With the introduction of Cross Laminated Timber (CLT) into North America and gaining popularity it is of interest to the design and code development community to have codified provisions to facilitate the design of CLT structures. This paper addresses the design aspect of CLT panels subjected to combined bending and compressive axial...
An investigation was carried out on CLT panels made from Sitka spruce in order to establish the effect of the thickness of CLT panels on the bending stiffness and strength and the rolling shear. Bending and shear tests on 3-layer and 5-layer panels were performed with loading in the out-of-plane and in-plane directions. ‘Global’ stiffness measurements were found to correlate well with theoretical values. Based on the results, there was a general tendency that both the bending strength and rolling shear decreased with panel thickness. Mean values for rolling shear ranged from 1.0 N/mm2 to 2.0 N/mm2.
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.
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.
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.