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1TECHNICAL MANUALA Nucor Company

OVERVIEW of LIGHT GAUGE STEEL FRAMING

Making of Light Gauge Steel

Light gauge steel framing members (also called cold-formed steel) are made from structural-quality sheet steel thats formedinto shapes either through press-braking blanks sheared from sheets or coils, or more commonly, by roll-forming the steelthrough a series of dies. Unlike hot-formed structural I-beams, neither process requires heat to form the shape, thus the name

cold-formed steel. Light gauge steel products are usually thinner, faster to produce, and cost less than their hot-formedcounter-parts.

Roll Forming

Roll Forming is a process in which a strip of metal, usually in coil form, is continuously passed through a series of roller diesand progressively formed to the desired shape. Tandem sets of rolls (known as roll stations) shape the metal stock in a series

of progressive stages until the desired cross-sectional configuration is obtained. In many cases roll forming eliminatesmultiple stage production, sub-assembly and finishing operations. Any number of sub-assembly operations can be

continuously combined in the roll forming operation. Because of the progressive manner in which bending takes place, thereis little or no change in cross-sectional area of the work piece.

Roll forming mills generally fall into two categories, outboard and inboard mills. Outboard mills have housings that supportboth ends of the roll tooling shafts. If the shafts are supported at one end only (in cantilever fashion), the mill is said to be of

the inboard variety.

Inboard mills typically are used for thinner materials and for strip edge forming. Sometimes, both inboard and outboardfeatures are incorporated into the same roll forming mill.

Advantages and Limitations of the Process

Cold roll formed shapes can offer superior surface finish. Sharp, clean contours can be maintained. The absence ofdie marks on the material often eliminates the need for additional finishing.

Almost unlimited part lengths are possible. The only limitations on part length are dictated by material handling andshipping capabilities.

Once tooling is made, almost any length and multiple lengths can be produced from the same set of tooling.

Hollow or semi-hollow shapes can be produced with relatively thin walls. Although it is not usually feasible toroll form extremely large components made from thin material (such as rectangular air ducts), roll forming can

effectively be utilized to form the edges of flat material which is later bent into large sheet metal ducts.

The high speed, continuous nature of roll forming lends itself to economic production of large volumes of parts. It cannot, however, normally be used to produce shapes of varying cross-section or parts which have different dimensions

on one end than on the other.

Many additional operations, such as punching, notching, welding, and bending, that otherwise would have to be

performed as secondary operations can be incorporated into the roll forming line, reducing handling and processingcosts. For example, labels can be applied to the shape as an in-line process.

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Pre-punching in-line allows holes or slots to be included in the shape that cannot be done as a secondary operation,

because of their location or features of the part.

Parts can be swept into a continuous radius or rolled into a circular ring such as a bicycle rim.

Roll formed materials generally have a strength advantage over competing processes in structural rigidity applications.

The same tooling can be used to roll a shape out of different materials.

Almost any bendable material can be roll formed. Since roll formed parts are made from sheet metal, the design ofthe product is limited to material of constant thickness and does not provide the opportunity to strengthen bends

with fillets such as in hot rolled shapes or extrusions.

Two different materials can be formed simultaneously to produce a clad shape in one operation.

Two distinct parts can be run together to form one assembly.

Press Braking

Most press brakes are manually fed. The operator holds the work piece between the punch and die against the appropriate

gauge, providing the pre-set dimension for the bend. One type of press brake operation is air bending of sheet metal into astraight-line angle. The punch pushes the work piece into the die cavity. Throughout the entire operation, the work piecetouches only the tip of the punch and the two edges of the lower die. When the force of the upper die is released, the work

piece springs back to form a final angle. The amount of spring back is directly related to material type, thickness, grain andtemper.

In situations requiring dimensional accuracy and angular precision, another forming process is required called Coining or

Bottoming. Coining requires having a punch and die manufactured to the desired final bend angle and forcing the work

piece completely into the die. Coining reduces spring-back; however, this process is limited by the tonnage capacity of thepress brake.

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Advantages and Limitations of the Process

The fundamental advantage of the press brake as a forming tool lies in its flexibility. The use of standard vee-dies

allows economical set-ups and run times on small lots and prototypes. Almost any part size and formed shape can beaccommodated with the standard die sets, eliminating the cost and lead time associated with press form tooling.

Modern press brakes with programmable back gauges using multiple die set-ups have made this forming processmuch more competitive for longer runs.

In cases where product designs require specially shaped tooling, press brake die costs and lead times are

relatively modest.

The enormous range of work piece sizes, which can be accommodated in the press brake, is another significantadvantage. Parts may be as long as the ram (within tonnage limits) and part width is constrained only by the ability toremove the work piece from the machine after forming.

Light Gauge Steel Shapes

Cold-formed steel (CFS) is a term commonly used to refer to cold-formed steel members with design thicknesses ranging from0.0188 to 0.1017 inches (0.48 to 2.58 mm). These members may be wall studs, track, floor joists, roof rafters, bridging

channels, furring channels, or related accessories (see Figure on next page). CFS construction can use individual steelcomponents or prefabricated panels, assembled on site using self-tapping screws to create a whole building structure.

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TYPICAL COLD-FORMED STEEL SECTIONS

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Light Gauge Steel Material and Thickness

Materials

The specifications for the sheet steels that are typically used for either structural or non-structural light gauge steel framing

members are given in ASTM A1003. ASTM A1003 covers the chemical, mechanical and coating requirements for steel sheetused in the manufacture of cold-formed steel framing members such as studs, joists, and track. ASTM A1003 was developed in

order to incorporate requirements for metallic-coated, painted metallic-coated, or painted nonmetallic-coated steel sheet usedfor cold-formed framing members into a single standard. According to the ASTM A1003 standard, Structural Grade Type H steel

is intended for structural framing members and non-structural grade steel is intended for non-structural framing members.

Thickness

The use of the gauge number when ordering or specifying sheet steel thickness is an obsolete concept. The table provides

the correlation between the gauge number and the mil designation thickness. The thickness designations and values areconsistent with standard industry practice, as published by the Steel Framing Alliance and the Steel Stud ManufacturersAssociation (SSMA) document Product Technical Information (see Table). It is recommended that thickness measurements be

taken in the middle of the flat of the flange or web of the cross section.

Design Thickness

Section A3.4 of the AISI North American Specification for the Design of Cold-Formed Steel Structural Members, 2001 Edition,American Iron and Steel Institute, Washington, DC permit the minimum delivered thickness of a cold-formed steel member

to be 95% of the design thickness.

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Studs and Tracks

A stud is a basic cold-formed steel shape used for structural framing members (such as studs, joists, headers, beams, girders,and rafters). The name comes from the members C shaped cross-sectional configuration consisting of a web, flange and

lip. It is also called a C-section. The Figure shows the cross-section and defines the different parts of the C-Shape. Webdepth measurements are taken to the outside of the flanges. Flange width measurements also use outside dimensions. The

lip is the part that extends from the flanges at the open ends. The lip typically increases the strength characteristics of themember by acting as a stiffener to the flange.

Tracks are used for applications such as top and bottom plate for walls and band or rim joists for flooring systems. A track hasa web and two flanges, but no lips. Track web depth measurements are taken to the inside of the flanges. The Figure shows

the cross-section and defines the different parts of the track.

Physical Dimensions

Cold-formed structural steel members are produced to comply with the ANSI/AISI Standard for Cold-Formed Steel Framing

General Provisions. Stiffening lips for studs are standardized based on the flange width as shown in the Table. Inside bendradii are also shown in the table.

CORRELATION BETWEEN GAUGE NUMBER

AND MIL DESIGNATION

Designation

(mils)

Minimum Uncoated

Thickness (in.)

Design Thickness

(in.)

Reference Gauge

Number

ASTM C955

Color Code

18 0.018 0.0188 25

21 0.021 0.022 24

27 0.027 0.0283 22

30 0.030 0.0312 20

33 0.033 0.0346 20 White

43 0.043 0.0451 18 Yellow

54 0.054 0.0566 16 Green

68 0.068 0.0713 14 Orange

97 0.097 0.1017 12 Red

118 0.118 0.1242 10

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MINIMUM STIFFENER SIZE FOR C-SHAPED MEMBERS

MAXIMUM INSIDE BEND RADIUS FOR C-SHAPED MEMBERS

Section Flange Width (in.) Design Lip Stiffener (in.)

S125 1 1/4 3/16

S137 1 3/8 3/8

S162 1 5/8 1/2

S200 2 5/8

S250 2 1/2 5/8

Designation(mils)

Reference GaugeNumber

Bend Radius (in.)

18 25 0.0937

21 24 0.0937

27 22 0.0937

30 20 0.0937

33 20 0.0937

43 18 0.0937

54 16 0.113

68 14 0.143

97 12 0.203

118 10 0.248

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STUD (S) TRACK (T)

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A universal identification and designation system was developed by the steel industry to overcome the varied designationapproaches that were produced by each individual manufacturer. The designation is used to identify not only a specific

steel framing member, but also in identifying the section properties of that same member through the use of the producttechnical information document.

The new universal designator system The Right STUF easily identifies any common light gauge steel framing member. This

new labeling system directly addresses and helps eliminate the problems associated with a lack of standards among steel studproducers. The new universal designator system uses the web depth, flange width, and minimum base metal thickness of theframing member, in conjunction with S-T-U-F designators:

S = Stud or Joist Sections with Flange Stiffeners (Cee Shapes)

T = Track Sections

U = Cold-Rolled Channel or Channel Studs (without Flange Stiffeners)

F = Furring Channels

L = Angle or L-header Sections

The flange width and web depth of steel members are expressed in 1/100th inches, and the minimum base metal thickness

is expressed in mils (1/1000th inches). Examples of the new designation system are shown.

MEMBER DESIGNATION

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Standard Designation Illustration - Stud

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Standard Designation Illustration - Angle

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Standard Designation Illustration - Joist

Corrosion Protection

Building owners expect their structures to last for a lifetime or more. Therefore, it is critical that framing materials have theproper protection to provide this longevity. With steel, the proper protection comes in the form of galvanizing. Galvanizing isthe process whereby steel is immersed into a bath of molten zinc to form a zinc coating.

Steel sheets, before being rolled into coils, are generally sent through a hot-dipped galvanizing process that applies a

metallic zinc coating to protect the steel from rust. Coated steel, therefore, is designed not to rust while on the constructionjob site, during construction, or after construction. A protective barrier (i.e., zinc) on the surface that does not allow moisture

to contact the steel prevents corrosion of steel framing members. Zinc galvanizing also protects the steel by acting as asacrificial coating and provides long-term integrity against rusting. If steel gets scratched, dented, cut, or punched, thecoating will continue to protect the exposed area sacrificially. This reaction causes the zinc to expand across the exposed steel

and reseal the protective barrier.

The galvanizing process can apply a number of different coatings that vary in appearance and coating thickness. Three

different types of coatings are commercially available for cold-formed steel:

Galvanized - This is the standard process of continuous coating with pure zinc. The finished coating provides good

corrosion resistance and excellent sacrificial protection.

Galfan - This type of coating contains aluminum in addition to zinc. It has an improved corrosion resistance compared to

galvanized coatings.

Galvalume - This type of coating contains higher percentage of aluminum and added silicone to zinc. It provided asuperior corrosion resistance compared to galvanized coatings.

The degree of corrosion protection is measured by the coating weight (ounces per square foot) or by thickness (mils ormicrons) of the coating. A G60 coating for example, has a total weight of 0.60 oz/ft2 (both sides) and a 0.51 mils (0.013 mm)

nominal thickness per side.

The minimum metallic coating for cold-formed steel members must comply with ASTM A1003 Standard Specification for SteelSheet, Carbon, Metallic- and Nonmetallic-Coated for Cold-Formed Framing Members. ASTM A1003 minimum coating

designations assume normal exposure conditions that are best defined as having the framing members enclosed within abuilding envelope or wall assembly within a controlled environment. When severe exposure conditions are probable, such asindustrial atmospheres, arid regions or marine atmospheres, consideration should be given to specifying a heavier coating.

800Joist web depth

8 deep

SStud or Joist with

lips

1621-5/8 Flange

(1.625)Min. base metalthickness in mils

(0.054 = 54 mils)

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Other approved metallic coatings shall be permitted provided the alternate coatings can be demonstrated to have a

corrosion resistance that is equal to or greater than the corresponding hot-dipped galvanized coatings (i.e. G40 and G60) andprovides protection at cut edges, scratches, etc.

ASTM C955 provides the following table for the minimum coating requirements for cold-formed steel framing used in load

bearing applications:

Minimum Coating Requirements

Coating Designator

Steel Component Reference ASTM Standard

A653/A 653M

(Zinc Coated)

A792/A792M

(Al-Zinc)

A875/A 875M

(Zinc-5% AI)

Structural G60/Z180 AZ50/AZ150 GF30/ZGF180

Non-Structural G40/Z120 AZ50/AZ150 GF30/ZGF135

Direct contact with dissimilar metals (such as copper, brass, etc.) should be avoided in order to prevent corrosion. The use ofnon-conductive non-corrosive grommets at web penetrations or through the use of non-metallic brackets (a.k.a. isolators)

fastened to hold the dissimilar metal building products (such as piping) away from the steel framing could be used to preventcorrosion.

Builders should be careful in placing steel in wet or damp building materials, as well as the potential for those materials to

absorb water during the buildings life, as both circumstances may accelerate corrosion. The Table below provides theminimum corrosion protection of steel members subjected to normal exposure.

Minimum Coating Requirements

Zinc Coated A Zinc Iron B 55% AI-Zinc C Zinc-5% D

G90

G60 A60

N

AZ 50

AZ 50 GF 45

GF 30

Notes:

A Zinc-coated steel sheet as described in ASTM A653/A653M.

B Zinc-iron alloy coated steel sheet as described in ASTM A653.

C 55% Aluminum-zinc alloy coated steel sheet as described in ASTM A792/A792M

D Zinc- 5% aluminum alloy coated steel sheet as described in ASTM A875/A875M

E In accordance with the requirements of A 1003.

F ISO International Standard 9223.

The metallic coated substrate shall meet all the prescribed requirements. In addition, the

paint film shall have a minimum thickness of 0.5 mil per side (primer plus top coat) with a

minimum primer thickness of 0.1 mil per side.

Non-metallic coated substrate shall be painted after roll forming and shall have a minimum

paint thickness of 1.0 mil on all surfaces including edges. Use of painted product is limited to

environments where the rate of corrosion is low; typically areas such as interiors of buildings

and areas of low rainfall and low humidity as defined by ISO 9223, category 1 and 2 E,F.

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Cold-Formed Steel Contact with Wood

Metallic coated steel does not react with dry wood. Dry pressure-treated lumber is also not corrosive to zinc and no specialrequirements are needed to fasten steel to wood framing. Galvanized nails and screws have been successfully used to join

wood and steel for years.

Cold-Formed Steel Contact with Other Metals

An electrochemical reaction occurs between dissimilar metals or alloys that can cause corrosion of one metal and protection

of the other when they are in contact. This reaction will only occur when the dissimilar metals are connected in an electrolytemedium (such as moisture). In normal indoor environments, moisture levels are usually very low and, consequently the

galvanic action between dissimilar metals is much lower than those occurring in outdoor environments. Steel framingmembers are generally coated with zinc or aluminum alloy. Both zinc and steel will react adversely with brass and copper used

for plumbing installations this is known as a galvanic reaction or galvanic corrosion and can lead to durability problemsjust like other forms of corrosion. Steel framing members can be easily isolated from other metals by plastic insulators or grommets.

Cold-Formed Steel Contact with Mortar and Plaster

Fresh mortar and plaster may attack zinc and zinc alloy coating when damp, but corrosion ceases when the materials dry.

Cold-Formed Steel Contact with Drywall and Insulation Products

Drywall, mineral wool, cellulose, and rigid foam insulating products do not react with galvanized steel.

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Performance of Light Gauge Steel in Homes

Steel framing members:

Steel framing members located in an indoor atmosphere (such as wall and floor framing) have a very low rate of corrosion.

Studies showed that the corrosion of zinc is lower than 0.1 microns per 3-year period in houses located in different rural, urban,marine, and industrial atmospheres. It can be concluded that a typical G40 zinc coated steel (10 microns = 0.39 mils) shouldlast for more than 200 years [AISI Publication RG-9605, Durability of Cold-Formed Steel Framing Members, American Iron and

Steel Institute, Washington, DC].

An ongoing research project at the NAHB Research Center is investigating the corrosion rate of light gauge steel framing inresidential dwellings. The research program is a five-year monitoring study where galvanized steel samples installed in wall,

ceiling, attic and decks of steel framed homes are retrieved at 1-year, 3-year, and 5-year intervals. The steel samples arelocated in steel houses in:

Miami, Florida

Long Beach Island, New Jersey

Leonardtown, Maryland

Hamilton, Canada

The results of the 1-year and the 3-year samples showed negligible corrosion of the steel and provided an estimated life

expectancy of the structure (house framing) at approximately 250 years.

The University of Hawaii is also conducting a similar ongoing project in Hawaii, where steel samples are located throughoutthe island and retrieved at specific time intervals.

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Light Gauge Steel Construction Methods

The three basic light gauge steel assembly methods are stick-built construction, panelized systems, and pre-engineeredsystems.

Stick-Built Construction

Stick-built construction is virtually the same in wood and steel. This framing method has actually gone through a transformationincorporating many of the techniques used in panelized construction. The steel materials are delivered to the job-site in stock

lengths or in some cases cut to length. The layout and assembly of steel framing is the same as for lumber, exceptcomponents are fastened together using screws, pins, clinches (or other approved fasteners) rather than nailed. Steel joists

can be ordered in long lengths to span the full width of the building. This expedites the framing process and eliminates lapjoints. Sheathing and finish materials are fastened with screws or pneumatic pins.

Panelized Systems

Panelization consists of a system for pre-fabricating walls, floors and/or roof components into sections. This method ofconstruction is most efficient where there is a repetition of panel types and dimensions. Panels are most effectively fabricated

in a manufacturing environment with strong quality control procedures. A jig is developed for each panel shape. Steel studsand joists are cut-to-length, placed into the jig and fastened either by screws, welding or clinching.

Shop panelization can offer several significant advantages to the builder. The panel shop provides a controlled environmentwhere work can proceed regardless of weather conditions. Although the panels must be transported from the panel shop to

the job, most often the cost advantages of panelization offset the added transportation costs.

A major benefit of panelization is the speed of erection. A job can usually be framed in about one quarter of the time requiredto stick-build.

Pre-Engineered Systems

Because of steels high strength and design flexibility, innovative systems are possible which are not possible using othermaterials. Engineered systems typically space the primary load carrying members more than 24 inches on center, sometimes

up to 8 feet. These systems use either secondary horizontal members to distribute wind loads to the columns or lighter weightsteel in-fill studs between columns.

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Manufacturing Tolerances

Manufacturing tolerances for load bearing (structural) cold-formed steel members are given in ASTM C 955 (see Table 1) while

those for non-load bearing (nonstructural) members are given in ASTM C 645 (see Table 2).

Table 1 - Manufacturing Tolerances for Structural Members (See Figure 1 on page 19)

1. All measurements shall be taken not less than 1 ft (305 mm) from the end.

2. Outside dimension for stud; inside dimension for track.

Dimension 1 Item Checked Studs, in. (mm) Track, in. (mm)

A

B2

C

D

E

F

G

H

I

Length

Web Width

Flare

Overbend

Hole Center

Width

Hole Center

Length

Crown

Camber

Bow

Twist

+3/32 (2.38) + 1/2 (12.7)

-3/32 (2.38) -1/4 (6.35)

+1/32 (0.79) +1/32 (0.79)

-1/32 (0.79)` +1/8 (3.18)

+1/16 (1.59) +0 (0)

-1/16 (1.59) -3/32 (2.38)

+1/16 (1.59) NA

-1/16 (1.59) NA

+1/4 (6.35) NA

-1/4 (6.35) NA

+1/16 (1.59) +1/16 (1.59)

-1/16 (1.59) -1/16 (1.59)

1/32 per ft (2.6 per m) 1/32 per ft (2.6 per m)

1/2 max (12.7) 1/2 max (12.7)


1/2 max (12.7) 1/2 max (12.7)


1/2 max (12.7) 1/2 max (12.7)

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Table 2 - Manufacturing Tolerances for Non-Structural Members (See Figure 1 on page 19)

1. All measurements shall be taken not less than 1 ft (305 mm) from the end.

2. Outside dimension for stud; inside dimension for track.

Dimension 1 Item Checked Studs, in. (mm) Track, in. (mm)

A

B2

C

D

E

F

G

H

I

Length

Web Width

Flare

Overbend

Hole Center

Width

Hole Center

Length

Crown

Camber

Bow

Twist

+1/8 (3.18) + 1(25.40)

-1/4 (6.35) -1/4 (6.35)

+1/32 (0.79) +1/8 (3.18)

-1/32 (0.79) -0 (0)

+1/16 (1.59) +0 (0)

-1/16 (1.59) -3/16 (4.76)

+1/8 (3.18) NA

-1/8 (3.18) NA

+1/4 (6.35) NA

-1/4 (6.35) NA

+1/8 (3.18) + 1/8 (3.18)

-1/8 (3.18) - 1/8 (3.18)

1/32 per ft. (2.6 per m) 1/32 per ft (2.6 per m)

1/2 max (12.7) 1/2 max (12.7)


1/2 max (12.7) 1/2 max (12.7)


1/2 max (12.7) 1/2 max (12.7)

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Figure 1 Manufacturing Tolerances

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Steel offers homes and buildings a product that termites and other bugs cant eat, shifting soil cant crack, and fire and

extreme weather cant destroy. Buildings that are made from recyclable material will not rot, are environmentally friendly,non-toxic, and very affordable. Steel structures can be built with any type of foundation and can be finished with any

material available: brick, stucco, siding, etc. The completed building incorporates the many inherent advantages to building

with steel, such as:

Strength: Steel offers the highest strength-to-weight ratio of any framing material.This strength allows for the use of less material while framing a stronger structure. The strength of steel makes it the materialof choice in areas subject to natural disasters such as hurricanes, tornadoes, and earthquakes. Steel framed structures can

be designed to withstand wind forces of 150 MPH and other natural disasters required by code in each area.

Safety:The strength of steel offers greater protection to you and your family during hurricanes, tornadoes, earthquakes,and thunderstorms.The high strength of steel and the positive connections that the fasteners provide allow for greater protection duringhurricanes and high winds. The non-combustible properties of steel means that the framing material will not start a fire,

or contribute fuel to a fire once it has started. Steel also offers a safer environment during lightning storms due to the factthat it provides a direct path to the ground. This reduces the chance of explosions, secondary fires, or personal injury.

Energy Efficient: The fact that steel is dimensionally stable eliminates the settling associated with other framingproducts. This reduces air infiltration and lowers utility bills.Combining steel-framed exterior walls with other systems results in energy savings and helps preserve our precious

forest resources. The energy transmission through a wall is directly related to the resistance (R) provided by construction.Increasing the R-value, or resistance, means less heat will be transmitted. Research has shown that the wall R-value is

not affected much by the thickness of the steel stud. Because the stud web thickness is small compared to otherdimensions, the heat conducted through the stud web is somewhat limited. Where higher R-values are required, the useof exterior insulated sheathing, such as extruded polystyrene or polyisocyanurate foam, forms an effective thermal break

and increases R-values significantly.

Environmental: Steel is 100% recyclable, making steel the material of choice for the next generation.Steel is a product that is 100% recyclable, making it an environmentally friendly material. Steel is recognized by TheHealthy House Institute as the framing material of choice due to the fact that it does not contain resins or other

chemicals found in other framing materials. Also, steel does not out-gas as other materials do. Steels environmentalbenefits make it the building material that our kids can be proud of. Steel is hypoallergenic-no allergy problems arecaused by steel. Steel is the most recycled product on earth today.

Quality: Steel structure will not warp, crack, twist, bow, rot, shrink, orswell which leads to superior quality for years to come.Every piece is straight and dimensionally stable, thus straight, plumb walls are quickly and easily achieved. Walls remain

straight and corners square for the life of the building.

Advantages of Steel Framing

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Steel studs, tracks, joists and trusses are manufactured according to strict standards of strength and consistency. This

uniformity results in straight walls, properly joined headers, and cost savings on the job. Choosing steel framing is not onlypractical, but it ensures that you get a product of superior quality. Building owners can enjoy substantial savings in long-term

maintenance costs, higher resale values, and peace of mind.

Non-combustible: Steel will not burn, eliminating the third leading type of house fires, those that are started in theframing of the building.Flexible: Steel can be designed for longer spans that create more open floor plans and fewer load bearing walls.

The strength of steel allows for the design of larger spans, creating more open floor plans. Steel is also easily remodeled dueto the fact that there are generally fewer load-bearing walls. Connections are made with screws/bolts that have specific design

strength and can easily be taken apart to allow for building expansions.

Termite Proof: Steel is impervious to termites and other wood boring insects, thus eliminating the structural damagethat can be caused by these insects. Steel provides health benefits to builders and owners because they do not requirepesticides or other chemicals used in wood framing.Value: The price of steel is more stable than other building materials allowing the use of steel to be cost-effective.

Builders can get a much longer price guarantee on steel vs. wood. Steel framed ceilings and walls are straighter and stronger,

window and door openings are square and floors are less prone to squeaks. Some insurance companies offer discounts onsteel framed structures.

Code Acceptance: Steel framing is backed by national building codes, and is accepted into the International BuildingCode (IBC), CABO One and Two Family Dwelling Code, the International Residential Code (IRC), and NFPA Code.Benefits to Builders

Lighter than other framing materials Easy material selection Straight walls and square corners

Residential steel framing members are manufactured with pre-punched holes for piping and electrical wiring,

minimizing prep work Windows and doors open and close as they should Small punch list

Less scrap and waste (2% for steel vs. 20% lumber) Price stability (prices on steel have been flat since 1980 and are not volatile) Environmental selling and green positioning

Consumer perceives steel as better

Benefits to Consumers Strength results in safer structures, less maintenance and slower aging of structure

Fire safety Not vulnerable to termites and other wood-destroying insects Not vulnerable to any type of fungi or organism

Less probability of foundation problems Less probability of damage in an earthquake

Less probability of damage in high winds Insurance rates

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Fastening of Light Gauge Steel Framing

Cold-formed steel framing members can be connected or fastened using any or a combination of the following fasteningmethods:

Screws

Screws are by far the most common fasteners used in framing cold-formed steel members (see Figure 1). Self-drilling, tappingscrews are the most prevalent fastener. Screws are typically applied with a positive-clutch electric screw gun.

Screws are available in sizes ranging from No.6 to No.1/4, with No.6 to No.10 being the most common. Lengths typically varyfrom 1/2 inch (12.7 mm) to as much as 3 inches (76 mm) depending on the application. Screws are generally 3/8 inch (9.5 mm)

to 1/2 inch (12.7 mm) longer than the thickness of the connected materials so that a minimum of three threads extendsbeyond the connected material. It is important that the drill point be as long as the material thickness being fastened to

drill effectively. The correct fastener type and length of each application should be selected by consulting the screwmanufacturers specifications and catalogs.

Screw Point Type

1. Self-drilling tapping screws (see Figure 2) are externally threaded fasteners with the ability to drill their own hole andform or cut their own internal mating threads into which they are driven without deforming their own thread and

without breaking during assembly. Self-drilling screws are high-strength, one-piece, one-side-installation fasteners.These screws are typically used with 33 mil (0.8 mm) steel or thicker. They are also used when fastening two or morepieces of steel of any thickness. Self-drilling point styles are listed as #2, #3, #4 and #5. The higher the number, the

thicker material the screw is designed to drill. The self-drilling point style requires more consideration due to the varietyof thicknesses and possibility of multiple layers being joined.

2. Self-piercing tapping screws (see Figure 3) are externally threaded fasteners with the ability to self-pierce metallic

material, form a sleeve by extruding metallic material and tap their own mating threads when driven. Self-piercingscrews are high-strength, one-piece, one-side-installation fasteners, with sharp point angles under 30. Theself-piercing point style is recommended for connections of less than 33 mil (0.84 mm) steel.

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Screw Body Diameter

The body diameter of a screw is related to the nominal screw size as shown in Table 1. Most connections are made with aNo. 8 screw, except when attaching gypsum wallboard where No. 6 screw is typically used.

Table 1 Screw Body Diameter

Screw Length

The length of the screw is measured from the bearing surface of the head to the end of the point as shown in Figure 4. For

example, the length of a flat or countersunk head is measured from the top of the head to the end of the point. A pan headscrew length is measured from under the head (bearing surface) to the end of the point.

The length of self-drilling screws may require special consideration since some designs have an unthreaded pilot section orreamer with wings between the threads and the drill point as shown in Figure 5. These features may be necessary for certain

applications such as applying wood sheathing to a steel floor joist. The long pilot point or reamer is required to allow the screwto drill through the material before engaging the threads. If the threads engage before the pilot hole is drilled completely, a

gap may result in the connection. This can result in a squeaky floor or screw-pops through certain finishes.

Threads

Self-piercing and self-drilling screws (see Figures 2 and 3) intended for cold-formed steel applications generally have a coarse

thread (e.g., 10-16x5/8 HWH SD, would indicate a 10 diameter, 16 threads per inch, 5/8 (16 mm) length, hex washer head,self-drilling screw.) There are also many self-drilling screws that have fine threads for use in thicker steel. Manufacturers

recommendations should be followed.

Head Styles

Common head styles include flat, oval, wafer, truss, modified truss, hex washer head, pan, bugle, round washer, and pancake

(see Figure 6). Specialty features may also be on the head, one of which is cutting nibs under the head of a flat head design.Cutting nibs are designed to aid in counter sinking the flat head design in dense materials. The drive system may be a Phillips,square or other proprietary design. Which style is specified may be determined by the application, preference, and

availability. However, hex head screws are typically used for heavier structural connections. Round washer screws are typicallyused for general framing connections. Low profile heads are used on surfaces to be finished with gypsum board. Bugle head

screws are typically used to attach sheathing products.

Screw Number Designation Nominal Diameter, d, (in)

6 0.13807 0.15108 0.1640

10 0.190012 0.21601/4 0.2500

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Screw Body

The body of the screw includes the threads and any designed special features. These special features may include a shankslot. This is a section cut out of the shank for chips of material to have a place to escape, relieving driving torque. The shankslot is located directly above the drill point of the screw.

Drive Types

Drive types are usually determined by availability and preference. Common drive types are shown in Figure 7.

Drill Capacity

Drill capacity is defined as the total thickness the screw is designed to drill. If a fastener is chosen with a drill point that is toolarge, it may result in a stripped connection. If the drill point is too small the screw may fracture and break. The drive type andhead style are typically related to individual preference, but may be a consideration for each application. An example of a

misapplication is the use of a hex washer head in a framing connection. If drywall is specified as the finish material, the hexwasher head will cause a bulge in the drywall finish.

Screw Requirements

For all connections, screws should extend through the steel a minimum of three exposed threads as shown in Figures 8 and9. Screws should penetrate individual components of a connection without causing permanent separation between the com-

ponents. Screws should be installed in a manner such that the threads and holes are not stripped.

Screw Point Style

Self-drilling point styles are defined in the Society of Automotive Engineers (SAE), J-78 document for Self-Drilling Tapping

Screws. The self-drilling point style requires consideration due to the variety of thicknesses and possibility of multiple layersbeing joined. Self-drilling point styles are listed as #2, #3, #4 and #5. The higher the number, the thicker material the screw is

designed to drill (refer to Table 2 and Figure 10).

Screw Designation

Screws are typically designated by the diameter, thread, head style, point type, and length as shown in Figure 11.

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Stripped Screws

It is unreasonable to expect that there will be no stripped screws in a connection. Research at the University of Missouri-Rollahas shown that the structural performance of a single-shear screw connection is not compromised if screws in the connectionhave been inadvertently stripped during installation. The results of the UMR research have been incorporated into the AISI

General Provisions Standard which stipulates that stripped screws in direct tension shall be considered ineffective. Stripped

screws in shear shall be permitted to be considered effective provided the number of stripped screws considered effectivedoes not exceed 25% of the total number of screws (for each connection) considered effective in the connection.

Screw Spacing and Edge Distance

The AISI Specification stipulates that the center-to-center spacing of screws be at least 3 times the screw diameter. During

installation if this spacing is only 2 times the diameter the structural performance of the connection will be reduced. Guidelinesfor center-to-center spacing of less than 2 times the diameter are not stipulated because the screw head diameter precludes

a smaller spacing.

Pneumatically Driven Pins

Pneumatic pins and nails are specifically designed with spiral grooves or knurls on the nail shaft to penetrate the steel (seeFigure 12). Similar to wood framing, drive pins and nails are used with air guns. Wood sheathing (such as sub-flooring) can be

fastened to steel members with drive pins. Care should be taken to follow manufacturer recommendations to avoid problemssuch as squeaky floors. Additional guidance on pneumatically driven pins is provided in the Light Gauge Steel Engineers

Association document Pneumatically Driven Pins for Wood Based Panel Attachment.

Bolts

Bolts are typically used to anchor cold-formed steel members to foundations. The most common anchors used in steel

construction are anchor bolts, mudsill anchors, anchor straps, mushroom spikes, and powder-actuated anchors. Washers andnuts should be properly installed and tightened where required. Bolts connecting CFS to concrete shall have bolt holes spaced

a minimum of three bolt diameters on center. The distance from the center of the bolt hole to the edge of the connectingmember shall not be less than one and one-half bolt diameters.

Mudsill Anchors: Anchors that fit in the bottom track to hold the wall down, usually available from specialty fastenercompanies, such as Simpson Strong-Tie, or fabricated in the field.

Anchor Straps: Steel straps that are embedded in the slab and bend up to attach to the wall studs. Mushroom Spikes: Expansion bolts that expand in pre-drilled concrete holes, typically used to hold down bottom track

or rim joists.

Powder Actuated Fasteners: Pins fired by a special gun to hold the bottom track down to the foundation.

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Welds

Welded (see Figure 13) areas must be treated with a corrosion resistant coating, such as a zinc rich paint. This is done tomaintain acceptable durability of a welded connection. Additional guidance on welding of cold-formed steel members isprovided in the Light Gauge Steel Engineers Association document Welding Cold-Formed Steel.

Clinches

Clinching is a method of joining two pieces of sheet metal by pressing them together into a die that forms a connection sim-ilar to a rivet. This technology, although not new, has only recently been used for attaching residential steel framing members.

Clinched connections are especially popular in factory settings and panelized construction. Figure 14 illustrates some clinchedjoints that are currently available.

The majority of clinched connections are made with pneumatic or hydraulic tools, although manual clinchers are available. A

clincher makes a connection by driving a punch into a die through overlapping material. When the material is forced to thebottom of the die, the die begins to mushroom. The die expands to allow full development of the connection. When thepunch reaches its final position, it is withdrawn and the die returns to its original shape. The result is a connection very

similar to that of a rivet. The strength of a clinched connection is approximately the same as that of a self-drilling screw. Theclinching process will not harm the galvanized coating on framing members. Many of the currently available clinching tools

are limited to use in a warehouse/factory environment. It is usually difficult to loosen connections when necessary. Clinchingequipment is currently not widely available.

Additional guidance on clinching of cold-formed steel members is provided in the Light Gauge Steel Engineers Associationdocument Clinched (Integral) Fastening of Cold-Formed Steel.

Adhesives

The use of adhesive in residential and light commercial cold-formed steel structural application is not common. Adhesives are

primarily used in factory settings and panelized construction. Adhesives are also used between floor joists and floorsheathing and between wall studs and wall covering.

Powder Actuated Fasteners

Powder actuated fastening systems consist of specially designed fasteners, installation tools, and powder loads which aredesigned to function in combination to provide optimum performance. Powder actuated fasteners need to be used withprecision and accuracy in the field to ensure proper application. The use of powder actuated fastening systems in the

construction industry developed rapidly because of the significant speed of installation, which resulted in considerable cost

savings. These systems provide the contractor with the ability to fasten into concrete, masonry, and structural steel withoutpre-drilling holes. For most applications, this eliminates time consuming layout or hole spotting resulting in faster installationand reduced costs. In addition, powder actuated fastening systems are completely portable and are ideal for locations that

are difficult to access. Today, powder actuated fastening technology has become the standard method of attachment for manyapplications in the construction industry.

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Rivets

Rivets are structural fasteners used primarily in the aircraft, bridge and auto industries. Rivets are formed by first drillingslightly oversized holes (via the use of number drills) in the metal so that the rivet can easily be introduced after debarring.The correct rivet size depends on the total metal thickness, called the grip. Then the rivet is squeezed. (Compression is

achieved by a rivet gun and a bucking bar. The pneumatic gun hammers on one side while the bucking bar, which issimply a heavy chunk of steel, provides the reaction on the other.) When the rivet shank is compressed, its diameter grows

until the hole is completely filled. When the rivet is further compressed, it can only grow further outside the hole and thus theformed head is shaped which also gives a correct formed head dimension.

Figure 2 - Self-Drilling Tapping Screw Figure 3 - Self-Piercing Screw

Figure 1 - Screws

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LIGHTGAUGESTEEL

FRAMING

The NU Way to Build.NUCONSTEEL.COM NUCONSTEEL, 2005. ALL RIGHTS RESERVED. NOT FOR RESALE, DUPLICATION OR DISTRIBUTION.

Figure 4 - Screw Length Measurement

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Figure 5 - Screw Grip Range

Figure 6 - Screw Head Type

Pan Head

Round Head

Round Washer

Mod. Truss (Lath)

Hex Head

Hex Washer

Truss Head

Oval Head

Flat Head

Trim Washer

Bugle Head

Pancake Head

Wafer Head

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Figure 7 - Screw Drive Types

Figure 8 - Fastening Sheathing to Steel

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Figure 9 - Fastening Steel to Steel

Figure 10 - Screw Point Style

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Figure 11 - Typical Screw Designation

Figure 12 - Pneumatically Driven Pins

(0.1900 in)

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Figure 13 - Welding of Cold-Formed Steel Framing

Figure 14 - Clinches

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Table 2 - Suggested Screw Sizes

FOR STEEL-TO-STEEL AND STRUCTURAL FLOOR SHEATHING-TO-STEEL CONNECTIONS

For SI: 1 in. = 25.4 mm

1 For screw point style, refer to Figure 10.

Screw Size Point Style1 Total Thickness of Steel (inches)

6 2 0.036 0.1008 2 0.036 0.100

10 2 0.036 0.11012 2 0.050 0.140

14 2 0.060 0.12018 2 0.060 0.1208 3 0.100 0.140

10 3 0.110 0.17512 3 0.110 0.210

14 3 0.110 0.22012 4 0.175 0.2201/4 4 0.175 0.250

12 4.5 0.145 0.31212 5 0.250 0.500

1/4 5 0.250 0.500

Figure 15 - a. and b. - Rivets

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