Innovative mass timber panels, known as composite laminated panels (CLP), have been developed using lumber and laminated strand lumber (LSL) laminates. In this study, strain distributions of various 5-layer CLP and cross-laminated timber (CLT) were investigated by experimental and two modelling methods. Seven (7) different panel types were tested in third-point bending and short-span shear tests. During the tests, the digital imaging correlation (DIC) technique was used to measure the normal and shear strain in areas of interest. Evaluated component properties were used to determine strain distributions based on the shear analogy method and finite element (FE) modelling. The calculated theoretical strain distributions were compared with the DIC test results to evaluate the validity of strain distributions predicted by the analytical model (shear analogy) and numerical model (FE analysis). In addition, the influence of the test setup on the shear strain distribution was investigated. Results showed that the DIC strain distributions agreed well with the ones calculated by the shear analogy method and FE analysis. Both theoretical methods agree well with the test results in terms of strain distribution shape and magnitude. While the shear analogy method shows limitations when it comes to local strain close to the supports or gaps, the FE analysis reflects these strain shifts well. The findings support that the shear analogy is generally applicable for the stress and strain determination of CLP and CLT for structural design, while an FE analysis can be beneficial when it comes to the evaluation of localized stresses and strains. Due to the influence of compression at a support, the shear strain distribution near the support location is not symmetric. This is confirmed by the FE method.
Southern Pine (SP) is one of the fastest growing softwood species in the Southern Forest of United States. With its high strength to weight ratio, SP becomes an ideal candidate for manufacturing engineered wood products such as cross laminated timber (CLT). Two batches of CLT panels were manufactured using visually graded SP lumbers in this study: pilot-scale panels in a laboratory setting and full-size panels in a manufacturing plant environment. The first batch of pilot-scale CLT panels was manufactured at Clemson University. The second batch of full-scale CLT panels (3m x 12.2m) was produced and CNC-sized by Structurlam in Penticton, Canada and shipped to Clemson University for testing. Four types of structural wood adhesives were selected in the panel production, namely Melamine Formaldehyde (MF), Phenol Resorcinol Formaldehyde (PRF), Polyurethane (PUR) and Emulsion Polymer Isocyanate (EPI). This paper presents the manufacturing process of SP CLT in a laboratory setting as well as structural performance verification of 3- ply SP CLT in terms of rolling shear and bending properties. The obtained performance data of 3-ply CLT in both major and minor strength directions is verified against PRG-320 Standard for Performance Rated Cross Laminated Timber. Tested results are presented and discussed.
An innovative multi-layer (3 and 5) composite laminated panel (CLP) with various layups were developed using sawn lumber and structural composite lumber (SCL) to address the rolling shear and gap issues of cross laminated timber (CLT). The bending properties including apparent and effective bending stiffness, shear stiffness, moment capacities and failure modes of CLPs were evaluated by a combination of modal tests and third-point bending tests of beam specimens cut from the panels. The static bending test results showed that the apparent bending stiffness values of 3-layer and 5-layer CLPs were up to 20% and 43% higher than the corresponding values of 3-layer and 5-layer generic CLT, respectively. The bending moment capacity values of 3-layer and 5-layer CLPs were up to 37% and 87% higher than the corresponding values of 3-layer and 5-layer generic CLT, respectively. The use of SCL in transverse layers eliminated the potential rolling shear failure in CLT and increased the stiffness properties. The apparent and effective bending stiffness predicted by shear analogy method had a good agreement with corresponding values measured by bending tests and/or modal tests. The prediction of bending moment capacity using shear analogy method cannot be validated due to the rolling shear failure and tension failure modes observed in certain groups.
The cross-laminated timber (CLT) technology is also perceived as a potential for utilization of lumber oflower grades and underused species, because the core layers perpendicular to the principle loading direction transferloads through rolling shear, which is not correlated to the grade of lumber. Current the product standard however specifies the minimum grade requirements for all lumber to be used as CLT laminations. In this study the effect of the presence of knots in the transverse core layer of CLT billets was examined in matched CLT samples where the heavy presence of knots in the transverse core layer was the only variable compared to knot free reference. All samples were tested as short-beams in three point bending and all failed in rolling shear in the transverse core layer. The presence of knots had no measurable effect on the shear capacity expressed as nominal MOR of the tested CLT beam samples
This paper presents an experimental study on rolling shear (RS) strength properties of non-edge-glued cross-laminated timber (CLT) made out of New Zealand Radiata pine (Pinus radiata) structural timber. CLT specimens with 35 and 20 mm thick laminations were studied to evaluate the influence of lamination thickness on the RS strength of CLT. Short-span three-point bending tests were used to introduce high RS stresses in cross layers of CLT specimens and facilitate the RS failure mechanism. Modified planar shear tests from the conventional two-plate planar shear tests were also used to evaluate the RS strength properties. It was found that two test methods yielded comparable RS strength properties and the lamination thickness significantly affected RS strength of the CLT specimens. The test results also indicated that the recommended characteristic RS strength values of CLT products in Europe and Canada might be over conservative. Also, it might be more efficient to specify different RS strength values for CLT with different lamination thickness given the minimum width-to-depth ratio of laminations is satisfied.
Cross-laminated timber (CLT) is a wood panel product that can be arranged in different ways. The advantage of utilizing CLT is the ability to use lamination even with low density materials or those that have defects, like knots. This study evaluated the bonding and bending performances of CLT utilizing domestic species in a shear wall or floor via a face bonding test of layers and a three-point bending test. The tests were carried out with three-layered CLT made up of Japanese larch and/or Korean red pine in various configurations. The layer arrangement for lamination was divided according to the species and grade of the wood. The out-of-plane and in-plane bending tests were conducted on the CLT according to the applicable direction in a wooden structure. The results of the bonding test showed that the block shear strength and delamination of all types of CLT met the BS EN 16351 (2015) standard requirements. The results of the bending test based on two wood species showed that the bending strength of the larch CLT was higher than that of the pine CLT in single species combinations. For mixed species combinations, the bending properties of CLT using larch as the major layer was higher than those using pine as the major layer. This demonstrated that the major layer had more influence on the bending properties of CLT and that Korean red pine was more suited for the minor layer of CLT.
International Conference on Biobase Material Science and Engineering
October 21-23, 2012, Changsha, China
The purpose of this study was to measure the rolling shear modulus of Cross Laminated Timber (CLT), which was achieved by conducting 3-point bending tests with variable span using downscaled sandwich specimens. Two types of sandwich specimens were employed: steel-wood-steel (SWS) and wood-wood-wood (WWW). Experimental results from SWS specimens were verified with those predicted from WWW ones through the shear analogy method. Effects of span-to-depth ratio (l/h) and growth ring orientation on rolling shear modulus (G RT ) were also examined. It was found that the average deflection of WWW specimens tested at l/h of 6.5 could be well predicted using the shear analogy method based on true elasticity of modulus (E m ) and G RT of the cross layer measured using SWS specimens under variable span tests. The results also showed that the cross layer of `in-between' growth ring orientation could gain the higher rolling shear modulus than that of flat sawn or quarter sawn one.
This paper presents an evaluation of overstrength based on an experimental study on dowelled connections in cross-laminated timber (CLT). Connection overstrength needs to be well understood in order to ensure that ductile system behaviour and energy dissipation can be achieved under seismic loading. Overstrength is defined as the difference between the code-based strength, using characteristic material strengths, and the 95th 4 percentile of the true strength distribution. Many aspects contribute to total connection overstrength, which makes its definition challenging. In this study, half-hole embedment tests were performed on CLT to establish embedment strength properties and three point bending tests were performed to determine the fastener yield moment. Different connection layouts, making use of mild steel dowels and an internal steel plate, were tested under monotonic and cyclic loading to evaluate theoretically determined overstrength values and study the influence of cyclic loading on overstrength. Experimental results were compared with strength predictions from code provisions and analytical models for ductile response under monotonic loading. It was found that cyclic loading does not significantly influence overstrength for connections that respond in a mixed-mode ductile way indicating that in future more expedient monotonic test campaigns could be used. This work also provides further experimental data and theoretical considerations necessary for the estimation of a generally applicable overstrength factor for dowelled CLT connections.
A reduction of the shear resistance was introduced with the crack factor kcr in Eurocode 5. The factor 0.67 corresponds to cracks that have a depth of 1/3 of the beam width. The aim of this project was to learn more about different types of cracks and their importance for the shear strength of glulam beams. The project started with tests of five types of glulam beams, with or without cracks. The cracks had different depths and locations, three beam types had cracks made by sawing and one type had cracks from moisturing and drying. The beam dimensions were 115 mm x 315 mm x 2600 mm. Five beams of each type with cracks were tested and ten beams without cracks. The beams were Swedish standard beams made of Spruce and taken from the normal production. Three-point bending method was used for the shear tests. The beams of type 1 without cracks got mostly bending failures; the characteristic shear strength was at least 3.5 MPa. Beams with sawn grooves got lower characteristic shear values and this means a reduced cross section should be used for beams with cut grooves along the beams. Beams with drying cracks got more shear failures, but the characteristic shear strength of the beams was about the same as for beams without cracks.