PM interaction diagram (concrete) 3

[envc77]

When checking a flexure and axial member, how to find out the safety of the member?

Often drawing PM interaction diagram ?
Or simply checking the equation of the safety ?

When you draw the PM interaction diagram , using the software or spread sheet ?

And tell me the software's name ( commercial or free)

 

[dik]

I use an excel spreadsheet that calculates the max P value without M, the balanced condition for P and M and the maximum M value. All of this is for a given bar arrangement.

I calculate the max P value allowed and then draw a series of lines through these 4 points. This is my interaction diagram. I then check loading conditions against this interaction diagram and hopefully all points fall within.

If not, then I change the bar arrangement. The spreadsheet then calculates maximum stirrup spacing and my standard details take care of the tie arrangement and spacing at the top and bottom. If shear is an issue, I do it by hand; I haven't had a chance to modify the spreadsheet to do this.

 

[dgkhan]

you mind giving me this spread sheet

 

[Lion06]

If you don't have access to a program like PCACOL, I would just construct an interaction diagram by hand. It's really pretty simple to do. I use the following points on the diagram:
Pure Axial Load, Decompression (where one face has 0 strain), Balanced Point (compression controlled point), Tension Controlled Point, and Pure Moment.
It is important to note that the phi factor will be the same for moment and axial depending on the strain in the steel.

 

[frv]

Plotting these three points will certainly work, but keep in mind that it's fairly conservative.

StructuralEIT, I believe this is what you meant, but it wasn't clear to me: at any given P,M point on the curve, there is only one phi factor which will be applied to both axial and flexural capacity, and which depends entirely on the strain in the extreme layer of steel (this is correct)

 

[csd72]

http://www.cement.org/buildings/Timesaving-Columns-IA.pdf

 

[csd72]

Also:

http://www.ce-ref.com/short_col.htm

http://www.strunet.com/concrete_column/ccol03.html

 

[JrStructuralEng]

ya dik, send that spreadsheet my way!

 

[southard2]

Florida Department of Transportation has a really good biaxial column analysis program. You can build arbitrary shapes, rectangular, square etc quickly and easily. Than enter your load case points and a MathCad spreadsheet will produce a 3D biaxial column. You can view the orbits or the PM diagrams. Really easy to use. The only draw back is that you must be using a short column. Moment amplification is not done for you.

http://www.dot.state.fl.us/Structures/proglib.htm

 

[Canderson]

dik-Can I get a copy of the spreadsheet you use for developing the points on the MP diagram?