Interfacial shear behavior of a high-strength pile to sleeve grouted connection

Lee, Jeong-Hwa,Won, Deok-Hee,Jeong, Youn-Ju,Kim, Seong-Hwan,Kang, Young-Jong Elsevier 2017 ENGINEERING STRUCTURES Vol.151 No.-

<P><B>Abstract</B></P> <P>A grouted connection is a type of structural composite connection member produced from two different-sized steel tubes and a grout annulus between them. The grouted connection has been widely used in offshore oil and gas platforms and wind turbine structures by simply grouting between the pile and sleeves. In general, the axial compression strength of the connection is known to be affected by the grout strength, shear-key spacing and radial stiffness parameters of the composite section. In this study, concentric and eccentric loading tests were performed to investigate the interfacial shear behavior of the high-strength grouted connections according to the shear-key spacings. The interface shear behaviors, focusing on the strength, failure mode, and strain of the grout and steel tubes, were evaluated by tests and finite element (FE) analysis. The test results showed that the primary strength of the connection was mainly affected by the grout strength, whereas the ultimate strength was affected by the yield strength of the sleeves and the friction coefficient between the steel tubes and grout. It was also concluded that the test results on the high-strength grouted connections were similar to those of previous studies on normal-strength grouted connections, and the eccentric loading did not reduce the axial capacity of the connection. Although the ultimate failure modes of the connections could not be considered in the current design equations, they may contribute to the safe design of high-strength grouted connections.</P> <P><B>Highlights</B></P> <P> <UL> <LI> This study investigated the interfacial shear behavior of high-strength grouted connections. </LI> <LI> Experimental studies were conducted to evaluate the strength and failure behavior of the connections. </LI> <LI> FE analysis was performed to elaborate upon the test results. </LI> <LI> The current design codes can enable the safe design of connections, although they do not consider the ultimate behavior of the sleeve and pile. </LI> <LI> The interfacial shear behavior of the connection was evaluated by the strength, failure mode, strains of the steel tubes and the grout annulus. </LI> </UL> </P>

PC 교량의 공극 검출을 위한 시멘트/탄소나노튜브 복합재료의 전기적 검측 성능 분석

나대연,최경후,강동훈,정원석 한국비파괴검사학회 2018 한국비파괴검사학회지 Vol.38 No.6

PC 교량에 사용되는 그라우트 충진이 불충분하게 되면 강연선 주위에 공극이 형성되며 이로 인한 수분 침투가 강연선의 부식을 촉진시켜 파단에 이르게 된다. 튜브 내부의 그라우트 충진 양을 육안으로 관찰할 수 없어 현재는 파단에 이르지 않는 이상 이를 조기에 검출하는 것이 불가능한 상황이다. 따라서, 이를 미리 탐지하여 교량의 안전성을 향상하기 위해 본 연구에서는 시멘트 그라우트에 탄소나노튜브가 첨가된 복합재료를 이용하여 공극률에 따른 전기적 저항 분석을 통한 검측 성능을 분석하였다. 매개 변수로 탄소나노튜브의 종류, 농도 및 시편의 공극률을 선정하여 전기적 저항과의 상관관계를 분석하였다. 실험 결과, 복합재의 공극률이 증가할수록 선형적으로 시편의 저항값이 높아짐을 확인하였다. Multi-walled carbon nanotube (MWCNT)가 0.1 wt% 포함된 복합재의 전기 전도성은 1.0 wt% 함량의 복합재보다 낮았지만, 공극 검출에 필요한 회귀분석 결정계수는 0.95 이상으로 나타났다. 상대적으로 전기적 성능이 뛰어난 Single-walled carbon nanotube (SWCNT)를 활용한 복합재의 경우에는 0.1 wt% 및 0.2 wt%의 경우 모두 전기 전도성이 MWCNT 복합재에 비해 높아 향후 더 적은 함량으로도 공극 검출이 가능한 기능성 복합재의 활용이 가능할 것으로 예상된다. When the grout filling used in prestressed concrete bridges is insufficient, pores are formed around the strand and water penetration occurs, causing the corrosion of the stranded wire and fracture. The amount of grout filling inside the tube cannot be visually observed; hence, an abnormal fracture cannot be detected early unless it reaches the fracture. Therefore, in order to improve the safety of bridges in advance, this study analyzed the performance of electrical resistivity analysis by porosity using composite materials made by adding carbon nanotubes (CNTs) to the cement grout. The CNT type, concentration, and porosity of the specimen were selected as the parameters, and the correlation with electrical resistance was analyzed. The results confirmed that the resistance of the specimen increased as the porosity of the composite decreased. The electrical conductivity of composite materials with multiwalled CNT (MWCNT) of 0.1 wt% was lower than that of composite materials with 1.0 wt% MWCNT, but the detection analysis was still viable since the regression coefficient for pore detection was higher than 0.95. For composite materials with 0.1 wt % and 0.2 wt% single-walled carbon nanotubes (SWCNTs), the electrical conductivity was higher than that of MWCNT composite materials. Therefore, it is expected that SWCNTs will enable the use of smaller amounts of functional composites to detect pores in the future.

Experimental Study on the Mechanical Performance of Grouted Specimen with Composite Ultrafine Cement Grouts

Maolin Tian,Lijun Han,Qingbin Meng 대한토목학회 2020 KSCE JOURNAL OF CIVIL ENGINEERING Vol.24 No.1

An experimental investigation was conducted in order to understand properties of grouts and grouted specimens. Three different cement types, i.e., composite ultrafine cement (CUC) that was independently developed, ultrafine cement (UC), and Portland cement (PC) were injected into broken red sandstone specimens on the basis of a self-designed grouting test equipment. After the grouting test, the effects on the mechanical behavior of grouted specimens were studied using an uniaxial compression test, macroscopic failure analysis and mesostructure analysis, as well as a comparison of the mechanical and structural properties of three types of grouted specimens was presented. The test results show that the compressive strength of grouted specimens improved in comparison to the rock residual strength, and the compressive strength of PC, UC and CUC grouted specimens increased by 23.0%, 59.6% and 101.5%, respectively. The failure modes of all grouted specimens were brittle failure, but only the CUC grouted specimen was failed along the new failure surfaces, indicating that CUC grouts can better bond the original cracks. The mesostructure characteristics obtained through the Digital 3D Video Microscope reveal the superior filling effect of the CUC grouts as well as verifying the macroscopic mechanical behavior.

그라우팅에 적합한 점성을 갖는 변형률 경화 시멘트 복합재료

이방연 한국구조물진단유지관리공학회 2012 한국구조물진단유지관리공학회 논문집 Vol.16 No.1

이 연구에서는 타설 과정에서 낮은 점성이 요구되는 구조물에 적합한 낮은 점성을 가지면서 다중균열에 의한 변형률 경화거동을 보이는 고인성 섬유복합재료를 제조하기 위한 재료와 제조 방법을 제시하고자 한다. 섬유복합재료의 낮은 점성과 고인성을 얻기 위하여 미시역학과 파괴역학에 기반한 이론적 해석 방법과 제조 기법을 적용하였다. 2~3MPa 범위의 인장강도를 갖는 복합재료에 적합한 최적의 섬유 양과 길이, 그리고 섬유와 매트릭스의 계면 특성을 미시역학과 안정상태 균열 이론을 이용하여 해석적으로 구한 후 여섯 가지 배합을 결정하였다. 여섯 가지 배합으로 제조한 실험체는 실험을 통하여 점성과 일축인장 성능을 검증하였다. 실험 결과 굳기 전에는 그라우팅에 적합한 낮은 점성을 갖으면서 굳은 후에는 1.5% 이상의 고인성을 갖는 변형률 경화 섬유복합재료를 제조할 수 있는 것으로 나타났다. This paper presents materials and processing technique to manufacture low viscous strain-hardening cementitious composite which is suitable for structures requiring low viscosity of materials. The micromechanics and fracture mechanics tools coupled with processing techniques were adopted to achieve low viscosity of composites as well as high tensile strain capacity. Optimal volume and length of fibers and interfacial properties between fibers and matrix for composites with tensile strength of 2~3MPa were determined on the basis of the micromechanical analysis and the steady-state cracking theory. Then six mixtures were determined and the experiment was carried out to evaluate the viscosity and uniaxial tensile performance of those. From the test results, it is verified that the strain-hardening cementitious composite with low viscosity suitable for grouting applications in fresh state as well as high ductility over 1.5% in hardened state can be feasible.

Effectiveness of CFRP jackets in post-earthquake and pre-earthquake retrofitting of beam-column subassemblages

Tsonos, Alexander G. Techno-Press 2007 Structural Engineering and Mechanics, An Int'l Jou Vol.27 No.4

This paper presents the findings of an experimental study to evaluate retrofit methods which address particular weaknesses that are often found in reinforced concrete structures, especially older structures, namely the lack of the required flexural and shear reinforcement within the columns and the lack of the required shear reinforcement within the joints. Thus, the use of a high-strength fiber jacket for cases of post-earthquake and pre-earthquake retrofitting of columns and beam-column joints was investigated experimentally. In this paper, the effectiveness of the two jacket styles was also compared.

새만금방조제 해수침투방지용 복합그라우팅 시공사례 연구

양형칠(Hyung-Chil Yang),김영훈(Young-Hun Kim),박세현(Se-Hyun Park),천병식(Byung-Sik Chun) 한국지반환경공학회 2010 한국지반환경공학회 학술발표회논문집 Vol.2010 No.5