Sung-Jun Pang

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 ...

Bending Strength of Korean Softwood Species for 120×180 mm Structural Members

The goal of this study is to investigate bending properties of domestic timber. Three representative struc- tural timber from Larix kaempferi, Pinus koraiensis, and Pinus densiflora, in the northeastern South Korea were selected. Visual grading for the timber was conducted based on KFRI notification 2009-01 and the bending strength for the timber was evaluated based on ASTM D 198 bending. The high percentage of grade 1 and 2 for Larix kaempferi shows that the KFRI notification was optimized for this species. The bending strength distributions from Pinus koraiensis and Pinus densiflora were very similar. It could be possible to specify the allowable bending properties of these two Specification using a united species group similar to spruce-pine-fir. Lastly, the bending strength of 120 × 180 mm structural members was higher than both existing values in KBC 2009 and design values for timber of imported species described in the NDS. Thus, 120 mm thick domestic softwoods could replace the commercial imported species and the KBC should be modified to provide design values for both timber and dimensional lumber, re- spectively, like NDS.

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.

Study of the Distribution Properties and LRFD Code Conversion in Japanese Larch

This study was performed to develop an LRFD (Load Resistance Factored Design) Code for Domestic Larch. To accomplish his, we evaluated bending, compression, tension and shear strength. The results of the strength evaluation were utilized to verify the distribution and code conversion. For bending, tension and compressive strength, the Weibull distribution was well-fitted, but for shear strength we observed a normal distribution. For evaluating the bending and compressive strength, a full-sized specimen was used. A small clear specimen was used to test tension and shear strength. Compressive strength in particular was found to be affected by tight knots, although there was little difference between grades. In the code conversion, the design value of the LRFD was larger than the existing allowable stress value in the Korean Building Code. However, the allowable stress in this study was about two times higher than the value listed in the Korean Building Code. This result induced the difference between the soft and hard conversions. For greater reliability, the accumulation of additional data is necessary and further studies should be performed

Indirect Detection of Internal Defects in Wooden Rafter with Ultrasound

The purpose of this research was development of quantitative ultrasonic test methodology for detecting internal defects in members of ancient wooden building. Connection part between wooden members and/or contacted or hidden part by wall of ceiling or other construction materials make it hard to apply direct way of ultrasonic test. So indirect way of ultrasonic test needed to be applied. Test methodology with newly developed prototype of ultrasonic system was proposed. Homogeneous material with polypropylene was also tested for establishing the criterion. Results showed that TOF(time of flight)-energy and pulse length were found out to be proper ultrasonic parameters for predicting depth of defect in wood different from polypropylene. It was not possible to directly apply prediction equation derived from polypropylene. Newly established prediction equation shows coefficient of determination of 0.73 for wood. Finally, defect of replaced rafter members was predicted with the coefficient of determination of 0.32. Various aspects of ultrasound propagation in wood including anisotropy need to be carefully considered to raise up the prediction accuracy.

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.

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

Alternative experimental method to evaluate moment-carrying capacity of traditional wood-to-wood joint with small scale experiment

Abstract The effect of scale ratio was investigated on a traditional dovetail post-beam joint with dimensional analysis. The dimensionless parameters for moment (M) are modulus of elasticity (E) and length (L), and the moment of a small-scale model is equal to the value calculated by dividing the moment of a full-scale structure by the cubed ratio. The theoretical results of moment resistance were checked among dovetail post-beam joints of different sizes. The average maximum and yield moment resistance increased as the scale ratio increased. However, when both moment values were divided by the cube of the scale ratio, the values were similar among the different scale ratio joints. This result shows that the moment resistance was satisfied with the dimensional analysis within the tested scale ratio and it would be possible to predict the structural characteristics by testing specimens with other scales.

Effect of incising on the long-term biodeterioration resistance of alkaline copper quaternary (ACQ) treated wood

The aim of this study was to investigate whether making incising for injecting alkaline copper quaternary (ACQ) into wood extends the wood’s biodeterioration resistance. The biodeterioration resistance was checked by comparing long-term residual ACQ in wood with a toxic threshold to fungi. The residual ACQ in wood was estimated by leaching ratios and a long-term emission model which was derived by leaching tests of full-sized ACQ treated wood. The initial retention and the amount of ACQ leached of incised specimens were higher than those of non-incised specimens. However, the initial retention had a larger impact on leaching ratio than amount of ACQ leached. As a result, the leaching ratios of incised specimens were lower than those of non-incised specimens. The results indicate that incised wood can be expected to have the biodeterioration resistance for a longer period of time than non-incised wood.