ANALYSIS OF FIRE RESISTANCE OF GLUED TIMBER (CLT PANELS)

ABSTRACT

The article is devoted to research into the fire resistance of laminated wood, in particular CLT panels. The relevance of the work lies in the fact that Russia, having a colossal forest resource, 25% of the world's timber reserves, remains a country that does not occupy a leading position in the volume of wooden house construction. The materials of domestic research are described in detail and the calculated characteristics of the fire resistance of CLT panels are given, options for treating CLT panels with fire retardants are considered. Scientific research methods are based on a theoretical review of the collected information and its further analysis. Corresponding conclusions have been made regarding the safety of using CLT panels as the main material in the construction of residential and public buildings and structures.

Keywords: CLT panel, fire resistance of laminated wood, charring rate of CLT panel.

The use of wood as a building material is now gaining momentum. In many leading countries, residential and public buildings are built from wooden structures. Most often, laminated wood is used in the construction of such facilities, in particular CLT panels and LVL timber. An example of such structures is the Groupe scolaire school/

INTRODUCTION

Laminated timber, also known as CLT panels (Cross Laminated Timber), is one of the most innovative and promising materials in the construction industry. This material consists of several layers of wood, which are bonded together with glue. Due to its structure and ability to withstand heavy loads, glued laminated timber has high strength and stability. However, an important aspect of its use is fire resistance. This study will analyze the fire resistance of CLT panels and present the results of experiments aimed at determining the possibility of their use in construction, taking into account fire safety requirements. This research is important for architects, engineers and builders who want to use glued beams in their projects to ensure the safety and reliability of the structure in the event of a fire.

LITERARY REVIEW

The first source for analysis is a study conducted by scientists from the University of Toronto. They studied the behavior of CLT panels in fire and concluded that this material has high fire resistance. Due to the way they are constructed, CLT panels retain their strength and fire resistance even at high temperatures. They resist burning and retard the spread of fire, making them safe for use in construction.

The second source is the work of scientists from the University of Canterbury, which also confirms the high fire resistance of CLT panels. They conducted experiments in which they studied the material's resistance to fire under various conditions. The results showed that CLT panels can withstand high temperatures for significant periods of time, making them an excellent choice for buildings that require increased fire resistance.

Thus, research allows us to conclude that CLT panels have high fire resistance. This material not only offers an environmentally friendly alternative to traditional building materials, but also guarantees the safety and durability of buildings. However, it is important to remember that in the event of a fire, all prescribed safety measures and rules for the use of CLT panels must be followed.

MATERIALS AND METHODS

CLT panels (cross-laminated timber) are an innovative material that has gained particular popularity in construction in recent years. One of the most important aspects to consider when using CLT panels is their fire resistance. This review will analyze sources devoted to the study of fire resistance of laminated veneer lumber.

The first source for analysis is a study conducted by scientists from the University of Toronto. They studied the behavior of CLT panels in fire and concluded that this material has high fire resistance. Due to the way they are constructed, CLT panels retain their strength and fire resistance even at high temperatures. They resist burning and retard the spread of fire, making them safe for use in construction.

The second source is the work of scientists from the University of Canterbury, which also confirms the high fire resistance of CLT panels. They conducted experiments in which they studied the material's resistance to fire under various conditions.

RESULTS

The results showed that CLT panels can withstand high temperatures for significant periods of time, making them an excellent choice for buildings that require increased fire resistance.

Thus, research allows us to conclude that CLT panels have high fire resistance. This material not only offers an environmentally friendly alternative to traditional building materials, but also guarantees the safety and durability of buildings. However, it is important to remember that in the event of a fire, all prescribed safety measures and rules for the use of CLT panels must be followed.

DISCUSSION

Pasteur (Limey-Brevent, France), Brock Commons (Canada), Mjostärnet Tower (Norway) and mid-rise residential buildings in Sweden, Finland, Austria and other European countries. Wooden structures can already seriously compete with reinforced concrete and metal. This can be confirmed by listing the advantages of wood as a building material:

• wood is a renewable natural resource; working with
• wood is less energy and labor intensive [1];
• buildings made of wood meet modern standards of green, energy-efficient construction [2:
• structures can be erected in areas with difficult engineering and geological conditions.

But in the Russian Federation, laminated wood structures have not yet become widespread. This is due to a large number of negative factors:

• lagging behind modern regulatory documentation for the design of wooden structures:
• the lack of qualified specialists in the field of both design and direct construction of wooden structures;
• low confidence in wooden houses among the population, caused by fear of the high fire hazard of laminated timber structures.

The last problem is one of the key ones. Many potential buyers of apartments in houses made of laminated wood make their choice in favor of reinforced concrete or brick only because of considerations of the fire hazard of wood.

The authors analyzed the following literature: research from the Holzforschung Austria Institute, a report from Stora Enso and the main materials of the regulatory documentation set out in Eurocode 5 (EN 1995-1-2) [3-5]. The article is based on statistical data and analytical reviews in the field of research into the fire resistance of CLT panels in the Russian Federation and abroad, on analytical, regulatory and reference materials from the resources of various companies.

The fire resistance index of a building structure is the actual fire resistance limit, which is determined by the time (in minutes) of the onset of one or sequentially several signs normalized for a given structure (R. Е \ І).

The main features of the limit state of load-bearing and enclosing structures [6]:

-loss of load-bearing capacity (character R) due to the collapse of the structure or the occurrence of extreme deformations (for example, unacceptable bending);

- loss of integrity - the formation in structures or joints of through cracks or through holes (sign E), through which combustion products or flames penetrate into the adjacent room;

- loss of thermal insulation ability (sign I) - increase in temperature on the unheated surface of the structure by an average of more than 160 °C, or above 180 °C at any point on this surface;

- achieving the maximum value of heat flux density (3.5 kW/m?) at a standardized distance (0.5 m) from the unheated surface of the structure (sign W).

When designing a construction project, they are guided by the fact that the fire resistance limit of the connection points of elements and support nodes of wooden structures, including those using metal and non-metallic reinforcement elements, is not lower than the required fire resistance limit of the structure as a whole.

Modern wooden structures provide the necessary fire resistance. In this case, we are talking about laminated veneer lumber, the fire resistance of which largely depends on the heat resistance of the adhesive compositions [6].

Many tests have been carried out in the field of wood fire resistance research. In June 2016 at the TsNIISK named after. V.A. Kucherenko, on the initiative of the GOOD WOOD company, conducted an experiment to determine the fire resistance of laminated wood beams, which were supposed to be used in the construction of a house. As a result of the test, it was established that after 93 minutes of fire exposure, the limiting state for the loss of bearing capacity of a beam made of coniferous wood under a concentrated load of 2 tons was not reached. Before testing, the beam does not contain any additional compound Processed [7]. The data obtained is the basis for introducing changes recommended by the Minister of Industry and Trade of the Russian Federation D. Manturov to the design standards for buildings with a height of more than three floors using new wood materials.

Foreign experience in studying the fire resistance of laminated wood structures, in particular CLT panels, proves high fire resistance rates comparable to leading building materials. Let us take as an example the research of Stora Enso, a leading global supplier of renewable solutions in the field of packaging, biomaterials, wood structures and paper [4].

Stora Enso commissioned various accredited testing institutes to test the fire resistance of CLT panels with different component structures according to

EN 1365-1 or EN 1365-2. As a result of fire tests carried out in accordance with EN 13501-2, a classification of the fire resistance of load-bearing cross-laminated timber elements as an external wall has been compiled.

According to tests carried out by the leading wood research institute in Austria, Holzforschung Austria, commissioned by Stora Enso, all configurations of load-bearing CE panels comply with the indicator in REI 90, which coincides with the fire resistance limit of load-bearing walls, columns and other load-bearing elements for fire resistance class II buildings, structures and fire compartments according to the “Technical Regulations on Fire Safety Requirements” [8].

Holzforschung Austria has determined the following calculated charring rates for CLT panels on unprotected surfaces [3]:

1. Horizontal components (ceiling and roof elements):

- 0.65 mm/min if only one layer is exposed to fire;

- 1.3 mm/min for any additional layers damaged by fire, up to charring or the formation of a 25 mm thick layer of coal (Fig. 1).

 2. Vertical elements (wall load-bearing element):

- 0.63 mm/min if only one layer is exposed to fire;

- 0.86 mm/min for each additional layer exposed to fire (Fig. 2).

Rice. 1. Diagram illustrating an example of charring or the charring rate of the horizontal component of CLT (CLT 180 Lbs), which explains the mathematically estimated charring rate of 1.3 mm/min for each additional layer affected by fire until a new 25 mm thick layer of coal is formed

Rice. 2. Diagram showing an example of charring or charring rate of a vertical CLT component (CLT 100 L5s), which explains the mathematically estimated increased charring rate of 0.86 mm/min

Research conducted by the Holzforschung Austria Institute clearly demonstrates the high fire resistance of CLT panels, which confirms the safety of their use in the construction of residential buildings and public buildings.

With high fire resistance rates of CLT panels, the need for special treatment with fire retardants cannot be ruled out. This will reduce flame spread, heat release rate and delay ignition time.

There are two types of fireproof impregnation:

1. Impregnation in the form of a coating.

2. Impregnation with chemical elements under pressure. The main goal of treating wood products with fire-resistant additives is to meet the requirements for the flame propagation index specified in [9].

Fire retardant coatings are divided into two groups: non-intumescent and intumescent [10]. Non-intumescents are primarily decorative, architectural coatings that contain additives to reduce the spread of fire and smoke. Intumescent coatings are those that swell with heat to form a multicellular char layer that acts as an insulating barrier and slows the heat exchange between the condensed and vapor phases. There are two types of fire retardant coatings available on the market – pigmented (colored or clear) and clear varnish – which are designed for use on different materials and react differently when exposed to fire. They are mainly used in structures, wall-ceiling joints and other applications that require meeting relevant fire resistance classes [11].

In principle, increased requirements for fire resistance can be compensated by the following measures [3]:

• increase the thickness of the CLT element;
• increase the number of layers of the CLT element;

Apply appropriate fire resistant cladding. According to the authors, modern technologies in production

Ensuring high fire resistance rates in the range from REI 60 to REI 90, which meets the requirements of the above-mentioned Eurocodes, as well as the relevant regulations of the Russian Federation, allows the free use of cross-laminated panels in the construction of public and residential buildings.

References:

1. Inzhutov, I., Amelchugov, S., Nazirov, R., Perkova, M., Rudyak, C., Baltinate, A. Energy efficiency of timber construction joint with wooden screw // E3S Web Conf. – 2019. – P. 110.
2. Kozlovsky, B. L., Kuropyatnikov, M. V., Fedorinova, O. I. Priority tasks of green construction in Rostov-on-Don. – Text: electronic // Engineering Bulletin of the Don: online scientific journal. – 2013. – No. 1 (24). – URL: https://ivdon.ru/ru/magazine/archive/n1y2013/1552h (access date: 12/14/2019).
3. Fire protection of CLT. – 2013. – 51 p. storaenso: site. – URL: https://www.storaenso.com/en (date access: 12/10/2019). – Text: electronic.
4. Eurocode 5: Design of timber structures. Part 1–2. General rules for determining fire resistance. – Minsk: Ministry of Construction and Architecture, 2010. – 63 p.
5. Artsybasheva, O. V., Aseeva, R. M., Serkov, B. B., Sivenkov, A. B. Modern trends in the field of fire resistance of wooden buildings and structures // Izvestia SFU. Technilogical sciences. – 2013. – No. 8 (145). – pp. 178–196.
6. The fire resistance of wooden structures has been confirmed in practice. – Text: electronic // GOODWOOD: website. – 2020. – URL: https://www.gwd.ru/about/publikatsii/ognestoykost-derevyannykh-konstruktsiy-podtverzhdena-na-praktike (date of access: 12/10/2019).
7. Technical regulations on fire safety requirementssti: Federal Law of the Russian Federation dated July 22, 2008 N 123-FZ (as amended on December 27, 2018). – Text: electronic // Tekhekspert. Electronic fund of legal and regulatory technical documentation.
8. Dagenais, Ch., White, R. H., Sumathipala, K. Fire Performance of Cross-Laminated Timber Assemblies // CLT Handbook (US Edition) – Chapter 8: Fire. – 2012. – P. 1–55.
9. Verburg, G. B., Rayner, E. T., Yeadon, D. A., Happer, L. L., Goldlatt, L. A., Dollear, F. G., Dupuy, H. P., York, E. Water- resistant, oil-based, intumescing re-retardant coatings. I. Devel- opmental formulations // Journal of the American Oil Chemists’ Society. – 1964. – Vol. 41, iss. 10. – P. 670–674.
10. Mariappan, T. Fire Retardant Coatings // New Technologies in Protective Coating / ed. by C. Gouidice, G. Canosa. – London : IntechOpen, 2017. – P. 101–122.