Seismosoft | Earthquake Engineering Solutions

Dear Seismosoft community

I have a question about axial force in the elements.

I modelled in Seismostruct a cantilever beam with a 0.4x0.4m RC section, height 5m and a summit axial load equal to 10 Kn.
So, by hand calculation, we have that the distributed weight of beam is 0.4x0.4x25=4kN/m and the axial force diagram have la linear trend with 10kN in summit and 10+(4*5)=30 kN at the base.
If I run a linear static analysis, go in post-processor and display the axial force diagram I see a constant value of 20kN how you can see in the figure below.

Did I make something wrong? How can I resolve this issue?

Best regards
Giovanni

Hi Giovanni. I don't believe you have done anything incorrectly. It seems that the average axial load is determined by the software. If you subdivide the element, you will see the variation in axial load in the ensuing plots, with a value very near 30 kN at the base and very near 10 kN at the top. At least when I subdivided into 6 elements, this was the case.

For typical building frames, the variation in axial load is not as steep as is in your case, and an average value over the member length is likely appropriate. So the subdivision may be warranted in your case.

I hope this helps. Best of luck, Giovanni.