초고성능 섬유보강 콘크리트(UHPFRC)의 재료 특성 및 예측모델 1 : 응결 및 수축 특성과 인장거동 평가

류두열,박정준,김성욱,윤영수 대한토목학회 2012 대한토목학회논문집 A Vol.32 No.5A

최근 국내에서도 압축강도 180 MPa, 인장강도 10 MPa 이상의 초고성능 섬유보강 콘크리트(Ultra High Performance Fiber Reinforced Concrete, UHPFRC)가 개발되었다. 그러나 UHPFRC는 물-결합재비가 낮고 다량의 고분말 혼화재료를 혼입하며, 굵은 골재를 사용하지 않기 때문에 초기 재령에서의 자기수축이 크로, 표면이 급격히 건조하는 등 기존의 일반 콘크리트(Normal Concrete, NC) 및 고성능 콘크리트(High Performance Concrete, HPC)와는 다른 재료적 특성을 보인다. 그러므로 본 연구에서는 UHPFRC에 적합한 재료 실험 방법과 규정을 제안하고 극 초기 재령에서의 강도 특성을 평가하기위하여 응결 및 수축, 인장 실험을 수행하였다. 응결 실험 결과 파라핀 오일을 UHPFRC의 모르타르 표면에 적용할 경우 표면에서의 급격한 건조현상을 효율적으로 억제할 수 있는 것으로 나타났으며, 시멘트와 배합수의 수화반응을 지연 또는 촉진시키지 않는 것으로 나타나 응결 실험 시 표면건조 방지제로 적합한 것으로 판단되었다. 또한, 링-테스트를 수행하여 내부 강재 링의 온도와 변형률의 경향이 달라지는 시점을 수축 응력 발현 시점으로 정의하였으며, 이를 응결실험과 비교하여 본 결과 응결침에 걸리는 관입 저항력이 약 1.5 MPa일 때 수축 응력이 발현되는 것으로 나타났다. 이는 초결 및 종결보다 약 0.6시간, 2.1시간 빠른 것이며, 상기 시점을 UHPFRC의 자기수축 측정 시점(time-zero)으로 규정하였다. 마지막으로, 본 연구에서는 극 초기 재령 인장강도 측정 장비를 제작하여 초결시점에서부터 UHPFRC의 인장강도와 탄서예수를 측정하였으며, 이를 고려한 UHPFRC의 인장강도 및 탄성계수 예측식을 제안하였다. Recently, ultra high performance fiber reinforced concrete (UHPFRC) having over 180 MPa compressive strength and 10MPa tensile strength has been developed in Korea. Howerver, UHPFRC represents different material properties with normal concrete (NC) and conventional high performance concrete (HPC) such as a high early autogenous shrinkage and a rapid dry on the surface, because it has a low water-binder ratio and high fineness admixtures without coarse aggregate. In this study, therefore, to propose suitable experimental methods and regulations, and to evaluate mechanical properties at a very early age for UHPFRC, setting, shrinkage and tensile tests were performed. From the setting test results, paraffin oil was an appropriate material to prevent drying effect on the surface, because if paraffin oil is applied on the surface, it can efficiently prevent the drying effect and does not disturb or catalyze the hydration of cement. From the ring-test results, it was defined that the shrinkage stress is generated at the time when the graph tendency of temperature and strain of inner steel ring is changed. By comparing with setting test result, the shrinkage stress was firstly occurred as the penetration resistance of 1.5 MPa was obtained, and it was about 0.6 and 2.1 hour faster than those of initial and final sets. So, the starting time of autogenous shrinkage measurement (time-zero) of UHPFRC was determined when the penetration resistance of 1.5 MPa was obtained. Finally, the thensile strength and elastic modulus of UHPFRC were measured from near initial setting time by using very early age tensile test apparatus, and the prediction models for tensile strength and elastic modulus were proposed.

Study on Assembly and Tensile Performance of Circumferential Anchor Joint for Shield Tunnel Considering Roughness and Size of Structure

Gaole Zhang,Wenjun Zhang,Jiahao Li,Xinnan Zhou,Wang Liu,Jianbing Qi 대한토목학회 2023 KSCE Journal of Civil Engineering Vol.27 No.5

Anchor joint is conducive to improving the automation level of the shield tunneling method, whose mechanical behavior is still not fully clear due to the complicated interaction among various structural components. In this paper, a refined FEM model is established and adopted to investigate the anchor joints' assembly and tensile performance. The operation principles of the anchor joint are first introduced for better understanding. Then, a detailed description is presented for the developed refined FEM, including the material properties, structural features, and verification. After that, 76 working conditions in total are set, and an in-depth study is conducted to examine the influence of surface roughness, gap sizes, and strength grades on the assembly and tensile behavior of anchor joints both quantitatively and qualitatively. The results show that the surface roughness mainly influences the maximum assembly load and tensile capacity of anchor joints. The gap size obviously impacts both quantitative and qualitative assembly characteristics and tensile behavior for anchor joints, whose effect is more significant than the surface roughness. The strength grade has a different influence on the distinct mechanical behavior of anchor joints. There is a positive correlation between anchor joints' assembly and tensile behavior. To satisfy the requirement of enough tensile capacity and reasonable assembly difficulty, a good solution should be to reach an appropriate balance between the assembly and tensile behavior of anchor joints.

Experimental and numerical study on tensile capacity of composite cable-girder anchorage joint

Xuefei Shi,Yuzhuo Zhong,Haiying Ma,Ke Hu,Zhiquan Liu,Cheng Zeng 국제구조공학회 2023 Steel and Composite Structures, An International J Vol.49 No.2

Cable-girder anchorage joint is the critical part of cable-supported bridges. Tensile-plate anchorage (TPA) is one of the most commonly used types of cable-girder anchorage joints in steel girder cable-supported bridges. In recent years, it has been proposed by bridge designers to apply TPA to concrete girder cable-supported bridges to form composite cable-girder anchorage joint (CCGAJ). In this paper, the mechanical performance of CCGAJ under tensile force is studied through experimental and numerical analyses. Firstly, the effects of the external prestressing (EP) and the bearing plate (BP) on the mechanical performance of CCGAJ were investigated through three tests. Then, finite element model was established for parametrical study, and was verified by the experimental results. Then, the effects of shear connector forms, EP, BP, vertical rebar rate, and perforated rebar rate on the tensile capacity of CCGAJ were investigated through numerical analyses. The results show that the tensile capacity of CCGAJ depends on the first row of PR. The failure mode of CCGAJ using headed stud connectors is to form a shear failure surface at the end of the studs while the failure mode using PBLs is similar to the bending of a deep girder. Finally, based on the strut-and-tie model (STM), a calculation method for CCGAJ tensile capacity was proposed, which has a high accuracy and can be used to calculate the tensile capacity of CCGAJ.

Tensile Performance, Lap-Splice Length and Behavior of Concretes Confined by Prefabricated C‑FRCM System

Donguk Choi,Sorrasak Vachirapanyakun,Munckhtuvshin Ochirbud,Undram Naidangjav,Sangsu Ha,Youngho Kim 한국콘크리트학회 2021 International Journal of Concrete Structures and M Vol.15 No.6

Results of an experimental study aimed to evaluate tensile performance, lap-splice length of carbon fabric-reinforced cementitious matrix system (C-FRCM), and performance of concretes confined by C-FRCM are presented. Green high-strength mortar was used in this study which actively utilized recycled fine aggregate and fine waste glass powder to partially substitute cementitious binder. Test plans were developed in due consideration of prefabricated C-FRCM for strengthening concrete columns: 14 tensile tests, 12 lap-splice tests, and 6 uniaxial compression tests of plain concrete specimens confined by C-FRCM were performed. Test variable for the tensile test was number of fabric layers (one or two layers). Nominal strength of the C-FRCM with two fabric layers was 11.0 MPa while it was 7.4 MPa with one fabric layer in tension. Full strength of the carbon fabric was developed in all tensile tests while the C-FRCM with two fabric layers (with axial fiber amount = 0.59% by vol.) showed pseudo-ductile behavior. From the lap-splice tests in direct tension, an increased lap-splice length was required for the double fabrics over that for the single fabrics. The required splice length was about 170 mm for the single fabrics and it was about 310 mm for the double fabrics. Plain concrete cylinders and prismatic specimens were laterally confined by C-FRCM and subjected to uniaxial compression. All test results showed strain-softening behavior. Compressive strength increased by 10-41% while ductility also increased by 6-45% indicating applicability of the prefabricated type C-FRCM in the future.

Built-up H형강의 소재특성 및 용접성능에 관한 연구

최영한,김상섭 한국강구조학회 2018 韓國鋼構造學會 論文集 Vol.30 No.1

The use of a built-up H-beam (BH) that can easily manufacture a section is increasing. This is a basic study on standardization of BH. It confirmed the material properties of SM490 and SM520 steel such as yield strength, tensile strength, elongation, charpy absorbed energy, and else. The six BH specimens were manufactured with single-SAW or tandem-SAW. The welding performance was confirmed by collecting the macroscopic specimen and T-bar tensile specimen form the BH. As a result of the material property test, the properties of SM490 and SM520 which are made in Korea both satisfied the KS. As a result of the welding performance experiment, it is determined that the weld zone of BH has sufficient welding performance. Therefore, they are determined that the SM490 and SM520 steel are a proper material of BH, and the single-SAW and the tandem-SAW show a sufficient welding performance. 단면을 자유롭게 제작할 수 있는 Built-up H형강(BH)의 사용이 점점 증대하고 있다. 본 연구는 BH의 규격화를 위한 기초연구로SM490, SM520 강재의 항복강도, 인장강도, 연신율, 샤르피 흡수에너지 등의 소재특성을 확인하였다. 또한 single-SAW 및 tandem-SAW를활용하여 6개의 BH 공시체를 제작하였으며, 공시체에서 매크로시험편, T바 인장실험체를 채취하여 용접성능을 확인하였다. 소재특성시험결과 국내산 SM490, SM520 강재의 특성은 모두 KS를 만족하였으며, 용접성능실험 결과 BH의 용접부는 충분한 용접성능을 갖추었다고판단할 수 있다. 따라서 본 연구에서 사용된 국내산 SM490, SM520 강재는 BH의 소재로 적합한 것으로 판단되며, single-SAW, tandem-SAW는 충분한 용접성능을 발휘하는 것으로 사료된다.

고속 비상체의 충돌을 받은 섬유보강 모르타르의 내충격 성능 평가

김규용,남정수,미야우치 히로유키,Kim, Gyu-Yong,Nam, Jeong-Soo,Miyauchi, Hiroyuki 대한건축학회 2011 대한건축학회논문집 Vol.27 No.9

Recently, the damaged building and loss of life have been increasing by man-made disasters. In this study, the impact resistance performance of fiber reinforced concrete against high-velocity projectile was evaluated by using high pressure gas apparatus and AUTODYN. Plain mortar specimen was penetrated by steel projectile at 350 m/s and was fractured heavily at the backside. On the other hand, the PVA, PE and STF specimens reinforced with fiber have higher impact resistance than plain mortar, and were analyzed by Hughes equation. Finally, the impact resistance of specimens was calculated from viewpoint of fracture mode by AUTODYN and it was concluded that fiber reinforced concrete improve the impact resistance performance.

고속 비상체의 충돌을 받은 섬유보강 모르타르의 내충격 성능 평가

김규용(Kim Gyu-Yong),남정수(Nam Jeong-Soo),미야우치 히로유키(Miyauchi Hiroyuki) 대한건축학회 2011 大韓建築學會論文集 : 構造系 Vol.27 No.9

Recently, the damaged building and loss of life have been increasing by man-made disasters. In this study, the impact resistance performance of fiber reinforced concrete against high-velocity projectile was evaluated by using high pressure gas apparatus and AUTODYN. Plain mortar specimen was penetrated by steel projectile at 350 m/s and was fractured heavily at the backside. On the other hand, the PVA, PE and STF specimens reinforced with fiber have higher impact resistance than plain mortar, and were analyzed by Hughes equation. Finally, the impact resistance of specimens was calculated from viewpoint of fracture mode by AUTODYN and it was concluded that fiber reinforced concrete improve the impact resistance performance.

인장가새용 댐퍼의 내진성능에 대한 연구

엄승현(Eom Seung-Hyeon),김원기(Kim Won-Ki) 대한건축학회 2003 大韓建築學會論文集 : 構造系 Vol.19 No.7

In this study, joining method and shape of tensile brace dampers having excellent energy dissipation capacity are developed. The shape of the developed dampers is square. The joining method is that the brace and damper are combined by nuts. This damper system is applicable to single- or two-story steel structures. When seismic force inflicts on this system, impact energy is dissipated by mainly square dampers having the appointed seismic performance. The structure leads to a ductile failure of tensile braced frame compared to brittle one of common frame. The seismic performance was analyzed by using load-displacement curves.

고강도철근이 배근된 철근콘크리트 보의 휨성능 평가

홍건호(Hong Geon-Ho) 대한건축학회 2011 大韓建築學會論文集 : 構造系 Vol.27 No.1

Korean building code requirements provide that the yield strength of longitudinal reinforcement shall not exceed 550 ㎫ in flexural members. The purpose of this paper is to evaluate the possibility of yield strength increase up to 600 ㎫ or 700 ㎫ in flexural reinforcement. Total 8 simple beam specimens divided by 3 groups tested for evaluating the flexural performance. Main test variables were yield strength of longitudinal reinforcement, reinforcement ratio and cover thickness. Test data analyzed in the viewpoint of cracking load, ultimate flexural strength, load-deflection relationship, crack progress, failure aspects and ductility. Test results indicate that flexural capacity of the specimen is similar from a standpoint of unit strength-area of reinforcement, but ductility of the specimens with high strength reinforcing bars was reduced in high reinforcement ratio. Flexural stiffness of the specimens with high strength reinforcing bars was also reduced, and this phenomenon is well agreed with the reduction of effective moment of inertia Ie. This paper concluded that flexural strength can be calculated using the present code provision without any change, but deflection checkup will be needed when the flexural member design with high strength reinforcing bars.

Numerical simulation of compressive to tensile load conversion for determining the tensile strength of ultra-high performance concrete

Hadi Haeri,Nader Mirshekari,Vahab Sarfarazi,Mohammad Fatehi Marji 국제구조공학회 2020 Smart Structures and Systems, An International Jou Vol.26 No.5

In this study, the experimental tests for the direct tensile strength measurement of Ultra-High Performance Concrete (UHPC) were numerically modeled by using the discrete element method (circle type element) and Finite Element Method (FEM). The experimental tests used for the laboratory tensile strength measurement is the Compressive-to-Tensile Load Conversion (CTLC) device. In this paper, the failure process including the cracks initiation, propagation and coalescence studied and then the direct tensile strength of the UHPC specimens measured by the novel apparatus i.e., CTLC device. For this purpose, the UHPC member (each containing a central hole) prepared, and situated in the CTLC device which in turn placed in the universal testing machine. The direct tensile strength of the member is measured due to the direct tensile stress which is applied to this specimen by the CTLC device. This novel device transferring the applied compressive load to that of the tensile during the testing process. The UHPC beam specimen of size 150 × 60 × 190 mm and internal hole of 75 × 60 mm was used in this study. The rate of the applied compressive load to CTLC device through the universal testing machine was 0.02 MPa/s. The direct tensile strength of UHPC was found using a new formula based on the present analyses. The numerical simulation given in this study gives the tensile strength and failure behavior of the UHPC very close to those obtained experimentally by the CTLC device implemented in the universal testing machine. The percent variation between experimental results and numerical results was found as nearly 2%. PFC2D simulations of the direct tensile strength measuring specimen and ABAQUS simulation of the tested CTLC specimens both demonstrate the validity and capability of the proposed testing procedure for the direct tensile strength measurement of UHPC specimens.