TM 5-809-6/AFM 88-3, Chap. 6
CHAPTER 7
MECHANICAL SYSTEM STRUCTURES
7-1. General
7-4. Pipe supports
Pipe supports will be designed to resist the various forces to
Design of support features for mechanical systems such as
which the piping system will be subjected. As a minimum,
heating, ventilating, and air-conditioning (HVAC) systems
all pipe supports will be designed to carry the weight of the
(including items such as foundations, support frames, braces,
piping system plus water to account for hydrostatic testing.
and other items) will be in accordance with current practice,
Other forces including those due to wind, snow, seismic
sound engineering principles, and manufacturer*s
activity, thermal expansion and contraction, thrust, impact,
recommendations as appropriate. The minimum safety factor
etc., will be considered as appropriate for the details of the
for stability against overturning and for resistance against
system and materials being used. For systems conveying
sliding will be as set forth in paragraph 1-6. For design of
materials at temperatures other than ambient, consideration
structures associated with power plants, see applicable
will be given to the effect of thermal expansion and
portions of TM 5-811-6. Design of mechanical support
contraction on the support system. Where possible, the
systems for seismic restraint is covered in TM 5-809-
flexibility of the support structure will be considered to avoid
10/NAVFAC P-355/AFM 88-3, Chapter 13.
the need for slide bearings or similar construction. In any
case, appropriate allowance will be made for movement and
7-2. Equipment supports and enclosures
restraint to conform with the assumptions made in the pipe
system flexibility analysis. In regions of potential seismic
a. Static. Design of supports and enclosures for static
activity, particular attention will be given to assure that
equipment will consider the maximum weight and ec-
sufficient lateral support is provided.
centricity of the equipment as well as the required clearance
for access to and maintenance of the equipment. Lateral
7-5. Gas and air conveyances
supports and bracing will be provided as necessary to
Gas and air conveyances, particularly for hot gases, will be
maintain the stability of the equipment under lateral loading,
designed to meet fire protection requirements including
particularly seismic.
National Fire Protection Association (NFPA) 211. Design of
b. Rotating or vibrating. Design of supports and
supports for HVAC systems will comply with TM 5-8 10-
enclosures for vibrating or rotating machinery will consider
1.
the need for isolation pads, isolation joints, and damping
a. Large-scale ductwork. Large-scale ductwork refers to
devices either alone or in combination. Care will be taken to
ductwork typically associated with major supply air and hot
assure that the natural frequency of supports is sufficiently
gas conveyances, e.g., between the various components of
offset from the operating frequency of the equipment so that
large industrial or power generation boiler plants. Large-
there is no danger of objectionable or damaging resonant
scale ductwork may be of either circular or rectangular cross
vibration. Whenever practical, supports for rotating or
section and is usually constructed of steel. Structural design
vibrating equipment will be physically isolated from the
of large-scale ductwork will be in accordance with the
adjacent structure to prevent the transmission of vibration
following Sheet Metal and Air Conditioning Contractors*
into occupied areas. NAVFAC DM-7.3 and Design of
National Association (SMACNA) publications: Accepted
Structures and Foundations for Vibrating Machines by Arya,
O*Neill, and Pincus are among the references which will be
Industry Practice for Industrial Duct Construction,
Rectangular Industrial Duct Construction Standards, and
consulted for further guidance on structural design for
Round Industrial Duct Construction Standards. Design
vibrating equipment.
considerations will include forces exerted on the duct system
such as those due to gas pressure, dead and live loads, wind
7-3. Utility tunnels
loads, snow loads, seismic loads, and loads due to thermal
Utility tunnels will be provided for mechanical systems
expansion and contraction. In addition, the design will
where a number of systems follow the same general align-
consider the effects of elevated temperature which can reduce
ment. Design of utility tunnels and similar underground
the yield point and other mechanical properties of steel. The
structures will be in accordance with ASTM C 857 and
layout of duct systems will include a sufficient, but minimum
ASTM C 858 unless more stringent requirements are
number of expansion joints, adequate provisions for move-
imposed by the agency having jurisdiction.
ment, and appropriate restraint at supports. For duct with
large, circular cross sections, structural design may be based
on methods described in the Structural Engineering
7-1
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