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According to the requirements of Document Jian Biao [2006] No.77 issued by the former Ministry of Construction (MOC)—“Notice on Printing the Development and Revision Plan (First One) of National Engineering Construction Standards in 2006”, China Academy of Building Research, in conjunction with the organizations concerned, revised this code through extensive investigations and studies by earnestly summarizing the experiences in actual practices and by referring to the relevant international standards and foreign advanced standards as well as the relevant opinions.
The main contents of this code are: General, Terms and Symbols, General Requirements, Materials, Structural Analysis, Ultimate Limit States, Serviceability Limit States, Detailing Requirements, Fundamental Requirements for Structural Members, Prestressed Concrete Structural Members, Seismic Design of Reinforced Concrete Structural Members and the relevant appendixes.
There have been some significant changes in this code in the following technical aspects: 1. The provisions on the principles of structural scheme, design against progressive collapse of structures, design of existing structures and design of unbounded prestressing were supplemented; 2. The relevant provisions on the analysis of serviceability limit states were amended; 3. The ribbed steel reinforcement of Grade 500MPa was added, and the steel reinforcement of Grade 235MPa was replaced by plain round steel reinforcement of Grade 300MPa; 4. The relevant provisions on the design of combined loaded members were supplemented, and the expression for the calculation of shear and punching shear capacity were amended; 5. The relevant provisions on the cover thickness and anchorage length of steel reinforcement as well as on the minimum ratio of reinforcement of longitudinal load-carrying steel reinforcement were adjusted; 6. The relevant provisions on the seismic design of two-way shear columns, coupling beams, shear walls and other boundary members were supplemented and amended; 7. The relevant requirements of the seismic design of prestressed concrete members and slab-column joints were supplemented and amended.
The provisions printed in bold type in this code are compulsory ones and must be enforced strictly.
The Ministry of Housing and Urban-Rural Development is in charge of the administration of this code and the explanation of the compulsory provisions; the China Academy of Building Research is responsible for the explanation of specific technical contents. The relevant opinions and advice, whenever necessary, can be posted or passed on to the National Standard “Code for Design of Concrete Structures” Administrative Group of China Academy of Building Research (address: No. 30, Beisanhuan East Road, Beijing City, 100013, China).
Contents
1 General 1
2 Terms and Symbols 1
2.1 Terms 1
2.2 Symbols 3
3 General Requirements 6
3.1 General 6
3.2 Structural Scheme 7
3.3 Ultimate Limit States 8
3.4 Serviceability Limit States 10
3.5 Durability Requirements 13
3.6 Principles for Design Against Progressive Collapse 16
3.7 Principles for Design of Existing Structures 17
4 Materials 18
4.1 Concrete 18
4.2 Steel Reinforcement 21
5 Structural Analysis 26
5.1 General 26
5.2 Analysis Model 27
5.3 Elastic Analysis 28
5.4 Plastic Internal Forces Redistribution Analysis 29
5.5 Elastic-Plastic Analysis 30
5.6 Plastic Limit Analysis 31
5.7 Indirect Action Effect Analysis 31
6 Ultimate Limit States 32
6.1 General 32
6.2 Load-carrying Capacity of Normal Sections 32
6.3 Load-carryring Capacity of Inclined Sections 53
6.4 Load-carrying Capacity of Sections Subjected to Torsion 63
6.5 Punching Shear Capacity 72
6.6 Local bearing Capacity 76
6.7 Fatigue Analysis 79
7 Serviceability Limit States 87
7.1 Crack control 87
7.2 Deflection of Flexural Members 97
8 Detailing Requirements 101
8.1 Expansion Joint 101
8.2 Concrete Cover 102
8.3 Anchorage of Steel Reinforcement 103
8.4 Splices of Steel Reinforcement 106
8.5 Minimum Ratio of Reinforcement for Longitudinal Load-carrying Steel Reinforcement 109
9 Fundamental Requirements for Structural Members 111
9.1 Slabs 111
9.2 Beams 115
9.3 Columns, Joints and Brackets 123
9.4 Walls 132
9.5 Composite Members 134
9.6 Precast Concrete Structures 136
9.7 Embedded Parts and Connecting Pieces 138
10 Prestressed Concrete Structural Members 142
10.1 General 142
10.2 Calculation of Prestress Losses 153
10.3 Detailing of Prestressed Concrete Members 158
11 Seismic Design of Reinforced Concrete Structural Members 165
11.1 General 165
11.2 Materials 169
11.3 Frame Beams 170
11.4 Frame Columns and Columns Supporting Structural Transfer Member 174
11.5 Columns of Hinged Bent 184
11.6 Joints of Frame 186
11.7 Shear Walls and Coupling Beams 191
11.8 Prestressed Concrete Structural Members 204
11.9 Slab-column Joints 205
Annex A Nominal Diameter, Cross-sectional area and Theoretical Self-weight of Steel Reinforcement 208
Annex B Approximate Coefficient Method for Second Order Effect of Sway Structure 210
Annex C Constitutive Relations for Steel Reinforcement and Concrete and the Rule of Multi-axial Strength for Concrete 213
Annex D Design of Plain Concrete Structural Members 228
Annex E Calculation for Flexual and Axial Capacity of Circular, Annular and Arbitrary Cross Sections 233
Annex F Design Value of Equivalent Concentrated Reaction Used for Calculation of Slab-column Joints 239
Annex G Deep Flexural Members 244
Annex H Composite Beam and Slab Without Shores 250
Annex J Prestress losses of Curved Post-tensioned-Tendons Due to Anchorage Seating and Tendon Shortening 257
Annex K Time-dependent Losses of Prestress 263
Explanation of Wording in This Code 267
List of Quoted Standards 268
Code for Design of Concrete Structures
1 General
1.0.1 This code was formulated with a view to implementing the national technical and economic policies in the design of concrete structures, achieving safety, applicability and economy and guaranteeing quality.
1.0.2 This code is applicable to the design of buildings and other general structures made by reinforced concrete, prestressed concrete and plain concrete. But it is not applicable to the design of structures using light self-weight aggregate concrete and special concrete.
1.0.3 This code was formulated based on the principle of the current national standards “Unified Standard for Reliability Design of Engineering Structures” (GB 50153) and “Unified Standard Reliability Design of Building Structures” (GB 50068). This code gives the basic requirements for the design of concrete structures.
1.0.4 In addition to this code, the design of concrete structures shall also comply with those stipulations specified in the relevant current national standards.
2 Terms and Symbols
2.1 Terms
2.1.1 Concrete structure
the structure that is made mainly by concrete, including plain concrete structure, reinforced concrete structure and prestressed concrete structure, etc.
2.1.2 Plain concrete structure
the concrete structure that has no reinforcement or no load-carrying reinforcement
2.1.3 Steel rebar
a generic term for non-prestressing reinforcement used in concrete structural members
2.1.4 Prestressing tendon
a generic term for prestressing steel wires, strands and deformed steel rebars used in concrete structural members
2.1.5 Reinforced concrete structure
the concrete structure that is provided with load-carrying reinforcement
2.1.6 Prestressed concrete structure
the concrete structure that is provided with load-carrying prestressing tendons. The prestress is introduced through stretching or other methods
2.1.7 Cast-in-situ concrete structure
the concrete structure that is built by erecting form and integrally casting at its permanent location
2.1.8 Precast concrete structure
the concrete structure that is formed by assembling and connecting precast concrete members or parts
2.1.9 Assembled monolithic concrete structure
the concrete structure that is assembled by connecting precast concrete members or parts with steel reinforcement, connectors or prestressing force and is finished by casting concrete at connecting spots to form an integeral structure that responds to loads as one unit
2.1.10 Composite member
the structural member that is produced by combining precast concrete members (or existing concrete structural members) and cast-in-situ concrete but so interconnected that the combined components act together as a single member and respond to loads as one unit
2.1.11 Deep flexural member
the flexural member having span to height ratio less than 5
2.1.12 Deep beam
the simply-supported single-span beam having span to height ratio less than 2, or multi-span continuous beam having span to height ratio less than 2.5
2.1.13 Pretensioned prestressed concrete structure
the concrete structure that is built by tensioning prestressing tendons on pedestal first and then pouring concrete. The tendons and/or bars are then released from the pedestal and the prestress is introduced into concrete through bonding action
2.1.14 Post-tensioned prestressed concrete structure
the concrete structure in which the prestressing tendons are not tensioned until the concrete has reached the required strength. The stretched prestressing tendons are anchored on the concrete to establish prestress
2.1.15 Unbonded prestressed concrete structure
one type of the post-tensioned prestressed concrete structures, using unbonded prestressing tendons that can slide relative to concrete
2.1.16 Bonded prestressed concrete structure
the concrete structure in which the prestress is established by grouting or by directly contacting with concrete to form the mutual bonding between prestressing tendons and concrete
2.1.17 Structural joint
a generic term for gaps dividing a concrete structure according to the requirements of structural design
2.1.18 Concrete cover
concrete ranging from the outer edge of reinforcement to the surface of concrete member with a function to protect the reinforcement
2.1.19 Anchorage length
a length that is required for reinforcement to provide design stresses through bonding action between the surface of the reinforcement and concrete, or via bearing action between the folded end of the reinforcement and concrete
2.1.20 Splice of reinforcement
a structural form realizing the transfer of internal forces between reinforcement by such methods as binding and lapping, mechanical connecting and welding
2.1.21 Ratio of reinforcement
the ratio of the reinforcement areas (or volumes) to the specified cross-sectional area (or volume) of a concrete member
2.1.22 Shear span ratio
the ratio of the section bending moment to the shear force multiplied by effective depth
2.1.23 Transverse reinforcement
stirrup or indirect reinforcement perpendicular to longitudinal reinforcement
2.2 Symbols
2.2.1 Material properties
Ec—— Elastic modulus of concrete;
Es—— Elastic modulus of steel reinforcement;
C30—— Strength grade of concrete having a characteristic value of 30N/mm2 for the cube compressive strength;
HRB500—— Ordinary hot rolled ribbed steel rebar with a strength level of 500MPa;
HRBF400—— Fine grain hot rolled ribbed steel rebar with a strength level of 400MPa;
RRB400—— Remained heat treatment ribbed steel rebar with a strength level of 400MPa;
HPB300—— Hot rolled plain round steel rebar with a strength level of 300MPa;
HRB400E—— Ordinary hot rolled ribbed steel rebar with a strength level of 400MPa and having relatively high seismic performance;
fck, fc—— Characteristic value and design value of the axial compressive strength of concrete, respectively;
ftk, ft—— Characteristic value and design value of the axial tensile strength of concrete, respectively;
fyk, fpyk—— Characteristic values of the yield strength for steel rebars and prestressing tendons, respectively;
fstk, fptk—— Characteristic values of the ultimate strength for steel rebars and prestressing tendons, respectively;
fy, ——
Design values of the tensile strength and compressive strength for steel rebars, respectively;
fpy, ——
Design values of tensile strength and compressive strength for prestressing tendons, respectively;
fyv—— Design value of tensile strength for transverse reinforcement;
δgt—— Total percentage elongation of reinforcement at the maximum force, also referred to as uniform percentage elongation.
2.2.2 Actions and action effects
N—— Design value of axial force;
Nk, Nq—— Values of axial forces calculated in accordance with the characteristic combination and the quasi-permanent combination of loads, respectively;
Nu0—— Design value of the axial compression or axial tension load-carrying capacity of member section;
Np0—— Prestressing force applied to prestressed concrete where prestress in the normal direction of the concrete is equal to zero;
M—— Design value of bending moment;
Mk, Mq—— Values of bending moment calculated in accordance with the characteristic combination and the quasi-permanent combination of loads, respectively;
Mu—— Design value of the flexural capacity for the normal section of a member;
Mcr—— Cracking bending moment value for the normal section of a flexural member;
T—— Design value of torsional moment;
V—— Design value of shear force;
Fl—— Design value of localised force or concentrated reaction;
σs, σp—— Stresses in longitudinal reinforcement and in prestressing tendon respectively, in the calculation of load-carrying capacity for normal section;
σpe—— Effective prestress of prestressing tendon;
σl, ——
Losses of prestress at the corresponding stages for prestressing tendon in tension zone and compression zone, respectively;
τ—— Shear stress of concrete;
ωmax—— The maximum crack width calculated according to quasi-permanent loads combination or characteristic loads combination, and taking into account effects of long term action.
2.2.3 Geometric parameters
b—— Width of rectangular section, or web width of T-shaped or I-shaped sections;
c—— Thickness of concrete cover;
d—— Nominal diameter of steel reinforcement (hereinafter referred to as “diameter”) or diameter of circular section;
h—— Depth of section;
h0—— Effective depth of section;
lab, la—— Basic anchorage length, and anchorage length of longitudinal tensile reinforcement, respectively;
l0—— Effective span or length;
s—— Spacing of transverse reinforcement, spacing of spiral reinforcement or spacing of stirrups in the longitudinal direction of a member;
x—— Depth of concrete compression zone;
A—— Cross-sectional area of a member;
As, ——
Cross-sectional areas of longitudinal steel rebars in tension zone and compression zone, respectively;
Ap, ——
Cross-sectional areas of longitudinal prestressing tendons in tension zone and compression zone, respectively;
Al—— Local compression area of concrete;
Acor—— Core cross-sectional area of concrete surrounded by stirrups, spiral reinforcement or reinforcement mesh;
B—— Section rigidity of a flexural member;
I—— Moment of inertia of section;
W—— Elastic section modulus with respect to the extreme fiber in tension zone of section;
Wt—— Plastic torsional section modulus.
2.2.4 Calculation coefficients and miscellaneous
αE—— Ratio of the elastic modulus of steel reinforcement to the elastic modulus of concrete;
γ—— Plastic coefficient for section modulus of concrete members;
η—— Amplifying coefficient for eccentricity of axial force considering second order effect;
λ—— Ratio of shear span to effective depth for calculated section, namely M/(Vh0);
ρ—— Reinforcement ratio for longitudinal reinforcement;
ρv—— Volumetric reinforcement ratio for indirect reinforcement or stirrup;
——
Diameter of rebar, 20 represents the rebar having a diameter of 20mm.
3 General Requirements
3.1 General
3.1.1 The design of concrete structures shall include the following contents:
1 Design of structural scheme, including the structure selection, member layout and force transfer route;
2 Action and effects of action analysis;
3 Limit states design of the structure;
4 Detailing and connection measures of structures and members;
5 Durability and construction requirements;
6 Special performance design of such structure meeting special requirements.
3.1.2 This code adopts the probability-based limit states design method, the degree of reliability of structural members is measured by the reliability index, and the design is carried out by adopting the design expressions of partial factors.
3.1.3 The limit states design of concrete structures shall include:
1 Ultimate limit states: A structure or a structural member reaches the maximum load-carrying capacity and appears the fatigue failure or undue deformation unsuitable for loading continually or has progressive collapse due to the local failure of structure;
2 Serviceability limit states: A structure or a structural member reaches a certain specified limit value of serviceability or a certain specified state of durability.
3.1.4 The direct action (load) on a structure shall be determined in accordance with the current national standard “Load Code for the Design of Building Structures” (GB 50009) and the relevant standards; the seismic action shall be determined in accordance with the current national standard “Code for Seismic Design of Buildings” (GB 50011).
The indirect action and accidental action shall be determined in accordance with the relevant standards or the specific conditions.
Structural members directly bearing crane loads shall take the dynamic factor of crane loads into account. For fabrication, transportation and installation of precast members, the corresponding dynamic factors shall be taken into account. For cast-in-situ structures, the loads during the construction stage shall be taken into account if necessary.
3.1.5 The safety class and design working life of concrete structures shall meet the current national standard “Unified Standard for Reliability Design of Engineering Structures” (GB 50153).
The safety class of different structural members in a concrete structure should be the same as the safety class of the whole structure. The safety class of parts of the structural member may be adjusted properly according to their importance. For important members and critical force transfer positions in the structure, the safety class should be elevated appropriately.
3.1.6 The design of concrete structures shall take the technical level of construction and the feasibility of practical engineering condition into account. For concrete structures with special functions, the corresponding construction requirements shall be proposed.
3.1.7 The design shall explicate the purposes of the structures. The purposes and the aplication circumstances of the structures shall not be modified within the design working life without technical evaluation or design permission.
3.2 Structural Scheme
3.2.1 The design scheme of concrete structures shall meet the following requirements:
1 Reasonable structural system, member form and layout shall be selected;
2 The plan and elevation of the structure should be arranged regularly, the mass and rigidity of all parts should be uniform and continuous;
3 The force transfer path of the structure shall be simple and definite, and vertical members should be continuous and aligned;
4 The statically indeterminte structure should be adopted; important members and crucial force transfer positions shall have additional redundant constraints or have several load transfer paths;
5 Measures should be taken to reduce the effects of accidental actions.
3.2.2 The design of structural joints in concrete structures shall meet the following requirements:
1 The position and structural form of structural joints shall be determined reasonably in accordance with the load-carrying characteristics, architectural scale and shape, and service requirements of the structure;
2 The number of structural joints should be controlled, and effective measures shall be taken to reduce the adverse impacts of joints on the service function;
3 The temporary structural joints during construction stage may be arranged as required.
3.2.3 The connection of structural members shall meet the following requirements:
1 The load-carrying capacity of the connecting part shall ensure the force transfer between the connected members;
2 When the concrete members are connected with those made of other materials, reliable measures shall be taken;
3 The impact caused by the deformation of concrete member on connecting joints and adjacent structures or members shall be considered.
3.2.4 The design of concrete structures shall meet the requirements on material saving, ease of construction, reducing energy consumption and protecting environment.
3.3 Ultimate Limit States
3.3.1 The ultimate limit states design of concrete structures shall include the following contents:
1 The calculation of load-carrying capacity (including instability) shall be carried out for structural members;
2 Fatigue analysis shall be carried out for members undergoing repeated loads;
3 When seismic design is required, the calculation of seismic capacity shall be carried out;
4 The analysis of structural overturning, sliding or floating shall be carried out if necessary;
5 Regarding the important structures that may suffer from accidental actions and may cause serious consequences if collapsing, the design against progressive collapse should be carried out.
3.3.2 For persistent design situation, transient design situation and seismic design situation, if expressed in the form of internal force, the following design expressions shall be adopted for ultimate limit states design of the structural members:
γ0S≤R (3.3.2-1)
R=R(fc, fs, ak, …)/γRd (3.3.2-2)
Where γ0——The significance coefficient of structure: under the persistent design situation and transient design situation, this coefficient shall not be less than 1.1 for the structural members having the safety grade of Class I ; it shall not be less than 1.0 for the structural members having the safety grade of Class II; and it shall not be less than 0.9 for the structural members having the safety grade of Class III; under the seismic design situation, this coefficient shall be 1.0;
S——The design value of the effect for combination of actions at ultimate limit states: it shall be calculated according to the basic combination of actions under the persistent design situation and transient design situation; and it shall be calculated according to the seismic combination of actions under seismic design situation;
R——The design value of resistance of structural member;
R(·)——The function of resistance of structural member;
γRd——The uncertainty coefficient of the resistance model of structural member: it is taken as 1.0 for static design, and taken as values larger than 1.0 according to specific conditions for the structural members with large uncertainty; in the seismic design, γRd shall be replaced by the seismic adjustment coefficient of load-carrying capacity γRE;
fc, fs——The design values of the strength for concrete and steel reinforcement respectively, which shall be taken as the values in accordance with Sub-clause 4.1.4 and Sub-clause 4.2.3 of this code;
ak——The characteristic value of geometric parameter. If the variation of the geometric parameter has significant adverse impact on the structural behavior, ak may be increased or decreased by an additional value.
Note: γ0S in Expression (3.3.2-1) is the design value of internal force and is expressed by N, M, V, T in chapters of this code.
3.3.3 For the two-dimensional and three-dimensional concrete structural members, if the analysis is carried out according to the elastic or elastic-plastic method and the expression is in the form of stress, the concrete stress may be equivalently substituted into the design value of internal force in the zone and be calculated according to Sub-clause 3.3.2 of this code; or the design may be carried out by directly adopting the multi-axial strength criterion.
3.3.4 Where the ultimate limit states design of the structure under accidental actions is carried out, the design value S in Expression (3.3.2-1) shall be calculated according to the accidental combination and the significance coefficient of structure (γ0) shall be taken as a value no less than 1.0; the design values of strength of concrete and steel reinforcement (fc and fs) in Expression (3.3.2-2) shall be replaced by the characteristic values of strength (fck and fyk) (or fpyk).
Where progressive collapse analysis of structure is carried out, the function of load-carrying capacity of structural member shall be determined according to the principles stated in Section 3.6 of this code.
3.3.5 The ultimate limit states design of existing structures shall be carried out according to the following requirements:
1 Where ultimate limit states analysis is required for conducting safety reassessment, changing service purpose or extending the service life of existing structures, it should meet the requirements specified in Sub-clause 3.3.2 of this code;
2 Where existing structures are redesigned for the purpose of renovation, extension or consolidation, the calculation of ultimate limit states shall meet the requirements specified in Section 3.7 of this code.
3.4 Serviceability Limit States
3.4.1 On the basis of the functions and appearance requirements of the concrete structural members, the serviceability limit states shall be checked according to the following provisions:
1 For members requiring deformation control, the deformation shall be checked;
2 For members that are not allowed to crack, the tensile stress of concrete shall be checked;
3 For members that are allowed to crack, the width of cracks shall be checked;
4 For floor system having comfort requirements, the vertical natural vibration frequency shall be checked.
3.4.2 For serviceability limit states, reinforced concrete members and prestressed concrete members shall be checked respectively according to the quasi-permanent combination or characteristic combination of loads, and taking into account the influence of long-term actions, by adopting the following design expression:
S≤C (3.4.2)
Where S——The design value of the effect of load combination for serviceability limit states;
C——The limit value of the specified deformation, stress, crack width or natural vibration frequency when the structural member meets the serviceability requirements.
3.4.3 The maximum deflection of reinforced concrete flexural member shall be calculated according to the quasi-permanent combination of loads; the maximum deflection of prestressed concrete flexural member shall be calculated according to the characteristic combination of loads; the influence of long-term action of loads shall be considered in both calculations; the calculated values shall not exceed the deflection limit values specified in Table 3.4.3.
Table 3.4.3 Deflection Limit Values of Flexural Members
Member type Limit value of deflection
Crane girder Manual-operate crane l0/500
Electric-operate crane l0/600
Roof, floor and stair members If l0<7m l0/200(l0/250)
If 7m≤l0≤9m l0/250(l0/300)
If l0>9m l0/300(l0/400)
Note: 1 l0 in this Table is the effective span of members; to calculate the limit value of deflection of cantilever members, its effective span l0 shall be adopted as two times the actual cantilever length;
2 Values in parentheses in this Table are applicable to members that have comparatively high requirement on deflection in application;
3 If the member is cambered before fabrication and it is allowed in application, the camber value shall be deducted from the calculated deflection value during the deflection analysis; for prestressed concrete members, the inverted camber value caused by jacking force may be also be deducted;
4 The camber value during the fabrication of member and the inverted camber value caused by jacking force should not exceed the calculated deflection value of the member under the action of corresponding load combination.
3.4.4 The control of force-induced cracks for normal section of structural member shall be divided into three levels, and the classification and requirements of the control level shall meet the following provisions:
Level 1——For members on which cracks are strictly prohibited, if the calculation is in accordance with the characteristic combination of loads, tensile stress shall not occur at the extreme fiber in tension zone of concrete.
Level 2——For members on which cracks are generally prohibited, if the calculation is in accordance with the characteristic combination of loads, tensile stress at the extreme fiber in tension zone of concrete shall not be larger than the characteristic value of concrete tensile strength.
Level 3——For members on which cracks are allowed: as for reinforced concrete members, if the calculation is in accordance with the quasi-permanent combination of loads and considering the influence of long-term actions of loads, the maximum crack width of the member shall not exceed the limit values of maximum crack width as specified in Table 3.4.5 of this code. As for prestressed concrete members, if the calculation is in accordance with the characteristic combination of loads and considering the influence of long-term actions of loads, the maximum crack width of the member shall not exceed the limit values of maximum crack width as specified in Sub-clause 3.4.5 of this code; as for the prestressed concrete members of Environmental Category II-a, the calculation shall also be in accordance with the quasi-permanent combination of loads and the concrete tensile stress at the extreme fiber in tension zone of the member shall not be larger than the characteristic value of the concrete tensile strength.
3.4.5 The different crack control levels and the limit values of maximum crack width ωlim of structural members shall be selected from Table 3.4.5 according to the structure type and the environmental categories specified in Sub-clause 3.5.2 of this code.
Table 3.4.5 Crack Control Levels and Limit Values of Maximum Crack Width (mm) of Structural Members
Environmental category Reinforced concrete structure Prestressed concrete structure
Crack control level ωlim Crack control level ωlim
I Level 3 0.30 (0.40) Level 3 0.20
II-a 0.20 0.10
II-b Level 2 —
III-a and III-b Level 1 —
Note: 1 For flexural members of Environmental Category I in such areas where the annual average relative humidity is less than 60%, the limit value for the maximum crack width may be taken as the values in parentheses;
2 Under Category I environment, the limit value for the maximum crack width of reinforced concrete roof truss, bracket and crane girder requiring fatigue analysis shall be taken as 0.20mm; and for reinforced concrete roof beam and joist, the limit value shall be taken as 0.30mm;
3 Under Category I environment, the prestressed concrete roof truss, bracket and two-way slab system shall be checked according to the crack control level 2; under the Category I environment, the prestressed concrete roof beam, joist and one-way slab shall be checked according to the requirements for Category II-a environment as given in this Table; under the Category I and II-a environments, the prestressed concrete crane girder requiring the checking of fatigue shall be checked according to the members with crack control level no less than Level 2;
4 The crack control levels and the limit values of maximum crack width for prestressed concrete members are only applicable to the checking of normal section; the checking of the crack control of inclined section of prestressed concrete members shall meet the relevant requirements stated in Chapter 7 of this code;
5 For chimneys, silos and structures under liquid pressure, the crack control requirements shall meet the relevant provisions of special standards;
6 For structural members under Category IV and V environments, the crack control requirements shall meet the relevant provisions of special standards;
7 The limit values of the maximum crack width in this Table are used for the checking of maximum crack width caused by the action of loads.
3.4.6 For concrete floor systems, the vertical natural vibration frequency shall be checked according to the requirements of their service functions and should meet the following requirements:
1 The vertical natural vibration frequency of residential buildings and apartments should not be less than 5Hz;
2 The vertical natural vibration frequency of office buildings and hotels should not be less than 4Hz;
3 The vertical natural vibration frequency of large-span public buildings should not be less than 3Hz.
3.5 Durability Requirements
3.5.1 The durability of concrete structures shall be designed in accordance with the design working life and environmental categories, and the durability design shall include the following contents:
1 The environmental category in which the structure is located shall be determined;
2 The basic requirements on the durability of concrete materials shall be proposed;
3 The thickness of concrete cover for steel reinforcement in members shall be determined;
4 The technical measures for durability taken under different ambient conditions;
5 The inspection and maintenance requirements for structures in service shall be proposed.
Note: As for the temporary concrete structures, the requirements for durability of concrete may not be considered.
3.5.2 The category of exposure environment of concrete structure shall be divided according to the requirements of Table 3.5.2.
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Table 3.5.2 Environmental Categories for Concrete Structures
Environmental category Condition
I Dry indoor environment;
Submersion environment of non-aggressive static water
II-a Indoor humid environment;
Open-air environment of non-severe cold and non-cold areas;
Environment in non-severe cold and non-cold areas, directly contacting with non-aggressive water or soil;
Environment below the frost lines in severe cold and cold areas, directly contacting with non- aggressive water or soil
II-b Alternate wetting and drying environment;
Environment with frequently varying water levels;
Open-air environment of the severe cold and cold areas;
Environments above the frost lines in severe cold and cold areas, directly contacting with non-aggressive water or soil
III-a Environment in regions with varying water levels in winter in the severe cold and cold areas;
Environment affected by deicing salt;
Sea wind environment
III-b Environment of salty soil;
Environment under the action of deicing salt;
Seacoast environment
IV Sea water environment
V Environment affected by human action or natural corrosive substance
Note: 1 The indoor humid environment refers to the environment in which the member surface is at the dew or wet state frequently;
2 The division of severe cold and cold areas shall meet the relevant provisions of the current national standard “Thermal Design Code for Civil Building” (GB 50176);
3 The seacoast environment and sea wind environment should be determined by investigations and engineering experiences based on local circumstances, in consideration of the influence of the prevailing wind direction and windward and leeward positions of the structure;
4 The environment affected by deicing salt refers to the environment that is affected by the mist of deicing salt; the environment under the action of deicing salt refers to the environment that is splashed by deicing salt solution and buildings in areas where deicing salt is used, such as in car wash and parking structures;
5 Exposure environment of concrete structures refers to the environment that surrounds surfaces of concrete structures.
3.5.3 For concrete structures with design working life of 50 years, the concrete materials should be in accordance with Table 3.5.3.
Table 3.5.3 Basic Requirements on Durability of Structural Concrete Materials
Environmental category Maximum water-cement ratio Minimum strength grade Maximum chloride ion content (%) Maximum alkali content (kg/m3)
I 0.60 C20 0.30 Unlimited
II-a 0.55 C25 0.20 3.0
II-b 0.50 (0.55) C30 (C25) 0.15
III-a 0.45 (0.50) C35 (C30) 0.15
III-b 0.40 0.40 0.10
Note: 1 Chloride ion content refers to the percentage of chloride ions in the total amount of cementitous materials;
2 The maximum chloride ion content in concrete for prestressed member is 0.06%; the minimum concrete strength grade should be increased by two grades according to the table;
3 Requirements on the water-cement ratio and minimum strength grade of concrete for plain concrete members may be reduced appropriately;
4 If reliable engineering experience is available, the minimum concrete strength grade in the environmental category II may be reduced by one grade;
5 The concrete in the Category II-b and III-a environments of severe cold and cold areas shall be used with air entraining agent and may adopt relevant parameters in the parentheses;
6 Where the non-alkali activated aggregate is applied, the alkali content in the concrete may not be limited.
3.5.4 Concrete structures and members shall also employ the following technical measures for the durability:
1 The prestressing tendons in prestressed concrete structures shall be taken with such measures as surface protection, duct grouting and increasing the thickness of concrete cover according to specific conditions. The exposed anchored end shall be taken with effective measures, such as anchor seal and concrete surface treatment;
2 For concrete structures with requirements on impermeability, the impermeability grade of concrete shall meet the requirements of relevant standards;
3 In the humid environment in severe cold and cold areas, the structural concrete shall meet the requirements on freezing resistance, and the resistance class to freezing-thawing of concrete shall meet the requirements of relevant standards;
4 Cantilever members in Category II and III environment should adopt the structural form of cantilever beam-slab or may be added with protective coating on upper surfaces;
5 For structural members in Category II and III environments, surfaces of metal elements such as embedded parts, hooks and connecting pieces, shall have reliable rust prevention measures; as for the exposed metal anchorage devices of post-tensioning prestressed concrete, protection requirements are detailed in Sub-clause 10.3.13 of this code;
6 Concrete structural members in Category III environment may adopt corrosion inhibitor, epoxy coated steel reinforcement or other steel reinforcement having corrosion resistance; they may alternatively employ cathodic protection, or use replaceable parts.
3.5.5 In Category I environment, concrete structures with design working life up to 100 years shall meet the following requirements:
1 The minimum strength grade of concrete used in reinforced concrete structures and prestressed concrete structures is C30 and C40 respectively;
2 The maximum chloride ion content in concrete is 0.06%;
3 The non-alkali activated aggregate should be used. If alkali activated aggregate is used, the maximum alkali content in concrete shall be 3.0kg/m3;
4 The thickness of concrete cover shall meet Sub-clause 8.2.1 of this code; where effective surface protection measures are taken, the thickness of concrete cover may be reduced appropriately.
3.5.6 In Category II and III environment, concrete structures with design working life up to 100 years shall employ special effective measures.
3.5.7 For concrete structures in Category IV and V environment, the durability requirements shall meet those specified in the relevant standards.
3.5.8 Concrete structures shall also meet the following requirements within their design working life:
1 Periodical inspection and maintenance system shall be established;
2 Replaceable concrete members in design shall be replaced as specified;
3 Protective coating for surface of members shall be maintained or replaced as specified;
4 Visible durability defects of structures, if any, shall be treated timely.
1 General
2 Terms and Symbols
2.1 Terms
2.2 Symbols
3 General Requirements
3.1 General
3.2 Structural Scheme
3.3 Ultimate Limit States
3.4 Serviceability Limit States
3.5 Durability Requirements
3.6 Principles for Design Against Progressive Collapse
3.7 Principles for Design of Existing Structures
4 Materials
4.1 Concrete
4.2 Steel Reinforcement
5 Structural Analysis
5.1 General
5.2 Analysis Model
5.3 Elastic Analysis
5.4 Plastic Internal Forces Redistribution Analysis
5.5 Elastic-Plastic Analysis
5.6 Plastic Limit Analysis
5.7 Indirect Action Effect Analysis
6 Ultimate Limit States
6.1 General
6.2 Load-carrying Capacity of Normal Sections
6.3 Load-carryring Capacity of Inclined Sections
6.4 Load-carrying Capacity of Sections Subjected to Torsion
6.5 Punching Shear Capacity
6.6 Local bearing Capacity
6.7 Fatigue Analysis
7 Serviceability Limit States
7.1 Crack control
7.2 Deflection of Flexural Members
8 Detailing Requirements
8.1 Expansion Joint
8.2 Concrete Cover
8.3 Anchorage of Steel Reinforcement
8.4 Splices of Steel Reinforcement
8.5 Minimum Ratio of Reinforcement for Longitudinal Load-carrying Steel Reinforcement
9 Fundamental Requirements for Structural Members
9.1 Slabs
9.2 Beams
9.3 Columns, Joints and Brackets
9.4 Walls
9.5 Composite Members
9.6 Precast Concrete Structures
9.7 Embedded Parts and Connecting Pieces
10 Prestressed Concrete Structural Members
10.1 General
10.2 Calculation of Prestress Losses
10.3 Detailing of Prestressed Concrete Members
11 Seismic Design of Reinforced Concrete Structural Members
11.1 General
11.2 Materials
11.3 Frame Beams
11.4 Frame Columns and Columns Supporting Structural Transfer Member
11.5 Columns of Hinged Bent
11.6 Joints of Frame
11.7 Shear Walls and Coupling Beams
11.8 Prestressed Concrete Structural Members
11.9 Slab-column Joints
Appendix A Nominal Diameter, Cross-sectional area and Theoretical Self-weight of Steel Reinforcement
Appendix B Approximate Coefficient Method for Second Order Effect of Sway Structure
Appendix C Constitutive Relations for Steel Reinforcement and Concrete and the Rule of Multi-axial Strength for Concrete
Appendix D Design of Plain Concrete Structural Members
Appendix E Calculation for Flexual and Axial Capacity of Circular, Annular and Arbitrary Cross Sections
Appendix F Design Value of Equivalent Concentrated Reaction Used for Calculation of Slab-column Joints
Appendix G Deep Flexural Members
Appendix H Composite Beam and Slab Without Shores
Appendix J Prestress losses of Curved Post-tensioned-Tendons Due to Anchorage Seating and Tendon Shortening
Appendix K Time-dependent Losses of Prestress
Explanation of Wording in This Code
List of Quoted Standards
