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  1. What Is Structural Vibration and How Can It Be Controlled

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    Structural vibration is not an entirely uncommon occurrence in buildings the world over. Should rotating and reciprocating machinery be employed within a building’s structure, vibration is a common occurrence. These types of machinery tend to vibrate, and in the worst-case scenarios, this can lead to brackets and support failure and high rectification costs, not to mention reputational damage.

    The Issues Caused by High Levels of Vibration

    Simply put, structural vibration is caused when forces generated by machines such as compressors, pumps, chillers and air handling equipment cause the structural steels to vibrate. This can result in equipment failure, noise transfer, and – most importantly – safety concerns.

    Any vibrations are due to the building being mechanically resonant, or the vibrational sounds that occur when two objects vibrate at the same rate. In structures, this occurs when dynamic forces coincide with the natural frequencies of the supporting structure. At peak resonance, these forces are amplified, causing structural elements to vibrate above safe operating limits.

    Once erected, it is very costly to modify any structural substructures to fix a vibrational issue. However, if addressed promptly and proficiently at the design stage any vibration can be alleviated

    How to Control High Levels of Vibration

    To control structural vibration, an analysis of the different areas of the deck or platform should be undertaken. This is to ascertain the effect high levels of vibration are having on the structure. Once identified, structural engineers can then decide how to control or modify the vibration or isolate the vibration from different areas of the building to minimise any structural damage.

    This is a complex process, involving four distinct steps. These are as follows:

    • Use dedicated finite element analysis software to analyse complex dynamic load conditions
    • Identify natural frequencies and mode shapes
    • Perform the vibrational analysis to determine the structural vibrational responses and confirm the structure will satisfactorily meet all requirements
    • Conduct the test again to see if results can be replicated, analysing acceleration, velocities, displacement and stresses
    • Check to make sure that building fatigue is not causing the building to vibrate

    Common Causes of Structural Vibration

    Although there is a wealth of different causes of structural vibration, there are some that occur more commonly in buildings of all descriptions. These are as follows:

    Noise Vibration – this, typically, causes an issue in a factory or industrial environment, which is why it’s important to take steps to control the level of noise. Enclosing machines will reduce noise and minimising exceptionally loud machinery are sound noise management practices.

    Free Vibration – this is the natural response by a structure when impacted or subject to displacement. The response can often be determined by the properties of the structure, with any vibrational noise understood by examining the building’s mechanical properties.

    Forced Vibration – this occurs when one object forces another adjoining or interconnected object into vibrational motion. Forced vibrations occur when a system is continuously driven by an external force. There is a direct relationship between the amplitude of the forcing function and the corresponding vibrational level. The relationship is dictated by the structure’s properties.

    Random Vibration – this is very common.The easiest example is the vibration you feel when driving a car which is usually the result of a combination of the road surface, engine vibration, wind buffering or resistance on the exterior of the car. It is often described by using statistical parameters and the consideration the behaviours cannot be predicted.

    To learn more about structural vibration, or should you require the services or a learned and experienced structural engineer in Maidstone, call Adkins Consultants today on: 01622 236500.