Rolling Shear Properties of F2 Hybrid Pine used in Cross Laminated Timber (CLT)

Andrews, Cameron (2019) Rolling Shear Properties of F2 Hybrid Pine used in Cross Laminated Timber (CLT). [USQ Project]

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Cross laminated timber (CLT) is a modernised engineering solution that was developed in the 1990’s, first originating in Austria. This product has been recognised for its competitive nature by having a light weight to strength ratio, high axial strength and ability to withstand in and out of plane behavioural loads. With changes to the Australian building code in 2016, it has seen the regulations to timber buildings increase to 30m in height which recognises the demand for CLT in the industry.

With the continual concerning increase in CO2 emissions particularly in the building industry over the past few decades, there are growing societal expectations to develop more sustainable and environmentally friendly solutions. As an appropriate response to this concern, CLT creates a more environmentally advantageous solution when compared to typical Portland concrete elements. The demand is on the rise for CLT being used in multi-storey buildings due to its eco-friendly and cost effective solution. The F2 hybrid being investigated is reaching maturity in plantations around the Queensland region, where suitability needs to be carried out to determine if the F2 hybrid being able to fulfil the role as feedstock for the manufacturing plant.

The governing factor for failure in CLT when loaded in out of plane bending can be given by the induced stresses in either axes exceeding the orientations strength. This is a critical factor for the shear strength as this cross layer is the weak point for the CLT member. These shear stresses which cause shear strains in the radialtangential plane are referred to as the rolling shear stresses.

As an appropriate response to this demand and failure type of CLT, rolling shear properties focusing on strength, stiffness and behaviour are investigated in this study. Parameters influencing these shear properties are experimentally tested and compared with theoretical and finite element modelling (FEM) for data analysis. The parameters being investigated during the experimental analysis focus on growth ring orientation, growth ring width, location of the pith, geometry, clear wood and knotted wood. The experimental procedure utilises the Two Plate Shear Test, as a wide variety and quantity of parameters can be controlled to investigate singular influences on rolling shear properties.

Results indicated differences in the achieved peak load and deformation response between all specimens which was to be expected, due to the varying parameters analysed. The effect of knot influence varied significantly dependent on the size of the knot for both rolling shear modulus (GR) and strength (fR) which is to be expected of non-distributive fiber directions characterised by knot influence, causing variations in stresses around these knotted regions. The centre of the pith located on CLT specimens gave a more predictable response and had an increasing effect on GR but not on fR. Lower grain orientations were found to accompany lower achieved results for both GR and fR, where increases of these properties were observed with higher grain orientations, described by a polynomial regression. Variations in similar grain orientations were also characterised by the growth ring width, where the greater the growth ring width, accompanied greater GR and fR values. Regarding geometry, greater width (b1) / thickness (t1) values, were associated with lower values achieved for GR. However, inversely greater b1 / t1 values, were associated with higher values achieved for fR. A comparison of experimental results to the shear analogy theory for calculating effective rolling shear stiffness (GAeff) indicated a modification to account for lower grain orientations where the F2 hybrid is used as CLT, given in equation 5.4. Using Strand7, a FE model was developed, replicating the experimental test setup which was able to describe the behaviour of the CLT specimen under an applied loaded condition. Strain measurements were correlated between the two analysis methods for the localised region of strain gauge attachment.

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Item Type: USQ Project
Item Status: Live Archive
Faculty/School / Institute/Centre: Historic - Faculty of Health, Engineering and Sciences - School of Civil Engineering and Surveying (1 Jul 2013 - 31 Dec 2021)
Supervisors: Karunasena, Karu
Qualification: Bachelor of Engineering (Honours) (Civil)
Date Deposited: 09 Aug 2021 23:44
Last Modified: 26 Jun 2023 05:40
Uncontrolled Keywords: Cross laminated timber (CLT), Rolling Shear Properties, F2 Hybrid Pine

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