interaction Diagram, c>d'
I would use two d's for the case you mentioned one to the top steel and one to the bottom steel.
RE: Concrete Column Interaction Diagram, c>d'
RE: Concrete Column Interaction Diagram, c>d'
RE: Concrete Column Interaction Diagram, c>d'
RE: Concrete Column Interaction Diagram, c>d'
Part 1
RE: Concrete Column Interaction Diagram, c>d'
RE: Concrete Column Interaction Diagram, c>d'
RE: Concrete Column Interaction Diagram, c>d'
It will give you an interaction diagram for a circular column. However, I have never tried to verify the result by hand so use at your own risk.
RE: Concrete Column Interaction Diagram, c>d'
RE: Concrete Column Interaction Diagram, c>d'
Doug Jenkins
Interactive Design Services
http://newtonexcelbach.wordpress.com/
RE: Concrete Column Interaction Diagram, c>d'
The first question is that I was making a quite wild variety of sectional analysis worksheets, and between then not only those providing the ultimate strength of the section in compatibility of deformations, but also those that show the status of the section under some solicitation, different concrete stress-strains laws etc. It surely was for these that the referred case was found.
I found the issue quite casually whilst doing work in sectional analysis in the Mathcad worksheets (I spent around 2 years making almost exclusively the Mathcad worksheets, sectional analysis and other) it may be difficult for me to duplicate the then observed issue, and give a proper comment.
How it was produced is not, for in establishing equilibrium I was establishing guess values, say, of the depth of the neutral axis. You can start with a guess higher or lower in the section and then such input for the referred cases provided two different solutions, both of which satisfied equilibrium, and showed nothing that made them physically improper.
Maybe it was a case where tension in the concrete was taken into account. Then you have that till the cracking moment the neutral axis is at some height, then the crack develops and snaps to other position. Depending of your guess you find one or another; or you may find such thing as a result of considering or not tension in the concrete (pears with apples). If this was the case it would be only that I met the cracking moment in casual way, for intently was not, a situation where two neutral axis' depths were involved and different steel and concrete stresses develop, but I can't attest if such was the case, for I do not remember the thing as cracking moment related, only that I found the thing not be a problem from the viewpoint of reliability for use of the worksheet, since I found acceptable (to me) explanation to the alternative equilibriums presented.
RE: Concrete Column Interaction Diagram, c>d'
RE: Concrete Column Interaction Diagram, c>d'
For an ultimate load analysis ignoring concrete tension and with a rectangular or parabolic/rectangular concrete stress block there should be only one NA position for any given axial load.
Doug Jenkins
Interactive Design Services
http://newtonexcelbach.wordpress.com/
RE: Concrete Column Interaction Diagram, c>d'