Civil Engineering Infrastructures Journal
Year:2011 | Volume:45 | Issue:2|Papers Count:13

The aim of this paper is to present scalar potential functions for three-dimensional elastodynamic problems in transversely isotropic media defined by different cylindrical coordinate systems. To do so, the standard cylindrical coordinate system, elliptical cylindrical coordinate system and parabolic cylindrical coordinate system are considered. By virtue of Poisson’s representation, Lame solution and Chadwick-Trowbridge, the completeness of such representations is addressed. The representations given here are useful in the study of wave scattering from the circular, elliptical and parabolic edges.

In this Paper, the stiffness matrix of frame element with random material property (elastic modulus) is derived. Then, the relation between forces and displacements is presented and expansion of the obtained matrix is carried out using Taylor series. The result of this expansion is the mean values and Variability Function of nodal displacements.

In this paper a new method for nonlinear analysis of three dimensional reinforced concrete frames (3D-RCF) under cyclic and monotonic loading is proposed. Each reinforced concrete frame is divided into two types of joint and beam-column elements. The effect of bond-slip has been considered in the formulation of beam-column element. The effect of biaxial flexure and axial load on the cross section is assumed for nonlinear behavior while the effect of tensional behavior of beam-column element is assumed linear. The pull-out effect of reinforcing bar is considered in the formulation of joint elements. Formulation and relevant equations are displacement based upon which a computer program is developed. The reliability of the method has been assessed through the comparison of numerical and an experimental result by achieving of excellent agreement. Also the effect of bond-slip and bar pull-out occurring at joint on the response of RC frames is evaluated by utilizing various analyses.

Nowadays, water supply utilities in many parts of the world are concerned about water supply. Climate change, drought and population growth as well as immigration, are the most important factors for this situation. Because of limitation for availability of treated water, supplying healthy water even in areas with wet climate is difficult. In encounter with this challenge, reducing water losses in both trunk mains and distribution systems can be a temporary solution. In this research, a novel leak detection technique based on Frequency Response Method using transient flow analysis is presented in order to leak detection in water supply systems. In this method, in order to leak detection and location, steady-oscillatory flow in a pipe system, is generated by the sinusoidal maneuver of a valve in downstream of pipe and is analyzed in frequency domain with matrix transform. It is shown that leak presence in pipe, changes the shape of pressure frequency response. Pressure oscillation amplitude in even harmonies increases and in odd harmonies decreases. By this property, location of leak can be determined. Reliability of other methods depends on large amount of measured data in different parts of the system. The presented method, need to measure pressure and discharge data just in the location of valve. As an advantage of this method, leak discharge can be determined. By an example, the proposed methodology is evaluated and its advantages and disadvantages are distinguished.

Steel shear walls that are used in two (thin and stiffened) forms, are innovative systems for resistance against wind and earthquake lateral loads. The thin type of steel shear wall has recently attracted the researcher's interests. A major problem in the design of steel shear wall is the design of its supporting columns. This paper presents the laboratory test results on the investigations on the effect of stiffness of columns on the behavior and performance of thin steel shear wall. Accordingly four two-story one-bay half scale test samples of steel shear walls in which they differed only in the column properties, were tested under cyclic loading. Test results show that although the load carrying capacity, deformability and stiffness of the steel shear wall, increase due to increase in columns stiffness but these properties are not proportional to the stiffness of supporting columns. It was also observed that the steel shear walls are very much ductile /deformable and have high energy absorbing capacities.

In this paper, the Finite Element Model of a typical bridge bent has been created. The 3-D eight-node solid element with the ability of the consideration of concrete cracking in tension and crushing in compression has been employed for the modeling of concrete and the uniaxial tension–compression two-nodes element has been used for the modeling of longitudinal reinforcement. The transverse reinforcement has been included as the concrete element volumetric ratio. For the composite material modeling, the 3-D eight-node laminated element has been used to represent the layers of the material. First, the bridge bent has been modeled in the as-built as well as the retrofitted condition. The numerical analysis results are compared with previously reported experimental results. Good correlations between the numerical and the experimental results have been observed. With the consideration of the observed modes of failure of the composite materials during the experiments, some suggestions have been made here in order to improve the lateral load capacity as well as the ductility of the bent system. This consists of the use of appropriate addition of composite materials in various proposed ways and configurations at the junction of the column to the bent beam connections. Analysis results demonstrated that both the lateral load carrying capacity and ductility of the bridge bent will improve considerably with the aid of the suggested methodology.

In this paper, the effect of bedrock inclination on seismic performance of slopes is investigated. The study was conducted based on dynamic analysis of different slopes, evaluation of the earthquake acceleration in sliding mass, and calculating the permanent displacement of the slope, using Newmark sliding block. The investigation indicates that variation of the bedrock inclination, which results in a change in the predominant period of the slope (Ts), in conditions that the mean period of the time history of the acceleration on critical sliding surface (Tmt) and Ts are close to each other, causes the variation of the acceleration magnitude and the Newmark displacement in the sliding mass and they may reach to their maximum level. Typical results are presented and discussed. A two dimensional model of a typical slope was considered and conducting dynamic analyses, the slope performance was studied for different geometries, strength parameters and shear wave velocities. Such a performance has been studied by assessing the record of acceleration in sliding mass (the mass above the critical sliding surface) and calculating the slope displacement using Newmark method. It is shown that neglecting the effect of bedrock inclination, would lead to non-real results in assessing the seismic slope performance.

For analyzing and assessing the seismic vulnerability of masonry buildings, it is necessary to specify the main structural properties of walls such as stiffness, ultimate load bearing capacity, etc. Although micro modeling is essential in a brick wall, it is difficult and approximately impractical due to the pattern of arrangement of bricks and bed and head joints of mortar and their large quantity. In macro modeling, masonry materials are replaced with an equivalent homogeneous material. In the present research, a set of analytical equations was established for determining the mechanical properties of this equivalent homogeneous material. The results of the proposed method for homogenization of unreinforced brick walls were compared with those of detailed modeling in different situations of solid walls under in-plane loading, and it was found that this method provides suitable accuracy in estimation of the wall linear properties such as stiffness and the wall nonlinear properties such as ultimate strength. Additionally, this proposed modeling method is simple and quick and needs very little input data.

The purpose of this study is to determine the dynamic response rod embedded piles in transversely isotropic media under vertical excitation. To do this, hybrid element method has been used in which embedded structure, pile, has been simulated by using rod finite element and also radiation elements have been used for simulating infinite media around the pile. To determine soil-pile stiffness matrix we assemble dynamic stiffness matrix of the finite elements derived from continuous solution with the soil stiffness matrix determined by the inversion of compliance matrix taken from radiation element solution. Finally this matrix is condensed in term of defined degrees of freedom on top of the pile so that the pile impedance in its junction with superstructure in the form of complex number. By using parametric study on the number of elements, dimensionless frequency and aspect ratio, the convergence of impedance is evaluated and its accuracy is controlled by the previous studies of Novak and Liu.

During the past decade, there were a lot of studies on the effect of energy dissipating devices such as dampers for controlling structural response in earthquake. Using a suitable distribution of these devices may have extra advantages by minimizing torsional effects in buildings. This investigation deals with a comparison study performed between the experimentally observed and numerically predicted dynamic behavior of a 1.6 scale structure with viscous dampers. The setup consists of a one-story model with one-way stiffness asymmetry which is connected to a rigid base structure by two viscous dampers. Both structures were located on the shaking table and the tests were conducted using 6 earthquake records. Several damper distributions have been considered and for each one, lateral displacement, lateral acceleration and diaphragm torsion of the model were recorded. The separate tests on dampers show that their dynamic properties are completely dependent on frequency and amplitude of the motion. The comparison between the experimental and numerical model shows an acceptable similarity in the response time histories. The results indicates that asymmetry effects on lateral displacement is minimized if the damping center is located at a distance equal to stiffness eccentricity in the opposite side of stiffness center with respect to the center of mass. Also, if the damping center is located near the center of mass on the flexible side with a high damping radius of gyration, diaphragm torsion is minimized. No suitable distribution was found for controlling lateral acceleration in this research.

During the past decade, there were a lot of studies on the effect of energy dissipating devices such as dampers for controlling structural response in earthquake. Using a suitable distribution of these devices may have extra advantages by minimizing torsional effects in buildings. This investigation deals with a comparison study performed between the experimentally observed and numerically predicted dynamic behavior of a 1/6 scale structure with viscous dampers. The setup consists of a one-story model with one-way stiffness asymmetry which is connected to a rigid base structure by two viscous dampers. Both structures were located on the shaking table and the tests were conducted using 6 earthquake records. Several damper distributions have been considered and for each one, lateral displacement, lateral acceleration and diaphragm torsion of the model were recorded. The separate tests on dampers show that their dynamic properties are completely dependent on frequency and amplitude of the motion. The comparison between the experimental and numerical model shows an acceptable similarity in the response time histories. The results indicates that asymmetry effects on lateral displacement is minimized if the damping center is located at a distance equal to stiffness eccentricity in the opposite side of stiffness center with respect to the center of mass. Also, if the damping center is located near the center of mass on the flexible side with a high damping radius of gyration, diaphragm torsion is minimized. No suitable distribution was found for controlling lateral acceleration in this research.

The information content of satellite imageries as a mean for providing usable data for disaster forecasting and management, management of natural sources, remote sensing and photogrammetric applications has attracted the worldwide attentions during the last two decades. Since geometric correction of these images is the first and a crucial step for using them, a great deal of research efforts has already been focused on the subject worldwide. Two main approaches are used for geo-referencing of linear array imageries. The first approach is the so called rigorous model. This approach is based on the physical modeling of the motion and attitude variation of the imaging sensor during the acquisition time and is the most accurate and precise model for geometric correction. This model is based on the so called collinearity condition equations and needs the sensor calibration data and the orbital parameters of the satellite, which is not always accessible due to security and economic restrictions. The second approach, known as generic, is independent of any metadata information and solely relies on the ground control points. Varieties of generic models, from rational functions to simple DLT, are in use. However, the great difficulties with these approaches are their dependence on large number of well distributed GCPs. The most precise generic model which is used as a substitute for rigorous model is rational function model (FRM). It has been shown empirically that RFMs in terrain independent mode, which is calculated by fitting the rational function coefficients to the rigorous model, approaches the accuracy of rigorous model. Nevertheless, a very interesting parametric approach, which uses simple 2D to 3D affine transformation, has been experimentally proven to be very promising. This approach has been already evaluated by different researchers worldwide and reasonably accurate results in both flat and hilly terrains have been reported using only few numbers of GCPs. The theoretical basis that justifies the achieved accuracy is the fact that with the high resolution satellite images the very small camera field of view and the high flying altitude makes the incoming signals almost parallel. This renders the perspective geometry along the scan lines to approach the parallel geometry and effectively a homogenous geometry in the scan line and the direction of the satellite motion is produced. This particular geometry provides a simple linear relationship between the image space and the object space and makes a simple eight parameters affine transformation optimum for geo referencing applications. Simplicity of the formulation (i.e. only eight affine parameters for the entire scene and linear form of the equations), and also few numbers of required GCPs and the achieved accuracy makes this approach very attractive from the mapping point of view. The main intention of this paper is to evaluate the potential of the 3D affine transformation as applied to the Cartosat-1 images by implementing an approach which is independent of the field measurements. This is achieved by fitting the affine transformation parameters to the supplied rational function coefficients. Since this approach is not restricted to the field measurement for generating GCPs, a more realistic evaluation of the nature and the limitations of the affine transformation are achieved by generating well distributed fictitious GCPs. Other related issues such as the earth curvature and the influence of the terrain topography are also discussed and analyzed.