Effective cross-section of a timber beam exposed to natural fires

Huč, Sabina (author), Hozjan, Tomaž (author), Pečenko, Robert (author)

According to the Eurocode standards, advanced numerical models or the reduced cross-section method can be used to determine the mechanical resistance of timber structures under fire conditions. The method assumes a rectangular effective cross-section with full strength and stiffness and the cross-section of effective thickness without strength and stiffness after fire exposure. The effective thickness is the sum of the charring thickness and the zero-strength layer thickness, which are specified in the standards only for standard fire exposure. In the present paper, the analyses are combined with the reduced cross-section method and numerical fire, hygro-thermal and mechanical models to determine the charring thickness, zero-strength layer thickness and effective thickness of a simply supported timber beam under bending exposed to different natural fires. The results show that the three thicknesses increase with fire duration until the end values are reac hed at which the timber beam can withstand a prescribed natural fire. The end values for the charring thickness are between 18.2 mm and 72.1 mm, for the zero-strength layer thickness between 14.9 mm and 27.4 mm and for the effective thickness between 39.9 mm and 89.9 mm. The results also show that the end values of the charring thickness and the effective thickness depend on the maximum gas temperature. The end values of the zero-strength layer thickness depend on the linear cooling rate. Simple linear equations are proposed to account for these dependencies. Piecewise linear equations are also proposed to describe the temporal development of the three thicknesses.

• Language: English
• Keywords: charring depth, natural fire, reduced cross-section method, timber beam, zero strength layer
• Work type: Article
• Typology: 1.01 - Original Scientific Article
• Organization: FGG - Faculty of Civil and Geodetic Engineering; FKKT - Faculty of Chemistry and Chemical Technology
• Publication status: Published
• Publication version: Version of Record
• Year: 2025
• Number of pages: 16 str.
• Numbering: Vol. 83, iss. 2, art. 71
• PID: 20.500.12556/RUL-167610
• UDC: 69:539.4
• ISSN on article: 1436-736X
• DOI: 10.1007/s00107-025-02202-6
• COBISS.SI-ID: 227910147
• Publication date in RUL: 04.03.2025

Record is a part of a journal

• Title: European journal of wood and wood products
• Publisher: Springer Nature
• ISSN: 1436-736X
• COBISS.SI-ID: 22253061

Licences

• License: CC BY 4.0, Creative Commons Attribution 4.0 International
• Link: http://creativecommons.org/licenses/by/4.0/
• Description: This is the standard Creative Commons license that gives others maximum freedom to do what they want with the work as long as they credit the author.

Secondary language

• Language: Slovenian
• Keywords: globina oglenenja, naravni požar, metoda reduciranega prečnega prereza, leseni nosilci, nenosilen sloj