• Structural Engineering and Mechanics
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• v.5 no.5
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• pp.587-598
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• 1997

A numerical model for masonry is proposed by following an internal variable approach originally developed in the field of elastic-plastic analysis. The general features of the theoretical framework are discussed by focussing on finite element models applicable to incremental elastic-plastic problems. An extremum property is derived and its implications in terms of convergence for convenient algorithms are briefly discussed, by including the case of softening materials and damage effects. Next, a numerical model is presented, which is suitable for masonry, can be developed according to the same internal variable formulation and enjoys similar properties. Some numerical results are presented and compared with the response of a masonry shear wall subjected to pseudodynamic tests.

• Coupled systems mechanics
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• v.4 no.1
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• pp.19-36
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• 2015

Modelling and analysis of a brick masonry building involves uncertainties like modelling assumptions and properties of local material. Therefore, it is necessary to perform a calibration to evaluate the dynamic properties of the structure. The response of the finite element model is improved by predicting the parameter by performing linear dynamic analysis on experimental data by comparing the acceleration. Further, a nonlinear dynamic analysis was also performed comparing the roof acceleration and damage pattern of the structure obtained analytically with the test findings. The roof accelerations obtained analytically were in good agreement with experimental roof accelerations. The damage patterns observed analytically after every shock were almost similar to that of experimental observations. Damage pattern with amplification in roof acceleration exhibit the potentiality of earthquake resistant measures in brick masonry models.

• Computers and Concrete
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• v.19 no.2
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• pp.143-152
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• 2017

This paper has numerically investigated the changes of loading-induced stress in concrete with the corrosion time in the sulfate-containing environment. Firstly, based on Fick's law and reaction kinetics, a diffusion-reaction equation of sulfate ion in concrete is proposed, and it is numerically solved to obtain the spatial and temporal distribution of sulfate ion concentration in concrete by the finite difference method. Secondly, by fitting the existed experimental data of concrete in sodium sulfate solutions, the chemical damage of concrete associated with sulfate ion concentration and corrosion time is quantitatively presented. Thirdly, depending on the plastic-damage mechanics, while considering the influence of sulfate attack on concrete properties, a simplified chemo-mechanical damage model, with stress-based plasticity and strain-driven damage, for concrete under axial loading and sulfate attack is determined by introducing the chemical damage degree. Finally, an axially compressed concrete prism immersed into the sodium sulfate solution is regarded as an object to investigate the time-varying stress in concrete subjected to the couplings of axial loading and sulfate attack.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2009.10a
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• pp.259-262
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• 2009

The influence of pre-strain in low-cycle fatigue behavior of Fe-18Mn-0.05Al-0.6C TWIP steel was studied by conducting axial strain-controlled tests. As-received plates were deformed by rolling with reduction ratios of 10 and 30%, respectively. A triangular waveform with a constant frequency of 1 Hz was employed for low cycle fatigue test at the strain amplitudes in the range of ${\pm}0.4{\sim}{\pm}0.6$ pct. The results showed that low-cycle fatigue life was strongly dependent on the amount of pre-strain as well as the strain amplitude. Increasing the amount of prestrain, the number of reversals to failure was significantly decreased at high strain amplitudes, but the effect was negilgible at low strain amplitudes. A new model for predicting fatigue life of pre-strained body has been devised adding a correction term of ${\Delta}E_{pre-strain}$ to the energy-based fatigue damage parameter.

• Computers and Concrete
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• v.12 no.5
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• pp.585-612
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• 2013

The paper presents quasi-static numerical simulations of the behaviour of short reinforced concrete beams without shear reinforcement under mixed shear-tension failure using the FEM and four various constitutive continuum models for concrete. First, an isotropic elasto-plastic model with a Drucker-Prager criterion defined in compression and with a Rankine criterion defined in tension was used. Next, an anisotropic smeared crack and isotropic damage model were applied. Finally, an elasto-plastic-damage model was used. To ensure mesh-independent FE results, to describe strain localization in concrete and to capture a deterministic size effect, all models were enhanced in a softening regime by a characteristic length of micro-structure by means of a non-local theory. Bond-slip between concrete and reinforcement was considered. The numerical results were directly compared with the corresponding laboratory tests performed by Walraven and Lehwalter (1994). The advantages and disadvantages of enhanced models to model the reinforced concrete behaviour were outlined.

• Earthquakes and Structures
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• v.11 no.4
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• pp.649-664
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• 2016

A seismic damaged bridge may be hit again by a strong aftershock or another earthquake in a short interval before the repair work has been done. However, discussions about the impact of the unrepaired damages on the residual earthquake resistance of a steel bridge are very scarce at present. In this paper, nonlinear time-history analysis of a steel arch bridge was performed using multi-scale hybrid model. Two strong historical records of main shock-aftershock sequences were taken as the input ground motions during the dynamic analysis. The strain response, local deformation and the accumulation of plasticity of the bridge with and without unrepaired seismic damage were compared. Moreover, the effect of earthquake sequence on crack initiation caused by low-cycle fatigue of the steel bridge was investigated. The results show that seismic damage has little impact on the overall structural displacement response during the aftershock. The residual local deformation, strain response and the cumulative equivalent plastic strain are affected to some extent by the unrepaired damage. Low-cycle fatigue of the steel arch bridge is not induced by the earthquake sequences. Damage indexes of low-cycle fatigue predicted based on different theories are not exactly the same.

• The Korean Journal of Physiology and Pharmacology
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• v.10 no.4
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• pp.167-172
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• 2006

In the present study, we developed a simple method to predict the neuronal cell death in the mouse hippocampus and striatum following transient global forebrain ischemia by evaluating both cerebral blood flow and the plasticity of the posterior communicating artery (PcomA). Male C57BL/6 mice were anesthetized with halothane and subjected to bilateral occlusion of the common carotid artery (BCCAO) for 30 min. The regional cerebral blood flow (rCBF) was measured by laser Doppler flowmetry. The plasticity of PcomA was visualized by intravascular perfusion of India ink solution. When animals had the residual cortical microperfusion less than 15% as well as the smaller PcomA whose diameter was less than one third compared with that of basilar artery, neuronal damage in the hippocampal subfields including CA1, CA2, and CA4, and in the striatum was consistently observed. Especially, when mice met these two criteria, marked neuronal damage was observed in CA2 subfield of the hippocampus. In contrast, after transient BCCAO, neuronal damage was consistently produced in the striatum, dependent more on the degree of rCBF reduction than on the plasticity of PcomA. The present study provided simple and highly reproducible criteria to induce the neuronal cell death in the vulnerable mice brain areas including the hippocampus and striatum after transient global forebrain ischemia.

• Computers and Concrete
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• v.20 no.3
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• pp.351-360
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• 2017

This paper presents an efficient membrane finite element for the cyclic inelastic response analysis of RC structures under complex plane stress states including shear. The model strikes a balance between accuracy and numerical efficiency to meet the challenge of shear wall simulations in earthquake engineering practice. The concrete material model at the integration points of the finite element is based on damage plasticity with two damage parameters. All reinforcing bars with the same orientation are represented by an embedded orthotropic steel layer based on uniaxial stress-strain relation, so that the dowel and bond-slip effect of the reinforcing steel are presently neglected in the interest of computational efficiency. The model is validated with significant experimental results of the cyclic response of RC panels with uniform stress states.

• Coupled systems mechanics
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• v.8 no.1
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• pp.71-93
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• 2019

Finite element simulations of solid mechanics problems often involve the use of Non-Confirming Meshes (NCM) to increase accuracy in capturing nonlinear behavior, including damage and plasticity, in part of a solid domain without an undue increase in computational costs. In the presence of material nonlinearity and plasticity, higher-order variables are often needed to capture nonlinear behavior and material history on non-conforming interfaces. The most popular formulations for coupling non-conforming meshes are dual methods that involve the interpolation of a traction field on the interface. These methods are subject to the Ladyzhenskaya-Babuska-Brezzi (LBB) stability condition, and are therefore limited in their implementation with the higher-order elements needed to capture nonlinear material behavior. Alternatively, the enriched discontinuous Galerkin approach (EDGA) (Haikal and Hjelmstad 2010) is a primal method that provides higher order kinematic fields on the interface, and in which interface tractions are computed from local finite element estimates, therefore facilitating its implementation with nonlinear material models. The inclusion of higher-order interface variables, however, presents the issue of preserving material history at integration points when a increase in integration order is needed. In this study, the enriched discontinuous Galerkin approach (EDGA) is extended to the case of small-deformation plasticity. An interface-driven Gauss-Kronrod integration rule is proposed to enable adaptive enrichment on the interface while preserving history-dependent material data at existing integration points. The method is implemented using classical J2 plasticity theory as well as the pressure-dependent Drucker-Prager material model. We show that an efficient treatment of interface variables can improve algorithmic performance and provide a consistent approach for coupling non-conforming meshes in inelasticity.

• Computers and Concrete
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• v.27 no.5
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• pp.457-472
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• 2021

Reinforced concrete (RC) buildings in Taiwan have suffered failure from strong earthquakes, which was magnified by the non-ductile detailing frames. Inadequate reinforcement as a consequence of the design philosophy prior to the introduction of current standards resulted in severe damage in the column and beam-column joint (BCJ). This study establishes a finite element analysis (FEA) of the non-ductile detailing RC column, BCJ, and three-story building that was previously tested through a tri-axial shaking table test. The results were then validated to laboratory specimens having the exact same dimensions and properties. FEA simulation integrates the concrete damage plasticity model and the elastic-perfectly plastic model for steel. The load-displacement responses of the column and BCJ specimens obtained from FEA were in a reasonable agreement with the experimental curves. The resulting initial stiffness and maximum base shear were found to be a close approximation to the experimental results. Also, the findings of a dynamic analysis of the three-story building showed that the time-history data of acceleration and displacement correlated well with the shaking table test results. This indicates the FEA implementation can be effectively used to predict the RC frame performance and failure mode under seismic loads.