Year:2006 | Volume:40 | Issue:5 (99)|Papers Count:17

Pipes burst and leakage rates in water distribution networks are growing with increasing of pipes age. Therefore, pipe rehabilitation and replacement programs would be necessary during the pipes life time. This is a complicated problem in which budget restriction has an important impact. This paper introduces a simple model to determine the best time for leak detection and pipe replacement programs using pipes break records. Assuming a linear relationship between pipes break rate with time, the operation cost for three different steps of: pipe repair, leak detection and pipe replacement are evaluated and the best time for commencing of each scenario is calculated. To highlight advantages of the proposed methodology, it is applied to a pipe network in one of the Iranian cities. At first pipes break records are gathered for a period of six months using a standard format. Then the best time for leak detection and replacement programs are determined and sensitivity of the results to different parameters is evaluated. It can be concluded that the proposed methodology produces a powerful tool to be used in water distribution networks and help decision makers to choose the best option considering budget restrictions.

In this paper an analytical solution is presented for displacements and stresses of a three dimensional linear Green elastic transversely isotropic half-space subjected to an arbitrary, time-harmonic surface tangential force. The equations of equilibrium in terms of displacements are uncoupled by using a set of two potential functions introduced by Eskandari-Ghadi (2005) for electrodynamics problems. The Fourier expansion and Hankel transform in a cylindrical coordinate system with respect to angular and radial coordinates, respectively are employed to solve the boundary value problems for the potential functions. The development includes a set of transformed stress-potential and displacement potential relations that are useful in a variety of either static or dynamic problems. To verify the accuracy of the numerical evaluation of the present solutions, comparisons with existing solutions for an isotropic material are given. Different numerical results are also included to demonstrate the influence of the degree of the material anisotropy and the frequency of excitation on the response. The solutions for transversely isotropic material are also degenerated for the isotropic material response analytically and compared with existing analytical solutions. Solutions presented in this paper are important in development of boundary-integral-equations to analysis both dynamic anisotropic soil structure interaction problem and seismic waves scattering in anisotropic soils.

Thermo-buckling governing equations of sandwich panels are derived using computational variation methods. The derived equations are then solved using infinite series function, satisfying simple boundary conditions. The considered sandwich panel is composed of symmetrical composite layers. A numerical study is then carried out to compute thermal buckling stresses and is compared to the results obtained by other methods.

In this paper, dynamic properties and seismic behavior of single-storey building constructed by prefabricated 3D sandwich panel’s method is carried out under shaking table test. In this experiment, the specimen is tested in full-scale dimension. In this study, the seismic behavior of system under dynamic loading such as earthquake motions is obtained. Linear and non-linear characteristics of structure, deformations, stiffness and fracture mechanism are investigated. In analysis, comparison of the results obtained from the test and numerical analysis are presented. The result indicates the 3D-panel system, due to its high rigidity, can resist mainly in linear domain and has adequate load bearing capacity against seismic excitation. The results could help the unknown parameters of dynamic analysis and design of this system.

One of the most important stages of road design projects usually carried out at the first phase is the preliminary road routing. The first question arising for the designer regarding a route design is the information about various routes that the road should access to. The purpose of this research is presentation of an economically optimum model for road routing considering access to all the main points of the roads. The major capability of the model is considering areas that the road should not pass through for any reason. In this paper after describing a short history of the past studies in the field of road routing, the current methods are evaluated and consequently two mathematical models are presented for route location in plain areas. In the first method the harsh and difficult areas are not modeled, in the second model the forbidden areas are modeled in triangular forms and passing through these areas is prevented. A major point of road corridors design is that the road should be so designed that it could not pass through forbidden protected military or environmental fields. The major capability of the second method is predicting these areas in the optimum road corridor. An important point in the design of road corridors is determination of general route models, the access sequence to the points and know how of accessibility. Routes should be designed with a comprehensive and long term approach so that they create cost effective road networks. An important application of the presented mathematical models is therefore their utilization in provision of master highway and railroad corridor plans in plain areas. Such corridors may also be used in route location projects in larger scale maps, in plain areas. In this research the mathematical non-linear programming has been used for modeling.

In most of the tall buildings, a portion of the lateral load is carried by the shear walls. Such shear walls usually have openings for doors or windows. For interactive action of the shear walls existing at the two sides of the openings, the two shear walls are connected by so called "connecting beams" and hence, coupled shear walls are produced. In some cases, the necessary stiffness to withstand the lateral load may not be afforded because of the low depth of the connecting beams. In order to increase the capacity of the coupled shear wall, beams with high stiffness will be added to the system at particular levels and so, stiffened coupled shear wall will be produced. Such walls are under axial load resulting from their weight, and the axial load affects their behavior because of their excessive height. In this paper, a simple formulation for determining the critical load of the stiffened coupled shear wall under gravity force has been proposed using continuum medium assumptions, and then several examples have been solved using the proposed method. In order to indicate the capability of the proposed method, the results arising from the proposed method have been compared to the results arising from the ANSYS software model. Then, the effects of the stiffness and the position of the stiffening beam on the critical gravity load of the stiffened coupled shear wall have been investigated.

Structural optimization is a process by which the optimum design is aimed while satisfying all the defined constraints. In recent years, using laminated composite materials in fabrication of mechanical, airspace, marine and machine industries are of major attention, due to their high strength and light weight. One of the objectives of the present paper is seeking the optimum weight and cost of a laminated composite plate, while undergoing the heaviest load prior to a complete failure. Various failure criteria are defined for such structures in the literature. In this work, the Tsai-Hill is used as the failure criterion. The multiobjective function introduced here consists of weight, cost and failure loading. Therefore, one realizes that in this work a minimal-maximal objective function is to be optimized, thus, the weight and the cost will be minimized while the failure load for all the laminated plies is to be maximized. The design variables could be any combination of thickness, orientation of fibers and the material for each layer. The thickness of the layers could be considered continuous whereas the cost and the material for each layer to be discrete. With regard to the problem in hand, a decision was made to employ a newly introduced type of optimization technique called the Genetic Algorithms, based on a new type of selection, to handle the optimization process. The theory of analysis was based on the Classical Lamination Theory (CLT). Therefore, attempts were made to produce software for the analysis and the optimum design of laminated composite plates under any combination of design parameters. A number of problems were solved under two different models. First, a multi-objective optimization procedure under a new approach was introduced, where the problem is considered unconstrained. The second model, namely the constrained optimization problem, consists of secondary valued terms which were defined as constraints, while the objective function contained only the major term, as selected by the user. The verification of the results was made satisfactorily, as a consequence of which some benchmark examples were also attempted and recorded.

One of the new passive seismic control devices implemented in the steel frame structure is to utilize the smart materials such as shape memory alloys (SMA) in the members. This paper presents the development of a numerical algorithm to assess and examine the behavior of the super-elastic property of SMA braces in steel structures subjected to cyclic loading. Super-elastic material model of SMA and plasticity model of steel are implemented into the general purpose finite element program. Material and geometrical nonlinearities including the large strain deformation of the finite element formulation are employed. A displacement loading control history is applied to the frame in accordance with the SAC loading protocol. The results obtained from the analyses are compared with the available test data from the state of the art buckling restrained steel braces; which indicates that SMA bracings increases the overall frame ductility. Finally in order to have the deeper understanding of the behavior of the SMA bracing system, a force control loading protocol is also applied on the framed structures.

The ability of a structure that has experienced an earthquake to withstand the next earthquake is estimated by damage index. There are several damage indices that have been proposed by researchers to quantify the amount of damage to the structure. These are generally defined based on dynamic response of structure and its hysteretic characteristics. Due to time consuming and complicated process of nonlinear dynamic analysis and calculation of damage index via these methods, in this paper using a pushover analysis and employing the stiffness damage index, the deterioration of the stiffness of the structure in various performance levels is evaluated. The obtained results are compared to that of qualitative definitions of FEMA. For this purpose a computer program has been prepared that considering earthquake specifications and characteristics of any structure, automatically evaluates the damage in RCMRF in various performance levels. Eight samples of RCMRF that had been designed based on ABA and Iranian Standard No. 2800 and one sample that was designed based on FEMA for four performance levels were evaluated for damage and discussed on. The results of evaluations show that the proposed damage index can be a proper criterion for seismic performance evaluation of RCMRF. According to the results it seems that the criterion of drift in, FEMA and ATC, alone cannot be a correct and perfect criterion for performance and damage of structure.

Structures are basically designed to withstand the applied loads, which can come from the internal effects such as dead load and live load, or may made by environment such as wind load, earthquake, ice load, deluge, etc. Although it is evident that the amount and distribution of these loads is not certain and has a random nature, no serious attempt had been made to bring the statistical properties of load in structural design until 1960. In 1960’s, civil engineers started to reflect the random parameters of load and material resistance in the design codes. In Iran many code organizations have also tried to take into account the probability parameters of load and material resistance in structural design. Unfortunately, the statistical studies, which have already been made, are not based on climatic and construction condition in Iran. At the moment, to design the transmission line towers, a combination of different codes is often used, which are not completely compatible with the climatic condition in Iran. In the present paper, statistical parameters for wind speed and ice thickness, those that are amongst the important random variables in transmission line towers loading, were evaluated for four cities (Bandar-abbas, Yazd, Tehran and Shahre-kord) in Iran from different climatic conditions. Finally, the nominal values for these variables have been proposed to modify the Moshanir code (An Iranian company that provides loading codes for transmission towers).

In recent years steel plate shear walls are widely used in tall building construction especially in Japan and United states. Excellent seismic performance and saving the construction cost are the important reasons of using these systems. Two types of steel plate shear walls that conveniently used are stiffened and unstiffened types. Stiffened types are very costly and unstiffened types have some serviceability problems after earthquake event. An innovated type of steel shear wall which made up of corrugated steel plates is introduced. The structural Behavior of corrugated steel shear wall systems with its boundary columns and beams in each story is more or less similar to steel plate girders with corrugated webs and might remove most of stiffened and unstiffened steel shear wall` deficiencies. Reduced wall stiffness due to accordion effect, achieving a stiffened steel plate shear wall with relatively thin plates and mobilizing the inherent geometric stiffness of plate, ease of erection, good seismic performance and energy dissipation and visual esthetics in expose construction are main advantages of these structural systems. The behavior is investigated by FEM method. Theses analyses are geometrically and materially nonlinear and the relation between corrugated plate dimensions and its seismic performance are discussed.

In this article nonlinear behavior of multi-story asymmetric buildings is evaluated considering history of combinations of story shear and torsion in a space called SST (Story Shear and Torque Surface). The first step for understanding this behavior, in modifying these surfaces that represent all combinations of story shear and torque that applied statically to the structure and produce mechanisms in the story. Many factors influence the shape of the SST surface that effects of some factors such as strength of resisting planes in orthogonal direction, strength eccentricity and stiffness eccentricity is considered and their effects on the behavior of asymmetric buildings in evaluated considering 5, 8 and 12 story buildings. Results show that the SST surface with conjunction of the history of shear and torsion in stories produces a useful framework for understanding the behavior of asymmetric systems. Additionally, it is possible to predict the behavior of an asymmetric system using these surfaces even before any dynamic analysis. This method is applicable in both steel and concrete structures.

In this paper, foldable structures with scissor-like elements are investigated and then based on constraints geometric design of these structures is formulated for any curved shape. Method of geometric design of foldable structures with any curvature is investigated. Using given connections to these systems in this paper, two models with fixed geometry and variable geometry is designed and constructed on real scale, based on this formulation. Correct behavior of these models is a sample to proof the applicability of formulation and connections. To find the optimal geometry of barrel vaults that structure has minimum displacement, based on formulation, some Macro files are programmed to model barrels with any curvature with ANSYS. Many of barrels are analyzed as linear and geometrically nonlinear, and graph of displacements are illustrated. The results display that there is a special height for any span with two characteristics; the displacement of structure is minimum and the difference of linear and geometrically nonlinear analysis is minimum.

The performance of Tuned Liquid Dampers for structural motion control subjected to earthquake excitations and also considering nonlinear elastoplastic analysis is investigated in this paper. Previous related research works in this field mainly studied the performance of TLDs under the harmonic excitations and used the linear analysis. While, earthquake excitations are completely non-harmonic and have a relatively wider frequency band. In addition, most structures experience nonlinear deformations due to strong earthquakes. Considering the above-mentioned facts, this study was performed to answer the question that what is the performance of these dampers under the earthquake excitations and considering the entrance of the structure to the plastic deformation domain“. In this regard, the simplified single degree of freedom model of Nagasaki Airport Tower was used for numerical modeling. The dynamic responses of the model to the excitations of Elcentro, Naghan and Tabas earthquakes were calculated with and without TLDs. The results of this research show that TLDs have satisfying performance in the structural motion control under earthquake excitations similar to harmonic excitations so that in the cases of linear and nonlinear analysis the amplitude of the excitations could be reduced up to 30% and 70% respectively.