CHARACTERISATION OF CROSS LAMINATED TIMBER PROPERTIES
(2021) In TVSM-5000 VSMM01 20211Structural Mechanics
Department of Construction Sciences
- Abstract
- This project concerns an analysis of a hitherto untested method for determining the modulus of elasticity (MoE) and shear modulus parallel to grain, as well as the rolling shear modulus of cross laminated timber (CLT) through 3-point bending tests. A review of analytical models and methods is included, followed by an evaluation of the effect of the annual ring orientation and shear stress distribution at shear loading of individual board cross-sections. Lastly a validation of the results using 2D and 3D finite element (FE) models are presented.
A total of nine prismatic beams with a square cross section of 100×100 mm were cut centrically from a CLT plate with respect to the longitudinal boards. The beams were cut in two directions with... (More) - This project concerns an analysis of a hitherto untested method for determining the modulus of elasticity (MoE) and shear modulus parallel to grain, as well as the rolling shear modulus of cross laminated timber (CLT) through 3-point bending tests. A review of analytical models and methods is included, followed by an evaluation of the effect of the annual ring orientation and shear stress distribution at shear loading of individual board cross-sections. Lastly a validation of the results using 2D and 3D finite element (FE) models are presented.
A total of nine prismatic beams with a square cross section of 100×100 mm were cut centrically from a CLT plate with respect to the longitudinal boards. The beams were cut in two directions with respect to the outermost boards, resulting in two different layups and lengths. Six beams were cut with the outermost board in the longitudinal direction (with a length of 1500 mm), and three beams were cut with the outermost board in the transverse direction (with a length of 900 mm).
Each beam was tested at in-plane loading, and out-of-plane loading for two different spans, respectively, resulting in four tests for each beam and 36 tests in total. By using the test data within the linear-elastic range and performing a linear regression the equivalent stiffness could be evaluated. The results from the in-plane bending tests were used to characterise the MoE and shear modulus parallel to grain by means of Timoshenko theory. The results from the out-of-plane bending tests were used to characterise the rolling shear modulus by means of the Gamma method or Timoshenko theory.
The results were evaluated by comparing the calculated equivalent stiffness of FE-models (with homogenised material properties corresponding to the characterised stiffness properties) to the equivalent stiffness determined experimentally. The results show a promising reliability and validity for the beams with a length of 1500 mm when characterising the stiffness properties using Timoshenko theory, with respect to the shear stiffness being calculated for the gross area of the cross section. Thus, consideration of the shear stress distribution in the transverse boards should be reflected by modification of e.g. the effective area. The rolling shear modulus was characterised in the range of 64–89 MPa for the beams with a length of 1500 mm, with respect to Timoshenko theory, indicating realistic values and that the effect of annual ring pattern is accounted for. The Gamma method, however, resulted in characterised values of the rolling shear moduli that were considered too low with respect to the effect of annual ring pattern. (Less) - Popular Abstract (Swedish)
- Sedan korslimmat trä (KL-trä) utvecklades i centrala Europa för cirka 30 år sedan har dess användande inom byggnadssektorn ökat kraftigt. Dess många fördelar, som till exempel den snabba tillverkningen och monteringen, hållbarheten ur ett miljöperspektiv, samt goda bärförmåga i både längs- och tvärriktningen, är anledningar till detta. För att förbättra möjligheterna till effektivt materialutnyttjande behöver bland annat kostnadseffektiva och pålitliga testmetoder utvecklas för att enkelt kunna karakterisera styvhetsegenskaper hos KL-trä.
KL-trä produceras i fabrik och används framförallt som vägg- eller golvelement. När man dimensionerar KL-träelementen, framförallt golvelementen, är nedböjningen ofta en avgörande faktor. Nedböjningen... (More) - Sedan korslimmat trä (KL-trä) utvecklades i centrala Europa för cirka 30 år sedan har dess användande inom byggnadssektorn ökat kraftigt. Dess många fördelar, som till exempel den snabba tillverkningen och monteringen, hållbarheten ur ett miljöperspektiv, samt goda bärförmåga i både längs- och tvärriktningen, är anledningar till detta. För att förbättra möjligheterna till effektivt materialutnyttjande behöver bland annat kostnadseffektiva och pålitliga testmetoder utvecklas för att enkelt kunna karakterisera styvhetsegenskaper hos KL-trä.
KL-trä produceras i fabrik och används framförallt som vägg- eller golvelement. När man dimensionerar KL-träelementen, framförallt golvelementen, är nedböjningen ofta en avgörande faktor. Nedböjningen för golvelement styrs framförallt av tre styvhetsparametrar: elasticitetsmodulen och skjuvmodulen parallellt träets fiberriktning samt rullskjuvmodulen. Rullskjuvmodulen styr skjuvdeformationerna i tvärlagerna och denna styvhetsparameter är relativt svår att bestämma genom provning.
En vanlig metod för att karakterisera elastisicetsmodulen hos KL-trä är att belasta en KL-träskiva, eller balk, symmetriskt och med två identiska punktlaster. Därefter mäts den relativa nedböjningen mellan belastningspunkterna. Problemet med denna metod är att den relativa nedböjningen kan vara väldigt liten, vilket gör att noggrann mätutrustning behövs för att utföra provningarna. Dessutom bygger karakteriseringen av elasticitetsmodulen på den så kallade Gammametoden, där rullskjuvmodulen enligt europeiska standardiserade provningsanvisningar konservativt antas som 50 MPa.
Detta projekt syftade till att utvärdera om det går att bestämma de tre tidigare nämnda styvhetsparametrarna för en och samma provkropp, och på så vis slippa göra antaganden som kan leda till felaktiga resultat. Nio KL-träbalkar sågades ut ur en och samma skiva i olika riktning med hänsyn till de yttersta lamellerna. Balkarna belastades sedan av en punktlast för två efterföljande tester där balkarna roterades 90° kring sin egen axel mellan testerna. Denna procedur upprepades för två olika spännvidder för varje balk. Genom att utvärdera resultatet från provningarna med analytiska modeller som tar hänsyn till skjuvdeformationer, i detta fall Gammametoden och Timoshenkoteori, kunde elasticitetsmodulen och skjuvmodulen parallellt fiberriktningen samt rullskjuvmodulen karakteriseras.
Med nyttjande av finita elementmetoden (FE) kunde numeriska modeller skapas i syfte att simulera och analysera den alternativa testmetoden. De karakteriserade styvhetsparametrarna användes som indata i FE-modellerna. Genom att studera skillnaden mellan den jämförda parametern från provningarna och samma parameter i FE-modellerna kunde i bästa fall en avvikelse på mindre än 4 % konstateras. Dessutom var avvikelserna i resultaten konsekventa för samtliga balkar. Dessa resultat antyder på hög tillförlitlighet hos de karakteriserade styvhetsparametrarna samt att materialskillnader i träet beaktas av de karakteriserade styvhetsparametrarna. (Less)
Please use this url to cite or link to this publication:
http://lup.lub.lu.se/student-papers/record/9062526
- author
- Nilsson, Emil LU
- supervisor
- organization
- course
- VSMM01 20211
- year
- 2021
- type
- H3 - Professional qualifications (4 Years - )
- subject
- keywords
- CLT, cross laminated timber, in-plane loading, out-of-plane loading, beam, rolling shear modulus, experimental tests, FE-modelling
- publication/series
- TVSM-5000
- report number
- TVSM-5250
- ISSN
- 0281-6679
- language
- English
- id
- 9062526
- alternative location
- https://www.byggmek.lth.se/fileadmin/byggnadsmekanik/publications/tvsm5000/web5250.pdf
- date added to LUP
- 2021-08-18 09:30:53
- date last changed
- 2021-08-18 09:30:53
@misc{9062526,
abstract = {{This project concerns an analysis of a hitherto untested method for determining the modulus of elasticity (MoE) and shear modulus parallel to grain, as well as the rolling shear modulus of cross laminated timber (CLT) through 3-point bending tests. A review of analytical models and methods is included, followed by an evaluation of the effect of the annual ring orientation and shear stress distribution at shear loading of individual board cross-sections. Lastly a validation of the results using 2D and 3D finite element (FE) models are presented.
A total of nine prismatic beams with a square cross section of 100×100 mm were cut centrically from a CLT plate with respect to the longitudinal boards. The beams were cut in two directions with respect to the outermost boards, resulting in two different layups and lengths. Six beams were cut with the outermost board in the longitudinal direction (with a length of 1500 mm), and three beams were cut with the outermost board in the transverse direction (with a length of 900 mm).
Each beam was tested at in-plane loading, and out-of-plane loading for two different spans, respectively, resulting in four tests for each beam and 36 tests in total. By using the test data within the linear-elastic range and performing a linear regression the equivalent stiffness could be evaluated. The results from the in-plane bending tests were used to characterise the MoE and shear modulus parallel to grain by means of Timoshenko theory. The results from the out-of-plane bending tests were used to characterise the rolling shear modulus by means of the Gamma method or Timoshenko theory.
The results were evaluated by comparing the calculated equivalent stiffness of FE-models (with homogenised material properties corresponding to the characterised stiffness properties) to the equivalent stiffness determined experimentally. The results show a promising reliability and validity for the beams with a length of 1500 mm when characterising the stiffness properties using Timoshenko theory, with respect to the shear stiffness being calculated for the gross area of the cross section. Thus, consideration of the shear stress distribution in the transverse boards should be reflected by modification of e.g. the effective area. The rolling shear modulus was characterised in the range of 64–89 MPa for the beams with a length of 1500 mm, with respect to Timoshenko theory, indicating realistic values and that the effect of annual ring pattern is accounted for. The Gamma method, however, resulted in characterised values of the rolling shear moduli that were considered too low with respect to the effect of annual ring pattern.}},
author = {{Nilsson, Emil}},
issn = {{0281-6679}},
language = {{eng}},
note = {{Student Paper}},
series = {{TVSM-5000}},
title = {{CHARACTERISATION OF CROSS LAMINATED TIMBER PROPERTIES}},
year = {{2021}},
}