Vibration Isolation &

Seismic Restraint

Of Mechanical Systems

Ali Kemal Güney

Mechanical Engineer, M.Sc

20111

Vibration Isolation

Vibration Isolation

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Vibration Isolation

Vibration Isolation

Source:

ASHRAE (2011) Handbook – HVAC Application Chapter 48

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Vibration Isolation

Vibration can be isolated or reduced to a fraction of the original force with resilient mounts between the equipment and the supporting structure, provided that the supporting structure has sufficient stiffness and mass. Isolation efficiency is the percentage of vibratory force not transmitted to the support structure.

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Isolator Selection Key Points

Vibration isolators must be selected not only to provide required isolation efficiency but also to compensate for floor stiffness. Longer floor spans can be more flexible and thus more easily set into vibration. Floor spans, equipment operating speeds, equipment power, damping, and other factors are considered in Table 47. In specifying isolator deflection rather than isolation efficiency or transmissibility, a designer can compensate for floor stiffness and building resonances by selecting isolators that have more deflection than the supporting floor. To apply the information from Table 47, base type, isolator type, and minimum deflection columns are added to the equipment schedule. These isolator specifications are thenincorporated into mechanical specifications for the project.

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Isolator Selection Requirements

Requirements:

An overview of the procedure to select vibration isolators is as follows:

1. Establish total mass of equipment to be supported. This includes all equipment and support framework. The mass of piping connected to equipment may also need to be considered, because this may be partly supported from the equipment.

2. Establish operating mass (e.g., mass of water in a chiller or cooling tower).

3. Determine the location of supporting springs.

4. Calculate the distribution of weight onto each of the supporting springs using static force distribution methods.

5. Consider any dynamic forces that may change the mass distribution over thesupporting springs.

6. Select vibration isolators to achieve the minimum deflection based on the vibration-isolator spring constant as advised by the manufacturer.

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Isolator Selection (Table 47)

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Isolator Selection (Table 47)

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Isolator Selection (Table 47)

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Isolator Selection (Table 47)

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Isolator Types (Rubber Pads)

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Isolator Types (Rubber Mounts)

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Isolator Types (Open Springs)

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Isolator Types (Restrained Spring)

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Isolator Types (Hangers)

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Isolator Types (Thrust Restraint)

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Isolator Types (Inertia Base)

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Isolator Types (Structural Base)

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Isolator Types (Concrete Base)

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Isolator Types (Concrete Base)

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Isolator Types (Riser)

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Isolator Types (Riser)

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Isolator Types (Riser)

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Seismic Restraint

Seismic Restraint

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Seismic Restraint

Seismic Restraint

Sources:

IBC 2009 – International Building Code

NFPA 13 – National Fire Protection Association

FEMA – Federal Emergency Management Agency

ASHRAE – American Society of Heating, Refrigerating and Air Conditioning Engineers

SMACNA – Sheet Metal and Air Conditioning Contractors' National Association

UBC – Uniform Building Code

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Purpose of Seismic Restraint

Design and installation of seismic and wind restraints have the

following primary objectives:

• To reduce the possibility of injury and the threat to life.

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Purpose of Seismic Restraint

Design and installation of seismic and wind restraints have the

following primary objectives:

• To reduce long-term costs due to equipment damage and resultant downtime.

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Seismic Calculations

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Seismic Restraint

Seismic Restraint Bracing element

Can be selected as,

Rigid Non-Rigid

Profile Cable

Pipe

Angle

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Seismic Bracing Element

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Seismic Bracing Element

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Attachment Levels (Concrete)

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Attachment Levels (Steel)

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Seismic Applications

-Single Pipes

-Trapeze Pipe Supports

-Ducts

-Cable Trays, Busbars

-Suspended Equipments

-Wall Mounted Equipments

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Single Pipes (Cable)

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Single Pipes (Strut)

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Trapeze

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Trapeze (Cable / Strut)

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Ducts

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Ducts

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Cable Trays

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Cable Trays

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Cable Trays

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Cable Trays

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Busbar

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Suspended Equipments (Fans)

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Mounted Equipments (Trafo)

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Mounted Equipments (Panel)

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Mounted Equipments (AHU)

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Mounted Equipments (AHU)

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Mounted Equipments (Boiler)

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Mounted Equipments (Chiller)

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Mounted Equipments (Chiller)

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Mounted Equipments (Chiller)

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Chiller and Generators

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Fire Base and Risers

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Thank you…

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