سال:1397 | دوره: | شماره: |تعداد مقالات:10

1. Introduction: Precasting is defined as casting structures element in factory and connecting them in construction site. Therefore precast structures have different connections in comparison with monolithic ones. The purpose of this research is investigation of precast connections behavior because as a result of these connections, precast structures have a different seismic behavior. According to the recent studies, the most important problem in these structures is due to connection joints. Introducing of new connection and comparison of its behavior with conventional precast and monolithic connections is subjected to promote current weakness of precast structures in this research...

1. Introduction: Cohesive sediments are composed primarily of clay-sized material, which have strong interparticle forces due to their surface ionic charges. As particle size decreases, the interparticle forces dominate the gravitational force, and the settling velocity is no longer a function of only particle size. When, under certain conditions, the attractive forces exceed the repulsive ones, colliding particles stick together, forming agglomerations known as "flocs" with size and settling velocities much higher than those of the individual particles. This phenomenon is known as "flocculation" (Baldock et. al, 2004). In a flocculated cohesive sediment suspension, the settling unit is the floc rather than the individual particle. The settling velocity of cohesive sediment particles, also is called the fall velocity, is one of the key variables in the study of sediment transport and is important in understanding suspension, deposition, mixing and exchange processes (Partheniades, 2009). Adding a chemical solution in a mixture of water and sediment changes the physicochemical of the sediments and the flocculation of the clay particles may increase or decrease. Today, in many countries the wastewater is used for irrigation sector as an additional water resource. Wastewater in combination with other water resources change the physicochemical characteristics of the water and it causes changing in hydrodynamic behaviors which one of them is the effect of wastewater concentration on the fall velocity of cohesive sediments in channels and water transfer Systems (khastar-Boroujeni, 2018). Therefore this study focuses on the effect of urban wastewater on cohesive sediments transport to improve water quality and manage the irrigation systems. For this purpose, some experiments were carried out in an annular flume using a mixture of cohesive sediment and water with combination of three levels of wastewater for evaluating their effects on the fall velocity of cohesive sediments...

1. Introduction: Most investigations on the SPI (Standard Precipitation Index) have focused on drought analysis yet. A few researchers including Seiler et al. (2002) and Du et al. (2012) using monthly data showed SPI2, SPI12, and SPI24 have the potential to forecast floods occurrence. The present research aimed at using SPI for flood occurrence forecasting. The results of the study are important from two points of view: first, the applied model uses just one parameter that imposes less uncertainty through decreasing errors in preparing and introducing data to the model, and second, the model uses the most commonly available data with acceptable length everywhere; i. e. precipitation. While in drought analysis monthly scale is common, in this research the SPI was used in daily scale to fit the purpose of the study. For the case study, two different watersheds were selected; one in a humid area (Kasilian watershed in the north of Iran) and the other in a semi-dry region with a river of rainfall-snowy hydrologic regime (Kailak Darahsi watershed in the north-west of Iran)...

1. Introduction: The structure of the earth, atmospheric conditions, and hydrogeology, has led that groundwater levels in most parts of the world, including Iran, to decline significantly. This issue causes the large amount of soils above the ground water level to be in unsaturated state. Various activities associated with soils, such as subsurface explorations, foundation engineering and building constructions in unsaturated soils, etc., necessitates the study of the properties of unsaturated soils. One of the most important and fundamental properties of unsaturated soils is water holding capacity or soil suction. The soil-water characteristic curve (SWCC) has been found to be a conceptual and interpretative tool by which the behavior of unsaturated soils can be understood (Vanapali et al., 1999). The SWCC defines the relationship between soil matric suction (the difference between the air and water pressure in the soil) and the volumetric water content...

1. Introduction: In the present paper, the effects of a carbon nanotube on the moisture sensitivity of asphalt mixtures were investigated. Moisture sensitivity of asphalt mixtures is related to a phenomenon named stripping. The breaking of the bond between aggregate and asphalt binder is known as stripping (Xiao et al, 2010). Stripping reduces the strength of the material over the years which will manifest itself as rutting, corrugation, shoving, raveling, cracking, etc (Kodaii et al, 2012). Previous researches have introduced some additives for improving the moisture sensitivity of asphalt mixtures. Hydrated lime, Portland cement, polymeric material, and some other liquid anti stripping additives reduce the rate of moisture damage in asphalt mixtures. Recently, the use of nano materials in modifying different materials has become widespread (Alsaffar et al, 2014). In this study, a nano material named carbon nanotube with the quantity of 1, 2 and 3% was used for modification of asphalt binder. Moisture sensitivity of modified samples was investigated using indirect tensile strength test. In addition, the strength of modified samples was evaluated through marshal test...

1. Introduction: Lake Urmia is considered as one of the country’ s most important aquatic habitats and has experienced significant changes in recent years due to various factors, such as the climate changes (Abbaspour et al., 2012), anthropogenic activities (Zeinoddini et al., 2009) and the lack of a comprehensive management approach (Garousi et al., 2013) in the Lake Basin. Hence, the evaluation of changes in its different characteristics during decades is of great importance. In this study, changes in key parameters such as sea surface temperature, saline features and vegetation are studied using satellite imagery, remote sensing and fieldwork. The main purpose of this study is to conduct a supervised monitoring in order to evaluate Lake Urmia crisis in regard to humaninvolved factors such as the effects of the agriculture sector and the construction of the causeway bridge. Providing a comprehensive spatial database to determine the impact of each parameter on the Lake Urmia crisis is another objective of this study...

1. Introduction: Two phase gas-liquid flows occur in a wide variety of situations, i. e., in water supply systems, petroleum industry, pressurized tunnels and pipelines, culverts and water conduits (Mishima and Hibiki, 1996, Kabiri-Samani and Borghei, 2010). Air entrainment into a pipeline is a result of vortices at water intakes. Due to the severity of two-phase air-water flow at hydraulic systems, estimation of the dynamic pressure and pressure fluctuations in such systems is of great importance in practice (Yan et al., 2014). Most of the former studies have focused on two-phase gas-liquid flow in micro-channels and small pipelines, however, there is a lack of fundamental studies on pipelines with larger dimensions as used in hydraulic systems. Recently, some computational intelligence approaches such as ANN and ANFIS are very effectively used to predict complex problems with several parameters involved (Jang et al., 1997, Sebakhi, 2010, Fan and Yan, 2014). The present study focuses on estimation of dynamic pressure in two-phase air-water flow using ANN and ANFIS combined with PSO algorithm and subtractive clustering technique...

1. Introduction: Soil properties are affected by environmental conditions. Exposing of soil under multiple freeze thaw cycles may damage soil structure due to generated forces by water freezing and changes in mechanical and deformation features. Silty soils are highly susceptible for frost damage under the F-T cycles so, it is important to investigate their thermal and mechanical behavior. Thermal changes in susceptible soil often lead to irreversible creep deformation. The freeze and thaw cycles change soil engineering properties and mechanical behaviors by varying soil structure (Othman., 1992). A lot of research has devoted to study the effect of freezethaw cycles on the geotechnical properties of various soils (Wang et al., 2007). But, less laboratory works have studied the effect of freeze-thaw cycles on long term deformation and consolidation parameter of silty soil. Therefore, the aim of this paper is to determine the magnitude and rate of volume changes of soil specimen under 10 repeated cycles freeze and thaw which subjected to different vertical stresses...

1. Introduction: In the Civil Engineering field, we have to search a structure with lower weight and cost, to reach minimal energy and materials. Since using of Cellular and Castellated Beams can provide higher bending strength and stiffness without increasing the weight of the structure, therefore, in the recent years, they have lionized by most researchers. In some structures like bridges, in order to large stiffness and high strength, we have to use special beams with large dimensions and height. On the other hand, to solve this necessity, it is not possible to use hot-rolled Castellated Beams. So Castellated plate girders can be used. In this paper, it is denoted that castellated plate girders can be used in long spans as a convenient choice...

1. Introduction: One problem of accumulation and water flow is the increase in the kinetic energy experienced by the flow. Amortized energy regulators can be used to reduce this effect. If the kinetic energy of the falling flow is not controlled, considerable damage may be done to canals and downstream, structures. Due to the importance of making structures for energy dissipation lots of studies have been done so far that for instance studies of Peterka 1983 and Carvalho and Leandro (2012) must be noticed. A hydraulic jump is a common phenomenon that occurs downstream of hydraulic structures, such as weirs and grates which increase the fluid depth by converting from supercritical to subcritical flow conditions in a relatively short range. These jumps have an important role in the energy dissipation. The possibility of shrinking sections in the supercritical flow that may result from construction of a bridge foundation makes it necessary to calculate the energy dissipation caused by exposure to supercritical flow. In this study, supercritical flow behavior near sudden constrictions is evaluated...