فهرست مطالب

Scientia Iranica
Volume:19 Issue: 6, 2012

  • Transactions A: Civil Engineering
  • تاریخ انتشار: 1392/01/10
  • تعداد عناوین: 12
|
  • G.F. Sirca Jr., H. Adeli Pages 1355-1364
    A review of representative research reported in journal articles in the field of structural system identification published in journals since 1995 is presented. The paper is divided into five sections based on the general approach used: conventional model-based, biologically-inspired, signal processing-based, chaos theory, and multi-paradigm approaches. Most of the published papers deal with small and academic problems. System identification of large real-life structures with nonlinear behavior subjected to unknown dynamic loading such as strong ground motions is challenging. It is believed a multi-paradigm approach is the most effective strategy for system identification of large structures subjected to dynamic loading.
  • A. Mortezaei, H.R. Ronagh Pages 1365-1378
    In a strong earthquake, an RC column develops plastic deformations in regions often defined as plastic hinge regions. The formation of a plastic hinge in an RC column in these regions depends on the characteristics of the earthquakes as well as on the column details. Recordings from recent earthquakes have demonstrated that ground motions in near field to a rupturing fault can contain a large energy. This energy can cause considerable damage during an earthquake. Therefore, many recently designed and constructed buildings may require strengthening in order to perform well when subjected to near-fault earthquakes. Fiber Reinforced Polymers are considered to be a viable strengthening method due to their relatively easy and quick installation. In this paper, 1350 inelastic time-history analyses have been performed to predict the nonlinear behavior of FRP strengthened RC columns under both far-fault and near-fault earthquakes. The effects of axial load, height-depth ratio and the amount of longitudinal reinforcement, as well as different characteristics of earthquakes, are evaluated and the results are compared with the corresponding experimental data. Based on the results, simple expressions are proposed that can be used to estimate plastic hinge length of FRP strengthened RC columns subjected to both far- and near-fault earthquakes.
  • R. Zhang, H. He, D. Weng, H. Zhou, S. Ding Pages 1379-1390
    The toggle-brace-damper system has been proven to be the most effective system for the energy dissipation of stiff structures. However, the expected effect of the toggle-brace-damper system depends largely on its configuration, the use of steel braces and the installation mode. The existing design methods of toggle-brace-damper systems may be further improved. The analysis of different installation modes and experiments involving toggle-brace-damper systems are conducted to improve understanding of the influence of key factors and to provide design guidance. For toggle-brace-damper system tests, a vertical brace is installed in a steel frame to prevent out-of-plane instability. The calculation formulas for an upper toggle-brace-damper system and other configuration systems with consideration of the influence of brace deformation are studied in the paper. Test results show that the upper toggle-brace-damper system has the largest magnification factor, which is consistent with the theoretical analyses. The brace deformation and installation error cannot be ignored in the design of a toggle-brace-damper system. Installation error can also lead to out-of-plane instability of a toggle-brace-damper system. Moreover, the experimental results show that the magnification factor changes with loading and is different when force is applied in the push and pull directions.
  • A. Aghaei Araei, A. Soroush, S. Hashemi Tabatabaei, A. Ghalandarzadeh Pages 1391-1410
    This paper studies the behavior of a number of gravelly modeled materials by conducting large-scale triaxial testing. Undrained monotonic compression tests were carried out on the high compacted gravelly soil specimens with different fine content and stress levels. It was observed that high compacted gravelly soil specimens show dilative behavior at failure in a wide range of fine content. The effective stress paths of the materials having less than 10% and more than 22% of material finer than 0.2 mm are completely different. Variations of the CU material parameters with respect to the confining pressure, fine content, shape, strength and particle size were investigated. The CU material results were compared with those in CD conditions. The value of internal effective friction angle in CD conditions is slightly higher than those of the CU conditions. Moreover, where the volume strain in CD conditions is minimum, the excess pore water pressure in CU conditions decreases to zero.
  • M. Imani, A. Fahimifar, M. Sharifzadeh Pages 1411-1421
    In this study, two main failure modes of jointed rock foundations consisting general shear failure and failure due to excessive deformation are discussed. For each of these two modes, the method of determining ultimate bearing capacity is presented and the effect of joint spacing is also examined. For the former mode, an upper bound method of limit analysis is employed, while for the latter one, distinct element numerical modeling is used to investigate the effect of joint spacing on the bearing capacity. The calculations are performed for a rock mass containing two orthogonal joint sets that the orientation angle of the first joint set is 15°, 30° and 45° to the horizontal, respectively. A non-dimensional parameter called “Spacing Ratio” () is used to examine the effect of different joint spacing. This study shows that in the case of general shear failure mode, joint spacing does not have significant effect on the bearing capacity. In the failure mode induced by excessive deformation of the rock mass, for, increasing the results in decreasing the bearing capacity, however, for, the joint spacing does not significantly affect the bearing capacity.
  • M. Lashckarbolok, E. Jabbari Pages 1422-1430
    The Least squares approach is a robust and simple method for function approximation. Collocated Discrete Least Squares (CDLS) is a meshless method based on least squares technique enjoying symmetric and positive-definite properties. In this paper, the CDLS method is extended for the stream function-vorticity formulation of 2D incompressible Navier–Stokes equations. Shape functions are constructed using Radial Point Interpolation Method (RPIM) because of its robustness and simplicity. The accuracy of the proposed scheme is investigated through solving lid-driven cavity flow and backward facing step problems for the different Reynolds numbers.
  • M. Ghaemian, M. Sohrabi-Gilani Pages 1431-1436
    In the present paper، spatially variation input effects on seismic responses of arch dams have been studied. Recorded ground accelerations at the dam foundation interface of Pacoima dam during January 13، 2001 were used for the purpose of this investigation. A numerical finite element model was developed for dynamic analysis of the dam reservoir system. The modified version of NSAD-DRI finite element program was used for the analysis and the ground acceleration time histories were interpolated at all dam foundation interface nodal points. Total and pseudo static displacements as well as developed stresses due to uniform and non uniform excitations are obtained. The results reveal that multiple support excitations can have profound effects on the dam responses.
  • M. Ghodsian, M. Mehraein, H.R. Ranjbar Pages 1437-1444
    The results of experiments on the local scour due to free fall jets are presented in this paper. Experiments were conducted for various values of the densimetric Froude number, the relative tailwater depth, the relative drop height and the relative sediment size. It has been found that by increasing the sediment non-uniformity parameter the scour hole parameters decrease. Moreover, in non-uniform sediment, can be used instead of in the densimetric Froude number of the jet. By using the present and previous experimental data, new equations for the scour parameters were developed. The validity of the developed equations was checked by available prototype data on the scour depth.
  • U. Okkan Pages 1445-1455
    In this study, a Wavelet Neural Network (WNN) model is proposed for monthly reservoir inflow prediction by combining the Discrete Wavelet Transform (DWT) and Levenberg-Marquardt optimization algorithm-based Feed Forward Neural Networks (FFNN). The study area covers the basin of Kemer Dam which is located in the Aegean region of Turkey. Monthly meteorological data were decomposed into wavelet sub-time series by DWT. Ineffective sub-time series have been eliminated by using all possible regression method and evaluating the Mallows’ Cp coefficients to prevent collinearity. Then, effective sub-time series components have been used as the new inputs of neural networks. DWT has been also integrated with multiple linear regressions (WREG) within the study. The results of Wavelet Neural Network (WNN) model and WREG have been compared with conventional Feed Forward Neural Networks (FFNN) and multiple linear regression (REG) models. When the statistical-based criteria are examined, it has been observed that the DWT method has increased the performances of feed forward neural networks and regression methods. The results determined in the study indicate that the WNN is a successful tool to model the monthly inflow series of dam and can give good prediction performances than other methods.
  • A. Sezer Pages 1456-1462
    In this study, a fractal approach is employed to analyze the seismic history of Fethiye and Simav zones in the West of Turkey. In this scope, a database, including the set of earthquakes in two seismogenic zones, is compiled. Applying fractal dimension and probability concepts, it is aimed to find out the occurrence probability of earthquakes having magnitudes equal to or greater than a threshold level. The results are analyzed in detail and relationships among the fractal dimension, threshold magnitude, probability intercept, and critical time scale are presented. The analyses revealed that activities in the Fethiye Zone are more frequent and continuous than those in the Simav Zone. As mentioned in previous studies, the critical time scales at certain magnitude thresholds can be referred to as the lower limit of the recurrence period of earthquakes in these zones.
  • A. Baghlani Pages 1463-1472
    This paper demonstrates the effectiveness of a high-resolution numerical scheme in boundary-fitted curvilinear coordinates for simulation of flow at channel bends. Two-dimensional shallow water equations, which are transformed from physical domain to computational domain, are solved by a robust high-resolution scheme particularly developed for boundary-fitted curvilinear coordinates. Finite-volume method is adopted for discretization of governing equations in computational domain. Turbulence shear stresses are included in the model by eddy-viscosity approach. Moreover, the effect of secondary flow, which is significant in channel bends, has been included in the model and the results have been compared with the results achieved by neglecting this phenomenon. Secondary flow intensity is evaluated by an analytical approach; the deviation of bed shear stress from main flow is related to secondary flow intensity and is considered in the model as well. All numerical results are compared with experimental data and they show satisfactory agreement.
  • Yasir Khan, H. V., Aacute, Zquez-Leal, N. Faraz Pages 1473-1477
    In this paper, a Van der Pol–Duffing oscillator is studied. Governing equations are solved by using a newly proposed method, namely; the “Homotopy Perturbation Transform Method” (HPTM). The beauty of the paper is error analysis between the exact solutions, approximate solutions and numerical solutions, which shows that our approximate solutions converge very rapidly to the exact solutions. HPTM is not limited to the small parameter, such as in the classical perturbation method. The method gives an analytical solution in the form of a convergent series with easily computable components, requiring no linearization or small perturbation. Results indicate that this technique is very effective and simple for solving nonlinear oscillatory systems. The solution procedure confirms that this method can be easily extended to other kinds of nonlinear oscillator equations.