IRANIAN JOURNAL OF SCIENCE AND TECHNOLOGY TRANSACTION B- ENGINEERING
Year:2006 | Volume:30 | Issue:B1|Papers Count:13

In this paper, a genetic algorithm (GA) method is employed to determine the location of the critical non-circular slip surface giving the minimum factor of safety in conjunction with the magnitude of interslice forces and their points of application. A generalized method of slices satisfying both force and moment equations of equilibrium is adopted for stability calculations. The GA adopted here minimizes an objective function that has three terms, namely, error in equilibrium equations, safety factor and a penalty term. By minimizing this objective function, a critical slip surface (with minimum safety factor) is obtained that satisfies both force and moment equations of equilibrium and is kinematically admissible as well. No assumption is made regarding the location of the thrust line where its position is determined through the GA process. Furthermore, all slip surfaces are kinematically admissible and physically acceptable by considering a suitable penalty term. The proposed algorithm is applied to a number of problems and the results are compared with previous work and discussed in detail.

Use of fiber reinforced plastic (FRP) composites for strengthening of beams and columns in RC structures has attracted great attention in recent decades. However, less attention has been paid to strengthening RC connections with FRP laminates. In the current study, a finite element (FE) modeling has been proposed for the non-linear analysis of RC joints covered with FRP overlays. The model consists of the effects of anchorage slip and anchorage extension of the steel reinforcement in the connection zone. As for the credibility of the method, some available experimental works were modeled and non-linearly analyzed using ANSYS. The results showed that the model can predict the experimental works with good accuracy. At the end and as a case study, a base joint specimen was strengthened with FRP laminates in 7 different cases and the specimens were analyzed using the aforementioned modeling. The results showed that good ductility and strength enhancement could be achieved by employing correctly configured FRP laminates.

The determination of the optimal locations of controllers in active or semi active structural control has received very little attention. The optimal placement, compared with the non optimal case, provides control performance with a fewer number of controllers and smaller control force. In this research, the effect of the locations of the controllers on the control force and control performance was studied. This project uses the ‘Pole-Assignment’ method for the purpose of determining control forces, and for considering the semi active state. In the semi active control state system, the control force is determined by specifying a value to produce this state. During this study, two optimization methods have been used for active control. In the first method, all cases are studied to find the optimal case. Then several evaluation criteria have been used to find an optimal case. The second method is based on defining a performance index related to each story. In this method, with a series of repeatable operations, stories with a maximum index have been selected as optimum. The numerical examples show that the results of the first and second method are somewhat different. In addition, the findings of this study indicate that the number of controllers can be reduced in most cases. General results have been obtained for the optimal placement of controllers in common structures.

The dynamic interaction of fluid-solid systems has long been a subject of interest in many engineering fields. One of the most important problems of this nature, encountered in civil engineering, is the dynamic interaction of a dam and the reservoir under seismic loading. Recent research indicates the importance of this interaction and the resulting hydrodynamic forces, including the compressibility effects of water on the seismic response of concrete dams.In this thesis a combination of 2D finite-element and a closed form method based on a Eulerian approach is developed to study the dam-reservoir interaction effect. The mentioned procedure is used to investigate the interaction effect on stresses and displacements of the Kowsar Dam-reservoir system. To establish the accuracy of the method, the seismic response of the Pine Flat Dam is studied and the results are compared with other exact solutions.

In this paper, pore water pressure in the 15-Khordad dam, an earth fill dam constructed in a V-shaped valley with a clayey core and a height of 96 m was investigated following it's construction. Many vibrating-wire and standpipe piezometers were installed in the body of the dam. Pore water pressure monitoring was made from one week to ten months following the impoundment. The core was modeled by a finite element mesh, and 3-D transient and steady state analyses of pore pressures were performed and the results were compared with the monitored data. The trend in the monitored pore pressure was well modeled by the transient analysis. It was concluded that pore pressures in the cores of embankment dams may not achieve steady state conditions in some months, following the dam construction and impoundment. It was also observed that the selection of conductivity as a function of suction did not affect the results of modeling.

The main characteristic of the flow induced by groynes is the development of a recirculating flow area. An interaction between the recirculating flow and bed mobility leads to the development of a scour hole around the groyne, and a sediment deposition bar downstream. The simulation of the bed evolution around a groyne was investigated by linking a developed sediment transport model (STM-2D) to the FAST-2D flow model. The flow model was modified for the present study to simulate the detailed characteristics of the flow around the groyne. The previous study by the author indicated that the results of the numerical simulations compare well with the experimental data in two cases of the flows in flat-bed channels and in channels with complex-bed topography induced by a groyne. The present state of sediment transport relationships, in particular the relationships for alculating the bed-shear stress and the bed-load transport rate, was evaluated as an essential step for the computational simulation of the groynes performance. A depth-averaged version of the bed-shear stress relationship was modified with the inclusion of correction factors for the effects of the local spiral motion and of the local bed topography. Sediment transport relationships of Ackers and White, and of van Rijn (both deterministic and stochastic methods) were adapted. A number of difficulties were encountered in the development and validation of this model, nevertheless, substantial progress was made. This paper discusses the major uncertainties in the simulation process. It is concluded that modification of the conventional bed-shear stress relationship is not sufficient for simulating realistically the bed features behind the groyne. The development of a conceptual method for calculating the bed-shear stresses around groynes is a priority and recommended for future studies.

The implementation of boundary conditions in sub-critical and supercritical flow is quite different when using characteristics leading to programming difficulties with the associated numerical schemes. For supercritical flow, the de Saint Venant equations require two upstream boundary conditions and no downstream condition, whereas sub-critical flow requires one upstream and one downstream condition. The literature contains many approaches to accommodate both super- and sub-critical flows. Reducing or suppressing the convective term is one of the common methods which allows the same numerical scheme to be used for both regimes. In this paper, the impact of suppressing the convective term on the solution is investigated using the Method of Characteristics (MOC). A set of numerical experiments are carried out for this purpose using the commercial software MIKE11, and the results are compared and contrasted with MOC. Results show that significant changes in computed water depths occur in some situations by suppressing the convective term. In conclusion, in some cases the solution algorithm is significantly affected by this approximation. Also, since recent advances in numerical modeling of trans-critical flow are superior, this approximation should gradually be removed from the numerical simulation of open channel flow.

In this paper, based on the free vortex theorem and the momentum equation, a theoretical model to predict the pressure head distribution, the pressure coefficient, the end depth ratio (EDR), and flow discharge at the brink of free overfalls in channels of different cross sections with sub-critical flow is presented. Using available experimental and theoretical results of other investigators for rectangular, triangular, exponential, trapezoidal, inverted triangular ( D-shaped), inverted semicircular and also circular channels, the proposed method has been examined. The presented theory agrees well with the experiments.

In this paper, ant colony optimization (ACO) algorithms are proposed for reservoir operation. Through a collection of cooperative agents called ants, the near optimum solution to the reservoir operation can be effectively achieved. To apply ACO algorithms, the problem is approached by considering a finite horizon with a time series of inflow, classifying the reservoir volume to several intervals, and deciding for releases at each period with respect to a predefined optimality criterion. Three alternative formulations of ACO algorithms for a reservoir operation are presented using a single reservoir, deterministic, finite-horizon problem and applied to the Dez reservoir in Iran. It is concluded that the ant colony system global-best algorithm provides better and more comparable results with known global optimum results. As with any direct search method, the model is quite sensitive to setup parameters, hence fine tuning of the parameters is recommended.

Water network performance is defined as the ability to deliver a required quantity of water under sufficient pressure and an acceptable level of quality. A sound performance indicator is a Powerful tool for more efficient management of water systems. This paper introduces a methodology for performance assessment of water distribution networks based on quality parameters (such as residual chlorine, water age, etc.) and the head driven simulation method (HDSM). For hydraulic analysis of water networks a pressure dependent simulation model is used. This model is able to predict the hydraulic behavior of the system more realistically, especially during abnormal and critical conditions (e.g., outage of pumps and reservoirs, pipe breaks, leakage, excess demands, etc.). Also, a discrete-volume element method (DVEM) is applied for the analysis of water quality parameters. In the next step, using penalty curves based on the standard codes for quality parameters, the quality performance of the system is assessed. By evaluating a test network, the application of the new methodology is presented. The results are also compared with the widely used water quality simulator of EPANET 2 software, which uses the demand-driven simulation method (DDSM) as its hydraulic simulation engine. The DDSM models consider fixed demands regardless of nodal pressure variations. Consideration of HDSM leads to different pipe velocities, and therefore, different values for quality parameters. The results showed that the introduced procedure can help to assess the performance of quality parameters in water distribution networks more realistically than the existing demand-driven simulation based models.

In this research, a realistic methodology, in order to estimate a true O-D matrix for freight movement in a designated region, is presented. This means, having had an initial O-D matrix (exp. Waybill data) and traffic count in many intercity roads, one can estimate an O-D matrix, having minimum distance from the initial matrix, and reproducing the observed traffic by assigning to the network. In the first step, after conducting studies and field work, some special route choice patterns in an intercity network were recognized by heavy vehicle drivers. Using the Logit Formulation, some probable (pure stochastic) assignment models related to the condition of the case were developed. Also, due to existing errors in both information sources, waybill and traffic count information, after recognition and determination of errors amount and their precision, based on Analytical Hierarchy Process Method, reliability of the mentioned data sources was estimated. Hence, to approach the best model of O-D matrix estimation, an Entropy Maximization model with a composed objective function was calibrated. Thus, having a calibrated matrix estimation model and a developed a traffic assignment model as a sub-model, true freight O-D matrix could be estimate.

Static and pseudo-static analysis based on the Discrete Element Method (DEM) is presented for active and passive earth pressure distribution behind a retaining wall. Soil mass in the present model is treated as comprising blocks which are connected by elasto-plastic Winkler springs. The solution of this method satisfies all equilibrium and compatibility conditions. Examples are shown to demonstrate the applicability of the method for analyses of earth pressure behind a gravity wall, including pseudo-static pressure of earth and lateral pressure of non homogeneous soil. The applicability of DEM for analyses of reinforced soil structures and the advantages of this method over the conventional limit equilibrium method are also discussed.

A new approach to modeling injecting domain has been developed based on changing permeability coefficient in a certain form in theory of consolidation. The proposed model utilizes the variation of the coefficient of permeability with respect to the pore fluid pressure justifying flow characteristic below certain hydraulic gradients and void volume changes. A proposed numerical solution for heterogeneity of media with regards to the permeability coefficient also leads the results to a better grout extension solution. The potential of the proposed model is evaluated in predicting the propagation of grouting material due to a single injection bore hole. The general comparison indicates that this approach is capable of solving the injection boundary value problem.