Scientia Iranica
Volume:20 Issue: 1, 2013

A linear elastic layer of finite thickness bonded on a half-space each containing a transversely isotropic material is considered. A rigid circular disc attached to the interface of these two domains is considered to be affected by a rocking vibration of constant amplitude. With the aid of a scalar potential function, the equations of motion in each domain are solved using Fourier series and Hankel integral transforms. Because of the involved integral transforms, the mixed boundary value problem is changed to dual integral equations; which are reduced to Fredholm integral equations. Because of the complex integrand function existing in the dynamic case, analytical solution cannot be given in general. However, a closed-form solution is introduced for the static case, which itself degenerates to the solution for an isotropic case existing in the literature. The contact stress in between the rigid disc and the surrounding media, and the related impedance function are analytically determined in the static case. With the help of contour integration, the governing Fredholm integral equations are numerically evaluated in the dynamic case. The dynamic contact pressure and the impedance function are numerically evaluated in a general dynamic case. The shape induced singularity in the contact pressure is investigated in detail. Some numerical evaluations are given for different transversely isotropic materials to show the effect of anisotropy.

Land use/cover change detection is very important in the application of remote sensing. In the case of Synthetic Aperture Radar (SAR) acquisitions for change detection, the standard detector or change measure is based on the ratio of images. However, this measure is sensitive to the speckle effect. In this paper, we improve change detection methods using a new change measure. The measure uses a grey level gradient or intensity information and the fractal dimension. The proposed measure is partitioned into two distinct regions, namely, changed and unchanged, using some change detection methods like Support Vector Machines (SVM), Fuzzy -Means clustering (FCM) and artificial neural networks with a back propagation training algorithm. Experiments over the study area show that the results of implementing change detection methods are improved by using the proposed measure, in comparison to the classical log-ratio image. Also, results prove that the measure is very robust to the speckle effect.

This paper presents a scheme where the cubic -spline method is developed for Multi-Degrees-Of-Freedom (MDOF) systems. In the proposed approach, a straightforward formulation in a fluent manner was derived from the approximation of the response of the system with a -spline basis. In this way, there is no need to use a special pre-starting procedure to commence solving the problem. A simple step-by-step algorithm is implemented and presented to calculate the dynamic response of MDOF systems. Stability and accuracy analyses have been done in this paper. The results of the accuracy investigation were compared with some other state of the art methods. Actually, this method lies in cases of conditionally stable methods. The validity and effectiveness of the proposed method is demonstrated with two examples.

This paper summarizes observations made in the field, limited tests performed in the laboratory and analytical evaluation done on various forms of semi-engineered roof deck systems. The paper also highlights some of the critical issues involved in the design of semi-engineered roof deck systems subjected to high velocity winds.The roof structures of typical semi-engineered residences in countries such as India and Belize are believed to be able to resist the effects of severe winds. However, relatively recent cyclonic events have demonstrated that roof systems of the types typically built in Belize and India are indeed among the most vulnerable major component of semi-engineered buildings under high velocity winds. This paper highlights just how vulnerable the various components of these roof systems are to high velocity winds. The paper, sequel to a previously published paper, is partially based on work done in connection with a doctoral dissertation being undertaken by the primary author Thurton [1]. The paper includes some general results of some investigations done based on building techniques utilized in the construction of roof systems in urban communities of Belize and parts of India.

Grey relational degree analysis has been successfully adopted in various fields, but the existing grey relational analysis methods cannot deal with the three-dimensional panel data. In this paper, based on the grey convex relational degree for two-dimensional data and an approximation of the Hessian matrix for a discrete sequence, we propose a novel Grey convex Relational degree for the three-dimensional Panel Data (GRPD), which uses the similar characteristic of convexity among relevant factors to measure relational degree. An example of evaluation sustainable development is given to illustrate that the GRPD can more fully reflect the correlation degree among relevant factors.

In this article, the dynamic responses of a Timoshenko beam subjected to a moving mass, and a moving sprung mass are analyzed. By making recourse to Hamilton’s principle, governing differential equations for beam vibration are derived. By using the modal superposition method, the partial differential equations of the system are transformed into a set of Ordinary Differential Equations (ODEs). The resulted set of ODEs is represented in state-space form, and solved by means of a numerical technique. The accuracy of the results has been ascertained through comparing the results of our approach with those available from previous studies; moreover, a reasonable agreement has been obtained. The quantities of the dynamic response of the beam for the case of moving sprung mass are confronted with moving mass and also moving load cases. Through extensive numerical campaign, it is concluded that with respect to the applied values of suspension system properties, the deflections of the beam subjected to moving load case are an upper bound for moving sprung mass results.

A new formulation for the dynamic stability of cracked columns is proposed. In this formulation, a differential equation governing the free vibration of a cracked column subjected to compressive axial force is derived. The solution of the proposed equation needs only the end conditions for its solution (similar to that of intact beam columns). The equation is solved using the Laplace Transform. Both conservative and non-conservative forces are considered. The closed form solution is then used in the dynamic stability investigation of the cracked column with different boundary conditions. The accuracy, efficiency and robustness of the work are verified through numerical examples.

In this paper, the Charged System Search (CSS) algorithm and the force method are used for the simultaneous analysis and design of structures. Supervisor agents are introduced for the optimization procedure to enhance the exploration ability of the CSS. The presented method is applied to the design and analysis of some planer and space structures. A new formulation is presented for the objective function, and the accuracy and efficiency of the presented approach is examined by comparing the resulting design parameters and structural weight with those of other methods from literature.

The aim of this study is to investigate whether MRF steel structures that have been designed based on seismic codes, are able to resist progressive collapse with damaged columns in different locations under seismic loading.For this purpose, 3-D and 2-D push-over analysis of structures is carried out. The progressive collapse potential has been assessed in connection with 5 and 15-story buildings with 4 and 6 bays by applying the alternate load path method recommended in UFC guidelines.Member removal in this manner is intended to represent a situation where an extreme event, such as vehicle impact or past earthquake shock or construction error, may cause a critical column, as a result of local or global buckling, to lose a part or whole of its load bearing capacity.In contrast with 3-D models, two-dimensional frames represent a higher sensitivity to base shear reduction and element removal. In the case of middle column removal, the structure is more robust than in a corner column removal situation. The influence of story number, redundancy and location of critical eliminated elements has been discussed.

In this paper, a multi-objective optimization for the optimal design of sliding isolation systems for suppression of seismic responses of building structures is presented. Due to the presence of several parameters affecting the performance of sliding base isolation systems, applying a rigorous multi-objective optimization technique is inevitable. Hence, in this study, the genetic algorithm is used to find optimal values of isolator parameters, including coefficient of friction, mass of base raft and the damping ratio of the restoring force device. The restoring device, which is composed of a linear spring and a linear viscous damper, is attached to the base raft in order to minimize the during-event and after-event sliding displacement of the base raft. The simultaneous minimization of the building’s top story displacement and its acceleration, and also the base raft’s displacement, are considered as the objective functions. In order to satisfy the objective functions, a fast and elitist Non-dominated Sorting Genetic Algorithm (NSGA-II) is used to find a set of Pareto-optimal solutions. The isolated building is modeled as a shear-type structure having one lateral degree of freedom at each story level. A ten-story building is used for the numerical study and an ensemble of seven earthquake records is considered for the analysis. The results indicate that by applying the final design parameters obtained from the optimal values found by the NSGA-II approach corresponding to each individual record, the sliding isolator system effectively suppresses the structural seismic responses. Also, it is found that the restoring device with an optimal viscous damper might slightly reduce the performance of the isolation system, but is strongly effective in controlling the maximum base raft displacement and the residual base raft displacement.

Modeling flow discontinuities, due to a numerical approach, often pose severe challenges. In this way, a number of techniques like artificial viscosity (particularly for finite difference methods), shock fitting and etc. have been proposed. These techniques usually require ad-hoc terms which need to be adjusted through calibration. In this study, an efficient numerical model based on a shallow water equation is developed. The model uses a first-order centered (FORCE) scheme, in combination with the Surface Gradient Method, (SGM) for spatial discretization, and the third order Runge–Kutta algorithm for time integration. At first, it is demonstrated that the model is well-balanced, then, through several classical examples, such as a 1D dam-break on both dry and wet beds, transcritical flow over a bump, with and without shock, sub-critical flow over a bump, circular dam-break, small perturbation propagation, dam-break on a dry bed channel with varying widths and right-angled channel junctions, it is shown that the model is capable of capturing flow discontinuities. Furthermore, the model can simulate dry bed conditions, and also presents smooth symmetric results.