Seismic isolation is important for protection against nature’s fury

Earthquake engineering for the design of base isolation has emerged as one of the strongest tools for control of structural vibration. When the potentially dangerous earthquakes occur, it is the seismic mountings for the vibration isolation that come into play and protect the building or non-building structure from damage. The importance of the seismic isolation devices and seismic mounts is not understood by the people till they see the devastation with their own eyes. However, the awareness about the subject and the media coverage of natural disasters has made the people cautious about seismic isolators.

Seismic base isolator: The methodology used in the past was to add braced frames and shear walls to strengthen the structure from the impact of the earthquake. This action was increasing the rigidity of the structure making it vulnerable to the seismic impact. The

Seismic base isolator

Seismic base isolator

seismic base isolator is a workable approach that isolates the structure from the ground below, reducing the propagation of seismic shock into the structure. Besides reducing the structural damage, the seismic isolation results in the protection of the other equipment like computers, precision instruments, medical devices, and communication hardware from damage.

Seismic isolation for HVACs: The seismic restraint guidelines must be followed for the installation of suspended piping, ductwork, conduits and cable trays. While the seismic HVAC isolation separation mounts are to be used for the heavier equipment like air conditioners, chillers, and AHUs, the adequate use of hanging spring isolators is recommended for the piping and ducting. It is also recommended to use transverse and longitudinal braces for the suspended piping and ducts. The seismic isolator manufacturer is likely to guide you for the seismic mounting hardware.

Seismic mounts: The ordinary vibration mounts provide vibration isolation. However, this feature is combined with a multi-directional flexible restraint to prevent the movement of equipment under the seismic forces in a seismic isolator. Thus, the movement of the equipment relative to the supporting structure is restricted. However, there is a limit to the restraint capacity along any major axis and is capped at 12 mm. Similarly, the seismic brackets for packaged units are standardized steel brackets with rubber grommet washers to minimize the impact of the seismic shock forces at anchor locations.

Isolation hangers: The hanger springs are designed to reduce the vibration and noise

Isolation hangers

Isolation hangers

generated by the hanging equipment. The isolation hanger consists of a stamped bracket with a spring, cap and elastomer element. The springs have lateral spring stiffness almost equal to the vertical stiffness. The hanger spring also allows for a support rod misalignment through a 30-degree arc. The major applications for the isolation hangers are the isolation hanger duct and isolation hanger acoustic ceiling.

Among the seismic isolator manufacturers, Andre HVAC International Inc. has taken the lead in the product variety and availability of the seismic isolation units. Whether it is the seismic bracket or the HVAC vibration hangers you are likely to find the complete seismic solution at AHI.


Seismic mounts and their application

Seismic mounts are mechanical equipment designed to combine spring mount vibration isolation with multi-directional flexible restraint to limit equipment movement under seismic disturbance. While under the normal working conditions, these mounting provides efficient vibration isolation that are equivalent to open spring mountings but, when subjected to Seismic mounts and their applicationphysical displacements such as those generated by seismic forces, equipment motion relative to the supporting structure is restricted. At the maximum restraint capacity of each mounting type the movement of equipment is limited to less than 12mm along the major axis.

There are a wide range of seismic spring mounts including rubber seismic mount that are used in various industrial applications. Also available are cable restraints, which are used in conjunction with spring or rubber hangers for the seismic restraint of suspended piping and equipment. So depending on type of machine in use and the deflection requirement, one can select the right seismic mount. When correctly selected, integrated seismic mountings will allow conformance to the design requirements of various applications and other International Seismic Codes.

While there are a number of seismic isolators available in the market is advisable to Refer to the Isolator Selection Guide to obtain the necessary static deflection and then accordingly select the seismic mount required according to equipment load. The dynamic factor needs to be taken into account for all RCMS seismic mounts. Seismic Mounts use high performance coil springs that make them effective at damping wide range of frequencies. The internal stoppers are strong enough to support structures during earthquake and strong winds. But for an effective impact it is critical to select the right seismic equipment.

Seismic mounts or isolators designed to restrain seismic vibration and impact are-:

  • The Rugged steel housing is designed to handle high wind and seismic forces.
  • The Housing serves as blocking during equipment erection.
  • These seismic equipment’s feature a top plate that may be welded or bolted to equipment; allowing flexible design options.
  • The Housing height of each series of equipment are identical within each series.
  • The seismic restrained spring isolators have easily accessible bolt holes that offer simplified installation.
  • These seismic restrained isolators are powder coated housings and springs offer outstanding corrosion resistance.
  • The springs of the seismic isolators are easily accessed for replacement if in case the loads change.
  • The spring mounts are Color-coded for proper identification of load capacity and simple inspection.
  • Also, featuring elastomeric acoustical cup allows the equipment for better vibration isolation.

Speaking of its application the Seismic isolators or seismic mounts are used in a various industries and installed in various industrial applications that include

  • Cooling Towers
  • Chilling Units
  • Buildings
  • Scaffolding.
  • Other General industrial equipment
  • HVAC equipment and fan assemblies
  • Pumps, chillers and cooling towers
  • Condensing units
  • Generator sets& many other such applications.