Floor System Frequency Of Vibration Calculation

Modal mass m mod each mode of a system with several degrees of freedom can be represented by a system with generalised mass a single degree of freedom.

Floor system frequency of vibration calculation.

Supporting the floor system also af fects the natural frequency of the floor system. Where f is the natural frequency of the considered mode k mod is the modal stiffness m. For best results the frequency should be 15 hz or higher. People are often annoyed by and are very sensitive to vibrations in the 8 10 hz range.

Damping by furniture and finishing e g. Unlike the sdof system which has a single natural frequency and corresponding mode of vibration a continuous system theoretically has an infinite number of natural frequencies and associated modes. Watch what the system is doing. A beam may be thought of as a series of mass spring models joined together to form a continuous system.

This calculator gives the fundamental vibration frequency of a floor joist girder and the combined floor system. Design for sensitive equipment. In this mode the vibration reaches maximum amplitude in one position an antinode at mid span of the beam. False floor l spread of energy throughout the whole structure.

For floor vibrations to be acceptable the peak acceleration of the floor system which is a function of the floor system s natural frequency damping and effective weight must be less than or equal to the recommended acceleration which is equal to 0 5 percent of the acceleration of gravity for office and residential occupancies. The system has a fundamental frequency which corresponds to the first lowest mode of vibration. The additional benefit of making it easy to calculate the system natural frequency. In reality only f n and w require calculations.

Is the natural frequency of the floor system βis the modal damping in the floor system and w is the effective weight that moves because of the excitation. Floor systems and footbridges for vibration serviceability due to human activities. 6 floor vibration continuous systems a beam has a mass stiffness and boundary conditions at the supports that define its behaviour. If more flexibility is needed air springs are used.

If the forcing frequency is close to the natural frequency of the system and the system is lightly damped huge vibration amplitudes may occur. The natural frequency of the system assuming a single degree of freedom can be calculated by. Hz 1 3 13 2 1 2 1 2 1 g w kg. At first glance the criteria might look a bit formidable it certainly is different than the older criteria.

The simple spandeflection ag of the floor girder may be calculated in the same manner as a. Try this test for each type of excitation. The natural frequency of the floor system may then be estimated by the following formula 2 3 f 0 18i g aj ag 3 for concrete floor systems sup ported on walls 4gmay. Require the calculation of the first natural frequency of the floor system and the maximum amplitude of acceleration.

Observe the behavior when the excitation frequency coincides with the natural frequency of the system.