Seismosoft | Earthquake Engineering Solutions

To whom it may concern,
I am modelling a single storey single bay steel frame. The columns are consisted of I section, and the bottom beam is consisted of I section, and the top beam is consisted of I and T sections. The connections between the beam and column in four corners of this steel frame are made of several pins. I think the pin connection is semi-rigid(I am not sure about this). Should I use the link element to model these pins? Or use the constrain DOF? I understand these links will make a major effect to my structure. I has analyzed the eigenvalue analysis, however, the frequency is double of my experimental results. Could you please give me some suggestions about the link part? Thank you very much.

Best regards,
Summer

Have you considered moment releases if the beams are truly pinned? If the frequency is double your experimental result then it would seem that you model is too stiff, not too flexible. Perhaps the connections are 'semi-rigid', but closer to pinned than fixed?

If, in fact, the frequencies are double, then either the stiffness is 4 times too high or there is some mass you have mistakenly omitted from the model?

Hi huffte,
Thank you very much for your reply. I do not know how to consider moment release in Seismostruct software. Could you please suggest me how to do that? For all I sections, there are some stiffeners with the I section, and there are a lot of holes for these I section, but I do not know how to describe them, so I just simply use I section to represent the columns, I am not sure whether it will make some effects to this structure. Thank you for your help.

When you initially create the element, or when you edit an existing element by double-clicking on it in the connectivity list, you will notice the moment/force release dialogue as part of the editable information zhwang. I'll be interested to hear if this solves your problem.

Best of luck.

Thank you very much for your kind suggestions. It works.
I ticked the box in M2a and M3a for all the beams, when I try to run the analysis by considering the moment release, a warning comes out "Warning in the Element Connectivity module: Applying bending moment releases(M2a, M2b, M3a or M3b) to inelastic frame element (infrmFE, infrmFBPH, infrmDBPH, infrmDB) might lead to convergence difficulties in the medium to high inelasticity range. Are you sure you want to proceed?" Then, I press yes, and the analysis result for natural frequency is same with my experimental results now.

Now, I would like to continue the static time-history analysis to compare the hysteretic curves with the experimental hysteretic curves to confirm my model is correct. The vertical load for experimental tests was applied on the middle point of the top beam (80KN), but I do not know how to put the vertical load in middle point by seismostruct, so I try to place the vertical load in the connection point of column and top beam(40KN in each side). However, when I try to run the analysis, an error happened to tell me unable to apply the entire permanent load, analysis terminated. Could you please suggest me how to solve this problem?

Best regards,
Summer

Dear zhwang,

If you carry out a search in this Forum on the expression "unable to apply" you will find plenty of discussion on this matter. The following video on Seismosoft YouTube channel may also help you:
https://www.youtube.com/watch?v=p6tAyoofDog