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Papers by mojtaba labibzadeh

Journal of Earthquake Engineering

Fluid Mechanics Research International Journal

Periodica Polytechnica Civil Engineering

This paper is the first to present the results of a numerical comparison between the performances... more This paper is the first to present the results of a numerical comparison between the performances of two newly developed concrete columns namely: multi-tied spiral transverse reinforced (MTSTR) column and concrete-filled steel tube (CFST) column under eccentric compressive loads. The behavior of MTSTR columns under eccentric loads has not been studied until today and also this behavior is not compared to that of the CFST columns. The numerical models of these columns were constructed using the nonlinear finite element method and validated against the previously published experimental data in the literature. Concrete damage plasticity model and elastic-perfect plastic model were used to simulate the behavior of concrete core and steel of the columns, respectively. This provides the capability of modeling of the nonlinear large deformations of the columns. The obtained results show that the MTSTR columns can provide greater load carrying capacity, ductility, and energy absorption with...

KSCE Journal of Civil Engineering

Inverse Problems in Science and Engineering

Structural Engineering International

Engineering Structures and Technologies

The main purpose of this study is to investigate the effects of the stress path, size and shape o... more The main purpose of this study is to investigate the effects of the stress path, size and shape of the specimen, on the optimum values of the plastic input parameters of Concrete Damaged Plasticity-CDP- model of the ABAQUS software. This study concentrates on eccentricity, dilatation angle and viscosity input parameters. To finding optimum values of the mentioned parameters, an objective function which estimates the error of the model predictions was defined and tried to minimize. For evaluating the effect of the stress path on this optimization procedure, four different standard tests were simulated by the ABAQUS software: uniaxial compression, dual compression, dual-border cut specimen and three-point bending tests. For studying the effect of the size of the specimen, the three-point bending test, with three different sizes of the beam were modeled in the ABAQUS software. Furthermore, for investigating the effect of the specimen shape on the input parameters, a notched disk in a t...

Computational and Applied Mathematics

International Journal of Structural Integrity

Purpose The purpose of this paper is to present a new method for determining the input parameters... more Purpose The purpose of this paper is to present a new method for determining the input parameters of the concrete damaged plasticity (CDP) model of ABAQUS standard software. The existing available methods in the literatures are case sensitive, i.e., they give different input parameters of CDP for a unique concrete class used in different finite element (FE) simulation of concrete structures. In this study, the authors attempt to introduce a new approach for the identification of the input parameters of the CDP model, which guarantees the uniqueness and precision of the model. In other words, by this method, the input parameters obtained for a specific concrete class with a unique characteristic strength can be used for FE simulation of the different concrete structures which were constructed by this concrete without the need to additional modifications raised from any new application. Design/methodology/approach For the input parameter identification of the CDP model, different stan...

Mechanics & Industry, 2016

Abstract: A computational model simulating the behavior of the concrete subjected to the high tem... more Abstract: A computational model simulating the behavior of the concrete subjected to the high temperature environment has been presented here by means of micro-planes framework. The constitutive equations using damage formulations developed earlier by (Labibzadeh and ...

Abstract: Karun-1dam safety was examined through carrying over a 3D finite elements analysis. The... more Abstract: Karun-1dam safety was examined through carrying over a 3D finite elements analysis. The dam as well as its foundation and abutments have been modeled in a relatively exact manner. Furthermore, the vertical contraction joints were simulated in calculations. ...

Chinese Journal of Mechanical Engineering, 2015

A new technique is used in Discrete Least Square Meshfree(DLSM) method to remove the common exist... more A new technique is used in Discrete Least Square Meshfree(DLSM) method to remove the common existing deficiencies of meshfree methods in handling of the problems containing cracks or concave boundaries. An enhanced Discrete Least Squares Meshless method named as VDLSM(Voronoi based Discrete Least Squares Meshless) is developed in order to solve the steady-state heat conduction problem in irregular solid domains including concave boundaries or cracks. Existing meshless methods cannot estimate precisely the required unknowns in the vicinity of the above mentioned boundaries. Conducted researches are limited to domains with regular convex boundaries. To this end, the advantages of the Voronoi tessellation algorithm are implemented. The support domains of the sampling points are determined using a Voronoi tessellation algorithm. For the weight functions, a cubic spline polynomial is used based on a normalized distance variable which can provide a high degree of smoothness near those mentioned above discontinuities. Finally, Moving Least Squares(MLS) shape functions are constructed using a varitional method. This straight-forward scheme can properly estimate the unknowns(in this particular study, the temperatures at the nodal points) near and on the crack faces, crack tip or concave boundaries without need to extra backward corrective procedures, i.e. the iterative calculations for modifying the shape functions of the nodes located near or on these types of the complex boundaries. The accuracy and efficiency of the presented method are investigated by analyzing four particular examples. Obtained results from VDLSM are compared with the available analytical results or with the results of the well-known Finite Elements Method(FEM) when an analytical solution is not available. By comparisons, it is revealed that the proposed technique gives high accuracy for the solution of the steady-state heat conduction problems within cracked domains or domains with concave boundaries and at the same time possesses a high convergence rate which its accuracy is not sensitive to the arrangement of the nodal points. The novelty of this paper is the use of Voronoi concept in determining the weight functions used in the formulation of the MLS type shape functions.

International Journal of Structural Engineering, 2015

The effects of the lateral and corner openings as well as the impact of using carbon fibre reinfo... more The effects of the lateral and corner openings as well as the impact of using carbon fibre reinforced polymer sheets (CFRPs) on the RC two-way slabs' bearing capacity were investigated. To this end, at first, an enhanced finite element model of an actual laboratory sample of a reinforced concrete slab with central opening was simulated and verified using available experimental results. For concrete behaviour simulation, a sophisticated material model named damaged-plasticity model which can predict well the nonlinear behaviour of concrete from the initial steps of loading scenario up to the failure state was formulated and identified. For verifying the identification, two concrete beam test setup were simulated and the obtained results were compared with the laboratory test results. It was declared that the combined 45 and 90 degrees arrangement of CFRPs can affect more efficiently in strengthening weakened slabs with openings than the other CFRPs arrangements.

Determination of water surface elevation in tidal rivers is a very complex problem. In these rive... more Determination of water surface elevation in tidal rivers is a very complex problem. In these rivers, two phenomena are effective (fluvial flows at the upstream of them and tidal height at the downstream of them). Because of independency of these phenomena, combination of their return period needs a suitable theory. Joint probability method is a theory for combination of independent phenomena. This method shows a combined coefficient. The value of this coefficient related to type of joint probability method. In this research, three methods were considered (desk study joint probability method, analytic joint probability method and developed joint probability method by researcher). Three methods were applied in Karun River in Iran. Observed data showed that developed joint probability method by researcher has the best fitting to them. Link of the paper: https://www.wflpublisher.com/Abstract/1888

European Journal of Environmental and Civil Engineering, 2015

Structural Engineering International, 2015

Journal of Performance of Constructed Facilities, 2014

Strength degradation of mass concrete of the Dez concrete arch dam was evaluated using inverse an... more Strength degradation of mass concrete of the Dez concrete arch dam was evaluated using inverse analysis methods. A threedimensional nonlinear finite element model (FEM) was developed here for such an evaluation by considering the effect of interaction between vertical adjacent blocks of the dam. The special attention was paid to the thermal loads. The Young's modulus and Poisson's ratio and thermal expansion coefficient of mass concrete of the dam were selected as variable indices for monitoring the strength degradation of dam concrete in the proposed model. An iterative solution scheme was performed to determine the mentioned indices in such a way that a predefined error function would be minimized. An error function has been considered as the sum of the squares of the errors in the nodes of the mesh. An error in a node was defined as the difference between computed displacement vector based on the developed model and the recorded displacement vector with the instruments located in the dam body. The sequences of the solution method have been presented in the paper. The unique characteristic of the suggested method is the contribution of thermal loads in the inverse analysis. The obtained results indicated that the mass concrete of the dam has experienced approximately 34% reduction in its initial elastic modulus, 15% enlargement in its initial Poisson's ratio, and 25% reduction in its initial thermal expansion coefficient during its 42-year life period (1965-2007). According to the fundamentals of theory of elasticity, it is concluded that the failure surface (the eigenvalues of elastic tensor establish a failure surface for concrete in stress space) of the concrete material of the Dez dam has been contracted significantly. This reduction is strongly thought to be attributable to aggressive hygro-thermo-mechanical effects on downstream parts and may be the result of hygo-thermo-chemo (namely calcium leaching)mechanical effects at upstream parts of the dam based on similar evidence recorded in the scientific research.

Trends in Applied Sciences Research, 2010

Applied Mechanics and Materials, 2011

Abstract For supplying of water demands in the downstream of dams, optimization of released water... more Abstract For supplying of water demands in the downstream of dams, optimization of released water from reservoir of dam is necessary. Released water from reservoir is related to discharge of inflow to reservoir, volume of evaporation from reservoir and storage of ...