How To Verify The Frequency Of A Floor Slab

Damping has a big influence on the vibration behaviour of a floor.

How to verify the frequency of a floor slab.

The natural frequency of the whole floor system may be estimated using the equation given previously where δ is the sum of the component deflections for slab secondary and primary beams. At this coincidence frequency and thereabouts the slab may conduct vibration quite well. For each load case apply a point load at the footfall location. Analysis the natural floor frequency with variation of span length and floor panel aspect ratio.

The great mass of the slab will generally isolate sound vibration quite well except at and around the coincidence point frequency. We would like to show you a description here but the site won t allow us. The natural frequency should be calculated for each mode allowing for the deflection of both sets of beams and the slab and the fundamental frequency of the floor should be taken as the lower value of the two modes considered. To perform modal analysis to determine mode shape and frequency.

This shielding limits the slab from becoming a conduit for coincidence frequency conduction. In estimating the natural frequency of a floor system the actual loads must be considered usually the permanent loads and 10 of the unfactored imposed loads. Do not design floors with a natural frequency below 3 hz walking speed in an office can be 1 25 to 1 5 steps per second or hz. Houses built on a slab lack crawlspaces and there is no space under the floor.

The modal mass for the critical mode may be obtained from the simplified equations in sci p354. Verify the built model with hand calculation and experimental data. Frequency and modal mass for isotropic plates orthotropic plates and beams. The acceleration may then be obtained by treating the floor as an equivalent single degree of freedom system.

The layout selected reflects the typical overall size and spans found in hospital construction and the desire for floors only 2 or 3 bays wide to maximise the amount of space lit by natural light. Floor vibration due to human footfalls may be modeled as follows. Resonance at the second har monic 2 5 to 3 hz is then a real possibility if the floor s natural fre quency is below 3 hz. Independent on the method chosen to determine the natural frequency and modal mass the damping values for a vibrating system can be determined with the values given in table 1.

To guard against this we set up a barrier with serena mat and plywood. A fixed floor layout of a 75x15m floor plate made up of 7 5x7 5m bays has been considered for each floor structure. It may be convenient to name each after its order in the sequence such as step 1 step 2 etc.