RU2518599C1 - Method of flame retardance of i-shaped building column - Google Patents

Abstract

FIELD: fire safety.

SUBSTANCE: steel column I-beam is equipped with fastening nuts and set screws with countersunk heads and with a screwed pointed end. The elements of the face sheet are attached closely to the shelves of the column I-beam, the elements of facing slabs - close to the wall of the I-beam. The element thickness of the fireproofing facing is determined in advance, taking into account its thermophysical properties of materials and the heating conditions of the shelves and the wall of the I-beam in a fire.

EFFECT: improvement of reliability of fastening the elements of large size facing, increase in fire-resistance rating of the steel column, reduction of risk of breakdown of the column in the initial stage of fire.

12 cl, 2 dwg, 1 tbl

Description

The invention relates to the field of fire safety of buildings and structures (hereinafter referred to as buildings) and relates to a method of constructive fire protection of a steel supporting rod of a column made in the form of a column I-beam, using large-sized sheet, plate and roll cladding as the cladding material.

Unprotected steel structures of a building when exposed to fire in a fire quickly (after 15 ÷ 20 min) lose their bearing capacity, collapse themselves and contribute to the collapse of other building structures, which leads to significant material losses.

A known method of fire protection of an I-beam of a building, including fire-resistant lining of a steel I-beam with reinforced concrete slabs of cellular concrete, hollow-core gypsum slabs or plates, vermiculite slabs and asbestos-cement sheets; Bartellemi B., Kriupa J. Fire resistance of building structures / trans. with french - M.: Stroyizdat, 1985, - 216 p. (Chap. 4; Sec. 4.2. Materials and methods of protection, Fig. 4.2; 4.4-4.6; p. 94 ÷ 98) / [1].

The reasons that impede the achievement of the technical result indicated below when using the known method of fire protection of an I-beam of a building include the fact that a significant number of carcass elements are used in the known method and, as a result, the consumption of fire protection material and metal for the manufacture of a carcass for fireproof cladding is increased; when designing voids and gaps between the wall and the flanges of the I-beam and the plates of the protective lining, increase the cross-sectional dimensions of the lined column (the cross-sectional area increases by 75 ÷ 85%), reducing the design limit of fire resistance of the fireproof column by 25 ÷ 30%; reliability of fastening of elements of large-sized sheet and plate cladding is reduced; reduce the corrosion resistance of the steel supporting rod and maintainability fire retardant cladding (if possible mechanical damage and through spalls).

A known method of fire protection of an I-beam column of a building containing a steel I-beam and fire-retardant cladding of large-sized sheets and plates mounted on the relate, the gap between the fire-retardant cladding and the faces of the protected steel supporting rod take at least 25 mm; the fireproof cladding frame is made in the form of a frame consisting of steel longitudinal and transverse elements with a height of 40 ÷ 75 mm; fastening the steel elements of the frame between themselves is carried out by self-tapping screws 5 × 25 ÷ 5 × 45; / Romanenkov I.G., Levites F.A. Fire protection of building structures. - M .: Stroyizdat, 1991 .-- 320 p. (Ch. 4 Constructive fire protection methods; Sec. 4.2 - Large-sized sheet, plate and roll cladding; Fig. 8, p.131-133) ./ [2].

The reasons that impede the achievement of the technical result indicated below when using the known method of fire protection of a building column include the fact that a significant number of carcass elements are used in the known method and, as a result, the metal consumption for the manufacture of a carcass for fireproof cladding is increased; when designing voids and gaps between the wall and the flanges of the I-beam and the plates of the protective lining, increase the cross-sectional dimensions of the lined column (the cross-sectional area increases by 80 ÷ 95%; the consumption of lining materials - by 45 ÷ 50%), reducing the design limit of fire resistance of the fireproof column by 25 ÷ thirty%; reliability of fastening of elements of large-sized sheet and plate cladding is reduced; the corrosion resistance of the steel supporting rod and the maintainability of the fireproof lining are reduced (if it is possible to obtain mechanical damage and through spalls).

A known method of fire protection of an I-beam column of a building, in which a steel supporting rod with anchors on its side faces, is equipped with a frame made of C-shaped profiles, consisting of longitudinal elements with bends along the edges of the shelves and transverse elements; the cladding of sheet materials is attached at a ratio of 40 ÷ 50 mm with the formation of gaps between the flanges of the I-beam (the empty space between the shelves and the wall of the I-beam No. 20 and the cladding elements in the cross section of the fire-resistant column is A _empty = 650 cm ² ) / А.с. SU 887755 MKI-3 Е04В 1/94 Building unit of the building / Yu.V. Pokrovsky, V.V. Fedorov, M.M. Karbochinsky and others; application 02.21.80; publ. 12/12/81; Bull. No. 45 / [3].

The reasons that impede the achievement of the technical result indicated below when using the known method of fire protection of an I-beam of a building include the fact that a significant number of carcass elements are used in the known method and, as a result, the metal consumption for the manufacture of a carcass for fireproof cladding is increased; when designing voids and gaps between the wall and the flanges of the I-beam and the plates of the protective lining, increase the cross-sectional dimensions of the lined column (the cross-sectional area increases by 60 ÷ 70%; the consumption of lining materials - by 40 ÷ 45%), reducing the design limit of fire resistance of the fireproof column by 25 ÷ thirty%; reliability of fastening of elements of large-sized sheet and plate cladding is reduced; the corrosion resistance of the steel supporting rod and the maintainability of the fireproof lining are reduced (if it is possible to obtain mechanical damage and through spalls).

The closest technical solution to the invention in terms of features is a method of fire protection of an I-beam column of a building, in which the steel supporting rod is formed by frame elements and sheet cladding, which is attached to the frame on the relate; frame elements are made of steel profiles with bends, and the supporting rod is provided with anchors, providing a gap of 60 ÷ 80 mm between the supporting rod and the lining. Cladding elements of sheet material are fixed to the frame elements with self-tapping screws; / A.S. SU No. 773218 MKI-3 Е04В 1/94 Building element / Yu.V. Pokrovsky, V.V. Fedorov and others; declared 04/13/79; publ. 10.23.80, Bull. No. 39 / [4] - taken as a prototype.

For reasons that impede the achievement of the technical result indicated below when using the known method of fire protection of an I-beam of a building adopted as a prototype, the known method uses a significant number of frame elements and, as a result, increases the metal consumption for the manufacture of a frame for fireproof cladding; when designing voids and gaps between the wall and the flanges of the I-beam and the plates of the protective lining, increase the cross-sectional dimensions of the lined column (the cross-sectional area increases by 75 ÷ 85%), reducing the design limit of fire resistance of the fireproof column by 25 ÷ 30%; reliability of fastening of elements of large-sized sheet and plate cladding is reduced; the corrosion resistance of the steel supporting rod and the maintainability of the fire retardant lining are reduced (if it is possible to obtain mechanical damage and through spalls); it is not justified to determine the thickness of the elements of sheet fire-retardant cladding of the steel supporting rod of the column, depending on the degree of fire resistance of the building and the thermophysical properties of the cladding materials.

The invention consists in the following.

 The problem to which the claimed invention is directed, consists in a rational way to increase fire resistance and operational reliability of a fire-protected I-beam of a building, as well as to improve fire-technical and economic indicators of fire protection of steel structures of buildings.

EFFECT: increased reliability of fastening of elements of a large-sized sheet and plate fire-retardant lining of an I-beam column and frame elements for it; reduction in the number of frame elements for fire retardant cladding; weight reduction of metal and facing materials; simplification of the manufacture of fire-retardant cladding frame elements; a decrease in the cross-sectional area of the fire-protected double tee column by 75 ÷ 95%; increasing the fire resistance of a steel column with a supporting rod in the form of a column I-beam by 25 ÷ 30%; increased safety during fire fighting and rescue and recovery operations; reduction of possible fire losses; improving the reliability of the fireproof columns during normal operation of the building and in a fire; simplification of installation of frame elements and fire retardant cladding; increasing the rigidity of the connection of the columnar I-beams with sheets and plates of the cladding and the resistance of the fire retardant cladding to mechanical stress; increasing the efficiency of fire protection of a steel supporting rod with a large-sized cladding; increasing the corrosion resistance of the steel column I-beam and the maintainability of fire retardant cladding in the event of local mechanical damage; reducing the complexity of mounting frame elements and fire retardant cladding elements; reduction in welding and wet construction processes; substantiation by the engineering calculation of the thickness of the elements of the sheet and plate fire-retardant cladding of a steel column I-beam depending on the degree of fire resistance of the building, the thermal diffusion of the cladding materials and the heating conditions of the shelves and walls of the I-beam in case of fire.

The specified technical result when using the invention is achieved by the fact that in the known method of fire protection of an I-beam of a building in which the bearing rod is equipped with sheet cladding, the feature is that the bearing rod is made in the form of a steel column I-beam and each end of the steel bearing rod is provided with fixing nuts and installation nuts countersunk screws and screwed-in pointed ends and straight slot; set screws to the shelves of the columnar I-beam fasten contact, closely elements of the sheet fire-retardant cladding, to the wall of the I-beam fasten contact, flush elements of the plate fire-retardant lining; the thickness of the cladding elements is determined taking into account the thermal diffusion of its materials, the heating conditions of the shelves and walls of the I-beam and the degree of fire resistance of the building.

Other features of the method are that the anticorrosion layer is preliminarily applied to the surface of the steel supporting rod. Elements of sheet fire retardant cladding are made of gypsum cladding sheets. Elements of a plate fireproof cladding are in the form of plates of basalt fiber. The elements of the flame retardant cladding are in the form of Rockwool mineral wool slab products.

The length of the screwed end of the set screw into the elements of the plate fire-retardant cladding takes at least l _min ≥0.2 · h, - here h is the height of the steel column I-beams. The outer surfaces of the fire retardant cladding elements are covered with a layer of fiberglass. The outer surfaces of the elements of the fireproof columns are plastering. The thickness of the elements of fire retardant cladding δ _{o, mp,} mm, column I-beam is determined by the mathematical expression (1):

$${\delta }_{o,mp}=0.7\cdot C\cdot D^{0.8}{}_{ar}/m_o\text{,}(\mathrm{one})$$

where C is the degree of fire protection of a steel column I-beam;

D _ar is an indicator of thermal diffusion of the cladding material, mm ² / min;

m _o - an indicator of the heating conditions of the column I-beam (0.5 ÷ 1).

The value of the fire protection limit of a separate layer of complex cladding τ _{u, co} , min, calculated by the formula (2):

$${\tau }_{u,co}=65\cdot m_o\cdot {({\delta }_{co}/D_{ar})}^{1.41}\text{,}(2)$$

where m _o - an indicator of the heating conditions of the cladding layer, (0.5 ÷ 1);

δ _co - the thickness of a single layer of fire retardant cladding, mm;

D _ar is the thermal diffusion index of the cladding material, mm ² / min (Table 1).

Table 1 Indicators of thermal diffusion of materials, D _ar , mm ² / min, fire retardant lining Material D _ar , mm ² / min one 2 1. Plaster plates and sheets; drywall 1.1. Fireproof gypsum plasterboard sheets, ρ = 1200 kg / m ³ , ω = 4% 19.9 1.2. Plasterboard sheets standard (GKL), ρ = 1100 kg / m ³ , ω = 4% 19.1 1.3. Plaster plates (GOST 6428); ρ = 1200 kg / m ³ , ω = 4% 19,4 1.4. Plaster plates (GOST 6428); ρ = 1100 kg / m ³ , ω = 4% 17.8 1.5. Facing gypsum sheets (dry plaster; GOST 6266; ρ = 800 kg / m ³ , ω = 5% 17.6 2. Stucco 2.1. Gypsum dry; ρ = 900 kg / m ³ , ω = 20% 10.5 2.2. Perlite on gypsum; ρ = 600 kg / m ³ , ω = 10% 9.7 2.3. Perlite-vermiculite; ρ = 600 kg / m ³ , ω = 10% 10,2 2.4. Perlite on cement; ρ = 400 kg / m ³ , ω = 8% 17.0 2.5. Cement-sand; ρ = 1930 kg / m ³ , ω = 2% 24.2 2.6. Cement-sand; ρ = 1600 kg / m ³ , ω = 2% 19.0 2.7. Cement-lime-sand; ρ = 1700 kg / m ³ 21.0 3. Mineral-wool products “Rockwool” 3.1. Plate P 200; ρ = 200 kg / m ³ , ω = 5% 17.9 3.2. Plate P 150; ρ = 150 kg / m ³ , ω = 5% 22.9 3.3. Plate P 100; ρ = 100 kg / m ³ , ω = 5% 33.5 3.4. Mats M-50; ρ = 50 kg / m ³ , ω = 5% 68.8 3.5. Mats M-35; ρ = 35 kg / m ³ , ω = 5% 99.6 Note - ρ is the density of the material, kg / m ³ ; ω is the humidity,%; D _ar - an indicator of thermal diffusion of the cladding material, mm ² / min

The indicator of the heating conditions of the column of an I-beam is calculated by the power equation (3):

$$m_o={0.7}^{\delta x/\delta \mathrm{at}}\text{,}(3)$$

where δ _x and δ _y - the thickness of the flange of the column I-beam along the axes X and Y, mm

The causal relationship between the totality of the features and the technical result of the invention is as follows: the use of the proposed method of fire protection of the I-beam of the building provides the simplicity and reliability of fastening the elements of large-sized cladding and frame elements for it through the use of set screws with countersunk head with a long screwed pointed end and hard connection (welding) of the fixing nut to the shelves of the column I-beam; a reduction in the mass of metal for the manufacture of carcass elements of the fire-retardant cladding is performed by reducing the number of carcass elements; a 75–95% reduction in the cross-sectional area of the fireproof I-beam column due to the lack of void space between the steel supporting rod and the lining; increasing the fire resistance of a steel column with a supporting rod in the form of a column I-beam by 25 ÷ 35% due to the filling of the void space inside the cross section of the column; increasing safety during extinguishing during emergency rescue and restoration operations, as well as reducing losses from fire due to increased fire resistance limits of the building's supporting structures; improving the reliability of the fire-protected columns during normal operation of the building and in fire conditions is possible due to increased rigidity in contact with the column I-beams with sheets and cladding plates, as well as designing the thickness of the cladding elements according to the proposed calculation method, depending on the fire resistance of the building, thermal diffusion indicators of the cladding materials and conditions for heating shelves and walls of an I-beam in case of fire.

Figure 1 shows a cross section of a fire-resistant I-beam with contact attachment of sheet and plate cladding elements to a steel supporting rod, where the following notation is adopted: 1 - steel column I-beam; 2 - anti-corrosion layer; 3 - sheet fireproof lining; 4 - plate fireproof lining; 5 - set screws (with countersunk head with a screwed-in pointed end and a straight slot); 6 - fixing nut (for the set screw); 7 - countersunk head of the set screw; 8 - asbestos cord; 9 - fiberglass (plaster); 10 - adhesive layer; mortar (b and h are the width of the shelf and the height of the I-beam; B and H are the width and height of the cross-section of the fireproof column; d and δ _s are the thickness of the wall and shelves of the I-beam; δx and δy are the thickness of the fire protection of the I-beam along the X and Y axes).

Figure 2 shows a cross-section of a fire-resistant column with a steel supporting rod in the form of a column I-beam No. 20 K-2 (legend No. 1 ÷ 10 is shown in _figure 1; here δ _GKLO and δ _Roc are the thickness of the sheet and plate fire-retardant lining, respectively ); for example, calculation.

Information confirming the possibility of applying the invention to obtain the above technical result.

During the reconstruction of the university’s academic building, the project provides for fireproof steel columns from a rolling profile. Characteristics of the building and its supporting columns: functional fire hazard class - F 4.2; degree of fire resistance - I (first); class of constructive fire hazard - СО (not fire hazardous); number of floors - 6; the required fire resistance of the supporting column F _{and, n} = 120 min (Table 21, Federal Law of the Russian Federation No. 123-2009); steel supporting rod - column I-beam No. 20 K-2, the height of the I-beam h = 198 mm; shelf width b = 200 mm, wall thickness d = 7 mm; shelf thickness δ _s = 11.5 mm; the cross-sectional area of the I-beam A = 53 cm ² .

Fire protection of the I-beam shelves - sheet fireproof lining - fireproof gypsum plasterboard (GKLO) with a thickness of δ ₁ = 12.5 mm; fire protection of the I-wall - plate fire-retardant lining - mats from rockwool M-50 mineral wool.

The degree of fire protection of the columned tee is calculated by the mathematical expression (2):

$$C=In({\tau }_{uo}/48\cdot {(\mathrm{one}-J_{\sigma s})}^3),(\mathrm{four})$$

at the intensity of power stresses J _σs = 0.5;

$$C=In(0.2\cdot {\tau }_{uo}),(5)$$

where C is the degree of fire protection of the column I-beam, cm;

τ _uo - fire protection limit of cladding elements, min;

In is the natural logarithm.

The fire protection limit of the cladding is calculated by the formula (6):

$${\tau }_{uo}=F_{u,mp}-{\tau }_{us}\text{,}(6)$$

where F _{u, mp} is the required fire resistance of the supporting column, min;

τ _us - fire resistance of the column I-beam without fire-retardant lining, min.

Construction work on the fire protection of the I-beam columns of the building is carried out at positive and negative air temperatures.

Example:

Given: steel supporting rod - column I-beam from a rolling profile No. 20 K-2; the required fire resistance limit of the supporting columns for the building of the I (first) degree of fire resistance F _{u, mp} = 120 min (Table 21 of the Federal Law No. 123-2009 g); fire resistance of a column I-beam without fire protection τ _us = 20 min; fire retardant lining of columns of a double tee - fireproof drywall sheets (GKLO), thermal diffusion index - D _GKLO = 20 mm ² / min; an indicator of the heating conditions of the I-beam shelves m ₀₁ = 0.75; lining of a wall of an I-beam - mineral wool mats M-50 of the Rockwool product; thermal diffusion index - D _Roc = 68.8 mm ² / min; the indicator of the heating conditions of the wall of the I-beam is m ₀₂ = 0.5 (with bilateral heat supply).

Determine the thickness of the elements of sheet and plate cladding.

Decision:

1) The limit of fire protection of the cladding is calculated by the formula (6):

τ _uo = F _{u, mp} -τ _us = 120-20 = 100 min.

2) The degree of fire protection of the columned I-beam with a complex cladding (with J _σs = 0.5) was calculated according to the logarithmic equation (5):

C = In (0.2 · τ _uo ) = In (0.2 · 100) = In20 = 3.

3) The required thickness of the sheet of fire-retardant cladding for the shelves of the columnar I-beam with refractory plasterboard sheets (at m ₀₁ = 0.75) is calculated according to the representative equation (1):

δ _{mp, GKLO} = 0.7 · C · D ^0.8 _GKLO / m ₀₁ = 0.7 · 3 · 20 ^0.8 / 0.75 = 31 mm.

4) The number of layers of lining of the shelves of the columnar I-beam from refractory plasterboard sheets with a thickness of δ ₁ = 12.5 mm each sheet:

n _GKLO = δ _{mp, GKLO} / δ ₁ = 31 / 12.5 = 2.5; accepted n _GKLO = 3 sheets.

5) The required thickness of the plate fire-retardant cladding for the wall of the columnar I-beam with Rockwool mineral wool products in the form of M-50 mats (with two-sided heat supply in fire conditions m ₀₂ = 0.5) is determined by the formula (1):

δ _{mp, Roc} = 0.7 · C · D ^0.8 _Roc / m ₀₂ = 0.7 · 3 · 68.8 ^0.8 / 0.5 = 120 mm> b / 2 = 200/2 = 100 mm ;

accepted δ _{mp, Roc} = 120 mm.

The structure of the fire protection method for a steel column includes: preparing the surface of a steel column I-beam - 1 and applying an anti-corrosion layer - 2; selection of materials for fire retardant cladding; calculation of the thickness of the cladding elements; manufacturing elements of sheet fire retardant cladding - 3 and plate fire retardant cladding - 4; installation of fixing nuts - 6 on the ends of the shelves of a steel column I-beam - 1 with a step of 500 ÷ 1000 mm along the length (height) of the column; assembly of elements of sheet fire-retardant cladding - 3 and fixing them with set screws - 5 on the shelves of a steel column I-beam - 1; applying an adhesive layer - 10 to the surface of the wall and shelves of a steel columnar I-beam - 1 and gluing to them the elements of a plate fire-retardant lining - 4; screwing in each set screw - 5 with countersunk head - 7 and with a pointed end into the elements of the plate fire-retardant cladding - 4 to a depth l _to ≥0.2 · h (here h is the height of the column I-beam - 1); installation in the grooves (at the locations of the fixing nuts) of an asbestos cord - 8; covering the surface of the elements of the fire-retardant plate cladding - 4 with fiberglass - 9 (if necessary).

The proposed invention for the installation of a fire-protected I-beam column of the building was used in the reconstruction of the educational building No. 2 of the SASU (Samara, 2010/2011).

Information sources

1. Bartellemi B., Kruppa J. Fire resistance of building structures / Per. with french - M.: Stroyizdat, 1985 .-- 216 p. (Chap. 4, Sec. 4.2 Materials and methods of protection; Fig. 4.2; 4.4 ÷ 4.6; pp. 94-98).

2. Romanenkov I.G., Levites F.A. Fire protection of building structures. - M .: Stroyizdat, 1991 .-- 320 p. (Chap. 4 Structural methods of fire protection; Sec. 4.2. - Large-sized sheet, plate and roll cladding; Fig. 8, p.131 ÷ 133.

3. A.S. SU No. 887755 MKI-3 Е04В 1/94 Building node of the building / Yu.V. Pokrovsky, V.V. Fedorov, M.M.Karabochinsky et al .; application 02.21.80; publ. 12/07/81, Bull. No. 45.

4. A.S. SU No. 773 218 MKI-3 Е04В 1/94 Building element / Yu.V. Pokrovsky, V.V. Fedorov, V.V. Filippov; application 04/13/79; publ. 10.23.80, Bull. Number 39.

Claims (12)

1. The method of fire protection of an I-beam column of a building in which the bearing rod is equipped with sheet cladding, characterized in that the bearing rod is made in the form of a steel column I-beam and each end of the steel bearing rod is provided with fastening nuts and set screws with countersunk heads and with screwed-in pointed ends and straight ends slot; set screws to the shelves of the columnar I-beam fasten contact, closely elements of the sheet fire-retardant cladding, to the wall of the I-beam fasten contact, flush elements of the plate fire-retardant lining; the thickness of the cladding elements is determined taking into account the thermal diffusion of its materials, the heating conditions of the shelves and walls of the I-beam and the degree of fire resistance of the building. 2. The fire protection method according to claim 1, characterized in that the anticorrosion layer is preliminarily applied to the surface of the steel supporting rod. 3. The method of fire protection according to claim 1, characterized in that the elements of the sheet of fire retardant cladding are made of gypsum cladding sheets. 4. The method of fire protection according to claim 1, characterized in that the elements of the slab fire retardant cladding are in the form of plates of basalt fiber. 5. The method of fire protection according to claim 1, characterized in that the elements of the slab fire retardant cladding are in the form of rock wool "Rockwool". 6. The method of fire protection according to claim 1, characterized in that the length of the screwed end of the set screw into the elements of the plate fire retardant cladding is not less than l _min ≥0.2 · h, here h is the height of the steel column I-beam. 7. The method of fire protection according to claim 1, characterized in that the outer surfaces of the elements of the fire retardant cladding are coated with a layer of fiberglass. 8. The method of fire protection according to claim 1, characterized in that the outer surfaces of the elements of the fireproof columns are plastered. 9. The method of fire protection according to claim 1, characterized in that the thickness of the elements of the fire retardant lining δ _{o, mp} , mm, column I-beam is determined by the mathematical expression (1):
δ _{o, mp} = 0.7 · C · D ^0.8 _ar / m _o ;
where C is the degree of fire protection of the column I-beam; D _ar is an indicator of thermal diffusion of the cladding material, mm ² / min; m _o - an indicator of the heating conditions of the column I-beam (0.5 ÷ 1). 10. The method of fire protection according to claims 1 and 9, characterized in that the value of the fire protection limit of an individual layer of the complex cladding τ _{u, co} , min, is calculated by the formula (2):
τ _{u, co} = 65 · m _o · (δ _co / D _co ) ^1.41 ;
where m _o - an indicator of the heating conditions of the cladding layer, (0.5 ÷ 1);
δ _co - the thickness of a single layer of fire retardant cladding, mm;
D _co - an indicator of thermal diffusion of the cladding layer, mm ² / min. 11. The method of fire protection according to PP.1 and 9, characterized in that the indicator of the heating conditions of the shelf of the column I-beam is calculated by the power equation (3):
m ₀ = 0.7 ^{δx / δy} ;
where δ _x and δ _y are the thickness of the fire protection of the shelf of the column I-beam along the axes X and Y, mm 12. The method of fire protection according to claim 1, characterized in that the construction work on fire protection of the I-beam columns of the building are carried out at positive and negative air temperatures.

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