Light Gauge Steel Framing

Metal: Light Gauge Steel (CSI Divisions 05 and 09)

• Shares advantages with wood light framing: versatile, flexible, noncombustible, insect-attack immune, lighter weight, and stable due to factory production.
• Disadvantages include: frequent bracing needs because of thinness, heat conduction, thermal bridging requiring special attention, and smaller labor pool.
• Trusses can be made from light gauge steel.

Framing Methods

• Framing parallels wood construction techniques.
• Steel joists are placed 12-24 inches apart and framed into tracks or channels.
• Web stiffeners or reinforcing are used where loads may cause joist buckling.

Sizing

• Available in various sizes.
• Tracks are similar to sill/sole plates.
• Furring channels (hat channels) use light gauge steel members.
• Depths of 7/8 or 1-1/2 inches; widths of 1-1/4 inches at the raised surface, 2-1/2 inches at the base
• Allow flat wall finishes over irregular surfaces.
• Provide concealed spaces for plumbing, wiring, and thermal insulation.
• Z-furring channels and adjustable furring options available.

Headers

• L-headers are used above doors or windows.

Accessories

• Jamb studs are pre-made for doors and windows with deeper returns and secondary returns.
• Sheet metal thickness: the bigger the gauge the smaller the thickness
• Loadbearing: 12-20 gauge
• Nonloadbearing

Steel Cutting and Fastening

• Circular saws can cut steel.
• Fastening methods include welding (plug, slot, flare vee).

Metal: Steel Construction (Division 05)

• Steel is one of three commonly used noncombustible materials, along with concrete and masonry.
• Used for buildings of all sizes.
• It's versatile but expensive.

Material Properties

• Cast iron: 2-4% carbon, strong in compression, less in tension, brittle, prone to sudden failure.
• Steel: Less than 2% carbon.
• Wrought iron: Little to no carbon, strong in tension, weaker in compression, malleable, easily shaped, relatively soft.
• Carbon content dictates steel properties. Too much carbon leads to hardness but brittleness; too little makes it soft and malleable.
• Mild steel: Low carbon (.3%), small amounts of other alloys like nickel and chromium, improves strength and toughness, reasonably strong, highly ductile, easily welded, equally strong in tension and compression.

Steel Making Process

• Combines ore, limestone, and coal.
• Charging scrap: Scrap metal is charged into furnace.
• Meltdown begins: Electrodes are lowered, and electric current is applied, using external energy.
• Oxygen is injected to oxidize impurities and enhance heating, flux is added to remove impurities.
• Additional scrap may be added after melting.
• The molten mixture is sampled, adjusted, and poured; alloying elements may be added.

Casting and Rolling

• Steel is cast into shapes ranging from plain rectangles/rounds to beam blanks/blooms.
• Structural shapes are made in a rolling mill after reheating blanks to the necessary temperature.

Shapes

• W10 X 30: Wide-flange shape, nominally 10 inches deep, weighing 30 pounds per lineal foot. Wide-flange (W-shape): Common for beams and columns.
• Channels, angles, tees: Used for trusses and lighter-weight framing.
• American Standard: Traditional I-beam, less structurally efficient than a W-flange of the same weight.

Other Steel Products

• Deforming steel in its cold state increases its strength by realigning the steel crystals.
• Corrugated steel decking is rolled from steel sheets.
• Steel studs and joists are common.
• High-strength wire is used for concrete prestressing strands.
• Hollow Structural Sections (HSS): For beams and columns, made by cold or hot forming steel strip, commonly square; used for trusses and efficient column sections.
• Open Web Steel Joists: Lightweight trusses made from hot and cold components, depths ranging from 8 inches to 6 feet, spaced 2-10 feet on center.

Alloys

• Traditional mild steel: Minimum 36ksi yield strength.
• Contemporary high-strength (low alloy steels): Stronger steel allows for weight savings and element size reductions, lowering overall costs.
• Weathering steel: Brown texture, allows surface rust for protection, used in highways and bridges to eliminate protective coatings.
• Stainless steel: Added nickel and chromium, forms a self-protecting oxide layer against corrosion.

Joining Methods

• Riveting: White-hot fastener inserted and hammered, mainly in historical structures.
• Carbon bolting (unfinished bolts): Common, relatively low strength, removable, for light framing.
• High strength bolt: Stronger than common bolts, used for primary structural connections.

Connection Types

• Bearing type connection: Bolt body resists movement, bears against hole sides, bolt stressed in shear, and some slippage occurs before full strength.
• Slip critical connection (friction type): Bolt tension is vital, resists movement via friction between faying surfaces, bolt ends up stressed in tension, and there's no slippage under normal loads.

Installation Verification

• Turn of the nut method: Nut tightened an additional fraction after snug fit, tightness verified with a torque wrench.
• Load indicator washers: Protrusions flatten when bolt is adequately tightened.
• Tension control bolt: A metal bit snaps off when tightened.

Welding

• Welding fuses surfaces with additional metal.
• Prevents oxidation with gas during the process.
• V-groove weld: Requires properly shaped and spaced joints.
• Bevel weld
• Fillet weld: Relatively easy, minimal joint preparation.
• Puddle weld (plug): Fastens metal decking to structural steel members.

Welding Testing

• Visual inspection
• Liquid penetrant testing
• Magnetic particle testing
• Ultrasonic testing
• Radiographic testing
• Eddy current testing

Connections

• Shear connection: Joins the web of the beam, not the flanges, allowing rotation.
• Shear tabs
• Moment connection: Connects the web of the beam to the column with bolted angles.
• Top and bottom flanges of the beam are field-welded to the column with full penetration welds.
• Column is reinforced with plated to carry bending forces from beam flanges into column
• Transfers gravity loads and bending forces.
• Beam restrained from rotations (AISC Fully Restrained). Beam flanges connect across the joint with full penetration fillet welds. Stiffener plates may be used to resist forces on column and beam flanges
• Dog bone cut: Creates a zone of weakness for seismic resistance, flanges are welded to the column
• End plate connection: Plate is welded to the beam and bolted to the column. It's semi-rigid or AISC partially-restrained.
• Beam-girder connection: Top flanges align, coping the upper flanges of the beams so that the tops of the beams can be made level with top of the girder
• Column splice connection: Welded or spliced, frequently located at roughly waist height, avoids interference with beam-column connections

Bracing

• Diagonal bracing: Stable, triangular geometry; uses shear connections that are free to rotate.
• Eccentric bracing: Variation of diagonal bracing; allows for plastic hinge development during seismic events.
• Moment resisting frame: Some or all connections are moment connections, resisting rotations.
• Shear walls: Mostly of concrete, stabilize frames with shear connections, often in tall buildings.
• Long spans made of castellated beams, welded plate girders, steel rigid frames, steel trusses, lenticular trusses, arches, and tensile structures.

Glass and Glazing (Division 08)

• Glass is made of silica (sand).

Glass Manufacturing

• Crown Glass Process: glass spun into circles.
• Cylinder Glass Process
• Plate glass: high optical quality, made in sheets.
• Float glass: Modern glass production, annealing furnace (lehr) gradually cools the glass to avoid locked-in stresses

Glass Treatment

• Annealing: Gradually cools the glass to avoid locked-in stresses; used in double-glazed windows.

Definitions

• Glazing: Installation of glass in a glazed opening.
• Glazier: Installer of glass.
• Lights (lites): Individual pieces of glass.

Properties and Thickness

• Glass consists of sand, lime, soda ash, alumina, and potassium oxide.
• It is a supercooled liquid.
• Thickness ranges from 1/8 inch for small windows in low buildings to 1 inch for larger lites in high-rise buildings.
• Thickness is determined by the size of the lite and wind loads.

Glass Strength

• Heat-strengthened glass: Annealed glass is reheated and cooled rapidly.
• Used for windows exposed to heavy wind pressures.
• 2x as strong as annealed glass.
• Tempered glass: Annealed glass is cut to size, reheated, and cooled rapidly.
• More expensive, 4x as strong in bending.
• Used for glass doors without frames.
• Noticeable optical distortions.

Safety Glazing

• Laminated glass: Glued together for extra strength, like plywood, loses some optical clarity and light.

Architectural Glass

• Patterned (frosted) and fritted glass types.
• Spandrel glass hides floor connections and HVAC systems.
• Reflective glass mitigates heat and is aesthetic.

Performance Measures

• VT (Visible Light Transmittance): Measures transparency to visible light.
• SHGC (Solar Heat Gain Coefficient): Indicates effectiveness in reducing heat gain from solar radiation.
• LSG(Light to Solar Gain): Measure of overall energy conserving potential of the glass.
• Visible light transmittance divided by the solar heat gain coefficient

Glazing Unit Thermodynamics

• Clear float glass transmits short-wave radiation and emits equal long-wave radiation.
• Reflective glass reflects more short-wave radiation and more long-wave radiation outside.
• Double glazing with reflective coating reflects most short-wave radiation and emits more long-wave radiation on the outside.
• Low-E (Emissivity) coatings use transparent metallic coatings to improve thermal performance, usually on surface 2 (and sometimes surface 3). Improves thermal performance

Insulating Glass Units (IGU)

• Multiple glass panes with sealed air space to reduce conductance.
• Double glazing has two sheets, triple glazing has three.
• The space is filled by air or inert gas.
• Various spacers are used, including warm-edge spacers.
• Performance is measured in U-values.
• Caps at 8 feet because the argon stops working

Installation

• Small lights held by glazier's points and sealed with putty.
• Large lights use lockstrip gaskets (dry glazing).
• Butt-joint glazing eliminates vertical mullions with silicone sealant.
• Suspended glazing systems (glass mullion system) are used for high walls of glass and lobbies.

Roofing

• Low-slope roofs: 2 inches per foot or less.

Components

• Structural wood panels
• Corrugated steel decking
• Sitecast/precast concrete
• Roof sheathing

Prefab Roofing Panels

• Metal roofing panels can span with slopes as low as 1/4 inch per foot.
• Secured to framing members with metal clips.
• Absence of any structural decking

Substrate Boards

• Used over roof decks for a smoother surface, increased fire resistance, and moisture resistance.
• Fastened with screws and oversized washers to resist wind uplift.

Sloping

• Tapering and tapered insulation are used for slope.
• Rigid foam insulation over corrugated steel decking is common.
• Gypsum board on top of plywood acts as stable, durable substrate board for the roof membrane.
• 7 times lighter than conventional concrete
• Insulation values can be enhanced with higher R-value foam insulation boards.

Low-Slope Roof Membranes

• Bituminous: Staggered hot asphalt and felt layers with gravel on top.
• Single-ply: Factory-made plastic or rubber sheets heat-welded or glued at seams.
• Fluid-applied: Seamless, spray hose application.

Details

• Cant strips create gradual transitions to walls since, ideally, 90 degree switches are avoided in roofing applications.
• Metal and membrane flashings seal edges and penetrations.

Steep Roofs

• Shingles are small, overlapping roofing units with staggered vertical joints.

Materials

• Wood: Prone to decay, erosion, and fire; replace every 15-25 years.
• Asphalt: Durable, with mineral granules for color and UV protection; installed over solid sheathing and asphalt felt underlayment; flexible and inexpensive; change every 15-25 years
• Metal flashings at roof edges prevent water seepage.
• Slate: Heavy, noncombustible, lasts 60-80 years, expensive.
• Clay: Glazed or unglazed, heavy, noncombustible, lasts 30-75 years.
• Concrete: Heavy, noncombustible, lasts 30-75 years.
• Metal: Can be expensive (lead, copper, zinc, stainless steel) or less expensive (aluminum, metallic coated steel, ferrous steel); may patina or have high-performance paint.
• Zinc coatings provide galvanic protection.

Seams

• Standing seam: Folded together
• Flat seam: Nailing and folding
• Batten seam: Metal folded over a piece of wood

Installation

• Traditionally installed over skip sheathing or tangled filament breather mat for air circulation.

Green Roofs

• Protect the membane from UV radiation and temperature extremes
• Extensive: 2-4 inches of soil, low maintenance, drought-tolerant plants, moderate roof loads.
• Cool roofs are painted bright white.

Waterproofing & Materials

• Roofing and wall assemblies use waterproofing materials.
• Light gauge steel, glass, roofing use these CSI divisions.
• Light and heavy gauge steel use shapes and nomenclature.

Exterior Wood and Barriers

• Air and water barriers make the wood structure "tight to the weather".
• Wood absorbs water and needs a barrier between exterior and interior wood.
• Building felt (No. 15 or No. 30) or house wrap (synthetic woven polypropylene fibers) allow the structure to dry and act as permanent air and water barriers after sheathing.
• Wall water resistive barriers are moisture-resistant and permeable to moisture vapor ("breathable").
• Moisture within the wall should diffuse outward in most exterior wall designs.

Vents

• Roof ventilation removes moisture from leaks or condensation.
• Reduces roofing temperatures
• Reduces the risk of ice damming in cold climates

Vents and Terms

• Ventilated roofs have eaves, drip edges, fascia, soffit, and ventilation strips.
• Gutters catch leaves.
• Vents include mushroom, ridge, gable, and soffit vents.
• The location determines on how much rain is usual for the area

Unventilated Roofs

• Do not require ventilation when insulation is positioned above the roof sheathing.

Flashing

• Uses air and water barriers. A membrane of metal or synthetic material applied from bottom to top. Fastened by peel and stick, roll on, nail on, etc.

Siding

• Vented siding has spaces for airflow between the air and water barrier and siding.
• Patterns include plain bevel, rabbeted bevel, v shiplap, cove shiplap, v-groove tongue and groove, and board and batten.
• Corners can be woven or use corner boards.
• Siding venting ties into vented attic systems, where rising hot air pulls cooler air through soffit vents and escapes through vents.