RU2347214C1 - Method of determination of fire resistance of traversally reinforced stone walls of building - Google Patents

Abstract

FIELD: physics; measuring.

SUBSTANCE: invention concerns to field of fire safety of buildings. Trial of traversally reinforced stone walls and building bafflers spend without fracture on a complex of individual exponents of quality, estimating quantity of an actual limit of fire resistance on losses of the integrity bearing and heat-insulating abilities. For this purpose determine the geometrical sizes of stone walls, heating requirements, support and fastenings of walls, buckling coefficient, percent of reinforcing of a laying on volume; exponents of density, humidity, a thermal conduction, a heat capacity and thermal diffusion of a material of traversally reinforced stone walls; quantity of a standard loading at trial for fire resistance and a degree of a voltage of dangerous sections of stone walls. Limits of fire resistance of traversally reinforced stone walls determine on polyparametric dependences.

EFFECT: determination of fire resistance without natural thermal action, increase of reliability of quality assurance and non-destroying trials, decrease in economic expenses.

15 cl, 3 wdg

Description

The invention relates to the field of fire safety of buildings and structures (hereinafter - “buildings”). In particular, it can be used to classify transversely reinforced stone walls of buildings according to their resistance to fire. This makes it possible to justify the use of existing stone walls with an actual fire resistance limit in buildings of various classes according to their structural fire hazard.

The need to determine the fire resistance of reinforced stone walls and partitions (hereinafter referred to as the “walls”) arises during the reconstruction of a building, strengthening of its parts and elements, bringing the fire resistance of the stone walls of the building in accordance with the requirements of modern standards, during the examination and / or restoration of stone walls after a fire .

During the reconstruction of a capital building, it is possible to reconstruct and redevelop the premises, change their functional purpose, replace stone walls and equipment. This affects the change in the required fire resistance of the building and its flame retardant structures.

A known method of determining the fire resistance of the stone walls of a building according to the results of a study of the consequences of a natural fire. This method includes determining the position of the walls in the building, assessing the condition of the walls by inspection and measurement, making control samples of the stone, determining the time of the onset of the limiting state by the loss of the bearing capacity of the structure, that is, collapse in a fire / Ilyin N.A. The consequences of fire on reinforced concrete structures. - M .: Stroyizdat, 1979. P.34-35; 90 / [1].

The reasons that impede the achievement of the following technical result when using the known method include the fact that in the known method, the fire resistance limits are determined approximately by the results of a study of the consequences of a past fire. A detailed study determines the long-term work of an expert. At the same time, it is impossible to determine the fire resistance of natural stone walls having different sizes and other external loads. It is difficult to compare the results obtained with standard fire tests of similar stone walls. Therefore, this method is expensive, has little technological ability to re-test, time-consuming and dangerous for testers.

There is a method of evaluating the fire resistance of stone walls according to the results of full-scale fire tests of a building fragment in which the structures are inspected, the moisture of the masonry material is determined, the static load on the walls is assigned according to the actual operating conditions of the building, the factors affecting the value of the fire resistance / NPB 233-97 are determined. Buildings and fragments of buildings. The method of full-scale fire tests. General requirements. - M .: VNIIPO, 1997. S.6-12 / [2].

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 there are high economic costs for conducting fire tests, monitoring the state of stone walls in an experimental fire is difficult and unsafe, due to differences in the thermal regime of the experimental and standard fires it is difficult to determine the true values of the fire resistance limits of stone walls, the reasons for the destruction of the stone walls of the fragment may not be established due to the diversity of simultaneously operating fire factors. The limit state of fire resistance of a stone wall may not be reached due to earlier destruction of the bending elements of the fragment coating / Fire resistance of buildings. V.P. Bushev, V.A. Pchelintsev, B.C. Fedorenko, A.I. Yakovlev. - M.: Stroyizdat, 1970. S.252-256 / [3].

The closest method of the same purpose to the claimed invention by a combination of features is a method for determining the fire resistance of stone walls of a building by testing, including technical inspection, determining the type of stone and mortar wall, class of reinforcement, percentage of reinforcement by volume of masonry with mesh reinforcement, revealing the conditions for its support and fastenings, determination of the time of the onset of the limit state by the loss of the bearing capacity of the wall under the standard load in a standard fire / GOST 3 0247.1-94. Building constructions. Test methods for fire resistance. Bearing and enclosing structures. - M., 1995. - 7 p. / [4] - 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, tests are carried out on samples of stone walls, which are affected only by constant and continuous loads in their calculated values with a reliability coefficient equal to unity , i.e. design regulatory loads.

Tests are carried out on special bench equipment in fire furnaces until the destruction of samples of stone structures. 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 sized and differently loaded stone structures, do not provide the necessary information about the effect of individual quality indicators of a stone structure on its fire resistance.

Determining the fire resistance of a stone wall by a single quality indicator, for example, by thickness, as a rule, underestimates the suitability of using stone walls in a building of a given degree of fire resistance.

The economic costs of testing increase due to the cost of erecting a sample of a stone structure at the installation site of the heating furnaces and to create a standard thermal regime in them. By a small number of tested samples (2-3 pieces) it is impossible to judge the actual state of the walls 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 stone walls, their actual dimensions, the influence of mesh reinforcement, the conditions for heating the dangerous section of the walls being tested.

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 transversely reinforced stone walls in a fire; in determining the actual fire resistance limits of stone walls during the design, construction and / or operation of a building; in reducing economic costs when testing structures for fire resistance.

EFFECT: elimination of fire tests of stone structures in a building or its fragment; reducing the complexity of determining the fire resistance of stone walls; expanding the technological capabilities for determining the actual fire resistance of variously loaded stone walls of any size and the possibility of comparing the results with tests of similar building structures; the ability to test stone walls for fire resistance without disturbing the functional process in the building; reduction in economic costs of testing; preservation of the serviceability of the building during inspection and non-destructive testing of stone walls; simplification of conditions and shortening of the test period of stone walls for fire resistance; the use of polyparametric dependence to determine the fire resistance of reinforced stone walls; increased accuracy and expressiveness of the test; getting the opportunity to solve the inverse problems of fire resistance of walls and using the method of selecting variable values of their design parameters; the use of integral structural parameters to determine the fire resistance of stone structures and the simplification of the mathematical description of the process of thermal resistance of loaded stone walls; increasing the reliability of the test results of a group of the same type of stone walls; clarification of individual quality indicators of reinforced stone walls, affecting their fire resistance; the ability to determine the guaranteed fire resistance of stone walls by 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 stone walls of a building by testing, including technical inspection, establishing grades of brick, stone and masonry mortar, steel grade, type of reinforcement, class of reinforcement by tensile strength, identification conditions of support and fastening of stone walls, the establishment of the ultimate state of fire resistance, the determination of the time of the onset of the ultimate state of fire resistance transverse about reinforced stone walls under standard load, the peculiarity is that the test of the transversely reinforced stone walls of the building is tested without destruction, using a set of individual quality indicators of stone walls, the number and location of sections in which quality indicators are determined are specified, technical inspection is supplemented with instrumental measurements of the geometric dimensions of transversely reinforced stone walls in dangerous sections, measurements of the diameters of the mesh reinforcement, mesh sizes and pitch grids, mounted stone and mortar strength, size and shape of the stone, masonry joints thickness and quality of the fill, define cross-sectional area and transverse reinforcement of masonry; identify a scheme for heating dangerous sections of stone walls in a fire; experimentally determine the density of masonry, its moisture in a natural state, the indicators of thermal conductivity, heat capacity and thermal diffusion of masonry in a fire; find temporary resistance to masonry compression; the degree of reinforcement of dangerous sections of stone walls; set the standard load on the stone walls when tested for fire resistance, the value of the intensity of power stresses in dangerous sections, using the obtained unit quality parameters of transversely reinforced stone walls:

m _o - coefficient of the conditions for heating the cross section of the walls (1 ÷ 5);

k ₀ is the coefficient of the conditions of bearing walls on the base (0.75 ÷ 1.0);

J _σk is the intensity of power stresses in dangerous sections of transversely reinforced stone walls (0 ÷ 0.95);

h is the minimum size of the thickness of the stone walls, mm;

φ _s is the coefficient of longitudinal bending of stone walls with transverse mesh reinforcement (0.05 ÷ 1.0);

µ ₀ is the percentage of masonry reinforcement by volume (0.1 ÷ 1.0)%;

D _sk - an indicator of thermal diffusion of reinforced masonry, mm ² / min;

R _sku - temporary compression resistance of reinforced masonry, MPa;

- calculate the fire resistance of stone walls with transverse mesh reinforcement by loss of bearing capacity F _{u (R)} , min, by the formula (1):

the fire resistance of reinforced stone walls by the loss of heat-insulating ability f _{u (J)} , min, is calculated by the formula (2):

the fire resistance limit for integrity loss F _{u (E)} , min, stone walls without openings is taken equal to 0.99 · F _{u (R)} , min, calculated by the formula (3):

the actual fire resistance of stone walls with transverse mesh reinforcement according to three limit states F _{u (REJ)} , _min , min, is taken from the smallest of the values calculated by formulas (1) ÷ (3).

The next feature of the proposed method is that the value of the coefficient of the conditions for heating the cross section of the wall (m _o ) is determined by the formula (4):

where P and P _o - respectively, the full perimeter of the cross section of the wall and part of the perimeter, heated in case of fire, mm

A feature of the proposed method lies in the fact that the intensity of power stresses in a dangerous section of load-bearing stone walls from the standard load during fire tests is determined from the condition (5):

where γ _n is the level of responsibility of the walls of the building;

R _u ; R - respectively, the temporary resistance and the calculated compression resistance of the masonry, MPa;

N _ρ - normative load during fire tests of reinforced stone walls, kN;

N _cc - load-bearing capacity of reinforced stone walls when tested for fire resistance, kN.

A feature of the proposed method is that the transverse mesh reinforcement of masonry in volume is determined by the formula (6):

where µ ₀ is the percentage of masonry reinforcement by volume (%);

V _s ; V _k - volumes of mesh reinforcement and masonry, mm ³ .

A feature of the proposed method is that the coefficient of longitudinal bending of stone walls with transverse mesh reinforcement is determined without using normative tables according to the formula (7):

where φ _s is the coefficient of longitudinal bending of stone walls with transverse mesh reinforcement (0.05 ÷ 1.0);

ξ _к is the deformability index of masonry walls with mesh reinforcement, calculated by the dependence (8):

or

where h is the minimum thickness of the stone walls, mm;

r is the radius of inertia of the section, mm;

l ₀ - the estimated height of the stone walls, mm;

α _sk is the elastic characteristic of the masonry with mesh reinforcement, determined by the formula (9):

α is the elastic characteristic of unreinforced masonry, taken depending on the type of masonry and the strength of the solution (200 ÷ 1500);

R _u ; R _sku - respectively, temporary compressive strength of unreinforced and reinforced masonry, MPa.

A feature of the proposed method is that the coefficient of the conditions of the platform supporting the stone walls on an elastic base is calculated by the formula (10):

where δ _CHF - the thickness of the horizontal weld joint platform in place a stone wall and an elastic base (5≤δ _Swiss ≤20 mm).

A feature of the proposed method is that the temporary resistance of masonry with transverse mesh reinforcement during axial compression is determined by the formula (11):

where R _sku ; R _u - respectively, temporary compressive strength of reinforced and unreinforced masonry, MPa;

R _sn - regulatory resistance of the reinforcement in the masonry, MPa;

µ _about - the percentage of masonry reinforcement by volume, (%).

A feature of the proposed method is that the thermal diffusion index of the reinforced masonry at t _m = 450 ° C is determined by the formula (12):

where µ _o is the percentage of masonry reinforcement by volume, (%);

D _sk - an indicator of thermal diffusion of reinforced masonry, mm / min.

D _sm = 462.4 mm ² / min - an indicator of thermal diffusion of reinforcing steel;

D _KK - the indicator of thermal diffusion of unreinforced masonry, mm ² / min, determined by the formula (13):

where λ _about ; With _about - respectively, the thermal conductivity (W / (m · ° C)) and specific heat (kJ / (kg · ° C)) unreinforced masonry at t _n = 20 °;

b; d - thermal indicators of thermal conductivity (W / (m · ° C)) and heat capacity (kJ / (kg · ° C)) of masonry at an averaged temperature t _m = 450 ° C;

γ _about ; ω is the density of the unreinforced masonry in the dry state, kg / m ³ , and its moisture content under operating conditions,%, by weight.

A feature of the proposed method is that for the individual quality indicators of transversely reinforced stone walls of the building, affecting the value of the fire resistance limit, take: the geometric dimensions of the dangerous section, the height and thickness of the walls, the conditions of abutment of the walls on the base, the thickness of the masonry joints and the horizontal joint in the assembly the junction of the walls and the base; temporary compressive strength of reinforced and unreinforced masonry, percentage of transverse reinforcement with nets by volume of masonry, class of reinforcement in tensile strength, standard resistance of reinforcement in reinforced masonry; elastic characteristics of reinforced and unreinforced masonry, longitudinal bending parameters of reinforced stone walls, moisture, density, thermal conductivity and specific heat of reinforced and unreinforced masonry, thermal diffusion of masonry; bearing capacity of reinforced stone walls; standard load on stone walls when tested for fire resistance; the magnitude of the intensity of power stresses in their dangerous sections.

A feature of the proposed method lies in the fact that non-destructive tests are carried out for a group of transverse reinforced stone walls of the same type, the differences between the strength of the masonry and the fluidity of the reinforcement are mainly due to a random factor.

A feature of the proposed method is that the number of tests n _{uc of a} single quality indicator of transversely reinforced stone walls, with a probability of a result of 0.95 and an accuracy of 5%, is taken according to the formula (14):

where υ is the sample coefficient of variation of the test results,%.

A feature of the proposed method is that the heating pattern of the cross sections of the test stone walls in a fire is determined depending on the actual location of the building parts.

A feature of the proposed method is that in the case when all the individual quality indicators of the transversely reinforced stone walls, with M more than 9 pieces, are within the control limits, the minimum integer number of walls in the sample according to the plan of shortened tests M _min , pieces, is assigned from the condition (fifteen):

where M is the number of similar structures in the building, pcs.

A feature of the proposed method is that in the case when at least one of the individual quality indicators of the transversely reinforced stone walls goes beyond the control limits, the minimum number of walls in the sample according to the norm (M _n , pcs) is calculated by the formula (16):

A feature of the proposed method lies in the fact that in the case when at least one of the individual quality indicators of transversely reinforced stone walls goes beyond the boundaries of permissible limits or M≤5 pcs, all the same type of building walls are subjected to non-destructive testing individually.

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

The elimination of fire tests of the stone walls of an existing building and their replacement with non-destructive tests reduces the complexity of determining their fire resistance, extends the technological capabilities of detecting the actual fire resistance of variously loaded stone walls of any size, makes it possible to test stone walls for fire resistance without disturbing the functional process of the building under study, as well as comparing the results with standard tests of similar unreinforced stone walls and preserving eniya serviceability surveyed the building without disturbing the bearing capacity of its structures during the test. Therefore, the conditions for testing stone walls for fire resistance are greatly simplified.

Reducing the economic costs of testing include reducing the cost of the construction and fire tests of structural samples.

The use of a mathematical description of the process of resistance of unreinforced stone walls to standard thermal testing and the use of constructed parametric nomograms increase the accuracy and expressiveness of their fire resistance assessment.

The use of polyparametric dependence (1) is convenient due to the simplicity and the possibility of solving inverse fire resistance problems of transversely reinforced stone walls and the application of the method of selecting variable values of their design parameters.

The use of integral parameters, such as the degree of stress of the calculated section of the stone walls and the thermal diffusion index of the masonry, simplifies the mathematical description of the process of wall resistance by the sign of loss of heat-insulating ability.

The proposed technical solution provides for testing not one, but groups of the same type of stone walls. This allows you to 5-15 times increase the number of tested structures and increase the reliability of the test results and technical inspection of the building. Determination of the fire resistance of stone walls by only one quality indicator, for example, by the thickness of walls or partitions, leads, as a rule, to underestimating their fire resistance limit, since the effect on it of variations of individual quality indicators of stone walls 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 assessment of the fire resistance of stone walls is provided for not by one indicator, but by a set of individual indicators of their quality. This allows you to more accurately take into account the real fire resistance of stone walls.

The complex of individual quality indicators of stone walls that affect their fire resistance limits, determined by non-destructive tests, has been clarified.

The minimum number of non-destructive tests of a single quality indicator of unreinforced stone walls has been clarified. The accepted size of the sample from the total number of the same type of stone walls of the building provides reliability, reduces the time and complexity of testing.

Figure 1 shows the conditional strip of a stone wall with mesh reinforcement length l, mm, width b = 1000 mm, loaded with a uniformly distributed standard load N _ρ , kN / pog · m;

Figure 2 shows a cross section 1-1 of figure 1 of a stone wall with a thickness of h, mm; wall section heating scheme; reinforcement of the cross section of a stone wall;

Figure 3 shows a longitudinal section 2-2 of figure 1; wall section heating scheme; reinforcement of the longitudinal section with grids C1.

1 - stone wall with mesh reinforcement: longitudinal section with C1 stacks (mesh pitch, S, mm);

2 - heat flow of a standard fire, t _article , ° С;

3 - cross section of a stone wall with mesh reinforcement; section dimensions b × h;

4 - masonry seams filled with mortar and reinforcing nets with rod outlets to control the laying of nets;

5 - standard load N _ρ , kN / pog · m;

6 - rectangular reinforcing mesh C1 (diameter of the rods d, mm; mesh size C, mm);

7 - the heated part of the perimeter of the cross section of a stone wall, P _o , mm.

Thermophysical characteristics of building materials for masonry (including the values of D _km , mm ² / min) are given in table 1.

Table 1
Thermophysical characteristics of building materials Material Density ρ _s , kg / m ³ Humidity ω,% The parameters of thermal conductivity (W / m · ° C) and heat capacity of the material (kJ / kg · ° C) Heat diffusion _coefficient D _km (mm ² / min) λ ₀ b C ₀ d one 2 3 four 5 6 7 8 1. Wall masonry from expanded clay concrete stones (GOST 6133) on cement-sand mortar with a density of 1800 kg / m ³ 1.1 Stones, γ = 1200 kg / m ³ 1270 5 0.85 0.24 0.84 0.58 19.6 1.2 Stones, γ = 1000 kg / m ³ 1060 5 0.28 0.22 0.84 0.54 15.6 1.2 Stones, γ = 800 kg / m ³ 880 5 0.23 0.20 0.84 0.50 13.0 2. Wall masonry from small cellular concrete blocks on a cement-sand mortar (γ _о = 1200 kg / m ³ ) with a joint thickness of 12 mm 2.1 Blocks of gas and foam concrete, γ = 1000 kg / m ³ 1060 6 0.25 0.12 0.84 0.4 11.7 2.2 The same, γ = 800 kg / m ³ 880 6 0.22 0.12 0.84 0.4 10,4 2.3 The same, γ = 600 kg / m ³ 700 5 0.17 0.12 0.84 0.4 8.84 3. Cement, lime and gypsum mortars 3.1 Cement-sand 1800 2 0.58 0.35 0.84 0.63 20.1 3.2 Complex (sand, lime, cement) 1700 2 0.52 0.35 0.84 0.63 19.54 3.3 Calcareous 1600 2 0.47 0.35 0.84 0.63 19.23 3.4 Cement slag 1400 2 0.41 0.35 0.84 0.63 19.90 3.5 The same 1200 2 0.35 0.34 0.84 0.62 20.63 3.6 Cement perlite 1000 7 0.21 0.33 0.84 0.62 14.64 3.7 The same 800 7 0.16 0.32 0.84 0.62 15,52 3.8 Gypsum-perlite 600 10 0.14 0.31 0.84 0.60 17.26 3.9 The same, porous 500 6 0.12 0.30 0.84 0.60 21.56 3.10 The same 400 6 0.09 0.30 0.84 0.58 24.10 4. Brickwork of ceramic stone and brick on a cement-sand mortar (γ _о = 1800 kg / m ³ ) 4.1 Stone ceramic large-format hollow from porous ceramics, γ _about = 600 kg / m ³ 670 one 0.13 0.21 0.88 0.38 18.26 4.2 The same, γ _about = 800 kg / m ³ 890 one 0.18 0.22 0.88 0.40 16.95 4.3 Ceramic hollow stone (250 × 120 × 138 mm) γ _о = 800 kg / m ³ 960 one 0.2 0.22 0.88 0.40 16.84

Continuation of table 1 one 2 3 four 5 6 7 8 4.4. The same, γ _about = 1000 kg / m ³ 1130 one 0.26 0.23 0.88 0.42 17.95 4.5 The same, γ _about = 1200 kg / m ³ 1300 one 0.32 0.23 0.88 0.42 17.47 4.6 The same, γ _about = 1400 kg / m ³ 1460 one 0.39 0.23 0.88 0.42 18.12 4.7 Brick trepilny corpulent single thickened, γ _about = 900 kg / m ³ 1090 2 0.3 0.22 0.88 0.42 18.80 4.8 The same, γ _about = 1000 kg / m ³ 1170 2 0.34 0.22 0.88 0.42 19.26 4.9 Brick single hollow ceramic reinforced, γ _about = 1000 kg / m ³ 1170 one 0.28 0.22 0.88 0.42 17.37 4.10 The same, γ _about = 1200 kg / m ³ 1330 one 0.34 0.22 0.88 0.42 17.70 4.11 The same, γ _about = 1400 kg / m ³ 1480 one 0.4 0.22 0.88 0.42 18.10 4.12 Ceramic solid single thickened bricks, γ _о = 1600 kg / m ³ 1640 one 0.45 0.22 0.88 0.42 17.95 4.13 The same, γ _about = 1800 kg / m ³ 1800 one 0.56 0.22 0.88 0.42 17.0 4.14 The same, γ _about = 2000 kg / m ³ 1960 one 0.66 0.22 0.88 0.42 22.61 5. Brickwork of silicate brick and stone on a cement-sand mortar (γ _о = 1800 kg / m ³ ) 5.1 Full single brick, γ _about = 2000 kg / m ³ 1960 2 1.06 -0.36 0.88 0.61 21.91 5.2 The same, γ _about = 1800 kg / m ³ 1800 2 0.78 -0.35 0.88 0.60 24.1 5.3 Hollow single and thickened bricks, γ _о = 1600 kg / m ³ 1640 2 0.68 -0.35 0.88 0.60 26.41 5.4 Hollow 11-hollow thickened brick and stone, γ _о = 1400 kg / m ³ 1500 2 0.64 -0.35 0.88 0.60 15.44 5.5 Hollow 14-hollow thickened brick and stone, γ _о = 1300 kg / m ³ 1400 2 0.52 -0.35 0.88 0.60 12,42 5.6 The same, γ _about = 1200 kg / m ³ 1300 2 0.43 -0.35 0.88 0.60 10.1 5.7 Masonry of slag brick and stone (γ _о = 1400 kg / m ³ ) on a cement-sand mortar (γ _о = 1800 kg / m ³ ) 1500 1,5 0.52 -0.35 0.88 0.60 11.84 Here λ ₀ and C ₀ are the values of thermal conductivity, W / m · ° C, and heat capacity, kJ / kg · ° C, of building materials at t _n = 20 ° C, respectively;
bud - respectively, thermal coefficients of thermal conductivity and heat capacity of materials, multiplied by 1000.

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

The sequence of methods for determining the fire resistance of transversely reinforced stone walls of buildings is as follows.

First, a visual inspection of the building is carried out. Then determine the group of the same type of transversely reinforced stone walls and their total number in it. The sample size of the structures of the same type is calculated. Assign a set of individual quality indicators for stone walls that affect fire resistance. The conditions for fixing the ends and dangerous sections of the stone walls are revealed. The number of tests of a single indicator of the quality of stone walls is calculated depending on its statistical variability. Then, single quality indicators of transversely reinforced stone walls and their integral parameters are evaluated, and finally, the fire resistance of the tested walls is found from them.

Visual inspection means checking the state of stone walls, including identifying the conditions of fastening and loading of individual walls, determining the brand of brick and mortar, the presence of cracks and spalls, the minimum size of wall thickness, indicators of reinforcing walls with steel mesh (diameter of the rods, mesh size, mesh pitch, percentage masonry reinforcement; see table 2); class of reinforcement in tensile strength; conditions for heating the cross section of the walls, indicators of thermal diffusion of the reinforced masonry in case of fire, the elastic characteristic of the masonry; the standard load on the walls when tested for fire resistance.

During the inspection, groups of similar structural elements are determined. A group of structural elements in a building is understood to mean the same type of stone walls made and erected under similar technological conditions and under similar operating conditions.

For verification calculations of the bearing capacity of transversely reinforced stone walls, the height and thickness of the walls, the distance between the floors of the building, the ratio of the height of the wall to its thickness are determined;

type of stone walls: bearing, self-supporting, fire walls, partitions, from panels and large blocks, with facings;

type of supports of stone walls: rigid (l ₀ = 0.7 · N), elastic;

the thickness of the solution under the supports; expansion joints in the walls, the distance between the joints;

type of masonry: from brick or ceramic stones, from concrete or natural stones; from cellular concrete stones;

type of masonry, depending on the brands of brick and stones; masonry group depending on the grades of the solution; type of masonry: reinforced, unreinforced.

The minimum integer number of structures in the sample according to the plan of normal or reduced tests is assigned from the conditions (15 and 16).

Example 1. With the number of the same type of stone walls in the group M = 120 pieces, the number of subjects is taken according to the norm M _n = 5 + M ^0,5 = 5 + 120 ^0,5 = 16 pieces,

8 шт.according to the shortened plan M _min = 0.3 · (15 + M ^0.5 ) = 0.3 · (15 + 120 ^0.5 )

8 pcs

With the number of stone walls in the group M≤5, they are checked individually. The number and location of sites in which the quality indicators of stone walls are determined are determined as follows. In stone walls having one dangerous section, sections are placed only in this section. In stone walls having several dangerous sections, the test areas are placed evenly on the surface with the obligatory location of part of the sections in dangerous sections.

The main single quality indicators of transversely reinforced stone walls that determine fire resistance include: the geometric dimensions of the walls and the minimum dimensions of the thickness of the dangerous section; conditions of support and heating of the walls, the value of the coefficient of longitudinal bending; masonry compressive strength, humidity, density, thermal conductivity and heat capacity in natural conditions; masonry thermal diffusion index (thermal diffusivity) in a fire; percentage of masonry reinforcement; stress intensity in a dangerous section.

table 2
Percentage of reinforcement of cross sections of stone structures with steel grids (with the location of the grids in each masonry seam) Rebar diameter d, mm Cell Size C, mm 30 × 30 40 × 40 50 × 50 60 × 60 70 × 70 80 × 80 100 × 100 The percentage of steel reinforcement µ,% (volume) one 2 3 four 5 6 7 8 1. The grid spacing S = 77 mm (ordinary brick h = 65 mm) 3 0.61 0.46 0.37 0.31 0.26 0.23 0.18 four 1,1 0.82 0.66 0.55 0.47 0.41 0.33 5 1.7 1.27 1,02 0.85 0.73 0.64 0.51 6 2.45 1.84 1.47 1.23 1.05 0.92 0.74 2. The grid spacing S = 100 mm (thickened brick h = 88 mm) 3 0.47 0.36 0.28 0.24 0.2 0.18 0.14 four 0.84 0.63 0.5 0.42 0.36 0.32 0.25 5 1.31 0.98 0.78 0.65 0.56 0.49 0.39 6 1.89 1.42 1.13 0.94 0.81 0.71 0.57 3. The grid spacing S = 150 mm (stone h = 138 mm) 3 0.32 0.24 0.19 0.16 0.14 0.12 0.09 four 0.56 0.42 0.34 0.28 0.24 0.21 0.17 5 0.87 0.65 0.52 0.44 0.37 0.33 0.26 6 1.26 0.94 0.75 0.63 0.54 0.47 0.38

The number of tests of a single quality indicator of transversely reinforced stone walls, with a probability of a result equal to 0.95, and an accuracy rate of 5%, is determined by the formula (5); the coefficient of variation of the sample υ = ± 100 · σ / A;

arithmetic mean A = (l / n) · Σm _i (here m _i is the result of the i-th test);

standard deviation from mean σ = ± [(l / (n-1)) · Σ (x _i ) ² ] ^0.5 ; (here Σ (x _i ) ² is the sum of the squares of all deviations from the mean);

the average error ΔА = ± σ / (2 · n) ^0.5 .

Checked geometric dimensions are the minimum wall thickness and its height. Dangerous sections of stone walls are assigned in places of greatest moments from the action of the normative load during fire tests, taking into account changes in the coefficient of longitudinal bending of the walls along their height (length).

The dimensions of the walls are checked with an accuracy of ± 1 mm; crack width - with an accuracy of 0.05 mm; diameter of the rods - with an accuracy of 0.1 mm.

Strength testing of bricks, stones and mortar of stone structures included in the sample or checked individually, is performed by non-destructive tests using mechanical and ultrasonic devices [1, p.31-38].

Indices of masonry thermal diffusion under thermal exposure are determined at 450 ° C. To calculate its integral parameter by the formula (3), the density of the masonry and concrete in the natural state, their moisture content, as well as the thermal conductivity coefficients and the specific heat capacity of the masonry at 450 ° C are determined.

Using the obtained integral parameters m _o ; k _o ; φ _s ; h mm J _σk ; µ _about ; R _sku , MPa; D _sk , mm ² / min, according to dependence (1), the fire resistance of the transversely reinforced stone walls of the building is found, F _u , min.

The guaranteed fire resistance limit of stone walls F _{u (REJ)} , min, is calculated by the polyparametric dependence (1) with a corresponding change in design parameters: wall thickness h, mm, coefficient of heating and abutment walls m _o and k _o ; longitudinal bending φ _s , index of temporary compressive strength of masonry R _sku , MPa, thermal diffusion of masonry, D _sk , mm ² / min, intensity of stress stress J _σк .

Example 2. Determination of fire resistance of a stone wall with a thickness of 2 bricks (h = 510 mm) with mesh reinforcement by loss of integrity (E), bearing (R) and heat-insulating (J) ability.

Initial data: Wall made of clay plastic pressing brick of grade 100 on a solution of grade 75;

the estimated wall height l _o = 3000 mm;

calculated longitudinal force N = 1250 kN (125 tf);

the eccentricity of the application of longitudinal force e = 50 mm;

continuous load N _dl = 0.9 · N = 0.9 · 1250 = 1125 kN (112.5 tf);

standard load N _ρ = N _dl / k _n = 1125 / 1.2 = 937.5 kN (93.75 tf);

the calculated cross-sectional area A = 0.51 · 1 = 0.51 m ² > 0.3 m ² ;

the elastic characteristic of unreinforced masonry a = 1000 (table 15 SNiP II-22-81);

design cross-section of the wall n × b = 510 × 1000 mm;

section heating - 1 sided; the full perimeter of the calculated cross section Р = 2 · (h + b) = 2 · (510 + 1000) = 3020 mm;

the heated part of the perimeter of the cross section Р _о = b = 1000 mm;

the coefficient of heating conditions for the calculated wall section is calculated by the formula (4):

m _o = (P / P _o ) ^1.2 = (3020/1000) ^{l, 2} = 3.77;

Thermal diffusion masonry of solid bricks of clay (γ = _about 2000 kg / m ³⁾ for cement-sand mortar (γ = _about 1800 kg / m ³⁾ of Table 1: D _kk = 22.61 mm ² / min ;

temporary masonry compressive resistance R _u = 2 · 1.7 = 3.4 MPA;

also, the estimated R = 1.7 MPa;

mesh reinforcement ⌀4 Bp-I (B500); R _s = 219 MPa;

mesh size C = 32 mm; mesh pitch - two rows of masonry - S = 154 mm;

the percentage of mesh reinforcement µ _o = 0.4%;

temporary compressive strength of the reinforced masonry - according to the formula (9):

R _sku = R _u + 2 · R _sn · µ _o / 100 = 3.4 + 2 · 243 · 0.4 / 100 = 5.3 MPA;

elastic characteristic of reinforced masonry

a _sk = a · R _u / R _sku = 1000 · 3.4 / 5.3 = 640;

the deformability index of masonry stone walls with mesh reinforcement is calculated by the formula (8):

ξ _sk = 0.75 · a _sk · (h / l _o ) ² = 0.75 · 640 · (510/3000) ² = 13.87;

the coefficient of longitudinal bending of a stone wall with mesh reinforcement is calculated by the formula (7):

φ _s = ξ _sk / (ξ _sk +1) = 13.87 / (13.87 + 1) = 0.93;

with a coefficient of thermal conductivity of the steel reinforcement D _{s, cm} = 462.4 mm ² / min and the laying of the clay brick _kk D = 22.61 mm ² / min Thermal diffusion stone masonry wall with reinforcing mesh is calculated by the formula (12) :

D _sk = (µ _o · D _{s, cm} + (100-µ _o ) · D _kk ) / 100 = (0.4 · 462.4 + (100-0.4) · 22.61) / 100 = 24 , 37 mm ² / min;

the design resistance of the reinforced masonry is calculated by the formula (27) SNiP II-22-81:

R _{sk, 1} = R + 2 · µ _o · R _s / 100 = 1.7 + 2 · 0.4 · 219/100 = 3.45 MPa> R _u = 3.4 MPa, take R _sk = 3, 4 MPa;

the bearing capacity of N _cc , kN, of stone walls with mesh reinforcement (with m _o = 1; ω = 1) is calculated by the formula (29) SNiP II-22-81:

N _cc = m _g · φ _s · R _sk · A · (1-2 · e _o / h) · ω = 1 · 0.93 · 3.4 · 0.51 · 10 ³ (1-2 · 50 / 510) 1 = 1290 kN (129 tf);

the bearing of the walls on an elastic base with δ _wel = 20 mm, - k _o = 0.75;

level of responsibility of building II (second): coefficient of the level of responsibility of structures (SNiP 2.01.07-85 *, adj. 7): γ _n = 0.95;

the intensity of power stresses in a dangerous section of stone walls (N · 2/3) is calculated by the formula (5):

J _σk = γ _n · (N _ρ / N _cc ) · (R / R _u ) = 0.95 · (937.5 / 1290) · (1.7 / 3.4) = 0.345.

The fire resistance of a transversely reinforced stone wall by the loss of bearing capacity F _{u (R)} , min, is calculated by the formula (1):

The fire resistance of a transversely reinforced stone wall by integrity loss F _{u (E)} , min, is calculated by the formula (3):

F _{u (E)} = 0.99 · F _{u (R)} = 0.99 · 1255 = 1240 min (20.7 h).

The fire resistance of a transversely reinforced stone wall by the loss of heat-insulating ability F _{u (J)} , min, is calculated by the formula (2):

F _{u (J)} = 4.5 · (h / D _sk ) ² = 4.5 · (510 / 24.37) ² = 1970 min (33 hours).

Therefore, the actual fire resistance limit of a transversely reinforced stone wall with a thickness of h = 510 mm in terms of loss of integrity, load-bearing and heat-insulating ability F _{u (REJ)} = 1240 min (20.7 hours).

Example 3. Determination of fire resistance of a stone wall with a thickness of h = 250 mm (1 brick) with mesh reinforcement.

The perimeter of the calculated section of the partition:

P = 2 · (h + b) = 2 · (250 + 1000) = 2500 mm;

the heated part of the perimeter of the cross section P _o = b = 1000 mm;

the coefficient of the heating conditions of the calculated section is calculated by the formula (4):

m _o = (P / P _o ) ^1.2 = (2500/1000) ^1.2 = 3;

the deformability index of masonry stone walls with mesh reinforcement is calculated by the formula (8):

ξ _sk = 0.75 · a _sk · (h / l _o ) ² = 0.75 · 640 · (250/3000) ² = 3.33;

the coefficient of longitudinal bending of the stone wall - according to the formula (7):

φ _s = ξ _sk / (ξ _sk +1) = 3.33 / (3.33 + 1) = 0.77.

Next, we use the source data of the previous example: k _o = 0.75; J _σk = 0.36; µ _o = 0.4%; D _sk = 24.37 mm ² / min; R _sku = 5.3 MPA.

The fire resistance of a transversely reinforced stone partition with a thickness of h = 250 mm by the loss of bearing capacity F _{u (R)} , min, is calculated by the formula (1):

The fire resistance of a transversely reinforced stone partition with a thickness of h = 250 mm by integrity loss F _{u (E)} , min, is calculated by the formula (3):

F _{u (E)} = 0.99 · 390 = 385 min (6.4 h).

The fire resistance of a transversely reinforced stone partition with a thickness of h = 250 mm by the loss of heat-insulating ability F _{u (J)} , min, is calculated by the formula (2):

F _{u (J)} = 4.5 · (h / D _sk ) ² = 4.5 · (250 / 24.37) ² = 475 min (8 hours).

Therefore, the actual fire resistance limit of a transversely reinforced stone partition with a thickness of h = 250 mm F _{u (REJ)} = 385 min.

The proposed method was applied during field inspection of the stone partitions of a residential building in Samara. The results of non-destructive tests of reinforced stone partitions h = 250 mm; D _km = 24.2 mm ² / min; φ _o = 0.75; l _o = 3000 mm; J _σo = 0.36; m _o = 1.63; R _sku = 5.3 MPa; showed the limits of fire resistance: by loss of bearing capacity and integrity F _{u (RE)} = 210 min (3.5 hours); also, by the loss of heat-insulating ability F _{u (J)} = 475 min (8 hours); the actual (minimum) limit of fire resistance of the partition F _{u (REJ)} = 210 min (3.5 h).

Therefore, the claimed invention meets the condition of "industrial applicability".

Information sources

1. Ilyin N.A. The consequences of fire on reinforced concrete structures. - M.: Stroyizdat, 1979. - 128 p. (see p. 16; 34-35).

2. Buildings and fragments of buildings. The method of full-scale fire tests. General requirements: NPB 233-97. - M .: VNIIPO, 1997 .-- 14 p.

3. Fire resistance of buildings / V.P. Bushev, V.A. Pchelintsev, A.I. Yakovlev, etc. - M .: Stroyizdat, 1970. - 261 p. (see p. 252-256).

4. GOST 30247.1-94. Building constructions. Test methods for fire resistance. Bearing and enclosing structures. - M., 1995 .-- 7 p.

5. SNiP II-22-81. Stone and arched structures. Design Standards. - M .: Stroyizdat, 1983 .-- 40 p.

Claims (15)

1. A method for determining the fire resistance of transversely reinforced stone walls of a building by testing, including technical inspection, establishing grades of brick, stone and masonry mortar, steel grade, type of reinforcement, class of reinforcement according to tensile strength, identifying conditions of abutment and fastening of stone walls, establishing limit state on fire resistance, determining the time of occurrence of the limit state on fire resistance of transversely reinforced stone walls under standard load, differing in those m, that the test of the transversely reinforced stone walls of the building is carried out without destruction, using a set of individual quality indicators of the stone walls, the number and location of the sites in which the quality indicators are determined, technical inspection is supplemented by instrumental measurements of the geometric dimensions of the transverse reinforced stone walls in dangerous sections, by measuring the diameters of the mesh reinforcement, mesh sizes and mesh pitch, establish the strength of the stone and mortar, the size and shape of the stones, the thickness of the joint masonry and the quality of their fields define square cross section laying and transverse reinforcement; identify a scheme for heating dangerous sections of stone walls in a fire; experimentally determine the density of masonry, its moisture content in a natural state, the indicators of thermal conductivity, heat capacity and thermal diffusion of masonry in a fire; find temporary resistance to masonry compression; the degree of reinforcement of dangerous sections of stone walls; set the standard load on the stone walls when tested for fire resistance, the magnitude of the intensity of power stresses in dangerous sections, and using the obtained unit quality parameters of transversely reinforced stone walls:
m _o - coefficient of the conditions for heating the cross section of the walls (1 ÷ 5);
k ₀ is the coefficient of the conditions of bearing walls on the base (0.75 ÷ 1.0);
J _σk is the intensity of power stresses in dangerous sections of transversely reinforced stone walls (0 ÷ 0.95);
h is the minimum size of the thickness of the stone walls, mm;
φ _s is the coefficient of longitudinal bending of stone walls with transverse
mesh reinforcement (0.05 ÷ 1.0);
µ ₀ is the percentage of masonry reinforcement by volume (0.1 ÷ 1.0)%;
R _sku - temporary compression resistance of reinforced masonry, MPa;
D _sk - an indicator of thermal diffusion of reinforced masonry, mm ² / min,
calculate the fire resistance of stone walls with transverse mesh reinforcement by the loss of bearing capacity F _{u (R)} , min, by the formula (1)

fire resistance of reinforced stone walls by the loss of heat-insulating ability F _{u (J)} , min, calculated by the formula (2)
F _{u (J)} = 4.5 · (h / D _sk ) ² ;
the fire resistance limit for integrity loss F _{u (E)} , min, stone walls without openings is taken to be 0.99 · F _{u (R)} , min, calculated by the formula (3)
F _{u (E)} ≈0 99 · F _{u (R)} ;
the actual fire resistance of stone walls with transverse mesh reinforcement according to three limit states F _{u (REJ), min} , min, is taken from the smallest of the values calculated by formulas (1) ÷ (3). 2. The method according to claim 1, characterized in that the value of the coefficient of the conditions for heating the cross section of the wall (m ₀ ) is determined by the formula (4)
m ₀ = (P / P _o ) ^1,2 ,
where P and P _o - respectively, the full perimeter of the cross section of the wall and part of the perimeter, heated in case of fire, mm 3. The method according to claim 1, characterized in that the intensity of the power voltage in a dangerous section of the bearing stone walls from the standard load during fire tests is determined from the condition (5)
J _σk = γ _n · (R / R _u ) · (N _ρ / N _cc ),
where γ _n is the coefficient of the level of responsibility of the walls of the building;
R _u ; R - respectively, the temporary resistance and the calculated compression resistance of the masonry, MPa;
N _ρ - normative load during fire tests of reinforced stone walls, kN;
N _cc - load-bearing capacity of reinforced stone walls when tested for fire resistance, kN. 4. The method according to claim 1, characterized in that the transverse mesh reinforcement of the masonry in volume is determined by the formula (6)
μ ₀ = (V _s / V _k ) 100
where µ ₀ ^{_ the} percentage of reinforcement of the masonry by volume,%;
V _s ; V _k - volumes of mesh reinforcement and masonry, mm ³ . 5. The method according to claim 1, characterized in that the coefficient of longitudinal bending of stone walls with transverse mesh reinforcement is determined without using regulatory tables according to the formula (7)
φ _s = ξ / (ξ _to +1)
where φ _s is the coefficient of longitudinal bending of stone walls with transverse mesh reinforcement (0.05 ÷ 1.0);
ξ _к - deformation index of masonry walls with mesh reinforcement, calculated according to dependences (8) and (8a)
ξ _k = 0.75 · α _sk · (h / l ₀ ) ² ;
or
ξ _k = 9 · α _sk · (r / l ₀ ) ² ;
where h is the minimum thickness of the stone walls, mm;
r is the radius of inertia of the section, mm;
l ₀ - the estimated height of the stone walls, mm;
α _sk is the elastic characteristic of the masonry with mesh reinforcement, determined by the formula (9)
α _sk = α · R _u / R _sku ;
α is the elastic characteristic of unreinforced masonry, taken depending on the type of masonry and the strength of the solution (200 ÷ 1500);
R _u ; R _sku - respectively, temporary compressive strength of unreinforced and reinforced masonry, MPa. 6. The method according to claim 1, characterized in that the coefficient of the conditions of the platform supporting the stone walls on an elastic base is calculated by the formula (10)
k ₀ = 0,85- (δ _CHF -5) / 150;
where δ _CHF - the thickness of the horizontal weld joint platform in place rock wall with an elastic base (5 <δ _CHF <20 mm). 7. The method according to claim 1, characterized in that the temporary resistance of the masonry with transverse mesh reinforcement with axial compression is determined by the formula (11)
R _sku = R _u + 2 · R _sn · µ _o / 100;
where R _sku ; R _u - respectively, temporary compressive strength of reinforced and unreinforced masonry, MPa;
R _sn - regulatory resistance of the reinforcement in the masonry, MPa;
µ _about - the percentage of masonry reinforcement by volume,%. 8. The method according to claim 1, characterized in that the thermal diffusion index of the reinforced masonry at t _m = 450 ° C is determined by the formula (12)
D _sk = (µ _o · D _sm + (100-µ _o ) · D _kk ) / 100;
where µ _o is the percentage of masonry reinforcement by volume,%;
D _sk - an indicator of thermal diffusion of reinforced masonry, mm ² / min;
D _sm = 462.4 mm ² / min - an indicator of thermal diffusion of reinforcing steel;
D _KK - the indicator of thermal diffusion of unreinforced masonry, mm ² / min, determined by the formula (13)

where λ _o ; With _o - respectively, the coefficient of thermal conductivity (W / (m · ° C)) and specific heat (kJ / (kg · ° C)) unreinforced masonry at t _n = 20 °;
b; d - thermal indicators of thermal conductivity (W / (m · ° C)) and heat capacity (kJ / (kg · ° C)) of masonry at an averaged temperature
t _m = 450 ° C;
γ _o ; ω is the density of the unreinforced masonry in the dry state, kg / m ³ , and its moisture content under operating conditions,% by weight. 9. The method according to claim 1, characterized in that for the individual quality indicators of the transversely reinforced stone walls of the building, affecting the value of the fire resistance limit, take the geometric dimensions of the dangerous section, the height and thickness of the walls, the conditions of abutment of the walls on the base, the thickness of the masonry joints and horizontal a seam at the junction of the walls and the base; temporary compressive strength of reinforced and unreinforced masonry, percentage of transverse reinforcement with nets by volume of masonry, class of reinforcement in tensile strength, standard resistance of reinforcement in reinforced masonry; elastic characteristics of reinforced and unreinforced masonry, longitudinal bending parameters of reinforced stone walls, moisture, density, thermal conductivity and specific heat of reinforced and unreinforced masonry, thermal diffusion of masonry; bearing capacity of reinforced stone walls; standard load on stone walls when tested for fire resistance; the magnitude of the intensity of power stresses in their dangerous sections. 10. The method according to claim 1, characterized in that non-destructive tests are carried out for a group of the same type of transversely reinforced stone walls, the differences between the strength of the masonry and the fluidity of the reinforcement which are caused mainly by a random factor. 11. The method according to claim 1, characterized in that the number of tests n _{and a} single quality indicator of transversely reinforced stone walls with a probability of a result of 0.95 and an accuracy of 5% are taken according to the formula (14)
n _is = 0.15 · υ ² ≥6,
where υ is the sample coefficient of variation of the test results,%. 12. The method according to claim 1, characterized in that the heating pattern of the cross sections of the test stone walls in a fire is determined depending on the actual location of the parts of the building. 13. The method according to claim 1, characterized in that in the case when all individual quality indicators of transversely reinforced stone walls with M more than 9 pcs. are within the control limits, the minimum integer number of walls in the sample according to the plan of shortened tests M _min , pcs. appoint from condition (15)
M _min = 0.3 · (15 + M ^0.5 ) ≥5,
where M is the number of similar structures in the building, pcs. 14. The method according to claim 1, characterized in that in the case when at least one of the individual quality indicators of the transversely reinforced stone walls goes beyond the control limits, the minimum number of walls in the sample according to the norm (M _n , pcs.) Is calculated by the formula (16)
M _n = 5 + M ^0.5 ≥8. 15. The method according to claim 1, characterized in that in the case when at least one of the individual quality indicators of the transversely reinforced stone walls goes beyond the permissible limits or M≤5 pieces, all the same type of building walls are subjected to non-destructive testing individually.

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