INTERNATIONAL JOURNAL OF INDUSTRIAL ENGINEERING AND PRODUCTION MANAGEMENT (IJIE) (INTERNATIONAL JOURNAL OF ENGINEERING SCIENCE) (PERSIAN)
Year:2008 | Volume:19 | Issue:8-2 (SUPPLEMENT CIVIL ENGINEERING)|Papers Count:11

One of the most effective methods for seismic performance improvement of reinforced concrete (RC) elements is the external confinement by the wrapping of FRP sheets. As a result of FRP confinement, the constitutive model of concrete in compression i.e. the stiffness, compressive strength and ultimate strain of concrete can be completely changed. In this research the 3-dimensional nonlinear finite element program, COM3 (developed at the University of Tokyo) has been used for modeling of concrete samples confined with various amount of FRP. The effect of different parameters (stiffness, strength and thickness of FRP sheet) on the compression stress-strain curves of confined concrete is investigated. Through a numerical parametric study, the effect of confinement level on the Elasto-Plastic and Fracture (EPF) model (plastic strain and fracture parameter), is examined and based on which some equations for constitutive model are developed. In development of these equations, the effect of clear distance between FRP straps (incomplete confinement) is also considered. After modeling of the FRP-confined concrete specimens and verification of the analysis results with existing experimental samples, the effective parameters in the amount of FRP covers' confinement were determined through sensitivity analysis. The place of FRP rupture in mean compressive stress-strain curve is also determined by means of developing a relation for the circumferential strain of concrete specimen in terms of axial strain and confinement level.

In this paper a new methodology for non revenue water (NRW) analysis is proposed. The method is able to analyze components of NRW in water distribution networks. NRW is basically divided into two main real and apparent losses. In the first section based on minimum night flow measurements background and bursts losses are evaluated. In this method a preliminary estimation is made for background losses. Then using analytical procedure, field activities, pressure measurement and hydraulic analysis, an improved and more accurate value is obtained for background losses and unreported bursts. Combination of the Bursts And Background losses Estimation (BABE) and Fixed and Variable Discharge Area (FAVAD) concepts increases the accuracy and applications of the proposed approach. Finally the proposed methodology is applied in a selected district metered area (DMA) in the city of Tabriz and components of NRW are evaluated and capabilities of the model are highlighted.

The problem of Airline planning has to tally been divided in to four sub problems i.e.: flight scheduling, fleet assignment, aircraft routing and maintenance and crew scheduling In this paper for the first time a "Mathematical Integrated Model" for Airline planning, considering all sub- problems continuously, is build up and presented. But because the developed model is a kind of large scale, solving it trough routine "Operation Research" methods seemed to be impossible; so that methods called "Meta-Heuristic" is used, such as "Generic Algorithm". The presented model is solved for an Iranian International Airline using the generic algorithm method. The model s output, added to arrival and departure times for each origin- destination, it also determines kind of fleet assigned, aircraft assigned in each fleet to respective flight and related flight crews.

This paper presents the results of a two phase Euler-Euler simulation of seepage flow through granular media for upward flow conditions in soils. The simulation first deals with the fluidization process in a stable granular soil. The first fluidization in the sand column is studied and the stable fluidization condition is reached by the development of particle repulsion and the effect of inertia on the resistance of the granular bed. Considering Richardson's expansion law, porosity changes with the flow rate variation are described based on the rarefaction waves. In this study the variation of water and soil phases before and after the critical hydraulic gradient are evaluated. The results of the simulation reveal that the variation of soil pressure before and after the critical hydraulic gradient are inverse and the Terzaghi's effective stress theory is valid only to the onset of the first fluidization. In the second part of the paper, the fluidization and internal erosion processes in the artesian conditions in internally unstable soils are discussed. In internally unstable soils the finer soil particles are able to move through the constrictions of the coarse particles. This may lead to internal erosion and as a result the critical hydraulic gradient drastically increases. The erosion phenomenon is described using the theory of continuum mechanics for the soil consisting of stationary grains, movable grains and the fluid. The continuity and momentum equations are derived for the soil and based on this theory a numerical two phase model for the erosion and fluidization of particles are presented. The results reveal that by the commencement of erosion, the porosity of the soil decreases and the flux of eroded particles increases with time.

Many meshless methods are presented in recent years for solving partial differential equations. In this paper, a Generalized Finite Difference meshless method was developed for the solution of two-dimensional elliptic problems. A fully Least Squares method is used in both function approximation and the discretization of the governing differential equations. The discretized equations are obtained via a discrete least squares method in which the sums of the squared residuals are minimized with respect to unknown nodal parameters in the inner and boundary nodes. In this process no numerical integration is needed and the obtained equations are symmetric and positive definite. The mesh less shape functions are derived using the Moving Least Squares method of function approximation. The proposed method has the additional advantages of the producing symmetric, positive definite matrices even for non-self adjoin operators. The method is tested against two elliptic two-dimensional examples including Poisson and Seepage problems in steady state form.

In accordance with some codes of practice for seismic resistant design of buildings (e.g. Iranian Standard No. 2800 - 3rd edition), bond-beams and tie-columns must be used in all load carrying walls of unreinforced masonry buildings. Building integrity and behavior of structural components such as walls can be improved by anchoring the floors and roof to the walls and by confining the walls. Capacity curves of such load carrying walls in seismic prone areas of Iran should be determined. For this purpose, two identical specimens of confined masonry walls have been made and experimental work on them have been carried out under static monotonic lateral loading. After gathering the experimental data, the same wall has been modeled by finite element analysis. In the model, the masonry panel has been assumed to be continuum and studied by multisurface plasticity Rankine-Hill model with low orthotropic factor. Since the reinforced concrete (RC) bond-beams and tie-columns may be cracked, the Rankine yield surface is used in their modeling. Sliding, cracking, and gap opening at the interface between the masonry panel and the surrounding bond-beams and tie-columns has been modeled too. Based on the experimental and numerical results, the obtained crack pattern and capacity curves are compared and good agreement is found.

Freezing depth is one the important climatic indices in the field of agriculture, civil engineering and etc. This parameter depends on different factors such as astronomical factors, temperature of surface air, amount of humidity, soil characteristics such as texture, heat capacity, thermal conductivity, and specific heat. In this study, for investigating the effect of air temperature on freezing dept, a soil freezing apparatus was made which is able to produce temperatures up to-23°C. To measure and record the soil temperatures at depths of 10, 20, 50, and 70 cm, a direct measurement system was designed. Sensors of the system include electronic thermostat, which was inserted at different depths of soil. Variation of temperature measured by these sensors, were transferred to a transformer, and the results of measurements transferred to a computer in the form of binary codes. These codes were processed by a computer program and converted to a numerical form. After the calibration, several experiments were conducted using soil bins of different textures including clay, clay-sand, and sand a moisture content of 0, 10, and 15 percent. The results of experiments are summarized as following: Freezing depth of soil in dry state (0% moisture content) for soils having smaller pores (such as clay), is less than soils having larger pores (such as sand). The advancing speed of freezing front has also a similar trend. By increasing the soil moisture (0% to 10%), for all soils the depth of freezing and the advancing speed of freezing front were increased. This condition in soils having finer texture is more pronounced than the soils of coarse texture. By increasing the amount of soil moisture content, the clay soil maintains its moisture throughout its depth, while in sandy and clay-sandy soils, the moisture content decreasing from top to the bottom (due to drainage). This phenomenon affects the advancing speed of freezing front of these soils. Finally, the correlation between the time of soil freezing (t), and the temperature at different depths during the freezing process (T), was investigated, and concluded that it can be written in the form of { T= (a * b) + c * td/b+td}, which is significant at 1% level for all three types of soils.

In this article, a new energy dissipater (Yielding steel) will be introduced. This dissipater is made of two short plates, and is installable at the brace ending of braced frames, in order to increase the ductility and earthquake energy absorbent. When an earthquake happens, the dissipater member absorbs significant part of applied energy to the structure by entering to inelastic phase and forming axial plastic hinges. In this way it prevents other structural members from entering to inelastic phase and also buckling of braced members, or it may postpone them. The splats are designed in a way that enters to inelastic phase before the brace buckles. This article inspects the stability and hysteretic behavior of this dissipater. The stresses and deflections have been studied by using a nonlinear finite elements analysis under cyclic loadings in ANSYS software. The results indicate that existence of plates has effectively increased the ductility and in addition to easy installation of this member at the end of the brace, we can expect of a suitable fuse performance from it.

In this paper, the behavior of reinforced concrete beams is studied using an experimental modal analysis. This analysis was carried out on the test results of nine concrete beam specimens. These beams were loaded gradually in different loading steps until failure. Six of the specimens were strengthened with externally bonded CFRP sheets when load reached approximately half of the predicted failure load. After every loading step, each specimen was suspended by elastic cables for vibration test. The frequency response functions (FRF) of the specimens were obtained in the vibration tests. The eignfrequencies and mode shapes were measured by analyzing the frequency response functions (FRF) and their variations during the loading steps were discussed. The changes of stiffness of the specimens were determined by Modal Assurance Criterion (MAC). In some of the specimens strengthened with CFRP sheets, the reduction of eigenfrequencies and the increase of the I-MAC values, based on the second vibrating mode shape, were less than 42 and 39 percent from the values associated with the unstrengthened specimen. These values show the effectiveness of the FRP strengthening and agree with the experimental observations.