First Mode Period of Steel MRF

[JRCM]

Greetings!

I recently noticed that the building period of steel structures in Seismostruct is unusually large. In our manual computations, we expected a period of around 0.6 secs for a 5-story building. However, the software gave us a value of more than 2 secs. Is there a fix for this?

Thank you.

[JRCM]

For the sake of testing, I tried using the building wizard to quickly create steel and concrete structures with 7 bays, 5 storeys (3m each), and 4 frames. The reinforced concrete structure had a first mode period of 0.522 secs, while the equivalent steel structure had a period of 1.722 secs. What could be the cause of such a large discrepancy?

[huffte]

I don't think it is necessarily a "discrepancy". The natural period is dependent on many factors - member size, connection fixity, overall geometry, etc. It is certainly not out of the question for a 5-story building to have a long period. I would suggest examining to ensure that everything in the SeismoStruct model matches assumptions you made in your hand calculations, column bases are the same in both cases (pinned or fixed), masses are the same for both, etc.

Best of luck.

[seismosoft]

The wizard create a sample model that is not necessarily correct technically, for instance in steel buildings there are no steel braces (which is the main reason for the very large fundamental period). It is just a way to introduce the program quickly to new users.
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