To reduce vibration transmission, we use “Vibration Isolators” which is the use of a resilient material between structure and machine.  When dealing with earthquakes, the floor moves horizontally and vertically in random directions through range of frequencies.  If the floor frequency was very high compare with isolation system, the machine would be isolated and remain motionless in space.

If the floor frequency was very low, the machine would move with the structure.  During most seismic events, the range of input frequencies includes the system resonance so that the isolation springs act as amplifier with the machine to develop enough motion to damage or fly free of the springs.

This problem has been recognized for quite some time, but until very recently the criteria for the restraint of these machines generally came from the Uniform Building Code.

Snubbers from Mason Industries, Inc (USA) are designed to provide all-directional restraints to vibration isolated machines or equipment against loads from earthquakes.  Typical models are: Z-1011 and Z-1225.

Z - 1011	Z - 1225

Z-1011 seismic snubbers are all-directional and engage to restrain equipment only when movement due to an earthquakes is experienced.  The contact surfaces would have to be resilient, have a predictable stiffness and be sufficiently thick so as to allow adequate time for deceleration in order to keep the force down to the 4 g level.  A minimum air gap of ” to ¼” would allow for errors in alignment, minor shifting, hole location tolerances and elevation tolerances.  Clearances should be factory set and located to maintain centering during installation.  A simple release mechanism should be included to release the snubbers after positioning and attachment to both the equipment and the structure.

Type Z-1011 series consists of interlocking steel members restrained by shock absorbent rubber materials compounded to bridge bearing specifications.

Features:

• Load capacity range from 500 to 2500 lbs
• Replaceable 19 mm thick all-directional bridge bearing quality neoprene

Applications:

• Limiting the movement of floor mount equipment
• To resist earthquake forces and prevent the overturning of equipment

Z-1225 all-directional seismic snubbers series consists of interlocking steel members restrained by a one-piece molded neoprene bushing of bridge bearing neoprene.  It is a simpler design primarily used when only static analysis is required.

Features:

• Load capacity range from 250 to 5000 lbs
• Replaceable 6 mm thick bushing
• Neoprene bushings could be rotated to insure no short circuits exits before systems are activated

Applications:

• Limiting the movement of floor mount equipment
• To resist earthquake forces and prevent the overturning of equipment