Fire Technology

, Volume 54, Issue 5, pp 1113–1148 | Cite as

Simulation of the Fire Resistance of Cross-laminated Timber (CLT)

  • Joachim SchmidEmail author
  • Michael Klippel
  • Alar Just
  • Andrea Frangi
  • Mattia Tiso


Cross-laminated timber, typical abbreviations CLT or XLAM, is currently one of the most innovative product in building with wood. This solid engineered timber product provides advantages compared to other solid timber slabs as the dimension stability, i.e. swelling and shrinkage, is controlled by the crosswise laminations. As for other components, the fire resistance has to be verified for this type of product. While fire testing is time consuming and costly, simulations provide flexibility to optimize the product or to develop simplified design models for structural engineers. In this paper, a simulation technique is presented which can be used to determine the fire resistance of CLT. The technique was then used to develop simplified design equations to be used by engineers to predict the behavior of CLT in fire resistance tests and verify its fire resistance. Following existing models, the simplified design model aims for a two-step process whereby in a (i) first step the residual cross section and in (ii) a second step the load bearing capacity of the partly heated residual cross section is determined. The presented simulations consider the effective thermal–mechanical characteristics of wood exposed to standard fire and perform an advanced section analysis using a temperature profile corresponding to the actual protection and the location of the centroid together with the possibility of plasticity on the side of compression. It was shown that simulation results agree well with test results and that they can be used to determine layup specific modification factors used by the reduced properties method or zero-strength layers used by the effective cross section method. It was shown that the use of the zero-strength layers is favorable compared to the modification factors to calculate the resistance of the residual cross section. This is due to the large range of modification factors answering the typical layup of CLT comprising layers with their fiber direction cross the span direction. Subsequently, the methodology was used to determine design equations for initially unprotected and protected three-, five- and seven-layer CLT in bending and buckling. While the zero-strength layer for glulam beams in bending is assumed to be 7 mm (0.3 in), for CLT the corresponding value is in most of the cases between 5 mm and 12 mm but is different for other loading modes such as buckling (wall elements) and depending on the applied protection.


Cross-laminated timber Modelling Structural fire design Fire design model Fire tests 

List of symbols


Width (mm)


Depth for charring related measures (mm)


Modulus of elasticity (N/mm2)


Strength (N/mm2)


Half-length of the window (m)


Depth for member related measures (mm)




Modulus of inertia (mm4)


Reduction or modification factor


Bending moment resistance (N m)


Number of layers


Length (m)


Heat flux (kW m−2)


Temperature (°C)


Time (min)


Deflection of the bending member


Section modulus (mm3)


Length coordinate along the axis



Convective heat transfer coefficient (Wm−2K−1)


Emissivity or strain




Density (kg/m3)



Zero strength and stiffness


Reference moisture content


Normal temperature














Moment (in bending)






Heat flux (kW m−2)


Temperature (°C)


Time (min)







The research described here was conducted at SP Trätek, Stockholm, as a part of the FireInTimber project within the European Wood-Wisdom-Net framework. It is supported by industry through the European Initiative Building With Wood and public funding organizations. The authors would like to acknowledge COST FP1404 where a task group works with this type of product. The test specimens were produced and delivered by Martinsons Trä (Sweden) and Stora Enso Austria. A part of the fire tests were assisted, evaluated and reported by Per Willinder to be included in his Bachelor thesis. The analysis of the reference test results using the Maximum Likelihood Method was conducted by Jochen Köhler.


  1. 1.
    Falk A, Dietsch Ph, Schmid J (2016) In: Proceedings of the Joint Conference of COST Actions FP1402 & FP1404 Cross laminated timber: a competitive wood product for visionary and fire safe buildings, joint conference of COST Actions FP1402 & FP1404 Cross Laminated Timber. KTH Royal Institute of TechnologyGoogle Scholar
  2. 2.
    Schmid J, König J (2010) Cross Laminated timber in fire. SP Report 2010:11, StockholmGoogle Scholar
  3. 3.
    Frangi A, Fontana M, Hugi E, Jübstl R (2009) Experimental analysis of cross-laminated timber panels in fire. Fire Saf J 44:1078–1087CrossRefGoogle Scholar
  4. 4.
    Aguanno M (2013) Fire resistance tests on cross-laminated timber floor panels: an experimental and numerical analysis, Master Thesis, Carleton University, CanadaGoogle Scholar
  5. 5.
    Hasburgh L, Bourne K, Peralta P, Mitchel P, Schiff S, Pang W (2016) Effect of adhesives and ply configuration on the fire performance of Southern pine cross-laminated timber. In: Conference proceedings of the World Conference on Timber engineering in Vienna, 2016. WCTE 2016, Vienna, AustriaGoogle Scholar
  6. 6.
    Mestek P, Kreuzinger H, Winter S (2008) Design of cross laminated timber (CLT). In proceedings of the 10th World Conference on Timber Engineering. Miyazaki, JapanGoogle Scholar
  7. 7.
    Lie T T (1977) A method for assessing the fire resistance of laminated timber beams and columns. Can J Civil Eng 4(2):161–169CrossRefGoogle Scholar
  8. 8.
    EN 1995-1-2 Eurocode 5: Design of timber structures–Part 1-2: General–Structural fire design (2004) European Committee for Standardization, BrusselsGoogle Scholar
  9. 9.
    Schaffer E L, Marx C M, Bender D A, Woestel F E (1986) Strength validation and fire endurance of glued-laminated timer beams, Forest Products Laboratory, Research paper FPL 467, MadisonGoogle Scholar
  10. 10.
    Buchanan A H, Abu A K (2017) Structural design for fire safety. Wiley, New YorkGoogle Scholar
  11. 11.
    Schmid J, König J, Just A (2012) The reduced cross section method for the design of timber structures exposed to fire—background, limitations and new developments. Struct Eng Int 22(4):514–522CrossRefGoogle Scholar
  12. 12.
    Schmid J, König J, Köhler J (2010) Fire-exposed cross-laminated timber-Modelling and tests.” World Conference on Timber EngineeringGoogle Scholar
  13. 13.
    Franssen J M, Kodur V K R, Mason J (2005) User’s manual for SAFIR 2004—A computer program for analysis of structures subjected to fire. University of Liege, Department Structures du Génie Civil—Service Ponts et Charpentes. Liege, BelgiumGoogle Scholar
  14. 14.
    Källsner B, König J (2000) Thermal and mechanical properties of timber and some other materials used in light timber frame construction. In: Proceedings of CIB W18, Meeting 33, Delft, Lehrstuhl für Ingenieurbau, University Karlsruhe, Karlsruhe, GermanyGoogle Scholar
  15. 15.
    Schmid J, Just A, Klippel M, Fragiacomo M (2015). The reduced cross section method for evaluation of the fire resistance of timber members: discussion and determination of the zero-strength layer. Fire Technol 51(6):1285–1309CrossRefGoogle Scholar
  16. 16.
    ISO 834-1 (1975) Fire resistance tests—elements of building construction. Geneva: International Organization for StandardizationGoogle Scholar
  17. 17.
    Standard test methods for fire tests of building construction and materials (ASTM E 119). West Conshohocken, PA: ASTM.Google Scholar
  18. 18.
    Babrauskas V (2005) Charring rate of wood as a tool for fire investigations. Fire Saf J 40(6):528–554CrossRefGoogle Scholar
  19. 19.
    Schmid J, Brandon D, Werther N, Klippel M (2018) Thermal exposure of wood in standard fire resistance tests, Fire Saf JGoogle Scholar
  20. 20.
    EN 1991-1-2 Eurocode 1: Actions on structures—Part 1-2: General actions—Actions on structures exposed to fire (2002) European Committee for Standardization, BrusselsGoogle Scholar
  21. 21.
    König J (2004) Structural fire design according to Eurocode 5—design rules and their background. Fire Mater 29(3):147–163CrossRefGoogle Scholar
  22. 22.
    Just A, Joachim S, Ostman B (2012) Fire protection abilities provided by gypsum plasterboards. In: World Conference on Timber Engineering, Auckland, 16–19 July 2012Google Scholar
  23. 23.
    Schleifer V (2009) Zum Verhalten von raumabschliessenden mehrschichtigen Holzbauteilen im Brandfall. Doctoral dissertation, ETH Zurich, SwitzerlandGoogle Scholar
  24. 24.
    König J, Wallej L (2000) Timber frame assemblies exposed to standard and parametric fires. Part 2: A design model for standard fire exposure. Trätek report I0001001. StockholmGoogle Scholar
  25. 25.
    EN 338:2003 (2012) Structural timber—Strength classes. European Standard. European Committee for Standardization, BrusselsGoogle Scholar
  26. 26.
    Thunell B (1941) Hållfasthetsegenskaper hos svenskt furuvirke utan kvistar och defekter. Royal Swedish Institute for Engineering Research, Proceedings No. 161, StockholmGoogle Scholar
  27. 27.
    Blass H, Görlacher R (2003) Brettsperrholz–Grundlagen. Holzbau-Kalender 2. (2002) S:580–598. (in German)Google Scholar
  28. 28.
    Blass H J, Fellmoser P (2004) Design of solid wood panels with cross layers. In: 8th world conference on timber engineering, 14(17):6Google Scholar
  29. 29.
    Steiger R, Köhler J (2005) Analysis of censored data - examples in timber engineering research. Proceedings of CIB W18, Meeting 38, Karlsruhe, Lehrstuhl für Ingenieurbau, University Karlsruhe, Karlsruhe, GermanyGoogle Scholar
  30. 30.
    CLT: Handbook Cross-laminated Timber (2013) FPInnovationsGoogle Scholar
  31. 31.
    ISO 834-1 (1999) Fire-reseistance tests—Elements of building construction—Part 1: General requirements. International Organisation for Standardisation, ISO. Geneva, SwitzerlandGoogle Scholar
  32. 32.
    Östman B, Mikkola E, Stein R, Frangi A, König J, Dhima D, Hakkarainen T, Bregulla J (2010) Fire safety in timber buildings. Technical guideline for Europe. SP. 2010:19Google Scholar
  33. 33.
    Lineham SA, Thomson D, Bartlett AI, Bisby LA, Hadden RM (2016) Structural response of fire-exposed cross-laminated timber beams under sustained loads. Fire Saf J 31(85):23–34.CrossRefGoogle Scholar
  34. 34.
    Lange D, Boström L, Schmid J, Albrektson J (2014) The influence of parametric fire scenarios on structural timber performance and reliability. SP Report 35. Boras, SwedenGoogle Scholar
  35. 35.
    Tiso M, Just A, Klippel M, Schmid J, Brandon D (2017) Zero-strength layers for timber frame assemblies in a standard fire. In: Proceedings of the INTER Meeting 2017, Kyoto. Paper 50-16-3. Karlsruhe, GermanyGoogle Scholar
  36. 36.
    Konig J (2000) A design model for load-carrying timber frame members in walls and floors exposed to fire. CIB Working Commission 18Google Scholar
  37. 37.
    Werther N (2016) Einflussgrößen auf das Abbrandverhalten von Holzbauteilen und deren Berücksichtigung in empirischen und numerischen Beurteilungsverfahren. Doctoral dissertation, Technische Universität MünchenGoogle Scholar
  38. 38.
    König J, Schmid J (2007) Bonded timber deck plates in fire. Proceedings of CIB W18, Meeting 40, Bled, Slovenia. Lehrstuhl für Ingenieurholzbau, University of Karlsruhe, Karlsruhe, GermanyGoogle Scholar
  39. 39.
    Kippel M, Leyder C, Frangi A, Fontana M, Lam F, Ceccotti A (2014) Fire tests on loaded cross-laminated timber wall and floor elements. Fire Saf Sci 11:626–639.
  40. 40.
    Klippel M, Schmid J, Frangi A (2012) The Reduced Cross section Method for timber members subjected to compression, tension and bending in fire. Proceedings of CIB-W18 Meeting, Växjö, SwedenGoogle Scholar
  41. 41.
    Menis A, Fragiacomo M, Clemente I (2012) Numerical investigation of the fire resistance of protected cross-laminated timber floor panels. Struct Eng Int 22(4): 523–532CrossRefGoogle Scholar

Copyright information

© Springer Science+Business Media, LLC, part of Springer Nature 2018

Authors and Affiliations

  1. 1.ETH Zurich, IBKZurichSwitzerland
  2. 2.Tallinn University of TechnologyTallinnEstonia
  3. 3.Research Institutes of SwedenStockholmSweden

Personalised recommendations