Product Overview

Safety Factor
The design loads given for strut beam
loads are based on a simple beam
condition using allowable stress of 25,000
psi. This allowable stress results in a
safety factor of 1.68. This is based upon a
virgin steel minimum yield strength of
33,000 psi cold worked during rolling to
an average yield stress of 42,000 psi.
Aluminum typically has an elastic modulus
which is
1
/3 that of steel even though they
may have identical strength. As a result,
the deflection of aluminum channel will
be three times that of steel channel under
equal loading. In areas where structures
will be subject to general viewing,
deflection can produce a displeasing
effect. To the untrained eye, a sagging
channel may appear to be a result of
poor design or excessive loading. This is
not usually the case. Many properly
designed channel installations will show
a noticeable deflection at their designed
loads. In areas where cosmetics are not
important, deflection should not be a
factor. Designing an entire installation
based on minimal deflection could result
in an over designed structure. This
translates into increased material and
installation cost. Where cosmetics are
important, it may be necessary to limit the
deflection to an aesthetically pleasing
amount. This “acceptable deflection”
amount is typically given as a fraction
of the span.
1/240 span deflection is
typically the limit where the amount of
deflection appears negligible. For
example, a beam span of 240” would be
allowed 1” (240/240) of deflection at the
mid point. A 120” span would only be
allowed
1
/2” (120/240) of deflection. The
maximum load for the channel must be
limited in order to remain under these
deflection requirements. The allowable
load resulting in 1/240 span deflection is
posted in the beam load chart for each
channel size.
For even more stringent deflection
requirements, an allowable load is listed
in the beam load charts which results in
1/360 span deflection. This amount of
deflection is sometimes used for beams in
finished ceilings that are to be plastered.
Twisting & Lateral Bracing
Loading of strut on long spans can cause
torsional stress, resulting in the tendency
of the strut to twist or bend laterally. This
phenomenon reduces the allowable beam
loads as shown in the beam loading
charts. It is recommended that long spans
be supported in a manner to prevent
twisting (fixed ends), and that the channel
have adequate lateral bracing. Many
typical strut applications provide this
support and bracing inherently. Piping,
tubing, cable trays, or conduits mounted
to the strut with straps and clamps
prevent twisting or lateral movement. If
no such lateral support exists, contact the
factory for loading recommendations.
Columns
Columns are vertical members which
carry loads in compression. One common
example of a channel column is the
vertical members of a storage rack.
In theory, a column will carry a load equal
to its cross sectional area multiplied by
the ultimate compressive stress of the
material of which the column is made. In
reality, there are many factors affecting
the load capacity of a column, such as the
tendency to buckle or twist laterally
(torsional-flexural buckling), the type of
connection at the top or bottom, the
eccentricity of the load application, and
material imperfections. Several of these
failure modes have been considered in
the allowable column load tables shown in
the “Channel” section of this catalog.
Cooper B-Line strongly recommends that
the engineer perform a detailed study of
the many variable conditions before the
selection process begins.
Design Factors to be Considered
The loading capacity of channel depends
primarily on the material, its cross-
sectional design, and the beam or column
loading configuration. It should be noted
that if two lengths of channel have
identical designs and configurations, the
one made of the stronger base material
will support a larger load. Therefore, any
comparison of channel should begin by
determining whether the materials are
approximately equal in strength.
The column loading chart for each
channel lists the allowable load for each
channel in compression. This load varies
depending on the support condition or “K-
factor”.
Several “K-factors” are listed, which
correspond to the following support
conditions:
K = .8 pinned top - fixed bottom
K = .65 fixed top - fixed bottom
K = 1.0 pinned top - pinned bottom
K = 1.2 free top - fixed bottom
There are a number of physical properties
which are important to the complete
design of a channel member; the “section
modulus” designated as “Sx” or “Sy”,
“moment of inertia” designated by “Ix” or
“Iy”, and the “radius of gyration” which is
given as “rx” or “ry”.
Every structural material has its own
maximum or ultimate stress, which is
usually expressed in “pounds per square
inch” (pascals). Any load which causes a
member to fail is referred to as its
“ultimate” load. In order to prevent
channel from being accidentally loaded up
to or beyond its ultimate load, a safety
factor is included into the design. The
ultimate load is divided by the safety
factor to obtain the “recommended” or
“allowable” working load.
When evaluating channel under various
beam conditions, it is often more
convenient to compare in terms of the
ultimate or recommended “bending
moment”. Simple equations show the
stress is directly proportional to the
bending moment.
Therefore, comparing bending moments
can save time in repeated calculations.
The chart containing Formulas on
Common Beam Loadings (following page)
shows how to calculate the bending
moment for various configurations and
load conditions. It should be noted that
the bending moment is usually not
constant, but varies along the length of
the span. However, the channel must be
designed for a single point, which is the
point of maximum bending moment.
For information regarding dynamic or
seismic design, contact Cooper B-Line’s
Home Office.
GENERAL INFORMATION
Torque
The torque values given throughout the
catalog are to be used as a guide only.
The relationship between the applied
torque or torque wrench reading and the
actual tension created in the bolt may be
substantially different. For example, a dry
non-lubricated bolt with a heavy plating
may rate 50% as ef
ficient as a bolt which
is lubricated with a mixture of heavy oil
and graphite. Other important factors
af
fecting torque-tension relationships
include friction under the bolt head or nut,
hole tolerances, and torque wrench
tolerances.
Accuracy of many commercial
torque wrenches may vary as much as
plus or minus 25%.
Charts and Tables
Charts and tables in this section are
compiled from information published by
nationally recognized organizations and
are intended for use as a guide only.
Cooper B-Line recommends that users of
this information determine the validity of
such information as applied to their own
application.
Technical Data
Technical Data
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