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Volume 23, Issue 2 (Summer 2019)
Abstract

Introduction
Global warming and climate change are nowadays significant challenges for humankind. It is widely and generally accepted that the increase of greenhouse gases emissions (GHGs) in the atmosphere are caused by anthropogenic effects especially in modernized and industrialized countries. Consequently, cleaner energy generation is needed in order to reduce global GHGs emissions (Waewsak et al., 2014). Wind energy becomes today a promising option to complement the conventional energy source, especially in region where the existing power plants are not sufficient to match the increasing electricity demand. This success is principally due the rapid growth of the wind technology which led the wind power to be more competitive by reducing the cost of electricity produced (Djamai and Merzouk, 2011). Since there has no comprehensive wind potential study in Kermanshah province, it is necessary to pay this important subject to reply for increased demand of electricity. Thus this paper aimed to assess economical usage of wind power in Kermanshah province.   
Methodology
In this study we assessed economic feasibility of wind energy usage at 13 sites in Kermanshah province. In order to carry out the research, 3-hour wind speed data in 2009 to 2013, topography, land cover and obstacle maps were used, and ten models of wind turbines with different rated power were investigated. It has been calculated Capacity Factor, Operating Probability of wind turbines, and Annual Energy Production for selected turbines in 0.03m surface roughness using WAsP and Windographer software. Economical evaluation was down by Net Present value method and benefit costs analysis (B/C) in 13 sits and 10 models of wind turbines. Also in this research it was used Extra Investment Analysis (EIA) method to choose the best project from the initial Selected Projects. After investigation of cost analysis, it was determined the most economical wind turbine and site for utilization wind energy in Kermanshah province.
Results and discussion
The maximum Capacity Factor of selected turbines has calculated in Gilanqarb (46.4%), Tazeabad (44.2%) and Somar (39.2%). This is because of different wind climatology of these sites in comparison with the other sites in the Kermanshah province. In the other words orography characteristics of these sites leads to more nocturnally mean wind speed.
The costs of the construction and maintenance of a wind farm include initial Capital Costs (turbine price and costs civil work), and also operation, maintenance and Repair costs. On the other hand, the proceeds from the sale of electricity generated should be borne by the costs incurred. The cheapest turbine is 500- kW machine with 707 thousand dollars and the most expensive is 2000- kW machine with 2900 thousand dollars.
Benefit costs analysis indicated wind power plant construction in Gilanqarb area is more economical than other areas with all turbines except for 1300- kW machines which is more  economical in Tazeabad. Also the most economical machine is 2000- kW turbine in Gilanqarb area. The cost of wind power plant construction whit one 2000- kW turbine is 15.4 Billion toman right now, while the proceeds from the sale of electricity generated is 21.49 Billion toman in life time of machine. So this project is the most economical with benefit-cost ratio equal to 1.4 in comparison with other project in the study area. Obviously, the results of economic analysis will also be different if the prices used in economic analysis, such as the price of a turbine, the price of electricity or the exchange rate change.
Conclusion
 The results showed 750- kW and 800- kW machines have maximum Operating Probability of wind turbines and also it was the highest in Tazeabad site with 80 to 89%. While Capacity Factor has the highest value for 500- kW machine in all sites. Of course this turbine has the highest value in Gilanqarb (46.4%), Tazeabad (44.2%) and Somar (39.2%) sites. The most Annual Energy Production (AEP) acquired for 2000- kW turbine which is due to its high rated capacity. Calculated AEP for selected turbines vary between about 2 GWh in Kangavar to 6.7 GWh in Gilanqarb in the year.
Benefit-Cost index showed that wind power plant construction in Gilanqarb area is more economical than other areas with more turbines, and also the most economical machine is 2000- kW turbine in this area. Finally Calculations showed that usage of wind energy is not economical with any turbine in Eslamabad-Qarb, Kangavar, Sarpol-zahab, Ravansar, Sonqor, Harsin, Javanrood and Qasre-Shirin.
 

Volume 23, Issue 2 (5-2023)
Abstract

Accelerated construction methods are extensively used worldwide to reduce the negative impacts of bridge construction on urban traffic. These methods usually require prefabricating parts of the bridge off-site, which reduces on-site construction time and improves the quality and safety of construction. While the use of precast elements for bridge decks is relatively common, using precast elements for bridge piers is a recent development, especially in high-seismicity regions. Prefabrication of bridge piers can further expedite the construction of bridges. Moreover, the use of precast elements can be combined with a self-centering capability, through which the earthquake-induced damage and cost of post-earthquake repairs are greatly reduced. Despite a number of previous numerical and experimental studies on the behavior of precast, self-centering bridge piers, limited information is available on the selection of design parameters for such piers, and important decisions such as the prestressing force needed to achieve suitable seismic behavior remains to a large extent uncertain. This study aims to investigate the seismic behavior of concrete bridges consisting of precast self-centering piers, in which unbonded, post-tensioned tendons are used for self-centering and reinforcing steel is used to dissipate earthquake energy. A two-dimensional numerical model was developed in OpenSees to simulate the behavior of concrete bridges consisting of precast self-centering piers. The model consisted of fiber elements to model concrete and mild steel, as well as truss elements to model unbonded post-tensioning steel. The model also involved the use of zero-length sections to model the bond-slip behavior of mild steel bars. The modeling approach was validated based on experimental results available in the literature on cyclic loading of four bridge piers. To evaluate the effects of various design parameters on the behavior of precast segmental bridge piers, 9 segmental piers with different percentages of prestressing force and reinforcing steel were designed according to 2017 AASHTO LRFD Bridge Design Specifications. All piers were designed to possess similar nominal flexural capacities. The piers were then subjected to monotonic, cyclic, and dynamic time history analyses. The results showed the positive effects of prestressing in delaying cracking and reducing the residual drifts of precast bridge piers. Increasing the prestressing force ratio up to 10 percent of compressive strength of the pier cross section was observed to improve the overall seismic behavior of the structure, above which a further increase in the prestressing level may result in a diminished performance. The optimal value for the prestressing force ratio, which resulted in the most desirable behavior for cyclic and dynamic loadings was therefore found between 0.1 and 0.15. In piers with a prestressing ratio above 0.15, a decrease was observed in the area of hysteresis loops, which was accompanied by negative stiffness of the base shear versus drift curve. Moreover, the residual drift of the pier increased when prestressing ratios greater than 0.15 were used. The maximum drift of the structure was found to be insensitive to the prestressing force ratio. The results of this study are of great value for optimal design of precast, self-centering bridge piers in high-seismicity regions.

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