Jung-Kwon Oh

Moment-Carrying Capacity of Dovetailed Mortise and Tenon Joints with or without Beam Shoulder

This study aimed to evaluate the influence of beam shoulder on the moment-carrying capacity of traditional post-beam joints, dovetailed mortise, and tenon joints. The specimens were manufactured by a computer numerical controlled (CNC) cutting machine with Japanese larch six-ply glulams (glued laminated timber), and moment-carrying capacity was investigated by static loading tests. The results of the tests indicated that the moment resistance, joint stiffness, and failure modes were different with or without beam shoulder. The results also indicated that all joints types underwent significant deformation without breaking and maintained after the yield point. The failure mode, which included post splitting, shear failure of mortise branches, or embedment failure of tenon, was dependent on the presence of the beam shoulder. The results indicated that the beam shoulder significantly affected the performance of the post-beam joint. It was concluded that the beam shoulder reinforced the dovetailed mortise and ...

Quantification of knots in dimension lumber using a single-pass X-ray radiation

The knot depth ratio (KDR) evaluation method was designed to quantitatively evaluate the amount of knot in dimension lumber by a single-pass X-ray radiation. To verify the proposed method, KDR values for 38-mm-thick specimens were predicted, and they were compared with the actual measured KDR values. The knot is surrounded by the transition zone, and the density of the knot and the transition zone is higher than the clear wood. Because the average density of the transition zone was similar to the knot density, it was found that the proposed method gives the KDR values for the knot area including the transition zone. The coefficients of determination between the predicted and measured KDR values were 0.87 and 0.83 for Japanese larch and red pine specimens, respectively. Using the KDR information, the ratio of knot area including transition zone to cross-sectional area was calculated. The presence of latewood and earlywood in the same path of the X-ray radiation caused discrepancies in the estimation of KDR values because the density of latewood is much higher than that of earlywood. Fortunately, latewood and earlywood are repeated in a cross section, so the amount of overestimation and underestimation was expected to be nearly identical. As expected, the relationship between the predicted area ratio and the real area ratio of knot and transition zone was strong with R2 values of 0.89 and 0.93 for Japanese larch and red pine specimens, respectively.

Shear Performance of PUR Adhesive in Cross Laminating of Red Pine

Cross laminated timber (CLT) has been an rising issue as a promising building material replacing steel-concrete in mid story rise construction. But, there was no specific standard for CLT because it had been developed in industrial section. Recently, new draft for requirements of CLT was proposed by EN which suggested to evaluate the performance of adhesive in CLT by the same method as glulam. But, it has been reported that shear performance of cross laminated timber is governed by rolling shear. There- fore, block shear tests were carried out to compare parallel to grain laminating and cross laminating using commercial one component PUR (Poly urethane resin). The result showed that the current glulam standard for evaluating bonding performance is not appropriate for CLT. Beacause shear strength of cross lami- nating decreased to 1/3 of parallel to grain laminating and this strength was representing shear performance of wood itself not the bond. However, cross laminating showed no significant effect on wood failure. Thus, wood failure can be used as a requirement of CLT bonding. Based on the results, cross laminating effect should be included when evaluating adhesive performance of CLT correctly and should be con- sidered as an important factor.

Influence of crossing-beam shoulder and wood species on moment-carrying capacity in a Korean traditional dovetail joint

This study investigated the interaction effects of a crossing beam on the moment-carrying capacity of a Korean traditional dovetail joint. In particular, the length of the crossing-beam shoulder (Bs) and the wood species were varied as important factors. Clearly, the Bs acts as a fastener that improves the performance of timber joints by preventing splitting failure parallel to the grain. All the specimens experienced tension failure by tension force in the direction perpendicular to the grain; therefore, the tension strength perpendicular to the grain could be considered an important property, and standard values could be determined to develop a formula for predicting the structural behavior of the joints or the structural design codes of the joints. The results of the tests indicated that the moment resistance of the joints increased as the length of the crossing Bs and the density of the wood species increased. Joint stiffness results also indicated that the joints became stiffer when the crossing beam had shoulders, but the results were not affected by the length of the Bs. In addition, the joint stiffness was proportional to the density of the wood species.

Prediction of compressive strength of cross-laminated timber panel

Compressive strength of cross-laminated timber (CLT) is one of the important mechanical properties which should be considered especially in design of mid-rise CLT building because it works to resist a vertical bearing load from the upper storeys. The CLT panel can be manufactured in various combinations of the grade and dimension of lamina. This leads to the fact that an experimental approach to evaluate the strength of CLT would be expensive and time-demanding. In this paper, lamina property-based models for predicting the compressive strength of CLT panel was studied. A Monte Carlo simulation was applied for the model prediction. A set of experimental compression tests on CLT panel (short column) was conducted to validate the model and it shows good results. Using this model, the influence of the lamina’s width on the CLT compressive strength was investigated. It reveals that the CLT compressive strength increases with the increase in the number of lamina. It was thought that repetitive member effect (or dispersion effect) is applicable for the CLT panel, which was explained by the decrease of the variation in strength. This dependency of the number of lamina needs further study in development of reference design values, CLT wall design and CLT manufacturing.

Evaluation of Allowable Bending Stress of Dimension Lumber; Confidence Levels and Size-adjustment

The aim of this study was to investigate the processes for evaluating the allowable bending stress. The confidence levels and the size-adjustment in standards were reviewed with experimental data. The results show that, (1) KS F 2152 was more strict than others overseas standards due to the higher confidence level. The 5% NTL of bending strengths by a method in KS F 2152 were lower than the overseas stand- ards and more specimens were required for evaluating the structural properties according to KS F 2152. (2) Due to the absence of size-adjustment method in domestic standards, the specified size and the ex- ponential parameters on the size-adjustment equation were reviewed by size factors. The specified size (width: 286 mm, length: 6096 mm), and the exponential parameters (w: 0.29, l: 0.14) will be suitable for developing the allowable bending stress in domestic standard. (3) The size adjusted allowable bending stresses of No. 2 grade Korean pine were lower than the allowable stresses tabulated in KBC even though less strict method (75% confidence level) to calculate 5% value was used. The allowable stresses tabulated in KBC are needed to be reviewed by continuous experimental data.

Parametric study on the capability of three-dimensional finite element analysis (3D-FEA) of compressive behaviour of Douglas fir

Abstract This study is aiming at the simulation of wood compression (C) at a macroscopic level by means of a three-dimensional finite element analysis (3D-FEA) of solid wood and evaluation of the capability and limitations of this approach. C-Tests were carried out on Douglas fir according to ASTM D 143. The specimens included the 25×25×100 mm3 cuboid bars for longitudinal (L), radial (R) and tangential (T) directions and the conventional 50×50×150 mm3 blocks for the perpendicular to grain (⊥) direction. Two sets of wood parameters were developed and the 3D-FEA was implemented for the two types of specimens. The 3D-FEA worked successfully provided that the stress state coming from the total wood C was uniform. However, in case of the dominance of local compressive behaviour such as bearing, crushing and fibre shear, a microscopic-level modelling technique is needed for correction of the material parameters. More details on the limitations and difficulties of 3D-FE implementation for wood were discussed.

Elasto-plastic Anisotropic Wood Material Model for Finite Solid Element Applications

A simplified material model, which was efficiently implemented in a three-dimensional finite solid element (3D FE) analysis for wood was developed. The bi-linear elasto-plastic anisotropic material theory was adopted to describe con- stitutive relations of wood in three major directions including longitudinal, radial and tangential direction. The assump- tion of transverse isotropy was made to reduce the requisite 27 material constants to 6 independent constants including elastic moduli, yield stresses and Poissons ratios in the parallel, and perpendicular to grain directions. The results of Douglas fir compression tests in the three directions were compared to the 3D FE simulation incorporated with the wood material model developed in this study. Successful agreements of the results were found in the load-deformation

Effect of Test Zone Selection for Evaluating Bending Strength of Lumber

ABSTRACT This study investigated the effect of test zone selection for evaluating bending strength of visually grad-ed lumber. This will contribute to the understanding of two different methods under different standards. In method Ⅰ, the major defect was randomly placed in the test specimen. In method Ⅱ, the major defect was randomly placed in the maximum moment zone (MMZ). The results showed that the method Ⅱ is more accurate for reflecting the effect of defects governing the grade of lumber. Unless the maximum strength-reducing defect (MSRD) is placed in MMZ, the evaluated value would be higher than that of MSRD. For evaluating the modulus of rupture (MOR) of visually graded lumber in test set-up of Method I, the Eq. (5) needs to be considered. Keywords : modulus of rupture, bending strength, bending test, lumber, strength-reducing defect 1. INTRODUCTION The exact structural strength of lumber must be known for it to be used efficiently in struc-tural applications which directly affect life, safe-ty, and protection of property. To determine these properties a representative sample has to be tested. As an international standard, ISO 13910 has been established for specifying sam-pling, full-size testing and evaluation procedures for assessing structural properties of sawn tim-ber which must fit engineering design codes. However, different regions in the world have still different testing standards (Wang, et al., 2005). To use lumber tested by different stand-ards, the differences between testing procedures should be checked. The maximum strength-reducing defect (MSRD) was located randomly in the maximum moment zone (MMZ) in In-grade testing program in North American (Evans et al., 2001). ASTM D198 allows the test zone selection procedure to be varied depending on the purpose of test. Meanwhile, ISO 13910 and AS/NZS 4063 adopt a completely random selection approach and the test piece should be selected from ran-dom locations within a piece of timber.The nonparametric tolerance limits, makes no

Feasibility of Non-Korean Standard Glulam Using a Lower Grade Lamina of Japanese cedar for Structural Use

Japanese cedar has low density and poor mechanical performance. Manufacturing glue-laminated timber (glulam) is the best way to compensate for its poor mechanical performance. The Korean Standard (KS) confines outermost lamina of glulam to higher grade than E8, but the yield of higher than grade E8 from logs is only 6.5%. Therefore, the aim of this study is to investigate the possibility of non-Korean-Standard glulam in structural applications. Allowable stresses determined by both hand-calculation and Monte-Carlo simulation show a higher allowable stress than that of the KS-standard glulam of 6S-22B. In the Korean Standard (KS), knot characteristics are not taken into account. Japanese cedar has relatively small knots. We believe that the small knots in Japanese cedar contribute to a higher allowable stress than the KS-standard glulam would predict. The species classification of KS is required to be further subdivided into sub-species groups based on knot characteristics.