• 제목/요약/키워드: Average stiffness

검색결과 224건 처리시간 0.022초

보재의 손상에 따른 비계용 작업발판의 강성 변화에 대한 실험적 연구 (An Experimental Study on the Stiffness Change of Scaffold Working Plate caused by Damage of Cross-beam)

  • 성용원;강민국;원정훈
    • 한국안전학회지
    • /
    • 제36권5호
    • /
    • pp.27-35
    • /
    • 2021
  • This study investigated the change in stiffness and deflection of a scaffold working plate caused by damage to a cross-beam in the plate. Experiments were conducted considering various load and damage conditions of cross-beams. A cross-beam falling off from the working plate was considered damaged. The load-displacement curves of specimens at the center of the uniform load showed that the working plate stiffness decreased by 14.66%-1.89%, depending on the load interval due to the damage of one cross-beam. A reduction in the stiffness of 33.94%-40.76% resulted from the damage of two cross-beams. Moreover, the displacement increased by an average of 25% when one cross-beam was damaged and an average of 65% when two cross-beams were damaged. Therefore, damage to the cross-beam in the working plate can potentially cause accidents and harm workers. As the load increases, the risk of an accident due to the aforementioned damage also increases because the stiffness remarkably decreases with the load increase. Further, the damage to the cross-beam mainly reduces the stiffness but increases the displacement rather than the strength of the working scaffold plate.

공간적으로 보강된 복합재료의 강성예측 (Stiffness Prediction of Spatially Reinforced Composites)

  • 유재석;장영순;이상의;김천곤
    • Composites Research
    • /
    • 제17권5호
    • /
    • pp.25-38
    • /
    • 2004
  • 본 연구에서는 라드와 기지의 강성행렬의 중첩을 통해서 임의의 방향에서 공간적으로 보강된 복합재(SRC)의 강성을 예측하였다. 예측치를 실험과 비교하기 위하여 SRC의 물성치를 측정하였다. 라드방향에서는 강성행렬의 중첩을 통해서 예측된 물성치가 실험치와 일치하였고, 라드에서 벗어난 방향에서는 연성행렬의 중첩을 통해서 예측된 물성치가 실험치와 비교적 일치하였다. 이런 이유로 강성행렬과 연성행렬의 중첩을 공간적으로 조합한 물성치 조화함수를 이용하여, SRC의 모든 방향에서 물성치를 예측하였다. 이러한 물성치 조화함수를 이용한 결과, 예측치와 실험치가 라드방향과 라드에서 벗어난 방향 모두에서 일치하였다

탄성칼슘에 성상이 종이물성에 미치는 영향 (Effect of Particle Shape and Size of Calcium Carbonate on Physical Properties of Paper)

  • 한영림;서영범
    • 펄프종이기술
    • /
    • 제29권1호
    • /
    • pp.7-12
    • /
    • 1997
  • This study was intended to investigate the proper shape and size of calcium carbonate for the improvement of paper properties and its end use performance. We loaded calcium carbonate of various shapes and size in the handsheet and measured their physical and optical properties. Results obtained from the study are summarized as follows : 1. Due to different particle shapes and sizes, precipitated calcium carbonate (PCC) contributed greater to bulk improvement than ground calcium carbonate (GCC). Scalenohedral form of PCC produced the bulkiest sheet, GCC made the sheet bulkier as average particle size increases. 2. Tensile strength increased as average particle size was increasing. GCC kept tensile strength more effectively than PCC. The effect of particle size on tensile strength was much more pronounced as filler addition level was increasing. 3. Over the average particle size of 6.99$\mu$m, GCC gave much higher burst strength and internal bond than PCC did. In the filler levels of 20% and 30%, GCC by using bigger size fillers showed 50~100% improvement in some cases than PCC at the same filler content. 4. Tear strength increased as average particle size was increasing. At the filler level of 30%, PCC decreased tear greatly. 5. Over the average particle size of 13.56$\mu$m, GCC kept bending stiffness greater than PCC. Due to its shape, Scalenohedral form of PCC showed higher stiffness than others at the same particle size. 6. Cubic and acicular form of PCC improved light scattering coefficient very effectively. Light scattering coefficient of GCC decreased as average particle size increased. 7. Both of particle shape and size of filler were important factor in developing optical properties and bending stiffness. Particle size was the only important factor in developing other strength properties

  • PDF

Dynamic stiffness based computation of response for framed machine foundations

  • Lakshmanan, N.;Gopalakrishnan, N.;Rama Rao, G.V.;Sathish kumar, K.
    • Geomechanics and Engineering
    • /
    • 제1권2호
    • /
    • pp.121-142
    • /
    • 2009
  • The paper deals with the applications of spectral finite element method to the dynamic analysis of framed foundations supporting high speed machines. Comparative performance of approximate dynamic stiffness methods formulated using static stiffness and lumped or consistent or average mass matrices with the exact spectral finite element for a three dimensional Euler-Bernoulli beam element is presented. The convergence of response computed using mode superposition method with the appropriate dynamic stiffness method as the number of modes increase is illustrated. Frequency proportional discretisation level required for mode superposition and approximate dynamic stiffness methods is outlined. It is reiterated that the results of exact dynamic stiffness method are invariant with reference to the discretisation level. The Eigen-frequencies of the system are evaluated using William-Wittrick algorithm and Sturm number generation in the $LDL^T$ decomposition of the real part of the dynamic stiffness matrix, as they cannot be explicitly evaluated. Major's method for dynamic analysis of machine supporting structures is modified and the plane frames are replaced with springs of exact dynamic stiffness and dynamically flexible longitudinal frames. Results of the analysis are compared with exact values. The possible simplifications that could be introduced for a typical machine induced excitation on a framed structure are illustrated and the developed program is modified to account for dynamic constraint equations with a master slave degree of freedom (DOF) option.

Modified sigmoid based model and experimental analysis of shape memory alloy spring as variable stiffness actuator

  • Sul, Bhagoji B.;Dhanalakshmi, K.
    • Smart Structures and Systems
    • /
    • 제24권3호
    • /
    • pp.361-377
    • /
    • 2019
  • The stiffness of shape memory alloy (SMA) spring while in actuation is represented by an empirical model that is derived from the logistic differential equation. This model correlates the stiffness to the alloy temperature and the functionality of SMA spring as active variable stiffness actuator (VSA) is analyzed based on factors that are the input conditions (activation current, duty cycle and excitation frequency) and operating conditions (pre-stress and mechanical connection). The model parameters are estimated by adopting the nonlinear least square method, henceforth, the model is validated experimentally. The average correlation factor of 0.95 between the model response and experimental results validates the proposed model. In furtherance, the justification is augmented from the comparison with existing stiffness models (logistic curve model and polynomial model). The important distinction from several observations regarding the comparison of the model prediction with the experimental states that it is more superior, flexible and adaptable than the existing. The nature of stiffness variation in the SMA spring is assessed also from the Dynamic Mechanical Thermal Analysis (DMTA), which as well proves the proposal. This model advances the ability to use SMA integrated mechanism for enhanced variable stiffness actuation. The investigation proves that the stiffness of SMA spring may be altered under controlled conditions.

Damage assessment of shear buildings by synchronous estimation of stiffness and damping using measured acceleration

  • Shin, Soobong;Oh, Seong Ho
    • Smart Structures and Systems
    • /
    • 제3권3호
    • /
    • pp.245-261
    • /
    • 2007
  • Nonlinear time-domain system identification (SI) algorithm is proposed to assess damage in a shear building by synchronously estimating time-varying stiffness and damping parameters using measured acceleration data. Mass properties have been assumed as the a priori known information. Viscous damping was utilized for the current research. To chase possible nonlinear dynamic behavior under severe vibration, an incremental governing equation of vibrational motion has been utilized. Stiffness and damping parameters are estimated at each time step by minimizing the response error between measured and computed acceleration increments at the measured degrees-of-freedom. To solve a nonlinear constrained optimization problem for optimal structural parameters, sensitivities of acceleration increment were formulated with respect to stiffness and damping parameters, respectively. Incremental state vectors of vibrational motion were computed numerically by Newmark-${\beta}$ method. No model is pre-defined in the proposed algorithm for recovering the nonlinear response. A time-window scheme together with Monte Carlo iterations was utilized to estimate parameters with noise polluted sparse measured acceleration. A moving average scheme was applied to estimate the time-varying trend of structural parameters in all the examples. To examine the proposed SI algorithm, simulation studies were carried out intensively with sample shear buildings under earthquake excitations. In addition, the algorithm was applied to assess damage with laboratory test data obtained from free vibration on a three-story shear building model.

지역사회 건강한 성인에서 알코올 섭취량 및 폭음과 동맥경직도의 관련성 (Relationship of Average Volume of Alcohol Consumption and Binge Drinking to Arterial Stiffness in Community-Dwelling Healthy Adults)

  • 권순석;이영훈
    • 농촌의학ㆍ지역보건
    • /
    • 제37권1호
    • /
    • pp.23-35
    • /
    • 2012
  • 지역사회 성인을 대상으로 알코올 섭취량과 동맥경직도의 관련성을 파악하였으며, 아울러 폭음과 동맥경직도의 관련성을 살펴보았다. 지역사회기반 코호트 연구에 참여한 50세 이상 성인 5944명을 대상으로 하루 평균 알코올 소비량(g/day)과 월 폭음 빈도를 조사하였다. 상완-발목동맥 맥파전도속도(baPWV)를 측정한 후 남녀 각각에서 baPWV 4사분위에 해당하는 집단을 'high baPWV'로 정의하였다. 남성 알코올 섭취군의 교차비는 비음주군과 비교해서 유의한 차이가 없었지만, >40.0 g/d 알코올 섭취군의 교차비는 유의하게 증가하였다. 모든 여성 알코올 섭취군의 교차비는 비음주군에 비해서 유의한 차이가 없었다. 남성에서는 비폭음군에 비해 주 1회 미만 폭음군 및 주 1회 이상 폭음군의 high baPWV에 대한 교차비가 유의하게 증가하였다. 여성에서는 비폭음군에 비해 주 1회 이상 폭음군의 교차비가 유의하게 증가하였다. 남녀 모두에서 적당한 음주는 동맥경직도의 위험성이 낮은 반면, 과도한 음주는 동맥경직도의 위험성이 증가하였으며, 전반적으로 알코올 섭취량과 baPWV로 측정한 동맥경직도 사이에는 J자 형태의 관련성이 있었다. 또한 알코올 섭취량을 포함한 기존의 심혈관 위험요인과는 독립적으로 남녀 모두에서 폭음이 동맥경직도와 유의한 관련성이 있었다.

Research on the tightening strategy of bolted flange for contact stiffness of joint surface

  • Zuo, Weiliang;Liu, Zhifeng;Zhao, Yongsheng;Niu, Nana;Zheng, Mingpo
    • Structural Engineering and Mechanics
    • /
    • 제83권3호
    • /
    • pp.341-351
    • /
    • 2022
  • During bolted flange assembly, the contact stiffness of some areas of the joint surface may be low due to the elastic interaction. In order to improve the contact stiffness at the lowest position of bolted flange, the correlation model between the initial bolt pre-tightening force and the contact stiffness of bolted flange is established in this paper. According to the stress distribution model of a single bolt, an assumption of uniform local contact stiffness of bolted flange is made. Moreover, the joint surface is divided into the compressive stress region and the elastic interaction region. Based on the fractal contact theory, the relationship model of contact stiffness and contact force of the joint surface is proposed. Considering the elastic interaction coefficient method, the correlation model of the initial bolt pre-tightening force and the contact stiffness of bolted flange is established. This model can be employed to reverse determine the tightening strategy of the bolt group according to working conditions. As a result, this provides a new idea for the digital design of tightening strategy of bolt group for contact stiffness of bolted flange. The tightening strategy of the bolted flange is optimized by using the correlation model of initial bolt pre-tightening force and the contact stiffness of bolted flange. After optimization, the average contact stiffness of the joint surface increased by 5%, and the minimum contact stiffness increased by 6%.

수력 원통형 터빈 가이드 베어링의 저부하/저편심 성능향상 설계 - 패드 선단 테이퍼의 도입 (Low-Load/Low-Eccentricity Performance Improvement Designs for Hydro Power Application of Cylindrical Turbine Guide Bearings - Introduction of Pad Leading-Edge Tapers)

  • 이안성;장선용
    • Tribology and Lubricants
    • /
    • 제33권2호
    • /
    • pp.65-70
    • /
    • 2017
  • In vertical hydro/hydraulic power turbine-generator applications, traditionally, cylindrical turbine guide bearings (TGBs) are widely used to provide turbine runner shafts with smooth rotation guides and supports. All existing cylindrical TGBs with simple plain pads have drawbacks such as having no pressure generation and film stiffness at the no-load condition and in addition, at the low-load/low-eccentricity condition, having very low film stiffness values and lacking design credibility in the stiffness values themselves. In this paper, in order to fundamentally improve the low-load/low-eccentricity performance of conventional cylindrical TGBs and thus enhance their design-application availability and usefulness, we propose to introduce a rotation-directional leading-edge taper to each partitioned pad, i.e., a pad leading-edge taper. We perform a design analysis of lubrication performance on $4-Pad{\times}4-Row$ cylindrical TGBs to verify an engineering/technical usefulness of the proposed pad leading-edge taper. Analysis results show that by introducing the leading-edge taper to each pad of the cylindrical TGB one can expect a constant high average direct stiffness with a high degree of design credibility, regardless of load value, even at the low-load/low-eccentricity condition and also control the average direct stiffness value by exploring the taper height as a design parameter. Therefore, we conclude that the proposed pad leading-edge tapers are greatly effective in more accurately predicting and controlling rotordynamic characteristics of vertical hydro-power turbine-generator rotor-bearing systems to which cylindrical TGBs are applied.

공간적으로 보강된 복합재의 기계적 물성치 예측 (Prediction of Mechanical Properties for Spatially Reinforced Composites)

  • 유재석;김천곤;홍창선;김광수
    • 한국복합재료학회:학술대회논문집
    • /
    • 한국복합재료학회 2000년도 추계학술발표대회 논문집
    • /
    • pp.177-182
    • /
    • 2000
  • This paper predicted the equivalent stiffness of spatially reinforced composites (SRC) using the volume average of a fiber rod and matrix stiffness, and the strength of SRC using the stiffness reduction and the modified Tsai-Wu composite failure theory. Those equivalent engineering constants are used to analyze the mechanical behavior and the failure of SRC structures. Because the distribution of equivalent engineering constants is varying with the change in SRC shape, we made a program that predicts engineering constants of SRC. Both 3-D and 4-D SRC show the smallest tensile modulus and the largest shear modulus at the maximum rotated direction from each rod. Also the strength properties show the same tendency.

  • PDF