Fireproof and decoration integrated steel beam fireproof design method and steel beam

Abstract

The invention relates to the technical field of building steel structure fire protection, and particularly provides a fire protection and decoration integrated steel beam fire protection design method and a steel beam. The critical temperature Tc of the steel beam and the highest temperature Ts, max within the designed fire endurance tm are calculated; whether the steel beam meets the fireproof design requirement or not is judged, and if not, a fireproof and decorative integrated structure is designed; the highest temperature Tps, max of the steel beam and the highest temperature Tps, max within the designed fire endurance tm are calculated; whether the fireproof and decorative integrated structure in the steel beam meets the fireproof design requirement or not is judged, and if not, the thickness and / or the material of the fireproof and decorative integrated structure are / is changed till the fireproof and decorative integrated structure meets the fireproof design requirement. The fireproof and decorative integrated steel beam comprises a steel beam body and a fireproof and decorative integrated structure. The method is based on the critical temperature method, the accuracy is higher, and calculation is simpler, more convenient and faster.

Description

Technical Field

[0001] The invention belongs to the technical field of fire protection of building steel structures, and in particular relates to a fire protection design method for a fire-proof and decorative integrated steel beam and a steel beam. Background Art

[0002] Steel structures have attracted attention from the industry due to their good earthquake resistance, fast construction speed, and environmental sustainability. Their proportion in my country's modern building structure system is increasing, but steel structures also have a disadvantage that cannot be ignored, that is, poor fire resistance. Under high temperatures, the internal lattice structure of steel changes, and its yield strength, elastic modulus, etc. are reduced, resulting in a significant decrease in the bearing capacity and stability of the components. The critical temperature of commonly used construction steel is around 540°C, while for building fires, the fire temperature is mostly 800-1200°C. Under such high temperature conditions, steel components without any protective measures will soon undergo plastic deformation. According to the test results of the standard time heating curve, the fire resistance limit of exposed steel components is only 0.25 hours.

[0003] In order to provide reliable fire protection for steel structures and extend their fire resistance time, the "Technical Code for Fire Protection of Building Steel Structures" GB51249-2017 (hereinafter referred to as the "Code") has provided some fire protection construction practices, such as the use of non-expanding fire retardant coatings for protection, fireproof board protection, external concrete protection, fireproof coating and fireproof board composite protection, etc. Some of these measures for steel beams still have many problems and disadvantages, such as the cumbersome construction of external concrete and the need for maintenance, the fireproof board coating cannot solve the problem of filling the internal space of the H-beam flange, the insufficient durability of the expandable fire retardant coating, and the rough and loose non-expandable fire retardant coating that cannot meet the decoration requirements.

[0004] In order to solve the pain points in the above fireproof construction methods, the fireproof decoration integrated construction method formed by using aerated concrete blocks and other materials to cover the steel beams, and adding fireproof coatings, plastering mortar and other fireproof protective layers came into being. A series of experimental studies and numerical simulations have also proved its effectiveness. However, the relevant fireproof design methods given in the "Specification" are not applicable to steel beams using this fireproof decoration integrated structure. The design method of the "Specification" assumes that the temperature of the entire component section is uniformly distributed. In fact, in the fireproof decoration integrated construction method, the two sides of the steel beam web are filled with blocks, and the steel beam is often exposed to fire on three sides in the fire scene. Therefore, its temperature distribution should be gradually reduced from bottom to top, which is inconsistent with the assumptions in the "Specification". At the same time, the "Specification" does not give the corresponding steel component temperature calculation or correction formula. Under limited conditions, if the highest temperature of the steel beam is to be accurately obtained, it can only be obtained through numerical simulation methods. This method is cumbersome and inefficient, and requires a large learning and time cost, which is inconvenient for designers to use. In summary, the research gaps in related fields and the lack of relevant standards have brought certain difficulties to the fire protection design of steel beams with integrated fire-proof and decorative structures. Summary of the invention

[0005] In view of the problems existing in the above-mentioned prior art, the present invention provides a fire protection design method for a fire-proof and decorative integrated steel beam and a steel beam.

[0006] In a first aspect, the present invention provides a fire protection design method for a fire-proof decorative integrated steel beam, comprising the following steps:

[0007] Step 1: Obtain the fire protection design parameters of the steel beam;

[0008] Step 2: Obtain the design fire resistance limit t of the steel beam without fire protection measures. m The maximum temperature T s,max ;

[0009] Step 3: Based on the fire protection design parameters of the steel beam, determine the critical temperature T of the steel beam without fire protection measures. c ;

[0010] Step 4: Based on the maximum temperature T of the steel beam without fire protection measures s,max and critical temperature T c Determine whether the steel beam meets the fire protection design requirements. If the steel beam meets the fire protection design requirements, the steel beam is no longer provided with a fire protection decoration integrated structure. If the steel beam does not meet the fire protection design requirements, a fire protection decoration integrated structure is designed according to the design fire resistance grade of the steel beam that needs to be designed for fire protection.

[0011] Step 5: Based on the performance parameters of the fireproof decorative integrated structure, the steel beam is obtained under the condition of setting fire protection measures at the design fire resistance limit t m The maximum temperature T ps,max ;

[0012] Step 6: The maximum temperature T of the steel beam under the condition of setting fire protection measures ps,max and critical temperature T c To determine whether the fireproof decorative integrated structure in the steel beam meets the fire protection design requirements. If it does not meet the fire protection design requirements, change the thickness and / or material of the fireproof decorative integrated structure, and return to step 5 until the fireproof decorative integrated structure meets the fire protection design requirements.

[0013] Furthermore, in step 5, when fire protection measures are provided, the steel beam has a design fire resistance limit t m The maximum temperature T ps,max It is obtained by iterative processing, wherein the iterative processing steps include:

[0014] Step 5.1: Use the steel beam temperature T at time t ps Get the temperature rise ΔT of the steel beam within a time step Δt ps ;

[0015] Step 5.2: Set the steel beam temperature T at time t+Δt ps Updated to the steel beam temperature T at time t ps and temperature rise ΔT ps sum;

[0016] Step 5.3: Repeat steps 5.1 and 5.2 for the steel beam temperature T ps Perform iterative processing to obtain the steel beam temperature T at different times ps and the design fire resistance limit t m The highest steel beam temperature T ps As the steel beam is designed to have a fire resistance limit of t m The maximum temperature T ps,max .

[0017] Furthermore, in step 5, when fire protection measures are provided, the steel beam has a design fire resistance limit t m The maximum temperature T ps,max Iterate according to the following formula to get:

[0018]

[0019]

[0020] Where, ΔT psrepresents the temperature rise of the steel beam in (t, t+Δt) when fire protection measures are set; Δt represents the time step; α i represents the comprehensive heat transfer coefficient of the steel beam; F i represents the surface area of ​​the steel beam per unit length that is exposed to fire; V represents the volume of the steel beam per unit length; k represents the parameter of the delaying effect of the steel beam web filling material on the temperature rise of the lower flange; ρ s and c s Respectively represent the density and specific heat of steel; T g represents the average temperature of hot flue gas at time t; T ps It indicates the temperature of the lower flange of the steel beam at time t when fire protection measures are set;

[0021] In the above formula, t f and b represent the thickness and width of the steel beam flange respectively; α1, α2, α3 represent the comprehensive heat transfer coefficients of the lower side, left side and right side of the lower flange of the steel beam respectively; λ1, λ2 and λ3 represent the equivalent thermal conductivity of the materials used in the fire-proof decorative integrated structure on the lower side, left side and right side of the lower flange of the steel beam respectively; d1, d2 and d3 represent the thickness of the fire-proof decorative integrated structure on the lower side, left side and right side of the lower flange of the steel beam respectively.

[0022] Furthermore, in step 2, when no fire protection measures are provided, the steel beam has a design fire resistance limit of t m The maximum temperature T s,max It is obtained by iterative processing, wherein the iterative processing steps include:

[0023] Step 2.1: Use the steel beam temperature T at time t s Get the temperature rise ΔT of the steel beam within a time step Δt s ;

[0024] Step 2.2: Set the steel beam temperature T at time t+Δt s Updated to the steel beam temperature T at time t s and temperature rise ΔT s sum;

[0025] Step 2.3: Repeat steps 2.1 and 2.2 for the steel beam temperature T s Perform iterative processing to obtain the steel beam temperature T at different times s and the design fire resistance limit t m The highest steel beam temperature T s As the steel beam is designed to have a fire resistance limit of t m The maximum temperature T s,max .

[0026] Furthermore, in the step 2, without setting fire protection measures, the steel beam has a design fire resistance limit of tm The maximum temperature T s,max Iterate according to the following formula to get:

[0027]

[0028] α=α c +α r

[0029]

[0030] In the formula, ΔT s represents the temperature rise of the steel beam in (t, t+Δt) without fire protection measures; Δt represents the time step; α represents the comprehensive heat transfer coefficient of the steel beam; α c represents the heat transfer coefficient of convection; α r represents the thermal radiation heat transfer coefficient; ρ s and c s They represent the density and specific heat of steel respectively; F represents the surface area of ​​steel beam exposed to fire per unit length; V represents the volume of steel beam per unit length; T g represents the average temperature of hot flue gas at time t; T s represents the internal temperature of the steel beam at time t when no fire protection measures are set; ε r represents the integrated emissivity; σ represents the Stefan-Boltzmann constant.

[0031] Furthermore, in step 4, according to the case where no fire protection measures are set, the maximum temperature T of the steel beam is s,max and critical temperature T c The steps of judging whether the steel beam meets the fire protection design requirements include:

[0032] If the critical temperature of the steel beam is T c ≥ Maximum temperature of steel beam T s,max , it means that the steel beam meets the fire protection design requirements and the steel beam is no longer equipped with an integrated fire protection decoration structure;

[0033] If the critical temperature of the steel beam is T c <The maximum temperature of the steel beam T s,max , it indicates that the steel beam does not meet the fire protection design requirements.

[0034] Furthermore, in step 6, according to the case where fire protection measures are provided, the maximum temperature T of the steel beam is ps,max and critical temperature T c The steps for judging whether the fireproof decorative integrated structure in the steel beam meets the fireproof design requirements include:

[0035] If the critical temperature of the steel beam is T c ≥ Maximum temperature of steel beam T ps,max, it indicates that the steel beam meets the fire protection design requirements;

[0036] If the critical temperature of the steel beam is T c <The maximum temperature of the steel beam T ps,max , it indicates that the steel beam does not meet the fire protection design requirements.

[0037] Furthermore, the fire protection design parameters of the steel beam in step 1 include the design fire resistance grade, the design fire resistance limit t m , section strength load ratio R, component stability load ratio R', stability coefficient of steel beam at room temperature and air heating curve.

[0038] Further,

[0039] The cross-sectional strength load ratio R is obtained by the following formula:

[0040] M u =γW n f

[0041] Where R represents the cross-sectional strength load ratio of the steel beam under fire; M represents the maximum bending moment design value of the steel beam under fire; M u represents the bending bearing capacity of the steel beam at room temperature; γ represents the plastic development coefficient of the steel beam section; W n represents the net section modulus of the most unfavorable section of the steel beam; f represents the yield strength of the steel at room temperature;

[0042] The component stable load ratio R' of the steel beam is obtained by the following formula:

[0043]

[0044] Where R' represents the component stable load ratio of the steel beam under fire; M su It represents the overall stable bearing capacity of the steel beam at room temperature; represents the stability coefficient of the steel beam at room temperature; W represents the gross section modulus of the steel beam; β b The equivalent bending moment coefficient that represents the overall stability of the steel beam; λ y represents the slenderness ratio of the steel beam to the weak axis yy between the lateral support points; A represents the gross cross-sectional area of ​​the steel beam; h represents the full height of the steel beam section; t1 represents the thickness of the compression flange of the steel beam; η b represents the influence coefficient of asymmetric cross section of steel beam; ε k represents the steel grade correction factor; l1 represents the distance between the lateral support points of the compression flange of the steel beam; i y It represents the radius of gyration of the rough section of the steel beam to the weak axis y-axis;

[0045] The expression of the air heating curve of the steel beam is as follows:

[0046] T g =345lot 10 (8t+1)+T0

[0047] Where, T g It represents the average temperature of hot smoke at time t when the fire develops; t represents the duration of the fire; T0 represents the temperature of the indoor environment before the fire.

[0048] In the second aspect, the present invention also proposes a fireproof decorative integrated steel beam, which is designed using the above-mentioned method. The fireproof decorative integrated steel beam includes a steel beam and a fireproof decorative integrated structure; the fireproof decorative integrated structure includes aerated concrete blocks and / or fine stone concrete filled on both sides of the steel beam, and the fireproof decorative integrated structure also includes plastering mortar and / or non-expanding fire retardant coating applied to the bottom of the beam.

[0049] The beneficial effects of the present invention are:

[0050] 1. A simplified calculation method for the cross-sectional temperature field of steel beams with integrated fireproof decoration structures on three sides is provided. At present, the "Specification" does not provide a corresponding temperature calculation formula. If you want to accurately obtain the temperature of the steel beam after setting up the fireproof structure, you can only use a numerical simulation method with cumbersome steps and low efficiency, which requires a large learning and time cost and is inconvenient to use.

[0051] 2. The uneven temperature distribution of the steel beam cross section after the adoption of the integrated fire-proof and decorative structure is taken into consideration, making the calculation results more realistic and more accurate. The design method in the "Code" assumes that the temperature of the entire component cross section is uniformly distributed.

[0052] 3. The calculation method proposed in the present invention takes into account the fire protection effect of a variety of lightweight and non-lightweight materials at the same time. Compared with the "Specifications" which require separate consideration of lightweight and non-lightweight materials when calculating the temperature of steel components, the material types are diversified and the scope of application is wider.

[0053] 4. Compared with protection measures such as non-expanding fire-retardant coating protection, coated fire-proof board protection, external concrete protection, and composite protection of fire-retardant coating and fire-retardant board, the integrated fire-proof decoration structure solves some of the pain points. While ensuring a good fire-proof effect, it also meets the requirements of building decoration, and it is convenient to construct, cost-controlled, and environmentally friendly.

[0054] 5. The present invention can be widely used in the fire protection design of various steel structure buildings using fireproof decorative integrated structural steel beams, and provide technical support and reliable guarantee for the promotion of this structure in engineering. The present invention first gives a simplified calculation formula for the maximum temperature of the cross section of the fireproof decorative integrated steel beam, and then proposes a fire protection design and fire resistance verification method for the fireproof decorative integrated steel beam based on the critical temperature method. The method is basically consistent with the numerical analysis results and has strong applicability. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] Figure 1 It is a schematic diagram of the process of the present invention;

[0056] Figure 2 It is a structural schematic diagram of an implementation mode of the fireproof decorative integrated steel beam of the present invention;

[0057] Figure 3 It is a structural schematic diagram of another embodiment of the fireproof decorative integrated steel beam of the present invention;

[0058] Figure 4 This is a structural schematic diagram of another embodiment of the fireproof decorative integrated steel beam of the present invention;

[0059] Figure 5 It is a structural schematic diagram of another embodiment of the fireproof decorative integrated steel beam of the present invention;

[0060] Figure 6 This is a structural schematic diagram of another embodiment of the fireproof decorative integrated steel beam of the present invention.

[0061] In the figure: 1- facing mortar; 2- non-expanding fire retardant coating; 3- H-shaped steel; 4- masonry mortar; 5- aerated concrete block; 6- saddle nails; 7- C-type hot-dip galvanized steel wire mesh; 8- fine stone concrete; 9- steel bars. DETAILED DESCRIPTION

[0062] The present application is further described in detail below with reference to the accompanying drawings and specific implementations:

[0063] Embodiment 1

[0064] like Figure 2 As shown, the fireproof decorative integrated steel beam proposed by the present invention includes an H-shaped steel 3 with a cross-section of H300×100×6×10, and also includes a fireproof decorative integrated structure composed of fireproof filling materials. The overall beam width is 200mm, and the bottom of the beam is a non-expansion type fireproof coating 2 with a coating thickness of 20mm. Both sides of the H-shaped steel 3 are filled with aerated concrete blocks 5, and the surface mortar 1 is applied.

[0065] like Figure 1 As shown, the design method of the fireproof decorative integrated steel beam includes the following steps:

[0066] Step 1: Obtain the fire protection design parameters of the fire-proof decorative integrated steel beam; the fire protection design parameters of the steel beam include the design fire resistance grade, the design fire resistance limit t m , section strength load ratio R, component stability load ratio R', stability coefficient of steel beam at room temperature and air heating curves, and may also include steel performance parameters.

[0067] Among them, the section strength load ratio R is obtained according to the following formula:

[0068]

[0069] M u =γW n f

[0070] Where R represents the cross-sectional strength load ratio of the steel beam under fire; M represents the maximum bending moment design value of the steel beam under fire, in units of (N·mm); u represents the bending bearing capacity of steel beams at room temperature, in units of (N·mm); γ represents the plastic development coefficient of the steel beam section; W n Indicates the net section modulus of the most unfavorable section of the steel beam, unit (mm 3 ); f represents the yield strength of steel at room temperature, unit (N / mm 2 );

[0071] The component stable load ratio R' of the steel beam is obtained according to the following formula:

[0072]

[0073] Where R' represents the component stable load ratio of the steel beam under fire; M su It represents the overall stable bearing capacity of the steel beam at room temperature, in units of (N·mm); It represents the stability coefficient of the steel beam at room temperature; W represents the gross section modulus of the steel beam, unit (mm 3 );β b The equivalent bending moment coefficient that represents the overall stability of the steel beam; λ y It indicates the slenderness ratio of the steel beam to the weak axis yy between the lateral support points; A indicates the gross cross-sectional area of ​​the steel beam, in units of (mm 2 ); h represents the full height of the steel beam section; t1 represents the thickness of the compression flange of the steel beam, unit (mm); η b It represents the influence coefficient of asymmetric cross section of steel beam. For biaxially symmetrical cross section, η b =0;ε k Indicates the steel grade correction factor; l1 indicates the distance between the lateral support points of the compression flange of the steel beam, unit (mm); i y It represents the radius of gyration of the rough section of the steel beam relative to the weak axis y-axis, in mm.

[0074] The expression of the air heating curve of the steel beam is as follows:

[0075] T g =345log 10 (8t+1)+T0

[0076] Where, T g It represents the average temperature of hot smoke when the fire develops to time t, in (℃); t represents the duration of the fire, in (s); T0 represents the temperature of the indoor environment before the fire, in (℃).

[0077] The temperature rise calculation for indoor fires in common buildings can be based on the above-mentioned temperature rise curve. When there is a reliable basis for accurately determining the temperature changes under actual fire, the temperature rise calculation can also be performed according to the actual fire temperature rise curve.

[0078] In this embodiment, the cross-sectional strength load ratio of the steel beam is R=0.6, and the stability coefficient of the steel beam at room temperature is The component stable load ratio R'=0.788.

[0079] In addition, according to the "Code for Fire Protection Design of Buildings" GB50016-2014, the fire resistance level of the steel beam is determined to be level 1, and the fire resistance limit is 2h; according to the "Technical Code for Fire Protection of Building Steel Structures" GB51249-2017, the various performance parameters of steel are determined.

[0080] Step 2: Calculate the design fire resistance limit t of the steel beam without fire protection measures using the following formula: m The maximum temperature T s,max :

[0081]

[0082] α=α c +α r

[0083]

[0084] In the formula, ΔT s It represents the temperature rise of the steel beam in (t, t+Δt) without fire protection measures, in units of (℃); Δt represents the time step, in units of (s), and the value should not be greater than 5s; α represents the comprehensive heat transfer coefficient, in units of [W / (m 2 ·℃)]; α c Indicates the heat transfer coefficient of convection, taking 25W / (m 2 ·℃); α r Represents the thermal radiation heat transfer coefficient, unit [W / (m2·℃)]; ρ s and c sThey represent the density and specific heat of steel respectively; F represents the surface area of ​​steel beam exposed to fire per unit length, in units of (m 2 ); V represents the volume of steel beam per unit length, unit (m 3 ), F / V represents the cross-sectional shape coefficient of the steel beam; T g Indicates the average temperature of hot flue gas at time t, unit (℃); T s Indicates the internal temperature of the steel beam at time t when no fire protection measures are set, unit (℃); ε r represents the comprehensive radiation rate, which is generally taken as 0.7; σ represents the Stefan-Boltzmann constant, which is generally taken as 5.67×10-8W / (m 2 ℃ 4 ).

[0085] The highest steel beam temperature T at 2h when no fire protection measures are set is calculated by the above formula: s is 1048℃, that is, T s,max =1048℃;

[0086] Step 3: Based on the section strength load ratio R and the member stable load ratio R', calculate the critical temperature T of the steel beam without fire protection measures by the following formula: c .

[0087] T c =min(T c1 ,T c2 )

[0088] According to the cross-sectional strength load ratio R, T is calculated according to the following formula c1 :

[0089] T c1 =755-390R 1.2

[0090] According to the component stable load ratio R', T is calculated according to the following formula c2 :

[0091]

[0092] In the formula, represents the critical strength temperature; R represents the cross-sectional strength load ratio of the steel beam under fire; represents the critical temperature of stability; R' represents the component stability load ratio of the steel beam under fire; represents the stability parameter; represents the stability coefficient of the steel beam at room temperature. b <0.6, take φ b =0.6, min() represents the small value function.

[0093] The critical temperature T of the steel beam without fire protection measures is determined from the above calculation results. c It is 457℃.

[0094] T s,max With T c Compare and get T c ≤T s,max This indicates that steel beams without protective measures do not meet the fire protection design requirements and that an integrated fire protection decorative structure needs to be set up on the steel beams.

[0095] Step 4: Determine the performance parameters of the fire-retardant coating, masonry mortar, plastering mortar and autoclaved aerated concrete blocks of the fire-retardant decorative integrated structure according to the type test report and instructions provided by the manufacturer.

[0096] Step 5: According to the performance parameters of the fireproof decorative integrated structure, such as Figure 2 As shown in the figure, the steel beam is added with an integrated fireproof decoration structure, and the steel beam is calculated and analyzed. The following formula is used to obtain the design fire resistance limit t of the steel beam. m The maximum temperature T ps,max ;

[0097]

[0098] Where Δt represents the temperature rise of the steel beam in (t, t+Δt) when fire protection measures are set, in units of (℃); Δt represents the time step; α i represents the comprehensive heat transfer coefficient of the steel beam; F i represents the surface area of ​​the steel beam per unit length that is exposed to fire; V represents the volume of the steel beam per unit length; k represents the parameter of the delaying effect of the steel beam web filling material on the temperature rise of the lower flange; ρ s and c s Respectively represent the density and specific heat of steel; T g represents the average temperature of hot flue gas at time t; T ps It indicates the temperature of the lower flange of the steel beam at time t when fire protection measures are set, in degrees Celsius;

[0099] In the above formula, t f and b represent the thickness and width of the steel beam flange, respectively; F1 / V, F2 / V, F3 / V represent the cross-sectional shape coefficients of the lower, left and right blocks of the lower flange, respectively; α1, α2, α3 represent the comprehensive heat transfer coefficients of the lower, left and right sides of the lower flange of the steel beam, respectively; λ1, λ2 and λ3 represent the equivalent heat conductivity of the material used in the fireproof decorative integrated structure of the lower, left and right sides of the lower flange of the steel beam, respectively; d1, d2 and d3 represent the thickness of the fireproof decorative integrated structure of the lower, left and right sides of the lower flange of the steel beam, respectively;

[0100] k=A'(b-200)2 +[0.0105(d1-30) 2 +2.55](t f -15) 2 +0.4(d1-30) 2 +85

[0101] A'=(20t f +4d1+930)×10 -5

[0102] Where A' represents the delay coefficient.

[0103] The highest temperature T of the steel beam with integrated fireproof decoration structure at 2h is calculated by the above formula: ps is 428℃, that is, T ps,max =428℃;

[0104] Critical temperature T of steel beam related to steel beam load ratio R pc =T c =457℃.

[0105] Step 6: T ps,max With T pc Compare and get T pc >T ps,max , which shows that the integrated fireproof decoration structure meets the fire protection design requirements. Therefore, the integrated fireproof decoration structure can be used to carry out fire protection design of steel beams.

[0106] Embodiment 2

[0107] The fireproof decorative integrated steel beam proposed by the present invention comprises an H-shaped steel 3 with a cross-section of H400×120×6×8, and also comprises a fireproof decorative integrated structure composed of fireproof filling materials. The overall beam width is 200mm, and the bottom of the beam is a non-expansion fireproof coating 2 with a coating thickness of 15mm.

[0108] The design method of the fireproof decorative integrated steel beam of this embodiment comprises the following steps:

[0109] Step 1: Obtain the fire protection design parameters of the fire-proof decorative integrated steel beam; the fire protection design parameters of the steel beam include the design fire resistance grade, the design fire resistance limit t m , section strength load ratio R, component stability load ratio R', stability coefficient of steel beam at room temperature Steel performance parameters and air heating curve; the cross-sectional strength load ratio of the steel beam is R = 0.7, and the stability coefficient of the steel beam at room temperature is φ b =0.75, component stable load ratio R'=0.98.

[0110] In addition, according to the "Code for Fire Protection Design of Buildings" GB50016-2014, the fire resistance grade of the steel beam is determined to be level 2, and the fire resistance limit is 1.5h; according to the "Technical Code for Fire Protection of Building Steel Structures" GB51249-2017, the various performance parameters of the steel are determined; the ISO standard temperature rise curve is obtained according to the following formula.

[0111] T g =345log 10 (8t+1)+T0

[0112] Step 2: Calculate the design fire resistance limit t of the steel beam without fire protection measures using the following formula: m The maximum temperature T s,max :

[0113]

[0114] α=α c +α r

[0115]

[0116] The highest temperature T of the steel beam at 1.5h when no fire protection measures are set is calculated by the above formula: s is 1005℃, that is, T s,max =1005℃.

[0117] Step 3: Based on the section strength load ratio R and the member stable load ratio R', calculate the critical temperature T of the steel beam without fire protection measures by the following formula: c .

[0118] According to the cross-sectional strength load ratio R, T is calculated according to the following formula c1 :

[0119] T c1 =755-390R 1.2

[0120] According to the component stable load ratio R', T is calculated according to the following formula c2 :

[0121]

[0122] The critical temperature T of the steel beam without fire protection measures is determined from the above calculation results. c It is 335℃.

[0123] T s,max With T c Compare and get T c ≤T s,maxThis indicates that steel beams without protective measures do not meet the fire protection design requirements and that an integrated fire protection decorative structure needs to be set up on the steel beams.

[0124] Step 4: Determine the performance parameters of the non-expanding fire retardant coating, masonry mortar, plastering mortar and autoclaved aerated concrete blocks of the fire-proof decorative integrated structure according to the type test report and instructions provided by the manufacturer.

[0125] Step 5: According to the performance parameters of the fireproof decorative integrated structure, such as Figure 2 As shown in the figure, the steel beam is added with an integrated fireproof decoration structure, and the steel beam is calculated and analyzed. The following formula is used to obtain the design fire resistance limit t of the steel beam. m The maximum temperature T ps,max ;

[0126]

[0127] The highest temperature T of the steel beam with integrated fireproof decoration structure at 1.5h is calculated by the above formula: ps is 367℃, that is, T ps,max =367°C;

[0128] Critical temperature T of steel beam related to steel beam load ratio R pc =T c =335℃.

[0129] Step 6: T ps,max With T pc Compare and get T pc ≤T ps,max , indicating that the fireproof decoration integrated structure does not meet the fire protection design requirements and needs to be improved;

[0130] Return to step 4, increase the thickness of the fire retardant coating to 20 mm, and repeat the steps in step 5 to obtain the maximum temperature T of the steel beam with the integrated fireproof decoration structure at 1.5 h. ps,max 306℃;

[0131] Re-T ps,max With T pc Compare and get T pc >T ps,max , which shows that the integrated fireproof decoration structure meets the fire protection design requirements. Therefore, the integrated fireproof decoration structure can be used to carry out fire protection design of steel beams.

[0132] Based on the same inventive concept, the present invention also proposes a fireproof decorative integrated steel beam, which is designed using the above method. The fireproof decorative integrated steel beam includes a steel beam and a fireproof decorative integrated structure; the fireproof decorative integrated structure includes aerated concrete blocks and / or fine stone concrete filled on both sides of the steel beam, and the fireproof decorative integrated structure also includes plastering mortar and / or non-expanding fire retardant coating applied to the bottom of the beam.

[0133] The fireproof decorative integrated structure of the present invention includes a variety of construction methods.

[0134] Figure 2 The construction method is to fill aerated concrete blocks 5 on both sides of a steel beam (i.e., H-shaped steel 3) and apply facing mortar 1, and apply non-expansion fire retardant coating 2 on the bottom of the beam;

[0135] Figure 3 The two sides of the steel beam are filled with aerated concrete blocks 5 and coated with plaster mortar 1, and the bottom of the beam is also coated with plaster mortar 1;

[0136] Figure 4 A construction method in which one side of the steel beam is filled with aerated concrete blocks 5, the other side is filled with fine stone concrete 8, and both sides and the bottom of the beam are coated with plaster mortar 1;

[0137] Figure 5 A steel beam fireproof structural model in which both sides of the steel beam are filled with aerated concrete blocks 5 and coated with plastering mortar 1, and the bottom of the beam is coated with plastering mortar 1 or non-expansive fireproof coating 2;

[0138] Figure 6 The fireproof structural model of a steel beam is that one side of the steel beam is filled with aerated concrete blocks 5, the other side is filled with fine stone concrete 8, and both sides and the bottom of the beam are coated with plaster mortar 1.

[0139] like Figure 2 , Figure 3 and Figure 5 As shown, aerated concrete blocks 5 are arranged on both sides of the web of the steel beam, mortar is filled between the aerated concrete blocks 5 and the web, and the outer surface of the aerated concrete blocks 5 is coated with plastering mortar 1, and the bottom end of the lower flange of the steel beam can be coated with non-expansion fire retardant coating 2 or plastering mortar 1; Figure 4 and Figure 6 As shown, an aerated concrete block 5 is arranged on one side of the web of the steel beam, mortar is filled between the aerated concrete block 5 and the web, and the outer surface of the aerated concrete block 5 is coated with facing mortar 1, and fine stone concrete 8 is poured on the other side of the web of the steel beam, and steel bars 9 can be arranged inside the fine stone concrete 8, and the outer surface of the fine stone concrete 8 is coated with facing mortar 1.

[0140] The above are only preferred embodiments of the present invention, and the protection scope of the present invention is not limited to the above embodiments. All technical solutions under the concept of the present invention belong to the protection scope of the present invention. It should be pointed out that for ordinary technicians in this technical field, some improvements and modifications without departing from the principle of the present invention should also be regarded as the protection scope of the present invention.

Claims

1. A fire protection design method for fire-proof and decorative integrated steel beams, characterized in that: The following steps are involved: Step 1: Obtain the fire protection design parameters of the steel beam; Step 2: Obtain the design fire resistance limit t of the steel beam without fire protection measures. m The maximum temperature T s,max ; Step 3: Based on the fire protection design parameters of the steel beam, determine the critical temperature T of the steel beam without fire protection measures. c ; Step 4: Based on the maximum temperature T of the steel beam without fire protection measures s,max and critical temperature T c Determine whether the steel beam meets the fire protection design requirements. If the steel beam meets the fire protection design requirements, the steel beam is no longer provided with a fire protection decoration integrated structure. If the fire protection design requirements are not met, an integrated fire protection and decoration structure shall be designed according to the design fire resistance level of the steel beams that need to be designed for fire protection; Step 5: Based on the performance parameters of the fireproof decorative integrated structure, the steel beam is obtained under the condition of setting fire protection measures at the design fire resistance limit t m The maximum temperature T ps,max ; Step 6: The maximum temperature T of the steel beam under the condition of setting fire protection measures ps,max and critical temperature T c To determine whether the fireproof decorative integrated structure in the steel beam meets the fire protection design requirements. If it does not meet the fire protection design requirements, change the thickness and / or material of the fireproof decorative integrated structure, and return to step 5 until the fireproof decorative integrated structure meets the fire protection design requirements.

2. According to claim 1, a fireproofing design method for fireproofing and decorative integrated steel beams is characterized in that: In step 5, when fire protection measures are provided, the steel beam has a design fire resistance limit t m The maximum temperature T ps,max It is obtained by iterative processing, wherein the iterative processing steps include: Step 5.1: Use the steel beam temperature T at time t ps Get the temperature rise ΔT of the steel beam within a time step Δt ps ; Step 5.2: Set the steel beam temperature T at time t+Δt ps Updated to the steel beam temperature T at time t ps and temperature rise ΔT ps sum; Step 5.3: Repeat steps 5.1 and 5.2 for the steel beam temperature T ps Perform iterative processing to obtain the steel beam temperature T at different times ps and the design fire resistance limit t m The highest steel beam temperature T ps As the steel beam is designed to have a fire resistance limit of t m The maximum temperature T ps,max .

3. According to claim 2, a fireproofing design method for fireproofing and decorative integrated steel beams is characterized in that: In step 5, when fire protection measures are provided, the steel beam has a design fire resistance limit t m The maximum temperature T ps,max Iterate according to the following formula to get: Where, ΔT ps represents the temperature rise of the steel beam in (t, t+Δt) when fire protection measures are set; Δt represents the time step; α i represents the comprehensive heat transfer coefficient of the steel beam; F i represents the surface area of ​​the steel beam per unit length that is exposed to fire; V represents the volume of the steel beam per unit length; k represents the parameter of the delaying effect of the steel beam web filling material on the temperature rise of the lower flange; ρ s and c s Respectively represent the density and specific heat of steel; T g represents the average temperature of hot flue gas at time t; T ps It indicates the temperature of the lower flange of the steel beam at time t when fire protection measures are set; In the above formula, t f and b represent the thickness and width of the steel beam flange respectively; α1, α2, α3 represent the comprehensive heat transfer coefficients of the lower side, left side and right side of the lower flange of the steel beam respectively; λ1, λ2 and λ3 represent the equivalent thermal conductivity of the materials used in the fire-proof decorative integrated structure on the lower side, left side and right side of the lower flange of the steel beam respectively; d1, d2 and d3 represent the thickness of the fire-proof decorative integrated structure on the lower side, left side and right side of the lower flange of the steel beam respectively.

4. According to claim 1, a fireproofing design method for fireproofing and decorative integrated steel beams is characterized in that: In step 2, when no fire protection measures are provided, the steel beam has a design fire resistance limit of t m The maximum temperature T s,max The iterative processing step includes: Step 2.1: Use the steel beam temperature T at time t s Get the temperature rise ΔT of the steel beam within a time step Δt s ; Step 2.2: Set the steel beam temperature T at time t+Δt s Updated to the steel beam temperature T at time t s and temperature rise ΔT s sum; Step 2.3: Repeat steps 2.1 and 2.2 for the steel beam temperature T s Perform iterative processing to obtain the steel beam temperature T at different times s and the design fire resistance limit t m The highest steel beam temperature T s As the steel beam is designed to have a fire resistance limit of t m The maximum temperature T s,max .

5. According to claim 4, a fireproofing design method for fireproofing and decorative integrated steel beams is characterized in that: In the step 2, without setting fire protection measures, the steel beam has a design fire resistance limit of t m The maximum temperature T s,max Iterate according to the following formula to get: α＝α c +α r Where, ΔT s represents the temperature rise of the steel beam in (t, t+Δt) without fire protection measures; Δt represents the time step; α represents the comprehensive heat transfer coefficient of the steel beam; α c represents the heat transfer coefficient of convection; α r represents the thermal radiation heat transfer coefficient; ρ s and c s They represent the density and specific heat of steel respectively; F represents the surface area of ​​steel beam exposed to fire per unit length; V represents the volume of steel beam per unit length; T g represents the average temperature of hot flue gas at time t; T s represents the internal temperature of the steel beam at time t when no fire protection measures are set; ε r represents the integrated emissivity; σ represents the Stefan-Boltzmann constant.

6. The fire protection design method of a fire-proof and decorative integrated steel beam according to claim 1, characterized in that: In step 4, the maximum temperature T of the steel beam is s,max and critical temperature T c The steps of judging whether the steel beam meets the fire protection design requirements include: If the critical temperature of the steel beam is T c ≥ Maximum temperature of steel beam T s,max , it means that the steel beam meets the fire protection design requirements and the steel beam is no longer equipped with an integrated fire protection decoration structure; If the critical temperature of the steel beam is T c <The maximum temperature of the steel beam T s,max , it indicates that the steel beam does not meet the fire protection design requirements.

7. The fire protection design method of a fire-proof and decorative integrated steel beam according to claim 1, characterized in that: In step 6, according to the fire protection measures, the maximum temperature T of the steel beam is ps,max and critical temperature T c The steps for judging whether the fireproof decorative integrated structure in the steel beam meets the fireproof design requirements include: If the critical temperature of the steel beam is T c ≥ Maximum temperature of steel beam T ps,max , it indicates that the steel beam meets the fire protection design requirements; If the critical temperature of the steel beam is T c <The maximum temperature of the steel beam T ps,max , it indicates that the steel beam does not meet the fire protection design requirements.

8. The fire protection design method of a fire-proof and decorative integrated steel beam according to claim 1, characterized in that: The fire protection design parameters of the steel beam in step 1 include the design fire resistance grade, the design fire resistance limit t m , section strength load ratio R, component stability load ratio R', stability coefficient of steel beam at room temperature and air heating curve.

9. A fire protection design method for fire-proof and decorative integrated steel beams according to claim 8, characterized in that: The cross-sectional strength load ratio R is obtained by the following formula: M u =γW n f Where R represents the cross-sectional strength load ratio of the steel beam under fire; M represents the maximum bending moment design value of the steel beam under fire; M u represents the bending bearing capacity of the steel beam at room temperature; γ represents the plastic development coefficient of the steel beam section; W n represents the net section modulus of the most unfavorable section of the steel beam; f represents the yield strength of the steel at room temperature; The component stable load ratio R' of the steel beam is obtained according to the following formula: Where R' represents the component stable load ratio of the steel beam under fire; M su It represents the overall stable bearing capacity of the steel beam at room temperature; represents the stability coefficient of the steel beam at room temperature; W represents the gross section modulus of the steel beam; β b The equivalent bending moment coefficient that represents the overall stability of the steel beam; λ y represents the slenderness ratio of the steel beam to the weak axis yy between the lateral support points; A represents the gross cross-sectional area of ​​the steel beam; h represents the full height of the steel beam section; t1 represents the thickness of the compression flange of the steel beam; η b represents the influence coefficient of asymmetric cross section of steel beam; ε k represents the steel grade correction factor; l1 represents the distance between the lateral support points of the compression flange of the steel beam; i y It represents the radius of gyration of the rough section of the steel beam to the weak axis y-axis; The expression of the air heating curve of the steel beam is as follows: T g =345log 10 (8t+1)+T0 Where, T g It indicates the average temperature of hot smoke when the fire develops to time t; t indicates the duration of the fire; T0 represents the temperature of the indoor environment before the fire.

10. A fireproof decorative integrated steel beam, designed by the method according to claim 1, characterized in that: The fireproof decorative integrated steel beam includes a steel beam and a fireproof decorative integrated structure; the fireproof decorative integrated structure includes aerated concrete blocks and / or fine stone concrete filled on both sides of the steel beam, and the fireproof decorative integrated structure also includes plaster mortar and / or non-expanding fire retardant coating applied to the bottom of the beam.

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