What Is a Roof Joist?
According to Article 9.1.1 of the "Code for Design of Wood Structure Design 2005 Edition" of the People's Republic of China, light wood structure refers to a structural system mainly composed of wooden frame walls, wooden floor coverings and wooden roof systems. Civil buildings.
- Light wooden structure refers to the structural system mainly composed of wooden frame walls, wooden floor covers and wooden roof systems, and is suitable for civil buildings with three or less floors. [1]
- When adopting lightweight wooden structures, the requirements of the local natural environment and the use environment for the building shall be met, and reliable measures shall be taken to prevent corrosion of the wooden members or insects. Ensure that the structure reaches the expected design life.
- The layout of the light wooden structure should be regular, and the quality and stiffness should be uniform. All components should have reliable connections and necessary anchoring and support to ensure the bearing capacity, stiffness and good integrity of the structure.
- GB 50206-2002 "Code for Construction Quality Acceptance of Timber Structure Engineering"
- 2.0.7 Light-wood structure (wood-framle construction)
- Floor and roof, and form a frame structure, for 1 to 3 storey houses.
- A lightweight frame is a combination of closely spaced gauge components and overlays to form the structural foundation of a building. This structural foundation provides rigidity, supports interior and exterior cladding, and leaves voids for insulation.
- Lightweight frames are the most common method in the North American residential construction industry. This building form can also be used for larger commercial and public buildings. For example, the Forest Products Research Institute of Canada (Forintek), a forest product research base in Vancouver, Canada, has 9,300 square meters (100,000 square feet) of office and experimental buildings as an example of large-scale use of lightweight frame structures.
- The walls of a residential building may typically be 38 x 89 mm (2 x 4 inches in nominal size) and 2.4 meters (8 feet) high, while the walls of a Forintek building are 38 x 235 mm (2 x nominal size (10 inches) walls were built and the height from the floor to the ceiling was 5 meters (16 feet). The result: the building is strong enough to meet the stringent requirements of being a research site.
- When constructing a structural frame, the lightweight frame is made of gauge wood (usually 38 mm (2 in. Nominal size) wide sawn wood, depth up to 286 mm (12 in. Nominal size)), and equivalent dimensions. Into wood products. These major structural components are used in conjunction with the cladding components to provide rigidity to walls, floors and roofs. Generally, the spacing between lightweight frame components is no more than 600 mm (2 feet).
- Light frame is a functional and versatile construction method. A lightweight frame structure can be understood as a roof, floor and wall plane, which has the following functions:
- Structure: The wall can be designed as a load-bearing wall to transfer vertical loads to the foundation. The wall can also be designed as a shear wall to resist lateral forces from wind and seismic loads, which are both perpendicular and parallel to the wall direction. The roof and slabs are designed to withstand the building design loads and can be designed to act as transverse walls to resist deformation.
- Strength: The good structural performance of light frames is attributed to two main factors: load distribution and composite behavior. Load distribution means that there is an optional load transfer channel available when the accessory pressure is too high. Synthetic behavior refers to the effect of coverings and fasteners on the strength of sawn wood components. The result is a lightweight frame with reserve strength and stiffness.
- Shell: Used to provide a rigid covering material and also used as a building shell for external decoration.
- Insulation and decoration: The space between the frames is used to place the insulation layer, and the frame is used to install the steam compartment and interior decoration.
- The frame structure can be manufactured in advance. To speed up assembly, modules can be easily prefabricated under indoor working conditions, or use automated nailing systems. In addition, prefabrication work can also be performed on site, that is, the panel unit is manually lifted into place, or it is lifted into place by a crane when needed.
- Frame structures can be used for large buildings using small-scale construction techniques. The use of larger parts ensures adequate transfer of more pressure. In this way, lightweight frame structures can also be used for many commercial purposes.
- The use of lightweight frame trusses on roofs and floors allows spans greater than 20 meters (60 feet). Long spans can be achieved through the use of prefabricated I-shaped joists, laminated blocks (LVL), parallel blocks (PSL) or glued-layer blocks.
- Column walls using off-the-shelf materials and platform structures can easily reach 5 meters (16 feet) in height, and can be as high as 7 meters (23 feet) if customized. By using wooden I-shaped joists instead of standard timber wall bones, the wall height can also be enlarged, or the strength can be increased when strong wind loads are used as design parameters. In addition, the frame structure can also be used with beam-column structures when space is particularly required. The following figure shows one way to support a frame wall to support a concentrated beam load.
- Attach the base board to the foundation and start the installation of the first floor platform
- The size of the base board is 38 x 89mm (2 "x 4" nom.), Or a large board is laid flat on the foundation. It is the foundation of the structure, connecting the foundation and the superstructure. For residential buildings, fasteners are usually anchors with a diameter of 12.7mm (1/2 "), and the center distance of the foundation is 22.4m (8 ') or less, which can stabilize the base board.
- For large buildings, the downward device should be engineered to resist upward and shear forces due to wind and earthquakes. Anchor bolts shall be poured into the concrete foundation, or clinch anchor bolts shall be installed after the concrete is poured
- It is not recommended to insert the anchor bolt after the initial setting of the concrete, because the grip strength of the anchor bolt is uncertain.
- If installed after pouring, the base board can be placed horizontally on the mortar. If the foundation is horizontal, no mortar is needed. The joint between the foundation and the base board is sealed with a joint sealant to prevent air and moisture from entering. Otherwise, use a gasket between the concrete and the base board. In some parts of North America, base boards must be treated with anti-corrosion to prevent termite erosion.
- The light wall consists of vertical members called wall bones, attached to the top and bottom of the wall to horizontal slabs, and a layer of cladding attached to the structure.
- The wall can be a non-load-bearing wall (partition wall) or a load-bearing wall (exterior and internal load-bearing walls).
- If a structural wall is designed to withstand side loads, then this is a shear wall. Shear walls are used to withstand wind or seismic forces on the wall.
- Wooden joists are often used in residential and commercial buildings that span the length limit of timber. Even if the span and bearing requirements determine the use of prefabricated wooden I-shaped joists, or the use of floor and roof trusses, the connection between the wall and the floor, and the wall and the roof remain basically the same as when using standard timber joists .
- The internal load-bearing wall should be directly above the beam or wall, but it can also be located anywhere, as long as the joists and other supports are specially designed to withstand the load.
- The non-load-bearing wall perpendicular to the ground joist can be installed anywhere, but if it is placed parallel to the ground joist, the wall must be supported by the joist below or supported by the support between the joists.
- The cladding is usually constructed from the base board to form an additional sandwich between the wall structure and the foundation.
- Considering the upward impact of wind and earthquakes, it is necessary to construct a mechanical tensile connection device penetrating the joists. The function of the wall foundation is limited due to the withdrawal force.
- When designing lightweight wooden structure roofs, gauge lumber and roof joists are usually used for ordinary loads and spans, while prefabricated wooden I-shaped joists or trusses are suitable for larger spans and loads. The maximum length of finger joint joists and rafters is 12m (40Õ).
- In addition to supporting the weight of the roof with these load-bearing members, the cladding also increases the load-bearing capacity of these load-bearing members.
- The lightweight frame roof can be designed to have a partition function to resist the devastating effects of lateral loads caused by wind and seismic forces.
- With the help of some other materials, the balsa roof can be inclined or flat. For example, the trusses on the flat roof can be pre-fabricated to the proper slope for drainage.
Light wood frame crossbars and joists
- The diaphragm and joist should be continuous except that they must be joined above the vertical support. The openings on both sides are wider than twice the crossbar or joist spacing, so the number of crossbars and joists used should be doubled for extra strength.
Light wood roof truss
- Roof trusses must limit deflection. This is especially important for flat roofs, because the deflection of the flat roof can cause stagnant water and further increase the load.
- Some North American building codes list the spans and sizes of some of the more common wooden truss members used in residential buildings. In general, these tables are only applicable to roof trusses with a span of 12m (40 ') and a center distance of 600mm (2'). Special engineering analysis for larger spans and negative importance.
Light wood roof cladding
- Roof cladding can support the roof and increase its rigidity. Roof coverings can be made of sawn timber, plywood or oriented particle board. The table below outlines the approximate requirements for spacing and material thickness in the preliminary plan. The specific size should be adjusted according to the snow load in the actual situation.
- Typical roof span or truss spacing and cladding thickness
|
|
| |||
|---|---|---|---|---|---|
|
|
|
| ||
|
|
|
|
| |
|
|
|
| ||
|
|
|
| ||
|
|
|
| ||
|
|
|
|
|
|
|
|
|
| ||
|
|
|
| ||
|
|
|
| ||
|
|
|
|
| |
|
|
|
| ||
|
|
|
| ||
|
|
|
| ||
|
|
|
|
|
|
|
|
|
| ||
|
|
|
| ||
|
|
|
| ||
|
|
|
|
| |
|
|
|
| ||
|
|
|
| ||
|
|
|
| ||
- Note: The thickness of the cladding and the distance between supports vary with the actual building code. This information is for general reference only, please refer to specific actual building codes
- Sawn timber cladding should be vertical with joists or rafters, with supports on each side and staggered edges. Sawn timber cladding should continue to the asphalt tile and suspended ceiling, but the spacing should be the same as the size of the tiles in the shingle roof. Separated tiles allow air to circulate freely under the cladding to build up water-proof gas.
- When installing cladding (plywood and directional particle board), the surface texture is perpendicular to joists, rafters and trusses. Leave a gap of 6mm (1/4 ") between the connected plates to prevent the surface of the plates from expanding. If metal H clips, tongues, seams, or at least 38 x 38mm (2" x2 "nom.) Support Nailed into the frame firmly, supporting the board surface between the rafters, the relative minimum thickness of the cladding board can be relatively reduced.
Light wood structure roofing material
- Many roofing materials can be suitable for light wood roofs under different service conditions. The most commonly used materials for pitched roofs are western red cedar tiles, asphalt shingles and ceramic tiles. Flat roofs or low-slope roofs are usually combined roofs.