Fire doors and other structures are often divided into classes according to fire protection parameters. In this case, the markings EI, EI are used
Wor EIS. What do these symbols show? In what cases are they used?Before purchasing and installing a fire-resistant door, double-glazed windows and other ceilings, it is important to familiarize yourself with existing standards regarding fire safety requirements in a particular building.
Inconsistency installed door, windows, etc. the fire protection class required in a given room will serve as a reason for refusing to put the building into operation.
So, in general view EI fire safety class indicates the ability of a structure to withstand the onslaught of open fire in the event of fire for a certain time.
There are also additional characters added to EI:
EI
EI
S– and this is a generally accepted marking for doors with ventilation grille air duct.The fire resistance class is assigned based on tests of the product in a special fire chamber. If the test is completed successfully, the company receives an appropriate certificate.
Fire resistance limit
EI 60
EI 60 fire resistance limit
In this case, a door, window or ceiling corresponding to this class must last at least 60 minutes (one hour) without loss of structural integrity and prevent the spread of fire, combustion products, as well as high temperatures outside the room limited by the door.
Fire resistance limit
EI 45
EI 45 fire resistance limit
Structures with such a fire resistance limit can be installed in high-traffic areas, on staircase landings, in office and industrial buildings. In short, wherever 45 minutes should be enough for a complete and safe evacuation of residents or working personnel.
EI 45 fire resistance limit
applies not only to doors, but also to glazed coverings, including windows and partitions.Fire resistance limit
EI 30
One of the most affordable price options is EI 30 protection class. This means the ability of a structure to resist the spread of flame for half an hour - that is, at least 30 minutes.
Since the spread of fire is mainly facilitated by the presence of an influx of oxygen, such doors provide airtightness during a fire. Thanks to this, neither smoke nor elevated temperatures escape outside.
An additional advantage of doors and double-glazed windows with any degree of resistance EI, including EI 60, is their excellent noise and heat insulation characteristics.
EI 60 doors can be ordered both in a “warm” version and in a “cold” version, that is, intended for installation indoors or in the entrance area.
Fire resistance limit
EI 150
Then, as for example,
Usually in this case we're talking about on the manufacture of custom-made products according to individual customer requirements.
Often the thickness of both the working material and the fire-resistant outer coating increases.
However, the principle remains the same: EI 150 allows the spread of open flames and high temperatures to be contained for 150 minutes. They resort to such high fire protection in crowded places and in many hazardous industries.
To give an approximate assessment of the fire resistance limit of specific structures, during their development and design, the following points should be used:
The fire resistance threshold of layered fencing in terms of thermal insulation ability is comparable, and, in most cases, exceeds the totality of the resistance limits of individual layers. This indicates that large quantity layers of the building envelope does not reduce fire resistance. In some cases, additional layers may not play a significant role, for example, sheet metal cladding on the side that is not heated;
Enclosing structures with an air gap are on average 10% more fire-resistant than their counterparts without it. Moreover, its efficiency increases in proportion to the distance from the heating source, regardless of thickness;
The asymmetrical arrangement of layers affects fire resistance depending on the direction heat flow. It is recommended to place fireproof materials with low thermal conductivity in the most fire-hazardous place;
Increased humidity of structures slows down heating and increases fire resistance, except in cases where with increasing humidity the material becomes more fragile (which is especially true for products made of concrete or asbestos cement);
Fire resistance decreases with high loads- structures with the maximum stressed section serve as an indicator for determining the fire resistance limit;
The period of heat exposure also affects the material's ability to withstand high temperatures in a fire;
Structures whose heat resistance cannot be determined usually have a higher heat resistance limit than similar statically determinable structures. It is also important to take into account the additional forces resulting from temperature deformations;
The fire resistance of a structure does not depend on the flammability of the materials from which it is composed. Thus, thin-walled metal profiles have a minimum fire resistance limit, while wooden structures have a higher rate at the same ratio of the heated perimeter of the section to the area and impact force, temporary resistance or yield strength.
Attention! Combustible materials used in the design of a building, rather than fire-resistant or non-combustible materials, can greatly reduce the fire resistance of the entire structure. This is especially true when the burnout rate exceeds the warm-up rate.
To increase the resistance of structures to high temperatures and bring it to given parameters During construction, various types of fire retardant materials are used. They allow you to block the surface of the protected structure from the thermal effect and keep it in working condition for a certain period of time.
Fire retardant coatings are used for:
building structures which include columns, frames, trusses, blocks, slabs and floors;
air ducts and gas ducts with relevant safety requirements;
cabling, penetration through fire-resistant type fences;
containers with petroleum products, flammable and combustible liquids;
plastering, finishing with concrete or brick - relevant for structures designed for additional loads.
For these purposes, special facing slabs are used, protective screens, surface coating with fire retardants, impregnation of wooden structures with chemicals.
Systems that increase fire resistance limits are various types and consist of different materials. The most commonly used: heat-resistant fillers (vermiculite, expanded clay, basalt, etc.), binders inorganic basis(gypsum, cement), polymers that increase the overall resistance and strength of structural elements. The above systems can be used either independently or combined.
Upon contact with high temperatures, the organic components of the binder coating swell, simultaneously forming foam coke. Thus, the material burns out slowly, while the structure remains operational for a long time. Mineral coatings block heat flow by releasing large quantity pair, since they contain bound water. Thanks to this, the temperature rises gradually, and the structure is destroyed less intensively.
Installing a fire door is one of the main measures to ensure fire safety and protect the building from fire. Modern models carry out not only a protective function, but also a decorative one, due to the variety of style and color solutions.
In the absence of obstacles and unlimited air flow, the flame spreads very quickly. Regular doors are susceptible to fire, because they are often made of flammable wood or plastic, and have gaps between the box and the canvas. Fire doors are able to resist the spread of fire for some time, sufficient for people to leave the room. Fire doors retain their stability and integrity, not allowing smoke and flames to pass through.
In the manufacture of fire-resistant doors, non-combustible materials and modern fillers with fire-resistant properties are used. High-tech filling makes the door structure resistant to flames and gives it excellent heat and sound insulation qualities.
The filler consists of basalt fibers containing silicon dioxide or mineral wool slabs, and fills the door leaf from the inside. Silica or silicon dioxide holds constant temperature up to 1200 degrees, short-term up to 1700 degrees. The ability of basalt fibers to retain temperature depends on the length of the thread.
The main material from which fire-resistant materials are made door designs is a one-piece bent steel profile, whose melting point ranges from 700 to 1000 degrees. For steel to ignite, the flame temperature must exceed 2000 degrees. In turn, synthetic and wooden materials ignite at a temperature of about 220 degrees. Metal door structures resist open fire for up to 2 hours.
Main criteria when choosing a fire door:
A high-quality fire door has a special marking indicating the name of the manufacturing company, product name, batch number, fire resistance rating and description technological process door manufacturing.
The abbreviation REI denotes the fire resistance of a structure and is calculated in minutes.
R– losses bearing capacity, deformations and structural collapse.
In everyday life, the consumer has no need to be interested in the fire resistance characteristics of equipment and premises. Most citizens live with the goal of safe life, so fire resistance indicators and the availability of fire-fighting equipment are of interest exclusively to specialists in this field.
It is worth knowing the interpretation of the basic concepts of fire safety to all citizens after all, it can save health and even life. I propose to consider the common abbreviations of fire safety levels and the classification of fire hazard degrees and the factors that determine them.
The abbreviation can be found on the packaging some building materials and in buildings (often on signage near fire safety equipment). The interpretations differ somewhat from each other, but we will consider those listed in Construction norms and rules (SNIP). The Latin letters REI are interpreted as follows:
"R" indicates for loss of bearing capacity, in other words, it is the resistance of the building/material during fire. The loss of load-bearing capacity simultaneously characterizes the weakening of the level of thermal insulation and structural integrity.
The indicator is checked as follows: element of the structure or equipment amenable to fire treatment. The expert visually determines how long it takes for the material to reach its maximum deformation. Time is indicated in minutes.
The sustainability indicator is calculated not only in the field of fire safety. This concept is used for corrosion, pressure and other factors that can change the design of an object. It turns out that the load-bearing capacity indicator indicates the permissible load level.
"E" is characterized as loss of integrity. Experts determine the period of fire exposure, after which through cracks and holes will form on the material. Let’s say if the designation “60EI” is indicated on an object, this means that with fire treatment at 180%, the material begins to crack after 60 minutes.
The digital indicator always indicates the time, and the letter indicator always indicates the criterion being checked and the temperature.
“I” – Latin index, characterizing thermal insulation properties designs. It is also called the extreme flash point. The index characterizes the time period after which nearby objects heat up to the maximum level.
This type of object is not directly susceptible to fire. This often occurs after a loss of integrity, when fire and combustion objects penetrate through cracks in heated equipment.
Fire resistance is general characteristicsfire safety of the facility. If we are talking about a building, this level is determined based on fire safety indicators individual elements the buildings.
It is worth considering that the actual level will always be slightly lower than indicated, because the room does not consist of only walls. Wallpaper, fittings, and household items significantly increase the level of fire risk.
First of all, it is divided into actual and required. The required indicator is displayed in SNiP in the section “ Fire safety buildings and structures." When the structure of a building reaches a certain level, a team of experts checks the actual level, i.e. the actual level.
If it is lower than required, permission for further construction not issued. Each type of facility has its own permissible level of fire safety.
It is determined by the degree of fire resistance. There are 5 of them in total. The first degree is REI 120, and the fourth - REI 45 - is permissible levels For inside walls of residential premises. The same degrees for car windows will be slightly lower. The limits for the fifth degree criteria are not indicated.
The index is mainly influenced by the elements that make up the equipment or structure. First of all, objects are determined as flammable or non-combustible. Item of equipment is classified in the following way:
IN regulations“Fire Safety of Buildings and Structures” describes in detail the characteristics of materials.
Buildings are classified in a similar way, their indicators depend on the above levels of fire hazard of the elements. The indices for buildings are as follows:
To resort to using the following notation:
Fire resistance limit metal structures , which are not additionally protected, are usually small and are in the following ranges:
Exceptions to these two series include columns of massive cross-section, characterized by high values fire resistance limit of metal structures- R45. However, such designs are used quite infrequently.
In cases where the minimum acceptable value fire resistance limit of building structures(this does not include structures related to fire barriers) is R15 (or RE15), the use of unprotected steel structures is permitted regardless of their actual fire resistance limits with some exceptions. The latter include cases when the corresponding value fire resistance limit of load-bearing structures, according to the results of the tests, reaches only R8 or less.
The rapid loss of resistance to open fire by unprotected metal structures is a consequence of high thermal conductivity values with low heat capacity values. Increased thermal conductivity inherent metal elements, does not lead to the emergence of a temperature gradient inside the structural section. This is what it is main reason rapid increase in metal temperature up to a critical value. When these same values are reached, a sharp decrease in the strength of the material is observed, the structure comes to a state where it cannot withstand the load placed on it from the outside.
Compared to metal analogues, wooden structures are characterized by flammability. On fire resistance limits of wooden structures several factors influence: the time that passes from the beginning of the interaction of fire with the material until the actual ignition of the wood, the time spent from the beginning of combustion until the limit state is reached.
To improve the fire resistance of wood, they traditionally resort to applying several layers of plaster. A two-centimeter layer applied to a wooden column can increase fire resistance limit wooden structure up to R60. High efficiency all kinds of fire protection paint coatings, impregnation of wood with fire retardants.
The fire resistance of reinforced concrete structures is influenced by many factors, including the following: geometry features, load, dimensions of concrete layers, type of reinforcement used in construction, type of concrete and others.
In the event of a fire fire resistance limit of building structures can be achieved for a number of reasons:
To the most sensitive structural elements include bendable structures made of reinforced concrete. This fact can be explained by the fact that the working reinforcement of the tension zone, which provides the main contribution to the bearing capacity of structures, is protected from fire by a small concrete layer. This is a determining factor affecting the high rate of heating of the working fittings.
Article sent by: 12inches
ALLOWANCE
BY DETERMINING LIMITS FIRE RESISTANCE OF STRUCTURES,
LIMITS OF FIRE SPREAD THROUGH STRUCTURES AND FLAMMABILITY GROUPS OF MATERIALS
ATTENTION!!!
Developed for SNiP II-2-80 "Fire safety standards for the design of buildings and structures." Reference data is provided on the limits of fire resistance and fire spread for building structures made of reinforced concrete, metal, wood, asbestos cement, plastics and other building materials, as well as data on the flammability groups of building materials.
For engineering and technical workers of design, construction organizations and state fire supervision authorities. Table 15, fig. 3.
PREFACE
This Manual has been developed for SNiP II-2-80 "Fire safety standards for the design of buildings and structures." It contains data on standardized fire resistance indicators and fire danger building structures and materials.
Section 1 of the manual was developed by TsNIISK named after. Kucherenko (Doctor of Technical Sciences, Prof. I.G. Romanenkov, Candidate of Technical Sciences, V.N. Zigern-Korn). Section 2 was developed by TsNIISK named after. Kucherenko (Doctor of Technical Sciences I.G. Romanenkov, Candidates of Technical Sciences V.N. Zigern-Korn, L.N. Bruskova, G.M. Kirpichenkov, V.A. Orlov, V.V. Sorokin, engineers A.V. Pestritsky, V.I. Yashin); NIIZHB (Doctor of Technical Sciences V.V. Zhukov; Doctor of Technical Sciences, Prof. A.F. Milovanov; Candidate of Physical and Mathematical Sciences A.E. Segalov, Candidate of Technical Sciences A.A. Gusev, V.V. Solomonov, V.M. Samoilenko, engineers V.F. Gulyaeva, T.N. Malkina); TsNIIEP im. Mezentseva (candidate of technical sciences L.M. Schmidt, engineer P.E. Zhavoronkov); TsNIIPromzdanii (candidate of technical sciences V.V. Fedorov, engineers E.S. Giller, V.V. Sipin) and VNIIPO (doctor of technical sciences, professor A.I. Yakovlev; candidates of technical sciences V. P. Bushev, S.V. Davydov, V.G. Olimpiev, N.F. Gavrikov, engineers V.Z. Volokhatykh, Yu.A. Grinchik, N.P. Savkin, A.N. Sorokin, V.S. Kharitonov, L.V. Sheinina, V.I. Shchelkunov). Section 3 was developed by TsNIISK named after. Kucherenko (Doctor of Technical Sciences, Prof. I.G. Romanenkov, Candidate of Chemical Sciences N.V. Kovyrshina, Engineer V.G. Gonchar) and the Institute of Mining Mechanics of the Georgian Academy of Sciences. SSR (candidate of technical sciences G.S. Abashidze, engineers L.I. Mirashvili, L.V. Gurchumelia).
When developing the Manual, materials from the TsNIIEP of housing and the TsNIIEP of educational buildings of the State Civil Engineering Committee, MIIT Ministry of Railways of the USSR, VNIISTROM and NIPIsilicate concrete of the Ministry of Industrial Construction Materials of the USSR were used.
The text of SNiP II-2-80 used in the Guide is typed in bold. Its points are double numbered; the numbering according to SNiP is given in brackets.
In cases where the information given in the Manual is insufficient to establish the appropriate indicators of structures and materials, you should contact the TsNIISK im. Kucherenko or NIIZhB of the USSR State Construction Committee. The basis for establishing these indicators can also be the results of tests performed in accordance with standards and methods approved or agreed upon by the USSR State Construction Committee.
Please send comments and suggestions regarding the Manual to the following address: Moscow, 109389, 2nd Institutskaya St., 6, TsNIISK im. V.A. Kucherenko.
1. GENERAL PROVISIONS
1.1. The manual has been compiled to help project construction organizations and fire protection authorities in order to reduce the cost of time, labor and materials to establish the fire resistance limits of building structures, the limits of fire spread through them and the flammability groups of materials standardized by SNiP II-2-80.
1.2.(2.1). Buildings and structures are divided into five levels according to fire resistance. The degree of fire resistance of buildings and structures is determined by the fire resistance limits of the main building structures and the limits of fire spread through these structures.
1.3.(2.4). Construction Materials Based on flammability, they are divided into three groups: non-combustible, non-combustible and combustible.
1.4. The fire resistance limits of structures, the limits of fire spread through them, as well as the flammability groups of materials given in this Manual should be included in the design of structures, provided that their execution fully complies with the description given in the Manual. Materials from the Manual should also be used when developing new designs.
2. BUILDING STRUCTURES. FIRE RESISTANCE LIMITS AND FIRE SPREAD LIMITS
2.1(2.3). The fire resistance limits of building structures are determined according to the CMEA standard 1000-78 "Fire safety standards for building design. Method of testing building structures for fire resistance."
The limit of fire spread through building structures is determined according to the methodology given in Appendix 2.
FIRE RESISTANCE LIMIT
2.2. The fire resistance limit of building structures is taken to be the time (in hours or minutes) from the start of their standard fire test until the occurrence of one of the fire resistance limit states.
2.3. The SEV 1000-78 standard distinguishes the following four types of limit states for fire resistance: loss of load-bearing capacity of structures and components (collapse or deflection depending on the type of structure); to heat insulating. abilities - an increase in temperature on an unheated surface by an average of more than 160 °C or at any point on this surface by more than 190 °C compared to the temperature of the structure before testing, or more than 220 °C regardless of the temperature of the structure before testing; by density - the formation in structures of through cracks or through holes through which combustion products or flames penetrate; for structures protected by fire-retardant coatings and tested without loads, the limiting state will be the achievement of a critical temperature of the material of the structure.
For external walls, coverings, beams, trusses, columns and pillars, the limiting state is only the loss of the load-bearing capacity of structures and components.
2.4. The limit states of structures for fire resistance specified in clause 2.3 will be further referred to, for brevity, as I, II, III and IV limit states of structures for fire resistance, respectively.
In cases of determining the fire resistance limit at loads determined on the basis detailed analysis conditions that arise during a fire and differ from the normative ones, limit state we will denote the structures as 1A.
2.5. The fire resistance limits of structures can also be determined by calculation. In these cases, tests may not be carried out.
Determination of fire resistance limits by calculation should be carried out according to methods approved by the Glavtekhnormirovanie of the USSR State Construction Committee.
2.6. For an approximate assessment of the fire resistance limit of structures during their development and design, one can be guided by the following provisions:
a) fire resistance limit of layered enclosing structures according to thermal insulation ability equal to, and, as a rule, higher than the sum of the fire resistance limits of individual layers. It follows that increasing the number of layers of the enclosing structure (plastering, cladding) does not reduce its fire resistance limit in terms of heat-insulating ability. In some cases, the introduction of an additional layer may not have an effect, for example, when facing sheet metal on the unheated side;
b) the fire resistance limits of enclosing structures with an air gap are on average 10% higher than the fire resistance limits of the same structures, but without an air gap; the efficiency of the air gap is higher, the further it is removed from the heated plane; with closed air gaps, their thickness does not affect the fire resistance limit;
c) the fire resistance limits of enclosing structures with an asymmetrical arrangement of layers depend on the direction of the heat flow. On the side where the likelihood of a fire is higher, it is recommended to place fireproof materials with low thermal conductivity;
d) an increase in the humidity of structures helps to reduce the rate of heating and increase fire resistance, except in cases where an increase in humidity increases the likelihood of sudden brittle destruction of the material or the appearance of local spalls; this phenomenon is especially dangerous for concrete and asbestos-cement structures;
e) the fire resistance limit of loaded structures decreases with increasing load. The most stressed section of structures exposed to fire and high temperatures, as a rule, determines the value of the fire resistance limit;
f) the fire resistance limit of a structure is higher, the smaller the ratio of the heated perimeter of the cross-section of its elements to their area;
g) the fire resistance limit of statically indeterminate structures, as a rule, is higher than the fire resistance limit of similar statically indeterminate structures due to the redistribution of forces to less stressed elements that are heated at a lower rate; in this case, it is necessary to take into account the influence of additional forces arising due to temperature deformations;
h) the flammability of the materials from which the structure is made does not determine its fire resistance limit. For example, structures made of thin-walled metal profiles have minimum limit fire resistance, and structures made of wood have a higher fire resistance limit than structures made of steel with the same ratio of the heated perimeter of the section to its area and the magnitude of the operating stresses to the temporary resistance or yield strength. At the same time, it should be taken into account that the use of combustible materials instead of difficult-to-burn or non-combustible materials can reduce the fire resistance limit of the structure if the rate of its burnout is higher than the rate of heating.
To assess the fire resistance limit of structures based on the above provisions, it is necessary to have sufficient information about the fire resistance limits of structures similar to those considered in shape, materials used and design, as well as information about the main patterns of their behavior in case of fire or fire tests.
2.7. In cases where fire resistance limits are indicated in Table 2-15 for similar structures various sizes, the fire resistance limit of a structure having an intermediate size can be determined by linear interpolation. For reinforced concrete structures In this case, interpolation should also be carried out based on the distance to the axis of the reinforcement.
FIRE SPREAD LIMIT
2.8. (Appendix 2, paragraph 1). Testing building structures for fire spread consists of determining the extent of damage to the structure due to its combustion outside the heating zone - in the control zone.
2.9. Damage is considered to be charring or burning of materials that can be detected visually, as well as melting of thermoplastic materials.
The limit of fire spread is taken to be maximum size damage (cm), determined according to the test method set out in Appendix 2 to SNiP II-2-80.
2.10. Structures made using combustible and non-combustible materials, usually without finishing or cladding, are tested for the spread of fire.
Structures made only from fireproof materials should be considered not to spread fire (the limit of fire spread through them should be taken equal to zero).
If, when testing for fire spread, damage to structures in the control zone is no more than 5 cm, it should also be considered not to spread fire.
2.11. For a preliminary assessment of the fire spread limit, the following provisions can be used:
a) structures made of combustible materials have a horizontal fire spread limit (for horizontal structures - floors, coverings, beams, etc.) of more than 25 cm, and vertically (for vertical structures- walls, partitions, columns, etc.) - more than 40 cm;
b) structures made of combustible or hardly combustible materials, protected from fire and high temperatures by non-combustible materials, may have a horizontal fire spread limit of less than 25 cm, and a vertical limit of less than 40 cm, provided that the protective layer is in place during the entire test period (until the structure has completely cooled) will not warm up in the control zone to the ignition temperature or the beginning of intense thermal decomposition of the protected material. The structure may not spread fire provided that the outer layer, made of non-combustible materials, does not warm up in the heating zone to the ignition temperature or the beginning of intense thermal decomposition of the protected material during the entire test period (until the structure has completely cooled down);
c) in cases where the structure may have a different fire spread limit when heated with different sides(for example, with an asymmetrical arrangement of layers in the enclosing structure), this limit is set according to its maximum value.
CONCRETE AND REINFORCED CONCRETE STRUCTURES
2.12. The main parameters that influence the fire resistance limit of concrete and reinforced concrete structures are: the type of concrete, binder and filler; reinforcement class; type of construction; form cross section; element sizes; conditions for their heating; load magnitude and concrete moisture content.
2.13. The increase in temperature in the concrete cross-section of an element during a fire depends on the type of concrete, binder and fillers, and on the ratio of the surface affected by the flame to the cross-sectional area. Heavy concrete with silicate filler warms up faster than with carbonate filler. Lightweight and lightweight concretes warm up more slowly, the lower their density. The polymer binder, like the carbonate filler, reduces the rate of heating of concrete due to the decomposition reactions occurring in them, which consume heat.
Massive structural elements are better resistant to fire; the fire resistance limit of columns heated on four sides is less than the fire resistance limit of columns with one-sided heating; The fire resistance limit of beams when exposed to fire on three sides is less than the fire resistance limit of beams heated on one side.
2.14. The minimum dimensions of elements and distances from the axis of the reinforcement to the surfaces of the element are taken according to the tables of this section, but not less than those required by Chapter SNiP II-21-75 “Concrete and reinforced concrete structures”.
2.15. The distance to the reinforcement axis and the minimum dimensions of elements to ensure the required fire resistance limit of structures depend on the type of concrete. Lightweight concrete has a thermal conductivity of 10-20%, and concrete with coarse carbonate aggregate is 5-10% less than heavy concrete with silicate aggregate. In this regard, the distance to the axis of the reinforcement for a structure made of lightweight concrete or from heavy concrete with carbonate filler can be taken less than for structures made of heavy concrete with silicate filler with the same fire resistance limit of structures made from these concretes.
The fire resistance limits given in Tables 2-6, 8 apply to concrete with coarse silicate aggregate, as well as dense silicate concrete. When using carbonate rock filler, the minimum dimensions of both the cross-section and the distance from the axes of the reinforcement to the surface of the bending element can be reduced by 10%. For lightweight concrete, the reduction can be 20% at a concrete density of 1.2 t/m 3 and 30% for bending elements (see Tables 3, 5, 6, 8) at a concrete density of 0.8 t/m 3 and expanded clay perlite concrete with a density of 1.2 t/m 3.
2.16. During a fire, a protective layer of concrete protects the reinforcement from rapid heating and reaching its critical temperature, at which the fire resistance of the structure reaches its limit.
If the distance adopted in the project to the axis of the reinforcement is less than that required to ensure the required fire resistance limit of structures, it should be increased or additional thermal insulation coatings on the surfaces of the element exposed to fire *. Thermal insulation coating made of lime-cement plaster (15 mm thick), gypsum plaster(10 mm) and vermiculite plaster or mineral fiber insulation (5 mm) is equivalent to an increase of 10 mm in the thickness of the heavy concrete layer. If the thickness of the protective layer of concrete is more than 40 mm for heavy concrete and 60 mm for lightweight concrete, the protective layer of concrete must have additional reinforcement on the fire side in the form of a reinforcement mesh with a diameter of 2.5-3 mm (cells 150x150 mm). Protective thermal insulation coatings with a thickness of more than 40 mm must also have additional reinforcement.
* Additional heat-insulating coatings can be carried out in accordance with the “Recommendations for the use of fire-retardant coatings for metal structures” - M.; Stroyizdat, 1984.
Table 2, 4-8 shows the distances from the heated surface to the axis of the reinforcement (Fig. 1 and 2).
Fig.1. Distances to the reinforcement axis
Fig.2. Average distance to the reinforcement axis
In cases where reinforcement is located at different levels, the average distance to the axis of the reinforcement a must be determined taking into account the areas of the reinforcement ( A 1 , A 2 , …, A n) and their corresponding distances to the axes ( a 1 , a 2 , …, a n), measured from the nearest heated (bottom or side) surface of the element, according to the formula
.
2.17. All steels reduce their tensile or compressive strength when heated. The degree of resistance reduction is greater for hardened high-strength steel reinforcing wires than for low-carbon steel reinforcement bars.
The fire resistance limit of bent and eccentrically compressed elements with a large eccentricity for loss of bearing capacity depends on the critical heating temperature of the reinforcement. The critical heating temperature of the reinforcement is the temperature at which the tensile or compression resistance decreases to the value of the stress arising in the reinforcement from the standard load.
2.18. Tables 5-8 are compiled for reinforced concrete elements with non-prestressed and prestressed reinforcement under the assumption that the critical heating temperature of the reinforcement is 500 °C. This corresponds to reinforcing steels classes A-I, A-II, A-Iv, A-IIIv, A-IV, At-IV, A-V, At-V. The difference in critical temperatures for other classes of reinforcement should be taken into account by multiplying the fire resistance limits given in Tables 5-8 by the coefficient j or dividing the distances to the reinforcement axes given in Table 5-8 by this coefficient. Values j should be taken:
1. For floors and coverings made of prefabricated reinforced concrete flat slabs solid and multi-hollow, reinforced:
a) steel class A-III, equal to 1.2;
b) steels of classes A-VI, AT-VI, AT-VII, B-I, BP-I, equal to 0.9;
c) high-strength reinforcing wire of classes B-II, BP-II or reinforcing ropes of class K-7, equal to 0.8.
2. For floors and prefabricated roofs reinforced concrete slabs with longitudinal load-bearing ribs “down” and box-section, as well as beams, crossbars and girders in accordance with the specified classes of reinforcement: a) j= 1.1; b) j= 0.95; V) j = 0,9.
2.19. For structures made of any type of concrete, the minimum requirements for structures made of heavy concrete with a fire resistance limit of 0.25 or 0.5 hours must be met.
2.20. The fire resistance limits of load-bearing structures in Tables 2, 4-8 and in the text are given for full standard loads with the ratio of the long-term part of the load G ser to full load V ser, equal to 1. If this ratio is 0.3, then the fire resistance limit increases by 2 times. For intermediate values G ser / V ser The fire resistance limit is taken by linear interpolation.
2.21. The fire resistance limit of reinforced concrete structures depends on their static operating pattern. The fire resistance limit of statically indeterminate structures is greater than the fire resistance limit of statically determinable structures, if in places of action negative points the necessary fittings are available. The increase in the fire resistance limit of statically indeterminate bendable reinforced concrete elements depends on the ratio of the cross-sectional areas of the reinforcement above the support and in the span according to Table 1.
Table 1
The ratio of the area of reinforcement above the support to the area of reinforcement in the span |
Increase in the fire resistance limit of a bendable statically indeterminate element, %, compared to the fire resistance limit of a statically indeterminate element |
Note. For intermediate area ratios, the increase in fire resistance limit is taken by interpolation.
The influence of static indetermination of structures on the fire resistance limit is taken into account if the following requirements are met:
a) at least 20% of the upper reinforcement required on the support must pass above the middle of the span;
b) the upper reinforcement above the outer supports of the continuous system must be inserted at a distance of at least 0.4 l towards the span from the support and then gradually break off ( l- span length);
c) all upper reinforcement above intermediate supports must extend to the span by at least 0.15 l and then gradually break off.
Flexible elements embedded on supports can be considered as continuous systems.
2.22. Table 2 shows the requirements for reinforced concrete columns made of heavy and light concrete. They include requirements for the size of columns exposed to fire on all sides, as well as those located in walls and heated on one side. At the same time the size b applies only to columns whose heated surface is flush with the wall, or to the part of the column that protrudes from the wall and carries the load. It is assumed that there are no holes in the wall near the column in the direction of the minimum size b.
For solid columns round section as size b their diameter should be taken.
Columns with the parameters given in Table 2 have an eccentrically applied load or a load with random eccentricity when reinforced with columns of no more than 3% of the concrete cross-section, with the exception of joints.
The fire resistance limit of reinforced concrete columns with additional reinforcement in the form of welded transverse mesh installed in increments of no more than 250 mm should be taken according to Table 2, multiplying them by a factor of 1.5.
