Year:2008 | Volume:42 | Issue:4 (114)|Papers Count:14

In this paper a method is presented in details to solve a nonlinear partial differential equation which has many applications in engineering fields. The boundary condition is mixed to be able to define the value of function on its variation on the boundary. Examples are given to demonstrate the accuracy and efficiency of the method.

In this paper, a FE-BE procedure is implemented for dynamic analysis of concrete arch dams, in the frequency domain. The technique relies on the finite element method (FE) for the discretization of the dam body, while the foundation rock is handled by the boundary element (BE). Also, the well-known sub-structuring technique is applied to combine these two different methods. It should be emphasized that the usual method for calculating the required impedance matrix of the above mentioned boundary element is depended on the solution of a complex un-symmetric full linear system for each frequency, which is very time-consuming. This problem was remedied by an efficient technique in some previous works, especially in Tan and Chopra's work, which greatly reduces the computational time. In this efficient approach, the required impedance matrix is calculated merely for some excitation frequencies, called frequency stations. Then, the remained matrices are obtained by applying the polynomial interpolation, rapidly. The present approach is a modification of that procedure trying to have similar efficiency without imposing some limitation in any cases, contrary to the previous work. It should be noted that the prismatic canyon assumption was the great mentioned limitation in that work which is remedied by utilizing three-dimensional boundary element in the current study. Therefore, any arbitrary canyon shape could be considered as a foundation of the arch dams. Furthermore, a special purpose program is developed based on this new method and the response of the Morrow Point arch dam is studied as an example for some different cases. 

In the previous research, shape of concrete arch dams were modeled using quadratic and cubic polynomials along dams height, but in these formulations some details such as joints location, variable thickness starting points, abutments excavation, intersections of horizontal arches with sound rock and etc. were ignored because of the lack of parameters for dam geometry modeling. In the case of existence of inflection points in canyon shape, equations are inaccurate; consequently modeling the whole shape for more details is not possible. In this paper a new formulation using Hermite Spline equations for defining the geometry of double curvature concrete arch dams with parabola horizontal arch has been presented. In this model the geometry of the arch dam is created using 37 design parameters or as design variables in optimization process for future developments. In geometry modeling the details such as site topography triangulation, crown cantilever shape, horizontal arches, intersection of horizontal arches with sound rock, constant and variable thickness zones formulation has been developed carefully. One of the advantages of this new formulation is creating smooth and flexible shapes in comparison with Bofang’s cubic polynomials method. For three dimensional finite element analyses, three dominant loading cases have been considered. In order to considering the real construction conditions, Multi-stage grouting for dead load has been intended. For stress analysis in dynamic case the response spectrum method is used. For this purpose, a package has been developed. In order to design professional software, the object- oriented capabilities of FORTRAN90, such as: Module, Inheritance, Type, Dynamic arrays and etc. have been applied frequently. This software has automatic mesh generation for any canyon shape. In addition, this software package provides some useful information for geometry, finite element model and information for future optimization process. The developed software has been applied successfully for Shahid Rajaee arch dam. 

When the degree of saturation at intersection approaches one, Webster’s optimum cycle length equation becomes inapplicable, because the cycle length will becomes very big when the degree of saturation approaches one and will be fully unrealistic when the degree of saturation becomes greater than one. This is not a problem for HCM2000 method. But optimum cycle length calculation in this method has not specific equation and based on try and error to minimize delay time. Also this method requires many input parameters that made it expensive. In this paper new modified Webster’s optimum cycle length equations for some specific situation of geometric and phasing based on HCM2000 method have been presented that have not described problem. The purpose of this paper is ability to use of “total lost time within the cycle (L)” and “the sum of critical phase flow ratios (Y)” parameters and creation new minimum cycle length equation based on HCM2000 method. Regarding to this fact that intersection geometry and phasing is related to the optimum cycle length, four situations of intersection have been considered. After this stage the following step by step procedure was used: - having low traffic volume and low “L” - using “HICAP2000” software to calculate optimum cycle length-also using Webster’s equation to calculate optimum cycle length-increasing traffic volume and repeating the above steps-the above steps continue until degree of saturation at intersection approaches one-increasing “L” and repeating above steps - with renewed increased “L” and repeating above steps we have optimum cycle length for many of “L” and traffic volume at specific intersection After this method we used “SPSS” software to modeling new relationship between “L” and “Y” and finally new equations are presented for four situations of intersection. This method can be expanded for other geometry and phasing intersections. 

Breakwaters are the important and the costly ones of the marine structures. Composite breakwater is one of the common types in the world. Because of the progress in marine industry in Iran in recent years, designers have noticed this structure. Because of the sensitivity of composite breakwater to environmental conditions, also construction costs, difficulty of repair and maintenance and importance of structures on and behind the breakwater, design of composite breakwater must be very accurate. Estimation of optimum dimensions of composite breakwater in different hydraulic and geotechnique conditions of sea is an important problem for engineers. In this research with regard to a nonlinear wave field in front of structure, its dimensions have been optimized in various hydraulic and geotechnique conditions. The results of this research have been expressed in some applied graphs for optimum design of composite breakwaters. By using of these graphs designer can estimate optimum dimensions of structure in various conditions. So, a noticeable reduction in costs will occur. Additionally, results of this research can be used for attentively design of these structures in different environmental conditions of sea. 

Most of river engineering problems are complicated and need to be analyzed by three dimensional models of flow and sediment transport. Considering the fact that computers and numerical methods with great ability of flow and sediment transport simulation are developing quickly, using numerical modeling by engineers is inevitable. Nevertheless, before application, numerical models need to be verified in a wide range of engineering problems and their assumption should be clarified. This paper aims to investigate application of three dimensional numerical models in some complicated river engineering problems. To reach goals of this research, SSIIM2.0, which is a capable model of 3D flow and sediment transport, has been selected. This model was deployed for some intricate river engineering problems and its results were compared with some available experimental and field data. Results of this paper show applicability and accuracy of 3D numerical models in a wide range of river engineering problem. 

One of the most important and effective factors in prioritizing high accident prone segments of roads for pedestrians is accident cause which up to now has been neglected in current methods. Since accidents are not additives due to various reasons, prioritizing these segments without considering the accident cause makes the selection of high accident prone segments inaccurate. In this paper, by introducing the "Cause prioritizing model", a new model was developed in order to rank high accident prone segments for pedestrians with regard to accident cause in rural roads. In this method, by taking the accident frequency, accident severity and accident cause parameters are accounted and using one of the Multi Attribute Decision Making methods, the mentioned segments are prioritized. Using the model developed in this research will increase the accuracy and utility of high accident prone segments prioritizing process for pedestrians to a great extent. 

One of the major purposes of optimization in civil engineering is to perform a suitable design for the structure. This goal has to fulfill technical criteria and contain the minimum economical costs. Building frames are of the most customary civil engineering structures. Therefore, optimization of these types of structures could be of a great concern from the economical viewpoints. One of the current obstacles in such optimization problems is the local convergence debility. Thus, using means of tackling this problem seems necessary. Genetic Algorithm which is one of the optimization methods inspired by nature, has overcome this problem. In order to solve such problems, genetic algorithm needs a multiple analyses of structures. Therefore, in this study attempts were made to introduce and embed new formulae into a newly developed program to handle new techniques for selection and mutation as genetic operations. As for the aspects of application, the introduced techniques were inspected and investigated in the optimization of some planar and special braced steel frames. The outcome through comparisons proclaimed a considerable decrease in numbers of analyses as well as significant increases in the speed of convergence. 

Due to the probabilistic nature and uncertainties of structural parameters, reliability-based optimization will enable engineers to account for the safety of the structures and allow for its decision making applicability. Thus, reliability-based design will substitute deterministic rules of codes of practice. Space structures are of those types that have an exceedingly high range of applicability aspects in civil engineering. Therefore optimization of such structures with great and considerable number of members will be economically wise. For this purpose, the optimization process could be carried out using various mathematical models. One such model is to minimize weight while considering elements failure probability as constraints. Another form is to minimize weight and then regarding the whole structure system reliability as constraint. The third type could be to minimize failure probability as well as its weight, while taking into account the structural system reliability as the constraint. In this research each of the above forms were studied and the results were compared. Also, apart from reliability considerations for the members, the reliability of nodes was also taken into account. Node failure means that node displacement in at least one direction exceeds that of the allowable value. As well the effect of various stochastic parameters such as load, yield stress, modulus of elasticity and cross section were studied. The stochastic parameters discussed in this study are statistically independent and possess standardized normal distribution. To avoid local convergence during the process of optimization, Genetic Algorithms is used as means of optimization. This study show that with increasing the members or system admissible failure probability, optimum weight of structure increases, but with increasing the coefficient of variation of load or yield stress, optimum weight increases. 

The characteristics of near-fault ground motion are investigated considering heterogeneous slip distribution on the fault plane. Areas on the fault plane with large slip in compare with the average slip on the fault are known as asperity. The characteristics of strong ground motions in near-fault area are strongly affected by faulting parameters such as asperity location, maximum slip of asperity, rise time and rupture velocity on the fault plane. Based on theoretical Green’s function for infinite media, the near-fault pulse is simulated for finite fault model with different faulting specifications. Then, the variations of each fault parameter and site to fault distance on near-fault pulse characteristics are numerically examined and discussed. 

In this paper, time-domain dynamic analysis of dam - infinite reservoir is studied. A numerical method, discrete singular convolution (DSC), which seems to be efficient and simple, has been used to model the mixed boundary conditions. After a brief introduction, DSC is applied to model the equation of motion of fluid-structure with constant cross section subjected to El-Centro (1940) earthquake. To show the accuracy and reliability of DSC method, the results have been compared with the Lee & Tsai method as a benchmark. The results show the competency of the proposed method to model Dam-Reservoir systems. 

Thin-walled hollow steel columns, either circular or box shaped, are commonly used as piers in bridges. Recent earthquakes, e.g. Hyogoken-Nanbu or Kobe 1995, on the other hand have shown that these columns are vulnerable to damage when subjected to earthquake loading. This paper presents a new innovative thin-walled hollow steel column fabricated of corrugated plates, “thin-walled steel columns with corrugated section”, primarily to be used as piers in bridges and other structures as an alternative to circular or box thin-walled steel columns. Compared with the traditional steel columns, this new innovative thin-walled steel column might improve buckling behavior under combined axial and flexural loading, caused by earthquake excitations. For investigating the seismic performance of this new innovative thin-walled steel column and comparison of it with traditional thin-walled steel column, a series of parametric 3D-finite element analyses have been executed. The analyses results have shown that thin-walled steel columns with corrugated section can undergo large plastic deformations without significant, strength reduction, hence dissipate energy under cyclic loading. 

Large deformation causing damage due to uplift force is generated in buried pipeline located in shallow trenches in marshes and saturated soils. In this paper, existing common methods of pipeline anchorage are discussed and considering advantages and disadvantages of these methods, a new method of pipeline anchorage are studied and presented. In this new developed method, geo-textile materials are used for anchorage of large diameter pipeline. Laboratory and field experimental study are developed and effective parameters are deliberated considering load–displacement curves. Finally, a field study on a 30" diameter gas pipe is performed to admit the laboratory tests. Considering the laboratory and field study results, the anchorage of pipeline using geo-textile is recommended for anchorage of buried pipeline in marshes and saturated soils.