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The structural integrity of any building, be it residential or commercial, hinges on the proper design and construction of its structural components. This module aims to provide a comprehensive overview of these components, their functions, and the materials commonly used in their construction.
Building Structural Components
Foundations:
Function: Transfer the building's load to the underlying soil or rock.
Types:
Residential:
Slab-on-grade: A concrete slab resting directly on the ground.
Crawl space: A shallow foundation creating a space between the ground and the floor.
Basement: An underground foundation providing additional living or storage space.
Footings: Spread footings, strip footings, and pad footings.
Commercial:
Mat foundations: Large concrete slabs supporting the entire building.
Pile foundations: Used when soil bearing capacity is low, transferring loads to deeper, stronger soil or rock.
Caisson foundations: Similar to pile foundations, but with larger diameters.
Combined footings
Materials: Reinforced concrete, steel.
Key Considerations: Soil type, load bearing capacity, frost depth.
Framing:
Function: Provide the skeletal support for the building's walls, floors, and roof.
Types:
Residential:
Wood framing (stick framing): Using lumber for studs, joists, and rafters.
Engineered lumber: I-joists, laminated veneer lumber (LVL), and glued laminated timber (glulam).
Steel framing: Light-gauge steel studs and joists.
Commercial:
Steel framing (structural steel): Using heavy steel beams and columns.
Reinforced concrete framing: Using concrete columns and beams.
Post-and-beam construction: Utilizing heavy timber or steel beams and columns.
Components:
Walls: Studs, top plates, bottom plates, headers.
Floors: Joists, subflooring, bridging.
Roofs: Rafters, trusses, sheathing.
Materials: Lumber, steel, reinforced concrete, engineered wood products.
Walls:
Function: Provide vertical support, enclosure, and insulation.
Types:
Load-bearing walls: Transfer structural loads to the foundation.
Non-load-bearing walls (partition walls): Divide interior spaces.
Exterior walls: Provide weather protection.
Materials:
Wood framing with sheathing (OSB, plywood).
Concrete masonry units (CMU).
Brick masonry.
Steel studs with gypsum board.
Precast concrete panels.
Key Considerations: Load bearing capacity, insulation, fire resistance, moisture control.
Floors:
Function: Provide horizontal surfaces for occupancy and support loads.
Types:
Concrete slabs: Common in both residential and commercial buildings.
Wood joist systems: Used in residential construction.
Steel joist systems: Used in commercial construction.
Composite floor systems: Combining steel and concrete.
Materials: Concrete, wood, steel, composite materials.
Key Considerations: Load bearing capacity, fire resistance, sound insulation.
Roofs:
Function: Provide weather protection and structural support.
Types:
Sloped roofs (gable, hip, etc.): Common in residential buildings.
Flat roofs: Common in commercial buildings.
Truss roofs: Prefabricated roof structures.
Framed roofs (rafter systems).
Materials:
Wood framing with sheathing and roofing materials (shingles, tiles, metal).
Steel framing with metal roofing.
Concrete roofs.
Single ply membrane roofing (TPO, EPDM).
Key Considerations: Roof slope, wind resistance, snow load, waterproofing.
Structural Steel:
Function: Provide high-strength support for large spans and heavy loads.
Components:
Beams (I-beams, wide flange beams).
Columns (H-columns, box columns).
Trusses.
Girders.
Connections: Bolted connections, welded connections.
Applications: High-rise buildings, bridges, industrial structures.
Reinforced Concrete:
Function: Provide high compressive strength and durability.
Components:
Columns.
Beams.
Slabs.
Walls.
Reinforcement: Steel reinforcing bars (rebar) or wire mesh.
Applications: Foundations, columns, beams, slabs, shear walls.
Wall Framing Materials and Stud Types:
Wood Wall Framing:
Standard Studs:
These are the vertical framing members that form the main support of the wall.
They are typically spaced 16 or 24 inches on center (OC) to provide consistent support for sheathing and finishes.
Their primary function is to transfer vertical loads from the roof and upper floors to the foundation.
King Studs:
These are full-height studs that flank the sides of rough openings (for doors and windows).
They provide the main vertical support on either side of the opening.
They run from the bottom plate to the top plate.
Jack Studs (Trimmer Studs):
These are shorter studs that support the header above a rough opening.
They are nailed to the king studs and carry the load of the header.
They are critical for transferring the weight of the header and the loads above it down to the foundation.
Cripple Studs:
These are short studs that are used above or below a rough opening.
Above: They run between the header and the top plate.
Below: They run between the sill and the bottom plate.
They fill the space between the header/sill and the plates, providing support for sheathing and finishes.
Cripple studs are sometimes called infill studs.
Corner Studs:
These are studs that are used to create the corners of the wall.
They are usually made up of 3 studs nailed together to provide a solid corner to attach interior and exterior wall coverings.
Purpose of these Specific Studs:
Structural Integrity: King and jack studs are critical for maintaining the structural integrity of openings, preventing sagging or deformation.
Load Distribution: Cripple studs ensure even load distribution across the wall, preventing stress concentrations.
Framing Accuracy: Proper placement of these studs ensures accurate framing for doors, windows, and finishes.
An diagram showing the different types of studs and wall framing involved in residential wooden construction
Steel Framing (Stud Types):
Steel framing also utilizes studs, but they are formed from light-gauge steel.
The concepts of king studs, jack studs, and cripple studs apply, but the components are steel.
Steel studs are typically connected using screws or other mechanical fasteners.
The steel equivalents of the wood studs, perform the same function as their wooden counterparts.
Steel studs are labeled by their dimensions, and gauge, which is the thickness of the metal.
The track is the steel equivalent of the wood top and bottom plate.
Concrete Masonry Units (CMUs):
CMUs don't use "studs" in the traditional wood or steel framing sense.
Instead, the concrete blocks themselves form the structural wall.
Reinforcement, such as rebar and grout, is used within the CMU cores to enhance strength.
Wood or metal studs may be attached to the inner face of the CMU wall to allow for drywall finishing and installation of insulation.
An example of steel framing construction.
An example of CMU's used in construction
Headers are critical structural components in wall framing, particularly around openings for doors and windows. They play a vital role in transferring loads and maintaining the structural integrity of the wall. Understanding their function, construction, and proper installation is essential for any builder or framer.
Framing Headers: Spanning Openings with Strength
Function of Headers:
Load Transfer: Headers are designed to carry the weight of the wall above an opening, distributing it to the jack studs (trimmer studs) on either side.
Preventing Sagging: Without a properly sized header, the wall above an opening would sag or collapse under the vertical loads.
Creating Stable Openings: Headers ensure that door and window openings remain square and stable, allowing for proper installation and operation.
Types of Headers:
Lumber Headers:
Commonly constructed using multiple pieces of lumber (e.g., 2x8, 2x10, 2x12) nailed or screwed together.
The size and number of lumber pieces depend on the span of the opening and the loads they must carry.
Often, plywood or OSB is sandwiched between the lumber pieces to increase strength and prevent twisting.
Engineered Lumber Headers:
Laminated veneer lumber (LVL) and glued laminated timber (glulam) headers offer superior strength and dimensional stability compared to standard lumber.
They are manufactured by bonding multiple layers of wood veneer or lumber together, resulting in a stronger and more consistent product.
Engineered lumber headers are often used for larger spans or in areas with high loads.
Steel Headers:
Steel beams (e.g., I-beams, channel beams) are used for very large openings or in commercial construction where heavy loads are expected.
Steel headers provide exceptional strength and are often required in situations where lumber or engineered lumber is insufficient.
Built-Up Headers:
These are headers that are built on site, using lumber and plywood or OSB.
They are common in residential construction.
Header Sizing and Selection:
Span: The width of the opening directly affects the required header size. Larger spans require stronger headers.
Load: The amount of weight the header must support depends on the wall's construction and the loads from the roof and upper floors.
Building Codes: Local building codes specify minimum header sizes for various spans and loads.
Load Tables: Building professionals use load tables to determine the appropriate header size based on span and load requirements.
Image Showing a wide span associated with a garage door header.
A bay window header system for each of the 3 windows.
A typical load bearing wall door header.
Joists are horizontal structural members that play a critical role in supporting floors and ceilings. They provide a stable and level surface, distributing loads and preventing sagging. This section will cover the various types of joists, their functions, and proper installation techniques.
Floor and Ceiling Joists: The Horizontal Backbone
Floor Joists:
Function:
Support the weight of the floor, including live loads (people, furniture) and dead loads (subflooring, finishes).
Provide a level surface for flooring installation.
Transfer loads to the foundation or supporting walls.
Types:
Solid Lumber Joists:
Traditional joists cut from dimensioned lumber (e.g., 2x8, 2x10, 2x12).
Common in residential construction.
Sizing depends on span, spacing, and load requirements.
Engineered Lumber Joists (I-Joists):
Manufactured joists with a web (usually OSB) sandwiched between flanges (usually LVL or solid lumber).
Offer greater strength and longer spans than solid lumber joists.
More resistant to warping and shrinking.
Used in residential and commercial construction.
Open Web Joists (Trusses):
Steel or wood trusses used for long spans and heavy loads in commercial and some residential construction.
Provide open spaces for mechanical, electrical, and plumbing (MEP) systems.
Key Considerations:
Span: The distance between supports.
Spacing: The distance between joists (typically 12, 16, or 24 inches OC).
Load: The weight the joists must support.
Deflection: The amount of bending allowed under load.
Bridging/Blocking: used to prevent twisting and increase rigidity.
Ceiling Joists:
Function:
Support the weight of the ceiling finish (drywall, plaster).
Provide a surface for attaching ceiling finishes.
In some cases, support attic loads or roof loads.
Types:
Solid Lumber Joists:
Similar to floor joists, but often smaller in size.
Common in residential construction.
Engineered Lumber Joists:
Used in situations that require longer spans, or higher load capacity.
Ceiling Trusses:
Prefabricated trusses that combine ceiling joists and rafters.
Used for complex roof designs and vaulted ceilings.
Key Considerations:
Span: The distance between supporting walls.
Spacing: The distance between joists.
Load: The weight of the ceiling finish and any attic loads.
Attic Loads: If the attic is used for storage, joists must be sized accordingly.
Image showing wooden joists, bridging between joists as well as the support girder.
Image showing wooden joist system connecting along an exterior wall over a cement foundation.
Ceiling Joist system showing use of cripple joists and blocking to allow an attic access.
An example of a trussed attic framing.
Conventional framing for attic framing.
An example of a truss joist system used for for floor joists.
an example of i-beam type wooden joist.
Joists, as we've established, are vital for floor and ceiling support. However, they don't operate in isolation. They rely on other framing components to transfer loads and maintain structural integrity. This section will explore the various framing supports that joists connect to.
Additional Structural Components
Supporting Walls:
These are load-bearing walls that run perpendicular to the floor joists.
Joists are typically attached to the top plate of these walls.
The walls transfer the joist loads down to the foundation.
The supporting walls can be made of wood, steel, or CMU.
Beams:
Beams are horizontal structural members that span longer distances than joists.
They are used to support joists in areas where supporting walls are not present.
Beams can be made of lumber (built-up beams, LVL, glulam), steel (I-beams, wide flange beams), or reinforced concrete.
Joists are often attached to beams using joist hangers.
Ledger Boards:
A ledger board is a piece of lumber attached to a wall or beam to provide a support surface for joists.
They are often used when joists run perpendicular to a wall and need additional support.
Joist hangers are often used in conjunction with ledger boards.
Girders:
Girders are very large beams that support other beams or joists.
They are common in commercial construction, and in residential construction to support large spans.
They are usually constructed of steel or reinforced concrete.
Foundation Walls:
The foundation walls are the final load bearing component that transfers the weight of the house to the ground.
The sill plate is attached to the foundation wall, and the floor joists are attached to the sill plate.
An image showing a small support wall in a crawlspace with a concrete floor.
An image of a structural beam usually used for long stances.
A diagram showing a ledger board, joist hangers, joists, rim joist, and a sill plate.
Connection Methods:
Nailing/Screwing:
Common for connecting wood joists to supporting walls or beams.
Nails are generally required for framing applications due to framing nails ability to bend versus snap like screws.
Joist Hangers:
Metal connectors that provide a strong and secure connection between joists and beams or ledger boards.
They are required in many building codes.
Bolting:
Used for connecting steel beams or heavy lumber beams to supporting structures.
Welding:
Used for connecting steel joists and beams.
Image showing joists being hung by metal joist hangers.
A bottom plate is anchored into the masonry slab footer, or the masonry foundation walls by means of a threaded rod that prevents the wall from lifting from the foundation.
An image showing the depth of structural nails driven into structural wood materials. Indicating that 1/3 of the fasteners' length should be into each material attached.
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