Tree structure(Mokukouzo) iswoodenGood,building OfConstructionIn one of the main parts in terms of structural strengthwoodIt is a structure using.Also, in recent yearsWood-based materialSince the number of buildings using is increasing, this is sometimes called a wooden structure.

Classification by structural type of tree structure

Traditional construction

• ThickPillarとBeam,as well asPerseveranceIt is a structural type that penetrates each other's members using (nuki), and is fixed using a car chi (shachi) or a plug (komisen). (Like the conventional methodnailDo not use the fixing method that relies on or reinforcing hardware. )
• External forceIt resists deformation and deformation mainly by digging into the wood.Therefore, it has a structure that is tenacious even against large deformation.Earthquake,typhoonIt is a construction method suitable for the Japanese climate, which is often damaged by.
• Mistakes in the mouth and finishStrainAnd durability are fully considered.^[1].
• It's expensive.
• Mostly in old and large luxury homes.

Wooden frame construction method

• As a construction methodWooden frame construction methodOrConventional construction methodCalled.
• The structure is supported by columns and beams, but the width of the columns and beams is 3.5 inches (105 mm) to 4 inches (120 mm), which is narrower than the traditional construction method.
• Mainly for external force and deformationBraceSuch asBearing wallResist by.
• Unlike the traditional construction method, the joints between the members are very weak, soHole down hardware,Feather plate boltIt is indispensable to reinforce the hardware.
• JapanMany wooden houses use this construction method.It is rarely built outside of Japan.

Wooden frame wall construction method

• As a construction methodFrame wall construction methodOr2 x 4 (two-by-four) construction methodCalled.
• In the frame of woodStructural plywoodStruckwallとbedIt is a structural form supported by.
• Strongly coupled to external forces and deformationBearing wallとRigid floorTo catch it throughout the buildingrigidity-StrengthIt has a high structure and is tenacious against large deformation.
• Western countries (especiallyNorth America) Is the standard construction method for wooden houses,JapanBut1974年It began to be built around that time.
• 5-6 stories in Europe and Americahousing complexAs you can see in Japan, up to 4 stories are allowed in Japan.

Log assembly method

• It is a construction method in which logs are stacked side by side to make a wall, but this does not apply to the roof.
• Vertical threading that binds logs together against external force and deformationboltTo prevent slippage between logsDowelResist by.
• Mainly used in one-story houses.

Wood rigid frame construction method

• It is a structural form in which thick columns and beams are used and they are rigidly joined by means of so-called wooden construction.Rigid frame structure.
• It is difficult to completely rigidly join wooden columns and beams (even if hardware is used, the hardware easily sinks into the wood).Therefore, the member contacts must be treated as semi-rigid joints, not rigid joints.
• Because only columns and beams resist external forces and deformation,Bearing wallIs basically unnecessary, but partiallyBearing wallMay supplement the strength.
• It is used not only for houses but also for offices and public facilities.

Material properties

• woodHas a high specific strength (strength per unit weight).That is, it has high strength for its light weight.This isBasicsMeans that it can be relatively simple.
• Wood has high strength in the fiber direction, but low strength in the direction perpendicular to the fiber.
• Wood is not tenacious and causes brittle destruction.Therefore, tenacity must be ensured at joints (deformation of nails and bolts, digging into wood, etc.).

The nature of the joint

• The joints between woods are made so that the shearing force works in the direction of action.When joining a member that exerts a tensile force, it is converted to a shear joint using a splicing plate or the like.
• There are mainly the following methods for joining wood to each other.
  • nailJoining: Although the strength per piece is low, it is possible to easily make a joint with high rigidity and strength by driving in a large amount.
  • boltJoining: There is initial play, and it does not work with small deformation, but it exhibits extremely high strength and stickiness during large deformation.
  • Adhesive joining: Members are integrated and have high initial rigidity.The larger the bonding area, the higher the bonding strength.Durability varies depending on the quality of the adhesive.
• Since each joining method has a different resistance mechanism, even if different joining methods are used together.enduranceCannot be added.

Dealing with fire

Compared to other structures, the wooden structure uses combustible materials for the main parts in terms of structural strength.火災Has a weak property.Therefore, as a general rule, the outer wall, roof, and eaves areNon-combustible materialMust be finished with.In addition, the following fire prevention measures will be taken.

• KibeGypsum boardCover with a fireproof material to prevent the wood from being directly exposed to flames.
• Interior walls / ceilings for each roomGypsum boardCover with a fireproof material to delay the spread of fire to the next room or upstairs.In addition, the interior is as much as possibleNon-combustible materialFinish with.
• When wood burns, it forms a carbonized layer on the surface, and it takes time to burn out to the inside.Therefore, the structure should have only the part excluding the burning margin.Structural calculationAnd use wood with a thick cross section (burning margin design).

• Fire stop materials are provided in the hollow part inside the wall and the connecting part between the wall and the ceiling.
• Increase the rigidity of each floor (interlayer deformation angle 1/150 or less) to prevent the fireproof material from falling off during an earthquake.

Other,Fire insurance,Earthquake insuranceIn, the insurance premium is high for wooden houses with low fire resistance (not fireproof buildings, semi-fireproof buildings, or ministerial ordinance semi-fireproof structures).

Wooden house dense area

Local governments say that in metropolitan areas, old wooden houses are densely populated, and serious damage is expected due to fires and collapses in the event of a large-scale earthquake.Wooden house dense area(Kimitsu) "^[2](Ministry of Land, Infrastructure, Transport and TourismThe expression is "a densely populated urban area that is extremely dangerous in the event of an earthquake, etc."^[3]).Tokyo and special wards in TokyoEarthquake directly below the capitalEncourage rebuilding in "Special Zone for Incombustibility" in preparation for^[4]Each local government and the national government are proceeding with measures aimed at eliminating them.

Dealing with termites and decay

The wooden structure is a major part of the structural strengthTermiteBecause it uses a material that is vulnerable to decay, it tends to have lower durability than other structures.Therefore, as a general rule, antiseptic and ant-proof measures must be taken on the xylem within 1 m from the ground.In addition, the following measures will be taken.

• The entire ground at the bottom of the buildingReinforced concreteCover with moisture from the groundTermitePrevent the invasion of.Solid foundationIs desirable, butCloth foundationEven in the case of, lay reinforced concrete for moisture and ant prevention.
• Of the main part in terms of structural strengthwoodUse a dried one (preferably with a moisture content of 25% or less).
• Of the main part in terms of structural strengthwoodThe heartwood is preferable to the sapwood.
• Of the main part in terms of structural strengthwoodAs the tree species, those with high decay resistance and ant resistance are adopted depending on the place of use.

• It is desirable that the shape of the roof is simple and the eaves are as large as possible.
• On the indoor side of the outer wallMoisture proof layerInstall properly to prevent indoor moisture from entering the wall (unless the outer wall is entirely made of breathable material).
• Humidity generated indoorswindowAnd use ventilation equipment to actively discharge to the outdoors.

Environmental load of wooden structure

The tree structure is a structural type that has less impact on the environment than other structures.

• The wood used grows with natural energy such as sunlight, and is associated with manufacturing.carbon dioxideLow emissions.
• MaterialproportionIs lightweight, so it accompanies the transportation of materialscarbon dioxideLow emissions.
• Easy to process and assemble materials, so it accompanies construction workcarbon dioxideLow emissions.
• It has the effect of retaining carbon in the wood to the building during the life of the building.

Wooden structure of public buildings, etc.

In 2010, a law was enacted to promote the use of wood in public buildings.In addition to actively working on the use of timber in public buildings involving the government, it was decided to encourage local governments and private businesses to take measures to use timber.^[5].. The wooden construction rate of low-rise public buildings constructed by the government in 2018 reached 78.6% (98 out of 78 buildings).^[6].

footnote

References

• "Building Laws and Regulations" Building Regulations Editing Conference
• "Wooden house construction specifications (with commentary)" (Foundation) Housing Finance Promotion Association
• "Framework wall construction method housing construction specifications (with commentary)" (Foundation) Housing Finance Promotion Association
• "Wooden Structural Design Criteria / Explanation-Allowable Stress / Allowable Strength Design Method-" (Architectural Institute of Japan)
• "Design of allowable stress of wooden frame construction method housing" Japan Housing and Wood Technology Center

Related item

• Wooden building
• Wooden church
• Wooden 3 stories
• Reinforced concrete structure
• Steel structure(Steel structure)
• Steel frame reinforced concrete structure
• Aluminum structure

外部 リンク

• The 64th Tokyo Fire Department Statistics (23) Table 29 Fire status by structure of the fire source building
• Ministry of Land, Infrastructure, Transport and Tourism tsunami damage situation survey results of the Great East Japan Earthquake (second report) (PDF) (XNUMX. Relationship between inundation depth and building damage status by building structure)