• Title/Summary/Keyword: maximum deflection

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Development of Optimum Design Program for PPC Structures using DCOC (이산성 연속형 최적성 규준을 이용한 PPC 구조의 최적설계프로그램 개발)

  • 한상훈;조홍동;이상근
    • Computational Structural Engineering
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    • v.10 no.4
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    • pp.315-325
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    • 1997
  • This paper describes the application of discretized continuum-type optimality criteria (DCOC) and the development of optimum design program for the multispan partially prestressed concrete beams. The cost of construction as objective function which includes the costs of concrete, prestressing steel, non-prestressing steel and formwork is minimized. The design constraints include limits on the maximum deflection, flexural and shear strengths, in addition to ductility requirements, and upper and lower bounds on design variables as stipulated by the design Code. Based on Kuhn-Tucker necessary conditions, the optimality criteria are explicitly derived in terms of the design variables-effective depth, eccentricity of prestressing steel and non-prestressing steel ratio. The prestressing profile is prescribed by parabolic functions. The self-weight of the structure is included in the equilibrium equation of the real system, as is the secondary effect resulting from the prestressing force. An iterative procedure and computer program for updating the design variables are developed. Two numerical examples of multispan PPC beams with rectangular cross-section are solved to show the applicability and efficiency of the DCOC-based technique.

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A Study on Nonlinear Analysis of Reinforced Concrete Structures (철근(鐵筋)콘크리트 구조물(構造物)의 비선형(非線型) 해석(解析)에 관한 연구(硏究))

  • Chang, Dong Il;Kwak, Kae Hwan
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.7 no.2
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    • pp.69-77
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    • 1987
  • A finite element method has been developed to study the material nonlinear analysis of reinforced concrte structures. Concrete behavior under the biaxial state of stress is represented by a nonlinear constitutive relationship which incorporates tensile cracking, tensile stiffening effect between cracks and the strain-softening phenomenon beyond the maximum compressive strength. The concrete model used is based upon nonlinear elasticity by assuming concrete to be an orthotropic material and modeled as equivalent uniaxial stress-strain constitutive relationship using equivalent uniaxial strain. The streel reinforcement is assumed to be in a uniaxial stress state and is modeled as a bilinear, elasto-plastic material with strain hardening approximating the Bauschinger effect. In plane stress state, R.C. beams is modeled as a quadratic element that has two degrees of freedom in each node. And this results of finite element analysis are compared with the experimential results of midspan deflection, stresses and strains.

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Finite element model updating of long-span cable-stayed bridge by Kriging surrogate model

  • Zhang, Jing;Au, Francis T.K.;Yang, Dong
    • Structural Engineering and Mechanics
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    • v.74 no.2
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    • pp.157-173
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    • 2020
  • In the finite element modelling of long-span cable-stayed bridges, there are a lot of uncertainties brought about by the complex structural configuration, material behaviour, boundary conditions, structural connections, etc. In order to reduce the discrepancies between the theoretical finite element model and the actual static and dynamic behaviour, updating is indispensable after establishment of the finite element model to provide a reliable baseline version for further analysis. Traditional sensitivity-based updating methods cannot support updating based on static and dynamic measurement data at the same time. The finite element model is required in every optimization iteration which limits the efficiency greatly. A convenient but accurate Kriging surrogate model for updating of the finite element model of cable-stayed bridge is proposed. First, a simple cable-stayed bridge is used to verify the method and the updating results of Kriging model are compared with those using the response surface model. Results show that Kriging model has higher accuracy than the response surface model. Then the method is utilized to update the model of a long-span cable-stayed bridge in Hong Kong. The natural frequencies are extracted using various methods from the ambient data collected by the Wind and Structural Health Monitoring System installed on the bridge. The maximum deflection records at two specific locations in the load test form the updating objective function. Finally, the fatigue lives of the structure at two cross sections are calculated with the finite element models before and after updating considering the mean stress effect. Results are compared with those calculated from the strain gauge data for verification.

Development of a Robot Gripper For Handling Seedling Trays (육묘상자 취급을 위한 로봇 핸드의 개발)

  • Kim, Ki Dae;Cho, Sung Wha;Seo, Il Hwan;Lee, Hyun Dong
    • Korean Journal of Agricultural Science
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    • v.23 no.2
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    • pp.227-232
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    • 1996
  • It is a tedious job to handle seedling trays in a green house with human hands because of their fluctuation when they are moving. A robotic gripper for handling a seedling tray has been developed., which has two fingers consisting of the vertical and horizontal bars. The maximum deflections at the center of the seedling trays were measured with various lengths of the horizontal bars. The length of 250 mm was revealed to be optimal one, resulting less than 15 mm deflection with a $540{\times}270mm$ seedling tray, which was acceptable for a practical use. For this study a LM system was adopted to move the fingers. To validate this system the robotic gripper was installed on a Cartesian robotic manipulator and their performance was tested several times with great success. The robotic manipulator used in this study was a general one, so a special one for this robotic gripper needs to be developed in future.

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Dynamic Optimal Design of Continuous Beams (연속보의 동적 최적설계에 관한 연구)

  • 이병구;오상진;모정만
    • Computational Structural Engineering
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    • v.10 no.2
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    • pp.233-242
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    • 1997
  • The main purpose of this paper is to investigate the dynamic optimal design of continuous beams. The computer-aided optimization technique is used to obtain the near-optimal parameters of continuous beam. The computer program is developed to obtain the natural frequency parameters and the forced vibration responses to a transit point load for the continuous beam with variable support spacing, mass and stiffness. The model test data is in good agreement with the computer calculation, which serves to validate the mathematical analysis. The optimization function to describe the design efficiency is defined as a linear combination of four dimensionless span characteristics; the maximum dynamic stress; the stress difference between span segments; the rms deflection under the transit point load; and the total span mass. Studies of three span beams show that the beam with near-optimal parameters can improve design efficiency when compared to a uniform beam with even spacing of the same total span length.

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Mechanical and thermal properties of polyamide versus reinforced PMMA denture base materials

  • Soygun, Koray;Bolayir, Giray;Boztug, Ali
    • The Journal of Advanced Prosthodontics
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    • v.5 no.2
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    • pp.153-160
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    • 2013
  • PURPOSE. This in vitro study intended to investigate the mechanical and thermal characteristics of Valplast, and of polymethyl methacrylate denture base resin in which different esthetic fibers (E-glass, nylon 6 or nylon 6.6) were added. MATERIALS AND METHODS. Five groups were formed: control (PMMA), PMMA-E glass, PMMA-nylon 6, PMMA-nylon 6.6 and Valplast resin. For the transverse strength test the specimens were prepared in accordance with ANSI/ADA specification No.12, and for the impact test ASTM D-256 standard were used. With the intent to evaluate the properties of transverse strength, the three-point bending (n=7) test instrument (Lloyd NK5, Lloyd Instruments Ltd, Fareham Hampshire, UK) was used at 5 mm/min. A Dynatup 9250 HV (Instron, UK) device was employed for the impact strength (n=7). All of the resin samples were tested by using thermo-mechanical analysis (Shimadzu TMA 50, Shimadzu, Japan). The data were analyzed by Kruskal-Wallis and Tukey tests for pairwise comparisons of the groups at the 0.05 level of significance. RESULTS. In all mechanical tests, the highest values were observed in Valplast group (transverse strength: $117.22{\pm}37.80$ MPa, maximum deflection: $27.55{\pm}1.48$ mm, impact strength: $0.76{\pm}0.03$ kN). Upon examining the thermo-mechanical analysis data, it was seen that the E value of the control sample was 8.08 MPa, higher than that of the all other samples. CONCLUSION. Although Valplast denture material has good mechanical strength, its elastic modulus is not high enough to meet the standard of PMMA materials.

Effect of Mix Ingredients on Modulus of Elasticity of High-Strength Concrete (고강도 콘크리트의 탄성계수에 미치는 배합재료의 영향평가)

  • 장일영;박훈규;이승훈;김규동
    • Journal of the Korea Concrete Institute
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    • v.14 no.1
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    • pp.67-75
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    • 2002
  • For the design of concrete structures in the serviceability limit state, the uniaxial static modulus of elasticity may be a most important parameter. In particular, this may be so just for a deflection control of the structure. Even in new concrete codes, however, the elastic modulus is normally presented on the form of general empirical relationships with the compressive strength and density of concrete. Normally, there is a large uncertainty associated with the general equations obtained by regression. Thus, in a typical plot of static modulus of elasticity vs. compressive strength, a large scatter can be observed at same strength. The aim of this study is to present the method for obtain the maximum modulus of elasticity at same compressive strength. In the present paper report the effects of mix ingredients on the modulus of elasticity of high-strength concrete. The test of 284 cylinder specimens arc conducted for type I with 11 % replacement of fly-ash cement concretes. Different water-hinder ratio, amounts of water and coarse aggregate as variables were investigated. And also analyzed it statistically by using SAS.

Modelling and Analysis of Roll-Type Steel Mat for Rapid Stabilization of Permafrost (II) - Parametric Analysis - (영구동토 급속안정화를 위한 롤타입강재매트의 모델링과 해석(II) - 변수해석 -)

  • Moon, Do Young;Kang, Jae Mo;Lee, Janggeun;Lee, Sang Yoon
    • Journal of the Korean Geosynthetics Society
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    • v.13 no.4
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    • pp.109-117
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    • 2014
  • Using the finite element analysis model presented in accompanying paper, parametric study was performed in this paper. Various parameters were considered such as the width of wheel loads-induced permanent plastic deformation, backfill, equivalent thickness and orthogonal characteristic of steel mats. The effects of these parameters were analyzed for vertical and rotational displacements, maximum moment and tensile stress. From the parametric studies, it is found that great vertical deflection and tensile stress above allowable flexural tensile strength are developed in steel mats by the wheel loads-induced permanent plastic deformation. Backfill or increasing the thickness of steel mats is a feasible solution on this problem.

Flexural Behavior of Reinforced Concrete Beams Considering Steel Corrosion (철근의 부식을 고려한 RC보의 휨파괴 거동)

  • Eo, Seok-Hong;Lee, Chang-Hyun;Lee, Sang-Jun
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.15 no.5
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    • pp.3251-3259
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    • 2014
  • This paper presents experimental and analytical research results to predict nonlinear flexural behavior of corroded reinforced concrete beams. For this purpose, a series of test and an analytical simulation using the Maaddawy's model were carried. Test specimens of total 12 RC beams were placed in accelerated corrosion status using salt water spray test chamber for 5 months and 10 months, after they were preloaded up to 30% and 60% of the maximum load corresponding to nominal flexural strength. The test results showed that flexural strength and ductility decreased to 5.4% and 43% at the most respectively due to breakdown of bond at the steel-concrete interface. Comparative study between the analytical predictions and the experimental results showed that the Maaddawy's model can be applied to predict a real corroded RC flexural members.

Buckling resistance, bending stiffness, and torsional resistance of various instruments for canal exploration and glide path preparation

  • Kwak, Sang-Won;Ha, Jung-Hong;Lee, WooCheol;Kim, Sung-Kyo;Kim, Hyeon-Cheol
    • Restorative Dentistry and Endodontics
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    • v.39 no.4
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    • pp.270-275
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    • 2014
  • Objectives: This study compared the mechanical properties of various instruments for canal exploration and glide-path preparations. Materials and Methods: The buckling resistance, bending stiffness, ultimate torsional strength, and fracture angle under torsional load were compared for C+ file (CP, Dentsply Maillefer), M access K-file (MA, Dentsply Maillefer), Mani K-file (MN, Mani), and NiTiFlex K-file (NT, Dentsply Maillefer). The files of ISO size #15 and a shaft length of 25 mm were selected. For measuring buckling resistance (n = 10), the files were loaded in the axial direction of the shaft, and the maximum load was measured during the files' deflection. The files (n = 10) were fixed at 3 mm from the tip and then bent $45^{\circ}$ with respect to their long axis, while the bending force was recorded by a load cell. For measuring the torsional properties, the files (n = 10) were also fixed at 3 mm, and clockwise rotations (2 rpm) were applied to the files in a straight state. The torsional load and the distortion angle were recorded until the files succumbed to the torque. Results: The CP was shown to require the highest load to buckle and bend the files, and the NT showed the least. While MA and MN showed similar buckling resistances, MN showed higher bending stiffness than MA. The NT had the lowest bending stiffness and ultimate torsional strength (p < 0.05). Conclusions: The tested instruments showed different mechanical properties depending on the evaluated parameters. CP and NT files were revealed to be the stiffest and the most flexible instruments, respectively.