Operations and application of seismic mounts for industrial areas prone to earthquake

As per principles of law of conservation of energy, it states that energy is neither created nor destroyed, it is only transforms from form to another or transferred from one object to another. Based on these principles, Mechanical vibrations are nothing but just a form of energy interchange between kinetic and potential energy.  Even in case of vibrations, the energy from the source or creator (mechanical elements like motors, engines, pumps etc.) gets transferred to the adjacent elements like structure and other mechanical elements of the system. Vibrations are also often caused due to external factors like the earthquake which has a direct impact on machines. So, to protect industrial machines from such high frequency vibrations the structures need be equipped with equipment’s like seismic mounts.

Seismic mounts are widely used instruments in locations that are prone to earthquakes or seismic disturbances and considered a potential hazard. Seismic mounts help isolate and dissipate   vibrations caused due earthquake to ensure protection of installed equipment. Basic features of seismic mounts are to offer rugged/ rigid support through its fabricated steel construction and heavy duty stable steel springs. They are equipped with acoustic isolation pad which dampens seismic vibrations.  Seismic mounts for mechanical equipment are designed to combine spring mount vibration isolation with multi-directional flexible restraint to limit equipment movement under seismic disturbance.

In normal operating situations, the seismic mountings provide vibration isolation generally equivalent to open spring mountings but, when subjected to physical displacements such as those generated by heavy seismic forces, equipment motion relative to the supporting structure is restricted. When correctly selected, seismic isolators will allow conformance to the design requirements and offers strong stability to the structure. Seismic isolators are equipped with multiple options depending on the load and structural stability required at the given time. Strong housing combined with spring and rubber provides maximum isolation from seismic vibrations and safeguards loaded mechanical equipment’s. Depending upon the application and loading arrangement single steel spring loaded seismic mounts or multiple steel springs loaded seismic mounts are used.

The construction of seismic isolators offers maximum flexibility which enables easy movement and re-location of mechanical equipment while also offering maximum support and resistance to the high frequency vibrations. The housing shall serve as blocking and, restraining bolts have a neoprene bushing between the bolt and the housing. One of the most common construction includes hot dipped galvanized steel housing, oil-resistant high frequency spring base isolation cup and resilient rubber base cup to provide acoustical isolation from vibrating steel spring components. Since housings are bolted or welded in position, there is an internal isolation pad. Housing are designed to resist all seismic forces.

When selecting a seismic mount, it is recommended that the calculated mass of equipment is increased 10-20% to avoid overloading of any mounting. For equipment using more than four mountings, ensure to distribute and locate them so that each mounting has equal loading. If this cannot be done, mounting selection must be made on the basis of matching static deflections as closely as possible. Seismic spring mountings shall permit freedom of equipment motion at normal operating conditions but restrain the equipment from excessive motion when subjected to foundation displacement in any direction.



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