CN106372358A - Fire-resistance calculation method for rectangular cross-section stainless steel beam - Google Patents

Abstract

The invention discloses a practical fire-resistance calculation method for a building stainless steel structure, and in particular relates to method for calculating the extreme bearing capacity and the critical temperature of a rectangular cross-section stainless steel beam. According to the method disclosed by the invention, the extreme bearing capacity of the rectangular cross-section stainless steel beam at high temperature (uniform temperature) is directly calculated according to a modified bearing capacity reduction coefficient, the extreme bearing capacity of the rectangular cross-section stainless steel beam at high temperature (non-uniform temperature) is directly calculated according to modified non-uniformly distributed cross-section ambient temperature distribution self-adaptive coefficients, and the critical temperature of the rectangular cross-section stainless steel beam is directly calculated according to simple calculation equations of stainless steel beam critical temperature proposed by taking a maximum cross-section bending moment and a cross-section resistance moment as parameters. By adjusting the coefficients of conventional Eurocode stainless steel beam bearing capacity calculation equations and by simplifying critical temperature calculation equations, fire-resistance calculation equations applicable to the rectangular cross-section stainless steel beam are provided.

Description

A kind of square-section stainless steel beam Fire resistance method

Technical field

The present invention relates to the practical Fire resistance method of building stainless steel structure, more particularly, to square-section stainless steel beam Ultimate bearing capacity and the computational methods of critical temperature.

Background technology

The purpose of Fire resistance is the fire resistance for solution structure and component, at present, domestic with regard to stainless steel component Fire-resistance test research report only have Southeast China University's fourth small peak stainless steel column, it is steady to the stainless steel column of axial compression in paper Determine coefficientCoefficient in expression formulaCarry out matching, remaining yet there are no with regard to the fire resistance research of stainless steel component or structure Report.The external fire resistance research with regard to stainless steel beam is also few, at present, only " european norm " (en 1993-1-2) and " Europe rule Calculate Guide Book " (2006) give Fire resistance method about stainless steel beam, and the bend-carrying capacity under room temperature calculates partially In conservative, it is safe, but the bend-carrying capacity under high temperature is calculated relatively dangerous.In addition, l.gardner and k.t.ng Et al. on the basis of existing test data, new suggestion and correction are proposed to the Fire resistance formula of stainless steel beam, formula is relatively For complexity.

Content of the invention

The technical problem to be solved in the present invention is that the Fire resistance method of existing square-section stainless steel beam is relatively conservative, It is not enough at high temperature reach safety need, or formula is complicated, the difficulty of calculating is huge.

For solving above-mentioned technical problem, the technical solution used in the present invention is: a kind of fire-resistance of square-section stainless steel beam Computational methods, comprise the following steps:

1) ultimate bearing capacity under uniform temperature for the calculating square-section stainless steel beam:

11) bearing capacity reducing coefficient under calculating 1～3 class section stainless steel beam high temperature:

(f_2,θ/f₂)(γ_m0/γ_m,fi)

(1)

In formula: f_2,θThe corresponding intensity of stainless steel material 2% overall strain under high temperature,

f₂The corresponding intensity of stainless steel material 2% overall strain under room temperature,

γ_m0The bearing capacity partial safety factor in section surrender (inclusion local buckling),

γ_m,fiMaterial property correlation partial safety factor under fire；

12) calculate stainless steel beam bend-carrying capacity value of calculation under revised uniform temperature distribution:

m_fi,θ,rd=(f_2,θ/f₂)(γ_m0/γ_m,fi)m_rd

(2)

In formula: m_rdTotal cross-section plasticity bend-carrying capacity under room temperature, or total cross-section elasticity bend-carrying capacity under room temperature；

2) ultimate bearing capacity under non-uniform temperature for the calculating square-section stainless steel beam:

21) calculate revise along section ambient temperature uneven distribution adaptation coefficient:

φ=6 × 10^-7θ²-7×10^-5θ+1.0364(100≤θ≤800)

(3)

In formula: theta temperature；

22) calculate stainless steel beam anti-bending bearing capacity value of calculation under the non-uniform temperature distribution revised:

m_{Fi, t, rd}=m_{Fi, θ, rd}(κ₂/ φ)=(6 × 10^-7θ²-7×10^-5θ+1.0364)m_{Fi, θ, rd}/κ₂

(4)

In formula: m_{Fi, θ, rd}Bend-carrying capacity under uniform temperature,

κ₂It is distributed adaptation coefficient along beam length non-uniform temperature；

3) critical temperature of calculating square-section stainless steel beam:

31) calculate the critical temperature revised:

In formula: θ critical temperature,

M is further applied load in the maximal bending moment of beam section generation,

W beam elastic cross-section resistance moment,

f₂The corresponding intensity of the overall strain of stainless steel material 2% under room temperature.

The foundation Europe classification of described 1-3 classification, and the criteria for classification adopting is the section criteria for classification of room temperature.Described step Correction critical temperature in rapid 31), according to

Parametric Analysis, show that the factor of impact stainless steel beam critical temperature most critical is the maximum being produced by load Section turn moment m and section resistance moment w, proposes the simple computation formula of stainless steel beam critical temperature with m and w for parameter.

Further, described step 12) in uniform temperature under the bend-carrying capacity computational methods of stainless steel beam be:

Under room temperature, the bend-carrying capacity of 1 class and 2 class section stainless steel beams:

The bend-carrying capacity of 3 class section stainless steel beams:

In formula: w_plPlastic section resistance moment,

w_el,minElastic cross-section resistance moment,

f_0.2Stainless steel material nominal-ultimate strength under room temperature,

γ_m0The bearing capacity partial safety factor in section surrender (inclusion local buckling).

The invention has the advantage that compared with existing computational methods, computational methods of the present invention calculate simplicity, precision is higher, can It is directly used in square-section stainless steel beam Fire resistance to calculate.

Brief description

Fig. 1: stainless steel beam is not the bend-carrying capacity ratio under temperature and uniform temperature.

Fig. 2: the critical temperature under different loads is contrasted with 180 × 100 × 4 cracking under different temperatures.

Fig. 3: the critical temperature under different loads is contrasted with 180 × 100 × 5 cracking under different temperatures.

Fig. 4: the critical temperature under different loads is contrasted with 180 × 100 × 6 cracking under different temperatures.

Specific embodiment

With reference to the accompanying drawings and examples this invention is further elaborated with.

Embodiment 1:

This embodiment describes the square-section stainless steel beam Fire resistance method under high temperature (uniform temperature) in detail.

First with FEM (finite element) model, the bearing capacity under three-face fire rectangle tube section stainless steel beam room temperature and high temperature is entered Row calculates, then carries out calculating contrast using the Fire resistance formula in existing related specifications, thus to the Fire resistance in specification Formula improves, and chooses the test specimen basic parameter being calculated and is shown in Table 1.

Table 1 test specimen basic parameter

By ultimate flexural capacity under uniform temperature for the calculated each test specimen of FEM (finite element) model the results detailed in Table 2.

The uniform temperature limit inferior bend-carrying capacity of table 2 FEM calculation

Understood according to the section classification in " european norm ": under room temperature, sb1, sb2, sb3, sb4, sb6, sb7, sb8, sb9 Belong to 1 class, sb10 belongs to 2 classes, sb5 belongs to 3 classes；Under high temperature, sb4, sb5 and sb10 belong to 3 classes, and remaining is 1 class.The present invention adopts With the section classification in " Europe calculates Guide Book ", that is, the section classification under high temperature is identical with the section classification under room temperature, with Ensure the concordance of bearing capacity formula.

Bend-carrying capacity meter under stainless steel beam test specimen sb1～sb10 room temperature and high temperature can be calculated according to modular formula Calculation value, refers to table 3.

Bend-carrying capacity value of calculation under the uniform temperature that table 3 modular formula calculates

Comparison sheet 2 and table 3 understand, formula calculates for the bend-carrying capacity under room temperature and relatively guards, and is safe, but right Calculate relatively dangerous in the bend-carrying capacity under high temperature it is therefore desirable to revise the bearing capacity formula under high temperature.Contrast table 2 Bend-carrying capacity under bend-carrying capacity and room temperature under the high temperature of middle FEM calculation, its reduction coefficient is shown in Table 4.

The high-temperature load reduction coefficient of table 4 FEM calculation

According to stainless steel material mechanical property test as a result, it is possible to obtain intensity under 2% overall strain for the stainless steel material Reduction coefficient f_2,θ/f₂, ratio refers to table 5.

Table 5 reduction coefficient

Comparison sheet 4 and table 5, find the reduction coefficient of the two closely, therefore consider to replace table with the reduction coefficient in table 5 Reduction coefficient in 4, thus obtaining uniform temperature bend-carrying capacity computing formula under revised high temperature, is shown in formula (2).

Embodiment 2:

This embodiment describes the square-section stainless steel beam Fire resistance method under high temperature (non-uniform temperature) in detail.

Test specimen sb1～pole under uneven temperature for the sb10 can be obtained by analysis of Heat Transfer model and fire-resistance analysis model Limit bend-carrying capacity.Refer to table 6 along ultimate flexural capacity result of calculation under uneven for the cross-section temperature.

The uneven temperature limit inferior bend-carrying capacity of table 6 FEM calculation

Ultimate flexural capacity under contrast specimen sb1～sb10 uneven temperature and uniform temperature, its ratio refers to table 7.

The ultimate flexural capacity ratio of table 7 FEM calculation

As shown in Table 7, the bend-carrying capacity under bend-carrying capacity under uneven temperature for the stainless steel beam and uniform temperature Ratio is gradually increased with the rising of temperature, and before 500 DEG C, amplification is less, more than 500 DEG C after amplification larger, reach 700 DEG C Amplification is gradually reduced again afterwards.In " Europe calculates Guide Book ", the suggestion value with regard to this ratio is 1/ κ₁, when beam four sides is subject to fire When, κ₁=1, when the beam three-face fire not taken precautions against fire, κ₁=0.7.This regulation is less reasonable, and one is because when beam four When face is subject to fire, however it remains the non-uniform temperature along section thickness, if thickness is less can be suitable for, if thickness is excessive, take κ₁ =1 shows slightly conservative；Two are because when beam three-face fire, 1/ κ₁=1.43, this has over-evaluated stainless steel beam under three-face fire Bearing capacity.Therefore, the present invention will be to κ₁It is modified.Go out to be applied to uneven temperature and uniformly according to the Coefficient Fitting in table 7 The formula of the bearing capacity ratio of temperature, matched curve is as shown in figure 1, fitting formula is shown in formula (4).

Embodiment 3:

The critical temperature that this embodiment describes square-section stainless steel beam in detail calculates computational methods.

Solve bend-carrying capacity at a temperature of certain for the stainless steel beam and be actually a load after being heated process (stable state), and Practical structures are dead load temperature-rise periods (transient state) by fire effect, both and imcomplete equivalent.Beam is at certain temperature θ Bearing capacity can reach m, but critical temperature under load m for the beam may not reach temperature θ it is also possible to exceed temperature θ.Choose and cut Face a size of 180 × 100 × 4,180 × 100 × 5, the test specimen (i.e. t1, t2, t3) of 180 × 100 × 6, compare three Critical temperature (being shown in Table 8) under bearing capacity under test specimen different temperatures and different loading ratio, as shown in Figure 2.

Critical temperature under the different loading ratio of table 8

As shown in Figure 2, ask the curve of bearing capacity to be higher than totally the curve asking critical temperature under dead load under constant temperature, when section When moment of flexure is less greatly, temperature difference is less, is gradually increased with moment of flexure, and temperature difference is also gradually increased.That is, in reality In structure, when Liang Shouhuo reaches critical temperature, load is not ultimate bearing capacity now, and beam still can continue to hold Heated up by certain time.But due to there is certain dynamic effect in deformation process, deformation can be increasingly faster, so with deforming Limit value and rate of deformation limit value come that regulation critical temperature is a need for although showing slightly conservative, but are also rational.

From Parametric Analysis, the factor affecting stainless steel beam critical temperature most critical is to be produced by load Heavy in section moment of flexure m and section resistance moment w, the present invention proposes the simple computation public affairs of stainless steel beam critical temperature with m and w for parameter Formula.

The material mechanical performance of critical temperature and rustless steel itself is closely bound up, corresponding to 2% overall strain in table 5 first Strength reduction factor is fitted, and with reduction coefficient η as independent variable, temperature θ is dependent variable, obtains formula (8).

It can be assumed that making the maximum temperature in beam surface when temperature raises in terms of the load-deformation curve trend of stainless steel material When the corresponding intensity of material 2% overall strain at degree is equal to the maximum stress on section, beam will enter inefficacy, by formula (8) η change (m/w)/f into₂, based on finite element analyses, and consider the uneven impact of temperature, add 30 on the right side of formula (8), Thus obtaining the computing formula (5) of critical temperature.

Claims (2)

1. a kind of Fire resistance method of square-section stainless steel beam is it is characterised in that comprise the following steps:

1) ultimate bearing capacity under uniform temperature for the calculating square-section stainless steel beam:

11) bearing capacity reducing coefficient under calculating 1～3 class section stainless steel beam high temperature:

(f_2,θ/f₂)(γ_m0/γ_m,fi)(1)

In formula: f_2,θThe corresponding intensity of stainless steel material 2% overall strain under high temperature,

f₂The corresponding intensity of stainless steel material 2% overall strain under room temperature,

γ_m0The bearing capacity partial safety factor in section surrender (inclusion local buckling),

γ_m,fiMaterial property correlation partial safety factor under fire；

12) calculate stainless steel beam bend-carrying capacity value of calculation under revised uniform temperature distribution:

m_fi,θ,rd=(f_2,θ/f₂)(γ_m0/γ_m,fi)m_rd(2)

In formula: m_rdTotal cross-section plasticity bend-carrying capacity under room temperature, or total cross-section elasticity bend-carrying capacity under room temperature；

2) ultimate bearing capacity under non-uniform temperature for the calculating square-section stainless steel beam:

21) calculate revise along section ambient temperature uneven distribution adaptation coefficient:

φ=6 × 10^-7θ²-7×10^-5θ+1.0364 (100≤θ≤800)(3)

In formula: theta temperature；

22) calculate stainless steel beam anti-bending bearing capacity value of calculation under the non-uniform temperature distribution revised:

m_fi,t,rd=m_fi,θ,rd(κ₂/ φ)=(6 × 10^-7θ²-7×10^-5θ+1.0364)m_fi,θ,rd/κ₂(4)

In formula: m_fi, bend-carrying capacity under θ, rd uniform temperature,

κ₂It is distributed adaptation coefficient along beam length non-uniform temperature；

3) critical temperature of calculating square-section stainless steel beam:

31) calculate the critical temperature revised:

$\mathrm{\&theta;}=\left\{\begin{array}{cc}-6435.5{\left(\frac{m}{{\mathrm{wf}}_2}\right)}^3+6711.2{\left(\frac{m}{{\mathrm{wf}}_2}\right)}^2-2760.6\left(\frac{m}{{\mathrm{wf}}_2}\right)+1162.2& 0\&le;\frac{m}{{\mathrm{wf}}_2}\&le;0.6\\ -7692.9{\left(\frac{m}{{\mathrm{wf}}_2}\right)}^3+21837{\left(\frac{m}{{\mathrm{wf}}_2}\right)}^2-21053\left(\frac{m}{{\mathrm{wf}}_2}\right)+6958.3& 0.6<\frac{m}{{\mathrm{wf}}_2}\&le;1\end{array}\right.$

In formula: θ critical temperature,

M is further applied load in the maximal bending moment of beam section generation,

W beam elastic cross-section resistance moment,

f₂The corresponding intensity of the overall strain of stainless steel material 2% under room temperature.

2. as claimed in claim 1 a kind of Fire resistance method of square-section stainless steel beam it is characterised in that described step 12) under the uniform temperature in, the bend-carrying capacity computational methods of stainless steel beam are:

Under room temperature, the bend-carrying capacity of 1 class and 2 class section stainless steel beams:

$m_{p1,rd}=\frac{w_{p1}{f}_{0.2}}{{\mathrm{\&gamma;}}_{m0}}---\left(6\right)$

The bend-carrying capacity of 3 class section stainless steel beams:

$m_{el,rd}=\frac{w_{el,min}{f}_{0.2}}{{\mathrm{\&gamma;}}_{m0}}---\left(7\right)$

In formula: w_plPlastic section resistance moment,

w_el,minElastic cross-section resistance moment,

f_0.2Stainless steel material nominal-ultimate strength under room temperature,

γ_m0The bearing capacity partial safety factor in section surrender (inclusion local buckling).