M. AUGUSTIN Institute for Timber Engineering and Wood Technology Graz University of Technology CROSS LAMINATED TIMBER (CLT) AND THE AUSTRIAN PRACTICE Educational Materials for Designing and Testing of Timber Structures – TEMTIS Seminar Horsens / Denmark, 11 th September 2008

2 Outline What is “Cross Laminated Timber (CLT)“ ? Current production volume Examples of erected buildings R&D-Activities about CLT at Graz University of Technology CLT in standards Load carrying model and verification of stresses for CLT-plates Further tests concerning CLT at Graz University of Technology

3 Cross Laminated Timber – Basic idea and Product Distribution of mechanical properties in the log 5-layered CLT-element Utilisation of side-boards

4 CLT – Production volume Production volume: 2008About m³ (+52 %) →To high amount for the market →Price will decrease (about 20 % in the next three years) Source: Timber Online / 2007 Arguments PRO CLT: →Massive construction, less layers in the construction, buffer for heat and moisture →High degree of prefabrication possible →Easy assembling and short duration for erection →Flexibility of utilisation Arguments CONTRA CLT: →High price

5 CLT – Examples of erected buildings “Austria-House” (2006) Turin / Italy Building Research Centre Step 2 (2007) Graz / Austria

6 CLT – Examples of erected buildings Multi-storey building (2001) Vienna / Austria “Wandritsch-Bridge” (1998) St. Lorenzen / Austria

7 AREA 1_SSTC Shell and Spatial Timber Constructions (SSTC) TMC using CLT MODULE 2 Connection Technique MODULE 4 Development of Systems Architectural Potential Case Studies MODULE 3 Guidelines Building Physics Leading Details MODULE 1 Mechanical Aspects Structural Analysis Verification Procedure R&D-Activities concern. CLT – Institute for Timber Engineering and Wood Technology / holz.bau forschungs gmbH // TUG

8 Limit states Topics: “System effects“ “Laminating effects“ Subproject “Load carrying capacity“ (for elements loaded as plates and panels) Topic: Creep behaviour Subproject “Creep“ Objective Load carrying model CLTDeformation factor CLT Ultimate Limit State Serviceability Limit State Further tests: Properties perpendicular to grainVibration properties of CLT-floors

9 CLT in standards Eurocode Currently no proposals for the verification of CLT-elements DIN A verification procedere is given in this standard Verification of stresses on each single layer: in accord. with EN 338D → This procedere leads to conservative results because no “homogenisation effects“ are considered ! → The development of an European standard is initiated by the Austrian Standardisation Organisation (ON).

10 Applied to layered products: e.g. Glulam -35% 1 65, ,,,              dm m dm m dm m fff h t   

11 Subproject “Load carrying capacity of CLT in bending“ Objective of the research work Results of tension tests: f t,0, l,05 = 12,5 N/mm² COV t = 39,4 % Method

12 Test results 0,00 5,00 10,00 15,00 20,00 25,00 30,00 35,00 40,00 45, Number of lamellas in the outer layers Mean value and COV of edge normal strength f m,c f m,c,mean [N/mm²] 5 # series ‚4u‘f m,g,mean = 42,4 N/mm² COV = 9,5 % 19 # series ‚1u‘f m,g,mean = 44,2 N/mm² COV = 20,1 % 37,2 39,0 39,4 37,3 mean value 0,0% 2,0% 4,0% 6,0% 8,0% 10,0% 12,0% 14,0% 16,0% 18,0% COV [%] 16,1% 14,4% 12,5% 7,6% COV

13 5 % - quantile values and system factor for CLT Number of lamellas in the outer layers f m,c,05 [N/mm²] 25,00 26,00 27,00 28,00 29,00 30,00 31,00 32,00 33,00 34, % fractile and k sys of edge normal strength f m,c 8 k sys,CLT 1,00 1,05 1,10 1,15 1,20 1,25 1,30 1,00 1,09 1,14 1,19 system effect 27,3 29,8 31,3 32,6 5% fractile 19 # series ‚1u‘f m,g,05 = 29,0 N/mm² 1,1 proposal k sys

14 Beam Model for GLT including the variation of the base material according to EN 1194:1999 e.g.: Load carrying model for CLT loaded in bending

15 Load carrying model for CLT loaded in bending Beam Model for GLT including the variation of the base material

16 Load carrying model for CLT loaded in bending Model for CLT

17 Model for CLT Load carrying model for CLT loaded in bending

18 Load carrying model for CLT in bending - based on test results Test results 31,3 29,6 1,1 k sys Analy. results Factor 12,5 f t,0,l, ,8 3,15 a (COV t = 39,4 %) 29,0 28,6 1,20 k h (h = 110 mm, b = 110 mm) 27,3 26,9 0,94 k CLT/GLT Load carrying model for CLT loaded in bending

19 Proposed Model for CLT for reference higth h = 150 mm (without considering of width) Load carrying model for CLT loaded in bending

20 Proposal of a Beam Model for CLT – Comparison with older data Single result of one 9 layer CLT element (width 2000 mm); 3) Single result of one 7 layer CLT element (width 2000 mm); 2)  37,5 39,1 2) 42,9 2) 39,4 3) ~ 35 % 19,3 (n = 80) old results (1998)  26,8 (n = 50) 45,547,830,4 %New results 1) 5 layer CLT made of solid edge glued panels (spruce); 1) [N/mm²] [%][N/mm²]  12,5 f t,0,l,05 28,131,339,4 %presented f m,c,05,≥4 calculated f m,c,05,=4 test results COV t Load carrying model for CLT loaded in bending

21 Verification in technical approvals Specifications in technical approvals

22 Comparison of verification approvals DIN 1052 C 24 f t,0,l,k = 14,0 COV = 35 % C 40 f t,0,l,k = 24,0 COV = 25 % 15,6 0,65∙f m,k 26,0 0,65∙f m,k 29,0 1,21∙f m,k 38,3 0,96∙f m,k Comparison of verification proposals Proposal TUG

23 Determination of stresses in CLT-elements loaded in bending Shear stresses S eff Normal stresses I eff Determination of stresses for CLT

24 kA G,eff S eff I eff Ratio of shear-deformation on the total deflection (single-span beam with uniformly distributed load) 0% 5% 10% 15% 20% 25% 30% 35% 40% 45% 50% Ratio l / h Ratio w V / w ges beam Area of utilisation in practice - plate isotrop spruce CLT 5-layered Determination of deformations for CLT Determination of deformations of CLT-elements loaded in bending

Number of layers kA G,eff S eff I eff Effective second moment of area of the cross section Determination of stresses in CLT-elements loaded in bending

26 kA G,eff S eff I eff Number of layers Effective statical moment of the cross section Determination of stresses in CLT-elements loaded in bending

27 kA G,eff S eff I eff Number of layers Effective area of the cross section Determination of stresses in CLT-elements loaded in bending

28 k A G,eff S eff I eff Shear correction factor κ for CLT cross sections with consideration of the material values in accord. to DIN ,20 0 1,2 2,4 3,6 4, Number of layers n Shear correction factor κ 4,87 4,11 3,88 3,783,73 3,70 Shear correction factor Determination of stresses in CLT-elements loaded in bending

29 k A G,eff S eff I eff E 90 =0 Shear correction factor for a three layered-element Determination of stresses in CLT-elements loaded in bending

30 k A G,eff S eff I eff Shear correction factor κ in the case of uneven thickness ratio of the layers 0 1,2 2,4 3,6 4,8 6 0,00,10,20,30,40,50,60,70,80,91,0 Thickness ratio of the layersΣt 0 /h Shear correction factor κ C24_7s 7s_95% C24_3s 3s_95% C24_5s 5s_95% C24_infinite-s infinite-s_95% h = 100 mm t 0 = 24 mm t 90 = 52 mm h = 100 mm t 0 = 36 mm t 90 = 28 mm Shear correction factor for CLT built up with uneven layers thickness Determination of stresses in CLT-elements loaded in bending

31 k A G,eff S eff I eff Shear correction factor κ with variation of the ratio G 090 / G Ratio G 090 / G 9090 Shear correction factor κ  _3-layers  _5-layers  _7-layers DIN 1052:2004 C24 approvalC30 approval Shear correction factor with variation of the ratio G 090 / G 9090 Determination of stresses in CLT-elements loaded in bending

32 k A G,eff S eff I eff Material properties EN 338 (all strength- classes) 1) C 24 (in accord. with the approvals) 2) C 30 (in accord. with the approvals) 2) G 9090 = G 090 /10G 9090 = 50 [N/mm 2 ] 3-layered 4,96,57,0 5-layered 4,15,45,9 7-layered 3,95,15,5 1) E 0 /E 90 = 30; E 0 /G 090 = 16; G 090 /G 9090 = 10 2) Für C24: E 0 /E 90 = 30; E 0 /G 090 = 16 Für C30: E 0 /E 90 = 30; E 0 /G 090 = 16 Shear correction factor with values from standards Determination of stresses in CLT-elements loaded in bending

33 - without openings CLT wall elements under homogeneous shear (shear stiffness) experimental and theoretical solution (doctoral thesis in process: Th. Moosbrugger) - with openings u = 5 mm a = 75 mm  u/a= ua 60 mm G plate,mean = 229 N/mm² (5 tests, COV = 0.16) board spacing: board width: u/a= ≈ 0.29 practical range 229 / 750  0.3 Determination of stresses in CLT-elements loaded as panel

34 Creep behaviour of CLT-elements Specimens with two cross sections: GLT and CLT Test setup: 4 – point – bending test according to EN 408 Futher details tests: Tests with two climates (55%/20°C; 78%/20°C) and two stress levels (about 3 N/mm² and 8 N/mm²) Sl.1 - low Sl.2 - high Climate 2 Sl.1 - low Sl.2 - high Climate 1 GLT  CLT Stress - level Climate + 38,5 % + 46,5 % + 19,3 % +41,9 % Results k def,CLT,5-layer SC 10,85 SC 21,10 Proposals for standardisation Approximatly values for Plywood

35 Compression perpendicular to grain of CLT-cubic specimens E c,90,mean = 500 N/mm² f c,90,k = 3,0 N/mm² Strength Stiffness Test setup: Tests on specimens with different number of layers, position of the board in the log, built-up factor and loading situations

THANKS FOR YOUR ATTENTION ! Contact DI Manfred AUGUSTIN Scientific Assistent +43 (0) Inffeldgasse 24, A-8010 Graz / Austria