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Steel
Framing Frequently asked Questions |
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On this page you will find answers to many
common questions about steel framing. These
FAQs are organized by subject but you may find
the subject you’re interested more quickly
by conducting a simple search. If you use Explorer
as your browser, just press Control and the
“F” key at the same time (Ctrl+F),
then type in the word or words that describe
the subject about which you would like more
information.
If you do not find your subject in this section,
you can contact the Hotline by click
here
The GalvInfo Center is a resource
for information on the use and performance of
metallic-coated steel sheet products; products
coated with zinc-containing coatings. The GalvInfo
Center provide technical assistance on subjects
like corrosion behavior, forming, joining, environmental
issues e.t.c. click
here
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General Technical Questions |
| Question:
Assuming the following typical scenario:
22 ga. 3-5/8” full-height (to underside
of structure) metal stud partitions with
5/8” gypsum board on both sides.
Is channel bridging necessary and/or recommended?
Answer:
In this condition, where both sides
of the wall are sheathed all the way
up to the ceiling, channel bridging
through the punchouts is not needed.
The reason for channel bridging through
the punchouts is to restrain the studs:
from both rotation and lateral weak-axis
bending. When the sheathing is attached
to both flanges of the stud, all the
way from the bottom to the top of the
stud, it provides restraint to the stud:
for both rotation and lateral bending.
Adding the cold-rolled channel would
be redundant, and not add any strength
or stiffness to the wall.
The American Iron and Steel Institute
“Standard for Cold-Formed Steel
Framing – Wall Stud Design,”
provides a design methodology for sheathing
braced design of studs carrying both
lateral and axial loads. There are some
limits to the axial capacity of the
stud based on the strength of the sheathing,
but since your example is for 27 mil
framing, this is a non-structural member
and therefore not carrying loads from
the structure above. The design methodology
also provides an additional load combination
to be checked when sheathing braced
design is used, but this is typically
not necessary on interior partitions
carrying the 5 psf interior lateral
load.
Question:
Iam working on preliminary ideas for adding
a 14ft wide addition onto the side of
an existing metal building. After looking
through the SSMA details, I did not see
any details for framing a metal stud roof
with a 2 on 12 slope or a slope along
those lines. The addition would have a
single slope roof. I was just wondering
if this is a common practice and if there
are any details available for this.
I have attached a preliminary sketch.
Answer:
Thank you for your question! This is
a common application for Cold-Formed
Steel framing, and there are some details
for the connections; but not specifically
for the 2:12 sloped rafter bearing on
the top of wall. A couple of ways to
do this:
Using a web-to-web connection, as shown
in the attached photos, will work and
provide a positive uplift connection.
Note that headers cannot be at the top
of the wall in this configuration; they
must be low enough to not interfere
with the rafter. Note that installers
can use a strongback on the inside face
of the wall to temporarily support and
align the studs and the rafters.
Using a traditional top plate, and
using a clip angle to act as both the
rafter support and a web stiffener.
It is an engineering judgment issue
on what the bearing width is when the
sloping joist only bears on part of
the top track; but with a thick enough
clip, or a stiffened clip, this may
not be an issue. Note that in both cases,
the rafters must align with studs.
For the wall framing to foundation
connections, several anchor and fastener
manufacturers have some details; I have
included some from the Standard for
Cold-Formed Steel Framing - Prescriptive
Method for your use. These are also
available in electronic format from
the Cold-Formed Steel Engineers Institute
and the Steel Framing Alliance at www.cfsei.com
or www.steelframing.org.
CFSEI and SFA members have access to
free downloads of these details; others
may purchase them for a nominal fee.
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Question: What
type of barrier should be used in between
the steel and treated lumber (sill plate).
Answer: Thank
you for your question. Several options exist
for a barrier between pressure treated wood
and steel framing. Anything that isolates
the two should work: tar impregnated building
paper, foam insulation strips, gaskets,
and vapor barrier material will all work
to some extent. Beware of
products such as air or moisture barriers
that have micro-perforations, and can permit
small amounts of the pressure treatment
chemicals to seep out and contact the steel.
Note that by using borate treated wood,
there will not be a need to use barrier
protection, because the borates are not
corrosive to steel. The Steel Framing Alliance
has an issue
paper on pressure treated wood, that
gives information on the types of treatment,
as well as some other options
for protection of steel framing.
Question: Does
steel framing product need to have some approval
on them or anyone can buy the production line
and manufacture the studs and track according
to the building codes and materials of let's
say the city of Los Angeles CA? What does
it take to become a manufacturer of steel
framing?
Answer: There
is no specific process for becoming a manufacturer
of steel framing, and there are several
levels of manufacturers out there. At one
end of the spectrum are the manufacturers
who have bought a machine, and begin rolling
material from coils or forming material
on a brake press. Some of these manufacturers
have no quality control program, no testing
program, and sometimes buy their coils and
sheets without mill certifications or test
reports. On the other end of the spectrum,
members of the Steel Stud Manufacturers
Association (SSMA) are required to maintain
an in-house quality control program, turn
in annual audits, and have all of their
material either mill certified or tested.
Also, all material is required to be marked
in accordance with the applicable building
code. The marking requirements are different
for different codes, but all require some
form of marking.
The real question is what sort of requirements
are in place in the specific jurisdiction
where you are interested in installing your
framing members. You mention the city of
Los Angeles: they require specific research
reports and verification calculations be
submitted, and will issue a research report
such as the one issued to SSMA (http://www.ssma.com/cola_2004.pdf).
Other jurisdictions may require nothing
other than a manufacturer's material certification,
stating that the material complies with
code. The American Iron and Steel Institute
has developed a series of standards that
have been adopted into the building code.
The AISI's Standard for Cold-Formed Steel
Framing - General Provisions gives a list
of some of the requirements for framing
members: compliance with specific ASTM standards,
manufacturing tolerances, marking requirements,
and corrosion protection. This is a start.
From there, you should check with the specific
jurisdiction to see what additional requirements
are in place before framing materials may
be used in a structure.
Although not a code requirement in all
jurisdictions, I strongly urge you to set
up a quality control program for your incoming
material and manufacture, if you are considering
manufacturing steel framing. Guidelines
for this program are available from the
International Code Council Evaluation Service
at http://www.icc-es.org/Criteria/index.cfm.
The Acceptance Criteria that apply to framing
members are AC10 and AC46. Note that the
SSMA does not provide guidelines for setting
up framing operations, and in fact does
not admit members unless they have already
been manufacturing and selling steel framing
for at least two years. There is an association
for rollformers that may be able to give
you additional information on equipment
and manufacturing: the Fabricators &
Manufacturers Association, at www.fmanet.org.
Question: We want
to use stainless steel masonry veneer tie
system that uses stainless steel screws into
the steel studs. I'm concerned about
galvanic action. If this is a valid concern
what can i do to the studs for protection.
Answer: “A
minimum #10 self-tapping screw is recommended.
Screws used to attach exterior sheathing
and ties can be either carbon steel or stainless
steel… Stainless steel screws are
acceptable even though a galvanic potential
exists between stainless steel and carbon
steel. This is possible because of an area-relationship
principle where the surface area of the
steel stud is much larger than that of the
screw which results in a decreased corrosion
potential.”
The BIA
tech note is an excellent resource for
other questions about steel framing in brick
veneer systems. The American Iron and Steel
Institute also has a Steel
Stud Brick Veneer design guide, available
online from the Steel Framing Alliance or
the Light Gauge Steel Engineers Association.
Many issues on thermal and moisture control
that are not discussed in the BIA document
are included in the AISI document.
Question: Want
to hang an LCD TV that weighs about 75 pounds
from a sheetrocked wall that has metal studs
inside of unknown thickenss. I have a metal
bracket that spans two metal studs but don't
know the best way to secure the bracket through
the sheetrock to the metal studs. Special
Anchors? Sheet metal screws (what size?).
Answer: Thank
you for your question. The attachment of
screw fasteners into cold-formed steel is
covered in section E4 of the North American
Specification for the Design of Cold-Formed
Steel Structural Members (American Iron
and Steel Institute, 2001, with 2004 supplement)
as referenced in the International Building
Code. The Steel Stud Manufacturers Association
has summarized shear data from an earlier
version of the
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Floor Members and Systems |
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Question: I am
building a sub floor using 16 gauge 10X 2 in
studs. I plan to use Grabber 12-16 3/4 in screws.
Metal to metal. Could you let me know how many
screws I need per attachment. or the spacing
that I need for it. This is a design for 50
ksi.
Answer: Thank
you for your question. Based on your description
of the floor framing, my assumption is that
you are using 54 mil thick material, and number
12 screws. Based on the (Fasteners Screws
and Welds) table from http://www.ssma.com/ssmatechcatalog.pdf
of the Steel Stud Manufacturers Association,
you can get 394 pounds of shear and 196 pounds
of pullout in a steel-to-steel connection.
With 50 ksi material, you will be able to
get even higher values. Since you are using
all Grabber screws, you may want to check
with them on capacity: often, values in a
manufacturer’s data report will be higher
than those based on the American Iron and
Steel Institute (AISI) specification, since
the AISI data has to account for variability
between manufacturers. See also note 4 in
the attached table: the nominal strength of
the screw must be at least 3.75 times the
allowable load. The manufacturer’s data
should be able to give you that information.
If you are attaching different thicknesses
together or different strengths of sheet steel
together, you must use the attached table
or published values for both sheets: the thinner
material will have a smaller capacity, and
material with lesser yield will have smaller
capacity. The portion of the design code that
covers this is section E4 of the North American
Specification for the Design of Cold-Formed
Steel Structural Members (AISI, 2001 with
2004 supplement). This is available from the
AISI
store. For a full version of the attached
SSMA catalog, you can go to http://www.ssma.com/ssmatechcatalog.pdf,
or call 312-456-5590 to have a hard copy mailed
to your office.
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Wall Members and Systems
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Question: Where
can one find additional information regarding
header design?
Answer: For addition
information regarding header design, additional
design information can be found by contacting
the Center for Cold-Formed Steel Structures,
ccfss@umr.edu
or the Steel Framing Alliance technical hotline,
1-800-79 STEEL.
Question: I have
a question regarding ASTM C1007, I have a standard
cited in some literature that states " Stud
to track connections shall be accomplished with
self-drilling screws so that the connection
meets of exceeds the design load required at
the connection". Does this standard no longer
exist? and if it does not, what took it's place.
Is a screw no longer required and if not what
is required for the stud to track connection?
Answer: ASTM
C1007 still exists, and is available from
the ASTM website www.astm.org.
The latest version is C1007-04. Section 8.3
of this standard states, ?Stud to track connections
shall be designed to meet or exceed the design
loads required.? Section 6 discusses connection
of the track to the structure, as well as
welds and screws. Section 6.3 states, "Steel
drill screws shall be of the minimum diameter
indicated by the design of that particular
attachment detail. Penetration through joined
materials shall not be less than three exposed
threads." Section 8.4 and 8.5 require
stud to track connection, but do not require
that this connection be made by screws. Welds,
rivets, clinches, crimps, and other connecting
devices have been used successfully to comply
with these requirements. The ?Standard for
Cold-Formed Steel Framing ? Wall Stud Design?
(AISI, 2005) gives additional information
on design of the stud / track connection.
This standard has been adopted by the 2006
International Building Code, and is available
from the American Iron and Steel Institute
or the Steel Framing Alliance (http://store.steelframingalliancestore.com/wallstuddesign.html).
Note that C1007 is for structural studs: 33mil
or greater, and carrying axial loads or lateral
loads greater than 10 psf. If you are designing
non-structural framing, ASTM C645 describes
the non-structural members, and ASTM C754
gives installation requirements. For the loadbearing
framing members described in ASTM C1007, see
ASTM C955 for member requirements.
Question: Are there
specific provisions in the 2003 IBC for the
anchorage of load bearing exterior and non load
bearing exterior light gauge metal walls to
the foundation? What do you recommend?
Answer: There
are not specific provisions in the International
Code Council's International Building Code
(IBC) for anchorage of cold-formed steel framed
walls; but there are provisions in the International
Residential Code (IRC) for these walls. The
IRC not only has details for this connection,
but references the Standard for Cold-Formed
Steel Framing - Prescriptive Method (AISI
2001) for anchorage, which is typically anchor
bolts through the bottom track at 4' on center.
For non-prescriptive construction, there are
several different methods for wall anchorage
that are acceptable depending upon the load
and the seismic zone. The most common method
is powder actuated pins. Companies like Hilti
and ITW Ramset have technical data on the
holding power in structural steel and concrete;
for the bearing in cold-formed steel, use
the bolt bearing equations in chapter E of
the North American Specification for the Design
of Cold-Formed Steel Structures (AISI, 2001).
These also may be used for other anchorage
to concrete, such as expansion bolts, threaded
anchors (such as Tapcon and Kwik-Con,) Spike
anchors by Powers Rawl, and others. Recent
developments in epoxy anchors have made them
very popular with cold-formed steel framing;
they can be installed in the exact location
required, and the edge distance and spacing
restrictions are less than the expansion anchors.
Question: Must an
L-header extend over and be attached to each
king stud if there are multiple king studs?
Answer: No. The
Standard for Cold-Formed Steel Framing - Header
Design only requires that the L-header lap
over one bearing stud at each end.
Question: In certain
applications, such as with two adjacent windows,
it is desired to run one header over both openings.
How would such a multi-span header be designed?
Answer: The Standard
for Cold-Formed Steel Framing - Header Design
applies only to single-span conditions. Multi-span
headers would need to be designed in accordance
with the AISI North American Specification
for the Design of Steel Structural Members.
Question: How do
I calculate the deflection of a header beam?
Answer: According
to the Commentary on the Standard for Cold-Formed
Steel Framing - Header Design, a conservative
estimate of the vertical deflection of back-to-back
or box headers can be based on the full moment
of inertia of the two C-shape sections alone.
The procedure to calculate the vertical deflection
of an L-header is undefined because the L-header
is an indeterminate assembly consisting of
two angles, cripple studs, and track sections
interconnected by self-drilling screws. However,
the test results indicate that the measured
deflections at an applied load that equal
to the design load was less than L/240, which
should be acceptable in most applications.
Question: What load
combinations are appropriate for the design
of a header?
Answer: The Commentary
to the Standard for Cold-Formed Steel Framing
- Prescriptive Method for One and Two Family
Dwellings provides a detailed description
of the loads, load combinations and design
checks that are appropriate for headers. The
appropriate load combinations are:
| Gravity |
Uplift |
| 1.4D |
0.9D - 1.6W |
| 1.2D + 1.6L + 0.5(Lr or S) |
1.2D + 0.5(Lr or S) + 0.5L - 1.6W
|
| 1.2D + 0.5L + 1.6(Lr
or S) |
1.2D + 1.6(Lr or S) - 0.8W |
Question:
When assembling a back-to-back or box header,
must the track directly beneath the C-shaped
sections face up or down?
Answer: The
Standard for Cold-Formed Steel Framing -
Header Design allows the track directly
beneath the C-shaped sections to face either
way. Typically, the track would face down
when cripple studs and a head track are
used to frame the opening and would face
up when the opening extends to the bottom
side of the header beam and no cripple studs
and separate head track are needed.
Question: When
using steel framing in fire rated wall systems,
is the thickness of the steel the minimum,
or the maximum? I understand that steel transmits
heat, so I thought that the thickness shown
might be the maximum.
Answer:
Each type of header offers certain advantages
and disadvantages; however, the relatively
new L-header offers significant material,
fabrication and installation savings. Due
primarily to the limitations of the testing
that has been performed; the Standard for
Cold-Formed Steel Framing - Header Design
limits L-headers to a maximum span of 16 feet.
L-headers also have limited uplift capacity
and, therefore, may not be suitable for certain
high wind areas.
Question: Can
the moment capacity of the header beam be
based on a composite section of the C-shape
sections plus the track above the header beam,
the track beneath the header beam, and/or
the cripple studs and head track beneath the
header beam?
Answer:
The Standard for Cold-Formed Steel Framing
- Header Design requires a track section above
and beneath the C-shape sections and prescribes
their connection to the C-shape sections with
2 No. 8 screws at 24" on center. Intentionally,
this screw spacing does not provide adequate
restraint to sufficiently engage the track
sections to act compositely with the C-shape
sections. This would require a much closer
and cost prohibitive screw spacing and would
need to be designed in accordance with the
AISI North American Specification for the
Design of Steel Structural Members.
Question: Why
doesn't the Standard for Cold-Formed Steel
Framing - Prescriptive Method for One and
Two Family Dwellings seem to require a check
for wind uplift on back-to-back or box headers?
Answer:
Within the applicability limits of the Prescriptive
Method, uplift due to wind was checked and
was found to never control the selection of
back-to-back or box headers. Therefore, the
tables only consider gravity loads.
Question: Must
my header design conform to the design rules
contained in the Standard for Cold-Formed
Steel Framing - Header Design?
Answer:
Yes. The Standard for Cold-Formed Steel Framing
- Header Design has been adopted by reference
in the 2003 ICC and NFPA building codes and
thus is legally required when the local building
code adopts the these building codes. Headers
that fall outside the applicability limits
of the limitations of the Header Design standard
must be designed in accordance with the AISI
North American Specification for the Design
of Steel Structural Members.
Question: When
using steel framing in fire rated wall systems,
is the thickness of the steel the minimum,
or the maximum? I understand that steel transmits
heat, so I thought that the thickness shown
might be the maximum.
Answer:
The thickness shown in the UL listings is
the minimum. See the info from the UL website
below on cold-formed steel framing.
Question: In the
UL listings for fire ratings, the thickness
is given in gauge. I know that some of the
tests were done many years ago, and thicknesses
and tolerances may have changed. Are the thicknesses
still current?
Answer:
Unless otherwise indicated in the individual
designs, the following minimum metal thickness
tables shall apply where a metal gauge designation
is stated. Metal gauges are no longer referenced
in ASTM Standards. It is still an industry
practice to specify steel components by gauge.
Because many of the designs contained herein
refer to metal gauge the following information
is to be used as a guide where field questions
occur. The tables shown herein are to be used
as a reference and the local Authority Having
Jurisdiction shall be consulted if discrepancies
exist between these tables and a local code
requirement. Due to structural considerations
and fire performance considerations the minimum
thickness tables are different for steel deck
(floor or roof), load bearing studs and non-load
bearing studs.
The minimum thickness for
load bearing steel studs is based upon ASTM
C955-96, "Load-Bearing (Transverse and Axial)
Steel Studs, Runners (Tracks) and Bracing
or Bridging for Screw Application of Gypsum
Panel Products and Metal Plaster Bases". The
color code denoted by the ASTM Standard is
also shown below. For load bearing steel studs,
the minimum bare metal thickness shall be
as follows:
|
Gauge |
Color Code |
Min ThknsBare Metal In. |
| 20 |
White |
0.0329 |
| 18 |
Yellow |
0.0428 |
| 16 |
Green |
0.0538 |
| 14 |
Orange |
0.0677 |
For non-load bearing studs,
the minimum thickness is based upon the gauge
conversion table found in the 1997 Uniform
Building Code. For non-load bearing steel
studs, the minimum bare metal thickness shall
be as follows.
| Gauge |
Min ThknsBare Metal In. |
| 25 |
0.018 |
| 24 |
0.021 |
| 22 |
0.027 |
| 20 |
0.033 |
| 18 |
0.044 |
| 16 |
0.055 |
For additional information
on steel-framed wall and floor-ceiling assemblies,
there is a searchable directory on the Steel
Framing Alliance web site, at www.steelframing.org.
Also, for additional information on the details
and limitations of these systems, go to the
UL web information page on these assemblies:
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Roof Members and Systems
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Truss and Component Assemblies |
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Fasteners and Connectors
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Lateral Systems |
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Fire, Acoustic and Thermal |
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Question: Can mold
grow on steel studs?
Answer:
That's a good question, and one that requires
a little background for the answer.
Mold requires three things
to grow:
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The mold spores, which
exist everywhere there is air; every breath
we take, unless we are in a medical clean
room, contains thousands of mold spores.
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Moisture.
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Organic material, which
provides the food for the mold.
Steel does not contain any
organic material, and therefore cannot support
mold growth. However, if someone or something
has left a residue of organic material on
the steel framing, there is a chance that
given the right conditions, mold could grow.
As with any framing material,
the best practice is to keep the steel studs
dry. Even if they get wet during construction,
or there is a one-time event such as a pipe
bursting in a wall, there should be no long-term
problem if the cavity is dried out properly.
It is persistent wetting, such as a steady
plumbing or roof leak, which causes the greatest
risk of supporting mold. Even then, the mold
will most likely grow on organic surfaces,
such as the paper facing of the gypsum board
or wood framing members, rather than steel.
In steel framing, when everything is clean
and dry, there will be no opportunity for
the mold to grow.
Note that the Steel Framing
Alliance has an excellent publication on this
issue: listed under the - About Steel Framing
- bar on the home page, go to -Issue Papers
- for a free download of the issue paper on
mold.
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Cold Formed Steel (CFS) with other materials |
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Corrosion |
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Question: Wouldn't
enamel coated steel provide better rust protection
for a steel frame home rather than galvanized
steel.
Answer:
Enamel painted steel without a galvanized
coating below does not provide a better protection.
The reason is that zinc, through its sacrificial
galvanic action, can "heal" cuts, scratches,
and abrasions in the steel. With the rough
handling that construction products receive,
as well as the cutting, drilling, shearing,
and fastening of members, the coating gets
cut and scraped away. The galvanized coating
works better than the enamel at covering areas
that are cut or scratched.
Some of the very best coatings
for steel products are painted over galvanized.
The automotive industry has come a long way
over the past 20 years in providing better
coatings, and this is what they use in several
applications. If for some reason the paint
is cut or scratched, the zinc below the paint
can help provide protection, and reduce the
chance of blistering where moisture gets below
the paint surface and rust progresses.
Enamel over galvanized would
be a very effective coating for steel framing.
However, due to the cost, not many manufacturers
make such a product. There are some specialty
coil coaters that will paint material to be
rolled into framing members. As part of the
interior exposed drum wall in the Georgia
Dome, studs were galvanized, painted, and
then covered with a thin sheet of protective
plastic before they were rolled into the "C"
shape. As installers put the framing into
place, they removed the plastic. After over
10 years of exposed, in-place service, these
studs (which can be seen from the seating
area and playing field) are still in excellent
condition.
Please see "Corrosion
protection for life."
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Membership |
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Definitions |
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AISI American Iron and Steel
Institute |
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ASCE American
Society of Civil Engineers |
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AWCI Association of the Wall
and Ceiling Industry |
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CASE Council of American
Structural Engineers |
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CCFSS Center for Cold-Formed
Steel Structures |
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COFS Committee on Framing
Standards |
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COS Committee on Specifications
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CSSBI Canadian Sheet Steel
Building Institute |
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LGSEA Light Gauge Steel Engineers
Association, a Council of the Steel Framing
Alliance |
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MBMA Metal Building Manufacturers
Association |
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MCA Metal Construction Association
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NAAMM National Association
of Architectural Metal Manufacturers |
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NAHB National Association
of Home Builders |
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NCSEA National Council of
Structural Engineers Associations |
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SFA Steel Framing Alliance
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SSMA Steel Stud Manufacturers
Association |
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STCA Steel truss and Component
Association |
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WTCA Wood Truss and Component
Association |
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