Impact of knots on the fracture propagating along grain in timber beams

Jockwer, Robert; Serrano, Erik; Gustafsson, Peter; Steiger, René

doi:10.1080/20426445.2016.1275093

Cited by 9 publications

(4 citation statements)

References 7 publications

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“…PRG320 is the only one of these three standards that restricts the inclusion of knots over and above structural grading requirements. Given that knots show good potential for central layers because of their good rolling [23] and longitudinal shear [21,22] performance, it would be beneficial to utilize them in CLT. But given their negative impact on bond performance, it would be unwise not to restrict their inclusion, as they could reach a level that is detrimental to the bond performance of the panel.…”

Section: Maximizing Out-of-grade Into Cltmentioning

confidence: 99%

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Maximizing the Use of Out-of-Grade Hybrid Pine in Engineered Wood Products: Bond Performance, the Effect of Resin Streaking, Knots, and Pith

Cherry,

Karunasena,

Manalo

2023

Forests

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The evolution toward small-diameter and fast-growing plantation timbers such as the Pinus elliotti var. elliottii (Engelm) × Pinus caribaea var. hondurensis (Sénéclauze) (PEE×PCH) hybrids around the world is producing large volumes of core wood that are falling short of structural sawn timber grading requirements. Engineered timber products such as cross-laminated timber (CLT) and glue-laminated (glulam) offer potential solutions to value-adding this resource, but the bond performance of this feedstock and the extent to which current standards and guides address its common characteristics for bond performance need to be understood. This study investigated the bond quality and performance of clear defect-free, low stiffness out-of-grade PEE×PCH and evaluated this performance using the pass/fail criteria of the CLT bond performance requirements of three national CLT standards. 5-layer CLT delamination samples and shear block test samples were glued using one-component polyurethane (PUR). This process was repeated for common occurring characteristics in this resource of resin, knots, and pith to understand their impact and inform an evaluation on the need to restrict their inclusion. Clear samples had an average glue line delamination of 2.9% and an average glue line wood failure of 96.7%. Resin achieved 9.3% and 92.6%, respectively. While knots had the lowest performance at 24.4% and 77.4%, respectively. When pith was at or adjacent to the glue line, wood failure occurred through the pith and its immediate surrounding fiber. Shear strength and wood failure tests were carried out on glulam and CLT-oriented samples. CLT knot samples were tested in two load orientations. Glulam-oriented samples in clear, resin, pith, and knots achieved an average shear strength of 8.5 MPa, 8.2 MPa, 7.9 MPa, and 8.2 MPa, respectively, and wood failure of 86%, 85%, 90%, and 69%, respectively. CLT-oriented samples in clear and resin both achieved average shear strengths of 4.0 MPa; 0°-loaded and 90°-loaded pith samples achieved 3.6 MPa and 2.4 MPa, while 0°-loaded and 90°-loaded knot samples achieved 4.2 MPa and 4.7 MPa respectively. Average wood failures were 90%, 89%, 96%, 96%, 83%, and 51%, respectively. PRG320 was found to be the most restrictive standard. Resin, knots, and pith were not addressed in the evaluation of delamination or shear strength in any standard, and PRG320 was the only standard to restrict these characteristics over and above structural grading rules. The amount and type of characteristics present vary considerably in structurally graded wood, and even more so for this out-of-grade resource. It was determined that the negative impact that resin, knots, and pith have on bond quality and bond performance calls for some restriction of their inclusion in order to achieve the author’s interpretation of the intended bond performance requirements of the CLT standards, which currently do not address these characteristics well or at all. A proposed modification to the PRG320 effective bond area was presented as a proactive solution.

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Section: Maximizing Out-of-grade Into Cltmentioning

confidence: 99%

“…In fact, the majority of publications focus on the bonding of mature rather than juvenile wood [20]. Moreover, researchers intentionally excluded large knots from their studies [18,20] even though knots have shown good shear performance [21][22][23][24], which is desirable for inner layers in glue-laminated timber (Glulam) and CLT.…”

Section: Introductionmentioning

confidence: 99%

Maximizing the Use of Out-of-Grade Hybrid Pine in Engineered Wood Products: Bond Performance, the Effect of Resin Streaking, Knots, and Pith

Cherry,

Karunasena,

Manalo

2023

Forests

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“…Developing timber structure buildings is conducive to achieving the national goals of peaking carbon emissions and carbon neutrality. timber columns are the main compressive components in timber structure buildings, but natural defects in wood, such as knots and cracks, limit their application in timber column components [2]. Therefore, reasonable and effective reinforcement methods are crucial for timber column components.…”

Section: Introductionmentioning

confidence: 99%

Advancements in the Study of FRP-Reinforced Timber Columns under Axial Compression

Yan

2024

AJST

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FRP reinforcement technology, with its numerous outstanding advantages, has been widely applied to the strengthening of timber column structures, making related research of significant social and engineering practical relevance. This paper reviews the research achievements in the axial compression performance of FRP-reinforced timber columns from both domestic and international sources. It analyzes advancements in four aspects: types of FRP, number of FRP layers, the impact of knots, and models of ultimate compressive strength and finite element models. A comprehensive analysis and comparison of existing research shortcomings and unresolved issues are provided. Finally, some references and suggestions for further research and application of FRP-reinforced timber columns are offered.

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“…The assumptions for the analysis were taken from the theory of laminar flow around a still obstacle [ 10 , 20 ]. In one model, steeped elliptic obstacles reflected knots, and the fluid flow path represented fiber deflection [ 21 , 22 , 23 , 24 ]. Another model involving flow-grain analogy was suggested by Guindos [ 25 ].…”

Section: Introductionmentioning

confidence: 99%

Near-Surface Mounted Reinforcement of Sawn Timber Beams-FEM Approach

Burawska-Kupniewska

Beer

2021

Materials

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The demand for timber has increased significantly in recent years. Therefore, reliable tools are needed to predict the mechanical properties of sawn timber, especially for structural applications. Very complex models require a lot of input data for analysis, which cannot always be guaranteed, especially in industrial practice. Thus, a simplified model for material description was developed and assessed with experiments (static bending tests carried out in accordance with the guidelines suggested in the European standard EN 408) and an analytical approach (gamma method according to the guidelines given in the European standard EN 1995). The effective stiffness was calculated as a major parameter, which has an influence on the elements’ behavior. The model included a near-surface mounted (NSM) local reinforcement technique, with CFRP strips of Scots pine timber beams being subjected to bending stresses. It is anticipated that the developed model can be a starting point for the repair engineering field, contributing to decision-making regarding conservation technique selection and range. Next, improvements of the model will provide more and more realistic results for numerical analysis in terms of the obtained failure mechanisms for sawn timber elements.

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Impact of knots on the fracture propagating along grain in timber beams

Cited by 9 publications

References 7 publications

Maximizing the Use of Out-of-Grade Hybrid Pine in Engineered Wood Products: Bond Performance, the Effect of Resin Streaking, Knots, and Pith

Maximizing the Use of Out-of-Grade Hybrid Pine in Engineered Wood Products: Bond Performance, the Effect of Resin Streaking, Knots, and Pith

Advancements in the Study of FRP-Reinforced Timber Columns under Axial Compression

Near-Surface Mounted Reinforcement of Sawn Timber Beams-FEM Approach

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