Year:2004 | Volume:38 | Issue:2 (84)|Papers Count:14

In this study, we have proposed a mathematical Programming model for the tactical planning of freight railways, which addresses the train Formation Problem. This problem results in a multi-commodity network flow formulation that contains both integer and continuous variables. The modular structure of the statement allows consider the special conditions of the network under study and to testing various operating policies.In this paper, the model developing process is described using a simple hypothetical network. Finally the results are represented and interpreted. Some of the model outputs are the economic train size, high priority costs, and the formation plan for the freight trains.

In this paper, some parameters affecting the dynamic behavior of cantilevered truss bridges under earthquake loadings are studied. For this purpose, Three bridges, each with three spans of 360, 552 and 744 meters have been designed according to AASHTO. The effects of uniform and no uniform ground motions at all supports, wave propagation velocity, seismic input wave travel and coherency on the longitudinal direction are evaluated. The effect of spatial correlation in the transverse direction is not very important because of relatively smaller width of bridges. Therefore, in the transverse direction, uniform ground motions are considered at all supports. Three dimensional linear dynamic analysis of bridges under earthquakes are carried out using artificial spatial incoherent Gaussian seismic ground motions. The simulated ground motions satisfy a prescribed, or target local power spectrum and a target coherency function. No stationary characteristics are introduced by superimposing a time dependent envelop function. The simulated ground motions in the longitudinal and two perpendicular transverse directions have been considered simultaneously.

The run-up of long water waves traveling at high speed across the oceans is one of the most important factors in the design of a coastal structure. As a result, a number of empirical formulas, analytical results, and numerical techniques have been developed to predict the wave run-up elevation. The utility of these formulas and schemes depends on their ability to predict the wave run-up and their convenience of use. However, in the empirical formulas, the coefficients can not provide insight into the nature of the physical processes involved. But analytical asymptotic formulas, indeed could provide considerable insight into the process because, the parameter dependence is explicit in the coefficients. The first objective of this study is to generalize the wave run-up formulas for both periodic and solitary waves on composite (multi-slope) beaches using the linear shallow water wave equations. This task will be accomplished by expanding the existing solution of simple slope beaches for periodic and solitary waves.The second objective is to solve the linear shallow water equations numerically using finite difference method to check the validity of the derived formulas. A number of figures are presented showing a comparison between the analytical and numerical results.

Earthquake accelerograms are needed for dynamic analysis of structures. Preliminary data obtained from recording instruments may include some errors that their sources and values should be evaluated and corrected appropriately. In this study, at first step, earthquake recording instruments are introduced and explained. Then the noise (error) sources of accelerograms and processing methods of earthquake data are reviewed. Filtering techniques are also assessed from the view point of Earthquake Engineering. For this purpose, different methods for the determination of correction frequency are reviewed and finally the standard w-2 model introduced by Brune (1970) is selected. In this study, 78 earthquake records are selected from Mahdavians study. In this selection, two parameters are considered:(1) Causative earthquake of the record and(2) The soil type of at recording station. A computer program is developed to calculate Fourier amplitude spectra of three recorded components and to plot them. By comparing the calculated spectra and the standard w-2 model, correction frequency is determined and then records are corrected using SWS processing software. Effect of different parameters like magnitude, epicenter distance and local site conditions are evaluated. Correction frequencies are estimated and Fourier amplitude spectra are plotted before and after the correction. Finally, several correction frequency bands are presented for different site conditions of recording stations.

In many practical measurements, the compressive strength, fc, of standard cubic or cylindrical specimens are considered as actual strength of concrete used in structural elements. However, there are numerous parameters which cause the standard compressive test not to represent actual strength of castled materials, e.g. concrete casting, environment and curing conditions, vibrations and so on. The mentioned difference is, more remarkable in shot Crete which is used in 3D light weight sandwich panels. In this system the thickness of shot Crete wythe is about 50 mm which is minimum based on ACI recommendation for provision of core specimens. The presented work tries to show the estimation of compressive strength of standard cylinder and concrete cores taken from 3D standard elements in 60 specimens and, also, to manipulate experimental relations between these two methods. The current study is concluded with a reduction factor, which shall apply to the standard cylinders strength, fc , as to achieve the actual compressive strength.

The Phenomenon of wave-induced liquefaction has arrested increasing attention in recent years in considering the integrity of near shore and offshore installations such as pipelines, anchors, platform structures and breakwaters.There are two different mechanisms for wave-induced liquefaction, namely transient and residual liquefaction, depending on the way the excess pore pressure is generated. The former is generated by the transient or oscillatory nature of the excess pore pressure which occurs periodically during a storm responding to wave. The latter which is caused by the residual or progressive nature of the excess pore pressure occurs after a certain cycles of waves. This paper presents a procedure for analysis of wave-induced residual liquefaction. A model for generation of pore water pressure is used and effect of simultaneous dissipation is included in the analysis. In this model the shear stress is calculated for a seabed of finite thickness by use of an analytical approach. Then the governing equation for the generation and dissipation of pore water pressure is formulated and solved by a numerical method. This solution is validated with the analytical solution of the simplified cases and it is also compared with the undrained analysis. Then the effects of several pertinent wave and soil parameters on the liquefaction potential are examined in detail. This procedure is for free field conditions however it can be used as a first approximation in the presence of structures.

Elastoplastic models which have been developed in critical state framework show good capability in predicting soil behavior. In this paper, the effect of state parameter on improving the prediction of an elastoplastic constitutive model in state boundary surface framework has been studied. The original model, because of not considering the state of soil, can be used only for a small range of stresses and void ratios for which the model has been calibrated. After evaluating and finding the deficiencies of the model using experimental results, it is modified to consider state of the soil. Evaluation of modified model shows that consideration of state of soil in the model has significantly improved its capability in predicting soil behavior.

The nonlinear behavior of single bay, single story frames composed of the castellated beams has been investigated by means of the finite element analyses of detailed models of sample frames under a combination of vertical and horizontal loads. The frames consisted of castellated beams of various lengths (number of castellation). At the same time, two different types of columns have been considered (battened columns as well as the solid web columns) and their lateral deflection behavior have been compared. In addition to the frames consisting of single castellated beams, frames with double castellated beams with the by-pass type of connections have also been studied. Both traditional and strengthened by-pass connections have been discussed. The effects of the initiation and penetration of plasticity, the formation of the vierendeel type of mechanism and the lateral - tensional buckling of the web-post have been investigated, in particular. A comparison of the results obtained from the finite element studies with the previous tests carried out by the first author, indicates close agreement, which demonstrates the effectiveness of the finite element analyses procedures adopted in the estimation of the nonlinear behavior of such frames.

In this paper a new anti-hour glassing mode stabilization procedure is presented for the heptahedral finite elements. An explicit dynamic large deformation elastoplastic framework is used to implement the one point quadrate heptahedral element. The element is designed to perform well for the analysis of composite plates and structures where multiple cracks without any predefined direction are expected to occur. The stabilization procedure is based on the standard assumed strain method previously developed by Simo, Belytchko and others. Several numerical simulations have been carried out to verify the developed algorithm and to assess the performance of the element.

Its about one decade that the technique of reinforcing soil slopes with vertical geosynthetics has been presented. Many theoretical and experimental studies have been performed in these reinforced geotechnical structures. In the reported experimental works on vertically reinforced soil slopes, arching phenomenon has been observed and reported. Theoretical studies have indicated that the consideration of arching effects increases the safety factor against failure, significantly. In this research the arching effects in both horizontal and vertical directions in the vertically reinforced slopes are considered by the use of common approaches of soil slope analysis. At first, the shape and position of three dimensional slip surface are determined by consideration of arching effects and then the safety factor is calculated by the conventional limit equilibrium method. In this method, uniform surcharge on the crest of slope, pore water pressure and the horizontal pseudo statically seismic loading can be considered. By considering the arching, the failed wedge is smaller, so with controlling both the size of wedge and safety factor, it is possible to reach the optimum design for slopes with vertical geosynthetic reinforcements.

Accurate analysis of pierced shear walls by FEM needs many small elements in the domain of the structures because of openings existence. On the contrary, by modeling this structure with BEM, it is only necessary to discretize the boundaries which are less than the domain.In this paper, DRM/BEM is used for calculation of natural frequencies of shear walls (especially pierced shear walls). Through this application, several radial basis functions (RBF) are considered. Then an RBF is proposed which has more accuracy in finding natural frequencies. The accuracy of the results are compared with solutions obtained based on FEM as bench marks. In conclusion, by parametric studies some wrathful points are proposed.

Scouring is a two phase flow and has been experimentally studied. Culverts are used to transfer the flow from one side of roads or banks to the other side. This experimental work is conducted to study the scouring down stream of a pipe culvert. The scour hole properties is a function of various parameters like: discharge, height of drop, tail water depth, diameter of the pipe and sediment size. In this study, variations of scour hole dimensions, and changes of the ridge caused by scouring were correlated to: pipe diameter, drop height, dens metric Froude number and tail water depth. It was observed that depth and width of the scour hole and the height of the ridge increase with the increasing the pipe diameter, but the length of scour hole decrease. Moreover, it was observed that increasing the tail water depth, width and depth of the scour hole decrease, but the length of scour hole and height of the ridge increases. In addition, with increasing the drop height, depth and width of scour hole and height of the ridge increase, but length of scouring hole decrease. The ratio of the scour hole dimensions and the height of the ridge to the drop height was related to Tw/D (tail water to pipe diameter ratio), SN (dens metric ّFroude number) and Hc/D (drop height to pipe diameter ratio).

One of the objectives of utilizing stepped spillways is to increase energy dissipation along spillways and consequently decreasing dimensions of stilling basins. This influences the economical evaluation of the design by reducing costs. The hydraulics of flow over stepped spillways has been investigated by many researchers for the last decade. These investigations have resulted in many hydraulic relationships. Several equations regarding head-loss and friction factor have been developed. Most of these equations are based on an average depth or consider a constant friction factor. In this study, the most effective hydraulic variables have been considered to obtain a general relationship for the friction factor and used in the calculation of water surface profiles along stepped spillways. This relationship has been calibrated by using experimental data and a nonlinear optimization technique. Accuracy of the obtained relations have been evaluated by comparing their results with real ones.