General Purpose Finite Element Program Research Articles

Fundamental modes of tank-liquid systems under horizontal motions

This paper reports results on the fundamental impulsive modes of vibration of cylindrical tank-liquid systems anchored to the foundation under horizontal motion. The analyses are performed using a general purpose finite element (FE) program, and the influence of the hydrostatic pressure and the self-weight on the natural periods and modes is considered. The roof and walls are represented with shell elements and the liquid is modeled using two techniques: the added mass formulation and acoustic finite elements. Tank height to diameter ratios from 0.40 to 0.95 were used, with a liquid level at 90% of the height of the cylinder. The effect of the geometry on the fundamental modes for the tank-liquid systems is studied using eigenvalue and harmonic response analyses. Similar fundamental periods and mode shapes were found from these two approaches. The fundamental modes of tank models with aspect ratios ( H / D ) larger than 0.63 were very similar to the first mode of a cantilever beam. For the shortest tank ( H / D = 0.40 ) , the fundamental mode was a bending mode with a circumferential wave n = 1 and an axial half-wave ( m ) characterized by a bulge formed near the mid-height of the cylinder.

Frame element with lateral deformable supports: Formulations and numerical validation

This paper presents the theory and the numerical validation of three different formulations of nonlinear frame elements with nonlinear lateral deformable supports. The governing differential equations of the problem are derived first and the three different finite element formulations are then presented. The first model follows a displacement-based formulation, which is based on the virtual displacement principle. The second one follows the force-based formulation, which is based on the virtual force principle. The third model follows the Hellinger–Reissner mixed formulation, which is based on the two-field mixed variational principle. The selection of the displacement and force interpolation functions for the different formulations is discussed. Tonti’s diagrams are used to conveniently represent the equations governing both the strong and the weak forms of the problem. The general matrix equations of the three formulations are presented, with some details on the issues regarding the elements’ implementations in a general-purpose finite element program. The convergence, accuracy, and computational times of the three elements are studied through a numerical example. The distinctive element characteristics in terms of force and deformation discontinuities between adjacent elements are discussed. The capability of the proposed frame models to trace the softening response due to softening of the foundation is also investigated. Overall, the force-based and the mixed models are much more accurate than the displacement-based model and require very few elements to reach the converged solution. The force-based element is slightly more accurate than the mixed model, but it is more prone to numerical instabilities as it involves inverting the element flexibility matrix.

Hysteretic Model of Stiffened Shear Panel Dampers

A properly designed two-way stiffened (stiffened both in longitudinal and transverse directions) shear panel can sustain large deformation without pinching and consequent strength degradation. Hence it can be used as an effective passive energy dissipating damper (PEDD) in building and bridge structures to absorb seismic energy. In this Technical Note, a series of steel shear panels with 1, 2, or 3 two-way stiffeners has been analyzed under cyclic loading by the general-purpose finite element program ABAQUS, in which a modified two-surface model is incorporated to trace the material nonlinearity. Slenderness of web, Rw, is employed as a key parameter to investigate the hysteretic performance of stiffened shear panels. The sensitivities of the ratio of stiffener rigidity to optimum stiffener rigidity, γs∕γs*, the ratio of flange thickness to web thickness, tf∕tw, and aspect ratio, α, are also investigated. Finally, a simplified bilinear model for stiffened shear panels acting as a PEDD is presented in this Technical Note based on FEM results. The proposed model is expected to get use in the time-history analysis of engineering structures that employ the PEDD to mitigate seismic hazard.

Constitutive modeling and finite element methods for TRIP steels

A constitutive model that describes the mechanical behavior of steels exhibiting “TRansformation Induced Plasticity” (TRIP) during martensitic transformation is presented. Multiphase TRIP steels are considered as composite materials with a ferritic matrix containing bainite and retained austenite, which gradually transforms into martensite. The effective properties and overall behavior of TRIP steels are determined by using homogenization techniques for nonlinear composites. A methodology for the numerical integration of the resulting elastoplastic constitutive equations in the context of the finite element method is developed and the constitutive model is implemented in a general-purpose finite element program. The model is calibrated by using experimental data of uniaxial tension tests in TRIP steels. The problem of necking of a bar in uniaxial tension is studied in detail. The constitutive model is used also for the calculation of “forming limit diagrams” for sheets made of TRIP steels; it is found that the TRIP phenomenon increases the strain at which local necking results from a gradual localization of the strains at an initial thickness imperfection in the sheet.

Nonlinear Viscoelastic Analysis of Composites using Competing Micromechanical Models

Micromechanical models for a study of nonlinear viscoelastic (NVE) response of composite laminae are developed and their performance compared. A single integral constitutive law proposed by Schapery and subsequently generalized to multiaxial states of stress is utilized in the study for the matrix material. This is used in conjunction with a computationally facile scheme in which hereditary strains are computed using a recursive relation suggested by Henriksen. Composite response is studied using two competing micromodels, a simplified square cell model (SSCM) and a finite element based self-consistent cylindrical model (FECM). The algorithm is developed assuming that the material response computations are carried out in a module attached to a general purpose finite element program used for composite structural analysis. It is shown that the SSCM as used in investigations of material nonlinearity can involve significant errors in the prediction of transverse Young’s modulus and shear modulus. The errors in the elastic strains thus predicted are of the same order of magnitude as the creep strains accruing due to viscoelasticity. The FECM on the other hand does appear to perform better both in the prediction of elastic constants and the study of creep response.

Hyperelasticity Model for Finite Element Analysis of Natural and High Damping Rubbers in Compression and Shear

Rate-independent monotonic behavior of filled natural rubber and high damping rubber is investigated in compression and shear regimes. Monotonic responses obtained from tests conducted in both regimes demonstrate the prominent existence of the Fletcher–Gent effect, indicated by high stiffness at low strain levels. An improved hyperelasticity model for compression and shear regimes is proposed to represent the rate-independent instantaneous and equilibrium responses including the Fletcher–Gent effect. A parameter identification scheme involving simultaneous minimization of least-square residuals of uniaxial compression and simple shear data is delineated. The difficulties of identifying a unique set of hyperelasticity parameters that hold for both compression and shear deformation modes are thus overcome. The proposed hyperelasticity model has been implemented in a general purpose finite element program. Finite element simulations of experiments have shown the adequacy of the proposed hyperelasticity model, estimated parameters, and employed numerical procedures. Finally, numerical experiments were conducted to further explore the potential of the proposed model, and estimated parameters in analyzing rubber layers of a base isolation bearing subjected either to compression or to a combination of compression and shear.

Prediction of Ultrasonic Guided Wave Dispersion in Bent Pipes Using Finite Element Analysis and 2-D Fourier Transform

In this paper, the dispersion curves of a bent cylindrical pipe are obtained by using the 3-dimensional finite element modeling and 2-dimenstional Fourier transform. The transient responses of the bent pipe are calculated by using a general-purpose finite element program, and the displacements are extracted at a series of sequential points as a function of spatial position and time, u(x,t). Then 2-dimentional FFT of u (x,t) offers U (k,ω), the relation between wave number and angular frequency so that the phase velocity and group velocity can be calculated. In addition, verification of the result is made by the mode identification using wavelet transform. The modes invoked by both methods agree very well.

Ultimate Bending Capacity and Buckling of Pressurized 90 deg Steel Elbows

The paper examines the nonlinear elastic-plastic response of internally pressurized 90 deg pipe elbows under in-plane and out-of-plane bending. Nonlinear shell elements from a general-purpose finite element program are employed to model the inelastic response of steel elbows and the adjacent straight parts. The numerical results are successfully compared with real-scale experimental measurements. The paper also presents a parametric study, aimed at investigating the effects of diameter-to-thickness ratio and moderate pressure levels on the ultimate bending capacity of 90 deg elbows, focusing on the failure mode (local buckling or cross-sectional flattening) and the maximum bending moment. Special attention is given to the response of 90 deg elbows under out-of-plane bending moments.

Finite element analysis and theoretical study of punching shear strength of concrete bridge decks

The problem of punching shear usually arises in reinforced concrete slabs subjected to concentrated loads and particularly in concrete bridge decks due to development of an internal arching system. Ongoing research revealed that the governing mode of failure of concrete bridge decks is not flexure and that using a flexural design method usually led to unnecessary high levels of steel reinforcement. This paper examines the applicability of nonlinear finite element formulation of restrained concrete bridge decks. A general purpose finite element program ANACAP was employed in this study. The accuracy of the nonlinear finite element analysis is demonstrated using test results conducted by other researchers. The results of the finite element analysis are also compared with those obtained from a rational model. The experimental results and the theoretical model provide insight to the fundamental behavior of concrete bridge decks.Key words: bridges, concrete, deflections, FRP, punching, reinforcement, slabs.

Analytical Model for Sheathing-to-Framing Connections in Wood Shear Walls and Diaphragms

A new analytical model for sheathing-to-framing connections in wood shear walls and diaphragms is discussed in this paper. The model represents sheathing-to-framing connections using an oriented pair of nonlinear springs. Unlike previous models, the new analytical model is suitable for both monotonic and cyclic analyses and does not need to be scaled or adjusted. Furthermore, the analytical model may be implemented in a general purpose finite element program, such asABAQUS, or in a specialized structural analysis program, such as CASHEW. To illustrate, the responses of a 4.88 3 14.6 m plywood diaphragm and a 2.443 2.44 m oriented strand board shear wall are predicted using the new analytical model.

Constitutive model for the elastic–plastic analysis of porous sintered materials

It is a known fact that it is very difficult to implement the algorithm of plasticity of porous materials in FEM commercial programs for different types and characteristics. The aim of this paper is to put forward a flexible model of plasticity of porous materials by implementing it into the general purpose finite element program ABAQUS®. A modified algorithm is developed in this paper which takes into account the effect of an isotropic work hardening of the porous material. This is incorporated into the FEM program to yield a flexible solution for different yielding criterion. The present criterion is compared with other known published work and was found to be in good agreement. It was found that all the failure criteria used were successfully implemented using the newly developed algorithm. Also, the present criterion is adequately adjusted to fit all other results obtained from other criteria of failure. Finally, some of these published criteria had not been implemented previously for use in the FEM programs, but in this paper were made to do so. Other theoretical results will also be presented.

비선형 지반-구조물 상호작용해석을 위한 새로운 복합법

이 논문에서는 비선형 지반-구조물 상호작용해석을 위한 새로운 시간-주파수영역 복합법을 제시하였다. 제안한 방법은 등가선형 지반-구조물 상호작용해석 프로그램과 범용 비선형 유한요소해석 프로그램을 동시에 사용하는 실용적인 방법이다. 이 방법에서는 먼저 주파수영역에서 등가선형 지반-구조물 상호작용해석을 수행하여 유한요소 영역의 경계면에서 응답을 구한 다음, 이를 범용 비선형 유한요소해석 프로그램에 의한 비선형 동적해석의 시간의존 경계조건으로 입력한다. 제안된 방법의 검증을 위하여 2차원 지하철 정거장 구조물에 대한 지진해석을 수행하였다. 이를 위하여 등가선형 지반-구조물 상호작용해석 프로그램 KIESSI-2D와 비선형 유한요소해석 프로그램 ANSYS를 사용하였다 수치적인 해석결과로부터 이 연구에서 제안한 방법의 타당성을 확인할 수 있었다. This paper presents a novel hybrid time-frequency-domain method for nonlinear soil-structure interaction(SSI) analysis. It employs, in a practical manner, a computer code for equivalent linear SSI analysis and a general-purpose nonlinear finite element program. The proposed method first (calculates dynamic responses on a truncated finite element boundary utilizing an equivalent linear SSI program in the frequency domain. Then, a general purpose nonlinear finite element program is employed to analyze the nonlinear SSI problem in the time domain, in which boundary conditions at the truncated boundary are imposed with the responses calculated in the previous frequency domain SSI analysis, In order to validate the proposed method, seismic response analyses are carried out for a 2-D underground subway station in a multi-layered half-space, For the analyses, a equivalent linear SSI code KIESSI-2D is coupled to ANSYS program. The numerical results indicate that the proposed methodology can be a viable solution for nonlinear SSI problems.

Nonlinear Response and Failure of Steel Elbows Under In-Plane Bending and Pressure

The paper investigates the response of elbows under in-plane bending and pressure, through nonlinear finite element tools, supported by experimental results from real-scale tests. The finite element analysis is mainly based on a nonlinear three-node “tube element,” capable of describing elbow deformation in a rigorous manner, considering geometric and material nonlinearities. Furthermore, a nonlinear shell element from a general-purpose finite element program is employed in some special cases. Numerical results are compared with experimental data from steel elbow specimens. The comparison allows the investigation of important issues regarding deformation and ultimate capacity of elbows, with emphasis on relatively thin-walled elbows. The results demonstrate the effects of pressure and the influence of straight pipe segments. Finally, using the numerical tools, failure of elbows under bending moments is examined (cross-sectional flattening or local buckling), and reference to experimental observations is made.

FEM Modeling of Induction Hardening Processes in Steel

A modeling system for analyzing the integrated induction hardening processes was developed based on a general-purpose finite element program, with the capability to analyze the whole process from electromagnetic-induced thermal heating to final hardening. A coupled electromagnetic-thermal model was applied to study the induction heating process, which includes consideration of nonlinear material characteristics on temperature. Also, arrangement of AC current density distribution was conducted to simulate practical induction coil structure and magnetic concentrator effects to achieve desired heating patterns for later quenching and hardening analysis. Quenching analysis can provide cooling curve at any location in a heat-treated workpiece based on heat transfer principles. In hardening analysis, phase transformation was studied and an algorithm was developed to determine volumetric content of micro-structural constituents formed from austenitized phase in quenching process, based on analysis of the interaction between cooling curve and material time-temperature-transformation (TTT) diagram. Finally, hardness value was converted from martensite content based on a developed formulation. Validation was preliminary conducted based on comparison of hardening pattern of induction hardening of an automotive spindle with complex surface.

Application Of Pseudo-symmetric Technique In Dynamic AnalysisOf Concrete Gravity Dams

A new approach is presented for seismic analysis of concrete gravity dams in the time domain. The technique is based on symmetric formulation of dam-reservoir systems utilizing pressure degrees of freedom in the fluid domain. The method is explained initially in relation to other available techniques. Following from this, the analysis of a typical concrete dam is considered as a verification example by utilizing a modified program based on this technique. The methodology introduced is very convenient and can be easily implemented in general-purpose finite element programs with regard to their fluid-structure interaction modules.

Numerical Analysis of Tall Buildings Considering Dynamic Soil-Structure Interaction

Three-dimensional finite element analysis in time domain on dynamic soil-pile-structure interaction of a practical engineering is carried out in this paper. General-purpose finite element program ANSYS is used in the analysis. Commonly used equivalent linearity model is chosen as constitutive relation of soil. Viscous boundary of soil is implemented in ANSYS program. The influences of parameters, such as soil property, excitation, the rigidity of structure and buried depth, on dynamic characteristics, seismic response and interaction effect of SSI system are discussed.

Unilateral contact analysis and failure prediction in stone bridges

Unilateral contact analysis with friction can be performed by general purpose finite element programs, provided that the user has basic theoretical background knowledge. These mechanisms are of great importance for the safety evaluation and structural rehabilitation of monuments. This is demonstrated by the investigation of some damage scenarios for a stone bridge.

Numerical Analysis of Dynamic Soil-Box Foundation-Structure Interaction System

abstractThree-dimensional finite element analysis on soil-box foundation-structure interaction system is carried out. General-purpose finite element program ANSYS is used in the analysis. Commonly used equivalent linearity model is chosen as constitutive relation of soil, and the changing-status nonlinearity of soil-structure interface is considered by surface-to-surface contact element. The computational model and analysis method is verified through comparison study between the calculation and the shaking table test results, and issues drawn from the computational analysis are consistent with the test results. The calculations demonstrate that sliding and separation occur between the foundation and the soil, and it shows that great error will occur when the material nonlinearity of soil and the changing-status nonlinearity of soil-structure interface are not considered in calculation of soft soil. Finally, some important findings from the calculations are concluded.

Numerical simulation of die compaction and sintering

A method to simulate die compaction and sintering is presented. By implementing user defined routines for both processes into the general purpose finite element program ABAQUS quantitative predictions of density distributions and shape distortions can be obtained as well as the stresses in the tool components. By computational optimisation of the individual production steps suggestions can be made to improve the final properties. As an example for both die pressing and sintering a complex three-dimensional part is simulated and suggestions to improve dimensional accuracy are made. Finally, stresses in the tools are calculated showing that the deflections are large enough to cause punch to punch contact so that tool wear must be expected.

Simplified Analysis of Layered Soil-Structure Interaction

The interaction of an arbitrary structure with its foundation soil is treated by representing the stratified soil with the end of a linear elastic half space model with specific geometrical and elastic properties for its layers. The proposed procedure is based on a purely analytical treatment of the underlying soil model, as well as on the use of a structural model with fictitious supports inserted at the contact nodes of the foundation elements with the soil surface. The availability of a general purpose finite element program is a prerequisite in order to carry out the analysis of the structural model. The analysis for an arbitrary static loading is performed by using the stiffness matrices of the soil surface and of the structure with respect to their contact nodes. This approach provides a flexible framework to perform parametric studies to include the variability of soil properties. Three numerical examples are presented and the results are compared wiht those based on Winkler’s assumption of modulus of subgrade reaction.