Natural frequency checks (SLS) (Beams: BS 5950)
Tekla Structural Designer calculates the approximate natural frequency of the beam based on the simplified formula published in the Design Guide on the vibration of floors (Ref. 6) which states that Natural frequency = 18 / √ δ
In line with the calculation of natural frequency of 18 / √ δ for a pin ended beam with applied UDL, we calculate δ (in mm) as the maximum static instantaneous deflection based upon the composite inertia (using the short term modular ratio) but not modified for the effects of partial interaction as:
δ = %max δself+slab + %max δother dead + %max δlive
The engineer can specify:
- Percentage self wt + slab deflection (default 100%)
- Percentage other dead deflection (default 100%)
- Percentage live load deflection (default 10%)
- Factor of increased dynamic stiffness of concrete flange (default 1.1)
Note: Natural frequency is calculated for composite beams, but can also be optionally requested for pin ended non-composite beams by selecting Calculate natural frequency in the non-composite beam properties.