Displacement Control Method Research Articles

Force Method for Displacement Adjustment of Prestressed Cable Structures with Dynamic Relaxation Method

The stiffness of prestressed cable structure is provided by self-stress, and the self-stress of the structure is sensitive to external errors due to their high flexibility. Based on the basic theory of the force method (FM) and stochastic search technique, the linear displacement control problem was converted to an optimization question. Genetic algorithm (GA) is used to solve this optimization problem for prestressed structures of linear behavior. And then the dynamic relaxation method (DRM) is introduced to the linear displacement control method to achieve the non-linear displacement control for prestressed structures of non-linear behavior. The non-linear displacement control consists of two phases: (1) use the linear displacement control method as the controller step to determine the selection of actuation members and the variation of these selected members, and (2) use the DRM as the corrector step to calculate the equilibrium state of structures after linear controller deformation. A numerical example is conducted which shows that the non-linear control and the linear control both are in well agreement with the target values in the case of small displacement adjustment, while in the case of large displacement adjustment, the former is superior to the latter.

유공강판 전단연결재로 보강된 강관말뚝 머리의 인발실험

본 연구의 목적은 유공강판 전단연결재로 보강된 강관말뚝의 인발실험을 통하여 구조성능을 평가하는 것이다. 인발실험에 앞서 재료의 특성을 파악하기 위하여 콘크리트 압축장도 실험을 수행하였으며, 실험에 사용되는 철근 및 철판의 항복하중, 인장강도 및 연신율 등의 재료적 특성을 미리 파악하였다. 유공강판 전단연결재로 보강된 강관말뚝의 인발실험은 2,000kN 용량의 UTM을 이용하여 0.01mm/sec 재하속도의 변위제어 방법으로 실험을 수행하였다. 계측을 위하여 철근 및 유공강판 중앙에 strain gauge를 부착하였으며, 가력판과 충전콘크리트 사이의 상대변위 측정을 위하여 변위계(LVDT)를 설치하였다. 유공강판 전단연결재로 보강된 실험체의 항복하중은 각각 923.8kN과 981.1kN으로 기존 설계법에 의하여 제작된 실험체의 항복하중인 641.7kN에 비하여 1.44배 ~ 1.53배 증가됨을 알 수 있었다. 또한 유공강판 전단연결재로 보강된 실험체의 극한하중은 각각 1004.4kN과 1055.5kN으로 기존 설계법에 의하여 제작된 실험체의 극한하중인 813.7kN에 비하여 1.23배 ~ 1.29배 증가됨을 알 수 있었다. 반면, 유공강판 전단연결재로 보강된 실험체의 항복변위 및 극한상태의 변위는 기존 설계법에 의하여 제작된 실험체에 비하여 각각 0.61배 및 0.42배 감소됨을 알 수 있었다. 따라서 유공강판 전단연결재로 보강된 강관말뚝은 강성은 증가하고 상대변위 및 변형률은 낮게 측정되어 기존 말뚝머리 보강방법을 대체할 수 있는 적절한 보강방법임 알 수 있었다. The purpose of this study was to evaluate the structural capacity of steel pipe pile specimens reinforced with hollow steel plate shear connectors by pull-out test. Compressive strength testing of concrete was conducted and yield forces, tensile strengths and elongation ratios of re-bars and hollow steel plate were investigated. A 2,000kN capacity UTM was used for the pull-out test with 0.01mm/sec velocity by displacement control method. Strain gauges were installed at the center of re-bars and hollow steel plates and LVDTs were also installed to measure the relative displacement between the loading plate and in-filled concrete pile specimens. The yield forces of the steel pipe pile specimens reinforced with hollow steel plate shear connectors were increased 1.44-fold and 1.53-fold compared to that of a control specimen, respectively. Limited state forces of steel pipe pile specimens reinforced with hollow steel plate shear connectors were increased 1.23-fold and 1.29-fold compared to that of a control specimen, respectively. Yield state displacement and limited state displacement of steel pipe pile specimens reinforced with hollow steel plate shear connector were decreased 0.61-fold and 0.42-fold compared to that of a control specimen, respectively.

Cyclic fatigue of silica refractories – effect of test method on failure process

Silica refractories serving in high temperature industrial installations fail due to thermo-mechanical cyclic loads. The failure process was investigated by performing cyclic fatigue tests of several methods. In uni-axial compression the samples were tested either with constant force or displacement amplitude or with fixed upper displacement limit. In bending constant displacement amplitude tests were done. The investigation was supported by monotonic loading tests and microstructural analysis. It was determined that the fatigue failure occurs due to the degradation of interlocking in the crack wake. Cracking of larger grains is important for the crack initiation. The test set-up and the loading procedures significantly influence the potential to resist the crack propagation. Cyclic loading produces less brittle failure than monotonic loading. The displacement controlled method allows more gradual, less brittle, failure than the force controlled method. The potential of the crack arrest is less developed in bending than in compression.

A NEW ALGORITHM IN NONLINEAR ANALYSIS OF STRUCTURES USING PARTICLE SWARM OPTIMIZATION

Solving systems of nonlinear equations is a difficult problem in numerical computation. Probably the best known and most widely used algorithm to solve a system of nonlinear equations is Newton-Raphson method. A significant shortcoming of this method becomes apparent when attempting to solve problems with limit points. Once a fixed load is defined in the first step, there is no way to modify the load vector should a limit point occur within the increment. To overcome this defect, displacement control methods for passing limit points can be used. In displacement control method, the load ratio in the first step of an increment is defined so that a particular key displacement component will change only by a prescribed amount. In this paper the load ratio is obtained using particle swarm optimization (PSO) algorithm so that the complex behavior of structures can be followed, automatically. Design variable is load ratio and its unbalanced force is also considered as objective function in optimization process. Numerical results are performed under geometrical nonlinear analysis, elastic post-buckling analysis and inelastic post-buckling analysis. The efficiency and accuracy of proposed method are demonstrated by solving these examples. Â

H-M bearing capacity of a modified suction caisson determined by using load-/displacement-controlled methods

This paper presents a series of monotonically combined lateral loading tests to investigate the bearing capacity of the MSCs (modified suction caissons) in the saturated marine fine sand. The lateral loads were applied under load- and displacement-controlled methods at the loading eccentricity ratios of 1.5, 2.0 and 2.5. Results show that, in the displacement-controlled test, the deflection-softening behavior of load-deflection curves for MSCs was observed, and the softening degree of the load-deflection response increased with the increasing external skirt length or the decreasing loading eccentricity. It was also found that the rotation center of the MSC at failure determined by the load-controlled method is slightly lower than that by the displacement-controlled method. The calculated MSC capacity based on the rotation center position in serviceability limit state is relatively conservative, compared with the calculated capacity based on the rotation center position in the ultimate limit state. In the limit state, the passive earth pressures opposite the loading direction under load- and displacement-controlled methods decrease by 46% and 74% corresponding to peak values, respectively; however, the passive earth pressures in the loading direction at failure only decrease by approximately 3% and 7%, compared with their peak values.

Shake Table Test and Numerical Analysis of a Bridge Model Supported on Elastomeric Pad Bearings

Elastomeric pad bearings are widely applied in short- to medium-span girder bridges in China, with the superstructure restrained by reinforced concrete (RC) shear keys in the transverse direction. Field investigations after the 2008 Wenchuan earthquake reveal that bearing systems had suffered the most serious damage, such as span falling, bearing displaced, and shear key failure, while the piers and foundations underwent minor damage. As part of a major study on damage mechanism and displacement control method for short- to medium-span bridges suffered in Wenchuan earthquake, a 1:4 scale, two-span bridge model supported on elastomeric pad bearings were recently tested on shake tables at Tongji University, Shanghai. The bridge model was subjected to increasing levels of four seismic excitations possessing different spectral characteristics. Two restraint systems with and without the restraint of RC shear keys were tested. A comprehensive analytical modeling of the test systems was also performed using OpenSees. The experimental results confirmed that for the typical bridges on elastomeric pad bearings without RC shear keys, the sliding effect of the elastomeric pad bearings plays an important role in isolation of ground motions and, however, lead to lager bearing displacement that consequently increases the seismic risk of fall of span, especially under earthquakes that contain significant mid-period contents or velocity pulse components. It is suggested from the test results that RC shear keys should be elaborately designed in order to achieve a balance between isolation efficiency and bearing displacement. Good correlation between the analytical and the experimental data indicates that the analytical models for the bearing and RC shear key as well as other modeling assumptions were appropriate.

A curved triangular element for nonlinear analysis of laminated shells

A brief review of the laminated shell analyses is presented. The related literatures demonstrate that most previous studies deal with the quadrilateral or flat triangular elements and not the curved triangular element. Based on the continuum mechanic’s theory, a 6-node triangular isoparametric element is formulated for geometrically nonlinear analysis of laminated shells. To prevent the membrane and shear locking effects, the suggested scheme uses assumed strains for in-plane and transverse shear strains. Large displacements and rotations in the nonlinear analysis are included via the total Lagrangian description. Several popular benchmark problems are solved by the Generalized Displacement Control Method. The numerical results obtained are in good agreement with those published by other investigators.

On a path-following method for non-linear solid mechanics with applications to structural and cardiac mechanics subject to arbitrary loading scenarios

• Displacement-control method for arbitrary loading scenarios. • Cavity-volume-control method for multiple independently acting cavity-pressure loadings. • Adaptation of the displacement- and the cavity-volume control method to numerical modelling frameworks which do not possess the Kronecker delta property. • Computational modelling of the plastic post-buckling behaviour of shells. • Computational modelling of a bi-ventricular heart model. In computational solid mechanics path-following methods have been proven useful when dealing with non-monotonously evolving loading magnitudes as encountered e.g. in instability or softening behaviour. The present work derives from a displacement-based method a cavity-volume-based path-following method and considers its application specifically to cardiac mechanics problems. Both methods are able to account for an arbitrary number of simultaneously acting loading conditions. When applied to the Newton-Raphson method, the corresponding loading increments are computed by means of volume increments or point-wise prescribed displacement increments, respectively. No additional variables are required and the physics of the problem at hands is not altered. Both methods are implemented in an in-house meshfree modelling software and successfully applied to non-linear elastic and inelastic problems in structural mechanics. The cavity-volume control method, in particular, is demonstrated to accurately predict the highly non-linear elastic and anisotropic material behaviour encountered when modelling the heart. Albeit, the proposed methods can be equally used e.g. in finite element methods, they are very well suited for meshfree methods where the Kronecker delta property does not apply.

Corotational Formulation for Geometric Nonlinear Analysis of Shell Structures by ANDES Elements

The corotational (CR) kinematic description was a recent method for formulation of geometric nonlinear structural problems. Based on the consistent symmetrizable equilibrated (CSE) CR formulation, a linear triangular flat shell element with three translational and three rotational degrees of freedom (DOFs) at each of the three nodes was derived by the assumed natural deviatoric strain (ANDES) formulation, which can be used to the geometric nonlinear analysis of shell structures with large rotations and small strains. By taking variations of the internal energy with respect to nodal freedoms, the equations for the CR nonlinear finite element, including the tangent stiffness matrix and the internal force vector in the global coordinate system, were derived. The nonlinear equations were solved by using the generalized displacement control (GDC) method. It was shown through numerical examples that combing CR formulation and ANDES elements can accurately solve complex geometric nonlinear problems with large body motions. As revealed by the efficiency and reliability of the ANDES elements in tracing the nonlinear structural load–deflection response, it is demonstrated that some membrane elements and plate elements give better performance in the geometric nonlinear analysis of shell structures.

Effect of Augmentation Material Stiffness on Adjacent Vertebrae after Osteoporotic Vertebroplasty Using Finite Element Analysis with Different Loading Methods

Background: Vertebroplasty is an effective treatment for osteoporotic vertebral fractures, which are one of the most common fractures associated with osteoporosis. However, clinical observation has shown that the risk of adjacent vertebral body fractures may increase after vertebroplasty. The mechanism underlying adjacent vertebral body fracture after vertebroplasty is not clear; excessive stiffness resulting from polymethyl methacrylate has been suspected as an important mechanism. Objectives: The aim of our study was to compare the effects of bone cement stiffness on adjacent vertebrae after osteoporotic vertebroplasty under load-controlled versus displacementcontrolled conditions. Study Design: An experimental computer study using a finite element analysis. Setting: Medical research institute, university hospital, Korea. Methods: A three-dimensional digital anatomic model of L1/2 bone structure was reconstructed from human computed tomographic images. The reconstructed three-dimensional geometry was processed for finite element analysis such as meshing elements and applying material properties. Two boundary conditions, load-controlled and displacement-controlled methods, were applied to each of 5 deformation modes: compression, flexion, extension, lateral bending, and torsion. Results: The adjacent L1 vertebra, irrespective of augmentation, revealed nearly similar maximum von Mises stresses under the load-controlled condition. However, for the displacementcontrolled condition, the maximum von Mises stresses in the cortical bone and inferior endplate of the adjacent L1 vertebra increased significantly after cement augmentation. This increase was more significant than that with stiffer bone cement under all modes, except the torsion mode. Limitations: The finite element model was simplified, excluding muscular forces and incorporating a large volume of bone cement, to more clearly demonstrate effects of bone cement stiffness on adjacent vertebrae after vertebroplasty. Conclusion: Excessive stiffness of augmented bone cement increases the risk of adjacent vertebral fractures after vertebroplasty in an osteoporotic finite element model. This result was most prominently observed using the displacement-controlled method. Key words: Bone cements, displacement-controlled method, finite element analysis, loadcontrolled method, osteoporosis, osteoporotic fracture, polymethyl methacrylate, vertebroplasty

Progressive damage of laminated cylindrical/conical panels under meridional compression

Abstract The objective of this paper is to investigate the progressive failure behaviour of laminated cylindrical/conical panels under meridional compression considering geometric nonlinearity and evolving material damage. The evolving microscopic damage such as fiber breakage, matrix cracking, fiber matrix debonding etc. is modeled through a generalized macroscopic continuum theory within the framework of irreversible thermodynamics. The analysis is carried out using field consistent finite element approach based on first-order shear deformation theory. The nonlinear governing equations are solved using the Newton–Raphson iterative technique coupled with the adaptive displacement control method to trace the equilibrium path. The damage evolution equations are solved at every Gauss point using Newton–Raphson iterative technique within each iteration of a loading/displacement increment. To accurately model the transverse shear strain energy, shear correction factors are calculated using layers' properties and lamination scheme. The detailed study is carried out to highlight the influences of evolving damage, span-to-thickness ratio, lamination scheme, radius-to-span ratio, boundary conditions and semi-cone angle on the postbuckling response and failure load of laminated panels.

Numerical simulation for the estimation the jacking force of pipe jacking

For a pipe jacking construction, reducing the soil–pipe interface friction and providing enough jacking force are the most common approach to optimize the construction efficiency. In practice, jacking force is generally estimated by various empirical equations. However, the estimations of empirical equations frequently deviate from the reality. In this study, a model coupling finite element method and a displacement control method were applied to estimate the required jacking force in pipe jacking. Two cases were examined from Central Taiwan, where the primary geological foundation composed of gravel formations. Case A pertained to pipe jacking construction during which sewage pipes with a diameter of 2.4m were utilized. The monitoring data from this case were used to establish the jacking force estimation model. The jacking force history observed in Case B, in which sewage pipes of 1.0m diameter were used, was compared with those obtained by the developed model to demonstrate the applicability of the model. The results suggested the developed model can estimate the jacking force with a better accuracy towards the middle and the final stage of the pipe jacking process.

Study on crack propagation of adhesively bonded DCB for aluminum foam using energy release rate

Aluminum foam with initial crack, which has a closed cell form adhesively bonded, is studied to compare and analyze the crack propagation behavior by using both experimental and finite element analysis techniques. The specimen is loaded in Mode I type of fracture as 15 mm/min speed of a displacement control method. The experimental results were used to accommodate the finite element analysis performed with commercial software ABAQUS 6.10. First, using a video recording, five steps of experiment were selected at random and then the energy release rate was calculated. The estimated energy release rate was then used as fracture energy into the finite element analysis. Comparing the experimental axial load-displacement graphs and the finite element analysis results, roughly equivalent peak values were observed in the cohesive strength of the aluminum foam double cantilever beam. However, force versus displacement patterns showed somewhat different: little deformation was observed in aluminum foam, whereas adhesive parts in double cantilever beam were significantly deformed.

Concept Design of Cardiovascular Stents Based on Load Identification

The concept design is an important design phase for the cardiovascular stents. The topology optimization methods can be applied to the concept design of the cardiovascular stents. However, the interaction analysis between the stent and artery involves material nonlinearity, geometrical nonlinearity and boundary nonlinearity. The interaction analysis is not easy to be successful if these three types of nonlinearities are considered simultaneously. Therefore, the topology optimization process may be suspended if the nonlinear interaction analysis fails. The aim of this paper is to develop a design method to obtain the concept design of cardiovascular stents based on the load identification and homogenization method. A displacement control method is proposed to identify the design load of the cardiovascular stents. The identified design load is then applied to the stent and the nonlinear interaction analysis is replaced by the linear analysis. Further, the nonlinear analysis is completely avoided in the topology optimization process. The numerical results show that the proposed design method can obtain the legible concept design of cardiovascular stents.

Application of Peridynamic Theory to Nanocomposite Materials

The purpose of this paper is to describe the computational procedure developed to apply the Bond-based Peridynamic Theory to nanocomposite materials. The goal is to predict the Young’s modulus as a function of the filling fraction of different nanocomposite materials with an accuracy better than that of other methods (like Halpin-Tsai, Mori-Tanaka, FEA models). A displacement control method is adopted here in order to simulate the incremental application of an external load. The constitutive law considered is linear and thus the problem can be seen as a static-linear problem. A description of the model and of the “multiscale approach” is given, supported by a comparison between experimental data and simulation results for different nanocomposites.

접착제로 접합된 이중외팔보 알루미늄폼의 파괴 거동에 관한 연구

In this study, closed-cell aluminum foam with an initial crack was investigated to produce an axial load-time graph. Using the 10-kN Landmarks of MTS Corporation, a 15-mm/min velocity of mode I shape was applied to the aluminum foam specimen using the displacement control method. ABAQUS 6.10 simulation was used to model and analyze the identical model in three dimensions under conditions identical to those of the experiment. The energy release rate was calculated on the basis of an axial load-displacement graph obtained from the experiment and a transient image of the crack length, and then an FE model was analyzed on the basis of this fracture energy condition. The relation between load and displacement was discussed; it was found that the aluminum foam deformed somewhat less than the adhesive layer owing to the difference in elastic modulus.

Thermal Postbuckling Analysis of Functionally Graded Beams

Thermal buckling and postbuckling analysis of functionally graded (FG) beams is presented. The governing equations are based on the first-order shear deformation beam theory (FSDT) and the geometrical nonlinearity is modeled using Green's strain tensor in conjunction with the von Karman assumptions. For discretizing the governing equations and the related boundary conditions differential quadrature method (DQM) as a simple and computationally efficient numerical tool is used. Based on displacement control method, a direct iterative method is employed to obtain thermal postbuckling behavior of FG beams with different boundary conditions and geometrical parameters.

Study of Control Method Based on Hydromechanics for Hydraulic Impact of Open Hydraulic System in Concrete Pump

According to the working principle of open hydraulic system in concrete pump, and though the theoretical analysis on the phenomenon of hydraulic impact in direction changing process, it concluded that the impact pressure has a linear relation with the displacement of the main oil pump .To solve the hydraulic impact problem ,a variable displacement method was proposed .Under the requirement of piston not striking the bottom of cylinder and piston stroke control accuracy ,the authors optimized the pumping direction changing process time parameters and the displacement control time parameters . Though the AMESim modeling simulation and experimental study , the variable displacement control method is proved feasible on reducing the hydraulic impact in direction changing process.

On the effect of constraint parameters on the generalized displacement control method

In this work, we investigate the generalized displacement control method (GDCM) and provide a modification (MGDCM) that results in an equivalent constraint equation as that of the linearized cylindrical arc-length control method (LCALCM). Through numerical examples, we illustrate that the MGDCM is more robust than the standard GDCM in capturing equilibrium paths in regions of high curvature. Moreover, we also provide a geometric and physical interpretation of the method, which sheds light on the general class of path following methods in structural mechanics.

An advanced analysis method for three-dimensional steel frames with semi-rigid connections

This paper presents an advanced analysis method for three-dimensional semi-rigid steel frames accounting for three main nonlinear sources. The second-order effects are considered by the use of stability functions obtained from the solution of beam–columns under axial force and bending moments at two ends. The spread of plasticity over the cross section and along the member length is captured by monitoring the uniaxial stress–strain relation of each fiber on selected sections. The nonlinear semi-rigid beam-to-column connection is simulated by a 3D multi-spring element. The generalized displacement control method is applied to solve the nonlinear equilibrium equations in an incremental-iterative scheme. The nonlinear load–displacement responses and ultimate load results compare well with those of previous studies. It is concluded that using only one element per member with monitoring the end sections accurately likely predict the nonlinear responses of three-dimensional semi-rigid steel frames.