KBC 목재 못뽑기 기준허용내력 개선방안 연구 = (A) study on improvement of the KBC standard allowable holding power of nail and screw under axial load application for wood

다국어 초록 (Multilingual Abstract)

As woods have different characteristics and qualities depending on the tree speciess, types and directions, such characteristics must be fully understood when constructing wood facilities or structures, and the appropriate bonding/strengthening metal fittings. However, there are many construction cases where the constructors use the same type of nails regardless of the directional property, tree species and type of the wood used, or use nails which are not appropriate. The cases of construction works where use of metal fittings suitable for wood characteristics are relatively rare in Korea, as the foundational data on design standards such as strength and rigidity of the nail joint and clear specifications and details on the joint are lacking. For construction works considering these elements, the constructor must use the nails satisfying the relevant allowable holding power standard or the relevant design standards, while using appropriate nails fit for each type of wood product.

In this study, the holding power of nails under axial load application for wood was measured in terms of nail types, wood fiber directions and temperature/humidity, using the wood product most widely used in actual construction works; the result of the measurement was evaluated for its conformity to the standard allowable holding power specified in KBC 2009; and the usage standards required for nail-pullout design formula and standard that fits the measured holding power. The result is summarized below.

The nail holding power for wood measured in accordance with KS ISO 9087 was calculated through regression analysis to fit the KBC 2009 holding power formula. The result was considerably different from the result of the nail holding power from the previous KBC. The constant in the proposed formula was 5.76 and 6.27 while it was 9.7 in the KBC, demonstrating substantial discrepancy. As for the modulus succeeded to wood density(G), the result was 1.07 and 1.10 for the proposed formula while it was 2.5 for the KBC formula, showing more than 2-fold difference. Also, the KBC equation does not recognize differences in tree species and the significance of density(G) change was shown to be high, meaning the formula is only capable of very qualitative calculation of holding power. The formula proposed in this study, however, focuses on the changes of measured holding power and density depending on tree species and moisture states. The test result showed significant difference from the standard allowable holding power specified in KBC. To supplement such shortcomings of the KBC standards, this study derived a quantitative and substantive design formula for nail holding force for wood.

While the nail holding power increased in proportion to the diameter of the nails inserted into wood, some difference was found between the measured holding power of KS F ISO 9087 and the measured holding power of KBC. While the measured holding power increased by more than 1.5 times when the diameter increased from 10D to 16D, the holding power calculated with KBC only increased by 1.09 times. This result is due to the fact that the current KBC standard allowable holding power does not reflect the changes in nail diameter, even though such change may lead to significant differences. Also needed is the selection of coefficients to be added as the nail diameter changes.

Suggestions for improvement of allowable nail holding power for wood in KBC are as follows: more diverse nail types need to be considered, especially the types most widely used in the field; different fiber directional properties must be differentiated; also, future studies need to integrate much required design factors, for example by including the wood temperature/humidity into the integrated modulus, as wood is very sensitive to changes of moisture in the air.

목차 (Table of Contents)

• 目 次
• 제Ⅰ장 서 론 1
• 제1절 연구배경 및 목적 1
• 제2절 연구동향 3
• 제3절 연구범위 및 방법 5
• 제Ⅱ장 이론적 고찰 7
• 제1절 목제품 종류별 특성 7
• 1. 일반목재(침엽수 및 활엽수) 7
• 2. 공학목재(합판 및 OSB) 10
• 제2절 못을 이용한 목재의 접합 13
• 1. 목조건축용 못(KS F 4537) 13
• 2. 못뽑기 내력 실측 시험용 못 14
• 3. 목재 접합부 하자 발생 16
• 제3절 KS F ISO 9087:2004 목재의 뽑기 시험 20
• 제4절 KBC 2009 0805.4 못접합부 허용기준내력 산출 23
• 제Ⅲ장 목재의 섬유조직 및 밀도측정 26
• 제1절 개요 26
• 제2절 섬유조직 분석 27
• 1. 일반목재 27
• 2. 공학목재 29
• 제3절 목재 밀도 31
• 1. 기건밀도 33
• 2 전건밀도 34
• 3 섬유포화점 밀도 35
• 제4절 소 결 36
• 제Ⅳ장 못뽑기 내력시험 및 분석 38
• 제1절 개요 38
• 제2절 시험방법 및 항온항습 39
• 1. 못뽑기 내력시험 방법 39
• 2. 목재의 온습도 지속변화 46
• 제3절 함수율 변화 분석 48
• 1. 일반목재-SPF 48
• 2. 일반목재-Oak 50
• 3. 공학목재-합판 52
• 4. 공학목재-OSB 54
• 제4절 못뽑기 최대 내력 56
• 1. 일반목재-SPF 56
• 2. 일반목재-Oak 59
• 3. 공학목재-합판, OSB 62
• 제5절 실측내력 표준편차 65
• 1. SPF 못뽑기 실측내력 표준편차 65
• 2. Oak 못뽑기 실측내력 표준편차 67
• 3. 공학목재 직결나사못 못뽑기 실측내력 표준편차 69
• 제6절 시간경과에 따른 못뽑기 내력 변화 71
• 1. 일반목재-SPF-스테인리스못 71
• 2. 일반목재-SPF-철못 73
• 3. 일반목재-Oak-스테인리스못 75
• 4. 일반목재-Oak-철못 77
• 5. 공학목재-합판 및 OSB-직결나사못 79
• 제7절 소 결 81
• 제Ⅴ장 못뽑기 내력시험 결과와 KBC 기준허용내력 비교분석
• 및 개선방안 제안 83
• 제1절 개요 83
• 제2절 못뽑기 내력시험 결과와 기준허용내력 비교 84
• 1. 일반목재의 보통못 내력 비교 84
• 2. 공학목재의 직결나사못 내력 비교 86
• 3. 함수상태 변화에 따른 내력 비교 87
• 4. 온습도 지속 변화 후 내력 비교 88
• 제3절 실측내력을 이용한 간이식 제안 89
• 1. 보통못 호칭지름에 따른 실측 및 산출내력 비교 89
• 2. KBC 2009 보통못 기준허용내력 분석 91
• 3. KS F ISO 9087 못뽑기 실측내력의 회귀분석에 따른 제안식 93
• 제4절 못뽑기 설계기준의 부합성 평가 및 개선방안 제안 95
• 1. 실측내력과 산출식의 부합성 평가 95
• 2. KS F ISO 9087에 대한 평가 및 필요 제안 사항 96
• 3. KBC 2009 못 뽑기 내력에 대한 평가 및 필요 제안 사항 98
• 제5절 소 결 101
• 제Ⅵ장 결 론 103
• 참고문헌 105
• ABSTRACT 108
• 부 록 111