جستجوی مقالات مرتبط با کلیدواژه « شاخص قابلیت اطمینان » در نشریات گروه « فنی و مهندسی »

This paper demonstrates the use of the response surface method (RSM) to carry out probabilistic assessment of the bearing capacity of shallow footings seated near naturally occurring heterogeneous slopes. The method substantially reduces the number of Monte Carlo simulations required to carry out cumbersome probabilistic slope stability analyses. A finite element limit analysis model based on the lower bound theorem is developed. The soil behaviour in this model has been assumed to follow the associated plastic flow rule by conforming to the perfectly plastic Mohr-Coulomb failure criterion. The model then used to generate a large synthetic database of numerical results for the bearing capacity of shallow foundations resting on inherently variable natural slopes. To this end, a permutation of the key parameters is formed and lower bound FELA-based limit loads are sought through optimization in MATLAB. A closed-form solution is formulated using RSM-based polynomials. The response surface method equations, which are acquired from least squares regression analyses, are used to carry out probabilistic Monte Carlo simulations. The results of the current study clearly show that the earth slope angle of 75o would give rise to the diminished factor of safety, or in other words, the substantially augmented probability of failure compared to the other two slope angles considered. On the other hand, the slope angle of 45o renders higher factor of safety and lower probability failure as compared to the slope angle of 60o. Moreover, it is observed that constructing the foundation at a farther distance relative to the slope would cause the probability of failure to substantially diminish while leading the reliability index to enhance for the majority of the safety factor scenarios considered. Indeed, targeting a particular probability of failure or a specific reliability index would demand smaller factor of safety for greater soil-footing distances.

In medium-term planning of mult-carrier energy systems, the operator is required to schedule the outage of units for maintenance. The Main challenging is that there are concurrent resources in the system. These concurrent resources play key role in energy generation networks. In this paper, the scheduled maintenance is done in order to minimize the costs in the medium term while the reliability of multi-carrier systems and supply reliability is preserved. The proposed framework includes a bi-level programming model. The objective of the proposed model in the higher level is to minimize operating costs in the medium term and at the lower level, the objective is to maximize the reliability indices with corresponding constraints. The proposed model is tested on a local Multi-carrier System (Special Economic Zone in Assaluyeh), and the simulation results indicate that coordinated outage window unit, is more reliable than the separated scheduling models and therefore highlights the need to fix the models conventionally utilized by independent programming networks.

Various reliability indices have been defined by researchers for the water distribution networks. Due to the complexity and heterogeneous nature of distribution networks, results of indicies can vary substantially and municipalities have hard time to select the most practical indicies for their networks. This study was undertaken to develop a new method for identifying the best reliability index by considering various factors including the appropriate sensitivity to changes in network parameters, the appropriate shift in extreme conditions, the capability in covering critical condition, hydraulic condition, and water quality reliability. To accomplish the objective of the study, several water distribution networks were evaluated under multiple scenarios and the optimum reliability indices were verified with an example real water distribution network in Ahar. Controlling parameters included in scenario analysis for network reliability indices include: minimum, maximum and optimal pressure, residual chlorine in nodes, velocity in pipes, nodal pressure reliability, pipe velocity reliability, and nodal residual chlorine reliability . To evaluate the performance of defined index, a two-loop test (critical) were compared with the conventional single-lop test (normal). The performance assessment of indices obtained from this study showed that the index values ranged between 0.11 and 1.0, which indicate the normality and the appropriate sensitivity of the indices. Also, by increasing the residual chlorine of the reservoir, the network reliability index changed from 0.54 to 0.75 and then as the residual chlorine decreases in the distributon network the reliability index decreased back to 0.54. This appropriate shift in reliability index while changing residual chlorine in the network, cearly shows the the effectiveness of new method in determining the reliability indicies under extreme conditions. Also, the new method did not respond to the failure of some network components, as were evident with insignificant change in the indices values under critical conditions. From the results of this study generally can be concluded that the newly defined relability indices is an efficient way for evaluating the performance of water distribution networks.

Gradually, with urban population growth and development of Ahar city, old houses in the lanes and alleys are changing into high-rise buildings. In most of these buildings the regulations are violated. This issue has created a lot of problems for the inhabitants. The goal of the paper is to answer this question: "what is the consequence of high rise building constructions without observing urban rules and regulations on hydraulic performance of the Ahar water distribution network?" To answer this question, Ahar water distribution network was selected as a case study and its hydraulic performances were investigated in different situations.

In this study, we will investigate the possibility of using renewable energy resources in area where electrical energy is not supported. We will consider it as a micro-grid and we will try to supply its electrical energy by decreasing cost and having reliability in system. Generally, the main reason of designing and developing of distribution grid is responsible to growth of electrical consumption with maximum economic efficiency which the restriction of system is not made violation. Existing more elements in the distribution and sub-transmission networks have faced the designing and developing with problem where there are many decision variables. Advert of the distributed generation in distribution systems furthermore the changing operation of these systems provide this possibility to companies that can design systems with low cost. In this study, we aim to minimize the cost of the hybrid system of hydroelectric, wind, solar and battery and we will calculate LPSP index by GSO algorithm. It is designed and implemented for long-term network over 20-year.

Records in the near-fault areas indicate the strong vertical ground motion. Near-fault earthquakes are different from far-fault earthquakes due to the adverse effect of their vertical component, which can be very destructive for long span frames. The Vertical Component of earthquake is different from the horizontal component. Vertical component of earthquake occurs when the compression P waves separate. Whereas the horizontal component occurs as the shear S waves separate. The frequency content of vertical component of earthquake is higher than the horizontal component. The natural frequency of structures in the vertical direction is more than that of the horizontal direction. These factors may cause the resonance in the structures. The first step in the examination of the effects of vertical component of an earthquake on structures is identifying the stimulating source of vertical component of the earthquake, response spectrum of the vertical component and affecting parameters on the vertical component. In this research, the effect of horizontal and vertical components of earthquakes has been investigated in long span building frames by modeling two types of such structures with various openings sizes in a powerful finite element software. For this purpose, in the first phase of the study, the structures have first been evaluated under the effect of horizontal component of earthquake alone, and then, the vertical component of earthquakes has been added and performance of the structures has been evaluated again. To evaluate the performance of structures, both linear and nonlinear as well as static and dynamic analyses according to the seismic rehabilitation of structures guidelines have been performed. In the second phase of the study, for more confident evaluation, the reliability indices as suitable tool, recommended in recent researches, have been used. For this purpose, the amounts of moment, shear force, axial force of columns, and deflection of the long span beams have been calculated, and the corresponding reliability indices have been obtained by using an appropriate statistical software.

Underground tunnels, particularly, have distinct seismic behaviour due to their complete enclosure in soil or rock and their significant length. Therefore, seismic response of tunnel support systems warrant closer attention. The geological settings in which they are placed are often difficult to describe due to limited site investigation data and vast spatial variability. Therefore, the parameters which govern the design are many and their variabilities cannot be ignored. A solution to this issue is reliability based analysis and design. These real conditions of variability can only be addressed through a reliability based design.
The concepts of reliability has been less considered by the researchers in the engineering analysis and design of tunnels and underground spaces. Laso et. al (1995) studied the reliability in the designing of tunnel lining. Quing Lu et. al (2013) evaluated the reliability of the rock tunnels with respecting to several statuses of rupture mode. The studies conducted on the reliability of tunnels, mostly ignored the seismic design parameters as well as the consideration of reliability in the parameters of the surrounding tunnel soil.
Methodology and Approaches :In this research, response surface method (RSM), the reliability concept of Hasofer-Lind and finite element method (FEM) are composed in order to investigate the reliability of the lining of shallow underground tunnels. For this purpose, an underground tunnel with the height of 5m has been subjected to 7 earthquake records using finite element software ABAQUS. The random variables considered for surface response method are soil dynamic elasticity module, cohesion and internal friction angle of the soil. The reliability index has been approximated for axial force, flexural moment, shear force and displacement of tunnel by conducting trial and error tests on the three mentioned parameters.
Results and The results obtained in this research are briefly summarized as follows:The reliability index value is lower in the tunnel lining under seismic loads for all obtained responses, comparing to those under static loading. In the other words, the reliability of soil and tunnel systems are reduced concerning the random nature and criticality of loading as well as randomness of soil parameters .
The reliability index values are lower for the shear force response of the tunnel lining under Earthquake records, comparing to those of axial force and flexural moment. Consequently, it is recommended to retrofit the whole soil under earthquake loading against shear cracking.