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I have submitted the following Thre

I have submitted the following Thre

I have submitted the following Thre

Dear all

I have submitted the following Thread in the RESEARCH ENGINEERS- STAAD PRODUCTS Forum under the title,'A Simple problem but puzzling', which I came across in STAAD analysis

The problem is a little strange and defys logic. One of the forum members has confirmed  that the anamoly is seen not only in STAAD III but also in the other proven software like SAP2000.

Hence I thought that this is not a STAAD specific problem but common to other softwares also and therefore wish to bring to the civil forum.

May I request any of the Forum members to come up with some explanation/solution to this anamoly?

Thanks in anticipation


I had a peculier observation in analysing a simple single bay single storyed symmetrical frame,with fixed supports and with a uniformly distributed load on the beam.

A very simple problem to solve indeed. The moment at the column base shall be 50% of the moment at the top of the column. Since, we deal with only relative stiffnesses between the column and the beam at the junctions, the answer shall be same for the given load,irrespective of the actual stiffness of the members as long as the stiffness ratio between the beam and the column is unchanged.

I observe that the result is not so. For values of lower stiffnesses (lower I/L), the results are accurate. But the support moment at the column base reduces drastically (as low as 10% of the top moment for higher stiffnesses)if the stiffness of the individual members are increased keeping their ratios same. However, the other moments remain unchanged.

I am not able to find any logical reason for this.

I fear that this may give rise to a gross underestimation of column base moments leading to underdesign of foundations, if the results from the output are taken as correct.

Can anyone offer any reason for this?
Has anyone noticed this before?
Can anyone check this in any other proven software and inform the result?



RE: I have submitted the following Thre

Just a thought.

When you change the flexural stiffnesses, do you also make proportional changes to the axial stiffnesses (member areas), particularly in the beam ?

If not, then the axial deformation of the beam will become more significant as the flexural stiffnesses are increased.

ie, the base moment is only 50% of the top moment if the beam does not shorten, and the corners remain vertically above the column bases.  With increasing flexural stiffness in the columns, minor horizontal deflections at the corners become more significant, and less than 50% should be expected.

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