فهرست مطالب

science and Technology (B: Engineering) - Volume:33 Issue: 1, Feb 2009

Iranian Journal of science and Technology (B: Engineering)
Volume:33 Issue: 1, Feb 2009

  • Civil Engineering
  • تاریخ انتشار: 1387/12/05
  • تعداد عناوین: 10
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  • S. M. Zahrai, A. Shafieezadeh Pages 1-14
    Semi-active control systems having the adaptability aspects of active control methods along with the reliability and stability of passive controllers have been recently used to control structures against natural hazards. In this paper, a fuzzy logic based controller is designed to attenuate vibrations of a tall building under cross wind excitations. The building considered is the benchmark 76-story reinforced concrete office tower proposed for the city of Melbourne, Australia. A collection of semi-active dampers is used at the first story to apply control forces to the structure where the damping is found through the fuzzy logic controller. Higher levels of performance are achieved in mitigating structural responses, especially the average RMS displacement response through the application of the fuzzy controller. Also investigated in the present study is the robustness of the whole structure-controller system to uncertainties in the stiffness matrix in the form of multiplicative perturbations. Simulation results verify the superior performance of the semi-active fuzzy controller over the passive controller in response mitigation of the perturbed structure.
  • K. Badv, R. Farsimadan Pages 15-30
    Swelling and diffusion characteristics of GCL samples made in the laboratory were studied and the results compared with the results of an industrial GCL. A Swell-Diffusion apparatus was designed, fabricated, and used to perform the swelling and swelling-diffusion tests. Two types of available local geotextiles (Types I and II) with an available low quality Bentonite (LQB) were used to fabricate two types of GCL’s in the laboratory (Types A and B E-GCLs). The effect of stitching, applied stress, and wetting procedure, was investigated in swelling tests. For type A E-GCL, with no stitch and no applied stress, a maximum of 6 mm swell was observed. Under 12.5 kPa stress, the swell decreased to a maximum of 2 mm. When this GCL was stitched, a maximum of 1.8 mm and 1.4 mm swell with zero and 12.5 kPa stresses were shown, respectively. The swelling results showed that the wetting procedure (from top, from bottom, and both ways) has a negligible effect in maximum swell. The type B E-GCL (having better geotextile quality compared to type A) showed a maximum 2.3 mm swell with no stitch, and 1.6 mm swell when stitched. The industrial needle punched reinforced GCLs with high quality granular sodium bentonite, under 12.5 kPa stress and wetted from top and bottom, showed a maximum of 3 mm swell. The swell data obtained from these experiments are in reasonable agreement with the data reported in the literature for similar GCLs under comparable conditions. Diffusion experiments were performed for types A and B E-GCL’s, as well as for the industrial GCLs. The chloride diffusion coefficients for types A and B E-GCL’s ranged from 2.7x10-10 m2/s to 3.5x10-10 m2/s compared to 2.9x10-10 m2/s to 3.5x10-10 m2/s for the industrial GCLs, which is in good agreement.
  • A. Lashkari Pages 31-48
    Recently, the undrained anisotropic behavior of sand subjected to rotational shear has been a subject of great interest in both fields of experimental studies and constitutive modeling. Herein, based on the critical state concept and the bounding surface plasticity framework, a unified sand model is presented that is able to simulate the liquefaction of sand subjected to various stress paths, especially rotational shear. Using two anisotropy state parameters, the effect of soil anisotropy on the location of critical state line, dilatancy, plastic modulus, and flow direction is considered in constitutive equations. Finally, the simulative capability of the presented model is illustrated by comparison with the experimental data reported by independent research teams over a wide range of densities, stress paths, and stress levels.
  • M. A. L. Neshaei, M. A. Mehrdad, M. Veiskarami Pages 49-60
    Based on experiments, a model is introduced to calculate the vertical and horizontal distribution of undertow in the surf zone due to monochromatic and random wave attack for reflective beaches. The present model is a modification of the original model presented by Okayasu et al., [2] for natural, non-refiective beaches in which the wave set up, radiation stress and mass flux due to breaking waves are modified as described by Mehrdad and Neshaei [6] to include the effect of partially reflected waves. The results of experimental investigation and model development show that the existence of reflective conditions on beaches results in a reduction in the magnitude of undertow and modifies its distribution across the beach profile.
  • M. Tabesh, M. Dini Pages 61-77
    Water demand forecasting cannot be described by any mathematical function because it is a complicated function of a large number of interacting variables. In this paper, several fuzzy and neuro-fuzzy models are presented and their results for short-term water demand forecasting in Tehran are compared. Weather data from three Tehran weather stations is weighted with the Thissen method and effective input data parameters are selected with regression of weighted effective weather and consumption data. The effective parameters include daily average temperature, relative humidity percent and last day, last week and last year water consumption. Consumption of all days between last day and the last week were also used. For the construction of fuzzy models a fuzzy rule-based approach is applied. The working rules are formulated from a set of past observations such as the relation between the parameters and the given input/output data sets. For neuro fuzzy modeling the toolbox function of Adaptive Neuro-Fuzzy Inference System (ANFIS) constructs a Sugeno Inference System (SFIS). The membership function parameters are adjusted using a back propagation algorithm in combination with a least squares method. Outputs of the fuzzy and the neuro fuzzy models demonstrate that the results of fuzzy models do not show high accuracy, but neuro fuzzy models produce better results. Besides, outputs of the neuro fuzzy models with just water consumption inputs have high accuracy. A comparison of outputs with the results of the Artificial Neural Networks (ANN) approach shows the capability of the ANFIS model to predict Tehran water consumption.
  • H. R. Safavi, G. R. Bahreini Pages 79-94
    The increasing demand for water, especially in semiarid regions, poses new challenges for water resources managers. Hence, they must understand the interactions between surface water and groundwater systems, especially under uncertainty. In groundwater systems, uncertainty arises from boundary conditions and aquifer parameters, while in surface water systems, uncertainty stems from the natural variability of the climatic inputs such as precipitation, air temperature, and river flows and, to a lesser degree, from surface model parameters. The main objective of this paper is to present a simulation model for examining the interaction(s) between surface water and groundwater under geologic uncertainty. This model was specifically developed for the study of the Najafabad semiarid plain in Iran. The plain aquifer under study is recharged by lateral groundwater flow from boundaries, irrigation percolation, canals and river seepage, and precipitation directly on the plain. Groundwater flow and groundwater/surface-water interactions were simulated for steady and transient flow conditions using MODFLOW-2000 for average monthly stress conditions in the system during 2001-2004. Calibration of the model was performed by comparing simulated and observed heads, and observation measurements made on a monthly basis during 2002-2004 in 49 observation wells. The Monte Carlo method was used for uncertainty analysis and the investigation of how different model structure alternatives would affect the estimated parameter values. This procedure has a fairly general applicability including systems with scare measurements. The stochastic modeling and analysis for hydraulic conductivity and river conductance was performed using normal distributions under 100 realizations. The results show that return flows from irrigated lands and seepage from the Zayandehrood River form significant components of the water budget, while boundary conditions play a minor role in the total mass balance.
  • A non-hydrostatic free surface 2D vertical model usingdiscrete singular convolution (DSC) method
    M. M. Namin, K. Motamedi Pages 95-108
    This paper is an extension for the efficient implicit two-dimensional vertical model presented by previous investigators for simulating unsteady non-hydrostatic free-surface flows. Discrete singular convolution is used in order to improve the accuracy order of spatial derivatives. However, the conventional projection method only uses adjacent cells’ values (as a second order finite volume scheme), DSC method employs function values over a band width of cells. Besides, second order Runge Kutta approximation is used to improve temporal accuracy. The DSC method is used for free surface flows and gravity current for the first time. Comparison between this extension, conventional projection method and experimental observations shows that the DSC method has improved gravity current velocity prediction.
  • M. Karamouz, M. Imani, A. Ahmadi, A. Moridi Pages 109-121
    In this paper a probabilistic optimization model for determining flood management options is presented. The proposed model minimizes flood damages and costs based on optimal flood management options such as structural, non-structural, emergency and permanent actions in a probabilistic framework to consider risk in decision making. In the optimization model different discharge-elevation-damage-probability curves are used as the inputs which are developed based on routing floods with different return periods. The proposed methodology is applied to the Sefidrud river in the northern part of Iran. In this study, the HEC-RAS model is used for hydraulic routing of floods with different return periods along the river considering different types of flood management options. The estimated flood damage is the basis for comparing different options and determining appropriate actions. The results demonstrate the integration of various options in flood damage reduction and show the high potential of this approach in floodplain planning and management. The results also show the significant value of using the probabilistic approach in flood management and its applications in decision making.
  • M. H. Arslan, F. G. Gulay Pages 123-127
    Precast industrial plants in Turkey experienced considerable damage during the recent earthquakes in Turkey. The presented paper is based on a parametric study to evaluate the seismic performance of a code-designed moment-transferring scarfed connection that is widely utilized in precast industrial buildings in Turkey. Firstly, the seismic behavior of a typical symmetrically pitched double-bay precast framed system with a scarfed beam to the column connections was investigated. The coefficient of elastic rotational stiffness, Rθ, and maximum stress values were then obtained by finite element idealization with an approach of a repeated analysis. Finally, a parametric study was carried out for different values of Rθ in order to evaluate the effect of joint elasticity on the behavior of a precast frame under seismic action.
  • J. A. Zakeri Pages 129-132
    High-speed railway tracks require high quality track and accurate maintenance, but rail irregularities in main lines are inevitable. These irregularities are important sources for dynamic excitation. For the safety of trains at higher speed, the size of irregularities must be limited. In this paper, according to the Railways Standards, the wheel load reduction (WLR) ratio is introduced. Based on this ratio, the limitation for rail irregularity size is presented. Dynamic responses of track due to “V” shaped irregularity and rail corrugation is treated. A case study of rail corrugation is presented by real data measured from the Northeast district of Iranian railways.