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# Natural Frequency of composite concrete slabs

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## Natural Frequency of composite concrete slabs

(OP)
We have a metal decking flooring system with 130mm thick in-situ concrete slab, spanning on to beams at 2.5m-2.75m centres. The slab weighs 2.4kN/sqm, +1.5 kN/sqm finishes, and the live load is 6kN/sqm.
We are happy with the Natural Frequency of the steel beam, but would like to know what is an acceptable natural frequency for the slab itself.

### RE: Natural Frequency of composite concrete slabs

Check out Steel Tips - Vibration - September 1991
"Design Practice to Prevent Floor Vibrations" Steel Tips issue By Farzad Naeim, Sep. '91 (1.24MB PDF)
.  It can be found at http://www.aisc.org.

### RE: Natural Frequency of composite concrete slabs

I suggest three solutions for you:
1-Do a vibration test on your slab if it is already constructed.
If shear connections are adequately designed, the followings can also be done:
2- Consider equivalent beams wide center to center of the pannels or the effective width according to your design code, whichever is smaller, then calculate the equivalent section properties of the composite beam and calculate its vibrational behavior theoretically.
3-Perform a FEM dynamic analysis using any conventional software, say SAP2000 or SAP90, etc.
Good Luck

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