With the recent development of 3D printing technology, concrete materials are sometimes used in 3D printing. Concrete structures based on 3D printing have been characterized to have the form of multiple layer build-up. Unlike general concrete structures, therefore, the 3D-printed concrete can be regarded as an orthotropic material. The material property of the 3D-printed concrete's interface between layers is expected to be far different from that of general concrete bodies since there are no aggregate interlocks and weak chemical bonding. Such a difference finally affects the structural performance of concrete structures even though the interfaces are formed before initial setting of the concrete. Furthermore, it was confirmed that superimposed load from the accumulated layers increase the fracture energy of interface between two layers. The current study mainly reviewed the changes in fracture energy (toughness) with respect to various environmental conditions of such interface. Changes in fracture energies of interfaces between concrete layers were measured using low-speed Crack Mouth Opening Displacement (CMOD) closed loop concrete fracture test. The experimental results indicated reduction in fracture energy as well as tensile strengths. In order to improve the tensile strength of interfaces, use of bridging materials are suggested. Since it was assumed that reduction in fracture energy could be a cause of shear strength, in order to evaluate the reduced structural performance of concrete structure constructed with multiple interfaces by 3D printing technology, shear strength of RC beam by 3D printing technology was predicted and compared with plain RC beam. Based on the fracture energy measured in this study, MCFT theory-applied Vector 2 program was employed to predict the degree of reduction in shear strength without considering stirrups. Reduction factors were presented based on the obtained results to predict the reduction in shear strength due to interfaces before initial setting of the concrete.목 차
Abstract ⅰ
List of Tables ⅲ
List of Figures ⅳ
제 1 장 서 론 1
1.1 연구 배경 1
1.2 연구 목표 및 중요성 3
1.3 연구 내용 및 방법 5
제 2 장 파괴에너지 측정 실험 이론 및 분석 7
2.1 시험체 형상 및 실험 조건 7
2.2 파괴에너지 측정을 위한 실험 이론 10
2.3 파괴에너지 측정을 위한 실험계획 및 장비 16
2.3.1 자중에 대한 실험계획 및 장비 16
2.3.2 적층 소요시간에 따른 실험계획 및 장비 18
2.3.3 브릿징(Bridging) 재료의 적용 22
2.4 쪼갬인장시험 결과 (ASTM C496) 23
2.5 파괴에너지 측정시험 결과 및 분석 27
2.5.1 자중 조건과 적층 소요시간 조건이 적용된 시편의 파괴에너지 측정 시험 결과 27
2.5.2 브릿징(Bridging) 재료를 활용한 시편의 파괴에너지 측정 시험 결과 37
제 3 장 전단강도의 저감 예측 및 분석 41
3.1 접합면 형성에 의한 전단강도의 저감 추정 이론 41
3.2 접촉면의 요소에 대한 전단 응력 - 슬립 관계 44
3.3 전단강도 모델 검증 47
3.4 전단강도 저감에 따른 결과 및 분석 53
3.5 접합면을 갖는 RC 보에 대한 전단 감소 계수의 제안 59
제 4 장 결론 및 향후 과제 61
참고문헌 64
감사의 글 70Maste
