CN103324797A - Test and analysis method for overall fire resistance of high-rise steel frame structure - Google Patents
Test and analysis method for overall fire resistance of high-rise steel frame structure Download PDFInfo
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Abstract
The invention provides a test and analysis method for overall fire resistance of a high-rise steel frame structure. The method includes: establishing a temperature field finite element model and a mechanical field finite element model for a high-rise steel frame structure system; designing corresponding fire condition parameters according to standard fire conditions, establishing a fire dynamics model by a spatial air temperature rise model or by a fluid dynamics calculation procedure FDS to calculate spatial temperature fields under various fire conditions, and using an obtained time-varying spatial temperature field as a thermal boundary condition for the temperature field finite element model of the whole structure; calculating the finite element model by finite element software; calculating the temperature field finite element model by software, substituting the obtained finite element temperature field to the mechanical field finite element model, and calculating to obtain a mechanical field; estimating whether the structure system collapses or not or exceeds the design limits or not according to calculation results; performing quantitative analysis on fire loss economy, and judging the economy of a fire protection design scheme.
Description
Technical field
What the present invention relates to is a kind of technical method of Design of Steel Structures Against Fire of technical field of civil engineering, and specifically, what relate to is the whole fire resistance check analysis of a kind of tall steel frame method.
Background technology
In recent years, all kinds of high levels, super high steel structure have obtained rapidly and vigorous growth in China, yet, the steel fire performance is relatively poor, under the high temperature of fire effect, its mechanical property such as yield strength, elastic modulus etc. can obviously reduce, when temperature reaches 600 ℃, and can the whole strength and stiffness of basic forfeiture.The common disaster hidden-trouble of high-rise steel structure is large, and burning is fierce, spreads rapidly, and is difficult for putting out a fire to save life and property, and easily causes structural failure even collapses, and causes serious casualties and property loss.
China present architectural fire-protection methods institute foundation mainly be " Code for fire protection design of buildings " and design specificationss such as " Code for fire protection design of high rise buildings ".Yet traditional fire protection design can't adapt to the requirement of large-scale steel structure design of architecture, and the deficiency that embodies mainly contains:
(1) the structure fire resistant design method that is based on component test of standard employing.Thisly whether reaching the method for designing that ultimate limit state under the fire is determined the fire resistance period of structure with independent member, because not considering influencing each other of member in the one-piece construction, thereby is false.In addition, can not reflect the impact of load distribution and size and member institute constrained state in the Practical Project based on the anti-fiery design of member of test, thereby in structure analysis, also be difficult to reflect real force-bearing situation, thereby cause result dangerous or that too guard.
(2) traditional structure fire-resistant research adopts iso standard curve or uniform indoor temperature rise curve to come the temperature rise process of model configuration usually, and this and actual fire differ larger, thereby the exactly actual fire reaction of Simulation and analysis structure.In fact, because the unevenness that the temperature field in the actual fire distributes so that structural internal force heavily distributes, often causes readjusting of whole equilibrium system, take the lead in the on the contrary phenomenon destroyed of the structure that occurs sometimes keeping fire away adopts homogeneous temperature field can't reflect this globality characteristics.
Because the function of structure is bearing load as a whole, the destruction of single member under the fire might not mean integrally-built destruction, and it can cause the heavily distribution of structural stress, and one-piece construction still may have the ability that continues carrying.In the last few years, many scholars propose the research idea of integrality performance of the structure under the fire, Ka Dingdun tests and also shows, the structural integrity effect has important effect to the fire resistance that improves member, and the situation of single member has very big difference in the fire resistance of structural entity and the test.But holistic approach is owing to the restriction that is subject to analysis means and method is difficult to carry out always, and structure fire-resistant research is the main analytical approach that adopts based on member still.
Weak point for the research of tall steel frame fire resistance is: lack the comparatively whole fire resistance appraisal procedure of standard 1.; 2. structure analysis remains based on Partial frame, does not have the structural response of implementation space integral body to calculate; 3. although proposed the thought of Systematic Design, mainly focus on large span spatial structure, tall steel frame is still taked the design of traditional specifications method.4, lack economic analysis and recruitment evaluation.
Find through the literature search to prior art, publication number is the Chinese invention patent of 101251865A, this invention provides a kind of large-scale steel structure fireproof Systematic Method based on integral body, and the method and the inventive method technical essential comparison difference are:
(1) to invent described method mainly be for large-scale steel structure fireproof method for designing to 101251865A, the present invention focuses on check and the checking computations of Tall Frameworks one-piece construction fire resistance existing or that finish with design, and its target, flow process and performance index are all different.
(2) to invent the design result of described method be to satisfy the flameproof protection method of bearing capacity and normal operating condition to 101251865A, and the present invention also comprises the economy check except satisfying bearing capacity and normal request for utilization.
(3) 101251865A invents the fire load that described method requires the dangerous burning things which may cause a fire disaster quantity of statistics and each explosive area, and carry out accordingly the design of fire working, and carry out combination of load effect according to " construction steel structure fire protection design standard ", and the present invention proposes four kinds of standard fire operating modes, then carry out combination of load effect according to standard, standard the load case design analyzed of Tall Frameworks fire prevention.
(4) 101251865A invent described temperature field calculate only refer to FDS(Fire Dynamics Simulator) space temperature field of simulation gained.The present invention is then according to different spaces size and non-uniform temperature degree, determined that three kinds of inside fire atmosphere temperature rising models calculate the space temperature field change in time and space under the different situations.
Also find in the retrieval, Zhu Hang etc. are in the 4th phase in 2011 76 pages of " the Tall Frameworks Whole Response analyses under different fire scenarios " delivered of " steel construction " magazine, and this article utilizes the response of finite element analysis software ABAQUS simulation tall steel frame under fire effect.The distortion of structure under 4 kinds of typical fire scenarios and the internal force changing rule of member have been compared.This article weak point: 1. the temperature field is calculated and is still adopted traditional intensification computing method, does not realize the coupling of fire disaster simulation and structure analysis, and namely space temperature field can not put in the structure analysis, and this is the critical defect place in the traditional design method; 2. analysis of Heat Transfer is still calculated based on the internal temperature field of single member (beam), does not consider diabatic process and the impact of uneven temperature field, space of total system inside; 3. beam element is still adopted in structure analysis, has reduced the computational accuracy in influence of fire zone; 4. structure analysis remains based on plane framework, does not have the structural response of implementation space integral body to calculate; 5. although proposed four kinds of standard fire operating modes, but do not determine the condition of compatibility of intensification model, also do not provide the checking computations flow process of system, the gordian technique in the systematization check analysis is not realization also, and the internal relation between fire effect and the structural response does not obtain technology and embodies.
Summary of the invention
For defective of the prior art, the purpose of this invention is to provide the whole fire resistance check analysis of a kind of tall steel frame method.Take one-piece construction as object, adopt comparatively standardized step, consider simultaneously the impact of actual fire, realize not only economy but also reliable fire protection design scheme, overcome the deficiency of the anti-fire design of current traditional structure check analysis method, particularly overcome the expensive and whole fire resistance of full scale test and the shortcoming that fire prevention measure is difficult to quantize.
The present invention is achieved by the following technical solutions, may further comprise the steps:
The first step, at first (such as ANSYS, ABAQUS) sets up the steel frame finite element model in finite element analysis software, wherein analysis of Heat Transfer finite element model based on the temperature field is set up according to thermal conduction study and finite element theory in the temperature field, the mechanics field according to solid mechanics theoretical and finite element theory set up the mechanical analysis finite element model.
Second step is according to (a) bottom end bay fire; (b) middle layer end bay fire; (c) the vertical working fire of end bay; (d) the middle layer level designs corresponding fire working parameter to these four kinds of standard fire operating modes of working fire, with the whole fire resistance of check steel-frame structure.
In the 3rd step, according to the fire working of setting, determine Fire Field atmosphere temperature rising model and heating curve under each operating mode:
(1) less (floor area of building is less than 500m for area
2) the single chamber fire, can be by ISO834 standard fire curve curve, and suppose indoor constantly space temperature evenly distribute;
(2) for spatial altitude greater than 6m, floor area is greater than 500m
2Space, according to " construction steel structure fireproofing technique standard " (CECS200:2006) in formula 6.2.2 come the temperature-rise period in computer memory temperature field, and can consider the extra-stress impact that the space temperature field uneven distribution causes;
(3) when existing fire to spread on a large scale, when needing to consider to spread path and space temperature field uneven distribution state, need to adopt fire disaster simulation program FDS computer memory temperature field temperature-rise period, model fire disaster simulation model is then according to the design of fire working, the In-put design parameter, become space temperature field T (x, y, z when obtaining the body structure surface of conflagration area, and the heating curve of each finite element model unit node t).
The 4th step, carry out integrally-built heat-structure Coupling finite element method (fem) analysis: adopt software first the analysis of Heat Transfer finite element model to be calculated, become space temperature field T (x when aforesaid, y, z, t), be updated in the integrally-built analysis of Heat Transfer finite element model, by analysis of Heat Transfer, obtain structural system internal temperature field, again the structural system finite element temperature field that obtains is brought into the mechanics field that the mechanical analysis finite element model calculates structural system.
In the 5th step, carry out the mechanical property checking computations of structure fire-resistant: judge according to the mechanics field that obtains whether structural system has formed changeable mechanism, as forming changeable mechanism, then structural collapse; As do not form changeable mechanism, then judge according to the member residual deformation whether structure has exceeded the design allowed band; And according to the deformation time curve of member, obtain the fire resistance period of member, determine according to fire resistance period whether structure satisfies code requirement.
The 6th step, structure fire resistant design economic evaluation: by the economic evaluation model, carry out the quantitative analysis of fire damage economy, calculate fire damage, check it whether to satisfy the performance requirement of economic optimum.
Below specific implementation process of the present invention is described in further detail:
At first in finite element analysis software (such as ANSYS, ABAQUS) set up the steel frame finite element model.For the impact of more careful reflection fire on structure, stride or several striding in the scope in one of fire generation, according to true form and the size employing solid element structure solid model of member, and other positions of structure adopt beam elements to make up finite element models.
The structure of described heat transfer finite element model based on the temperature field comprises:
Make up solid model: stride or several striding in the scope in one of fire generation, according to true form and the size of member, according to the thermal parameter selection material model of material, adopt the entity hot cell to make up solid model;
Make up Rod Model: other regional structures can adopt the one dimension hot cell to make up models for temperature field, calculate to simplify, and raise the efficiency.
The construction step of described mechanical analysis finite element model comprises:
(1) constitutive model of steel is set: steel constitutive model at high temperature is set, can adopts steel constitutive model under the high temperature of advising among the european norm EuroCode3-1-2;
(2) make up solid model: stride or several striding in the scope in one of fire generation, according to true form and the size of member, according to the constitutive model of material, adopt solid element to make up solid model;
(3) make up Rod Model: other regional structures can adopt beam element to make up mechanical model, calculate to simplify, and raise the efficiency;
(4) displacement of finite element model and the boundary condition of power are set.
2. the design of fire working: according to four kinds of standard fire operating modes: (a) bottom end bay fire, (b) middle layer end bay fire, (c) the vertical working fire of end bay, (d) middle layer horizontal direction working fire designs corresponding fire working parameter; Can according to planimetric map, elevation drawing and the Decoration Design of building design stage, add up the fire load q (MJ/m in dangerous burning things which may cause a fire disaster quantity and each explosive area
2), and determine accordingly the fire scale (maximum heat rate of release Q) of every kind of fire working.
3. according to the fire working of setting, in fire disaster simulation program FDS, set up the fire disaster simulation model, then according to the design of fire working, the In-put design parameter, become space temperature field T (x, y, z when obtaining the body structure surface of conflagration area, and the heating curve of each finite element model unit node t).
4. integrally-built heat-structure Coupling finite element method (fem) analysis: the space temperature field Tg (x that the FDS fire disaster simulation is obtained, y, z, t), as the thermal boundary condition of temperature finite element model, then use program of finite element to carry out the structural thermal analysis, obtain structural system internal temperature field Ts (x, y, z, t) spatial and temporal distributions, concrete execution in step is:
1. define the parameters such as hot analysis type and radiation and convection;
2. read in the form document of preserving the fire disaster simulation result, the space temperature field T that will obtain through fire disaster simulation
g(x, y, z, t) is applied on the finite element model as boundary condition, and finds the solution calculating;
Use finite element program that the mechanical property of structural system under various fire working carried out computational analysis, obtain stress σ (T) and the distortion δ (T) of structural system.
5. judge the ultimate limit state of structural system according to the mechanics field that obtains.And according to the deformation time curve of member, obtain the fire resistance period of member, determine according to fire resistance period whether structure satisfies code requirement.
The ultimate limit state of described structural system is:
(1) the enough plastic hinges of structure generation form the changeable mechanism structural collapse;
(2) the structural entity forfeiture is stable;
As do not form changeable mechanism, then judge according to the member residual deformation whether structure has exceeded the design allowed band.Described residual deformation is judged: by the applicability requirement of Steel Structural Design, the suggestion of the limit value of residual deformation is:
Girder l/400
Secondary beam l/250
Post h/300
Wherein, l is the span of beam, and h is the height of post.
6. fire damage economy quantitative analysis: by the economic evaluation model, calculate fire damage, check it whether to satisfy the performance requirement of economic optimum.
Described economic evaluation model is specially: establishing the structure fire cost is P, and structure is destroyed by fire and repaired required cost is R, and the indirect economic loss that the building function forfeiture causes behind the fire is L, then performance requirement goal satisfaction following formula:
G=min(P+R+L)。
Compared with prior art, the present invention has following beneficial effect:
Existing steel frame structure fire-resistant check Main Basis standard adopts the structure fire resistant design method based on member, do not consider the load-bearing level, the influencing each other of member in member institute's constrained state and the one-piece construction, thereby be false, thereby dangerous or too conservative result caused.In addition, the anti-fire check of traditional structure is supposition temperature Homogeneous Analysis usually, do not consider the unevenness that the temperature field in the actual fire distributes, and the extra-stress that causes thus and stress redistribution phenomenon, differ larger with actual fire, thereby can not check exactly the actual fire reaction with analytical structure.Compared with prior art, method for designing of the present invention can solve the anti-fiery method for designing of traditional tall steel frame to integrally-built inapplicable problem, overcome the defective of classic method, realize more approaching actual comprehensive, comprehensive and economic systematization check analysis.
Description of drawings
By reading the detailed description of non-limiting example being done with reference to the following drawings, it is more obvious that other features, objects and advantages of the present invention will become:
Fig. 1 is check analysis process flow diagram of the present invention.
Fig. 2 is the standard fire working condition chart of the embodiment of the invention.
Fig. 3 is embodiment of the invention finite element model figure.
Fig. 4 is embodiment of the invention high-temperature material constitutive model.
Fig. 5 is embodiment of the invention fire space temperature field exemplary plot.
Embodiment
The present invention is described in detail below in conjunction with specific embodiment.Following examples will help those skilled in the art further to understand the present invention, but not limit in any form the present invention.Should be pointed out that to those skilled in the art, without departing from the inventive concept of the premise, can also make some distortion and improvement.These all belong to protection scope of the present invention.
In following examples, as shown in Figure 1, the technical operation that adopts in the detailed process is as follows:
1, the design of fire working.According to (a) bottom end bay fire; (b) middle layer end bay fire; (c) the vertical working fire of end bay; (d) four kinds of standard fire operating modes of middle layer horizontal direction working fire (as shown in Figure 2) design corresponding fire working parameter.Can according to planimetric map, elevation drawing and the Decoration Design of building design stage, add up the fire load q (MJ/m in dangerous burning things which may cause a fire disaster quantity and each explosive area
2), and determine accordingly the fire scale (maximum heat rate of release Q) of every kind of fire working.
Maximum fire source power Q can be calculated as follows:
In the formula:
Q
Max---maximum heat rate of release (kW)
q
i---the average fire load density (MJ/m of i burning things which may cause a fire disaster place subregion
2)
A
i---the effective flammable area (m of i burning things which may cause a fire disaster place subregion
2)
M---burning things which may cause a fire disaster number
The desirable t of fire hazard thermal rate of release Q curve (fire development situation) under the various operating modes
2Model:
Q=at
2
In the formula:
Q---HRR (kW)
A---time constant
T---the time (s)
For the situation that is difficult to add up property of fire source, maximum heat rate of release Q
MaxCan be according to table 1 value.
Design according to following steps for each fire working;
Table 1 fire scale is chosen table
2, according to the fire working of setting, at fire disaster simulation program FDS(Fire Dynamics Simulator) in set up the fire disaster simulation model, then according to the design of fire working, the In-put design parameter, become space temperature field T (x, y, z when obtaining the body structure surface of conflagration area, and the heating curve of each finite element model unit node t).
Use computational fluid dynamics calculation procedure FDS to set up the fire dynamics model and carry out computer simulation under the various fire working.Its concrete execution in step is:
1. correctly set up the calculating input file of FDS according to FDS " user manual ", wherein need to input following calculating parameter information: the hot physical property of the setting of the geometric configuration of buildings, burning things which may cause a fire disaster, fuel type, HRR, material, boundary condition, ventilation condition etc. in the size of computational fields, the size of space lattice, the computational fields.
2. move the FDS calculation procedure.FDS is by adopting senior method for numerical simulation to resolve the state variation that following equation obtains fire and flue gas.
Continuity equation:
Momentum conservation equation:
Energy conservation equation:
The component conservation equation:
State equation:
3. FDS calculates and will generate one or more output files after complete.The Output rusults of FDS mainly is concentration, mixing mark and hot-fluid and the radiation and convection etc. of density, temperature, pressure, rate of heat release, products of combustion.This method need to obtain space temperature field T
g(x, y, z, t).This result will input as the thermal boundary condition parameter of next step temperature field finite element Calculation of Heat Transfer.
3, integrally-built heat-structure Coupling finite element method (fem) analysis.Space temperature field Tg (the x that the FDS fire disaster simulation is obtained, y, z, t), as the thermal boundary condition of temperature finite element model, then use program of finite element to carry out the structural thermal analysis, obtain structural system internal temperature field Ts (x, y, z, t) spatial and temporal distributions, concrete execution in step is:
1. define the parameters such as hot analysis type and radiation and convection;
2. read in the form document of preserving the fire disaster simulation result, the space temperature field T that will obtain through fire disaster simulation
g(x, y, z, t) is applied on the finite element model as boundary condition, and finds the solution calculating;
Use finite element program that the mechanical property of structural system under various fire working carried out computational analysis, obtain stress σ (T) and the distortion δ (T) of structural system; Its concrete steps are:
1. still adopt the finite element model in the step 1, set various calculating parameters (yield strength, cross section parameter etc.), temperature variant material parameter (elastic modulus, thermal expansivity and Poisson ratio etc.) and constitutive relation;
2. carry out Load Combination according to " loading code for design of building structures ", load application is on structural system;
3. apply temperature load;
4. find the solution calculating.
Based on summary of the invention and foregoing description, being described in detail as follows of concrete Application Example:
1. problem description
The commercial complex building of certain company, underground 2 layers, 22 layers on the ground.Wherein 1～3 layer is the market, bottom floor height 5.1m, 2～3 high 4.5m layer by layer, Office Area, 4 layers～22 layers of position, floor height 3.6m, main building height overall 90.3m.Superstructure area 25420m2.
This engineering fire resistance rating one-level, the building classification is a class, 100 years tenure of use of buildings.Structure type is steel-frame structure.Local fortification intensity 6 degree, Site Soil classification two classes.Floor adopts the non-combined floor of profiled sheet.Safety classes of structure is one-level, and the Antiseismic building classification of setting up defences is Class B.
Materials for wall: adopt air-entrained concrete building block more than 0.000, unit weight is not more than 6kN/m3;
Fundamental wind pressure: 0.45kN/m2
Snow reference pressure: 0.4kN/m2
The structure live load:
Market: 3.0kN/m2;
Storeroom: 3.0kN/m2;
Elevator(lift) machine room, Air Conditioning Facilities: 7.0kN/m2;
Staircase: 3.5kN/m2;
Corridor, hall: 2.5kN/m2;
Balcony: 2.5kN/m2;
Office Area: 2.0kN/m2;
Microcomputer chamber: 2.5kN/m2;
Reference room: 2.0kN/m2;
Accessible roof live load: 0.5kN/m2 not;
Accessible roof live load: 2.0kN/m2;
According to (GB50045-95) 3.0.2 bar of current specifications " Code for fire protection design of high rise buildings ", fire resistance rating is that the fire endurance of the structural elements of one-level requires to be post 3.0h, beam 2.0h, floor 1.5h.The beam column fire endurance should adopt thick-layered fire coating greater than 1.5h.
Table 2 structure basic building block cross section
Support: H250X380X16X20, H250X380X14X18
Floor: water the thick armoured concrete slab of 80mm on the profiled sheet; Non-combined.
2. finite element model makes up
The present embodiment adopts finite element software ABAQUS, in the CAE of ABAQUS module, set up one-piece construction finite element model such as Fig. 3, the entity hot cell is selected DC3D20, C3D8I is selected in the entity structure unit, beam element is selected B32OS, and pole unit is selected the B32 unit, stipulates according to " construction steel structure fireproofing technique rules ", determine that the vertical load when structure fire-resistant is analyzed is: market 5.3kN/m2, Office Area 4.7kN/m
2
Normal temperature lower yield strength fy=355Mpa, elastic modulus E=2.06X105Mpa, Poisson ratio 0.3, the steel heat expansion coefficient is 1.4 * 10
-5, the material character under the high temperature adopts according to regulation among the european norm EuroCode3-1-2, and accompanying drawing 4 is the material constitutive curve of the high temperature of Q345 steel.
3. fire working design
In this example, according to building function and design, four kinds of standard fire operating modes are as follows:
Fire working one: bulk is one deck storeroom of 5.4mx5.7mx5.1m.Setting the burning things which may cause a fire disaster rate of heat release area is 250kW/m
2, fiery density of load is 1180/MJ.m
-2
Fire working two: floor area of building is about 1000m
2, three layers of market of high 4.5m are the clothes district, setting the burning things which may cause a fire disaster rate of heat release area is 250kW/m
2, fire source power is 15MW, fiery density of load is 676/MJ.m
-2
Fire working three: bulk is seven layers of reference room of 16.8m * 25.2m * 3.6m, and fire vertically spreads three layers.Setting the burning things which may cause a fire disaster rate of heat release area is 250kW/m
2, fiery density of load is 503/MJ.m
-2
Fire working four: bulk is eight layers of office of 8.4mx6.3mx3.6m, and level is to spreading.The fire density of load is 420/MJ.m
-2, fire source power is 18MW.
4. fire disaster simulation calculates
Use FDS to carry out fire disaster simulation, obtained the result datas such as surperficial environment temperature, hot-fluid and radiation of each member, thereby obtained the temperature field T of change in time and space
g(x, y, z, t) (as shown in Figure 5).Computer simulation can obtain according to architectural composition the uneven distribution that spreads path and space temperature field of actual fire, and checking computations are tallied with the actual situation more.This temperature field will be applied on the finite element model of one-piece construction temperature field accurately as thermal boundary condition.This technology is incited somebody to action so that the extra-stress that the thermograde that classic method can't be considered causes is calculated, thereby has improved computational accuracy and security.
Fire scenario according to determining utilizes FDS fire dynamic simulation software to carry out fire disaster simulation, obtains the atmosphere temperature rising curve of each scene.The analog parameter of all scenes is set as follows:
(1) in the simulation wall being set is adiabatic wall, does not consider the effect of mechanical smoke extraction;
(2) fuel only is distributed in ground, and air themperature was 20 ℃ before fire occured;
(3) in the possible situation of condition, set burning and be the controlled burning of fuel;
(4) fire source power is t
2Fire, Q=at
2(a is the burning things which may cause a fire disaster growth factor, the fire time of t for setting);
5. heat-structure Coupling finite element method (fem) analysis
This structure is pressed the fire-protection rating first design, post fire endurance 3 hours, and beam fire endurance 2 hours adopts thick-layered fire coating.The post fire resisting covering is 23mm, and the beam fire resisting covering is 18mm.Fire resistant coating heat-conduction coefficient, density and specific heat capacity are λ
i=0.093W/ (m ℃), ρ
i=680kg/m
3, c
i=1000J/ (kg ℃).
The space dynamic temperature field T that fire disaster simulation is obtained
g(x, y, z, t) data are applied on the structure temperature field finite element model of setting up in the step 1 carries out the Transient Thermal Analysis of structural entity, thereby obtains the internal temperature field situation of change that structural system is subjected to influence of fire.Then, system internal temperature field is applied in the structure field of force finite element model of setting up in the step 1 as temperature load.Structural load according to " construction steel structure fire protection design standard " (DG/TJ08-008-2000) and " loading code for design of building structures " (GB50009-2001) to carry out combination of load effect as follows:
q=1.0G
k+0.7Q
k+1.0ΔT
In the formula: G
k-permanent load standard value; Q
k-mobile load standard value; Δ T-member temperature changes (consideration temperature effect).
Find through analog computation, under four kinds of fire working, structural entity did not lose efficacy, and local failure only occurred.Structural response is summed up: structure is under vertical uniform load q, and the stress ratio of beam (design moment and moment capacity ratio) is 0.5-0.7 approximately, and the axial compression ratio of post is between the 0.2-0.45.Temperature rise period, beam mainly bears axial pressure and the moment of flexure that causes because of constraint, because being tied, hands over greatly girder, axial pressure is very remarkable, and the end of a part of beam and the cross section of span centre enter plasticity, and axial pressure reduces gradually and transfers pulling force in the cooling back rest, the dilatational strain of beam reduces, but because partial cross section produces plastic yield, the distortion of beam can not recover fully, has produced residual deformation.The column temperature of structure is less than 300 ℃, even less than 200 ℃, so axle power changes littlely, and the part pillar causes the part, cross section to enter plasticity because the expansion of beam produces moment of flexure, and the distortion of cooling rear pillar recovers substantially, and residual deformation is less, does not substantially affect to continue to use.
The performance index that proposes in the refer step 5: fire damage utilizes residual deformation to judge, corresponding limit value is girder l/400, and secondary beam l/250(l is beam span), post h/300(h is that post is high).Span is the residual deformation limit value 21mm of the beam of 8.4m as can be known, and height is 12mm for the residual deformation limit value of the post of 3.6m.According to analysis result, the residual deformation of the pillar in this engineering does not all surpass limit value, and the part beam exceeds limit value.
Table 3 scene 1 residual deformation statistics
Table 4 scene 2 residual deformations statistics
6. fire protection design economic evaluation
The structure fire cost is P, and structure is destroyed by fire and repaired required cost is R, and the indirect economic loss that the building function forfeiture causes behind the fire is L.
1, fire prevention cost P
Table 5 frie retardant coating consumption statistics
P=100.22m3x0.452t/m3x0.4 ten thousand/m3=18.12 ten thousand
2, structure is subjected to fire to destroy rehabilitation expense R
Steel construction replaced by the rear normal employing member of fire destruction or the way of strengthening member is repaired, and partly is out of shape comparatively slight need only proofreading and correct and gets final product, and component surface need be brushed frie retardant coating again.Adopt increase steel method for supporting to reinforce in this engineering, provincial standard DB11T638-2009 " house repairing Engineering Quantity List Pricing standard " with reference to Beijing, this project comprises: structure manufacture, transportation, installation flaw detection and mopping and protection material, the quantities computation rule is calculated in mass according to the member specification, suppose that the steel that adopts is supported for 100kg/m, long 5.5m, every beam needs two steel to support.
Table 6 adds steel support items unit price and calculates
Utilize Event Tree Method to calculate scene two, four probability such as table 6-10, architectural design tenure of use is 100 years again.
Table 7 fire scenario probability
Fire prevention is repaired steel and is supported mass M=0.1*5.5*6=3.3t
R=0.00034*100*3.3*1.98=0.222 ten thousand
3, the indirect economic loss L that the building function forfeiture causes behind the fire
The economic loss of this part can think and be directly proportional with quantities or the expense of structure repair, if but different buildings of concrete parameter and algorithm and deciding.Suppose that this ratio gets 10 in this project, then L=2.22 ten thousand.
For multiple design proposal, can according to said method process and compare.
Above specific embodiments of the invention are described.It will be appreciated that, the present invention is not limited to above-mentioned specific implementations, and those skilled in the art can make various distortion or modification within the scope of the claims, and this does not affect flesh and blood of the present invention.
Claims (5)
1. the check analysis method of the whole fire resistance of tall steel frame is characterized in that, may further comprise the steps:
The first step, at first in finite element analysis software, set up the steel frame finite element model, wherein the analysis of Heat Transfer finite element model is set up according to thermal conduction study and finite element theory in the temperature field, and the mechanical analysis finite element model is set up according to solid mechanics theory and finite element theory in the mechanics field;
Second step is according to (a) bottom end bay fire; (b) middle layer end bay fire; (c) the vertical working fire of end bay; (d) the middle layer level designs corresponding fire working parameter to these four kinds of standard fire operating modes of working fire, with the whole fire resistance of check steel-frame structure;
In the 3rd step, according to the fire working of setting, determine Fire Field atmosphere temperature rising model and heating curve under each operating mode;
(1) less for area is that floor area of building is less than 500m
2The single chamber fire, press ISO834 standard fire curve curve, and suppose that indoor constantly space temperature evenly distributes;
(2) for spatial altitude greater than 6m, floor area is greater than 500m
2Space, come the temperature-rise period in computer memory temperature field according to formula 6.2.2 in " construction steel structure fireproofing technique standard " (CECS 200:2006), and can consider the extra-stress impact that the space temperature field uneven distribution causes;
(3) when existing fire to spread on a large scale, when needing to consider to spread path and space temperature field uneven distribution state, adopt fire disaster simulation program FDS computer memory temperature field temperature-rise period, model fire disaster simulation model is then according to the design of fire working, the In-put design parameter, become space temperature field T (x, y, z when obtaining the body structure surface of conflagration area, and the heating curve of each finite element model unit node t);
The 4th step, carry out integrally-built heat-structure Coupling finite element method (fem) analysis: adopt software first the analysis of Heat Transfer finite element model to be calculated, be about to become when aforesaid space temperature field T (x, y, z, t) as thermal boundary condition, be updated in the integrally-built analysis of Heat Transfer finite element model, by analysis of Heat Transfer, obtain structural system internal temperature field, again the structural system finite element temperature field that obtains is brought into the mechanics field that the mechanical analysis finite element model calculates structural system;
The 5th goes on foot, and carries out the mechanical properties test of structure fire-resistant: judge according to the mechanics field that obtains whether structural system has formed changeable mechanism, as forming changeable mechanism, then structural collapse; As do not form changeable mechanism, then judge according to the member residual deformation whether structure has exceeded the design allowed band; And according to the deformation time curve of member, obtain the fire resistance period of member, determine according to fire resistance period whether structure satisfies code requirement;
The 6th step, structure fire resistant design economic evaluation: by the economic evaluation model, carry out the quantitative analysis of fire damage economy, calculate fire damage, check it whether to satisfy the performance requirement of economic optimum.
2. the check analysis method of the whole fire resistance of tall steel frame according to claim 1 is characterized in that, the structure of the finite element model of analysis of Heat Transfer described in the first step comprises:
Make up solid model: stride or several striding in the scope in one of fire generation, according to true form and the size of member, according to the thermal parameter selection material model of material, adopt the entity hot cell to make up solid model;
Make up Rod Model: except above-mentioned extraneous other regional structures adopt the one dimension hot cell to make up the analysis of Heat Transfer model.
3. the check analysis method of the whole fire resistance of tall steel frame according to claim 1 and 2 is characterized in that, the structure of the finite element model of mechanical analysis described in the first step comprises:
Make up solid model: stride or several striding in the scope in one of fire generation, according to true form and the size of member, according to the constitutive model of material, adopt solid element to make up solid model;
Make up Rod Model: except above-mentioned extraneous other regional structures adopt beam element to make up mechanical model;
The constitutive model of steel is set: steel constitutive model at high temperature is set, adopts steel constitutive model under the high temperature of advising among the european norm EuroCode3-1-2;
The displacement of finite element model and the boundary condition of power are set.
4. the check analysis method of the whole fire resistance of tall steel frame according to claim 1, it is characterized in that, described the 5th step, carry out the mechanical property checking computations of structure fire-resistant, namely judge the limiting design value whether structural system ultimate limit state occurs and whether exceed code requirement, the ultimate limit state of described structural system is:
(1) the enough plastic hinges of structure generation form the changeable mechanism structural collapse;
(2) the structural entity forfeiture is stable;
As do not form changeable mechanism, then judge according to the member residual deformation whether structure has exceeded the design allowed band; Described residual deformation is judged: by the applicability requirement of Steel Structural Design, the limit value of residual deformation is:
Girder l/400
Secondary beam l/250
Post h/300
Wherein, l is the span of beam, and h is the height of post.
5. according to claim 1 or the check analysis method of the whole fire resistances of 4 described tall steel frames, it is characterized in that, in the 6th step, described economic evaluation model, be specially: establishing the structure fire cost is P, structure is destroyed by fire and repaired required cost is R, and the indirect economic loss that the building function forfeiture causes behind the fire is L, then performance requirement goal satisfaction following formula:
G=min(P+R+L)。
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