Interaction curves - 1st quadrant only?

[ticpan]

Hello,

i'm checking pier section at ULS. Section is rectangular, with symmetric reinforcement all around the perimeter. When I run interaction curves ( Ax = const, My and Mz are variables ) analysis, it creates only first quadrant diagram. So, if i have load case which consists of Ax, My ( which is negative sign ), and Mz, the point which represents this LC won't be shown in interaction curve plot, because of negative My - point is not in the first quadrant. Sure, interaction curve is symmetrical when reinforcement and section are both symmetrical, so the solution might be to enter values of moments with positive sign.

The problem is more difficult to solve if we have both unsymmetrical section and reinforcement. All four quadrants have different curves, and because of that we can't just enter positive value moments,and place it in the first quadrant. 

Is there an option to plot full interaction curve ( 4 quadrants ), or any other way to solve this problem?

Best regards

[david.geeves · Accepted solution]

Hi Ticpan,

Thanks for pointing this out.  There is indeed a limitation in ASBD interaction diagrams that for My against Mz interaction diagrams only one quadrant representing positive values is produced at any one time.

However it is possible to get the full representation by rotating the complete section by 90 degrees, 3 times, and at each instance the interaction diagram represents a different quadrant.  This may sound a bit daunting but it is quite simple to rotate a section and in the 2016/2017 versions of the software it is possible to copy the section each time and have all four sections in one project file.  for the 2014 versions you can only work on one section file at a time and the rotation can be done from the section overview form (in the file menu).

The tabular results from the four  interaction curves can be easily copied to a spread sheet (with the help of the "text to columns" facility in the spreadsheet) and by ensuring that the correct +ve and -ve signs are observed a chart of the complete interaction diagram can be produced.  I attach a screencast video showing how this is done.

I hope this helps.  Please mark this post as a solution if this has answered your question to make it easier for others to locate in the forum.  Thanks

Kind regards

[ticpan]

Thanks for detailed explanation and video. I thought of this solution as well, but i was wondering if there is some quicker solution to this problem. Let's hope that in future versions it will be possible to get full interaction curve plotted - it doesn't seem as big job, but it makes design process much easier.

Best regards