1.       All discharge runs for a distance of 50' (15m) from the connected equipment shall be isolated from the building structure by means of specification 10 hangers or specification 5 floor isolators.  Spring deflection shall be a minimum of 0.75" (19mm). 

2.       All duct runs having air velocity of 1000 fpm (5 m/s) or more shall be isolated from the building structure by specification 11 hangers or 5 floor supports.  Spring deflection shall be a minimum of 0.75" (19mm). 

Seismic Restraint of Ductwork

a.             Restrain rectangular ducts with cross sectional area of 6 sq.ft. or larger (see table below). 

b.             Restrain round ducts with diameters of 28" or larger.

c.              Restrain flat oval ducts the same as rectangular ducts of the same nominal size.

2.       Transverse restraints shall occur at 30' (9mm) intervals or at both ends of the duct run if less than the specified interval.  Transverse restraints shall be installed at each duct turn and at each end of a duct run.

3.       Longitudinal restraints shall occur at 60' (18m) intervals with at least one restraint per duct run.  Transverse restraints for one duct section may also act as a longitudinal restraint for a duct section connected perpendicular to it if the restraints are installed within 4' (1.2m) of the intersection of the ducts and if the restraints are sized for the larger duct.  Duct joints shall conform to SMACNA duct construction standards. 

4.       The ductwork must be reinforced at the restraint locations.  Reinforcement shall consist of an additional angle on top of the ductwork that is attached to the support hanger rods.  Ductwork is to be attached to both upper angle and lower trapeze.

5.       A group of ducts may be combined in a larger frame so that the combined weights and dimensions of the ducts are less than or equal to the maximum weight and dimensions of the duct for which bracing details are selected.