Civil Engineering Association

dear all,
I'm facing a problem about this....
what are curve n angel means about???
can somebody explain??

best regards,

In ETABS the PM curve is generated for the each cutting plane of the member in the cross section. For example, if you have square concrete column. Etabs will generate a 3D profile of PM curves. The first curve will be generated for the angle = 0 (horizontal). At that time the rebar on the right side and left side will be in maximum tension and compression. Next it will increase the angle to next interval (for example 20 degree). In that case the cutting plane is not a horizontal line, but it will be a line drawn at 20 degree with horizontal and the rebar at ends of this line will be in compression and tension.

In short, if you have just a moment on your column in x axis then you need to check 0 degree result and if you have moment in only y axis then check 90 degree PM curve. If you both (bi axial moment) then you need to check all the angle to make sure your moment is within the PM curve of all the angles.

I know this sounds really confusing, but I would say the second paragraph above should answer your question. If not, don't hesitate to write me back.

brichard is absolutely right with his second paragraph. A 360 degree interaction diagram is used to check for biaxial moments. A set of moments about each axis can be resolved into a resultant and compared to the 3d interaction diagram.

In general the interaction curve represents all the PM combinations that are safe for this section. Every combination, which is represented by a point on the plane, should be inside or at least on the curve so as to be on the safe side of designing.

Another name of the Interaction Diagram is Capacity Surface. For me, the later makes more sense. I suggest that you should read the book - Reinforced Concrete Mechanics and Design (MacGregor) which you can download from our lovely site. This book includes almost everything about the interaction diagram (from the basic concept to method of calculation and worked example). In case that you need a more professional software to analysis the cross section and generate the diagram, you should consider CSi Section Builder or Gala.
Sincerely,

The software can do P-M diagram

PCA spColumn, previously PCA column
CSI Column
CSC S-Concrete

Please do not forget Xtract from Imbsen.
Is a little bit GUI unpolished but is very powerfull.
It calculates the PM interaction curve at any given angle. You can start with it to understand first the PM curve and after that the PM surface.

The diagram in ETABS shows 3D. What 'deviationz' said in post #3 is correct. You can use PROKON to understand the interation diagram for x and y axis. means 0 and 90 degree.

@ridz:

first, Sorry for my poor english.


angel means angel of neutral axis.


1)cloumm section is bisymmetric (both geometric shape and position of rebars must be bisymmetric):
for example : square,rectangle,circle,I-shape,box,pipe...



If You Specify one neutral axis angel, and move neutral axis from A to B,
then you can obtain one [Pn,Mnx,Mny] according to every new position of neutral axis.
All [Pn,Mnx,Mny] datas assemble one P-M curve.

For bisymmetric section, you iterate (or rotate) neutral axis angel from 0 degree to 90 degree,
then you obtain the entire P-M curves of your cloumm.

2)cloumm section is monosymmetric (both geometric shape and position of rebars must be monosymmetric):
for example : C-shape,T-shape,...

Rotate neutral axis angel from 0 degree to 180 degree.

3)cloumm section is arbitrary:
for example : L-shape or whatever you want.

Rotate neutral axis angel from 0 degree to 360 degree.

(07-15-2010, 11:43 AM)fashion Wrote: [ -> ]In general the interaction curve represents all the PM combinations that are safe for this section. Every combination, which is represented by a point on the plane, should be inside or at least on the curve so as to be on the safe side of designing.

But in the CSI dont appear any P-M point inside the curve (or surfece), how do you know if your interaction curve (or surface) works?

-Diquan

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