Civil Engineering Infrastructures Journal
Year:2012 | Volume:45 | Issue:5|Papers Count:11

In this research, application of some real-time operation methods on a single-reservoir system, Karoon IV, with decreasing sum of drinking, industry and agriculture deficit has been considered. These methods include standard operation policy (SOP), stochastic dynamic programming (SDP) and some types of operational rule curves with different orders of inflow and reservoir storage volume. To rank aforesaid, a multiattribute decision method, ELECTRE I, with combination of indices, objective function and reservoir performance criteria (reliability, resiliency and vulnerability) has been used. This ranking is accomplished in two different states including: (1) performances criteria and (2) objective function and performance criteria using the same weights for all criteria. Results show that rule curves were selected as the suitable policy in real-time operation and models validation has been presented by testing nominated curve for dry, normal and wet years.

Ties are designed and executed in order to prevent foundation mutual movements. According to the regulations of Iran and NEHRP, ties are designed for 10 and 25 percent of the greatest axial force (tensile and pressure) in either columns of two ends of ties, respectively. The question arising here is that how can ties be designed according to Iran and NEHRP regulation for a percentage of maximum axial loads of surrounding columns. To what stage of loading is their function effective to prevent relative settlement? When will plastic joints be formed? And finally for which forces should tie be designed in order to prevent formation of plastic joints? In these research 8 individual footings models together with linking tie were analyzed under nonlinear analysis in ANSYS software. For a better perception of effective parameters in tie designing, the changes of axial forces maximally between two columns (column bases) to the force of tie designing as well as relative settlement of tie were investigated in the following three conditions: 1-Studying horizontal distance of two Individual footings. 2- Studying the effect of type of soil in analysis of individual footing. 3- Studying the effect of gravity load in analysis of individual footing. It is obvious that by analysis of finite element models and studying their relative settlement we can evaluate the function of tie and answer the issues raised to some extent.

In order to study the effect of multi-support excitation of Earthquake Ground Motion on the seismic response of embankment dams, the dynamic response of the Masjed Soleiman earth dam is analyzed. In this research, the Spatially Variation of Earthquake Ground Motion (SVEGM) is introduced by ten different models. Consequently, the stochastic SVEGM model which accounts for both incoherence and wave passage effects is used to specify the non-uniform earthquake excitation. Based on the analysis results, the normal and shear stress distributions as well as the shear strain distribution and their maximum values on the dam body were estimated. Totally, the results of this research indicate that the distribution of stresses, strains and displacement in upstream-downstream direction of dam body increase by increasing the non- uniformity of the input excitation. This increment, which is depended to the number of uniform zone and is independent from the different coherency models, is almost between 50-180 per cent.

In order to simulate the bed scouring around piers, many researchers have developed sophisticated numerical algorithms. In this work, the numerical modeling of souring around cylindrical piers are performed by solution of the shallow water equations flow and depth averaged turbulent model equations coupled with the empirical relations for cohesive and granular beds. The shallow water flow equations include to the depth average continuity and motion and depth average turbulent model equations in horizontal Cartesian coordinate systems. For computation of bed erosion at each time step, the numerical results of turbulent flow model are combined with SRICOS empirical bed erosion empirical relations, which are derived from laboratory experiments. The governing partial differential equations of depth average turbulent flow are converted to discrete form using a vertex base finite volume method suitable for triangular unstructured meshes. Therefore, scouring due to flow around piers with arbitrary shape can be modeled. Several test cases of scouring on the cohesive and sandy beds around circular piers are modeled using the developed numerical model and the computed results are compared with the laboratory measurements reported for scouring in cohesive and granular bed around circular piers by the previous experimental workers. Despite of the simplicity and light computational work load of the introduced algorithm, the computed results show promising agreements with the anticipated trends.

The time dependent material behavior is of particular importance in the study of the behavior of boxed girder prestressed concrete bridges. The stage by stage balanced cantilever method of construction of segmental bridge contributes further in their time dependent performance. In this work, in order to study the performance of cantilever prestressed concrete bridges in a time - span of 35 years, an attempt has been made to account for the factors and actions influencing the material time dependent behavior such as creep, shrinkage, the variation of elastic modulus and the loss of prestressing. For this purpose, a case study has been carried out on a three span continuous prestressed box-girder bridge. A three dimensional finite-element model has been constructed for the nonlinear stage by stage analysis taking into account the balanced cantilever construction method of segmental bridges, including the effects of loading history and material time-dependent behavior. The analysis results have been discussed in terms of the variation of stresses and displacements during the time span under consideration.Finally, the effect of the time dependent material behavior on the performance of the bridge has been demonstrated and some suggestions have been made to improve the time dependent behavior of such bridge superstructures in the construction of new bridges as well as the retrofit of existing bridges.

This paper is concerned with the investigation of the interaction of a vertically-loaded disc embedded in a transversely isotropic half-space. By virtue of transform methods, the generalized mixed boundary-value problem is formulated as a set of dual integral equations, which, in turn, are reduced to a Fredholm equation of the second kind.In addition to including existing solutions for zero and infinite embedment as degenerate eases, the present analysis reveals a severe boundary-layer phenomenon which is apt to be of significance to this class of problems in general. The present solutions are analytically in exact agreement with the existing solutions for a half-space with isotropic material properties. To confirm the accuracy of the numerical evaluation of the integrals involved, numerical results are included for cases of different degree of the material anisotropy and compared with existing solutions. Further numerical examples are also presented to elucidate the influence of the degree of the material anisotropy on the response.

Dams are huge and expensive structures, and their safety is very important. Until now, many methods such as boundary element methods or combination of boundary element and finite element methods have been presented for the analysis of concrete dams which are computationally complicated. In this study, a new computer program is developed and dam-foundation rock interaction has been studied. In this paper, dam body and foundation rock is modeled in three-dimension (3-D) by using finite element discretization. Thereafter, the response of Morrow Point arch dam has been investigated with various ratio of foundation rock to dam concrete elastic moduli and empty reservoir condition. Also, the responses of dam with different cases of foundation rock are presented. In addition, this program can use damping solvent extraction method, so effect of damping solvent extracting on dynamic response of concrete arch dams has also been studied.

This paper investigates development of a finite element model to analyse PiezoCone Penetration Test (PCPT) in unsaturated porous soil. The study is carried out due to presence of a type of marine soil which contains Gas Hydrate. This componenet which can be found in seabed sediments of the continental shelf is stable under special conditions of temperature and pressure. By missing this required condition, the existing theories are unable to predict the soil behaviour, so a numerical code called θ-Stock (Gatmiri, 1997) developed to overcome this problem. The behaviour of soil is considered to be nonlinear elastic and the Piezocone penetration has been modeled in two steps. Interaction of different soil phases have been considered completely coupled. Also all mechanical and hydraulic properties of environment are supposed to be temperature dependent. The intial data of this modeling derived from some field observations in Guinea Golf. The results of this numerical model describe the dissipation and mechanical behavior of these gas hydrate bearing marine sediments with an acceptable accuracy and can be improved in the case of having access to sufficient field observations.

The main goal for this research is to make an in depth analysis for a transversely isotropic half-space under the effect of a circular rigid disc attached on the surface of the domain affected by a bending moment. To do so, the potential method is used to uncouple the Navier’s equilibrium equations. Utilizing both Fourier series and Hankel transforms, the potential function is determined. To find the unknown coefficients of the solution of differential equations involved in this paper, the boundary conditions are transforms into dual integral equations. The dual integral equation is analytically solved from which the displacements and stresses are determined based on displacement- and stresses-potential relations. The contact pressure is presented in a closed form format and illustrated to be discussed deeply. By numerical evaluation of the results and comparing the results for the simpler case of isotropic half-space both the validity and accuracy are shown.

Wavelet Analysis has called the attentions in numerical solutions of PDEs in recent years. Because of orthogonality and compact support of Daubechies scaling functions, these functions have excellent ability of providing good accuracy and convergence for the approximation of the solution in singularities. In this article the method of using these functions for numerical solving of PDE for Euler–Bernoulli beams is formulated. This procedure needs to calculate derivatives and integrals of scaling functions as the shape functions of wavelet-based finite element method. Because of non-explicit formulation and high oscillation of these functions, conventional methods -like Gauss method for integration- are not suitable and accurate. Thus some special methods are formulated for these requirements. The ability and high accuracy of wavelet-based beam element for different boundary conditions and loads is shown in some examples.

A fairly complete monitoring of soil-structure interaction was performed during the construction stages of Resalat tunnel, a large span highway twin tunnel, and the instrumentation results were processed and analyzed. This project is one of the limited numbers of urban tunnels with a large span of 16 m and a low overburden (6 to 30 m) which are excavated through soft ground and passes underneath several deformation-sensitive urban areas. The proximity of two large span tunnels makes this project very special. Excavation of each 16 m span tunnel was designed to be done in five stages by a sequential excavation method and the number of stages sometimes was increased to 8 and more in order to restrict the ground deformation and surface settlements. Since measurement of some geotechnical parameters of course grained alluvial of Tehran is extremely difficult and sometimes impossible by conventional laboratory tests or even in-situ tests, the inverse analysis of instrumentation data can be used as an effective alternative for assessment of these parameters. These parameters mainly include the coefficient of cohesion due to soil cementation C, at rest coefficient of soil lateral pressure Ko, and to some extent the modulus of elasticity E.In this paper, the construction stages of Resalat twin tunnel are simulated by a finite element based numerical model and the possible sets of geotechnical parameters of the host ground are assessed.