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According to the requirements of Notice on printing and distributing the development and revision plan on engineering construction standards and codes in 2009 (JIANBIAO [2009] No.88) issued by the Ministry of Housing and Urban-Rural Development of the People's Republic of China, the drafting group has revised this standard through extensive investigation and study, careful drawing of experience from engineering practices, and reference to relevant international and foreign advanced standards and on the basis of widely soliciting for opinions.
It covers the following main technical content: 1. General provisions; 2. Terms and symbols; 3. Materials; 4. Basic requirements; 5. Calculation for members; 6. Design for connections; 7. Square timber and log structures; 8. Glued laminated timber structures; 9. Light wood frame construction; 10. Fire protection design; 11. Timber structure protection.
The main revisions are as follows:
1. The provisions on timber grading and strength grade are improved, and the utilization range of domestic and imported wood species is enlarged;
2. The reliability of the strength design value of imported wood and wood products is analyzed and studied, and the strength design index in this standard is determined;
3. The relevant design provisions on square timber and log structures and composite timber structures are supplemented;
4. The design provisions on glued laminated timber structures and light wood frame construction are improved;
5. The provisions on stability calculation and connection design of timber structural members are improved;
6. The provisions on seismic design, fire protection design and durability design are supplemented and improved.
The provisions printed in bold type in this standard are compulsory and must be enforced strictly.
The Ministry of Housing and Urban-Rural Development is in charge of the administration of this standard and the explanation of the compulsory provisions, and China Southwest Architectural Design and Research Institute Corp., Ltd. is responsible for the explanation of specific technical content. During the implementation of this standard, the opinions or suggestions, if any, can be posted to China Southwest Architectural Design and Research Institute Corp., Ltd. (Address: No.866, North Section, Tianfu Avenue, Chengdu, 610042, Sichuan).
Standard for design of timber structures
1 General provisions
1.0.1 This standard is enacted, in the design of timber structures, to carry out the national policies on technology and economy, to ensure advanced technology, safety and applicability, economic rationality and quality, and to protect environment.
1.0.2 This standard is applicable to the design of square timber and log structures, glued laminated timber structures and light wood frame construction in architectural engineering.
1.0.3 In addition to this standard, the design of timber structures shall also comply with those stipulated in the current relevant standards of the nation.
2 Terms and symbols
2.1 Terms
2.1.1 timber structure
load-bearing structure which is made mainly of timber
2.1.2 log
trunk of a tree that has been cut down without barks, branches and tree-tips
2.1.3 sawn timber
finished or semi-finished wood of any dimensions that has been sawn from logs, divided into plank and square timber
2.1.4 square timber
sawn timber that has been sawn at right angles, with an aspect ratio less than 3 Square timber is also known as square-edged timber
2.1.5 plank
rectangular sawn timber with an aspect ratio greater than or equal to 3
2.1.6 dimension lumber
standardized lumber manufactured according to a set of specified dimensions (i.e. width and height of lumber section)
2.1.7 structural composite lumber
composite materials specially used for load-bearing structures, manufactured by veneer lumber, wood flakes and wood chips arranged along the length direction of members and laminated and glued by structural adhesive It includes laminated veneer lumber, parallel strand lumber, laminated strand lumber and oriented strand lumber, and other composite wood products with similar characteristics
2.1.8 glued lamina
plank used for manufacturing glued laminated timber, which is lengthened by glued finger joint
2.1.9 moisture content of wood
percentage of water mass in wood to the absolute dry weight of wood
2.1.10 parallel to grain
direction of grain of a timber member is same as length of a member
2.1.11 perpendicular to grain
direction of grain of a timber member is perpendicular to length of a member
2.1.12 an angle to grain
direction of grain of a timber member is at an angle to length of a member
2.1.13 glued laminated timber
wood product that is made by bonding glued lamina whose thickness is not exceeding 45mm parallel to grain, also known as glulam or structural glulam
2.1.14 cross laminated timber
wood products made of 15mm ~ 45mm thick laminates stacked orthogonal to each other and glued together, also known as orthogonal glulam
2.1.15 laminated log
wood products made by gluing sawn timber with a thickness greater than 30mm and no more than 4 layers parallel to grain It is commonly used in log cabins or beam-column timber structures
2.1.16 wood I-joist
bending member with I-shaped section composed of dimension lumber or structural composite lumber as the flange, wood-based structural panels as the web, and glued together with structural adhesives
2.1.17 stud
vertical bearing frame members arranged at a certain intervals within walling of light wood frame construction
2.1.18 visually stress-graded lumber
Timber graded by eyes
2.1.19 machine stress-rated lumber
timber whose strength grade is determined based on bending strength and modulus of elasticity measured by non-destructive test with a mechanical stress testing device
2.1.20 truss plate
steel plate with galvanize surface that is punched into connectors with teeth protruding to be connected with joints of light trusses or for elongation of tensile members
2.1.21 wood-based structural panels
load-bearing panels, including structural plywood and oriented strand board, which are manufactured by hot pressing raw materials such as veneer lumber or wood chips with structural adhesives
2.1.22 shear wall of wood-based structural panels
wall on which the wood-based structural panels are used and whose studs are made of dimension lumber, square timber or glued laminated timber, bearing the horizontal and vertical forces
2.1.23 finger joint
serrated butt joint connected by adhesive at the connection point. Finger joint is divided into finger joint of glued lamina and finger joint of glued laminated timber member
2.1.24 fast-growing wood
wood with fast growth, early maturity and short rotation
2.1.25 square timber and log structures
building structures that are mainly made of square timber or log as the load-bearing members
2.1.26 light wood frame construction
building structures of wall, floor slab and roof of wood members that consists of dimension lumber and wood-based structural panels or gypsum board
2.1.27 glued laminated timber structures
building structures that are mainly made of glued laminated timber as the load-bearing members
2.1.28 log cabins; log house
logs, square timbers and laminated logs with properly processed sections are used as basic members, which are stacked horizontally upward layer by layer, and staggered layer by layer in snap-in mode at the intersecting ends of the members. Log cabins are the timber structures with the cross-shaped wooden wall thus made as the main load-bearing system
2.1.29 CHUANDOU-style timber structure
timber frame that a row of wooden columns are erected along the depth of the house according to the spacing of roof purlins, which are directly supported by the wooden columns that are transversely tied together with square-column through the wooden columns rather than beams Every two timber frames are connected by a Dou-style square-column and Xianzi (like longitudinal keel) to form a load-bearing spatial timber frame
2.1.30 TAILIANG-style timber structure
timber frame that beams are stacked layer by layer along the depth of the house, by supporting a beam on a wooden column, and placing a shortened beam on the former beam where the shortened beam is supported by short column Roof purlins are placed at the beam ends of each layer
2.1.31 wood-frame shear wall structure
timber structure system in the square timber and log structures that bears horizontal forces by the wood frame that is mainly composed of ground beams, beams, transverse beams and columns, and whose studs are laid with wood-based structural panels
2.1.32 cross laminated timber structure
building structures with load-bearing members such as wall, floor board and roof board made of cross laminated timber Its structural form is mainly box structure or plate structure
2.1.33 dowel connection
connection mode in which members are connected with dowel-type fasteners. Dowel connection is also known as dowel-type connection. Dowel-type fasteners include bolts, dowels, hexagonal head wood screws, round nails and threaded nails
2.2 Symbols
2.2.1 Actions and effects
C——corresponding design limits for deformation, crack, etc.;
Cr——design value of shear-tension composite bearing capacity of truss plate;
M——design value of bending moment;
Mx, My——design value of bending moment at axis x and axis y of a member's section;
M0——design value of maximum initial moment in mid-span acted by transverse load;
Mr——design value of bending capacity of truss plate;
N——design value of axial force;
Nb——design value of tension which a safety bolt bears;
Nr——design value of bearing capacity of plate tooth;
N s——design value of anti-sliding bearing capacity of plate tooth;
Rd——resistance design value of structure or structural member;
Rf——design value of bearing capacity of residual timber member burned according to fire resistance rating;
Sd——design value of the action combination effect;
Sk——design value of effect of accidental combination of loads of damaged timber members checked after fire;
Tr——design value of tensile bearing capacity of truss plate;
V——shearing design value;
Vd——design value of shear bearing capacity of shear walls, floors and roofs;
Vr——design value of shear bearing capacity of truss plate;
Wd——design value of pullout bearing capacity of hexagonal head wood screw;
Zd——design value of shear bearing capacity of each shear surface of dowel-type fasteners;
Z——reference design value of shear bearing capacity;
ω——deflection calculated based on standard combination of load effect;
ωx, ωy——deflection calculated based on standard combination of load effect at axis x and axis y along member' s section;
2.2.2 Material property or structural design index
Cr1, Cr2——design value of shear-tension composite strength of truss plate along l1 and l2 directions;
E——average value of modulus of elasticity of wood material;
Ek——standard value of modulus of elasticity of wood material;
fck, fc——standard value and design value of compressive and bearing strength of wood material parallel to grain;
fcα——design value of bearing strength of wood material at an angle to grain;
fc, 90——design value of bearing strength of wood material perpendicular to grain;
fmk, fm——standard value and design value of bending strength of wood material;
ftk, ft——standard value and design value of tensile strength of wood material parallel to grain;
fvk, fv——standard value and design value of shear strength of wood material parallel to grain;
fvd——design value of shear strength of shear wall, floor and roof with wood-based structural panels;
fem——standard value of bearing strength of dowel slot of main member;
fes——standard value of bearing strength of dowel slot of secondary member;
fyb——standard value of bending strength of dowel-type fasteners;
ft, j, k, fm, j, k——standard value of tensile strength and standard value of bending strength in width direction of finger joint;
G——absolute-dry relative density of timber member materials;
Kw——shear stiffness of shear wall;
nr——design value of strength of plate tooth;
ns——design value of anti-sliding strength of plate tooth;
tr——design value of tensile strength of truss plate;
υr——design value of shear strength of truss plate;
βn——nominal linear charring rate of timber burning for 1.00h;
[ω]——deflection limit of a bending member;
[λ]——slenderness ratio limit of a compression member.
2.2.3 Geometric parameters
A——gross sectional area of the member, or the net area of the truss plate surface;
An——net sectional area of the member;
A0——calculated area of section of compression member;
Ac——area of bearing surface;
Be——effective width of floor and roof parallel to load direction;
b——width of member section;
bn——effective side length of section of variable-section compression member;
bt——calculated width of truss plate section perpendicular to the tensile force direction;
bv——width of shear surface, or width of shear section of truss plate parallel to shear direction;
d——diameter of log or dowel-type fastener;
def——effective carbonized layer thickness;
e0——initial eccentricity of member;
h——section height of member;
hd——effective length of the threaded part of the hexagonal head wood screw driven into the main member;
hn——net section height at notch of bending member;
hw——height of shear wall;
I——inertial moment of gross section of member;
i——radius of gyration of member section;
l——member length;
l0——calculated length of compression member;
le——calculated length of bending member;
lv——calculated length of shear surface
S——area moment of sectional area to neutral axis over the shear surface;
tm——thickness of thick member or middle member in case of single shear connection or double shear connection;
ts——thickness of thin member or edge member in case of single shear connection or double shear connection;
W——resistance moment of gross section of member;
Wn——resistance moment of net section of member;
Wnx, Wny——resistance moment of net section of member section along axis x and axis y;
α——included angle between top chord and bottom chord or included angle between the direction of force and direction of grain;
λ——slenderness ratio of compression member;
λB——slenderness ratio of bending member.
2.2.4 Calculating coefficients and others
a——calculating coefficient of support condition;
Cm——moisture content adjustment factor;
Ct——temperature environment adjustment factor;
KB——local compression length adjustment factor;
KZcp——local compression dimension adjustment factor;
kd——adjustment factor of design value of strength of wood material under the control of permanent load effect;
kn——bending moment influence coefficient of truss end joints;
kg——combined action coefficient of group bolts for shear bearing capacity of dowel-type fasteners;
kl——length calculation coefficient;
kmin——coefficient of minimum effective load-bearing length of dowel slot;
t—— fire resistance rating;
β——correlation coefficient of material shear deformation;
ρ——ratio of standard value of variable load to standard value of permanent load;
φ——stability factor of axial compression member;
φl——lateral stability factor of bending member;
φm——reduction factor of composite action of axial force and initial moment;
φy——stability factor determined based upon slenderness ratio λy when axial strut is perpendicular to y-y direction of the bending moment action plane;
ψv——strength reduction factor obtained due to non-uniform distribution of shear stress along length of shear surface;
γ0——structural importance factor;
γRE——seismic adjustment factor of bearing capacity of member.
3 Materials
3.1 Timber
3.1.1 Timber for load-bearing structure includes log, square timber, plank, dimension lumber, glued laminated timber, structural composite lumber and wood-based structural panels.
3.1.2 Square timber, log and plank may be visually stress-graded, and the material selection standard shall meet the requirements of A.1 in Annex A of this standard. The timber grade of square timber members visually graded and processed in factories shall meet those specified in Table 3.1.2, and the material selection standard shall meet the requirements of A.1.4 in Annex A of this standard. The grade standard of commercial timbers shall not be used to replace the timber grade specified in this standard.
Table 3.1.2 Timber grades of square timber members processed in factories
No. Member purpose Timber grade
1 Members for beams Ie IIe IIIe
2 Members for columns If IIf IIIf
3.1.3 When designing the members of the square timber and log structures, the corresponding timber grades shall be selected according to the main purposes of the members. The requirements for visually stress-graded lumber, if adopted, shall not be lower than those specified in Table 3.1.3-1; the requirements for square timber processed in factories, if used as beam-column members, shall not be lower than those specified in Table 3.1.3-2.
Table 3.1.3-1 Timber grade requirements of square timber and log members
No. Main purpose Minimum grade
1 Tensile or tension-bending member Ia
2 Bending or compression-bending member IIa
3 Compression member and secondary bending member IIIa
Table 3.1.3-2 Timber grade requirements of square timber members processed in factories
No. Main purpose Minimum grade
1 For beams IIIe
2 For columns IIIf
3.1.4 Square timber and logs shall be chosen from the tree species listed in Table 4.3.1-1 and Table 4.3.1-2 of this standard. Coniferous species shall be used for main load-bearing members; hard broadleaf wood, which is of fine and straight grain, no knots, no other defects and decay resistance, shall be adopted for important connectors.
3.1.5 The use of imported timber in timber structure engineering shall meet the following requirements:
1 Wood species with little natural defects and defects resulting from dryness and good decay-resistance shall be chosen;
2 Imported timbers shall have approved certification mark and be accompanied by relevant technical documents;
3 Imported timbers shall meet the relevant requirements of the state on animal and plant quarantine of imported timber;
4 Imported timbers shall be labeled in Chinese, and stored in order according to nations, grades and sizes. In no case shall the timbers be mixed together. During the period of storage, precautions shall be taken against fungi, decay and insects;
5 The tree species used for the first time in China shall be used according to the requirements of this standard after the physical and mechanical properties are determined by tests.
Foreword i
1 General provisions
2 Terms and symbols
2.1 Terms
2.2 Symbols
3 Materials
3.1 Timber
3.2 Steel and metal connectors
4 Basic requirements
4.1 Design principles
4.2 Seismic design requirements
4.3 Strength design indexes and deformation values
5 Calculation for members
5.1 Axial tension members and axial compression members
5.2 Bending members
5.3 Tension-bending and compression-bending members
6 Design for connections
6.1 Step joints
6.2 Dowel connections
6.3 Truss plates
7 Square timber and log structures
7.1 General requirements
7.2 Beams and columns
7.3 Walls
7.4 Floors and roofs
7.5 Trusses
7.6 Skylights
7.7 Bracings
8 Glued laminated timber structures
9 Light wood frame construction
9.1 General
9.2 Floor and roof
9.3 Walls
9.4 Light timber trusses
9.5 Light wood frame construction in composite buildings
9.6 Detailing requirements
10 Fire protection design
10.1 General
10.2 Construction details of fire protection
11 Timber structure protection
11.1 General
11.2 Waterproof and moistureproof
11.3 Biological hazard prevention
11.4 Corrosion prevention
Annex A Timber standard for load-bearing structures
Annex B Requirements for light wood frame construction
Annex C Inspection and maintenance requirements for timber structure
Annex D Design value of strength and modulus of elasticity for imported structural timber
Annex E Standard values of strength and modulus of elasticity for structural timber
Annex F Determination of characteristic values for manufactured structural timber
Annex G Strength design values and calculation requirements for cross laminated timber
Annex H Names of timber and main characteristics of common species in this standard
Annex J Key identification points, basic characteristics and main processing properties of main imported woods
Annex K Determination of the number of fasteners in members and the combination coefficient of common fasteners group bolts
Annex L Relative density of absolute-dry common species wood
Annex M Determination of design value of strength for truss plate
Annex N Design value of shear strength for wood-based structural panel shear wall
Annex P Design value of shear strength for wood-based structural panel floors and roofs
Annex Q Calculation method for vibration control of floor joists
Annex R Combustibility & fire-resistance ratings of timber structural members
Explanation of wording in this standard
List of quoted standards
