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Showing 11 results for Sadeghi

Sadeghi J.m., Youldashkhan M.,
Volume 3, Issue 1 (March 2005)
Abstract

In this paper, the main factors in the analysis of the railway concrete sleepers areinvestigated and new recommendations are made in order to improve the accuracy of the currentpractices in analysis of the railway track system. First, a comprehensive literature survey isconducted, then, FEM models for a railway track system are developed and used to discuss andevaluate the assumptions commonly used in the analysis of the railway track system. The analysisfactors investigated include stress distribution under a concrete sleeper, rail-seat load, anddynamic coefficient factor. Finally, recommendations and needs for continuation of the researchare presented.
N. Naderpajouh, A. Afshar, S.a. MirmohammadSadeghi,
Volume 4, Issue 4 (December 2006)
Abstract

The use of Value Engineering (VE) methodology in construction industry has grown significantly, mainly in view of its extensive benefits. The main task in evaluation phase of VE workshop is to assess alternative ideas, proposed for each function. This phase of VE, hence, could be deemed as a Multi Criteria Decision Making (MCDM) problem. This paper presents a fuzzy decision support system (DSS) to be employed in evaluation phase of VE. The proposed multi alternative decision model may be recommended where alternatives’ preferences ratios are different, and scores assigned to each alternative idea are uncertain. As use of VE has greater payoffs at the earlier stages of the construction projects, in which most of the criteria are still vague and not precisely defined, exploiting this DSS may result in more tangible model of decision making process and satisfactory outlook of VE studies in construction projects. A ranking methodology in a spreadsheet template is also provided to facilitate the ranking process. Performance of the proposed methodology is tested using a case example in the tunneling industry.
J. Sadeghi, P. Barati,
Volume 8, Issue 1 (3-2010)
Abstract

Current practices in railway track analysis and design are reviewed and discussed in this paper. The

mechanical behavior of railway track structure comprising of various components has not been fully understood due

to the railway track structural complexity. Although there have been some improvements in the accuracy of current

track design methods in recent decades, there are still considerable uncertainties concerning the accuracy and

reliability of the current methods. This indicates a need for a thorough review and discussion on the current practices

in the analysis and design of railway track systems. In this paper, railway design approaches proposed by various

standards along with the results of a wide range of technical researches are studied and necessary suggestions are

made for the improvement of current practices in the analysis and design of railway track


J. Sadeghi,
Volume 8, Issue 3 (September 2010)
Abstract

 Investigations on vibration behaviors of railway track systems were attempted in this research. This was made by conducting a comprehensive field investigation into the free vibration of track systems and response of tracks to train moving loads. In-situ modal analysis was used in a railway track field as an efficient method of investigating dynamic properties of railway track systems. Natural frequencies and mode shapes of the track system in different insitu track conditions were obtained for the fist time. The sensitivity of the natural frequencies of the track to the types of sleepers, fastening systems, ballast conditions, and rail joints were studied. Efficiency of rail welded joints in CWR tracks and the effects of replacing timber sleepers with concrete sleepers on dynamic behavior of a track were investigated. Advantages of flexible sleeper fastening system from the aspects of serviceability and passenger riding comfort were discussed. The effects of the track accumulative loading as a main indicator of ballast degradation on track dynamic behavior were studied. Rail deflections were calculated by using auto-spectra obtained from vibrations of the track under trainloads, leading to the development of a new mathematical expression for the calculation of the rail dynamic amplification factor.


Kabir Sadeghi,
Volume 9, Issue 3 (September 2011)
Abstract

An energy based damage index based on a new nonlinear Finite element (FE) approach applicable to RC structures subjected to cyclic, earthquake or monotonic loading is proposed. The proposed method is based on the evaluation of nonlinear local degradation of materials and taking into account of the pseudo-plastic hinge produced in the critical sections of the structure. A computer program is developed, considering local behavior of confined and unconfined concretes and steel elements and also global behavior and damage of reinforced concrete structures under cyclic loading. The segments located between the pseudoplastic hinges at critical sections and the inflection points are selected as base-models through simulation by the proposed FE method. The proposed damage index is based on an energy analysis method considering the primary half-cycles energy absorbed by the structure during loading. The total primary half-cycles absorbed energy to failure is used as normalizing factor. By using the proposed nonlinear analytical approach, the structure's force-displacement data are determined. The damage index is then calculated and is compared with the allowable value. This damage index is an efficient means for deciding whether to repair or demolish structures after an earthquake. It is also useful in the design of new structures as a design parameter for an acceptable limit of damage defined by building codes.  The proposed approach and damage index are validated by results of tests carried out on reinforced concrete columns subjected to cyclic biaxial bending with axial force.


I. Ashayeri, M. Kamalian, M. K Jafari, M. Biglari, Ma. Mirmohammad Sadeghi,
Volume 12, Issue 2 (Transaction B: Geotechnical Engineering April 2014)
Abstract

This paper presents time domain fundamental solutions for the extended Biot's dynamic formulations of two-dimensional (2D) unsaturated poroelasticity. Unsaturated porous media is considered as a porous media in which the voids are saturated with two immiscible fluids, i.e. liquid and gas. At first, the corresponding explicit Laplace transform domain fundamental solution is obtained in terms of skeleton displacements, as well as liquid and gas pressures. Subsequently, the closed-form time domain fundamental solutions are derived by analytical inversion of the Laplace transform domain solutions. Finally, a set of numerical results are presented which verifies the accuracy of the analytically inversed transient fundamental solution and demonstrates some salient features of the elastic waves in unsaturated media..
K. Sadeghi,
Volume 12, Issue 3 (Transaction A: Civil Engineering September 2014)
Abstract

An analytical nonlinear stress-strain model and a microscopic damage index for confined and unconfined concretes together with a macroscopic damage index for reinforced concrete (RC) structures under cyclic loading are proposed. In order to eliminate the problem of scale effect, an adjustable finite element computer program was generated to simulate RC structures subjected to cyclic loading. By comparing the simulated and experimental results of tests on the full-scale structural members and concrete cylindrical samples, the proposed stress-strain model for confined and unconfined concretes under cyclic loading was accordingly modified and then validated. The proposed model has a strong mathematical structure and can readily be adapted to achieve a higher degree of precision by modifying the relevant coefficients based on more precise tests. To apply the proposed damage indices at the microscopic and macroscopic levels, respectively, stress-strain data of finite elements (confined and unconfined concrete elements) and moment-curvature data of critical section are employed. The proposed microscopic damage index can easily be calculated by using the proposed simple analytic nonlinear stress-strain model for confined and unconfined concretes. The proposed macroscopic damage index is based on the evaluation of nonlinear local degradation of materials and taking into account the pseudo-plastic hinge produced in the critical section of the structural element. One of the advantages of the macroscopic damage index is that the moment-curvature data of the critical section is sufficient in itself and there is no need to obtain the force-displacement data of the structural member.
Kabir Sadeghi,
Volume 14, Issue 5 (Transaction A: Civil Engineering 2016)
Abstract

A fast converging and fairly accurate nonlinear simulation method to assess the behavior of reinforced concrete columns subjected to static oriented pushover force and axial loading (sections under biaxial bending moment and axial loading) is proposed. In the proposed method, the sections of column are discretized into “Variable Oblique Finite Elements” (VOFE). By applying the proposed oblique discretization method, the time of calculation is significantly decreased and since VOFE are always parallel to neutral axis, a uniform stress distribution along each oblique element is established. Consequently, the variations of stress distribution across an element are quite small which increases the accuracy of the calculations. In the discretization of section, the number of VOFE is significantly smaller than the number of “Fixed Rectangular Finite Elements” (FRFE). The advantages of using VOFE compared to FRFE are faster convergence and more accurate results. The nonlinear local degradation of materials and the pseudo-plastic hinge produced in the critical sections of the column are also considered in the proposed simulation method. A computer program is developed to calculate the local and global behavior of reinforced concrete columns under static oriented pushover and cyclic loading. The proposed simulation method is validated by the results of tests carried out on the full-scale reinforced concrete columns. The application of the “Components Effects Combination Method” (CECM) is compared with the proposed “Simultaneous Direct Method” (SDM). The obtained results show the necessity of applying SDM for nonlinear calculations. Especially during the post-elastic phase, which occurs frequently during earthquake loading.


Kabir Sadeghi,
Volume 15, Issue 1 (Transaction A: Civil Engineering 2017)
Abstract

A nonlinear Finite Element (FE) algorithm is proposed to analyze the Reinforced Concrete (RC) columns subjected to Cyclic Biaxial Bending Moment and Axial Loading (CBBMAL). In the proposed algorithm, the following parameters are considered: uniaxial behavior of concrete and steel elements, the pseudo-plastic hinge produced in the critical sections, and global behavior of the columns. In the proposed numerical simulation, the column is discretized into two Macro-Elements (ME) located between the pseudo-plastic hinges at critical sections and the inflection point. The critical sections are discretized into Fixed Rectangular Finite Elements (FRFE). The basic equilibrium is justified over a critical hypothetical cross-section assuming the Kinematics Navier’s hypothesis with an average curvature. The method used qualifies as a “Strain Plane Control Process” that requires the resolution of a quasi-static simultaneous equations system using a triple iteration process over the strains in each section. In order to reach equilibrium, three main strain parameters (the strains in the extreme compressive point, the strains in the extreme tensile point and the strains in another corner of the section) are used as three main variables. The proposed algorithm has been validated by the results of tests carried out on full-scale RC columns. The application of the Components Effects Combination Method (CECM) is also compared with the proposed Simultaneous Direct Method (SDM). The results obtained show the necessity of applying SDM for the post-elastic phase, which occurs frequently during earthquake loading.


Dr. Kabir Sadeghi, Dr. Fatemeh Nouban,
Volume 15, Issue 5 (Transaction A: Civil Engineering 2017)
Abstract

This paper describes both global and local versions of an energetic analytical model to quantify the damage caused to reinforced concrete (RC) structures under monotonic, cyclic or fatigue loading. The proposed model closely represents the damage to structures and yields a damage index (DI) for the RC members. The model is cumulative and is based on the energy absorbed. The energy under the monotonic envelope curve at the failure of the member is taken as a reference capacity. The data required to apply the model in any given situation or member can be obtained either by numerical simulation or from experimental tests. An analytical computer program was developed to simulate numerically the response of RC members taking into account the nonlinear behavior of the materials and structures involved. The proposed model was verified by comparison with practical tests undertaken by other researchers on over 20 RC columns. The comparison demonstrates that the model provides a realistic estimation of the damage of the RC structural members. The comparison between values of the proposed DI calculated based on experimental test data and numerical simulation results for a cyclic loading case shows that to calculate DI, it is not necessary to perform expensive experimental tests and that using a nonlinear structural analytical simulation is sufficient. The results are also compared to a damage model proposed by Meyer (1988).


Dr. Ali Massumi, Dr. Kabir Sadeghi, Mr. Morteza Nekuei,
Volume 15, Issue 7 (Transaction A: Civil Engineering 2017)
Abstract

One of the main concerns in an essential or highly important building is finding the appropriate structural system, while the efficiency of each conventional structural system varies in different cases. In this paper a new multi objective structural configuration is proposed and its efficiency for protecting buildings against the multi-hazards including earthquake, explosion and typhoon is shown in a case study of a 10 stories building sample. To create the optimum and efficient configuration of the structural elements, and to make some large spans, a configuration including Vierendeel girders is used. In this type of configuration, the inner suspended floor parts protect the outer elements by balancing perimeter span loads. This system makes a new condition for the building to be protected against the progressive collapse due to the terrorism attacks. Furthermore, the partially suspended floors in special stories act like tuned mass dampers (TMDs), which are suitable to decrease the amplitude of the displacement response of the structure during an earthquake.



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