: A computer aided numerical model for the simulation of the in-plane bending strength of CLT beams is presented. The model uses the Monte-Carlo-Method to generate mechanical characteristics of board lamellae and is suitable for the investigation of statistical effects such as homogenisation and size effects. Six different types of CLT beams, varying in size and in layup, were tested to validate the model and except for beams with only one lamella in direction of the beam height good agreement was found between the experimental results and the model’s simulations.
At the Institute of Structural Engineering at the ETH Zurich numerous of investigations are
conducted to analyse the load bearing capacity of glued laminated timber beams. The investigations are part of the research project ’Influence of varying material properties on the load bearing capacity of glued laminated timber (glulam)’.
The investigations are taking place on 24 glulam beams with well-known material properties.
The glulam beams are fabricated out of 400 timber boards. From those boards the material
properties are investigated non-destructively within a former research project. During the glulam
fabrication it is particularly focused to keep the information of the timber boards; i.e. after the
glulam fabrication the position of each particular timber board within the glulam beam and
thus the position of each particular knot is still known.
The glulam beams are investigated during a 4-point bending test. On the glulam members
the load bearing capacity, the bending stiffness and the density is measured. Furthermore
local strains within the glulam beams are investigated using an optical coordinate-measurement
device. Following the test the failure is investigated in detail. Hereby the type of failure (knot
cluster, finger joint, clear wood) and the amount of failure (number of damaged lamellas) is
documented. Afterwards the failed glulam beams are loaded again to analyse the remaining
bending strength and the corresponding remaining bending stiffness.
The major aim of the experimental analysis is the investigation of the load bearing capacity
of glulam beams with well-known local material properties. The gained results can be used for
an investigation of the influence of local weak zones, such as knot clusters or finger joints, on the
load bearing capacity of glulam. In addition a data basis is produced to develop a new model
(or to evaluate existing models) for the estimation of the load bearing capacity of glulam.
An overview on the mechanical and physical properties of cross laminated timber (solid wood
panels) in the building industry and its use in timber construction is presented. Structure-property
relations for solid wood based materials are discussed. Important properties, such as strength, sorption, diffusion, thermal conductivity in relation to the board structure are presented. By varying the structure, the properties can be optimized over a wide range. The focus of this publication lies on experimental works performed by Swiss researchers at the ETH Zürich.
Development of cross laminated timber (CLT) manufacturing facilities will require an optimization of manufacturing parameters to ensure efficient production. This study examined the effects of press pressure, press time and the addition of water to bond surfaces for a CLT panel composed of southern pine lumber and polyurethane adhesive. Evaluation of the CLT panels used the five-point bending test for bending stiffness, bending strength and shear stiffness in addition to measuring the resistance to shear by compression loading. The shear strength and percent wood failure values obtained from the resistance to shear by compression loading. The optimal combination of manufacturing parameters studied was 100% press pressure and a press time of 80% of the manufacturer recommendations. The addition of water to the bondline surfaces was deemed unnecessary for CLT materials conforming to the PRG-320 standard. Comparison of mechanical properties with Grade V3 showed higher bending strength and shear stiffness values.
Effects of Component Ratio of the Face and Core Laminae on Static Bending Strenght Performance of Three-Ply Cross-Laminated Wood Panels with Sugi (Cryptomeria Japonica)
In order to improve the bending strength performance of three-ply laminated wood panels and use them as construction-grade panel materials, twelve types of three-ply cross-laminated wood panels whose percentages of core lamina thickness versus total lamina thickness were 33%, 50%, and 80% were made with sugi (Japanese cedar), and the effect of component ratio of the face and core laminae on their static bending strength performance was investigated.
The moduli of elasticity (MOE), proportional limit stresses and moduli of rupture (MOR), perpendicular (C type) and parallel (C type) to the grain of face laminae markedly increased or decreased with increasing percentage of core lamina thickness. The percentages of core lamina thickness at which each strength property value of C type became equal to that of C type ranged from 65% to 80%. At each percentage of core lamina thickness, the MOE and proportional limit stress of C type were higher in C (45) specimens having perpendicular-direction lamina of 45° annual ring angle in the core than in C (90) specimens having perpendicular-direction lamina of 90° in the core, whereas there was little difference in MOR between C (45) specimens and C (90) specimens. For 45° specimens having the core lamina thickness from 60% to 70%, MOE as well as MOR parallel and perpendicular to the grain of face laminae exceeded the corresponding requirement values of structural plywood with 21.0-mm thickness specified in Japanese Agricultural Standards.
CLT panels consist of several layers of lumber stacked crosswise and glued together on their faces. Prototype Sugi CLT floor panels were manufactured and bending and internal shear tests were carried out under the different parameters of lumber MOE, number of layers, thickness of lumber and thickness of CLT panels. On the basis of above tests, internal shear strength, bending stiffness and moment carrying capacity were estimated based on the lumber properties by Monte Carlo method. Bending stiffness EI of CLT panels could be estimated by adopting parallel layer theory and equivalent section area. Experimental moment carrying capacity showed 12% higher value than the calculated moment carrying capacity by average lumber failure method, and also showed 45% higher value than the calculated moment carrying capacity by minimum lumber failure method due to the reinforcement of the outer layer by the neighboring cross layer. Experimental internal shear force of CLT panel showed 30% higher value than the calculated one.
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