RU2695344C1 - Method of determining fire resistance of pipe concrete column of building - Google Patents

Abstract

FIELD: rescue service; fire fighting means.

SUBSTANCE: invention relates to the field of fire safety of buildings with reference to the classification of pipe-concrete columns based on their resistance to fire. Method comprises performance of technical inspection, establishment of type of concrete column, identification of conditions for its support and attachment, determining the time limit state on the basis of the loss of bearing capacity of the column under the test load under conditions of standard fire action, performance of evaluation tests without destruction by a set of single quality indicators of the string, in which technical inspection is accompanied by instrumental measurements of geometric dimensions of the column and its hazardous section, concrete and steel areas in dangerous section are installed, humidity and density of concrete in natural state, determining the concrete thermal diffusion indices, determining compression concrete ultimate resistance, intensity value of the stresses in the dangerous section, wherein determining the fire resistance of a pipe concrete column made from a metal pipe filled with concrete, wherein additionally determining the level of responsibility of the column for the purpose, determining critical force, rigidity of pipe concrete column and effect of column deflection on bending moment of longitudinal force, degree of reinforcement of column cross-section by metal pipe, determining resistance limit of compression of pipe metal, reduced thickness of pipe metal and time of resistance to fire action of metal pipe, unfilled with concrete, calculating duration of fire protection of concrete pipe metal and fire resistance of pipe concrete string from beginning of standard fire action to loss of bearing capacity (F_ur, min), which is determined using a given analytical expression.

EFFECT: enabling determination of the pipe concrete column fire resistance without natural fire action and high reliability of statistical quality control and non-destructive tests.

9 cl, 1 ex, 2 dwg

Description

The invention relates to the field of fire safety of buildings. In particular, it can be used to classify concrete pipes according to their resistance to fire. This makes it possible to justify the use of existing reinforced concrete structures with an actual fire resistance limit in buildings of various fire hazard classes.

A known method of evaluating the fire resistance of a building column by testing, including conducting a technical inspection, establishing the type of concrete and reinforcement of the structure, identifying the conditions for their support and fastening, determining the time of the onset of the ultimate state based on the loss of the bearing capacity of the structure under the test load under standard heat exposure / GOST 30247.1 -94. Building constructions. Fire test methods. Bearing and enclosing structures / [1].

The reasons that impede the achievement of the technical result indicated below when using the known method include the fact that in the known method, tests are carried out on a sample of a reinforced concrete column, which is affected only by constant and continuous loads in their calculated values with a reliability coefficient equal to unity.

Tests are carried out on special bench equipment in fire furnaces until the destruction of structural samples. The size of the samples is limited depending on the openings of stationary fire furnaces. Therefore, standard fire tests are time-consuming, not effective, not safe, have little technological capabilities for testing various sizes and variously loaded structures, and do not provide the necessary information about the effect of individual design quality indicators on its fire resistance. Assessment of the fire resistance of a reinforced concrete column by a single quality indicator, for example, by the thickness of the concrete protective layer, as a rule, underestimates the suitability of the column in a building with a given degree of fire resistance. By a small number of tested samples (2-3 pcs.) It is impossible to judge the actual condition of the columns of the building. The results of the fire test are single and do not take into account the diversity in fixing the ends of the reinforced concrete columns, their actual sizes, actual reinforcement and the heating circuit of the dangerous section of the test structure in a fire.

A known method for determining the fire resistance of a concrete pipe by identifying the temperature distribution over its cross section and determining the maximum load-bearing capacity of the column in a fire, comparing it with the test load / Barthelemy B., Kruppa J. Fire resistance of building structures / translation from French - M., Stroyizdat, 1985 .-- 216 p. (see Ch. 5 p. 5.2 Closed-section columns filled with concrete, p. 169-175) [2]

The disadvantage of this method lies in the complexity and inaccuracy of the results of thermotechnical and strength calculations of the loss of bearing capacity of a concrete column in a fire.

, мин / Патент №2281482 RU МПК G01N 25/50. Способ определения огнестойкости сжатых элементов железобетонных конструкций здания / Ильин Н.А., Бутенко С.А., Эсмонт С.В.; заяв. СГАСУ: 06.09.04; опубл. 18.02.06. Бюл. №22 /[3].The closest method of the same purpose to the claimed invention by the totality of features is a method for assessing the fire resistance of a reinforced concrete column of a building by testing, including technical inspection, establishing the type of concrete and reinforcement of the reinforced concrete column, determining the time of the onset of the ultimate state by the sign of loss of bearing capacity of the reinforced concrete column under test load under standard fire exposure. The reinforced concrete column is tested without destruction according to a set of individual quality indicators, the technical inspection is supplemented with instrumental measurements of the geometric dimensions of the reinforced concrete column and its dangerous section, the area of concrete and working reinforcement in a dangerous section is established, the density of concrete and its moisture content in the natural state and the value of the thermal diffusion index are determined concrete, find the ultimate resistance of concrete and reinforcement to compression, the degree of reinforcement of the design section of the column, tanavlivayut magnitude of the test load on the reinforced concrete column and a power value of the stress intensity in a predetermined section, and integral parameters obtained using concrete columns nomogram calculated actual fire limit

, min / Patent No. 2281482 RU IPC G01N 25/50. A method for determining the fire resistance of compressed elements of reinforced concrete structures of a building / Ilyin N.A., Butenko S.A., Esmont S.V .; application SASAS: 09/06/04; publ. 02/18/06. Bull. No. 22 / [3].

For reasons that impede the achievement of the technical result indicated below when using the known method adopted as a prototype, the use of a nomogram to determine the actual fire resistance of a reinforced concrete column gives calculation results with a greater error, in some cases, additional construction of graphs of the nomogram is required; in addition, when constructing a nomogram, reliability indicators of a reinforced concrete column for the purpose (level of responsibility) are not taken into account, the effect of deflection of an eccentrically compressed section of the column on the bearing capacity is not taken into account.

The essence of the invention is to establish indicators of fire safety of the building in terms of the guaranteed duration of resistance of the concrete pipe in a fire; in determining the actual fire resistance limits of the concrete pipe during the design, construction and operation of the building; in reducing economic costs when testing pipe concrete columns for fire resistance.

The technical result is the exclusion of fire tests in determining the fire resistance of a pipe concrete column of a building; reducing the complexity of evaluating the fire resistance of a concrete pipe column, expanding the technological capabilities of determining the actual fire resistance of variously loaded concrete columns of any size and the ability to compare the results with the test results of similar building columns; the ability to test structures for fire resistance without disturbing the functional process in the building; reduction in economic costs; maintaining the serviceability of the building during inspection and non-destructive testing of a concrete pipe string; simplification of conditions and shortening of the test period of columns for fire resistance; improving the accuracy and efficiency of determining the fire resistance of a concrete pipe.

The specified technical result in the implementation of the invention is achieved by the fact that in the known method for determining the fire resistance of a building column, including technical inspection, establishing the type of concrete of the column, identifying the conditions for its support and fastening, determining the time of the onset of the limiting state based on the loss of the bearing capacity of the column under test load in conditions of standard fire exposure, conducting assessment tests without destruction on a set of individual quality indicators to columns, during which technical inspection is accompanied by instrumental measurements of the geometric dimensions of the column and its dangerous section, the concrete and steel areas in the dangerous section, the moisture and density of the concrete in the natural state are determined, the thermal diffusion of the concrete is determined, the ultimate compressive resistance of the concrete and the magnitude of the stress intensity are determined in a dangerous section, a feature is that they determine the fire resistance of a concrete pipe column made of a metal pipe filled with concrete ohm, at the same time, the responsibility level of the column is additionally identified for the purpose, the critical strength, the rigidity of the concrete pipe and the influence of its deflection on the bending moment of the longitudinal force, the degree of reinforcement of the cross section of the column by the pipe metal are determined, the compression resistance of the pipe metal is determined, the reduced thickness of the pipe metal and time are determined resistance to fire exposure of a metal pipe unfilled with concrete, calculate the duration of fire protection of concrete with the metal of the pipe and the fire resistance of the concrete pipe bows from the start of the standard fire exposure to the loss of bearing capacity (F _ur , min), which is determined using the analytical equation (1):

where d _b is the diameter of the concrete section of the column, mm; J _σo is the intensity of power stresses in the dangerous section of the column, J _σo ≤1; α _mt is the degree of reinforcement of the cross section of the column with pipe metal, α _mt ≤1.66; γ _n - coefficient of the level of responsibility for the intended purpose: low - γ _n = 0.8; normal - γ _n = 1,0; increased - γ _n = 1,2; D _W - indicator of thermal diffusion of concrete, mm ² / min; τ _i.ozs - duration of fire protection of concrete with pipe metal, min; R _VP - the standard resistance of concrete to axial compression, MPa.

The intensity of the power stresses in the dangerous section of the concrete column I _{σо is} found using equation (2):

where M _ξ and M _ss is the bending moment from the calculated longitudinal force, taking into account the deflection of the column and, accordingly, the bending moment characterizing the ultimate bearing capacity of the column, kN⋅m.

The cross-sectional area of the pipe metal A _r , mm ^{2 is} calculated according to equation (3):

where d _mt and d _b - the outer diameter of the metal pipe and, accordingly, the diameter of the concrete section of the column, mm

The degree of reinforcement of the cross section of the column with the metal of the pipe α _{mt is} calculated according to equation (4):

where A _p and A _b - the cross-sectional area of the metal pipe and, accordingly, the cross-sectional area of the concrete columns, mm ² ; R _IP and R _VP - ultimate resistance of the pipe metal and, accordingly, the standard resistance of concrete to axial compression, MPa.

The reduced thickness of the pipe metal (θ _sr , mm) is determined by equation (5):

where δ _mt is the thickness of the pipe metal, mm; d _mt is the outer diameter of the metal pipe, mm

The time of resistance to the fire effect of a metal pipe unfilled with concrete (τ _{and, mt} ) is determined by equation (6):

where J _σo is the intensity of the initial stresses from the test load in the dangerous section of the column, J _σo ≤1; θ _sr is the reduced thickness of the pipe metal, mm.

The critical force N _cr , kN perceived by the concrete pipe column is calculated according to equation (7):

- расчетная длина колонны, м; π=3,14.where W ₀ is the stiffness of the concrete column;

- estimated column length, m; π = 3.14.

The stiffness of the concrete column (W ₀ ) is calculated according to equation (8):

- расчетная длина колонны, м; π=3,14; R_pc - нормативное сопротивление металла трубы при сжатии в составе трубобетонной колонны, МПа; А_р - площадь сечения металла трубы; k_b, k_s - коэффициенты для расчета жесткости бетона и стали соответственно: k_s=0,7;where E _p and E _b1 - modulus of elasticity of reinforcement and, accordingly, the modulus of deformation of compressed concrete with prolonged action of the load, MPa; I _p and I - the moment of inertia of the reinforcement and, accordingly, the concrete section relative to the center of gravity of the concrete section, mm ⁴ ;

- estimated column length, m; π = 3.14; R _pc is the standard resistance of the pipe metal during compression in the composition of the concrete column, MPa; And _p is the cross-sectional area of the pipe metal; k _b , k _s are the coefficients for calculating the stiffness of concrete and steel, respectively: k _s = 0.7;

- коэффициент, учитывающий влияние длительности действия нагрузки; δ_е - относительное значение эксцентриситета продольной силы, определяемое из соотношения (10):Where

- coefficient taking into account the effect of the duration of the load; δ _e - the relative value of the eccentricity of the longitudinal force, determined from the relation (10):

where d _mt is the outer diameter of the metal pipe, mm;

e ₀ is the eccentricity of the longitudinal force, mm;

R _pc - the standard resistance of the pipe metal, calculated by the equation (11):

where R _un - ultimate resistance of the pipe metal, MPa;

e - eccentricity of the applied force, taking into account random eccentricity, mm; δ _mt - pipe metal thickness, mm; d _mt is the outer diameter of the metal pipe, mm

For the individual quality indicators of a concrete pipe column affecting the fire resistance limit, take: the geometric dimensions of the metal pipe and its concrete section, the rigidity of the concrete pipe, the axial compression strength of concrete, the degree of reinforcement of the column section of the pipe metal pipe, the pipe metal resistance to compression, the elastic modulus of the pipe metal and the modulus of deformation of compressed concrete under continuous load, the intensity of power stresses in a dangerous section, the moisture and density of concrete in a natural state and figure concrete thermal diffusion length fireproofing concrete pipe metal.

The causal relationship between the totality of features and the technical result is as follows.

The exclusion of fire tests of a concrete pipe column of an existing building and their replacement with non-destructive tests reduces the complexity of evaluating its fire resistance, extends the technological capabilities of identifying the actual fire resistance limit of variously loaded columns of any size, makes it possible to test pipe concrete columns for fire resistance without disturbing the functional process of the building under examination, as well as comparing the results obtained with the results of standard tests of similar concrete pipes to the column, while maintaining the operational suitability of the building under examination without disturbing the bearing capacity of its structures during the test. Therefore, the test conditions of the pipe concrete columns of the building for fire resistance are greatly simplified. Reducing the economic costs of the test is achieved by eliminating the cost of dismantling, transportation and fire tests of a sample of concrete pipe.

The use of a mathematical description of the process of resistance of a loaded concrete pipe to a standard fire test and the use of the constructed polyparametric equation (1) increases the accuracy and efficiency of the design fire resistance assessment.

The use of integral structural parameters, such as: the degree of reinforcement of the cross section of the column with pipe metal and the thermal diffusion index of concrete, simplifies the mathematical description of the process of resistance of a loaded pipe-concrete column to fire exposure.

Evaluation of the fire resistance of a concrete pipe column based on only one quality indicator, for example, on the thickness of the pipe metal, leads, as a rule, to underestimation of its actual fire resistance, since the influence of variations of individual quality indicators on it has different signs, and a decrease in fire resistance due to one indicator can be compensated by others. As a result, in the proposed method, the fire resistance of a concrete pipe string is evaluated not by one indicator, but by a set of individual indicators of its quality. This allows you to more accurately take into account the real resource of fire resistance of the concrete pipe.

A set of unit quality indicators of a concrete pipe string, affecting fire resistance, determined by non-destructive tests, has been clarified.

Information confirming the possibility of carrying out the invention, with obtaining the above technical result.

A method for assessing the actual fire resistance of a concrete pipe column of a building is carried out in the following sequence. First, a visual inspection of the building structures is carried out. Then determine the group of the same type of concrete columns and their total number in it. The sample size of the same type of columns is calculated. Assign a set of individual quality indicators for concrete columns affecting fire resistance. The conditions for fixing the ends and dangerous sections of the concrete columns are revealed. The number of tests of a single quality indicator of a concrete pipe column is calculated depending on its statistical variability. Then, individual quality indicators of the concrete pipe string and its integral parameters are evaluated, and the design fire resistance limit of the tested string is found from them.

, °С.The invention is illustrated in the drawing, where the arrows show the direction of action of the high temperature of a standard fire

, ° C.

, - температура стандартного пожара, °С.The drawing shows a calculation scheme for the fire resistance of a concrete pipe: a longitudinal section (Fig. 1) and a cross section (Fig. 2), where the following notation is used: 1 - metal pipe, 2 - concrete; N is the longitudinal force, kN; e ₀ is the eccentricity of the longitudinal force relative to the center of gravity of the reduced section, mm; D _cir is the diameter of the concrete pipe, mm; r _b , r _s are the radii of the concrete section and the metal pipe, mm;

, - temperature of a standard fire, ° С.

The main single quality indicators of a pipe concrete column providing fire resistance include: geometric dimensions of a metal pipe and its concrete section, pipe concrete column stiffness, axial compression strength of concrete, degree of reinforcement of the pipe section of the column with pipe metal, pipe metal resistance to compression, power stress intensity in a dangerous section , moisture and density of concrete in its natural state, the thermal diffusion of concrete, the elastic modulus of the pipe metal and the deformation modulus of compressed concrete During prolonged exposure to load, the duration of fire protection of concrete with metal pipes.

Checked geometric dimensions are: the diameter of the dangerous section of the concrete column. The dimensions of the structure are checked with an accuracy of ± 1 mm; crack width accurate to 0.05 mm.

The proposed method allows you to take into account the real life of the concrete pipe columns in terms of fire resistance through the use of a set of individual indicators of its quality, as well as by taking into account the reliability indicators of the concrete columns for their intended purpose and indicators of its longitudinal deflection.

Example.

=18,5 МПа;

=25,3 мм²/мин); толщина трубы

=3,5 мм; марка стали трубы ВСт3КП (

=370 Н/мм²); площадь сечения металлической трубы А_р=4437 мм² (

=407 мм); продольные силы и моменты в верхнем опорном сечении: от вертикальных нагрузок N_ν=1500 кН; M_ν=30 кН⋅м; ветровая и кратковременные вертикальные нагрузки отсутствуют.Given: pipe-concrete column of the lower floor of the frame frame 4.8 m long; concrete section with a diameter d _b = 400 mm; class B25 concrete (E _b = 3⋅10 ⁴ MPa, R _b = 14.5 MPa;

= 18.5 MPa;

= 25.3 mm ² / min); pipe thickness

= 3.5 mm; steel grade of the pipe ВСт3КП (

= 370 N / mm ² ); the cross-sectional area of the metal pipe And _p = 4437 mm ² (

= 407 mm); longitudinal forces and moments in the upper support section: from vertical loads N _ν = 1500 kN; M _ν = 30 kN⋅m; wind and short-term vertical loads are absent.

It is required to identify the intensity of the power stresses of the upper reference section and to calculate the design limit of fire resistance of the concrete pipe.

Payment.

. Усилия от нагрузок равны:1) The section under consideration is located at a compliant termination, therefore η _ν = 1,0. We determine the coefficient η _h . In this case, the estimated length is taken equal

. The efforts from the loads are equal to:

M = M _ν = 30 kN⋅m; N = N _ν = 1500 kN;

e ₀ = M / N = 30/1500 = 0.02 = 20 mm;

where M, M _ν is the applied moment kN⋅m; N, N _ν - applied force kN⋅m; e ₀ is the eccentricity of the longitudinal force, mm.

e - eccentricity of the applied force, taking into account random eccentricity, mm;

e = e ₀ + e _a = 20 + 13.5 = 33.5 mm;

where e ₀ is the eccentricity of the applied force, mm; e _a - random eccentricity, mm, adopted by SP 266.13258000.2016 p. 7.1.1.5, 7.1.1.6/ [5]

2) Determine the stiffness W ₀ columns.

To do this, we calculate the coefficient for calculating the stiffness of concrete k _b :

- коэффициент, учитывающий влияние длительности действия нагрузки; δ_е - относительное значение эксцентриситета продольной силы.Where

- coefficient taking into account the effect of the duration of the load; δ _e is the relative value of the eccentricity of the longitudinal force.

, коэффициент, учитывающий влияние длительности действия нагрузки будет равен:Due to the lack of vertical short-term loads

, the coefficient taking into account the influence of the duration of the load will be equal to:

Insofar as

0.15≤δ _e ≤1.5;

where δ _e is the relative value of the eccentricity of the longitudinal force.

δ _e = e ₀ / h = 33.5 / 407 = 0.08 mm ⇒ take δ _e = 0.15

3) The moments of inertia of the concrete section and the entire reinforcement are respectively equal to:

и d_b - наружный диаметр металлической трубы и соответственно диаметр бетонного сечения колонны, мм;

- толщина металла трубы, мм.where I _p and I - the moment of inertia of the reinforcement and, accordingly, the concrete section, mm ⁴ ; π = 3.14;

and d _b is the outer diameter of the metal pipe and, accordingly, the diameter of the concrete section of the column, mm;

- pipe metal thickness, mm.

4) Then the stiffness of the pipe-concrete column (W ₀ , kN⋅m ² ) is taken from the condition:

- расчетная длина колонны, м; π=3,14; А_р - площадь сечения металлической трубы, мм²; Е_р - модуль упругости арматуры, МПа; I_p и I - момент инерции арматуры и соответственно бетонного сечения, мм⁴;where k _s = 0.7 is a coefficient for calculating the stiffness of steel; k _b - coefficient for calculating the stiffness of concrete;

- estimated column length, m; π = 3.14; And _p is the cross-sectional area of the metal pipe, mm ² ; E _p - modulus of elasticity of the reinforcement, MPa; I _p and I - the moment of inertia of the reinforcement and, accordingly, the concrete section, mm ⁴ ;

E _b1 = E _b / (1 + ϕ _{b, cr} ) = 3⋅10 ⁴ / (1 + 2.5) = 8571.5 MPa - deformation modulus of compressed concrete with prolonged load;

ϕ _{b, cr} = 2.5 - creep coefficient of concrete, taken according to table 6.12 SP 63.13330.2012 / [4];

R _pc is the standard resistance of the pipe metal during compression in the composition of the concrete column, MPa;

;

- предельное сопротивление металла трубы, МПа; е - эксцентриситет приложенной силы с учетом случайного эксцентриситета, мм;

- толщина металла трубы, мм;

- наружный диаметр металлической трубы, мм.Where

;

- ultimate resistance of the pipe metal, MPa; e - eccentricity of the applied force, taking into account random eccentricity, mm;

- thickness of the pipe metal, mm;

- the outer diameter of the metal pipe, mm

W ₀₁ = k _b E _b1 I + k _s E _p I _p = 0.167⋅8571.5⋅1256⋅10 ⁶ + 0.7⋅2⋅10 ⁵ ⋅90.25⋅10 ⁶ = 14.44⋅10 ³ kN ⋅m ² ;

where E _p and E _b1 - modulus of elasticity of reinforcement and, accordingly, the modulus of deformation of compressed concrete with prolonged action of the load, MPa; l ₀ - the estimated length of the column, m; π = 3.14; R _pc is the standard resistance of the pipe metal during compression in the composition of the concrete column, MPa; And _p is the cross-sectional area of the pipe metal; k _b , k _s - coefficients for calculating the stiffness of concrete and steel.

We accept the minimum value of stiffness W ₀ = 5.27⋅10 ³ kN⋅m ²

;

;

- расчетная длина колонны, м; π=3,14.where N _cr is the critical load, kN; W ₀ - the stiffness of the concrete column, kN⋅m ² ;

- estimated column length, m; π = 3.14.

η _h = 1 / (1-N / N _cr ) = 1 / (1-1500 / 2258) = 2.979;

where N and N _cr - vertical force and critical load, kN.

6) The calculated moment, taking into account the deflection of the column is equal to:

M = M _ν ⋅η _h = 30⋅2.979 = 89.37 kNm

The bending moment characterizing the ultimate bearing capacity of the column (M _ss , kN⋅m) is found by the formula:

- нормативное сопротивление бетона при сжатии в составе трубобетонной колонны, МПа; π=3,14; А_р - площадь сечения металлической трубы, мм²;

- предельное сопротивление металла трубы, МПа; R_pc - нормативное сопротивление металла трубы при сжатии в составе трубобетонного элемента, МПа;where r _b is the radius of the concrete section, mm; r _p is the radius of the middle surface of the pipe, mm;

- normative resistance of concrete during compression as a part of a pipe-concrete column, MPa; π = 3.14; And _p is the cross-sectional area of the metal pipe, mm ² ;

- ultimate resistance of the pipe metal, MPa; R _pc is the normative resistance of the pipe metal during compression in the composition of the concrete element, MPa;

- наружный диаметр металлической трубы, мм;

- толщина металла трубы, мм.Where

- the outer diameter of the metal pipe, mm;

- pipe metal thickness, mm.

- нормативное сопротивление бетона при сжатии в составе трубобетонной колонны;

- normative resistance of concrete during compression in the composition of the concrete column;

- площадь сечения бетона колонны; е - эксцентриситет приложенной силы с учетом случайного эксцентриситета, мм; а, b, с - постоянные определяемые по СП 266.13258000.2016/ [5];

- нормативное сопротивление бетона осевому сжатию, МПа;

- толщина металла трубы, мм;

- наружный диаметр металлической трубы, мм.Where

- cross-sectional area of concrete columns; e - eccentricity of the applied force, taking into account random eccentricity, mm; a , b, c - constants determined by SP 266.13258000.2016 / [5];

- standard resistance of concrete to axial compression, MPa;

- thickness of the pipe metal, mm;

- the outer diameter of the metal pipe, mm

The angle α is in accordance with SP 266.13258000.2016 / [5].

7) The value of the intensity of power stresses (J _σo ) in the cross section of the concrete pipe column is calculated according to equation (2):

J _σo = M _ξ / M _cc = 89.37 / 179.73 = 0.5;

where M _ξ and M _ss is the bending moment from the calculated longitudinal force, taking into account the deflection of the column and, accordingly, the bending moment characterizing the strength of the circular cross section, kN⋅m.

) трубобетонной колонны вычисляют по уравнению (4):8) The degree of reinforcement of the cross section of the column with metal pipes (

) pipe-concrete columns are calculated according to equation (4):

и

- предельное сопротивление металла трубы сжатию и соответственно нормативное сопротивление бетона осевому сжатию, МПа.where A _p and A _b - the cross-sectional area of the pipe metal and, accordingly, the cross-sectional area of the concrete columns, mm ² ;

and

- ultimate resistance of the pipe metal to compression and, accordingly, the standard resistance of concrete to axial compression, MPa.

9) The time of resistance to the fire effect of the metal of the pipe, unfilled with concrete, is calculated according to equation (6):

- приведенная толщина металла трубы, мм.where J _σo is the intensity of the initial stresses from the test load in the dangerous section of the column (J _σo ≤1);

- reduced thickness of the pipe metal, mm.

10) The duration of fire protection of concrete with metal pipes is calculated according to equation (7):

- показатель условий нагрева металла трубы (

=1/3);

- время сопротивления огневому воздействию металла трубы, незаполненной бетоном, мин.Where

- an indicator of the heating conditions of the pipe metal (

= 1/3);

- time of resistance to fire exposure of the metal pipe, unfilled with concrete, min.

11) The design limit of fire resistance of a concrete pipe by the loss of bearing capacity (F _ur , min) is calculated according to equation (1):

- степень армирования сечения колонны металлом трубы (

≤1,66);

- коэффициент уровня ответственности по назначению (пониженный -

=0,8; нормальный -

=1,0; повышенный -

=1,2);

- показатель термодиффузии бетона, мм²/мин;

- нормативное сопротивление бетона осевому сжатию, МПа;

- длительность огнезащиты бетона металлом трубы, мин.where d _b is the diameter of the concrete section of the column, mm; J _σo is the intensity of power stresses in the dangerous section of the column (J _σо ≤1);

- the degree of reinforcement of the cross section of the column with metal pipes (

≤1.66);

- coefficient of the level of responsibility for the intended purpose (low -

= 0.8; normal -

= 1.0; increased -

= 1,2);

- indicator of thermal diffusion of concrete, mm ² / min;

- standard resistance of concrete to axial compression, MPa;

- the duration of the fire protection of concrete with metal pipes, min

The studied column can be assigned the III degree of fire resistance, which corresponds to 45 min [6].

Information sources

1. GOST 30247.1-94. Building constructions. Test methods for fire resistance. Bearing and enclosing structures.

2. Barthelemy B., Kruppa J. Fire resistance of building structures / trans. with french - M., Stroyizdat, 1985 .-- 216 p. (Ch. 5, p. 5.2 Closed section columns filled with concrete, p. 169-175).

3. Patent No. 2281482 RU IPC G01N 25/50. A method for determining the fire resistance of compressed elements of reinforced concrete structures of a building / Ilyin N.A., Butenko S.A., Esmont S.V .; application SASAS: 09/06/04; publ. 02/18/06. Bull. Number 22.

4. SP 63.13330.2012 SNiP 52-01-2003. Concrete and reinforced concrete structures. Key Points. ”

5. SP 266.1325800.2016 Steel-reinforced concrete structures. Design rules.

6. "Technical regulation on fire safety requirements." Federal Law No. 123 - 2008, with rev. 2012, 2013

Claims (33)

1. A method for determining the fire resistance of a column of a building, including conducting a technical inspection, establishing the type of concrete of the column, identifying the conditions for its support and fastening, determining the time of the onset of the limiting state on the basis of loss of bearing capacity of the column under test load under standard fire exposure, conducting evaluation tests without destruction according to a set of individual indicators of the quality of the column, in which the technical inspection is accompanied by instrumental measurements of geometric their sizes of the column and its dangerous section, establish the area of concrete and steel in a dangerous section, the moisture and density of concrete in a natural state, determine the thermal diffusion of concrete, find the ultimate compressive resistance of concrete, the value of the intensity of power stresses in a dangerous section, characterized in that fire resistance of a concrete pipe column made of a metal pipe filled with concrete, while additionally identify the level of responsibility of the column for the purpose, determine the critical The strength, stiffness of the pipe-concrete column and the influence of the deflection of the column on the bending moment of longitudinal force, the degree of reinforcement of the cross-section of the column by the pipe metal, the limit of compression resistance of the pipe metal is determined, the reduced thickness of the pipe metal and the time of resistance to the fire effect of the metal pipe unfilled with concrete are calculated, the duration of concrete fire protection is calculated metal pipes and the fire resistance of the concrete pipe from the beginning of the standard fire exposure to the loss of bearing capacity (

, min), which is determined using the analytical equation (1)

; where d _b is the diameter of the concrete section of the column, mm; J _σo is the intensity of power stresses in the dangerous section of the column, J _σo ≤1; α _mt is the degree of reinforcement of the cross section of the column with pipe metal, α _mt ≤1.66; γ _n - coefficient of the level of responsibility for the intended purpose: low - γ _n = 0.8; normal - γ _n = 1,0; increased - γ _n = 1,2; D _W - indicator of thermal diffusion of concrete, mm ² / min; R _VP - the standard resistance of concrete to axial compression, MPa; τ _m.ozs - duration of fire protection of concrete with pipe metal, min. 2. The method according to p. 1, characterized in that the intensity of the power voltage in the dangerous section of the concrete pipe, J _σo ≤1 is found using equation (2)

where M _ξ and M _ss is the bending moment from the calculated longitudinal force, taking into account the deflection of the column and, accordingly, the bending moment characterizing the ultimate bearing capacity of the column, kN⋅m. 3. The method according to p. 1, characterized in that the cross-sectional area of the pipe metal A _r , mm ² , is calculated according to equation (3)

where d _mt and d _b - the outer diameter of the metal pipe and, accordingly, the diameter of the concrete section of the column, mm 4. The method according to p. 1, characterized in that the degree of reinforcement of the cross section of the column with the metal of the pipe α _{mt is} calculated according to equation (4)

where A _p and A _b - the cross-sectional area of the metal pipe and, accordingly, the cross-sectional area of the concrete columns, mm ² ; R _IP and R _VP - ultimate resistance of the pipe metal and, accordingly, the standard resistance of concrete to axial compression, MPa. 5. The method according to p. 1, characterized in that the reduced thickness of the pipe metal θ _sr , mm, is determined by equation (5)

where δ _mt is the thickness of the pipe metal, mm; d _mt is the outer diameter of the metal pipe, mm 6. The method according to p. 1, characterized in that the time of resistance to fire effect of a metal pipe, unfilled with concrete τ _{and, mt} , is determined by equation (6)

where J _σо is the intensity of the initial stresses from the test load in the dangerous section of the column, J _σо ≤1; θ _sr is the reduced thickness of the pipe metal, mm. 7. The method according to p. 1, characterized in that the critical force N _cr , kN, perceived by the concrete pipe, is calculated according to equation (7)

where W ₀ is the stiffness of the concrete column;

- estimated column length, m; π = 3.14. 8. The method according to p. 1, characterized in that the stiffness of the concrete column Zh _{0 is} calculated according to equation (8)

where E _p and E _b1 - modulus of elasticity of reinforcement and, accordingly, the modulus of deformation of compressed concrete with prolonged action of the load, MPa; I _p and I - the moment of inertia of the reinforcement and, accordingly, the concrete section relative to the center of gravity of the concrete section, mm ⁴ ;

- estimated column length, m; π = 3.14; R _pc is the standard resistance of the pipe metal during compression in the composition of the concrete column, MPa; And _p is the cross-sectional area of the pipe metal; k _b , k _s are the coefficients for calculating the stiffness of concrete and steel, respectively: k _s = 0.7;

Where

- coefficient taking into account the effect of the duration of the load; δ _e - the relative value of the eccentricity of the longitudinal force, determined from the relation (10):

where d _mt is the outer diameter of the metal pipe, mm; e ₀ is the eccentricity of the longitudinal force, mm; R _pc - the standard resistance of the pipe metal, calculated by the equation (11)

where R _un - ultimate resistance of the pipe metal, MPa; e - eccentricity of the applied force, taking into account random eccentricity, mm; δ _mt - pipe metal thickness, mm; d _mt is the outer diameter of the metal pipe, mm 9. The method according to p. 1, characterized in that for the individual quality indicators of the concrete column affecting the fire resistance limit, they take: the geometric dimensions of the metal pipe and its concrete section, the rigidity of the concrete column, the axial compression strength of concrete, the degree of reinforcement of the section of the column with metal pipes, pipe metal resistance to compression, intensity of power stresses in a dangerous section, moisture and density of concrete in its natural state, concrete thermal diffusion index, elastic modulus of pipe metal and mod l compressed concrete deformation upon prolonged loading action, the duration of fire protection concrete pipe metal.

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