VISCMA

General Guidance on the Use of Rod Stiffeners when Seismically Restraining Pipe, Duct, Electrical Distribution Systems

In mechanical, electrical, and plumbing distribution systems, hanger rods are used to provide the vertical (dead) load support, making the primary force imposed on them a tension force. However, when cables or rigid brace members are used to provide restraint against seismic forces, the hanger rods at the brace locations can be loaded with a …

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ASCE 7-16 Critical Code Updates For Wind

Throughout the country, local jurisdictions have started updating their building codes to match ASCE 7-16 and its associated IBC counterparts.  Because of this, it is important to investigate the code updates of the wind loads.  There are three major code updates in the ASCE 7-16 wind load calculations. Click to download

Deflection Relates to Vibration

The deflection of an isolator is defined as the difference in the original unloaded height of the isolator and the final loaded height of the isolator. This deflection is equivalent to the inverse of the natural operating frequency of the isolation device. Click to download

Q23

How do I run restraints for ductwork in fire rated hallways? ANSWER: This is a great example of the need for good phasing on a project. It may be that the restraints have to be installed crossed over the top of the ductwork and before the walls are put in place. It may mean that …

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Q22

Can I use wall penetrations as restraint points for ductwork? ANSWER: Yes, to some degree. It is best determined by a qualified seismic design engineer. Common practice is to use wall penetrations as lateral restraints if the wall is considered strong enough and the design forces small enough. Fire dampers, since they are made to …

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Q21

What is the size exemption for round or flat oval duct? ANSWER: The cross-sectional size exemption is for any shape of duct. SMACNA used to require all round ductwork 28″ larger in diameter to be restrained. This requirement is not used in IBC 2012/ASCE 7-10

Q20

Can I use the “12 inch rule” for ductwork? ANSWER: The “12 inch rule” exemption has been misapplied in many cases. The only way the 12″ exemption rule can apply is if the supports are designed to prohibit significant bending for all hangers on a run of duct. One method is to select hangers that …

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Q19

How far apart do the braces need to be? ANSWER: Industry standard practice uses a maximum of 30′ between transverse restraints and 60′ between longitudinal restraints for ductwork. Actual restraint locations will be determined by the seismic design engineer based on duct construction and design force levels.