There is a need of more advanced analysis for studying how the long-term behaviour of glued laminated timber structures is affected by creep and by cyclic variations in climate. A beam theory is presented able to simulate the overall hygro-mechanical and visco-elastic behaviour of (inhomogeneous) glulam structures. Two frame structures subjected to both mechanical and cyclic environmental loading are analysed to illustrate the advantages the model involved can provide. The results indicate clearly both the (discontinuous) inhomogeneity of the glulam products and the variable moisture-load action that occurs to have a significant effect on deformations, section forces and stress distributions within the frame structures that were studied
In a former paper by the authors , the elastic behavior of Cross Laminated Timber (CLT) and timber panels having periodic gaps between lateral lamellae has been analyzed. A thick plate homogenization scheme based on Finite Elements computations has been applied. The predicted behavior was in agreement with experimental results. In this paper, simplified closed-form solutions are derived in order to avoid FE modeling. Both cases of narrow gaps of CLT panels and wide gaps of innovative lightweight panels are investigated. CLT and timber panels with gaps are modeled as a space frame of beams connected with wooden blocks. The contribution of both beams and blocks to the panel’s mechanical response is taken into account, leading to closed-form expressions for predicting the panel’s stiffnesses and maximum longitudinal and rolling shear stresses. The derived closed-form solutions are in agreement with the reference FE results and they can be used for practical design purposes.
The design of cross-laminated solid timber (CLT) as load-bearing plates is mainly governed by serviceability criterions like maximal deflection and susceptibility to vibration. Hence, predicting the respective behavior of such plates requires accurate information about their elastic properties. According to product standards, the bending stiffness of CLT has to be assessed from 4-point bending tests of strip-shaped specimens, cut from the CLT panels. By comparing elastic properties of CLT derived by means of modal analysis of full panels with the results of bending tests on 100 mm and 300 mm wide strip-shaped specimens it is shown, that by testing single 100 mm wide strip-shaped specimens bending stiffness of full panels cannot be assessed correctly, whereas single 300 mm wide strips or averages of 5 to 6 100 mm wide strip-shaped specimens lead to acceptable results. Hence, strip-shaped specimens should only be used in the course of factory quality control or when assessing the bending stiffness of parts of CLT panels used as beam-like load-bearing elements but not to derive bending stiffness of gross CLT panels. Verification by carrying out static bending tests of gross CLT panels under different loading situations showed that alternatively to tests on strip-shaped specimens or estimations with the compound theory, the overall stiffness properties of CLT can be derived directly by a modal analysis of full-size panels.
The topic of this paper is the discussion of a proposal for the design of ribbed plates built-up with CLT (plate)- and GLT (ribs)- members. The suggested elastic model is based on the work of Abdelouahed  and Smith and Teng  for the strengthening of concrete members with FRP plates and will be applied for the mentioned loadcarrying timber elements. As a result so far it could be observed, that high peaks of shear and tensile stresses perpendicular to the interface (glue-line) occur due to the elastic consideration of the material. The model was evaluated by some pre-test which showed an acceptable correlation between the predictions of the model and a 2D-FEM analysis. It is evident, that the notches at the end of the rips must be reinforced by e.g. self-tapping screws or glued in rod to achieve effective solutions for this load carrying element. With the discussed model the shear and tensile stresses and forces resp. perpendicular to the interface can be computed.
In the present paper, the influence of periodic gaps between lamellas of Cross Laminated Timber (CLT) on the panel’s elastic behavior is analyzed by means of a periodic homogenization scheme for thick plates having periodic geometry. Both small gaps, due to the fabrication process of not-gluing lateral lamellas, and wider gaps are investigated. The results obtained with the periodic homogenization scheme are compared to existing closed-form solutions and available experimental data. It appears that the plate bending stiffness can be well predicted with both homogenization and simplified methods, while only the homogenization approach is in agreement with the experimental in-plane and out-of-plane shear behavior. The influence of several properties of CLT lay-up on the mechanical response is pointed out as well.
Cross laminated timber (CLT) is leading the evolution of wood construction throughout the world. As atwo-dimensional plate-like construction product, the in-plane elastic constants of CLT panels are the fundamental parameters for serviceability design. The elastic constants including moduli of elasticity (MOE) in major and minor strength direction ( and y) and in-plane shear modulus ( xy) of full-size CLT panels with different dimensions and layups from three CLT producers were measured by a non-destructive test (NDT) method developed by the first author. In total, 51 CLT panels were tested with most of the testing conducted at CLT mills. The measured values were used to examine the existing effective stiffness prediction models of CLT. Results show that k-method can be used for predicting and y values of industrial size CLT with a large length/ width to thickness ratio. xy cannot be well predicted by k-method and is greatly affected by edge bonding and gaps. Gamma method and shear analogy method can include the effect of transverse shear to different extents into account in predicting apparent or y. Shear analogy method appears to predict closer apparent to the measured values than gamma method for CLT with small length to thickness ratio. However, the effect of transverse shear on apparent y is not as much as predicted by shear analogy method for CLT panels with width from 1 to 3 meters. NDT by modal testing was proven to be an efficient mechanical property evaluation method for full-size CLT panels.