Other Common Uses of Light Gauge Steel Framing
Light gauge steel members are used to construct many components of fire-resistant buildings whose structures are made of structural steel, concrete, or masonry. These components include interior walls and partitions , suspended ceilings , and fascias, parapets, and backup walls for such exterior claddings as masonry veneer, exterior insulation and finish system (EIFS), glass-fiber-reinforced concrete (GFRC), metal panels, and various thin stone cladding systems . Light gauge steel members used for framing interior partitions and other non load bearing applications are properly referred to and speciÞ ed as nonstructural metal framing, as distinct from cold-formed metal framing, the latter term reserved for light gauge steel members used in structural applications and exterior wall cladding systems (even though both types of members are, in fact, cold-formed).
Light gauge steel studs can be combined with concrete to produce thin, but relatively stiff, wall panel systems. Both load bearing and non load bearing panels can be made that are suitable for use in residential and light commercial buildings. A variety of production methods are possible that generally involve casting an approximately 2-inch (50-mm)-thick concrete facing onto a framework of steel studs. The concrete may be site cast (on the building site) or precast (in a factory). The concrete-to steel bond may be created by a variety of devices welded or screwed to the studs that then become embedded in the concrete, such as stud anchors, sheet metal shear strips, welded wire reinforcing, or expanded metal. In load bearing applications, the concrete panels provide shear resistance while the steel studs provide most of the resistance to gravity loads and to wind loads acting perpendicular to the face of the panel.
FOR PRELIMINARY DESIGN OF A LIGHT GAUGE STEEL FRAME STRUCTURE:
- Estimate the depth of rafters on the basis of the horizontal (not slope) distance from the outside wall of the building to the ridge board in a gable or hip roof and the horizontal distance between supports in a shed roof. Estimate the depth of a rafter at 124 of this span, rounded up to the nearest 2-inch (50-mm) dimension.
- The depth of light gauge steel roof trusses is usually based on the desired roof pitch. A typical depth is one quarter of the width of the building, which corresponds to a 612 pitch.
- Estimate the depth of light gauge steel floor joists as 120 of the span, rounded up to the nearest 2-inch (50-mm) dimension.
- For load bearing studs, add up the total width of floor and roof slabs that contribute load to the stud wall. A 3 58 -inch (92-mm) or 4-inch (102-mm) stud wall can support a combined width of approximately 60 feet (18 m), and a 6-inch (152-mm) or 8-inch (203-mm) stud wall can support a combined width of approximately 150 feet (45 m).
- For exterior cladding backup walls, estimate that a 3 58 -inch (92-mm) stud may be used to a maximum height of 12 feet (3.7 m), a 6-inch (150-mm) stud to 19 feet (5.8 m), and an 8-inch (100-mm) stud to 30 feet (9.1 m). For brittle cladding materials such as brick masonry, select a stud that is 2 inches (50 mm) deeper than these numbers would indicate.
All framing members are usually spaced at 24 inches (600 mm) o.c. These approximations are valid only for purposes of preliminary building layout and must not be used to select final member sizes. They apply to the normal range of building occupancies such as residential, office, commercial,and institutional buildings. For manufacturing and storage buildings, use somewhat larger members. For more comprehensive information on preliminary selection and layout of structural members, see Edward Edward and Joseph Iano, The Architect’s Studio Companion (4th ed.), New York, John Wiley & Sons, Inc., 2007.
Advantages and Disadvantages of Light Gauge Steel Framing:
Light gauge steel framing shares most of the advantages of wood light framing: It is versatile and flexible; requires only simple, inexpensive tools; furnishes internal cavities for utilities and thermal insulation; and accepts an extremely wide range of exterior and interior finish materials. Additionally, steel framing may be used in buildings for which noncombustible construction is required by the building code, thus extending its use to larger buildings and those whose uses require a
higher degree of resistance to fire.
Steel framing members are signifficantly lighter in weight than the wood members to which they are structurally equivalent, an advantage that is often enhanced by spacing steel studs, joists, and rafters at 24 inches (600 mm) o.c. rather than 16 inches (400 mm) o.c. Light gauge steel joists and rafters can span slightly longer distances than nominal 2-inch (50-mm) wood members of the same depth. Steel members tend to be straighter and more uniform than wood members, and they are much more stable dimensionally because they are unaffected by changing humidity. Although they may corrode if exposed to moisture over an extended period of time, particularly in oceanfront locations, steel framing members cannot fall victim to termites or decay.
Compared to walls and partitions of masonry construction, equivalent walls and partitions framed with steel studs are much lighter in weight, easier to insulate, and accept electrical wiring and pipes for plumbing and heating much more readily. Steel framing,because it is a dry process, may be carried out under wet or cold weather conditions that would make masonry construction difficult. Masonry walls tend to be much stiffer and more resistant to the passage of sound than steel framed walls, however.
Light Gauge Steel Framing and the Building Codes:
Although light gauge steel framing members will not burn, they will lose their structural strength and stiffness rapidly if exposed to the heat of fire. They must therefore be protected from fire in accordance with building code requirements. With suitable protection provided by gypsum sheathing and gypsum wallboard or plaster, light gauge steel construction may be classified as either Type I or Type II Construction in the building code table, enabling its use for a wide range of building types and sizes.