The Influence of Panel Lay-Up on the Characteristic Bending and Rolling Shear Strength of CLT

Abstract

The objective of this study was to characterise the behaviour of cross laminated timber (CLT) panels and the influence of the panel lay-up on the failure strength. Three different panel configurations of thickness, 60 mm, 100 mm, and 120 mm, were loaded in the out-of-plane direction. The 60 mm and 120 mm panel configuration comprised three layers of equal thickness, and the intermediate 100 mm thick panel comprised five layers of equal thickness. The mean and characteristic bending and rolling shear strength of the panels were examined. The results show that the mean bending and rolling shear strength decrease with the panel thickness. The characteristic results have shown that there is an influence because of the number of boards within the panel. The characteristic bending strength values for the five-layer 100 mm thick panel were found to be higher than that of the three-layer 60 mm panel. The characteristic rolling shear values decreased in the five-layer panels, however, the increased number of layers subjected to the rolling shear results in a reduced variability in the rolling shear strength.2 of 15 used for the manufacture of CLT are generally conditioned to a moisture content (u) of 12 ± 2% and are visually or mechanically strength graded. The common strength classes according to EN 338 [2] are C24 for a homogeneous layup, C24 for longitudinal layers, and C16/C18 for the transverse layers in a combined layup. In general, the guidelines and requirements of the adhesive manufacturers must be followed in the manufacture of CLT panels. It must be stated that some parameters, such as the bonding pressure, the quantity of applied adhesive, and the moisture content of adherends, are based on experience with glulam production [3][4][5][6][7].Many studies have examined CLT and its uses in the timber construction industry. Its excellent in-plane and out-of-plane strength, rigidity, and stability have allowed larger and taller buildings to be built [3,[8][9][10][11][12]. In Europe, spruce is largely used when manufacturing CLT, however, many other timber species have been investigated worldwide. Fortune and Quenneville [11] aimed to establish the use of CLT in New Zealand using locally-grown Radiata pine, bonded using resorcinol adhesive. In Japan, Sugi timber CLT panels were manufactured by Okabe et al. [13]. In the United States, Hindman and Bouldin [14] produced CLT using Southern pine, which was tested to establish the bending strength, bending stiffness, and shear strength. The CLT panels made from Scottish Sitka spruce was investigated by Crawford et al. [15]. Four CLT panels for each panel configuration (three-and five-layers) were prefabricated using Sitka spruce boards, graded to C16, and bonded with polyurethane (PUR) adhesive. Established bending strengths and stiffnesses in-and out-of-plane were not dissimilar to commercially available CLT panels, manufactured in Central Europe. Similarly, a sample of the CLT panels were manufactured from Irish Sitka spruce by Sikora et al. [9]. Sikora et al. [9] test...

The Rolling Shear Influence on the Out-of-Plane Behavior of CLT Panels: A Comparative Analysis

“…The influence of shear deformations on the cross-layer has also been examined with three-point bending tests in Mastek et al [8] and in Minghao Li [9]. Recently, experimental tests and numerical models have also been presented in Franzoni et al [10], in which the influence of large and small gaps between lateral boards (lamellas) on mechanical behavior of CLT panels subjected to vertical loads with respect to its mid-plane has been highlighted, while experimental measurements of rolling shear properties on soft and hardwood species were carried out by Zhou et al [11] and O' Ceallaigh et al [5]. An extensive experimental campaign (consisting of 342 tests), aimed to evaluate the rolling shear properties of six timber species, with three different sawing patterns and three different aspect ratios of specimens, has been conducted by Ehahart and Brandner [12].…”

“…As far as the rolling strength is concerned, experimental tests carried out on large scale CLT panels made with three or five layers established a reduced range of characteristic value, from 1.0-2.0 MPa for European spruces, independently from the timber strength class. This topic is beyond the scope of the present paper because the effect of the rolling shear on the deformative flexural behavior of CLT panels is mainly investigated here, whereby additional information can be found in the reference literature works [5,12,14,16].…”

Comparison of Theoretical and Laboratory Out-of-Plane Shear Stiffness Values of Cross Laminated Timber Panels

“…Results based on 28 FEG specimens. 2 Results based on 3 FEG specimen and/or 3 SEG specimen. 3 Results based on 9 FEG specimen and/or 9 SEG specimen.…”

“…Several studies have investigated parameters that affect the rolling shear strength of CLT panels. O'Ceallaigh et al (2018) [2] tested the bending and shear strength of 3-and 5-layer CLT with different panel thicknesses. The study found that both, bending and rolling shear strength decreases with increasing panel thickness.…”

Growth Ring Orientation Effects in Transverse Softwood Fracture

“…The emergence of mass timber in the form of cross-laminated timber (CLT) over the past 20 years, however, has necessitated a closer look at strength properties in a plane perpendicular to the grain axis. In particular, for CLT cross laminations, so-called rolling shear [ 3 , 4 , 5 ] is among the dominant failure modes for certain CLT layups. Hence, the motivation for the work described in this paper is to better understand strength and fracture in the plane perpendicular to the grain axis of the wood.…”