Chul-Ki Kim

Unrecorded Higher Fungi of the Songnisan National Park

Abstract Fresh mushrooms were collected during survey field trips to the southern areas of Songnisan National Park for 24 days from April to November in 2002. Through this investigation, a total of 682 fungal collections were obtained and taxonomically amounted to 5 classes, 14 orders, 44 families and 202 species. Among them, six genera Diplomitoporus, Heterochaete, Hydnochaete, Loweporus, Scytinostroma and Tomentellina, and twelve species, Asterostroma cervicolor, Diplomitoporus crustulinus, Fomitopsis cajanderi, Heterochaete delicata, Hydnochaete tabacinoides, Hyphodontia sambuci, Hypoxylon deustum, Lopharia cinerascens, Loweporus roseoalbus, Phanerochaete chrysosporium, Scytinostroma odoratum and Tomentellina fibrosa were confirmed as new to Korea and registered here with descriptions.

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.

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

Evaluation of Friction Properties According to Normal Force and Direction of Wood Grain in Real Contact Area

In Korea, there has been a traditional post and beam wood construction with large roof load. Because a large friction is generated in wooden joint or members, it is important to evaluate the friction between wood members according to wood direction. Because most of studies have been concerned with friction between wood and steel, excluding effect of real area of contact, there are a few studies on the friction between wood members. The object of this study was to evaluate friction or coefficient of friction accord- ing to normal force and real area of contact of wood. With Japanese larch (Larix kaempferi) test speci- mens, five steps of normal force and combinations of test were prepared. Results indicated that normal force had almost no affection on the friction, however there was difference about friction or coefficient of friction according to real contact conditions of wood grain and contact area.

Improvement of robustness in ultrasonic attenuation spectroscopy for detecting internal insect damage in wood member of cultural heritage

Insect damage is one of the most serious problems in conservation of wooden cultural heritage buildings. Because this damage is quite small in a cross section, it is difficult to detect by conventional ultrasonic techniques. In the previous study, ultrasonic attenuation spectroscopy showed a feasibility to detect this small defect. But to apply this method to real inspection, the robustness needs to be improved. For improving the robustness, this study focused on inconsistency of ultrasonic spectrum measurement. To minimize the inconsistency, Spectra-averaging pretreatment was attempted. Even though this pretreatment would provide the better robustness, it can also make a negative effect on the accuracy in the detection of small damage. Therefore, the influence of the pretreatment on the prediction was investigated in this study. By ultrasonic attenuation spectroscopy, the number of drill hole was predicted. When comparing the accuracy in prediction using the pretreated spectra from the prediction without the pretreatment, the accuracy was not lower than that without the pretreatment or the previous study. Therefore, it was concluded that the Spectra-averaging pretreatment does not make a negative effect on the prediction.

Shear behavior of cross-laminated timber wall consisting of small panels

A cross-laminated timber (CLT) wall plays the role of resisting shear stress induced by lateral forces as well as vertical load. Due to the press size, CLT panels have a limitation in size. To minimize the initial investment, some glulam manufactures wanted to make a shear wall element with small-size CLT panels and panel-to-panel connections and wanted to know whether the shear wall would have equivalent shear performance with the wall made of a single CLT panel. In this study, this was investigated by experiments and kinematic model analysis. Two shear walls made of small CLT panels were tested. The model showed a good agreement with test results in the envelope curve. Even though the shear walls were made of small panels, the global peak load did not decrease significantly compared with the wall made of a single CLT panel, but the global displacement showed a large increase. From this analysis, it was concluded that the shear wall can be designed with small CLT panels, but displacement should be designed carefully.

Determination of Grades and Design Strengths of Machine Graded Lumber in Korea

국내외 기계등급제재목(구조재 및 층재)의 등급기준 및 설계강도 산출방법을 비교 분석하고 국내 제재산업 실정을 고려한 평균 탄성계수(modulus of elasticity, 이하 MOE) 기준방법 적용을 제안하였다. 먼저 올바른 기계등급제재목 기준 정착을 위해 기계등급구조재와 기계등급층재의 공통점과 차이점을 설명하였다. 최소 고정 MOE 기준 등급을 사용하는 국내 기준은 등급구분에는 편리하나 휨강도(modulus of rupture, 이하 MOR) 예측과 자원이용도 측면에서는 효율성이 낮은 것으로 파악되었다. 해외에서 사용되는 평균 MOE 기준 방법은 초기 컴퓨터 기반 작동을 요구하나 MOR-MOE 직선회귀에 근거한 합리적인 MOR 예측과 품질관리 측면에서 효율성이 높은 것으로 분석되었다. 무엇보다도 현 국내 기계등급구조재 등급체계는 수종별 강도 특성을 반영하지 못하고 있다는 것이 가장 큰 문제점으로 분석되었으며 이러한 결과를 기반으로 MOR-MOE 직선회귀분석에 근거한 기계등급제재목 등급기준 및 기준설계값 산출방법 적용을 제안하였다. 이를 통하여 궁극적으로 부가가치가 높은 국산 기계등급구조재 생산 활성화를 이루고, 기계등급구조재의 층재 전용 가능에 따른 구조용 집성재 가격경쟁력 제고 효과를 얻을 수 있다고 사료되었다.

Density calculation of wood by portable X-ray tube with consideration of penetrating depth

A portable X-ray apparatus generates soft X-rays which have a continuous wavelength (wide range). When using continuous wavelength X-rays, the mass attenuation coefficient of the soft X-rays is changed as the penetrating depth in wood increases, unlike monochromatic X-rays which are usually used for medical purposes. In safety inspections of historic buildings, penetrating depth varies in an X-ray radiograph. Computerized tomography (CT) is a powerful tool that helps determine the density information of the inner sections of buildings. Because only portable X-rays can be used in historic buildings and the penetrating depth can vary, the mass attenuation coefficient of wood according to penetrating depth needs to be investigated. Therefore, in this study, we developed a statistical method which takes into account the influence of the penetrating depth on a density calculation made by a portable X-ray apparatus. X-ray tests were conducted on wood specimens of various depths. From the results, a statically determined mass attenuation coefficient (SMAC) (