Year:2008 | Volume:42 | Issue:6 (116)|Papers Count:16

Tailings dams, due to methods and materials used in their construction are vulnerable structures to earthquake. In many cases storage of water over tailings is required to prevent aerial pollution or reduction in water consumption by the means of a recycling system, therefore failure of these kinds of dams not only induce affects similar to conventional water dams, but also may lead to irreversible damage to their surrounding environment due to toxic content of tailings. Sarcheshmeh Tailings dam, a rockfill dam with an inclined clay core, is 70 m height and necessity for increasing reservoir capacity has led to dam upgrading to a minimum level of 90 m; using downstream method. Different options have been studied in order to get the safest and most economical alternative. Vulnerability of dam site to earthquake has considerably affected the design issue. This paper represents the results of dynamic and pseudo-static analyses of this tailings dam. Dynamic analysis is carried out using the finite difference code FLAC (Fast Lagrangian Analysis of Continua, ITASCA).This code is able to take into account pore water pressure generation during construction and earthquake. Different acceleration time history records and soil models are used and results have been compared.

Jacket platforms are the most common kind of platforms in the Persian Gulf. One of the most important loading conditions in the design of jacket platforms is the sea-state loading. A sea-state loading consists of the simultaneous effects of environmental loadings e.g. wave, wind, and current loadings. Generally, jacket platforms are designed and assessed for two levels of sea loads: design and ultimate levels. The design load level is basically utilized to design structural elements and satisfy standards requirements, while the ultimate load level is applied to evaluate the ultimate capacity of the structure. The ultimate-load level has traditionally been applied for assessing existing structures under ultimate capacity. In these structures, the overall performance of the structure is of interest and consequently the ultimate capacity of the structure is the main concern. However, earlier studies have indicated that applying two loading levels in design of new platforms may increase the reliability of the structure. In this study, these two levels are estimated for design of new jacket platforms in the South Pars Field. For this purpose, first, target probabilities of failure are assigned to platforms in different categories of exposure. The categories of exposure are defined based on the recommendations of API-RP2A. Target probability of failure for each category of exposure is suggested considering not only values recommended by accepted sources in design of jacket platforms but also by taking into account conditions surrounding South Pars Field. In order to evaluate the ultimate-load level, the probability of failure of a new jacket platform is defined as a function of total base shear. The direct relation between total base shear and probability of failure is basically valid for platforms installed in water depth less than 100 (m) and is applicable to the major part of South Pars field. Based on earlier studies, a simple parametric equation relating total base shear to wave height is used and the parameters are approximated analyzing actual platforms. Eventually, reliability analysis is utilized to estimate the ultimate sea-state loading level. In this study an estimate for design-load level is obtained by assuming/anticipating the reserve characteristics of platforms beyond the design level to the nonlinear regime. The anticipated reserve capacities of jacket platforms are suggested for platforms with different number of legs and brace types. Using these, the design load level is calculated for platforms in different categories of exposure. As mentioned earlier, the structural elements, e.g. members, joints, and piles should be designed for this loading level. By way of illustration of the proposed procedure, a jacket platform is designed using two levels of sea loadings.

An experimental study is conducted on three ½ scales, single-story, single-bay, frame specimens. The first specimen was a reinforced concrete frame with solid-brick infill. The second specimen was a reinforced concrete frame with hollow clay perforated-brick infill. The last specimen was a reinforced concrete frame without any infill. These three specimens were tested by pseudostatic method. Different response parameters are investigated and results are compared with those resulted from analytical approach. The results of the experimental and analytical studies indicate that use of masonry infill increases the lateral stiffness of the reinforced concrete frame. The increase in the stiffness is almost the same for both types of infill considered in this study. Use of masonry infill also increases the ultimate strength of the reinforced concrete frame. However, the strength of the frame in the case of hollow clay-block decays much faster in compare with frame infilled with solid clay-bricks because of a faster rate of failure in hollow blocks. Using masonry infill increases the energy dissipation capability of the reinforced concrete frame. In the case of frame with solid clay-bricks infill, a much more uniform distribution of damages is observed in columns. Comparisons with analytical approach show that analytical method provides a good estimation of initial stiffness of solid-brick infill but its estimations of initial stiffness of perforated-brick infill and inelastic response of both types of masonry infill frames are not in good agreement with the experimental results.

A water distribution network is one of the important parts of infrastructure systems. The efficient management and proactive planning of capital investment of these assets are fundamental for efficient and effective service delivered by water companies. The direct economic costs (i.e. rehabilitation investment, repair costs, water loss, etc.) as well as indirect costs (i.e. service and traffic interruptions, etc.) related to water pipe bursts are rapidly increasing. The ability to predict burst rate in pipes is an important strategic key in order to optimization of rehabilitation decision in water distribution systems. Most networks suffer from lack of enough and reliable data for bursts and failures. In this study basic variables which influence on pipes burst and burst statistical analysis have been identified and evaluated. Then common methods for burst predicting are discussed. In order to identify logical, useful and understandable patterns of breaks data, a data mining methodology named evolutionary polynomial regression (EPR) is described. Starting from a hybrid evolutionary strategy, EPR searches for patterns in data and returns symbolic expressions/models. This approach is demonstrated through a detailed case study. Required data were collected from the Mashhad Water Company which includes both asset and bursts data recorded for year 1384. The whole database was divided into 8 material/diameter classes (from 64 mm to 300 mm). The resulting models for burst prediction in different zones contain explicitly recognizable independent variables. The expression models confirm that pipe age, diameter and length are the most important variables leading to pipe bursts. Also the effects of pressure on pipe burst prediction were implicitly investigated. It was found that pressure is an important parameter which influences number of breaks in a pipe network.

Ballast as a part of the railway system plays an important role in the operation of the railways and also has a great impact on repair and maintenance activities. Hence most of the repair and maintenance activities in traditional railway systems are due to the defections in the ballast layer and therefore most of the maintenance budget is spent on repairing these defects. These repair and maintenance activities are usually very costly and time consuming and force the line to be closed for quite a long time. These kinds of problems led to the elimination of the ballast layer and the use of some other elements such as concrete slabs or beam in railways. The results show that the time and money needed for repair and maintenance of concrete slab tracks are much less than ballasted tracks, the technical and economical evaluations also confirm these results. In this paper technical and economical aspects of slab track systems were investigated with the help of national and international experiences and it was concluded that they are competitive solutions to the ballasted tracks in passenger railways.

Curls and curves of a shell interweave its various strain modes and link them together. This interactional behavior has yet frustrated all attempts for the construction of shell templates, which needs for an individual element test in traditional approaches. Such a test fails to work for shell elements and must be reconstructed. In this paper, it is tried to study shell interactional behavior and strain entanglements via a microscopic investigation. This new view to the shell behavior reveals a simple method, in which shell templates are constructed by partitioning the stiffness matrix of a sample shell element into its components. Surly, sample elements have been qualified for their convergence in practice. The method is examined for axisymmetric cylindrical shell element.

In this research, using the Modified Compression Field Theory (MCFT), a new truss based model is proposed to predict the behavior of reinforced concrete coupling beams with diagonal reinforcement. The model is able to consider the effects of shear and axial forces and bending moment, simultaneously. The proposed model includes a nonlinear shear spring, an axial spring, two inclined truss members and some nonlinear springs for considering bending deformations. The results of the proposed model were compared with several test results conducted by the authors and other researchers. The comparison shows that the proposed model can predict shear behavior of coupling beams, appropriately.

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 sensitivity of composite breakwaters to environmental conditions, also construction costs, difficulty of repair and maintenance and importance of equipments on and behind the breakwater, design of composite breakwater must be very accurate. Goal of present research is assessment of effect of environmental parameters in design of composite breakwater. In this way sensitivity of geometric parameters of this structure to hydraulic specifications such as period, height and direction of waves and depth of water, has been analyzed. Also effect of sea bed soil type in dimensions of this structure has been evaluated. Comparison between analytical and experimental formulas in evaluation of wave forces on composite breakwaters has been done. The results of this research have been expressed in some applied graphs for evaluation of effects of hydraulic and geotechnic parameters in dimensions of composite breakwaters. Thus results of present work can be used for attentively design of these structures in different environmental conditions of sea.

The existing theory for wave propagation through a soil layer are not compatible with the real soil layers because in the theory the layers are flat and the sub-layers are parallel, while in real the soil layers are not flat and they may not be parallel. Thus, wave propagations through a corrugated interface are so important. In this paper, two-dimensional SH-wave propagation through a corrugated interface between two linear transversely isotropic half-spaces is assessed. In order to do this, Lord Rayleigh's method is accepted to express the non-flat surface by a Fourier series. In this way, the amplitude of the reflected and transmitted waves is analytically determined in terms of the incident SH-wave amplitude. It is shown that except for the regular reflected and refracted waves, some irregular reflected and refracted waves are exist, and the amplitudes of these waves vary in terms of the angle and frequency of incident wave, equation of surface, and the material properties of the domains. The numerical computations for some cases of different amplitude/wave-length ratio of the interface are done. This work is an extension of Asano's paper (1960) for a more complicated interface, where more non-zero coefficients are considered in expressing the equation of surface in the form of Fourier series. The analytical results for some simpler case of isotropic domain are collapsed on Asano's results (1960). In addition, the numerical evaluation is in good agreement with Asano's.

Reinforced concrete structures are designed and used in major industrial projects. It has been seen that many of these structures experience early age damages. R.C structures in Persian Gulf region are susceptible to rebar corrosion and lose of serviceability. In spite of this sever condition, little researches on durability of R.C structures have been carried out. This research is discussing about chloride threshold value in a R.C structure using half cell potential method. This thesis has been done in two parts: Laboratory experiment and a field study structure. As a field study, we have investigated on R.C structure in Kish Island for threshold value. It was found that materials used in concrete had the initial chloride of 0.03-0.05% by weight of concrete. After removing the cover and sampling, chloride content at the surface of rebar were determined. Chloride content has been also measured in different depths according to ASTM C114. Carbonation depth was measured in a part of the structure. To avoid further removal of concrete, locations chosen for measuring the depth of carbonation is as the same as locations selected for determining the chloride content. Inspections show that carbonation depth in a special point is a function of its distance from the floor. The maximum carbonation depth is about 30mm. Comparing the results derived from these experiments, chloride threshold value at the basement of the hotel was estimated. Considering this special environmental condition, chloride threshold value was determined 0.07% by weight of concrete. It should be mentioned that this chloride value can not be used in other parts of this structure or in other structures.

The capability of sand constitutive models is remarkably improved by taking into account the effect of soil state in their formulations. In this study, it has been shown that considering the effect of soil state leads to better simulation of soil instability of shear banding type. To this aim, constitutive equations of a state dependent sand model are explained first. Consequently, the general conditions of instability and then, the special condition of instability with respect to the model formulation has been obtained. Using the result of a number of plane strain tests, the state dependent model predictions for shear band have been compared with experiment results. It has been shown that, predictions obtained from a similar model which neglect the effect of soil state are less favorable.

Tensile strength and ductility are the most important characteristics of High Performance Fibre Reinforced Cementitious Composites (HPFRCC). In this regard, parameters such as: type of fibre, properties of matrix and characteristics of their interface play the main role in the behavior of HPFRCCs. The effect of straight and hooked steel fibres on the mechanical properties of FRCs has been extensively investigated. However, only limited investigations have been done on the properties of cementitious matrices reinforced with crimped steel fibres. The aim of this study is to achieve a HPFRCC using crimped steel fibres. The performed activities in this investigation can be divided into three stages: to achieve a very dense cementitious material to be used as an appropriate matrix, to find the optimum shape of crimped fibre to be compatible with the matrix, and finally to obtain a cementitious composite (using the matrix and the fibres found in the previous stages) with high tensile strength and ductility. In the first stage of this study, 140 mixes were cast and tested. A workable mix with the compressive strength of 170 N/mm2 was selected for the following stages. To find an optimum shape of reinforcing fibres, pull-out tests were performed on single crimped fibres with different wave length and amplitude, embedded in the matrix. The length and diameter of fibres were 20 mm and 0.3 mm, respectively. Among the tested shapes of crimped fibres, 2 mm wave length and 0.4 mm wave amplitude were found to be the optimum values. Finally, in the last stage of the study it was found that the addition of 4% (by volume) the crimped fibres to the matrix produces a workable HPFRCC with tensile strength of 24 N/mm2 and fracture energy as high as 9500N/m (i.e. about 160 times larger than that of ordinary concrete).

A two-dimensional two-phase numerical model is developed to predict transport and fate of oil slicks which resulted the concentration distribution of oil on the water surface. Two dimensional governing equation of fluid flow which consists mass and momentum conservation was solved using the finite difference method on the structured staggered grid system. The resulted algebric equations were solved by use of ADI (Alternating Direction Implicit) technique. In addition the wind speed and coriolis effect can be included in the current hydrodynamic model. Transport of oil slick was pridect by the two dimensinal particle tracking approach consists of Lagrangian method for advection processes, the Random Walk technique for horizontal diffusion process and the empirical equations for the fate processes. Different processes are considered and included in the developed model which are: advection, spreading, turbulent diffusion, evaporation, dissolution, vertical dispersion, emulsification, shoreline deposition and adsorption by bed sediment. Oil is divided into eight hydrocarbon components so this model is capable of considering the oil composition of some fractions with theirs characteristics. Comparison of results with analytical solution for standard problems represents a good degree of similarity. In addition, model is used in a case of oil spill in Persian Gulf to represent the application of model to real case studies.

Development of a numerical model which describes launching of offshore jackets from barge is presented in this paper. In this model, in addition to capabilities of commercial softwares, water entry forces on jacket members and an implicit Newmark solution technique are included. The results are in general agreement with other numerical softwares available (SACS). Fluid forces acting on jacket and the importance of each one is discussed. It is observed that water entry forces on horizontal jacket members are very significant and may locally govern the design of these members. This force is more important for horizontal slender members near the mud-line, which do not experience significant environmental loading in operating conditions. Therefore the water entry impact force with large magnitude can cause over-stress and/or ovalling of near mud-line members. It is also observed that taking water entry forces in account modifies the jacket trajectory only in a little extent.