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Transaction on Civil Engineering

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Transaction on Civil Engineering
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Transaction on Civil Engineering
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Transaction on Civil Engineering
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Transaction on Civil Engineering
 
Transaction on Mechanical Engineering

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Transaction on Mechanical Engineering
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Transaction on Mechanical Engineering
 
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Volume 17, Issue 2, 2010
Transaction on Civil Engineering


E ect of Anti-Vortex Plates on Critical Submergence at a Vertical Intake
 
        S.M. Borghei (Professor)
  • A.R. KABIRI-SAMANI [PhD.]

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One of the sources of disturbance at intakes is the occurrence of free-surface vortices with an air core. The most common solution for avoiding air-entrainment is the use of anti-vortex devices and, especially, plates for large pipe or shaft intakes. If plates are used, then, the geometry and position of them should be studied experimentally. Since only general guidance for use of plates is available, a study for the more precise placement of plates is needed. Hence, a comprehensive set of experiments have been carried out using rectangular plates with di erent dimensions and at various positions with respect to the vertical outlet pipe intakes and two di erent pipe diameters (D = 75 and 100 mm). The results of critical submergence with respect to the dimensions and positions of the plates are presented as graphs and equations. Thus, design guides and recommendations are provided.

Keywords:
Air entrainment

    Experimental data
      Intakes
        Pipe ow
          Plates
            Vortices.


Pseudo-Dynamic Active Earth Pressure Analysis of Inclined Retaining Walls Using Horizontal Slices Method
 
        A. Ghanbari (PhD.)
  • M Ahmadabadi [MSc.]

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Retaining walls may be constructed with an inclination angle of less than 90from the horizontal axis. In the present study, using the horizontal slices method and limit equilibrium principles, in addition to assuming variation of the seismic coecient with height, a new formulation is proposed to calculate the active seismic pressure on retaining walls. The general arrangement of the proposed pseudo-dynamic formulation allows analysis of inclined or vertical retaining walls in frictional, cohesive and cohesive-frictional soils. Results from the proposed method were compared with those of previous researchers under similar conditions and showed a negligible di erence. The horizontal slices method was able to assess an inclined wall, determine the active earth pressure distribution at di erent points along the wall height and consider the angle of failure wedge as a variable in the time domain. The ndings show that despite the accepted assumptions for conventional vertical walls the distribution of earth pressure on an inclined wall follows a non-linear pattern at each moment.

Keywords:
Inclined retaining wall

    Horizontal slices method
      Pseudo-dynamic
        Active earth pressure.


Analytical Approach for Flow over an Oblique Weir
 
        A.R. KABIRI-SAMANI (PhD.)

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Flow discharge over an oblique weir is greater than that over a straight or plain weir for the same water head due to its extra length with respect to the channel width or fully extended plain weir. In this study, a new theoretical approach is used for the hydraulics of oblique weirs. The main objective is to investigate the e ect of di erent hydraulic and geometric properties of the ow and the weir on the ow de ection angle and discharge coecients for free and submerged ow over oblique weirs. This approach is based on energy, momentum and continuity equations. For improving the performance of this kind of weir, one approach is to increase the ow de ection until it is perpendicular to the oblique weir for maximum use of the weir length. The submerged guide vanes have also been used and investigated theoretically. The data for calibration of the models are taken from Borghei et al.(2003). It is shown that by employing guide vanes, for some cases, the discharge coecient can be increased up to 33%. Finally, new relations were developed for practical purposes.

Keywords:
Oblique weir

    Analytical model
      Flow de ection angle
        Discharge coecient
          Guide vane.


Rotation as a General Operation for Con guration Processing
 
        A. Kaveh (Professor)
  • X. Jia [PhD.]
  • Q. Weng [PhD.]

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In this paper, a graph theoretical method is used to introduce three basic operations of con guration processing

    rotation, translation and re ection. The relationships between translation and rotation, and re ection and rotation, are established. Examples are then constructed using three di erent procedures of con guration processing. From the comparison and discussion of the results, it is concluded that rotation can be considered as a general operation of con guration processing.

    Keywords:
    Con guration processing
      Graph
        Rotation
          Translation
            Re ection.


Modeling of Moving Boundaries in Large Plasticity Deformations via an Enriched Arbitrary Lagrangian-Eulerian FE Method
 
        A.R. Khoei (Professor)
  • M. Anahid [PhD.]

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In this paper, a new computational technique is presented for the modeling of moving boundaries in large plastic deformations based on an enriched arbitrary Lagrangian-Eulerian nite element method. An Arbitrary Lagrangian-Eulerian (ALE) technique is employed to capture the advantages of both Lagrangian and Eulerian methods and alleviate the drawbacks of mesh distortion in Lagrangian formulation. An enriched nite element method is implemented based on the extended FEM technique to capture the arbitrary interfaces independent of element boundaries. The process is accomplished by performing a splitting operator to separate the material (Lagrangian) phase from the convective (Eulerian) phase, and partitioning the Lagrangian and relocated meshes with some sub-quadrilaterals whose Gauss points are used for integration of the domain of elements. In order to demonstrate the eciency of the enriched ALE nite element model in large deformations, several numerical examples including the coining problem with horizontal and vertical moving boundaries and a tensile plate with a moving interface are presented and the results are compared with those of the standard nite element and extended nite element methods.

Keywords:
Large plasticity deformations

    Arbitrary Lagrangian-Eulerian
      Enriched FEM
        Partition of unity
          Godunov technique.


Adaptive Behavior of Double Concave Friction Pendulum Bearing and its Advantages over Friction Pendulum Systems
 
        M. Malekzadeh (MSc.)
  • T. Taghikhany [PhD.]

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Double Concave Friction Pendulum (DCFP) bearing is a new generation of friction isolator that contains two separate concave sliding surfaces with di erent properties. Accommodating enhanced performance, compared to the Friction Pendulum System (FPS), is one of the most important bene ts of DCFP. Herein, the seismic behavior of structures isolated by DCFP bearings is compared with the response of the same buildings using the FPS bearing. Accordingly, a series of nonlinear dynamic analyses are carried out under ensembles of ground motions at three di erent hazard levels (SLE, DBE and MCE). Moreover, the adaptive behavior of DCFP and its advantages in protecting secondary systems is investigated. The probability of exceedance curves of peak roof acceleration, peak inter-story drift and peak isolator displacement is compared for two types of isolation system. The result supports the advantages of DCFP isolation systems.

Keywords:
DCFP

    Friction pendulum systems
      Base isolation.


Evaluation of Energy-Based Modal Pushover Analysis in Reinforced Concrete Frames with Elevation Irregularity
 
        M. Mofid (Professor)
  • M. J. Hashemi [MSc.]

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In nonlinear static (pushover) methods of analysis as an alternative to time history analysis, the capacity curve of the structure is established with respect to the roof displacement. Disproportionate increases in the roof displacement and even outright reversals of the higher modes can distort the capacity curve of the equivalent single degree of freedom system in these kinds of method, including MPA. To overcome this problem, recently, \Energy-Based" the Modal Pushover Analysis (Energy-Based MPA) method has been introduced. In this method, the absorbed energy and/or the external work in the pushover analysis is considered. Accordingly, the assessment of the Energy-Based MPA method is important in the seismic analysis of asymmetrical and tall buildings. In this paper, the seismic demands of concrete structures with irregularity in elevation are determined, using Energy-Based MPA. For assessment of the presented technique, the results are compared with those from the Non-Linear Time History Analysis (NL-THA). Seven examples including a 2-D simulation of a 12-story building are modeled, using the Opensees Code. For each case, di erent types of irregularity, such as mass, geometry and variations due to the di erence in elevation are considered. Story-drifts and oor-displacements are used as the main parameters for assessment of the results. Based on a study of the structural performance of the models, it has been made clear that di erent types of the above-mentioned irregularity in elevation do not have any signi cant e ect on the Energy-Based MPA method. Consequently, this method can be considered as an accurate alternative technique for NL-THA, to fairly estimate the seismic demands of structures.

Keywords:
Energy-Based MPA

    Time history analysis
      Elevation irregularity.


Simple Assessment Method to Estimate the Remaining Moment Capacity of Corroded I-Beam Sections
 
        Y. Sharifi (MSc.)
  • R. Rahgozar [PhD.]

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Corrosion of steel structures is a serious problem throughout the world. The most signi cant consequence of corrosion is reduction of the section size. This, in turn, leads to a reduction in the carrying capacity and structural safety. The analysis of existing structures may di er from the analysis of structures under design, especially if there is damage by corrosion. Common examples of corrosion that have been found in the petro-chemical industry include the loss of sections in anges and holes in the web. As there is no clear provision of recommendations for such cases in the present codes, there is a need for simple assessment methods to deal with them e ectively. The overall aim of this paper is to develop a simple method which can be used to make reliable estimates of the remaining moment capacity, using thickness loss information provided by visual inspection or measurements. The results of this study can be used for calculating the remaining service life, such as the moment capacity of deteriorated I-beams.

Keywords:
Uniform corrosion

    Thickness loss
      Steel structures
        Moment capacity.