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Behaviour of Loaded Cross-Laminated Timber Wall Elements in Fire Conditions

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Abstract

Cross-laminated timber (CLT) is increasingly being used in medium-rise timber buildings for a number of reasons, such as rapidity of construction, cost effectiveness and robustness. Like for other building materials, verification of the load-bearing performance in fire conditions is an important issue. Experimental fire tests have been performed on loaded CLT wall elements at research institutes in Sweden and Italy. In total, three large-scale and four medium-scale tests have been carried out. The aim was to gain information about initially protected and unprotected elements, to be used for classification and also for validation of calculation models. In the test series, reference tests at normal temperature were included to obtain information (e.g. stiffness, strength) about the material tested in fire conditions. In addition, model-scale fire tests were performed to investigate the loss in stiffness resulting from fire exposure and the effect of different protection types. Loaded fire tests varied in the range of 41.8 min to 120 min, depending on the CLT structure, the level of load, and the type of protection. Data on temperature within specimens and residual cross-sections were collected. Charring rates evaluated from experimental results were comparable with values proposed by Eurocode for the design of timber structures. Conservative solutions were obtained by using simplified design methods and comparing their results to test results and results of advanced modelling. It was shown that the load-bearing performance of CLT may show abrupt changes due to its layered structure. It is strongly recommended that a minimum residual depth depending on the CLT structure should be required in order to ensure robust building products.

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Abbreviations

E b :

Global modulus of elasticity in bending (N/mm2)

E c :

Axial modulus of elasticity in compression (N/mm2)

E c,buckling :

Axial modulus of elasticity obtained by means of buckling tests at normal conditions (N/mm2)

(EI)residual,cold :

Flexural stiffness of cold, charred residual cross-section (Nmm2)

(EI)residual,warm :

Flexural stiffness of heated, charred residual cross-section in fire situation (Nmm2)

P :

Load applied during fire tests (kN)

P buckling :

Failure load in buckling at normal conditions (kN)

P IVALSA :

Failure load at normal conditions calculated for specimen tested in fire situation (kN)

R :

Load-bearing capacity in buckling

S.D. :

Standard deviation

T :

Temperature (°C)

b :

Element width (mm)

b buckling :

Width of elements tested in buckling at normal conditions (mm)

b IVALSA :

Width of elements tested in fire situation (mm)

d char :

Charring depth for one-dimensional charring (mm)

d 0 :

Thickness of the zero-strength layer (mm)

d 0,E :

Thickness of the zero-strength layer for the buckling situation (mm)

e :

Edge distance of screws (mm)

f b :

Bending strength at normal conditions (N/mm2)

f c :

Compression strength at normal conditions (N/mm2)

f c,buckling :

Compression strength in buckling at normal conditions (N/mm2)

h :

Element cross-section depth (mm)

h ef :

Effective cross-section depth (mm)

h ef,layer1 :

Effective cross-section depth of the first CLT layer (mm)

h p :

Notional depth of fire protective panel (mm)

h residual :

Residual cross-section depth (mm)

h residual,layer1 :

Residual cross-section depth of the first CLT layer (mm)

k 2 :

Protection coefficient or insulation coefficient

k 3 :

Post-protection coefficient

k mod,E,fi :

Modification factor for modulus of elasticity in fire situation

l buckling :

Length of elements tested in buckling at normal conditions (mm)

l IVALSA :

Length of elements tested in fire situation (mm)

l 0,IVALSA :

Effective length of elements tested in fire situation (mm)

t :

Time of fire exposure (min)

t ch :

Time of start of charring of protected members (min)

t f :

Failure time of wall (min)

t f,pr :

Failure time of protection or stickability (min)

t test :

Time of test duration (min)

β 0 :

One-dimensional charring rate under standard fire exposure (mm/min)

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Author information

Authors and Affiliations

  1. Department of Civil, Environmental and Natural Resources Engineering, SP Technical Research Institute of Sweden, Wood Technology and Luleå University of Technology, Stockholm, Sweden

    Joachim Schmid

  2. Department of Architecture and Urban Planning, University of Sassari, Alghero, Italy

    Agnese Menis & Massimo Fragiacomo

  3. University of Trieste, Trieste, Italy

    Isaia Clemente

  4. CNR Ivalsa Trees and Timber Institute, San Michele all’Adige, Italy

    Giovanna Bochicchio

Authors
  1. Joachim Schmid
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  2. Agnese Menis
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  3. Massimo Fragiacomo
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  4. Isaia Clemente
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  5. Giovanna Bochicchio
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Corresponding author

Correspondence to Joachim Schmid.

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Schmid, J., Menis, A., Fragiacomo, M. et al. Behaviour of Loaded Cross-Laminated Timber Wall Elements in Fire Conditions. Fire Technol 51, 1341–1370 (2015). https://doi.org/10.1007/s10694-015-0516-8

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