• Title/Summary/Keyword: 응력증폭계수

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The Dynamic Effect of Highspeed Trains on Railway Bridges (고속철도 차량의 주행이 교량에 미치는 충격효과)

  • Yu, Chul Soo;Kang, Young Jong;Kim, Jong Heun;Kweon, Jae Hyun
    • Journal of Korean Society of Steel Construction
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    • v.10 no.2 s.35
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    • pp.187-199
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    • 1998
  • The highspeed railway bridge which support continuous and high moving mass evalute the dynamic state and make the displacement of the bridge makes more or less, but up to this time the bridges are designed by the static design concept. for example when we design bridge we use impact factor, which only times the static load makes dynamic load. But becouse it simples. it can't express all of the effects. And so, in this report we study the modeling method of the moving mass and the dynamic factor.

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Evaluation of State Parameter of Sands Using Dilatometer Test (딜라토미터 시험을 이용한 사질토의 상태정수 평가)

  • Choi, Sung-Kun;Lee, Moon-Joo;Hong, Sung-Jin;Lee, Woo-Jin
    • Journal of the Korean Geotechnical Society
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    • v.26 no.4
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    • pp.27-36
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    • 2010
  • In this study, a series of flat dilatometer tests are performed for Busan sand reconstituted in a large calibration chamber to evaluate the state parameter ($\Psi$). Experimental result shows that the horizontal amplification factor ($K_D/K_0$) is linearly related with state parameter in semi-logarithmic space, but the $K_D/K_0$ of OC specimen is smaller than that of NC specimen because of the horizontal residual stress by stress history of OC specimen. The relation between the normalized dilatometer modulus ($E_D/\sigma_m'$) and the state parameter is also linearly expressed in semi-logarithmic space, and the effect of stress history is relatively insignificant in this relation. However, the variation in $E_D/\sigma_m'-\Psi$ relation of NC state is slightly higher than that of OC state due to the effect of the stress level, and the correlation curve is descending with increase of confining stress. The comparison of test result with previous results of Ticino and Toyoura sands shows that the $E_D/\sigma_m'-\Psi$ relation of Toyoura sand is located on upper side than that of Busan and Tieino sands due to the effect of the higher compressibility, whereas the $K_D/K_0-\Psi$ relation of each sand is irregularly distributed.

Safety Evaluation of Carbon Fiber/Epoxy Composite Link Using Micromechanics of Failure Criterion (미시역학적 파손 기준을 이용한 탄소섬유/에폭시 복합재 링크의 안전성 평가)

  • Jae Ho Cha;Sung Ho Yoon
    • Composites Research
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    • v.36 no.3
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    • pp.154-161
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    • 2023
  • This study explored the feasibility of replacing a metal link with a carbon fiber/epoxy composite link and assessed its capacity to withstand a given load condition using failure criteria. The micromechanics of failure (MMF) criterion was employed to predict the failure mode of the composite material, and mechanical tests were conducted to obtain reference strength parameters for MMF. The findings revealed that the stress distribution was concentrated near the hole, and weaknesses were found around the hole and at the end of the link under bending conditions. Based on the failure index, matrix tensile failure was predicted at the end of the link, and fiber compression failure occurred near the hole. The methods and results obtained from this study can provide valuable guidelines for assessing the safety of composite materials under specific load conditions when replacing metal parts with carbon fiber/epoxy composites to achieve weight reduction.

Seismic analysis of tunnel considering the strain-dependent shear modulus and damping ratio of a Jointed rock mass (절리암반의 변형률 의존적 전단탄성계수 및 감쇠비 특성을 고려한 터널의 내진 해석)

  • Song, Ki-Il;Jung, Sung-Hoon;Cho, Gye-Chun;Lee, Jeong-Hark
    • Journal of Korean Tunnelling and Underground Space Association
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    • v.12 no.4
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    • pp.295-306
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    • 2010
  • Contrary to an intact rock, the jointed rock mass shows strain-dependent deformation characteristics (elastic modulus and damping ratio). The maximum elastic modulus of a rock mass can be obtained from an elastic wave-based exploration in a small strain level and applied to seismic analyses. However, the assessment and application of the non-linear characteristics of rock masses in a small to medium strain level ($10^{-4}{\sim}0.5%$) have not been carried out yet. A non-linear dynamic analysis module is newly developed for FLAC3D to simulate strain-dependent shear modulus degradation and damping ratio amplification characteristics. The developed module is verified by analyzing the change of the Ricker wave propagation. Strain-dependent non-linear characteristics are obtained from disks of cored samples using a rock mass dynamic testing apparatus which can evaluate wave propagation characteristics in a jointed rock column. Using the experimental results and the developed non-linear dynamic module, seismic analyses are performed for the intersection of a shaft and an inclined tunnel. The numerical results show that vertical and horizontal displacements of non-linear analyses are larger than those of linear analyses. Also, non-linear analyses induce bigger bending compressive stresses acting on the lining. The bending compressive stress concentrates at the intersection part. The fundamental understanding of a strain-dependent jointed rock mass behavior is achieved in this study and the analytical procedure suggested can be effectively applied to field designs and analyses.

Dynamic Factor of Safety Calculation of Slope by Nonlinear Response History Analysis (비선형 응답이력해석을 통한 사면의 동적 안전계수 계산)

  • Lee, Yonghee;Kim, Hak-Sung;Ju, Young-Tae;Kim, Daehyeon;Park, Heon-Joon;Park, Duhee
    • Journal of the Korean Geotechnical Society
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    • v.37 no.9
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    • pp.5-12
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    • 2021
  • Pseudo-static slope stability analysis method is widely used in engineering practice to calculate the seismic factor of safety of slope subjected to earthquake ground motions. Although the dynamic analysis method is well recognized to have the primary advantage of simulating the stress-strain response of soils, it is not often used in practice because of the difficult in estimating the factor of safety. In this study, a procedure which utilizes the dynamic analysis method to extract the transient dynamic factor of safety is devleoped. This method overcomes the major limitation of the pseudo-static method, which uses an empirically determined seismic coefficient to derive the factor of safety. The proposed method is applied to a slope model and the result is compared with that of the pseudo-static method. It is shown that minimum dynamic factor of safety calculated by the dynamic analysis is slightly larger than that determined from the pseudo-static method. It is also demonstrated that the dynamic factor of safety becomes minimum when the horizontal seismic coefficient and horizontal average acceleration are maximum.

Preliminary Study on the Development of a Performance Based Design Platform of Vertical Breakwater against Seismic Activity - Centering on the Weakened Shear Modulus of Soil as Shear Waves Go On (직립식 방파제 성능기반 내진 설계 Platform 개발을 위한 기초연구 - 전단파 횟수 누적에 따른 지반 강도 감소를 중심으로)

  • Choi, Jin Gyu;Cho, Yong Jun
    • Journal of Korean Society of Coastal and Ocean Engineers
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    • v.30 no.6
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    • pp.306-318
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    • 2018
  • In order to evaluate the seismic capacity of massive vertical type breakwaters which have intensively been deployed along the coast of South Korea over the last two decades, we carry out the preliminary numerical simulation against the PoHang, GyeongJu, Hachinohe 1, Hachinohe 2, Ofunato, and artificial seismic waves based on the measured time series of ground acceleration. Numerical result shows that significant sliding can be resulted in once non-negligible portion of seismic energy is shifted toward the longer period during its propagation process toward the ground surface in a form of shear wave. It is well known that during these propagation process, shear waves due to the seismic activity would be amplified, and non-negligible portion of seismic energy be shifted toward the longer period. Among these, the shift of seismic energy toward the longer period is induced by the viscosity and internal friction intrinsic in the soil. On the other hand, the amplification of shear waves can be attributed to the fact that the shear modulus is getting smaller toward the ground surface following the descending effective stress toward the ground surface. And the weakened intensity of soil as the number of attacking shear waves are accumulated can also contribute these phenomenon (Das, 1993). In this rationale, we constitute the numerical model using the model by Hardin and Drnevich (1972) for the weakened shear modulus as shear waves go on, and shear wave equation, in the numerical integration of which $Newmark-{\beta}$ method and Modified Newton-Raphson method are evoked to take nonlinear stress-strain relationship into account. It is shown that the numerical model proposed in this study could duplicate the well known features of seismic shear waves such as that a great deal of probability mass is shifted toward the larger amplitude and longer period when shear waves propagate toward the ground surface.

Effects of Post-Tensioning Tendons and Vehicle Speeds on Dynamic Response of Concrete-Filled Steel Tubular Tied Arch Girder (긴장재 및 차량속도 변화에 따른 콘크리트 충전 타이드 아치형 거더의 동적거동)

  • Roh, Hwasung;Hong, Sanghyun;Park, Kyunghoon;Lee, Jong Seh
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.31 no.3A
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    • pp.163-172
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    • 2011
  • The CFTA girder developed is a concrete filled steel tubular system with arched shape and external post-tensioning (PT) tendons which control the initial camber and the bending stress of the girder. In the present study the effects of the PT tendons on the dynamic behavior of the girder subjected to a moving vehicle load are numerically investigated. Various levels for the tendon quantity and the tendon forces are considered, using the existing FE model of the girder. The vehicle considered is a DB-24 truck and is modeled with two tracks-three axles. Equivalent-load pulse time histories are applied to each node to simulate the moving vehicle, depending on the time of arrival and the discretization. The vehicle speeds are varied from 40 km/hr to 100 km/hr with increment of 20 km/hr. The analysis results show that the tendon forces do not produce any influences on the dynamic responses of the girder. However the dymamic deflection of the girder increases when a smaller amount of tendons is used. The Dynamic Amplification Factors (DAF) are evaluated based on the static and dynamic responses. Much lower values of the DAF are obtained, even no tendons applied, than those provided by the design criteria of the AASHTO LRFD and the Korea Highway Standard Specification.

Impact Evaluation of Rubber Type, Hardness and Induced Prestress Force on the Dynamic Properties of a Damper (감쇠장치의 동적특성에 대한 고무의 종류, 경도 및 프리스트레스력의 영향 평가)

  • Im, Chae-Rim;Yang, Keun-Hyeok;Mun, Ju-Hyun;Won, Eun-Bee
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.26 no.6
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    • pp.167-174
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    • 2022
  • The objective of this study is to evaluate the dynamic properties of DUS (damping-up system) composed of the materials with excellent damping capacity, and to compare with those of the conventional hangar bolt. The main parameters are the type and hardness (𝜂H), of rubber and the prestress force (value converted from the compression strain (𝜂R) in the stress-strain relationship of rubber). The dynamic properties were examined from the natural frequency (𝜔n), maximum response acceleration (Am), amplification coefficient (𝛼p), maximum relative displacement (𝚫m), and damping ratio (𝜉D). The test results showed that the Am, 𝛼p, and 𝚫m values of DUS were 46.3%, 46.6% and 62.9% lower, respectively, and the 𝜉D value was 3.89 times higher, when compared to those of the conventional hangar bolt. In particular, the 𝛼p value was 1.3 for DUS, and 2.45 for the conventional hanger bolt, which were similar to those of rigid and flexible components specified in KDS 41 17 00, respectively. Consequently, in the optimal details of DUS, the 𝜂H values of 50 and 45 were required for the NR (natural rubber) and EPDM (ethylene propylene diene monomer), and the 𝜂R value of 5% was also recommended.

A Numerical Study on Improvement in Seismic Performance of Nuclear Components by Applying Dynamic Absorber (동흡진기 적용을 통한 원전기기의 내진성능향상에 관한 수치적 연구)

  • Kwag, Shinyoung;Kwak, Jinsung;Lee, Hwanho;Oh, Jinho;Koo, Gyeong-Hoi
    • Journal of the Computational Structural Engineering Institute of Korea
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    • v.32 no.1
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    • pp.17-27
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    • 2019
  • In this paper, we study the applicability of Tuned Mass Damper(TMD) to improve seismic performance of piping system under earthquake loading. For this purpose, a mode analysis of the target pipeline is performed, and TMD installation locations are selected as important modes with relatively large mass participation ratio in each direction. In order to design the TMD at selected positions, each corresponding mode is replaced with a SDOF damped model, and accordingly the corresponding pipeline is converted into a 2-DOF system by considering the TMD as a SDOF damped model. Then, optimal design values of the TMD, which can minimize the dynamic amplification factor of the transformed 2-DOF system, are derived through GA optimization method. The proposed TMD design values are applied to the pipeline numerical model to analyze seismic performance with and without TMD installation. As a result of numerical analyses, it is confirmed that the directional acceleration responses, the maximum normal stresses and directional reaction forces of the pipeline system are reduced, quite a lot. The results of this study are expected to be used as basic information with respect to the improvement of the seismic performance of the piping system in the future.

Evaluation of the Influence of Shear Strength Correction through a Comparative Study of Nonlinear Site Response Models (비선형 지반구성모델의 비교를 통한 전단강도 보정이 부지응답해석에 미치는 영향 평가)

  • Aaqib, Muhammad;Park, Duhee;Kim, Hansup;Adeel, Muhammad Bilal;Nizamani, Zubair Ahmed
    • Journal of the Korean Geotechnical Society
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    • v.36 no.12
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    • pp.77-86
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    • 2020
  • In this study, the importance of implied strength correction for shallow depths at a region of moderate to low seismicity with primary focus on its effect upon site natural period and mean period of the ground motion is investigated. In addition to the most commonly used Modified Kondner-Zelasko (MKZ) model, this paper uses a quadratic/hyperbolic (GQ/H) model that can capture the stress - strain response at large strains as well as small strain stiffness dependence. A total of six site profiles by downhole tests are used and 1D site response analyses are performed using three input motions with contrasting mean periods. The difference between non-corrected and corrected analyses is conditional on the site period as well as mean ground motion period. The effect of periods is analyzed by correlating them with the effective peak ground acceleration, maximum shear strains and amplification factors. The comparative study reveals that the difference is more prominent in soft sites with long site periods. Insignificant differences are observed when soil profiles are subjected to ground motion with very short mean period.