Bending and shear performance of Australian Radiata pine cross-laminated timber

Highlights

• Bending and shear behavior of Australian radiata pine cross-laminated timber.

• FEM analysis to predict bending and shear strength of CLT.

• Failure modes of CLT under out-of-plane bending and shear.

• Comparison of bending and shear stiffness of CLT between tests and theoretical.

Abstract

Cross Laminated Timber (CLT) is increasingly being used in commercial and residential construction in Australia due to its inherent strength and sustainability credentials. Until recently, infrastructure building projects using CLT have been reliant on imported products from overseas manufacturers. There is now a viable Australian grown and fabricated CLT product from Radiata pine. This paper summarises the experimental results on the mechanical behaviour of Australian Radiata pine CLT panels in out-of-plane bending and shear. Three-layer 105 mm thick panels and five-layer 145 mm panels with three different spans were tested. The results demonstrate strong correlations to existing theoretical models and were used to validate the finite element model (FEM) developed in this research.

The experimental results showed that the average bending stiffness of the CLT panels were marginally greater than theoretical values. The maximum bending strength for Radiata pine exceeded the characteristic strength of 14.0 MPa for grade XLG1 external laminas, with three-layer CLT samples averaging 28.7 MPa and five-layer CLT samples averaging 26.8 MPa. The maximum observed shear stresses ranged from 1.55 MPa to 2.18 MPa, which also exceeded the rolling shear characteristic strength of 1.2 MPa for the feedstock. The results also highlighted that the shear strength decreases with an increasing thickness of the CLT panel.

Introduction

The construction industry demands continual improvements for building materials that are fast and safe to erect, cost effective and sustainable [1], [2], [3]. CLT shows potential to address many of these requirements in the industry, with a high degree of prefabrication, high in-plane and out-plane strength and stiffness, and good acoustic and thermal performance [4], [5]. CLT is an engineered wood panel utilising at least three layers of timber boards glued together in orthogonal directions. This combination of layers eliminates much of the natural variability and the influence of defects in timber products when compared to plain sawn timber. CLT panels are frequently fabricated using timber offcuts or lower grade feedstock from other structural timber productions, thereby having a lower embodied energy, greenhouse gas emissions and high carbon sequestration compared to typical concrete construction [6]. As a result of these advantages, CLT is being used more widely in building construction [4], [7], [8].

CLT panels are made from different timber species that depend on local resources such as Kiri, Katsura, Sugi, Hinoki, Buna spruce pine (Europe and Canada) and Radiata pine (Australia and New Zealand). Previous research has focused on the flexural and shear performance of a variety of timber feedstock for CLT panels [4], [9], [10], [11], [12], [13], [14], [15], [16]. Hindman and Bouldin [9] performed four-point bending tests in order to evaluate the bending and shear properties of Southern pine CLT. Their results indicated an equal or higher shear resistance compared to the standard specified values of shear (i.e. GA_eff = 23 MN/m) and bending (i.e. EI_eff = 9.7 MNm) resistance [17]. Similarly, four-point bending tests were used to evaluate the stiffness and strength properties in the perpendicular and parallel directions to the principal plane of the CLT panels, which were made using spruce boards [11], [14]. Sikora et al. [14] assessed the effect of the panel thickness of Irish Sitka spruce CLT and found that the bending and rolling shear strength decreased with an increasing panel thickness. The bending creep performance of engineered wood products has been assessed by Park, et al. [10], where CLT panels from five different timber species were tested and they found that the creep deformation perpendicular to the grain was decreased by cross laminating. Fortune and Quenneville [12], Lewis et al. [18], Woodco [19], Iqbal [20] all investigated the shear and bending performance of CLT panels fabricated from New Zealand Radiata pine. These previous studies found that the bending and shear strength, and stiffness of CLT panels were equal to or higher than the standard specifications. However, there is limited research that has assessed the bending and shear performance of CLT panels fabricated using Australian Radiata pine.

This research investigates the bending and shear performance of Australian Radiata pine CLT panels using four-point bending tests and finite element (FE) analysis. Three different spans with two different thicknesses of CLT panels were tested to evaluate the bending and shear strength, and stiffness through experimental tests. The experimental results of this study also used to validate the FEM and predict the shear and bending performance of CLT panels with seven-layer.