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Showing 9 results for Elasto-Plastic

A.r. Khoei, S. Yadegari, M. Anahid,
Volume 4, Issue 3 (9-2006)

In this paper, a higher order continuum model is presented based on the Cosserat continuum theory in 3D numerical simulation of shear band localization. As the classical continuum models suffer from the pathological mesh-dependence in strain softening models, the governing equations are regularized by adding the rotational degrees-of-freedom to conventional degrees-of-freedom. The fundamental relations in three-dimensional Cosserat continuum are presented and the internal length parameters are introduced in the elasto-plastic constitutive matrix to control the shear bandwidth. Finally, the efficiency of proposed model and computational algorithm is demonstrated by a 3D strip in tensile. A comparison is performed between the classical and Cosserat theories and the effect of internal length parameter is demonstrated. Clearly, a finite shear bandwidth is achieved and the load-displacement curves are uniformly converged upon different mesh sizes.
M.h. Baziar, Sh. Salemi, T. Heidari,
Volume 4, Issue 3 (9-2006)

Seismic behavior of a rockfill dam with asphalt-concrete core has been studied utilizing numerical models with material parameters determined by laboratory tests. The case study selected for these analyses, is the Meyjaran asphalt core dam, recently constructed in Northern Iran, with 60 m height and 180 m crest length. The numerical analyses have been performed using a nonlinear three dimensional finite difference software and various hazard levels of earthquakes. This study shows that due to the elasto-plastic characteristics of the asphalt concrete, rockfill dams with asphalt concrete core behave satisfactorily during earthquake loading. The induced shear strains in the asphalt core, for the case presented in this research, are less than 1% during an earthquake with amax=0.25g and the asphalt core remains watertight. Due to large shear deformations caused by a more severe earthquake with amax=0.60g, some cracking may occur towards the top of the core (down to 5-6 m), and the core permeability may increase in the top part, but the dam is safe.
M. Rezaiee-Pajand, M. Riyazi-Mazloomi,
Volume 5, Issue 3 (9-2007)

In this research a new approach is proposed for elasto-plastic analysis of structures with truss elements. This method covers both perfectly plastic and hardening properties. The Proposed technique uses substituting virtual loads instead of modifying the stiffness matrix. To solve this kind of problems, complementary programming is utilized. Numerical examples demonstrate that elastoplastic analysis by this approach has very good convergence, rapidity, and accuracy.
Seyed B. Beheshti-Aval,
Volume 10, Issue 4 (12-2012)

A comparison between design codes i.e. ACI and AISC-LRFD in evaluation of flexural strength of concrete filled steel tubular

columns (CFTs) is examined. For this purpose an analytical study on the response of CFTs under axial-flexural loading is carried

using three-dimensional finite elements with elasto-plastic model for concrete with cracking and crushing capability and elastoplastic

kinematic hardening model for steel. The accuracy of the model is verified against previous test results. The nonlinear

modeling of CFT columns shows that the minimum thickness that recommended by ACI and AISC-LRFD to prevent local buckling

before the steel shell yielding for CFT columns could be decreased. The comparison of analytical results and codes indicates that

the accuracy of ACI method in estimation of axial-flexural strength of CFT columns is more appropriate than AISC-LRFD. The

ACI lateral strength of CFTs is located on upper bond of the AISC-LRFD’s provisions. AISC-LRFD estimates the lateral strength

conservatively but ACI in some ranges such as in short columns or under high axial load levels computes lateral strength in nonconservative

manner. Supplementary provisions for post local buckling strength of CFT columns should be incorporated in high

seismic region. This effect would be pronounced for column with high aspect ratio and short columns.

H. Shakib, Gh. R. Atefatdoost,
Volume 12, Issue 1 (3-2014)

An approach was formulated for the nonlinear analysis of three-dimensional dynamic soil-structure interaction (SSI) of asymmetric buildings in time domain in order to evaluate the seismic response behavior of torsionally coupled wall-type buildings. The asymmetric building was idealized as a single-storey three-dimensional system resting on different soil conditions. The soil beneath the superstructure was modeled as nonlinear solid element. As the stiffness of the reinforced concrete flexural wall is a strength dependent parameter, a method for strength distribution among the lateral force resisting elements was considered. The response of soil-structure interaction of the system under the lateral component of El Centro 1940 earthquake record was evaluated and the effect of base flexibility on the response behavior of the system was verified. The results indicated that the base flexibility decreased the torsional response of asymmetric building so that this effect for soft soil was maximum. On the other hand, the torsional effects can be minimized by using a strength distribution, when the centre of both strength CV and rigidity CR is located on the opposite side of the centre of mass CM, and SSI has no effect on this criterion.
M. Afzalirad, M. Kamalian, M. K. Jafari, A. Sohrabi-Bidar,
Volume 12, Issue 1 (1-2014)

In this paper, an advanced formulation of time-domain, two-dimensional Boundary Element Method (BEM) with material damping is presented. Full space two-dimensional visco-elastodynamic time-convoluted kernels are proposed in order to incorporate proportional damping. This approach is applied to carry out site response analysis of viscoelastic topographic structures subjected to SV and P incident waves. Seismic responses of horizontally layered site, semi-circular canyons, slope topography and ridge sections subjected to these incident waves are analyzed in order to demonstrate the accuracy of the kernels and the applicability of the presented viscoelastic boundary element algorithm. The results show an excellent agreement with recent published results obtained in frequency domain. Also, the effects of different material damping ratios on site response are investigated.
E. Lotfi, S. Delfan, A. Hamidi, H. Shahir, Gh. Fardi,
Volume 12, Issue 1 (1-2014)

In saturated soils, heating induces thermal expansion of both grains and the pore fluid. Lower thermal expansion coefficient of aggregates results in the increase of pore pressure and reduction of the effective stress besides subsequent volume changes due to the dissipation of pore pressure and heat transfer. Dissipation of thermally induced pore pressure with time is a coupled thermo-hydro-mechanical (THM) phenomenon, involving gradients of pore pressure and temperature, hydraulic and thermal flows within the mass of soil and changes in the mechanical properties with temperature. The objective of this paper is presentation of a numerical method to determine the effect of temperature on consolidation of clays. In this regard, the finite element code, PISA is used for one dimensional THM analysis of porous media. The analysis performed using both linear elastic and elastoplastic Cam clay models. Modified Cam clay model was applied in elastoplastic analysis. Variation of temperature, displacements and pore pressure determined with time and compared with numerical solutions of other researchers. Also it was indicated that implementation of coupled THM analysis yields better results for displacements compared to the hydro mechanical (HM) one. Application of elastoplastic constitutive model instead of linear elastic one indicated that preconsolidation pressure has an important effect on results of analysis.
R. Abbasnia, M. Aslami,
Volume 13, Issue 3 (9-2015)

A new model is proposed for two-dimensional simulation of the concrete fracture in compression. The model generated by using the Voronoi diagram method and with considering random shape and distribution of full graded aggregates at the mesoscopic level. The aggregates modeled by combining irregular polygons, which then is placed into the concrete with no intersection between them. By this new modeling approach, the simulation of high-strength concretes with possible aggregates fracture is also feasible. After generation of the geometrical model, a coupled explicit discrete element method and a modified rigid body spring model have been used for solution. In this method, all the neighboring elements are connected by springs. The mortar springs have Elasto-plastic behavior and considering normal concrete, the aggregate springs behave only elastically without any fracture. The proposed model can accurately predict the mechanical behavior of concrete under compression for small and large deformations both descriptively and quantitatively
Krzysztof Sternik,
Volume 15, Issue 3 (5-2017)

Constitutive model for saturated cohesive soils based on the bounding surface plasticity notion with anisotropic hardening law is presented in the paper. The model predicts inelastic behaviour of overconsolidated cohesive soils. The projection centre is the only point in the stress space which represents elastic soil behaviour. Approximation of the plastic modulus within the preconsolidation domain is made using the radial mapping rule between a projection centre and a reflecting point on the bounding surface. The projection centre changes its position each time when stress path turns rapidly of more than 90°. The configuration of the elliptic bounding surface is governed by preconsolidation effective pressure pc which depends on change of plastic both volumetric and deviatoric strain. Associated flow rule has been assumed in the formulation. Integration of constitutive relations is done according to forward Euler scheme with error control proposed by Sloan. The effectiveness of the proposed model is illustrated in both monotonic and cyclic loading in the homogeneous triaxial drained and undrained conditions.

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