Codeofchina.com is in charge of this English translation. In case of any doubt about the English translation, the Chinese original shall be considered authoritative.
Pursuant to the requirements of “Notice on issuing the development task of Guangdong provincial standard Code for fire resistance design of concrete structures in buildings” issued by Guangdong Provincial Housing and Urban-Rural Construction Department (YUEJIANKEHAN [2008] No.282), the code development group has prepared this code through extensive investigation, careful conclusion from the existing scientific research achievements and practical experience, reference to relevant standards at home and abroad, and extensive solicitation of opinions.
The main technical contents of this code include: 1 General provisions; 2 Terms; 3 Basic provisions; 4 Material properties; 5 Normal-strength concrete members; 6 High-strength concrete members; 7 Prestressed concrete members; 8 Steel reinforced concrete members; 9. Strengthened concrete members.
Guangdong Provincial Housing and Urban-Rural Construction Department is in charge of the administration of this code, and South China University of Technology is responsible for the explanation of specific technical contents. During the process of implementing this code, you are kindly requested to send your opinions and advice (if any) to School of Civil Engineering & Transportation, South China University of Technology (Address: No.381, Wushan Road, Tianhe District, Guangzhou, 510640, China).
Code for fire resistance design of concrete structures in buildings
1 General provisions
1.0.1 This code is formulated to reduce or avoid the damage of building concrete structure in fire, protect personal and property safety, and carry out fire resistance design of building concrete structure economically and reasonably.
1.0.2 This code is applicable to the fire resistance design of newly constructed, extended and renovated building concrete structures.
1.0.3 This code is formulated on the basis of the limit state for load bearing capacity of building concrete structure under fire and at high temperature.
1.0.4 In addition to this code, the fire resistance design of concrete structures shall also comply with those stipulated in the current relevant standards of China.
2 Terms and symbols
2.1 Terms
2.1.1 limit state for load bearing capacity at high temperature
state when the member or structure reaches the bearing capacity limit or is deformed and is not suitable for continued bearing under fire and at high temperature
2.1.2 standard fire temperature-time curve
average temperature-time curve in furnace for standard fire resistance test of building members given in international standard ISO 834
2.1.3 equivalent fire exposure time
if the action effect of fire on the member or structure in time t under the condition of non-standard fire temperature rise is the same as that on the same member or structure in time te under the condition of standard fire temperature rise, te is called the corresponding equivalent fire exposure time
2.1.4 temperature distribution in structural member
general term of temperature distribution at each point of members at any time under fire and at high temperature
2.1.5 temperature difference due to explosive spalling
difference between the temperature at a certain point on the central axis of the member section when considering explosive spalling and the temperature at that point when not considering explosive spalling
2.1.6 fire insulation
material or combination of materials arranged on the surface of a member to improve its fire resistance
2.1.7 ordinary steel bars
general term of all kinds of non-prestresseding steel barstendons
2.1.8 prestressing tendons
general term for the prestressed steel strand and prestressed steel wire
2.1.9 structural steel
general term for structural steels other than ordinary steel bars and prestressing tendons
2.1.10 normal-strength concrete
concrete with the strength grade inferior to C60
2.1.11 high-strength concrete
concrete with the strength grade not inferior to C50
2.1.12 steel reinforced concrete member
members provided with steel inside the concrete
2.1.13 strengthened concrete member
concrete members strengthened by enlarging cross-section method or sticking carbon fiber cloth and steel plate on concrete surface
2.2 Symbols
a——the angle between the connecting line from the combined axial pressure acting point to the center of gravity of the cross section and the z-axis;
az——the thickness of damaged layer;
az,500——the average depth from each point on the isotherm at 500℃ to the edge of the cross section;
A——the gross sectional area;
b——the section width of beam or column, and section limb thickness of specially shaped column;
c——the thickness of concrete cover of longitudinal bar;
c1——the specific heat capacity of non-combustible finishing layer;
ccT——the specific heat capacity of normal-strength concrete at high temperature;
cmin——the minimum thickness of concrete cover of the longitudinal load-bearing bar;
csT——the specific heat capacity of structural steel at high temperature;
C——the section circumference of beam or column;
d——the diameter of steel bar;
d0——the thickness of the non-combustible finishing layer converted into concrete;
d1——the actual thickness of non-combustible finishing layer;
e——the eccentricity;
e0——the distance from the combined axial pressure acting point to the center of gravity of the cross section;
e0y, e0z——the distance from the combined axial pressure acting point to the z-axis and y-axis passing through the center of gravity of the cross section;
fcT——the axial compressive strength of normal-strength concrete or high-strength concrete at high temperature;
fp——the tensile strength of prestressing tendons at normal temperature;
h——the thickness of slab, section height of column or beam, section limb height of specially shaped column;
h0——the effective height of beam section;
Ia——the section inertia moment relative to Za axis (Za is the axis passing through the center of gravity of the section and perpendicular to the connecting line from the combined axial pressure acting point to the center of gravity);
k——the increase coefficient of damaged layer thickness;
l0——the larger calculated span of two adjacent spans of the first inner support;
ldT——the length of the negative moment steel bar extending into the beams or slabs on both sides of the first inner support;
L——the calculated length of a column;
m——the span-height ratio of beam;
M——the mid-span combined bending moment of beam or slab calculated according to simply-supported beam or simply-supported slab at normal temperature;
Mu——the mid-span flexural load-bearing capacity of beam or slab at normal temperature;
n——the ratio of combined axial pressure to axial pressure-bearing capacity of cross section under normal temperature;
Nu——the axial bearing capacity of the member at normal temperature at the combined axial pressure acting point;
ra——the turning radius;
RdT——the bearing capacity of members or structures at high temperature;
RT——the fire resistance ratinglimit;
[RT]——the specified fire resistance ratinglimit;
SGk——the effect of standard value of permanent load (including secondary internal force caused by prestress);
SmT——the combined design value of action and effect of members or structures at high temperature;
SQk——the effect of standard value of floor or roof live load;
STk——the standard temperature action effect underin the fire;
SWk——the effect of standard value of wind load;
t——the temperature rise time;
te——the equivalent fire exposure time;
tf——the thickness of fireproof coating;
T——the material temperature;
Tg——the indoor air temperature after fire;
Tg0——the indoor air temperature before fire;
Tgm——the maximum indoor air temperature after fire;
x——the distance from a point on the central axis of the cross section of the high-strength concrete rectangular column to the explosive spalling surface;
αsT——the thermal expansion coefficient of structural steel at high temperature;
β——the percentage increase of flexural load-bearing capacity of strengthened beams or slabs in mid-span compared with that of non-strengthened beams or slabs at normal temperature;
γ0T——the structural fire resistance safety coefficient;
δT——the temperature difference due to explosive spalling on the central axis of the cross section of high-strength concrete rectangular column;
ε——the strain;
ε0, ε0T——the peak strain of normal-strength concrete or high-strength concrete at normal temperature and high temperature;
εcrT——the creep strain of prestressing tendons at high temperature;
, , ——the thermal expansion strain of normal-strength concrete, ordinary steel bars and prestressing tendons at high temperature;
η0.2T, ηpT——the reduction factor of conditional yield strength and tensile strength of prestressing tendons at high temperature;
ηcT——the reduction factor of axial compressive strength of normal-strength concrete or high-strength concrete at high temperature;
η1T——the reduction factor of tensile strength of normal-strength concrete at high temperature;
ηyT——the reduction factor of yield strength of ordinary steel bars or structural steel at high temperature;
λ——the slenderness ratio of column;
λ1——the thermal conductivity of non-combustible finishing layer;
λcT——the thermal conductivity of normal-strength concrete at high temperature;
λsT——the thermal conductivity of structural steel at high temperature;
μ——the ratio of combined axial pressure to axial bearing capacity of member at normal temperature at the force acting point;
ρ——the reinforcement ratio of all section longitudinal load-bearing bars;
ρ1——the density of non-combustible finishing layer;
ρc, ρcT——the density of normal-strength concrete at normal temperature and high temperature;
ρsT——the density of structural steel at high temperature;
ρt——the reinforcement ratio of longitudinal tensile bars;
σ——the stress;
σ0——the initial stress of prestressing tendons;
σct——the nominal tensile stress of concrete facing fire at normal temperature;
σpT——the stress of prestressing tendons at high temperature;
σrT——the stress relaxation loss of prestressing tendons at high temperature;
τ——the fire duration in its heydaythe duration of full developed fire;
vsT——the poisson's ratio of structural steel at high temperature;
χcT——the reduction factor of initial elastic modulus of normal-strength concrete or high-strength concrete at high temperature;
χpT——the reduction factor of elastic modulus of prestressing tendons at high temperature;
χsT——the reduction factor of elastic modulus of ordinary steel bars or structural steel at high temperature;
ψf——the frequent value coefficient of floor or roof live load;
ψq——the quasi-permanent value coefficient of floor or roof live load.
3 Basic provisions
3.1 Fire resistance requirements
3.1.1 The fire resistance rating of single-storey buildings, multi-storey buildings and high-rise buildings and the fire resistance limit of their load-bearing members shall meet the requirements of GB 50016 Code for fire protection design of buildings and GB 50045 Code for fire protection design of tall building.
3.1.2 Based on the limit state for load bearing capacity, the fire resistance design of load-bearing members or structures shall meet one of the following requirements:
1 Within the specified fire resistance limit, the load bearing capacity RdT of the load-bearing member or structure shall not be less than the action effect combination SmT determined according to 3.4.1, namely:
RdT≥SmT (3.1.2-1)
2 Under the combination of action effect determined according to 3.4.1, the fire resistance limit RT of load-bearing member or structure shall not be less than the specified fire resistance limit [RT], namely:
RT≥[RT] (3.1.2-2)
3.1.3 For high-rise buildings with a height greater than 200m and buildings with a safety level of Level I, it is advisable to carry out stress analysis on the whole structure under the action of fire. The method specified in Annex D may be used for the overall analysis of the structure under in the fire.
3.1.4 For general single-storey and multi-storey building structures except those specified in 3.1.3, only the members may be designed for fire resistance.
3.2 Temperature-time curve of fire
3.2.1 The air temperature of general indoor fire is calculated byusing the following standard fire temperature-time curve:
Tg-Tg0=345lg(8t+1) (3.2.1)
where,
Tg——the indoor air temperature after fire (℃);
Tg0——the indoor air temperature before fire (℃);
t——the temperature rise time (min).
3.2.2 When the relevant indoor parameters can be accurately determined, the air temperature of indoor fire may be calculated according to Annex A, or other reliable fire models after flashover may be used to calculate the air temperature of indoor fire.
3.2.3 When 3.2.2 is used to calculate the air temperature of indoor fire, the impact of fire on members may be equivalent to the impact of standard fire temperature-time curve on components within the equivalent fire exposure time te, and:
(3.2.3)
where,
te——the equivalent fire exposure time (min);
Tg0——the indoor air temperature before fire (℃);
Tgm——the maximum indoor air temperature after fire (℃), determined according to Formula (A-2) or Formula (A-3) in Annex A;
τ——the duration of fire in its heyday (min), determined according to Formula (A-5) or Formula (A-6) in Annex A.
3.3 Temperature distribution in structural member
3.3.1 The temperature field of beam, column and other bar members is simplified as two-dimensional temperature field on cross section, and that of walls, slabs and other plane members is simplified as one-dimensional temperature field along thickness direction.
3.3.2 The temperature distribution in structural member shall be calculated by thermal conductivity equation combined with corresponding initial conditions and boundary conditions. For normal-strength concrete rectangular section members under standard fire temperature rise conditions, the temperature field of members can also be determined according to Annex B.
3.3.3 When the surface of a member is provided with a non-combustible finishing layer, convert the thickness of the finishing layer into the thickness of concrete, and then determine the temperature field of the component according to 3.3.2. The converted thickness shall be calculated using Formula (3.3.3):
(3.3.3)
where,
d0——the thickness of the non-combustible finishing layer converted into concrete (mm);
d1——the actual thickness of non-combustible finishing layer (mm);
ρ1, c1, λ1——the density, specific heat capacity and thermal conductivity of non-combustible finishing layer, which can be determined according to GB 50176 Thermal design code for civil building for common;ycommonly used non0-combustible finishing layer.
3.3.4 The temperature difference due to explosive spalling on the central axis of the cross section of the high-strength concrete rectangular column shall be calculated using Formula (3.3.4):
(3.3.4)
where,
x——the distance from a point on the central axis of the cross section and the explosive spalling surface (mm). If the stirrup hook is 135º, the explosive spalling surface is taken as the concrete surface in the core area, as shown in Figure 3.3.4.
t——the temperature rise time (min);
δT——the temperature difference due to explosive spalling (℃) at the position x away from the explosive spalling surface on the central axis of the cross section.
Figure 3.3.4 Explosive spalling surface of high-strength concrete rectangular column
3.4 Action effect combination
3.4.1 The action effect combination of occasional design conditions is adopted in fire resistance design, that is, the following unfavorable expressions are adopted:
(3.4.1-1)
(3.4.1-2)
where,
SmT——the design value of action effect combination;
SGk——the effect of standard value of permanent load (including secondary internal force caused by prestress);
STk——the standard temperature action effect of structures or members under fire, which may not be considered for ordinary single-storey and multi-storey building structures;
SQk——the effect of standard value of floor or roof live load;
Swk——the effect of standard value of wind load;
ψf——the frequent value coefficient of floor or roof live load, which shall be determined according to GB 50009 Load code for the design of building structures;
ψq——the quasi-permanent value coefficient of floor or roof live load, which shall be determined according to GB 50009 Load code for the design of building structures;
γ0T——the structural fire resistance safety coefficient, which shall be taken as 1.15 for buildings with fire resistance rating of Grade I, and 1.05 for other buildings.
4 Material properties
4.1 Ordinary steel bars
4.1.1 The thermal conductivity, specific heat capacity, density and poisson's ratio of ordinary steel bars at high temperature adopt the corresponding parameters of structural steel in Table 4.3.1.
4.1.2 The thermal expansion strain of ordinary steel bars at high temperature shall be calculated using Formula (4.1.2):
where,
T——the material temperature (℃);
——the thermal expansion strain of ordinary steel bars at high temperature.
4.1.3 The reduction factor of yield strength of ordinary steel bars at high temperature shall be calculated using Formula (4.1.3):
where,
ηsyT——the reduction factor of yield strength of ordinary steel bars at high temperature;
4.1.4 The reduction factor of elastic modulus of ordinary steel bars at high temperature shall be calculated using Formula (4.1.4):
where,
χsT——the reduction factor of elastic modulus of ordinary steel bars at high temperature.
4.2 Prestressing tendons
4.2.1 The thermal conductivity, specific heat capacity, density and poisson's ratio of prestressing tendons at high temperature adopt the corresponding parameters of structural steel in Table 4.3.1.
4.2.2 The thermal expansion strain of prestressing tendons at high temperature shall be calculated using Formula (4.2.2):
where,
——the thermal expansion strain of prestressing tendons at high temperature.
4.2.3 The reduction factor of conditional yield strength of prestressing tendons at high temperature shall be calculated using Formula (4.2.3):
where,
η0.2T——the reduction factor of conditional yield strength of prestressing tendons at high temperature;
4.2.4 The reduction factor of tensile strength of prestressing tendons at high temperature shall be calculated using Formula (4.2.4):
where,
ηpT——the reduction factor of tensile strength of prestressing tendons at high temperature;
4.2.5 The reduction factor of elastic modulus of prestressing tendons at high temperature shall be calculated using Formula (4.2.5):
where,
χpT——the reduction factor of elastic modulus of prestressing tendons at high temperature.
4.2.6 The short-term high-temperature stress relaxation loss of prestressing tendons at high temperature shall be calculated using Formulae (4.2.6-1) ~ (4.2.6-3):
where,
t——the temperature rise time (min);
σrT——the stress relaxation loss of prestressing tendons at high temperature (N/mm2);
σ0——the initial stress of prestressing tendons (N/mm2);
fp——the tensile strength of prestressing tendons at normal temperature (N/mm2).
4.2.7 The creep strain of prestressing tendons at high temperature shall be calculated using Formula (4.2.7):
where,
t——the temperature rise time (min);
εcrT——the creep strain of prestressing tendons at high temperature;
σpT——the stress of prestressing tendons at high temperature (N/mm2);
fp——the tensile strength of prestressing tendons at normal temperature (N/mm2).
4.3 Structural steel
4.3.1 Physical parameters related to structural steel at high temperature shall be adopted according to Table 4.3.1.
Table 4.3.1 Physical parameters of structural steel at high temperature
Parameter Symbol Value Unit
Thermal expansion coefficient αsT 1.4×10－5 m/(m·℃)
Thermal conductivity λsT 45 W/(m·℃)
Specific heat capacity csT 600 J/(kg·℃)
Density ρsT 7,850 Kg/m3
Poisson's ratio vsT 0.3 —
4.3.2 The reduction factor of yield strength of structural steel at high temperature shall be calculated using Formula (4.3.2):
where,
ηyT——the reduction factor of yield strength of structural steel at high temperature.
4.3.3 The reduction factor of elastic modulus of structure steel at high temperature shall be calculated using Formula (4.3.3):
where,
χsT——the reduction factor of elastic modulus of structural steel at high temperature.
4.4 Normal-strength concrete
4.4.1 The thermal conductivity, specific heat capacity and density of normal-strength concrete at high temperature shall be calculated according to Formulae (4.4.1-1) ~ (4.4.1-3) respectively:
Foreword ii
1 General provisions
2 Terms and symbols
2.1 Terms
2.2 Symbols
3 Basic provisions
3.1 Fire resistance requirements
3.2 Temperature-time curve of fire
3.3 Temperature distribution in structural member
3.4 Action effect combination
4 Material properties
4.1 Ordinary steel bars
4.2 Prestressing tendons
4.3 Structural steel
4.4 Normal-strength concrete
4.5 High-strength concrete
4.6 Fire insulation materials
5 Normal-strength concrete members
5.1 General
5.2 Beams
5.3 Columns
5.4 Slabs
5.5 Walls
6 High-strength concrete members
6.1 General requirements
6.2 Column
6.3 Wall
7 Prestressed concrete member
7.1 General
7.2 Beam
7.3 Column
7.4 Slab
7.5 Roof trusses
8 Steel reinforced concrete member
8.1 Beam
8.2 Column
9 Strengthened concrete member
9.1 General
9.2 Beam
9.3 Slabs
9.4 Construction requirements
Annex A Air temperature of indoor fire
Annex B Sectional temperature distribution in structural members exposed to a standard fire
Annex C Simplified calculation method
Annex D Advanced calculation method
Annex E Fire resistance limit of steel reinforced concrete columns
Annex F Thickness of fireproof coating for carbon fiber cloth strengthened concrete beams and slabs
Explanation of wording in this code
List of quoted codes
Codeofchina.com is in charge of this English translation. In case of any doubt about the English translation, the Chinese original shall be considered authoritative.
Pursuant to the requirements of “Notice on issuing the development task of Guangdong provincial standard Code for fire resistance design of concrete structures in buildings” issued by Guangdong Provincial Housing and Urban-Rural Construction Department (YUEJIANKEHAN [2008] No.282), the code development group has prepared this code through extensive investigation, careful conclusion from the existing scientific research achievements and practical experience, reference to relevant standards at home and abroad, and extensive solicitation of opinions.
The main technical contents of this code include: 1 General provisions; 2 Terms; 3 Basic provisions; 4 Material properties; 5 Normal-strength concrete members; 6 High-strength concrete members; 7 Prestressed concrete members; 8 Steel reinforced concrete members; 9. Strengthened concrete members.
Guangdong Provincial Housing and Urban-Rural Construction Department is in charge of the administration of this code, and South China University of Technology is responsible for the explanation of specific technical contents. During the process of implementing this code, you are kindly requested to send your opinions and advice (if any) to School of Civil Engineering & Transportation, South China University of Technology (Address: No.381, Wushan Road, Tianhe District, Guangzhou, 510640, China).
Code for fire resistance design of concrete structures in buildings
1 General provisions
1.0.1 This code is formulated to reduce or avoid the damage of building concrete structure in fire, protect personal and property safety, and carry out fire resistance design of building concrete structure economically and reasonably.
1.0.2 This code is applicable to the fire resistance design of newly constructed, extended and renovated building concrete structures.
1.0.3 This code is formulated on the basis of the limit state for load bearing capacity of building concrete structure under fire and at high temperature.
1.0.4 In addition to this code, the fire resistance design of concrete structures shall also comply with those stipulated in the current relevant standards of China.
2 Terms and symbols
2.1 Terms
2.1.1 limit state for load bearing capacity at high temperature
state when the member or structure reaches the bearing capacity limit or is deformed and is not suitable for continued bearing under fire and at high temperature
2.1.2 standard fire temperature-time curve
average temperature-time curve in furnace for standard fire resistance test of building members given in international standard ISO 834
2.1.3 equivalent fire exposure time
if the action effect of fire on the member or structure in time t under the condition of non-standard fire temperature rise is the same as that on the same member or structure in time te under the condition of standard fire temperature rise, te is called the corresponding equivalent fire exposure time
2.1.4 temperature distribution in structural member
general term of temperature distribution at each point of members at any time under fire and at high temperature
2.1.5 temperature difference due to explosive spalling
difference between the temperature at a certain point on the central axis of the member section when considering explosive spalling and the temperature at that point when not considering explosive spalling
2.1.6 fire insulation
material or combination of materials arranged on the surface of a member to improve its fire resistance
2.1.7 ordinary steel bars
general term of all kinds of non-prestresseding steel barstendons
2.1.8 prestressing tendons
general term for the prestressed steel strand and prestressed steel wire
2.1.9 structural steel
general term for structural steels other than ordinary steel bars and prestressing tendons
2.1.10 normal-strength concrete
concrete with the strength grade inferior to C60
2.1.11 high-strength concrete
concrete with the strength grade not inferior to C50
2.1.12 steel reinforced concrete member
members provided with steel inside the concrete
2.1.13 strengthened concrete member
concrete members strengthened by enlarging cross-section method or sticking carbon fiber cloth and steel plate on concrete surface
2.2 Symbols
a——the angle between the connecting line from the combined axial pressure acting point to the center of gravity of the cross section and the z-axis;
az——the thickness of damaged layer;
az,500——the average depth from each point on the isotherm at 500℃ to the edge of the cross section;
A——the gross sectional area;
b——the section width of beam or column, and section limb thickness of specially shaped column;
c——the thickness of concrete cover of longitudinal bar;
c1——the specific heat capacity of non-combustible finishing layer;
ccT——the specific heat capacity of normal-strength concrete at high temperature;
cmin——the minimum thickness of concrete cover of the longitudinal load-bearing bar;
csT——the specific heat capacity of structural steel at high temperature;
C——the section circumference of beam or column;
d——the diameter of steel bar;
d0——the thickness of the non-combustible finishing layer converted into concrete;
d1——the actual thickness of non-combustible finishing layer;
e——the eccentricity;
e0——the distance from the combined axial pressure acting point to the center of gravity of the cross section;
e0y, e0z——the distance from the combined axial pressure acting point to the z-axis and y-axis passing through the center of gravity of the cross section;
fcT——the axial compressive strength of normal-strength concrete or high-strength concrete at high temperature;
fp——the tensile strength of prestressing tendons at normal temperature;
h——the thickness of slab, section height of column or beam, section limb height of specially shaped column;
h0——the effective height of beam section;
Ia——the section inertia moment relative to Za axis (Za is the axis passing through the center of gravity of the section and perpendicular to the connecting line from the combined axial pressure acting point to the center of gravity);
k——the increase coefficient of damaged layer thickness;
l0——the larger calculated span of two adjacent spans of the first inner support;
ldT——the length of the negative moment steel bar extending into the beams or slabs on both sides of the first inner support;
L——the calculated length of a column;
m——the span-height ratio of beam;
M——the mid-span combined bending moment of beam or slab calculated according to simply-supported beam or simply-supported slab at normal temperature;
Mu——the mid-span flexural load-bearing capacity of beam or slab at normal temperature;
n——the ratio of combined axial pressure to axial pressure-bearing capacity of cross section under normal temperature;
Nu——the axial bearing capacity of the member at normal temperature at the combined axial pressure acting point;
ra——the turning radius;
RdT——the bearing capacity of members or structures at high temperature;
RT——the fire resistance ratinglimit;
[RT]——the specified fire resistance ratinglimit;
SGk——the effect of standard value of permanent load (including secondary internal force caused by prestress);
SmT——the combined design value of action and effect of members or structures at high temperature;
SQk——the effect of standard value of floor or roof live load;
STk——the standard temperature action effect underin the fire;
SWk——the effect of standard value of wind load;
t——the temperature rise time;
te——the equivalent fire exposure time;
tf——the thickness of fireproof coating;
T——the material temperature;
Tg——the indoor air temperature after fire;
Tg0——the indoor air temperature before fire;
Tgm——the maximum indoor air temperature after fire;
x——the distance from a point on the central axis of the cross section of the high-strength concrete rectangular column to the explosive spalling surface;
αsT——the thermal expansion coefficient of structural steel at high temperature;
β——the percentage increase of flexural load-bearing capacity of strengthened beams or slabs in mid-span compared with that of non-strengthened beams or slabs at normal temperature;
γ0T——the structural fire resistance safety coefficient;
δT——the temperature difference due to explosive spalling on the central axis of the cross section of high-strength concrete rectangular column;
ε——the strain;
ε0, ε0T——the peak strain of normal-strength concrete or high-strength concrete at normal temperature and high temperature;
εcrT——the creep strain of prestressing tendons at high temperature;
, , ——the thermal expansion strain of normal-strength concrete, ordinary steel bars and prestressing tendons at high temperature;
η0.2T, ηpT——the reduction factor of conditional yield strength and tensile strength of prestressing tendons at high temperature;
ηcT——the reduction factor of axial compressive strength of normal-strength concrete or high-strength concrete at high temperature;
η1T——the reduction factor of tensile strength of normal-strength concrete at high temperature;
ηyT——the reduction factor of yield strength of ordinary steel bars or structural steel at high temperature;
λ——the slenderness ratio of column;
λ1——the thermal conductivity of non-combustible finishing layer;
λcT——the thermal conductivity of normal-strength concrete at high temperature;
λsT——the thermal conductivity of structural steel at high temperature;
μ——the ratio of combined axial pressure to axial bearing capacity of member at normal temperature at the force acting point;
ρ——the reinforcement ratio of all section longitudinal load-bearing bars;
ρ1——the density of non-combustible finishing layer;
ρc, ρcT——the density of normal-strength concrete at normal temperature and high temperature;
ρsT——the density of structural steel at high temperature;
ρt——the reinforcement ratio of longitudinal tensile bars;
σ——the stress;
σ0——the initial stress of prestressing tendons;
σct——the nominal tensile stress of concrete facing fire at normal temperature;
σpT——the stress of prestressing tendons at high temperature;
σrT——the stress relaxation loss of prestressing tendons at high temperature;
τ——the fire duration in its heydaythe duration of full developed fire;
vsT——the poisson's ratio of structural steel at high temperature;
χcT——the reduction factor of initial elastic modulus of normal-strength concrete or high-strength concrete at high temperature;
χpT——the reduction factor of elastic modulus of prestressing tendons at high temperature;
χsT——the reduction factor of elastic modulus of ordinary steel bars or structural steel at high temperature;
ψf——the frequent value coefficient of floor or roof live load;
ψq——the quasi-permanent value coefficient of floor or roof live load.
3 Basic provisions
3.1 Fire resistance requirements
3.1.1 The fire resistance rating of single-storey buildings, multi-storey buildings and high-rise buildings and the fire resistance limit of their load-bearing members shall meet the requirements of GB 50016 Code for fire protection design of buildings and GB 50045 Code for fire protection design of tall building.
3.1.2 Based on the limit state for load bearing capacity, the fire resistance design of load-bearing members or structures shall meet one of the following requirements:
1 Within the specified fire resistance limit, the load bearing capacity RdT of the load-bearing member or structure shall not be less than the action effect combination SmT determined according to 3.4.1, namely:
RdT≥SmT (3.1.2-1)
2 Under the combination of action effect determined according to 3.4.1, the fire resistance limit RT of load-bearing member or structure shall not be less than the specified fire resistance limit [RT], namely:
RT≥[RT] (3.1.2-2)
3.1.3 For high-rise buildings with a height greater than 200m and buildings with a safety level of Level I, it is advisable to carry out stress analysis on the whole structure under the action of fire. The method specified in Annex D may be used for the overall analysis of the structure under in the fire.
3.1.4 For general single-storey and multi-storey building structures except those specified in 3.1.3, only the members may be designed for fire resistance.
3.2 Temperature-time curve of fire
3.2.1 The air temperature of general indoor fire is calculated byusing the following standard fire temperature-time curve:
Tg-Tg0=345lg(8t+1) (3.2.1)
where,
Tg——the indoor air temperature after fire (℃);
Tg0——the indoor air temperature before fire (℃);
t——the temperature rise time (min).
3.2.2 When the relevant indoor parameters can be accurately determined, the air temperature of indoor fire may be calculated according to Annex A, or other reliable fire models after flashover may be used to calculate the air temperature of indoor fire.
3.2.3 When 3.2.2 is used to calculate the air temperature of indoor fire, the impact of fire on members may be equivalent to the impact of standard fire temperature-time curve on components within the equivalent fire exposure time te, and:
(3.2.3)
where,
te——the equivalent fire exposure time (min);
Tg0——the indoor air temperature before fire (℃);
Tgm——the maximum indoor air temperature after fire (℃), determined according to Formula (A-2) or Formula (A-3) in Annex A;
τ——the duration of fire in its heyday (min), determined according to Formula (A-5) or Formula (A-6) in Annex A.
3.3 Temperature distribution in structural member
3.3.1 The temperature field of beam, column and other bar members is simplified as two-dimensional temperature field on cross section, and that of walls, slabs and other plane members is simplified as one-dimensional temperature field along thickness direction.
3.3.2 The temperature distribution in structural member shall be calculated by thermal conductivity equation combined with corresponding initial conditions and boundary conditions. For normal-strength concrete rectangular section members under standard fire temperature rise conditions, the temperature field of members can also be determined according to Annex B.
3.3.3 When the surface of a member is provided with a non-combustible finishing layer, convert the thickness of the finishing layer into the thickness of concrete, and then determine the temperature field of the component according to 3.3.2. The converted thickness shall be calculated using Formula (3.3.3):
(3.3.3)
where,
d0——the thickness of the non-combustible finishing layer converted into concrete (mm);
d1——the actual thickness of non-combustible finishing layer (mm);
ρ1, c1, λ1——the density, specific heat capacity and thermal conductivity of non-combustible finishing layer, which can be determined according to GB 50176 Thermal design code for civil building for common;ycommonly used non0-combustible finishing layer.
3.3.4 The temperature difference due to explosive spalling on the central axis of the cross section of the high-strength concrete rectangular column shall be calculated using Formula (3.3.4):
(3.3.4)
where,
x——the distance from a point on the central axis of the cross section and the explosive spalling surface (mm). If the stirrup hook is 135º, the explosive spalling surface is taken as the concrete surface in the core area, as shown in Figure 3.3.4.
t——the temperature rise time (min);
δT——the temperature difference due to explosive spalling (℃) at the position x away from the explosive spalling surface on the central axis of the cross section.
Figure 3.3.4 Explosive spalling surface of high-strength concrete rectangular column
3.4 Action effect combination
3.4.1 The action effect combination of occasional design conditions is adopted in fire resistance design, that is, the following unfavorable expressions are adopted:
(3.4.1-1)
(3.4.1-2)
where,
SmT——the design value of action effect combination;
SGk——the effect of standard value of permanent load (including secondary internal force caused by prestress);
STk——the standard temperature action effect of structures or members under fire, which may not be considered for ordinary single-storey and multi-storey building structures;
SQk——the effect of standard value of floor or roof live load;
Swk——the effect of standard value of wind load;
ψf——the frequent value coefficient of floor or roof live load, which shall be determined according to GB 50009 Load code for the design of building structures;
ψq——the quasi-permanent value coefficient of floor or roof live load, which shall be determined according to GB 50009 Load code for the design of building structures;
γ0T——the structural fire resistance safety coefficient, which shall be taken as 1.15 for buildings with fire resistance rating of Grade I, and 1.05 for other buildings.
4 Material properties
4.1 Ordinary steel bars
4.1.1 The thermal conductivity, specific heat capacity, density and poisson's ratio of ordinary steel bars at high temperature adopt the corresponding parameters of structural steel in Table 4.3.1.
4.1.2 The thermal expansion strain of ordinary steel bars at high temperature shall be calculated using Formula (4.1.2):
where,
T——the material temperature (℃);
——the thermal expansion strain of ordinary steel bars at high temperature.
4.1.3 The reduction factor of yield strength of ordinary steel bars at high temperature shall be calculated using Formula (4.1.3):
where,
ηsyT——the reduction factor of yield strength of ordinary steel bars at high temperature;
4.1.4 The reduction factor of elastic modulus of ordinary steel bars at high temperature shall be calculated using Formula (4.1.4):
where,
χsT——the reduction factor of elastic modulus of ordinary steel bars at high temperature.
4.2 Prestressing tendons
4.2.1 The thermal conductivity, specific heat capacity, density and poisson's ratio of prestressing tendons at high temperature adopt the corresponding parameters of structural steel in Table 4.3.1.
4.2.2 The thermal expansion strain of prestressing tendons at high temperature shall be calculated using Formula (4.2.2):
where,
——the thermal expansion strain of prestressing tendons at high temperature.
4.2.3 The reduction factor of conditional yield strength of prestressing tendons at high temperature shall be calculated using Formula (4.2.3):
where,
η0.2T——the reduction factor of conditional yield strength of prestressing tendons at high temperature;
4.2.4 The reduction factor of tensile strength of prestressing tendons at high temperature shall be calculated using Formula (4.2.4):
where,
ηpT——the reduction factor of tensile strength of prestressing tendons at high temperature;
4.2.5 The reduction factor of elastic modulus of prestressing tendons at high temperature shall be calculated using Formula (4.2.5):
where,
χpT——the reduction factor of elastic modulus of prestressing tendons at high temperature.
4.2.6 The short-term high-temperature stress relaxation loss of prestressing tendons at high temperature shall be calculated using Formulae (4.2.6-1) ~ (4.2.6-3):
where,
t——the temperature rise time (min);
σrT——the stress relaxation loss of prestressing tendons at high temperature (N/mm2);
σ0——the initial stress of prestressing tendons (N/mm2);
fp——the tensile strength of prestressing tendons at normal temperature (N/mm2).
4.2.7 The creep strain of prestressing tendons at high temperature shall be calculated using Formula (4.2.7):
where,
t——the temperature rise time (min);
εcrT——the creep strain of prestressing tendons at high temperature;
σpT——the stress of prestressing tendons at high temperature (N/mm2);
fp——the tensile strength of prestressing tendons at normal temperature (N/mm2).
4.3 Structural steel
4.3.1 Physical parameters related to structural steel at high temperature shall be adopted according to Table 4.3.1.
Table 4.3.1 Physical parameters of structural steel at high temperature
Parameter Symbol Value Unit
Thermal expansion coefficient αsT 1.4×10－5 m/(m·℃)
Thermal conductivity λsT 45 W/(m·℃)
Specific heat capacity csT 600 J/(kg·℃)
Density ρsT 7,850 Kg/m3
Poisson's ratio vsT 0.3 —
4.3.2 The reduction factor of yield strength of structural steel at high temperature shall be calculated using Formula (4.3.2):
where,
ηyT——the reduction factor of yield strength of structural steel at high temperature.
4.3.3 The reduction factor of elastic modulus of structure steel at high temperature shall be calculated using Formula (4.3.3):
where,
χsT——the reduction factor of elastic modulus of structural steel at high temperature.
4.4 Normal-strength concrete
4.4.1 The thermal conductivity, specific heat capacity and density of normal-strength concrete at high temperature shall be calculated according to Formulae (4.4.1-1) ~ (4.4.1-3) respectively:
Contents of DBJ/T 15-81-2011
Foreword ii
1 General provisions
2 Terms and symbols
2.1 Terms
2.2 Symbols
3 Basic provisions
3.1 Fire resistance requirements
3.2 Temperature-time curve of fire
3.3 Temperature distribution in structural member
3.4 Action effect combination
4 Material properties
4.1 Ordinary steel bars
4.2 Prestressing tendons
4.3 Structural steel
4.4 Normal-strength concrete
4.5 High-strength concrete
4.6 Fire insulation materials
5 Normal-strength concrete members
5.1 General
5.2 Beams
5.3 Columns
5.4 Slabs
5.5 Walls
6 High-strength concrete members
6.1 General requirements
6.2 Column
6.3 Wall
7 Prestressed concrete member
7.1 General
7.2 Beam
7.3 Column
7.4 Slab
7.5 Roof trusses
8 Steel reinforced concrete member
8.1 Beam
8.2 Column
9 Strengthened concrete member
9.1 General
9.2 Beam
9.3 Slabs
9.4 Construction requirements
Annex A Air temperature of indoor fire
Annex B Sectional temperature distribution in structural members exposed to a standard fire
Annex C Simplified calculation method
Annex D Advanced calculation method
Annex E Fire resistance limit of steel reinforced concrete columns
Annex F Thickness of fireproof coating for carbon fiber cloth strengthened concrete beams and slabs
Explanation of wording in this code
List of quoted codes