Lateral strain-axial strain model for concrete columns confined by lateral reinforcement under axial compression

Chongchi Hou,Wenzhong Zheng 국제구조공학회 2022 Structural Engineering and Mechanics, An Int'l Jou Vol.84 No.2

The use of lateral reinforcement in confined concrete columns can improve bearing capacity and deformability. The lateral responses of lateral reinforcement significantly influence the effective confining pressure on core concrete. However, lateral strain-axial strain model of concrete columns confined by lateral reinforcement has not received enough attention. In this paper, based on experimental results of 85 concrete columns confined by lateral reinforcement under axial compression, the effect of unconfined concrete compressive strength, volumetric ratio, lateral reinforcement yield strength, and confinement type on lateral strain-axial strain curves was investigated. Through parameter analysis, it indicated that with the same level of axial strain, the lateral strain slightly increased with the increase in the unconfined concrete compressive strength, but decreased with the increase in volumetric ratio significantly. The lateral reinforcement yield strength had slight influence on lateral strain-axial strain curves. At the same level of lateral strain, the axial strain of specimen with spiral was larger than that of specimen with stirrup. Furthermore, a lateral strain-axial strain model for concrete columns confined by lateral reinforcement under axial compression was proposed by introducing the effects of unconfined concrete compressive strength, volumetric ratio, confinement type and effective confining pressure, which showed good agreement with the experimental results.

외부자켓에 의해 보강된 콘크리트 압축시편의 압축변형률 측정 및 보정

최은수,이영근 한국구조물진단유지관리공학회 2009 한국구조물진단유지관리공학회 논문집 Vol.13 No.2

콘크리트 공시편의 외부보강을 위해서 강판과 FRP 자켓을 이용하였다. 기존의 강판 또는 FRP 자켓 보강기법은 보강재와 콘크리트 사이에 접착제를 이용하여 시공하므로 콘크리트와 보강재가 합성거동 하게 된다. 그러나 본 연구에서 사용한 강판 보강기법은 외부압착에 의한 기법으로 강판과 콘크리트가 합성거동을 하지 않는다. 본 연구에서는 비합성거동과 합성거동을 하는 보강된 콘크리트 시편의 압축 변형률의 측정과 이를 보정하는 기법을 제시하였다. 비합성거동의 강판보강 콘크리트 시편의 압축변형률 측정은 강판의 표면에서 변형률을 측정하여 표시할 수 없으며, 시편에 설치하여 측정하는 compressometer를 사용할 수도 없었다. 따라서 시편의 상하단에 두꺼운 판을 설치하여 두 판사이의 변형을 측정한 후. 이를 압축변형률로 변환하였다. 합성거동을 하는 FRP 보강의 경우는 FRP 튜브 표면에서 측정되는 수직방향의 변형률을 콘크리트의 압축변형률로 사용이 가능하다. 그러나 튜브 표면의 수직변형률은 시편의 부풀음에 의한 인장변형률이 포함되어 있기 때문에 콘크리트의 압축변형률을 추정하기 위해서는 이를 보정하여야 한다. 보정된 압축변형률은 콘크리트 내부에서 측정한 변형률과 기존의 콘크리트 연속체 모델과 비교하였을 때, 만족한 결과를 보였다. 보정 전의 응력-변형률 곡선은 콘크리트의 연성거동 및 에너지 소산능력을 보정 전에 비해 낮게 평가할 위험성이 있다. In this study, steel and FRP jackets are used to confine concrete cylinders. The FRP jacket behaviors compositely with concrete since there is bonding between them. However, the used steel jacket in this study do not behavior compositely with concrete since there is not an adhesive between them. The steel jackets are attached by external forces and the welding. This study suggests the measuring method of the axial strain for the confined concrete cylinders showing noncomposite behavior with the jackets and the correcting method of the measured strain for the composite-behavior jackets. For the noncomposite-behavior steel jacket, the axial strain of the steel surface does not represent the axial strain of the concrete inside. Also, a compressormeter can not be used. Thus, the two rigid plates at the top and bottom of a cylinder are placed and the distance of the two plates are measured and used for estimating the axial strain of the concrete. For the composite-behavior FRP jacket, the vertical strain measured on the FRP surface can be used for estimating the axial strain of the concrete. However, the vertical strain on the FRP surface contains the tensile strain due to the bulge of the concrete and, thus, the tensile strain should be corrected from the vertical strain. The corrected verticals strains compared with the measured strain or a existing constitute model; the result is satisfactory. The uncorrected stress-strain curves have the potential to under estimate the ductile behavior and the energy-dissipation-capacity of the composite-behavior FRP jackets.

섬유-강판 복합플레이트로 보강된 콘크리트 압축부재의 압축성능

조백순(Cho Baik-Soon),최은수(Choi Eunsoo),정영수(Chung Young-Soo),김연욱(Kim Yeon-Wook) 대한토목학회 2011 대한토목학회논문집 A Vol.31 No.4A

콘크리트 공시체의 압축강도와 연성성능을 향상시키기 위하여 섬유-강판 복합플레이트 fiber-sheet and steel-plate composite plate(FSP))의 적용을 실험적으로 연구하였다. FSP 보강재료, 앵커볼트 설치방법, 콘크리트 압축강도 등이 고려된 FSP 보강 콘크리트 공시체의 압축실험을 실시하였다. FSP 보강 콘크리트 공시체의 압축실험결과, FSP는 콘크리트 공시체의 압축강도와 변형저항성능을 크게 향상시켰다. FSP 보강 콘크리트 공시체의 압축성능은 FSP 보강재 종류, 앵커볼트 사용방법, 콘크리트 압축강도에 영향을 받는 것으로 나타났다. 앵커볼트를 사용한 FSP 보강 콘크리트 공시체 실험에서 측정된 FSP의 파단변형률은 FRP 보강 콘크리트 압축부재 실험에서 측정된 FRP 파단변형률보다 크게 측정되었다. FSP 파단변형률의 크기는 FSP의 보강효과에 영향을 미친다. FSP 보강 콘크리트 공시체 압축실험에서 측정된 축방향변형률, 원주방향변형률, 체적변형률에 의한 FSP 내부 콘크리트의 손상상태를 분석하여 FSP 보강효과를 평가하였다. 연구결과, FSP 보강공법은 콘크리트 압축부재의 보강방법으로 실용적 기법이라 판단된다. The application of newly developed fiber-sheet and steel-plate composite plate (FSP) as a means of improving strength and ductility capacity of concrete cylinders under axial compression load through confinement is investigated experimentally in this study. An experimental investigation involves axial load tests of two types of FSP strengthening material, two anchoring methods, and three concrete strengths. The FSP-confined cylinder tests showed that FSP provided a substantial gain in compressive strength and deformability. The performance of FRP-confined cylinders was influenced by type of the FSP strengthening material, the anchoring method, and concrete compressive strength. The FSP failure strains obtained from FSP-confined cylinder tests were higher than those from FRP-confined cylinder tests. The magnitude of FSP failure strain was related to the FSP composite effectiveness. The effects of FSP confinement on the concrete microstructure were examined by evaluating the internal concrete damage using axial, radial, and volumetric strains. From the observations obtained in this investigation, it is believed that FSP is one of the best solutions for the confinement of concrete compressive members.

Bi-2223/Ag 고온 초전도 선재 변형에 따른 입계전류 특성

하홍수,오상수,하동우,심기덕,김상철,장현만,권영길,류강식 한국전기전자재료학회 2001 전기전자재료학회논문지 Vol.14 No.1

In this study, we fabricated Bi-2223/Ag high temperature superconducting tapes using PIT(Powder-In-Tube) process to apply the superconducting magnet, cable and etc. It is inevitable to deform the superconducting taps with axial strain for application. Therefore, for the characterization of the strain sensitivity of the superconducting properties, the degradation of Bi-2223/Ag tapes due to axial strain were investigated by measuring the critical current as a function of applied tension strain and external magnetic field. The critical current of Bi-2223/Ag tapes were decreased slightly up to 0.3∼0.4% applied strain but, drastically decreased more than these strains. Superconducting filament cores consisted of brittle ceramic fibers were broken easily by the large strain and current path were decreased simultaneously.

Thermal Gradients and Their Effects on Bending Behavior of Composite Girders with Trapezoidal Profiled Webs

Zhiyu Wang,Qifei Wang,Peiyan Huang,Guowen Yao,Rui Yang,Zhanbiao Chen 대한토목학회 2023 KSCE Journal of Civil Engineering Vol.27 No.2

Thermal gradient may have significant effect on the bending behavior of the composite girderwith trapezoidal profiled web. To quantify such an effect on the thermos-strain action,temperature elevation test and finite element modeling were carried out on the specimenswith the flange sensitive to bending and the web possessed adequate buckling resistance. Thecross-sectional thermal gradients for different location away from the middle of span weremeasured using thermocouples and correlated using Boltzmann sigmoid equations. Theapplicability of finite element model was validated against experiments in terms of thedistribution of thermal strain, deflections and axial strains. The axial strain distributions acrossthe flange width and along the longitudinal direction of girder were analyzed in details. Thetesting and finite element modeling results showed that, the deflections with applied loadsnear the middle of span subjected to maximum bending moment are notably influenced bythe increase of thermal gradient. The maximum axial strains at the upper surface and thelower surface of the bottom flange are obviously influenced by the temperature, especially forthe girders with relatively high span-depth ratios or thicker flanges. The thermal gradient at theupper surface of the bottom flange is relatively higher than that on lower surface for every10oC rise of temperature which meant that the upper surface of the bottom flange connectingtrapezoidal profiled webs is more sensitive to thermo-elastic action.

The Internal Force Relationship of Rectangular and I-section for Bi-linear Hardening Material with Limit Strain

Liu-Lian Li,Guo-Qiang Li 한국강구조학회 2016 International Journal of Steel Structures Vol.16 No.1

Based on bilinear stress-strain constitutive law σ = f (ε), the elastic to fully plastic analysis of bending of rectangular-section and bi-symmetrical I-section beams with the influence of axial load is presented for hardening material with limit strain. The variation of the applied bending moment with the axial force for the fully elastic, elastic-plastic, and fully plastic conditions is given in analytical form. The Internal force relationship of the elastic limit is the same for both hardening and non-hardening material and independent of the geometry of the beam section. However, for the elastic-plastic and plastic limits, the relationships are dependent of the hardening parameter βq, limit strain ε lim and the geometry of the beam section for neutral axis (N.A) inside the cross section. When N.A outside the cross section, the relationships are dependent of hardening parameter βq and limit strain ε lim but independent of the geometry of the beam section. The results given by the analytical expressions reduce to the ones for non-hardening material are in good agreement with the existing results.

변형률 측정기법을 통한 점용접부의 피로수명 예측

한규헌(Quhon Han),김동철(Dongchoul Kim) 대한기계학회 2011 대한기계학회 춘추학술대회 Vol.2011 No.10

Fatigue is the most critical failure mode of spot welded joints in automobiles. Although various approaches have been proposed for fatigue life estimation of spot welds, a practical tool for spot welds in a fully built vehicle has not been thoroughly established. Since the spot welds in the assembled vehicle generally are situated in complex geometries under multi-axial loading, the most effective tool for fatigue life estimation might be the direct strain measurement. Here, a practical and reliable technique for fatigue life prediction of spot-welds based on direct strain measurement is proposed. The developed technique shows that the fatigue life of spot welds can be estimated by a multiple strain-gauge pattern attached to the outer surface of the overlap sheets near the spot weld. The designed pattern measures strain signals from circumferentially aligned strain gauges, which effectively provide information for fatigue life prediction after a simple conversion process.

NUMERICAL SIMULATION OF CONVEX AND CONCAVE TUBES WITH CONSIDERATION OF STRAIN RATE SENSITIVITY

Ye, B.W.,Oh, S.,Cho, Y.B.,Sin, H.C. The Korean Society of Automotive Engineers 2007 International journal of automotive technology Vol.8 No.2

The present paper deals with the application of the explicit finite element code, PAM-CRASH, to simulate the crash behavior of steel thin-walled tubes with various cross-sections subjected to axial loading. An isotropic elastic, linear strain-hardening material model was used in the finite element analysis and the strain-rate sensitivity of mild steel was modeled by using the Cowper-Symonds constitutive equation with modified coefficients. The modified coefficients were applied in numerical collapse simulations of 11 types of thin-walled polygon tubes: 7 convex polygon tubes and 4 concave polygon tubes. The results show that the thin hexagonal tube and the thick octagonal tube showed relatively good performance within the convex polygon tubes. The crush strengths of the hexagonal and octagonal tubes increased by about 20% and 25% from the crush strength of the square tube, respectively. Among the concave tubes, the I-type tube showed the best performance. Its crush strength was about 50% higher than the crush strength of the square tube.

선조질강 소재의 단조공정 측면에서의 특징

엄재근(J. G. Eom),이추실(Q. S. Li),장성민(S. M. Jang),안순태(S. T. Ahn),손요헌(Y. H. Son),현성운(S. W. Hyun),김혁(H. Kim),윤덕재(D. J. Yoon),전만수(M. S. Joun) 한국소성가공학회 2009 한국소성가공학회 학술대회 논문집 Vol.2009 No.5

In this paper, plastic deformation behaviors of ESW105 and SCM435 steels are revealed by simulations and experiments. ESW105 is the special pre-heat-treated steel characterized by high initial yield strength and negligible strain-hardening behavior. The flow stresses of the two steels for large stain are calculated from tensile tests. Axial and lateral compressions of cylindrical bars are tested and simulated and the deformed shapes are compared to characterize the plastic deformation behaviors of the two materials. A forward extrusion process of a cylindrical bar is also simulated to reveal the difference. It has been shown that there are pretty much difference in plastic flow between ESW105 and SCM435 which causes from the difference in strain-hardening capability, implying that the experience-oriented design rules for common commercial materials may lead to failure in process design when the new material of ESW105 is applied without consideration of its plastic deformation behavior.

동결 온도와 재하속도에 따른 동결토의 일축강도 특성에 관한 실험적 연구

최헌우(Heon-Woo Choi),서영교(Young-Kyo Seo),안승만(Sung-Man An),조현주(Hyun-Ju Cho) 대한조선학회 2011 대한조선학회 학술대회자료집 Vol.2011 No.6

The mechanical properties governing the behavior of frozen soil structure have been interested design factors for some field applications. In this research, a series of laboratory tests were performed to investigate the compression strength properties of mixed soil(standard sand and kaolinite) in three different temperature such to the 5, 10 and 15 degrees below zero environment. The effects of strain rate(1.11*10-4 to 2.22*10-2) on the compressive properties of artificial soil have been determined experimentally using uniaxial compression test. Data included on the initial tangent modulus, compressive strength and failure strain.