RU2485488C2 - Method of determining fire-resistance of wood covering of building - Google Patents

Abstract

FIELD: fire-prevention facilities.

SUBSTANCE: in implementation of the method a check of individual values of quality of wood construction elements is carried out, then the dangerous sections are revealed, breed and type of wood, the value of its auto-ignition temperature, the type of rolling wood covering and ignitability values of its elements are revealed, the thickness and values of thermal diffusion of fire-retardant layer material for wood of the covering boarding is identified, and using the obtained values of quality of the elements, according to analytical expression, the fire resistance limit of wood covering of the building is revealed.

EFFECT: elimination of fire tests of wooden structures in the building, reduction of labour intensity in determining the fire resistance of wood covering with the structural fire protection, expanding the technological capabilities of determining the actual fire resistance of differently engineered wood coverings, the ability of the testing the wooden structures for fire resistance without violation of functional process in the building, improving the accuracy and expressiveness of testing.

9 cl, 7 dwg

Description

The invention relates to the field of fire safety of building structures. In particular, it can be used to classify wooden floors with structural fire protection in terms of their resistance to fire. This makes it possible to justify the use of existing wooden structures with an actual fire resistance limit and fire hazard class in buildings of various functional purposes.

Structural fire protection of wooden floors includes plastering, lining with fire retardant large-sized sheets and plates, the installation of fire-retardant suspended ceilings.

The need to determine the fire resistance and fire safety of wooden fireproof structures arises during the design, operation and reconstruction of a building, the need to strengthen its structures, bring the fire resistance and fire hazard of building structures in accordance with the requirements of the technical regulation, during examination and restoration of structures after a fire.

A known method for determining the fire resistance of a wooden floor of a building according to the results of a generalization of experimental fire tests. This method includes determining the position of the elements of wooden structures in the building and assessing the fire resistance of some types of wooden floors, depending on the design of the components of the floor and the applied layer of plaster / Manual for determining the fire resistance of structures, fire spread limits for structures and the combustibility of materials. / TSNIISK them. Kucherenko. - M .: Stroyizdat, 1985. - P.28-30 (Bearing wooden structures) / [1].

The reasons that impede the achievement of the technical result indicated below when using the known method include the fact that the known method does not indicate the place of destruction of the bending elements of wooden structures (hazardous sections) under fire conditions, the type of stress state, the level of loading and their influence on the value are not taken into account fire resistance of the wooden floor of the building.

A known method of determining the fire resistance of a wooden floor of a building by an improved calculation of its actual fire resistance by the method of successive approximations. With the known method for determining the fire resistance of wood flooring elements, they are heated according to the standard fire test mode, the elastic and thermophysical characteristics of wood at all points of the uncarbonized part of the cross section are assumed to be the same. The fire resistance limit of a wooden floor from the condition of loss of its bearing capacity in case of fire is defined as the sum of the time of ignition of the wood and the time of carbonization of the cross section until the limiting state of the element / Mosalkov, I.L. Fire resistance of building structures. / I.L. Mosalkov, G.F.Plyusina, A.Yu. Frolov. - M .: Special equipment, 2001. - P.201-236 (Calculation of the fire resistance of wooden structures) / [2].

For reasons that impede the achievement of the technical result indicated below when using the known method, the known method for determining the fire resistance of a wooden floor uses a very cumbersome algorithm for calculating the geometric characteristics of its cross section, while determining only the fire resistance of structures.

The closest method of the same purpose to the claimed invention by the totality of features is a method for determining the fire resistance of a wooden floor having structural fire protection by means of a fire test, including technical inspection (including determining the species and type of wood, establishing the actual and design dimensions), identifying conditions supporting wooden floors, determining the time of the onset of the limiting state by signs of loss of bearing and heat-insulating ability to structures under standard load under standard thermal exposure / GOST 30247.1-94. Building constructions. Fire test methods. Bearing and enclosing structures. - M .; 1995 .-- 7 p. / [3] - adopted as a prototype.

The reasons that impede the achievement of the technical result indicated below when using the known method adopted as a prototype include the fact that in the known method the tests are carried out on a design sample that is affected only by the design normative loads. 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 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 structural quality indicators on their fire resistance. By a small number of tested samples (2-3 pcs.) It is impossible to judge the actual state of the supporting structures 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 structures, their actual dimensions and the heating circuit of the dangerous section of the test structure in a fire.

The invention consists in the following. The problem to which the claimed invention is directed, is to establish fire safety indicators of a building in terms of the guaranteed duration of resistance of fire-resistant wooden floors in a fire; in determining the actual fire resistance limits of the wooden floor during the design, construction and / or operation of the building; in reducing economic costs when testing wood flooring for fire resistance.

EFFECT: elimination of fire tests of a wooden floor in a building; reduction of labor intensity in determining fire resistance indicators of wooden structures; expanding the technological capabilities of determining the actual fire resistance limit of variously designed wooden floors of any size and the possibility of comparing the results with tests of similar elements of wooden building structures; the possibility of testing the wooden floor for fire resistance without disturbing the functional process in the building; reduction in economic costs of testing; maintaining the serviceability of the building during inspection and non-destructive testing of wooden floors; simplification of conditions and shortening of the test period of a wooden floor for fire resistance; increased accuracy and expressiveness of the test; getting the opportunity to solve the inverse problems of fire resistance of wooden floors and the application of the method of selecting variable values of its design parameters; the use of integral structural parameters to determine the fire resistance of wooden floors and the simplification of the mathematical description of the process of thermal resistance of elements of wooden structures; taking into account the real resource of wood flooring for stability in a fire using a complex of individual indicators of their qualities; increasing the reliability of determining fire protection measures for wooden floors; simplification of taking into account the influence on the fire resistance of wooden floors of the features of the static working scheme; clarification of individual quality indicators of elements of a wooden structure, affecting its actual fire resistance; the possibility of determining the guaranteed fire resistance of a wooden floor according to its design parameters.

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 wooden floor of a building by testing, which includes conducting a technical inspection, identifying the type and effectiveness of structural fire protection, determining the time of occurrence of the ultimate state of a wooden floor according to the signs of fire resistance under standard heat exposure, a feature lies in the fact that the test is carried out without destruction by a set of individual indicators the qualities of constructive fire protection of the wooden binder of the supporting beams of the floor, technical inspection is supplemented by instrumental measurements of the geometric dimensions of the components of the wooden floor, the breed, the type of construction wood and the temperature of its ignition are revealed; identify the type of rolling of the wooden floor and the flammability indicators of its elements; reveal the thermophysical properties of the fire-retardant layer, its thickness and thermal diffusion indicators of materials for its manufacture; identify the conditions for attaching the wooden binder of the floor and the layer of fire protection; then, using the obtained indicators of the qualities of the components of the building floor, determine the value of its fire resistance limit - F _u , min.

The fire resistance of a wooden floor with structural fire protection by the loss of its heat-insulating ability F _{u (J)} , min, is determined by the algebraic expression (1):

where F _{u (J)} is the fire resistance of a wooden floor, with structural fire protection, by the loss of its heat-insulating ability, min;

k _o is the ignitability parameter of the components of the wooden floor;

δ _oz - the thickness of the fire-retardant layer for wooden hemming, mm;

D _OSS - an indicator of thermal diffusion of the flame retardant layer, mm ² / min.

The flammability parameter (k _о ) of the components of the wooden floor, taking into account the type of wood of the binder of the floor and the combustibility of the rolling materials on them, is calculated by the algebraic expression (2):

where k _o is the ignitability parameter of the components of the wooden floor;

k _m - temperature indicator of the wood species of the binder;

k _mountains - an indicator of the flammability of the materials of the run of the floor;

k _i - coefficients that take into account the structural design of the wooden floor, for example, the presence of voids and more.

An indicator that takes into account the influence of the temperature of the auto-ignition temperature of the wood of the binder on the fire resistance of a wooden floor with structural fire protection is found by the algebraic expression (3):

where k _m is the temperature indicator of the wood species of the binder;

t _cvp is the autoignition temperature of the binder wood, ° С.

The combustibility index of materials (k _mountains ) of the run-up of the floor is taken depending on the combustibility group of the materials:

Flammability Group NG (non-combustible) G1 (slightly combustible) G2 (moderately flammable) G3 (normally combustible) G4 (highly combustible) k _mountains 1.00 0.95 0.85 0.75 0.65

The thermal diffusion index of the materials of the fire-retardant layer D _OSS, mm ² / min, of the wooden floor is determined empirically or found depending on the thermophysical properties at an average temperature t _m = 450 ° C according to the algebraic expression (4):

where D _oz - an indicator of thermal diffusion of the material of the flame retardant layer, mm ² / min;

λ ₀ and С _о - respectively, the thermal conductivity coefficient (W / (m · ° С)) and specific heat (kJ / (kg · ° С)) of the fire protection material;

t _m = 450 ° C - the average temperature of the heating material over the cross section of the fireproof layer;

b and d are the thermal indicators of thermal conductivity and specific heat of the fire protection material;

ω and γ _s , respectively, the moisture content of the material,%, by weight, and the average density of the dry material of the fire retardant layer, kg / m ³ .

For a characteristic sign of the fire resistance of a wooden floor, the heating of the unheated surface of the fire-retardant layer to the self-ignition temperature of the wood is taken.

The following are the individual indicators of the quality of the wooden floor: the geometric dimensions of the components of the floor, the type of wood and the temperature of its ignition, the combustibility group of the material of the overrun floor; density, humidity and thermal indicators of thermal conductivity and specific heat and / or indicator of thermal diffusion of the material of the fireproof layer.

To increase the resistance to fire, a fire-retardant layer of wood flooring is applied over a rip or metal mesh attached to a wooden binder.

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

The elimination of the fire test of the wooden floor of an existing building and its replacement with a non-destructive test reduces the complexity of determining the fire resistance of the floor, expands the technological capabilities of detecting the actual fire resistance of variously designed wooden floors of any size, makes it possible to test the wooden floor for fire resistance without disturbing the functional process of the building under examination, as well as comparing results obtained with standard tests mi of similar wooden floors and maintaining the serviceability of the building under examination without disturbing the load-bearing capacity of its wooden structures during the test. Therefore, the conditions for testing the elements of wooden floors for fire resistance are greatly simplified.

Reducing the economic costs of testing include reducing the cost of dismantling, transportation and fire testing of wooden floors of the building.

The use of a mathematical description of the process of resistance of elements of wood flooring to standard thermal effects and the use of simple algebraic expressions increases the accuracy of identifying their fire resistance limits.

Determination of the fire resistance of a wooden floor by only one quality indicator, for example, by the thickness of the layer of fire-retardant coating, leads, as a rule, to underestimating their fire resistance, since the influence on it of variations of individual quality indicators of bent elements of wooden structures has different signs, and a decrease in the fire resistance due to indicator can be offset by others.

As a result, in the proposed method, the identification of the fire resistance of fireproof wood floors is provided not by one indicator, but by a set of individual quality indicators. This allows you to more accurately take into account the real fire resistance of wooden floors with structural fire protection.

The proposed technical solution takes into account a set of individual indicators of the quality of wood flooring, affecting their fire resistance, determined by non-destructive tests.

For parts of a wooden floor with a fire-retardant coating tested without power loads, it is customary to reach the limit state in fire resistance as the limit (critical) heating temperature (t _u , ° C) of the lower surface of the wood binder, that is, by the loss of the heat-insulating ability of the fire-retardant layer (J).

For the limiting heating temperature (t _u , ° C) of the wood flooring binder material, the self-ignition temperature (t _svp , ° C) of building wood is _taken , that is, the condition (5) is observed:

The self-ignition temperature of building wood: oak - 375 ° C; spruce - 397 ° C; pine - 400 ° C.

Example

Given: fireproof overlap with wood run (group of flammability of the material G3-normally combustible; flammability index of run k _mountains = 0.75); binder wood - pine (self-ignition temperature t _svp = 400 ° C); the thickness of the fire-retardant layer for the filing of the ceiling δ _oz = 20 mm (lime-sand plaster, thermal diffusion index D _oz = 19 mm ² / min).

It is required to identify the value of the fire resistance limit of a wooden floor with structural fire protection.

Solution: 1) The temperature index of the wood species for filing the overlapping load-bearing beams is calculated by the algebraic expression (3):

k _m = t _svp / 500 = _400/500 = 0.8.

2) the Flammability parameter of the overlap of the overlap is calculated by the algebraic expression (2):

k _o = k _gop · k _m = 0.75 · 0.8 = 0.6.

3) The fire resistance of a wooden floor based on the loss of the heat-insulating ability of the fireproof layer is calculated by the algebraic expression (1):

F _{u (J)} = 60 · k _o · (δ _oz / D _oz ) ² = 60 · 0.6 · (20/19) ² = 40 min.

4) The fire resistance of a wooden floor according to the signs of loss of bearing capacity - F _{u (R),} min, and integrity loss - F _{u (E),} min, according to experimental tests, is greater than the fire resistance limit for the loss of heat-insulating ability of structural fire protection - F _{u (J ),} min, that is, condition (6) is characteristic:

In Fig. 1, a part of a wooden floor is shown for calculating its fire resistance by the sign of loss of the heat-insulating ability of structural fire protection for board binder in a standard fire (t _ct , ° C):

1 - fire retardant layer (plaster 20 ÷ 30 mm);

2 - tug (width 10 ÷ 20 mm through 100 mm) or steel mesh (wire ⌀2 ÷ 4 mm cage 20 × 20 mm);

3 - the lower surface of the board binder;

4 - board binder (20 ÷ 25 mm);

5 - cranial bar (40 × 40) or (50 × 50 mm); 6 - rolling overlap;

7 - supporting beam (bars В × Н = (110 ÷ 225) × (120 ÷ 300 mm));

8 - clay coating - sand (20 ÷ 30 mm);

9 - flooring (40 mm); 10 - felt with roofing felt;

t _u = t _svp, ° С - self-ignition temperature of the binder wood;

t _ct , ° С - temperature of a standard fire.

Figure 2-7 shows the structural solutions of plastered wooden floors (with sound insulation):

overlap on the board filed 25 mm (figure 2);

the same, on the coast with a board binder 19-25 mm (figure 3);

the same, on a wooden run from the plates (figure 4);

the same on the shield rolls (figure 5);

coating with a slurry of cinder-concrete hollow stones (Fig.6);

also, with gypsum roll (Fig.7):

The designation of the elements 1-10 see the description of figure 1.

11 - plaster (20 mm)

12 - soundproofing filling (sand 50 mm); 13 - only;

14 - parquet 20 mm; 15 - filling;

16 - cardboard; 17 - lags 150/2 mm; 18 - plate (180/2 mm);

19 - shield roll; 20 - soundproofing plates (70 mm fiberboard);

21 - cinder block; 22 - dry plaster;

23 - slag concrete slab (30 mm); 24 - alabaster solution;

25 - gypsum block; 26 - sand (20 mm); 27 - linoleum;

28 - bitumen (roofing); 29 - smearing with bitumen or roofing;

30 - gypsum board with wooden slats (60 mm);

31 - metal mesh; 32 - triangular bar 50 mm;

33 - sand (60 mm).

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

The sequence of operations of the method for determining the fire resistance of wooden floors of buildings with structural fire protection is as follows.

First, a technical inspection of the building is carried out. Then determine the group of the same type of fireproof wooden floors and their total number in it. The sample size of the same type of overlap is calculated. Assign a set of individual quality indicators for the elements of wooden structures that affect fire resistance. The conditions of abutment, fastening of the ends and dangerous sections of the wooden floor are revealed. The number of tests of a single indicator of the quality of the wooden floor is calculated depending on its statistical variability. Then, individual quality indicators of the components of the wooden floor are evaluated, and finally, the actual fire resistance limit of the tested wooden floor with structural fire protection is found from them.

A technical inspection is understood as checking the condition of the components of a wooden floor, including identifying the conditions for supporting a wooden floor, determining the species and type of wood, the thermophysical characteristics of the fireproof layer.

Schemes for heating cross sections of the components of a wooden floor in a fire condition are determined depending on their actual location, laying adjacent structures that reduce the number of sides of the heating, and a device for constructive fire protection.

The main unit quality indicators of the components of a wooden floor that provide fire resistance include: the geometric dimensions of the element, the density and moisture of the wood in its natural state, the temperature of its ignition, the standard resistance of the wood to compression and bending, the stress intensity in a dangerous section, type, thickness and heat-insulating properties of the fire-retardant coating material of the components of the wooden floor of the building.

Verification of individual quality indicators of the components of the wooden floor, included in the sample or checked individually, is carried out by non-destructive tests using existing instruments.

Using the obtained quality indicators of the components of the wooden floor, the value of the fire resistance limit F _{u (J),} min.

The proposed method was applied during field inspection of wooden structures of the non-residential premises (Cascade LLC, Samara, 2010).

Information sources

1. A guide to determining the limits of fire resistance of structures, the limits of the spread of fire on structures and the combustibility of materials. / TSNIISK them. Kucherenko. - M .: Stroyizdat, 1985. - P.28-31 (Bearing wooden structures).

2. Mosalkov, I.L. Fire resistance of building structures. / I.L. Mosalkov, G.F.Plyusina, A.Yu. Frolov - M .: Special equipment, 2001. - P.201-236 (Calculation of the fire resistance of wooden structures).

3. GOST 30247.1-94. Building constructions. Test methods for fire resistance. Bearing and enclosing structures. - M .: IPK Publishing House of Standards, 1995. - 7 p.

Claims (9)

1. The method of determining the fire resistance of a wooden floor of a building by testing, including conducting a technical inspection, identifying the type and effectiveness of structural fire protection, determining the time of occurrence of the ultimate state of a wooden floor according to the signs of fire resistance under standard thermal effects, characterized in that the test is carried out without destruction according to a set of individual quality indicators of structural fire protection of the wooden binder of the floor beams, technical inspection lnyayut instrumental measurements of geometrical dimensions of components of wooden floors, identify breed construction grade wood and the amount of its autoignition temperature; identify the type of rolling of the wooden floor and the flammability indicators of its elements; reveal the thermophysical properties of the fire-retardant layer, its thickness and thermal diffusion indicators of materials for its manufacture; identify the conditions for attaching the wooden binder of the floor and the layer of fire protection; then, using the obtained indicators of the qualities of the components of the building floor, determine the value of its fire resistance limit - F _u , min. 2. The method according to claim 1, characterized in that the fire resistance of the wooden floor with structural fire protection by the loss of its heat-insulating ability - F _{u (J)} , min, is determined by the algebraic expression (1):
F _{u (J)} = 60 · k _o · (δ _oz / D _oz ) ² ;
where F _{u (J)} is the fire resistance of a wooden floor with structural fire protection by the loss of its heat-insulating ability, min;
k _o is the ignitability parameter of the components of the wooden floor;
δ _oz - the thickness of the fire-retardant layer for wooden hemming, mm;
D _OSS - an indicator of thermal diffusion of the flame retardant layer, mm ² / min. 3. The method according to claim 1 or 2, characterized in that the flammability parameter (k _о ) of the components of the wooden floor, taking into account the type of wood of the binder of the floor and the combustibility of the rolling materials on them, is calculated by the algebraic expression (2):
k _o = k _m · k _mountains · k _i ;
where k _o is the ignitability parameter of the components of the wooden floor;
k _m - temperature indicator of the wood species of the binder;
k _mountains - an indicator of the flammability of the materials of the run of the floor;
k _i - coefficients that take into account the structural design of the wooden floor, for example, the presence of voids and more. 4. The method according to claim 1 or 3, characterized in that the indicator, taking into account the influence of the temperature of the ignition temperature of the wood species of the binder on the fire resistance of the wooden floor with structural fire protection, is found by the algebraic expression (3):
k _m = t _svp / 500 = 2 · 10 ^-3 · t _svp ,
where k _m is the temperature indicator of the wood species of the binder;
t _svp - autoignition temperature of the binder wood, ° С. 5. The method according to claim 1 or 3, characterized in that the combustibility index of the materials (k _mountains ) of the run of the floor is taken depending on the combustibility group of the materials:
Flammability Group NG (non-combustible) G1 (slightly combustible) G2 (moderately flammable) G3 (normally combustible) G4 (highly combustible) k _mountains 1.00 0.95 0.85 0.75 0.65 6. The method according to claim 1 or 2, characterized in that the thermal diffusion of the materials of the fire-retardant layer is D _oz, · mm ² / min, the wooden floor is determined empirically or found depending on the thermophysical properties at an average temperature t _m = 450 ° C by algebraic expression (4):

where D _oz - an indicator of thermal diffusion of the material of the flame retardant layer, mm ² / min;
λ _about and With _about - respectively, the coefficient of thermal conductivity (W / (m · ° C)) and specific heat (kJ / (kg · ° C)) of the fire protection material;
t _m = 450 ° С - average temperature of heating the material over the cross section of the fireproof layer;
b and d are the thermal indicators of thermal conductivity and specific heat of the fire protection material;
ω and γ _s - respectively, the moisture content of the material, wt.%, and the average density of the dry material of the fire retardant layer, kg / m ³ . 7. The method according to claim 1, characterized in that for a characteristic feature of the fire resistance of a wooden floor, take the heating of the unheated surface of the fire retardant layer to the temperature of self-ignition of the wood. 8. The method according to claim 1, characterized in that for the individual indicators of the quality of the wooden flooring take: the geometric dimensions of the components of the flooring, the wood species and the temperature of its self-ignition, the combustibility group of the material of the run-up floor; density, humidity and thermal indicators of thermal conductivity and specific heat and / or indicator of thermal diffusion of the material of the fireproof layer. 9. The method according to claim 1, characterized in that to increase the resistance to fire exposure, a fire-retardant layer of wood flooring is applied over the shingles or a metal mesh attached to a wooden binder.

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