High fundamental period

[ARQLABS08]

Hi, I am concerned about the fundamental period in my model, it is a frame steel project with truss beams, it is 15 m high and with two offices buildings attached, the thing is that my fundamental period shows 2.46 seconds, and I consider that is too high for my project
I also use braces to reduce the period but instead of reduce it, increase it

So I come here to hear some ideas of what I could make wrong

Thanks beforehand

[Simau · Accepted solution]

@ARQLABS08 

If your objective is to reduce the natural period of the structure, first deactivate the "tension only" option because it is not compatible with the modal calculation.

In your model, you have to increase the stiffness in the Y direction, by adding bracings on the central row. Add also an amount on the lattices (see photo).
The period decreases to 1.38 s
Once satisfied with the result, you can move on to the nonlinear calculation.

Before running the modal analysis, modify the number of load cases in order to have Viento X just before the modal case.