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Volume 17, Issue 6, 2010
Transaction on Civil Engineering


Shear Strength Behavior and Soil Water Retention Curve of a Dual Porosity Silt-Bentonite Mixture
 
        M. Ajdari (MSc.)
  • G Habibagahi [Professor]
  • H. Nowamooz [PhD.]
  • F. Masrouri [Professor]
  • A. Ghahramani [Professor]

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Evaluation of soil shear strength is an important step in the stability analysis of earth structures, foundations and natural slopes. The shear strength profile of unsaturated soil is dictated by the suction profile. This pro le depends on the evaporation rate, depth of the water table and the soil water retention curve. In this paper, the soil water retention curve of a dual porosity silt-bentonite mixture is determined

    employing the vapor equilibrium method and osmotic suction technique, and the validity of these approaches is examined against the results from the filter paper technique. Besides, the effect of the stress state on the suction value is studied employing the filter paper method. Furthermore, the shear strength response of the material is evaluated for a wide range of suction values (0-287MPa) employing the direct shear apparatus. Results of direct shear tests show that the expansive clay behaves like a normal consolidated soil at suction values less than, or equal to, 20.5MPa, while its behavior is similar to the heavily over consolidated soils for suction more than 20.5MPa.

    Keywords:
    Shear strength
      Expansive clay
        Soil water retention curve
          Dual porosity.


Effect of Hydrostatic Pressure on Vibrating Rectangular Plates Coupled with Fluid
 
        N. Khorshidi (PhD.)

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This study is focused on the hydrostatic vibration analysis of a rectangular plate in partial contact with a bounded uid in bottom and vertical directions. A set of admissible trial functions is required to satisfy the clamped and simply supported geometric boundary conditions. The uid velocity potential satisfying uid boundary conditions is derived, and the wet dynamic modal functions of the plate are expanded, in terms of the nite Fourier series, for a compatibility requirement along the contacting surface between the plate and the uid. The natural frequencies of the plate coupled with sloshing uid modes are calculated using the Rayleigh-Ritz method, based on minimizing the Rayleigh quotient. The proposed analytical method is veri ed by comparing the presented results with the results obtained by three-dimensional nite element analysis. Finally, the in uence of boundary conditions, plate and tank dimensions, uid depth and hydrostatic pressure on natural frequencies is examined and discussed in detail.

Keywords:
Vibration

    Rectangular plate
      Sloshing uid
        Hydrostatic pressure
          Mod shape.


Stochastic Study of the Effect of Strong Ground Motion Variables on Input Energy
 
        A. Yazdani (PhD.)

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The input energy to a structure during an earthquake is an important measure of seismic demand. The elastic input energy in a multi-degree-of-freedom system can be computed from a Fourier Amplitude Spectrum (FAS) and the real part of the relative velocity transfer function of different modes. One of the essential characteristics of the seismological method is that it distills what is known about the various factors affecting ground motions into different functional forms and, for this reason, the modal analysis-based method in the frequency domain is very efficient in the computation and evaluation of earthquake input energy. The earthquake input energy reliability is dependent on ground motion variables. In this paper, to compare the effect of strong ground motion variables, the contribution of these sources of variability to the input energy's uncertainty is examined by using a stochastic analysis. The analytical results show that earthquake source factors and soil condition variables are the main source of uncertainty in the input energy spectra, while path variables, such as source-site distance, anelastic attenuation and upper crust attenuation, have relatively little effect.

Keywords:
Input energy

    Modal analysis
      Frequency domain
        Seismological Fourier spectrum.


Proposing a New Approach for Qualification of Natural Pozzolans
 
        M. Najimi (MSc.)
  • T. Parhizkar [PhD.]
  • A. R. Pourkhorshidi [MSc.]
  • F. Jafarpour [BSc.]
  • B. Hillemeier [Professor]
  • R. Herr [PhD.]

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Recognizing natural pozzolans and their qualities is one of the most important dilemmas in the field of cement and concrete. Although di erent methods have been published towards this aim, research shows some anomalies between the judgments of these methods. This paper aims to compare evaluation methods of natural pozzolans by considering their performance in concrete as a decision criterion in order to develop a guideline for their quali cation. Therefore, rstly, the main available methods are described. Then, the pozzolanic activity of natural pozzolans is investigated using these methods and compared with the performance in concrete. Finally, a guideline is proposed, based on the discussed methods.

Keywords:
Natural pozzolan

    Pozzolanic activity
      Strength activity index
        Frattini test
          Insoluble residue.


Laboratory Investigations on Wave Run-up and Transmission over Breakwaters Covered by Antifer Units
 
        A. Najafi-Jilani (PhD.)
  • M. Monshizadeh [MSc.]

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The e ect of a placement pattern of antifer units on the wave run-up and transmission was investigated in more than 380 laboratory tests. The main variables in the experiments were as follows: An antifer unit placement pattern, the breakwater front slope angle, the incoming wave height and steepness, and the still water depth. It was concluded that the wave run-up can be reduced by about 25% by changing the placement pattern from regular to irregular. The measured data were also applied to estimate the wave run-up on the antifer-covered breakwaters as a function of the standard run-up on smooth and impermeable slopes. The measured data of the wave transmission are applied to inspect the prediction equations mentioned in literature, and the predicted and measured data were compared and the deviations were discussed. Some modi cations were proposed to improve the accuracy of prediction equations of the wave transmission, especially for breakwaters covered by antifer units in regular and irregular placements.

Keywords:
Antifer units

    Wave run-up
      Wave transmission
        Placement pattern
          Laboratory investigation.


A Procedure for Predicting the Behavior of FRP Confined Concrete Using the FE Method
 
        D. Mostofinejad (PhD.)
  • H. Saadatmand [MSc.]

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The plastic behavior of concrete and enhancement of the ductility and compressive strength of reinforced concrete members are indispensable consequences of concrete confinement. Fiber Reinforced Polymers (FRP) are well known as confining materials for circular columns. This study describes how to predict the behavior of concrete con ned with Carbon Fiber Reinforced Polymers (CFRP) using a non-linear analysis. The results of 29 experimental studies are used, where con ning composites have been unidirectional CFRP. The stress-strain behavior of the concrete members from these experiments is estimated as bilinear curves and, by extracting the necessary data, speci c expressions for modeling of the nonlinear behavior of confined concrete are presented. The presented relationships are verified using the results of 16 distinct experiments. The relationships are applicable in the confinement modeling by considering the hoop rupture strain of the CFRP attached to the concrete, and by using the Tsai-Wu failure criterion. As part of the present study, concrete specimens confined with a CFRP composite were modeled with ANSYS software using the presented relationships. The results show the suitability of the model selected, such that the stress-strain curves obtained from the software are properly applicable in the parametric studies conducted on the confined concrete subjected to axial load and exural moment.

Keywords:
Confined concrete

    Column
      Fiber Reinforced Polymer (FRP)
        Finite Element Analysis (FEA).


Application of Endurance Time Method in Performance-Based Design of Steel Moment Frames
 
        H.E. Estekanchi (PhD.)
  • A. Mirzaee [MSc.]
  • A. Vafai [Professor]

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In this paper, application of the Endurance Time (ET) method in the performance-based design of steel moment frames is explained from a conceptual viewpoint. ET is a new dynamic pushover procedure that predicts the seismic performance of structures by subjecting them to a gradually intensifying dynamic action and monitoring their performance at various excitation levels. Structural responses at di erent excitation levels are obtained in a single time-history analysis, thus signi cantly reducing the computational demand. Results from three analyses are averaged to reduce the random scattering of the results at each time step. A target performance curve is presented based on the required performance criteria, as a continuous function of an increasing intensity measure. The actual performance is then plotted against this target performance based on the results of ET analysis. The overall performance of the structure can be anticipated by comparing the target to actual performance at various intensity levels and the design can be improved based on the observed performance. Results are indicative of a good potential for application of the ET method in the performance-based design of steel moment frames.

Keywords:
Dynamic pushover analysis

    Performance-based design
      Endurance time method
        Intensifying accelerograms.


Health Monitoring of Structures Using Few Frequency Response Measurements
 
        A.A. Golafshani (PhD.)
  • M. Kianian [MSc.]
  • E. Ghodrati [MSc.]

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The development of damage detection techniques for o shore jacket structures is vital for preventing catastrophic events. This paper applies a frequency response based method for the purpose of structural health monitoring. In this approach, the concept of a minimum rank perturbation theory is used. The feasibility of using a nite number of sensors and its e ect on damage detection capabilities is investigated. In addition, the performance of the proposed method is evaluated in the case of multiple damages. The aforementioned points are illustrated using the numerical study of a two dimensional jacket platform.

Keywords:
Damage detection

    Structural health monitoring
      Frequency response function
        O shore jacket platform
          Minimum rank perturbation theory