Depending on the application and type of base-mounted fan, either a concrete or steel base may be required. A typical isolation solution is a Vibro-Acoustics steel base in combination with FS isolators and thrust restraints.

PDFApplication Details
PDFMaster VIRS Pre-Submittal Package

SFS - Seismic Free Spring series provide vibration isolation for base mounted fans. The isolator has a seismic restraint housing for greater lateral and vertical support.

FS - Free Spring series provide vibration isolation for base mounted fans that installed on floor or base. These open spring isolators compress on neoprene cups and absorb low and high frequency vibrations.

IFB - Integral Fan Bases provide a common support for base mounted fans to increase rigidity and provide a method of attachment for vibration isolators. Steel bases are designed to fit the equipment and are available in any shape and size. Based on the application, Integral Fan Bases designs can work with any of Vibro-Acoustics’ floor-mounted isolators.

HCS and AHCS - Thrust Restraint series provide resistance to horizontal motion due to thrust from the air pressure from the fan. Applied in pairs, the HCS/AHCS thrust restraints include spring isolation as well as mounting brackets for attachment to the equipment.

Slab on Grade Design Considerations

Structure-Borne Vibration

Problem: Fans are the most common noise source in HVAC systems. If this vibration is transferred to the structure, it can create serious noise problems in many different areas.

Solution: Inertia base with spring type isolators.

Problem: Lateral Forces due to torque and static.

Solution: Thrust Restraints are required to counteract these forces sized based on fan specs.

Uneven Weight Distribution

Problem: Motor location causes center-of-gravity to be off-centered.

Solution: It is important to perform a center-of- gravity calculation and select the appropriate isolators for each location on the inertia base to avoid over- or under-loading isolators.

Seismic Requirements

Problem: Forces are determined by a number of factors including: project location, site class, risk category, component importance factor and equipment location equipment relative to the overall height of the building.

Solution: Certified anchorage calculations must be submitted to verify loading conditions are met for each piece of equipment.

Problem: Horizontal and vertical seismic forces are applied at the center of gravity of the unit. The resulting overturning moment creates tension and shear forces that can be very large.

Solution: All connections of the restrained spring isolators to the structure must be designed for these loads. For concrete attachments, this requires ICC-ES certified anchors.

Problem: Poor installation of concrete anchors.

Solution: IBC 2015 requires ICC-ES approved anchors for cracked concrete and Omega Naught Factor (Horizontal forces multiplied by 2.5).

Depending on the application and type of base-mounted fan, either a concrete or steel base may be required. A typical isolation solution is a Vibro-Acoustics steel base in combination with FS isolators and thrust restraints.

PDFApplication Details
PDFMaster VIRS Pre-Submittal Package

IFB - Integral Fan Bases provide a common support for base mounted fans to increase rigidity and provide a method of attachment for vibration isolators. Steel bases are designed to fit the equipment and are available in any shape and size. Based on the application, Integral Fan Bases designs can work with any of Vibro-Acoustics’ floor-mounted isolators.

SFS - Seismic Free Spring series provide vibration isolation for base mounted fans. The isolator has a seismic restraint housing for greater lateral and vertical support.

FS - Free Spring series provide vibration isolation for base mounted fans that installed on floor or base. These open spring isolators compress on neoprene cups and absorb low and high frequency vibrations.

HCS and AHCS - Thrust Restraint series provide resistance to horizontal motion due to thrust from the air pressure from the fan. Applied in pairs, the HCS/AHCS thrust restraints include spring isolation as well as mounting brackets for attachment to the equipment.

Upper Floor Design Considerations

Structure-Borne Vibration

Problem: Fans are the most common noise source in HVAC systems. If this vibration is transferred to the structure, it can create serious noise problems in many different areas.

Solution: Inertia base with spring type isolators.

Problem: Lateral Forces due to torque and static.

Solution: Thrust Restraints are required to counteract these forces sized based on fan specs.

Uneven Weight Distribution

Problem: Motor location causes center-of-gravity to be off-centered.

Solution: It is important to perform a center-of-gravity calculation and select the appropriate isolators for each location on the inertia base to avoid over- or under-loading isolators.

Seismic Requirements

Problem: Forces are determined by a number of factors including: project location, site class, risk category, component importance factor and equipment location equipment relative to the overall height of the building.

Solution: Certified anchorage calculations must be submitted to verify loading conditions are met for each piece of equipment.

Problem: Horizontal and vertical seismic forces are applied at the center of gravity of the unit. The resulting overturning moment creates tension and shear forces that can be very large.

Solution: All connections of the restrained spring isolators to the structure must be designed for these loads. For concrete attachments, this requires ICC-ES certified anchors.

Problem: Poor installation of concrete anchors.

Solution: IBC 2015 requires ICC-ES approved anchors for cracked concrete and Omega Naught Factor (Horizontal forces multiplied by 2.5).

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