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Transaction on Civil Engineering

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Volume 17, Issue 4, 2010
Transaction on Civil Engineering


Dynamic Properties of Gravelly Materials
 
        A. Aghaei Araei (MSc.)
  • H. R. Razeghi [PhD.]
  • S. Hashemi Tabatabaei [PhD.]
  • A. Ghalandarzadeh [PhD.]

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This paper studies the dynamic characteristics (i.e. shear modulus and damping ratio) of modeled gravelly soils used as construction materials in some rock-fill dams in Iran by conducting large-scale triaxial testing. Tested specimens were compacted to more than 95% maximum dry density, according to Modi ed Proctor, and tested according to ASTM D 3999. Accurate monitoring of strains by means of non-contact type displacement transducers to infinitesimal strains as small as 0.0001% enabled us to obtain Gmax with some extrapolation. Based on the available experimental results the ranges for G=Gmax 􀀀 and D 􀀀 are defined for materials with > 30% fine content and materials with < 15% fine content. The results clearly indicate the need for modification in previously proposed G=Gmax 􀀀 curves, particularly for gravels with > 30% fine content. Also, the suggested D 􀀀 curves lay out of the bounds of data reported by previous researchers, which may be due to the effects of testing frequency, fine content, and confining pressure. In addition, a predictive hyperbolic model for estimating normalized shear modulus (G=Gmax) versus shear strain ( ) is presented. Effects of the number of cyclic loadings over the shear modulus and damping ratio are also investigated.

Keywords:
Rock-fill

    Triaxial testing
      Shear modulus
        Damping
          Excess pore pressure.


Effect of Internal and External Shear Wall Location on Strengthening Weak RC Frames
 
        M.H. Arslan (PhD.)
  • M.Y. Kaltakci [Professor]
  • G. Yavuz [PhD.]

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Hundreds of thousands of Reinforced Concrete (RC) buildings have been either seriously damaged or have completely collapsed due to major earthquakes in recent years in Turkey, therefore, the construction of RC buildings gained momentum by the aid of scientific studies on strengthening. As well as mentioning the importance of the strengthening process using Shear Walls (SW) in RC buildings of poor earthquake performance, an experimental study carried out to analyze the in uence of the location of a SW on the existing system was also mentioned in this study. A total of three, two-storey, two-bay RC frames of 1/3 scale were produced for the experiments by expecting them to represent the behavior of the RC frames having weak earthquake strength

    two of which were strengthened with SWs. The main aim of this study is to compare the effectiveness of internal and external SW locations on strengthened weak, RC frame earthquake behavior. The strength, sti ness and ductility of the tested frames were compared within the light of numerical results obtained from the experiments. In the study, an overall comparison of strengthening methods was made in terms of applicability, usability and cost.

    Keywords:
    Experimental study
      Reinforced concrete
        Shear wall
          Strengthening
            Earthquake damage; Pushover


Lateral-Torsional Buckling of Retrofitted Steel I-Beams Using FRP Sheets
 
        M.Z. Kabir (PhD.)
  • A.E. Seif [MSc.]

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This study intends to present an analytical solution of lateral-torsional buckling of an Ibeam, which is retrofitted using FRP sheets. The analytical solution is based on calculating the total potential energy and applying the Rayleigh-Ritz method. It is supposed that the FRP sheet can be used on anges. Therefore, two cases of retro tting are the I-beam with Top-Bottom retrofitted anges (TB) and Bottom retrofitted ange Only (BO). It is also assumed that the ange and the FRP sheet are considered as a continuous hybrid element and the Classical Lamination Theory (CLT) can be applied. Subsequently, from the energy method, sti ness parameters of retro tted sections are produced for both cases of TB and BO and the critical moment is presented for the retro tted I-beam under positive end moments. Finally, numerical consideration and a parametric study with various fiber angles in a [+=􀀀] laminate sequence are used for both simple and clamped beams under some typical loadings, to inspect the e ects of FRP sheets on the development of the lateral-torsional buckling capacity. Moreover, FEM results are produced from numerical models made up of 2D shell elements to verify the analytical solution.

Keywords:
Lateral-torsional buckling

    Rehabilitation using FRP
      Steel members
        Classical lamination theory
          I-beams.


A New Approach for Estimating the Seismic Soil Pressure on Retaining Walls
 
        S. Maleki (Professor)
  • S. Mahjoubi [MSc.]

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The model incorporates nonlinearity in the behavior of near wall soil, wall exibility and elastic free eld soil response. This model can be employed in nonlinear modeling of retaining walls and bridge abutments. The advantages of this model are simplicity and exibility in addition to acceptable precision. Using this nite element model, an analytical study is conducted on several soil-wall systems using nonlinear time-history analysis by applying real earthquake records. Based on the results of these analyses, new seismic soil pressure distributions are proposed for di erent soil and boundary conditions. These distributions are shown to be more accurate than the popular Mononobe-Okabe equations.

Keywords:
Seismic analysis

    Retaining walls
      Soil pressure
        Soil-structure interaction
          Mononobe- Okabe
            Finite element analysis.


Experimental and Numerical Investigations on Flooding System of Iranian South-Coast Dry Docks
 
        A. Najafi-Jilani (PhD.)
  • M. Monshizadeh [PhD.]
  • A. Naghavi [MSc.]

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Experimental investigations were carried out on the ooding system of the Bandar-Abbas dry dock, located on the southern coast of Iran. The main goal of the investigation was to evaluate the ooding time, as well as the seawater ow speci cations, in the intake channels. The time variable upstream and downstream boundary conditions were simulated. The e ects of tidal uctuations on water discharge through the intake channels were inspected. The ow pattern around the bed over ow weirs of the intake channel was also investigated. The air trapping at the top of the main intake channel was recognized as an e ective phenomenon on the ooding rate. A numerical model is simultaneously developed to evaluate the ow pattern and the velocity and pressure domain in the watering channels. Applicable guidance about selection of the element type and optimization of the convergence rate of the numerical modeling was presented especially for ow simulation under unsteady boundary conditions and complex geometry. Numerical results were compared with corresponding laboratory measured data and a good agreement was obtained.

Keywords:
Graving dock

    Flooding system
      Tidal uctuations
        Numerical modeling
          Experimental investigations.


A Shortest Path Problem in an Urban Transportation Network Based on Driver Perceived Travel Time
 
        Y. Shafahi (PhD.)
  • H. Ramazani [MSc.]
  • S.E. Seyedabrishami [MSc.]

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This paper proposes a method to solve shortest path problems in route choice processes when each link's travel time is a fuzzy number, called the Perceived Travel Time (PTT). The PTT is a subjective travel time perceived by a driver. The algorithm solves the fuzzy shortest path problem (FSPA) for drivers in the presence of uncertainty regarding route travel time. For congested networks, the method is able to nd the shortest path in terms of perceived travel time and degree of saturation (congestion) along routes at the same time. The FSPA can be used to support the fuzzi cation of trac assignment algorithms. The applicability of the resulting FSPA for the trac assignment was tested in conjunction with incremental trac loading and was applied to a large-scale real network. The results of the trac assignment based on the FSPA, User Equilibrium (UE) and a stochastic loading network model (Dial's assignment algorithm) were compared to the observed volume for certain links in the network. We conclude that the proposed method o ers better accuracy than the UE or Dial's assignment algorithm for the network under testing.

Keywords:
Fuzzy sets

    Perceived travel time
      Route choice
        Shortest path
          Urban network.