• Structural Engineering and Mechanics
• /
• 제87권5호
• /
• pp.461-473
• /
• 2023

This study aims to solve for nonlinear cylindrical shell systems with a semi-analytical and numerical approach implementing the P-T method. The procedures and conditions for such a study are presented in practically solving and analyzing the cylindrical shell systems. An analytical model for a nonlinear thick cylindrical shell (TCS) is established on the basis of the stress function and Reddy's higher-order shear deformation theory (HSDT). According to Reddy's HSDT, Hooke's law in three dimensions, and the von-Kármán equation, the stress-strain relations are developed for the thick cylindrical shell systems, and the three coupled nonlinear governing equations are thus established and discretized as per the Galerkin method, for implementing the P-T method. The solution generated with the approach is continuous everywhere in the entire time domain considered. The approach proposed can also be used to numerically solve and analyze the nonlinear shell systems. The procedures and recurrence relations for numerical solutions of shell systems are presented. To demonstrate the application of the approach in numerically solving for nonlinear cylindrical shell systems, a specific nonlinear cylindrical shell system subjected to an external excitation is solved numerically. In numerically solving for the system, the present approach shows higher efficiency, accuracy, and reliability in comparison with that of the Runge-Kutta method. The approach with the P-T method presented is practically sound especially when continuous and high-quality numerical solutions for the shell systems are considered.

• 한국터널지하공간학회 논문집
• /
• 제11권3호
• /
• pp.255-264
• /
• 2009

본 연구에서는 2-Arch 터널의 3차원 거동 메카니즘에 관한 내용을 다루었다. 이를 위해 도심지 지하철에 적용된 2-Arch 터널을 고려하였으며 3차원 유한요소해석을 수행하여 좌우 터널의 이격거리, 지반조건, 토피고 등에 대한 매개변수연구를 실시하였다. 해석결과 토대로 다양한 조건에 대한 터널 천단침하 및 쇼크리트 응력, 중앙기둥 작용하중 등을 중점으로 분석하였으며, 그 결과를 토대로 좌우 터널 이격거리, 지반조건, 토피고에 따른 2-Arch 터널의 거동 메카니즘을 고찰하였다. 그 결과 숏크리트 라이닝 응력 및 중앙 기둥 작용하중은 후행터널 시공에 큰 영향을 받는 것으로 나타났으며 터널관통지층이 취약할 경우 후행터널이 선행터널의 거동에 영향을 미치는 영향거리가 증가하는 것으로 분석되었다. 본 논문에서는 해석 결과를 토대로 2-Arch 터널의 시공중 변위 및 숏크리트 라이닝 응력 변화 경향에 대한 구체적인 내용을 기술하였다.

• 한국터널지하공간학회 논문집
• /
• 제26권4호
• /
• pp.327-344
• /
• 2024

일반적인 터널 설계 및 해석 시 암반을 등방성으로 가정하나, 등방성 조건에서는 재료특성이 모든 방향에서 균일하므로 터널의 안정성이 높게 평가되는 경향이 있다. 그러나 실제 암반은 절리, 층리, 단층 등 불연속면이 존재하며 방향에 따라 재료의 특성이 다른 이방성 특징을 가진다. 이러한 암반의 이방성은 터널 굴착 시 발생하는 응력 분포에 큰 영향을 미쳐, 불균일한 터널 변형을 유발하고 손상 위험을 증가시키기 때문에 사전에 철저한 분석이 필요하다. 본 연구에서는 암반의 이방성에 따라 굴착 과정에서 발생하는 막장면과 터널이 굴착된 후 수렴된 위치에서 발생하는 변형과 응력 변화에 초점을 두었다. 탄성계수의 비율(E₁/E₂)에 따른 이방성지수(I_E)와 경사각을 변수로 선정하여 3차원 수치해석을 수행하였다. 결과적으로 이방성 지수가 증가할수록 터널에서 발생하는 변위가 증가하고 응력집중 현상이 크게 발생하였으며, 경사면이 터널과 접하는 부분에서 최대 변위가 발생하고 전단응력이 가장 크게 발생하는 것을 확인하였다.

• Steel and Composite Structures
• /
• 제36권5호
• /
• pp.553-568
• /
• 2020

Steel-concrete composite structures have been extensively used in building, bridges, and other civil engineering infrastructure. Shear stud connectors between steel and concrete are essential in composite members to guarantee the effectiveness of their behavior in terms of strength and deformability. This study focuses on investigating the shear stiffness of headed studs embedded in several types of concrete with wide range of compressive strength, and their effects on the elastic behavior of steel-concrete composite girders were evaluated. Firstly, totally 206 monotonic push-out tests from the literature were reviewed to investigate the shear stiffness of headed studs embedded in various types of concrete (NC, HPC, UHPC etc.). Shear stiffness of studs is defined as the secant stiffness of the load-slip curve at 0.5V_u, and a formulation for predicting defined shear stiffness in elastic state was proposed, indicating that the stud diameter and the elastic modulus of steel and concrete are the main factors. And the shear stiffness predicted by the new formula agree well with test results for studs with a diameter ranging from 10 to 30 mm in the concrete with compressive strength ranging from 22.0 to 200.0MPa. Then, the effects of shear stiffness on the elastic behaviors of composite girders with different sizes and under different loading conditions were analyzed, the equations for calculating the stress and deformation of simply supported composite girders considering the influence of connection's shear stiffness were derived under different loading conditions using classical linear partial-interaction theory. As the increasing of shear stiffness, the stress and deflection at the most unfavorable section under partial connected condition tend to be those under full connected condition, but the approaching speed decreases gradually. Finally, the connector's shear stiffness was recommended for fully connection in composite girders with different dimensions under different loading conditions. The findings from present study may provide a reference for the prediction of shear stiffness for headed studs and the elastic design of steel-concrete composite girder.

• 한국지반공학회:학술대회논문집
• /
• 한국지반공학회 2010년도 춘계 학술발표회
• /
• pp.523-534
• /
• 2010

A hybrid system of soil-nailing and compression anchor is proposed in this paper; the system is composed of an anchor bar (installed at the tip) with two PC strands and a steel bar. After drilling a hole, installing proposed hybrid systems, and filling the hole with grouting material, prestress is applied to the anchor bar to restrict the deformation at the head and/or to prevent shallow slope failures. However, since the elongation rate of PC strand is much larger than that of steel bar, yield at the steel bar will occur much earlier than the PC strand. It means that the yield load of the hybrid system will be overestimated if we simply add yield loads of the two - anchor bar and PC strands. It might be needed to try to match the yielding time of the two materials by applying the prestress to the anchor bar. It means that the main purpose of applying prestress to the anchor bar should be two-fold: to restrict the deformation at the nail head; and more importantly, to maximize the design load of the hybrid system by utilizing load transfer mechanism that transfers the prestress applied at the tip to the head through anchor bar. In order to study the load transfer mechanism in a systematic way, in-situ pullout tests were performed with the following conditions: soil-nailing only; hybrid system with the variation of prestress stresses from 0kN to 196kN. It was found that the prestress applied to the anchor system will induce the compressive stress to the steel bar; it will result in decrease in the slope of load-displacement curve of the steel bar. Then, the elongation at which the steel bar will reach yield stress might become similar to that of PC strands. By taking advantage of prestress to match elongations at yield, the pullout design load of the hybrid system can be increased up to twice that of the soil-nailing system.

• 열처리공학회지
• /
• 제24권2호
• /
• pp.92-98
• /
• 2011

The influence of the cooling condition after solution treatment on the high temperature fatigue resistance of 23Cr-26Ni heat resistant steel was investigated. Two different cooling conditions were applied to the steel after solution treatment at $1200^{\circ}C$ for 3 hours. One specimen was water quenched immediately after the solution treatment. The other one was furnace cooled at a rate of $0.5^{\circ}C/min$ down to $750^{\circ}C$ after the solution treatment. Then, both specimens were aged at $750^{\circ}C$ for 5 hours. Under two different heat treatment conditions, the low cycle fatigue (LCF) test was performed at $600^{\circ}C$ and room temperature (RT). Only cyclic hardening continued from the beginning until fracture at all strain amplitudes during LCF at $600^{\circ}C$. This phenomenon was attributed to the increase in the dislocation density due to cyclic deformation, which resulted in the interaction between the newly created dislocations and precipitates. Cyclic hardening followed by saturation and cyclic softening was observed at RT. Cyclic softening was attributed to the dislocation annihilation rate exceeding the dislocation generation rate. Other probable factor for cyclic softening was some cavities formed around grain boundaries after 20 cycles. WQ and FC have a similar LCF behavior at RT and $600^{\circ}C$ as shown in the cyclic stress response curves.

• 한국지반공학회논문집
• /
• 제31권2호
• /
• pp.5-11
• /
• 2015

비탈면의 안정성은 강우지속시간, 확률강우강도, 지반의 불포화특성, 지반강도 등에 의해 영향을 받는다. 최근 비탈면안정성 해석은 지반의 침투특성을 고려한 불포화해석을 수행하고 있으며, 불포화 토사비탈면에 대한 연구는 시간변화에 따라 지반의 변형과 응력분포해석을 고려할 수 있도록 하는 방향으로 진행되고 있다. 그러나 이와는 별개로 불포화사면의 침투특성은 강우강도나 지속시간 뿐만 아니라 비탈면의 지형여건과 녹화상태에 따라서도 침투정도가 다르지만, 이에 대한 영향은 고려하지 않고 있다. 본 연구에서는 비탈면경사 및 표면상태에 따른 침투를 고려하기 위하여 토양의 수리특성을 고려한 모형을 사용하고, 토사비탈면에 대한 불포화해석을 수행하여 비탈면 경사에 따른 영향을 파악하였다. 연구결과 비탈면 안정해석시 동일한 강우조건 하에서도 비탈면경사에 따른 침투율이 고려되어야 할 필요성을 제시하였다.

• 한국정밀공학회지
• /
• 제23권4호
• /
• pp.153-161
• /
• 2006

Micro-forming is a suited technology to manufacture very small metallic parts(several $mm{\sim}{\mu}m$). Micro-forming of $Zr_{62}Cu_{17}Ni_{13}Al_8$ bulk metallic glass(BMG) as a candidate material for this developing process are feasible at a relatively low stress in the supercooled liquid state without any crystallization during hot deformation. In this study, micro- formability of a representative bulk metallic glass, $Zr_{62}Cu_{17}Ni_{13}Al_8$. was investigated for micro-forging of U-shape pattern. Micro-formability was estimated by comparing $R_f$ values ($=A_f/A_g$), where $A_g$ is cross-sectional area of U groove, and $A_f$ the filled area by material. Micro-forging process was simulated and analyzed by applying finite element method. FEM simulation results showed reasonable agreement with the experimental results when the material properties and simulation conditions such as top die speed, remeshing criteria and boundary conditions were tightly controlled. The micro-formability of $Zr_{62}Cu_{17}Ni_{13}Al_8$ was increased with increasing load and time in the temperature range of the supercooled liquid state. Also, FEM simulation using a commercial software, DEFORM was confirmed to be applicable for the optimization of micro-forming process.

• Steel and Composite Structures
• /
• 제26권6호
• /
• pp.771-791
• /
• 2018

This paper deals with the low velocity impact response and dynamic stresses of composite sandwich truncated conical shells (STCS) with compressible or incompressible core. Impacts are assumed to occur normally over the top face-sheet and the interaction between the impactor and the structure is simulated using a new equivalent three-degree-of-freedom (TDOF) spring-mass-damper (SMD) model. The displacement fields of core and face sheets are considered by higher order and first order shear deformation theory (FSDT), respectively. Considering continuity boundary conditions between the layers, the motion equations are derived based on Hamilton's principal incorporating the curvature, in-plane stress of the core and the structural damping effects based on Kelvin-Voigt model. In order to obtain the contact force, the displacement histories and the dynamic stresses, the differential quadrature method (DQM) is used. The effects of different parameters such as number of the layers of the face sheets, boundary conditions, semi vertex angle of the cone, impact velocity of impactor, trapezoidal shape and in-plane stresses of the core are examined on the low velocity impact response of STCS. Comparison of the present results with those reported by other researchers, confirms the accuracy of the present method. Numerical results show that increasing the impact velocity of the impactor yields to increases in the maximum contact force and deflection, while the contact duration is decreased. In addition, the normal stresses induced in top layer are higher than bottom layer since the top layer is subjected to impact load. Furthermore, with considering structural damping, the contact force and dynamic deflection decrees.

• 대한기계학회논문집A
• /
• 제27권8호
• /
• pp.1398-1408
• /
• 2003

Tensile and LCF(low cycle fatigue) tests were carried out in air at wide temperature range 20$^{\circ}C$-750$^{\circ}C$ and strain rates of 1${\times}$10$\^$-4//s-1${\times}$10$\^$-2/ to ascertain the influence of strain rate on tensile and LCF properties of prior cold worked 316L stainless steel, especially focused on the DSA(dynamic strain aging) regime. Dynamic strain aging induced the change of tensile properties such as strength and ductility in the temperature region 250$^{\circ}C$-600$^{\circ}C$ and this temperature region well coincided with the negative strain rate sensitivity regime. Cyclic stress response at all test conditions was characterized by the initial hardening during a few cycles, followed by gradual softening until final failure. Temperature and strain rate dependence on cyclic softening behavior appears to result from the change of the cyclic plastic deformation mechanism and DSA effect. The DSA regimes between tensile and LCF loading conditions in terms of the negative strain rate sensitivity were well consistent with each other. The drastic reduction in fatigue resistance at elevated temperature was observed, and it was attributed to the effects of oxidation, creep and dynamic strain aging or interactions among them. Especially, in the DSA regime, dynamic strain aging accelerated the reduction of fatigue resistance by enhancing crack initiation and propagation.