MODARES TECHNICAL AND ENGINEERING
Year:2005 | Volume:- | Issue:21|Papers Count:9

In airfield concrete pavements, dowels are utilized in order to transmit part of wheel loads over the loaded slab to the unloaded one. A 3-dimensional finite element model of a doweled joint in a rigid pavement system is described. All of the components are modeled using continuum element; no plates, beams, or strings are used, and thus no artificial stiffness has to be assigned. A definition of joint efficiency based on load transferred through the dowel is introduced. The Results demonstrate the effect of varying the interface conditions between the dowel, slab and foundation. A study is also made on the influence of dowel misfit on joint performance. Furthermore, this study shows that shear stress is maximum for the dowel nearest to the point of loading and zero at the distance 1.15 times of radius of relative stiffness, whereas according to PCA, it is 1.8.    

In rock materials there are reactive silica including opal, chalcedonic, tridolomite, etc. which are reactant and generally present in aggregates in the production of concrete. These aggregates react with alkali derived from cement. An alkali - siliceous gel is formed due to this active silica which is then expanded and swollen over a period of time and gradually deteriorates the concrete. In execution of civil projects the potential of alkali reactivity of aggregates should be studied by means of required chemical, accelerating and complementary tests before using in concrete production. In this paper aggregates selected from quarries of different cities in Azerbeydjan Province are assessed in order to determine the reactivity aggregates of to be used in the concrete of several industrial projects, having conducted accelerating mortar prism test ASTM C 1260, chemical methods ASTM C 289, long term Concrete prizm CSA-A 23, 2-14A. Besides, aggregates deterioration test by means of sodium sulfate analysis and chemical test were carried out to determine the overall sulfate and chloride contents. Consequently the tests results have been used in the procedures of concrete mixing plan/design.      

Double layer grids are typical examples of prefabricated space structures and also one of the most popular forms of space frames .Since nowadays many double layer grids are constructed all over the world, optimization of their design has a great influence on decreasing the costs and used materials. Some techniques have been developed by Salajegheh et al. for cross-section optimization of double layer grids. In this research an attempt has been made to include a geometrical parameter in optimization process. To that end a two-phase method is presented. In the first phase of optimization the cross-section areas are optimized using optimality criteria method (OC) for different layer dimensions. In the second phase, quadratic interpolation method is used to optimize the depth of the structure. This new depth is replaced for one of the previous depths and the two-phase optimization process is repeated until convergence is achieved. Four examples with different topologies but the same loading and boundary conditions have been solved; this algorithm prepares the ground for the comparison of costs of different topologies and selection of optimal topology as well. For the solved example, the optimum topology among these topologies is determined.    

Nowadays, sediment control at intakes is an important problem in the hydraulic structures. Sediment transport causes many problems in channels, irrigation networks, and turbines in powerhouse and in river engineering. Sedimentation reduces the useful life of a reservoir. Since obstruction of river flow causes sediment deposition upstream of weirs, usually sluices must be constructed. This is especially true when weirs are of the overflow type. One of the main points regarding the removal of deposited sediment upstream of weirs and mainly in the vicinity of the inlet structures is the extent of the eroded area. Amongst different parameters affecting flow characteristics and therefore capacity of the flow to erode the bed upstream of the sluiceway are width and the optimum opening of the sluiceway. The sluicing processes during transition period are not well defined. Therefore experimental results on some effective parameters on the variation of sediment removal are reported in this paper. Experiments are done in a flume with 12 m length, 75 cm width and 80 cm depth. A diversion weir is built 1 rm. upstream of the channel end. In these paper experimental results on the effect of sluiceway width, flow discharge, gate opening, upstream Froude number, and ratio of gate opening to sluiceway width on the efficiency of sediment removal is reported. Four different widths, 8 different flow discharges in combination with eight different sluice gate openings are considered which results in 256 experimental data set. It is shown that increasing the sluiceway width generally results in increase of the sediment removal. However, this trend is more noticeable in the lower range of the sluiceway width and further increase in the higher range of the width will not make much difference in the sediment removal. Therefore, it is possible to find a range of optimum values for the sluiceway width. Also it is shown that for higher values of flow discharge, the extent of the eroded bed could reach to such an extent upstream of the intake structure, which decreases the efficiency of the sluiceway.      

Seismic behavior of steel frames is affected by dynamic and static behavior of frame's connections. One of the reasons for not using MR steel frames with semi-rigid connections in seismic areas has been the possibility of large displacements and instability of the structure. In this paper, seismic nonlinear behavior of moment resisting steel frames with mixed rigid and semi-rigid ductile connections is studied. For this purpose, the seismic nonlinear behavior of steel frames with 3, 4 and 6 spans, and 1, 3, 5, and 8 stories with 4 different forms of mixed rigid and semi-rigid connections and five different initial connection stiffness including zero and infinite stiffness. Under Naghan, Tabas and Elcentro earthquakes are analyzed. Maximum transverse displacements, frames' main period. Maximum base shear force, hysteresis behavior of connection, ductility demands of frames, and time history of transverse displacement are evaluated. The results show that it is possible to design moment resisting steel frames with particular forms of mixed use of rigid and semi-rigid connections so that under earthquake forces, resulting base shear and displacements be less than those in similar rigid frames.        

Hybrid reactor is a combination of two systems Up-flow Anaerobic Sludge Blanket (UASB) and Up-flow Anaerobic Filter (UAF). It has many advantages over other anaerobic systems. It has also shown good results in different industrial and sanitary wastewater treatment. Not many researches have been done in the treatment of cellulose industries' wastewater using hybrid system. Therefore this system was used for wood fiber wastewater treatment as a new study. In this study, a Plexiglas pilot system of 7 liter size with 11 sampling ports has been used. After 8 months of study, the COD removal efficiency has been increased from 50% to over 90% with the organic loading rate of 1 to 10 kg/m3-d. Results of a complete batch study indicated that hybrid reactor removed 92% of COD organic loading rate of 10 kg/m3-d. Results also showed that UAF system in hybrid reactor, acts as a separator of gas-liquid- solid phases. In another words, there is no need to use a separator device in hybrid reactor. This results in cost reduction in design and construction of the system.      

Part of flow spills over bank(s) and flows on flood plain(s) in any natural river flood events. This affects flow behavior and generates a complex interaction mechanism between flows in main channel and flood plains. More than two decades, various researchers associated with problems in rivers and flood flows attempt to understand different aspects of this phenomenon. Although many features of hydraulics in compound river channels still remain questionable, however, it has been developed considerably compared to sediment transport features. So far, almost all studies in hydraulics of sediment flood flows in compound open channels are performed in laboratories, controlled conditions. Therefore it is necessary investigate this type of flow in natural rivers. The sediment rating curves in compound natural rivers with varying cross sectional geometry has been investigated in this paper using the already developed envelope sections method (ESM) combined with the sediment transport formulation of Ackers and White. Due to relatively sufficient data available, the compound cross section of Minab River at Brenttin hydrometric station is selected as case study. The results of applying the developed method show that the measured sediment data are with in the limits of sediment rating curves for the upper and lower cross sections. This method may therefore be recommended to generate sediment rating curves in rivers with highly varied geometrical cross sections.      

Due to high cost of bitumen and inappropriate efficiency of flexible pavement in areas such as coastal regions, warehouses, aprons and heavily traffic places, RCC is a suitable replacement and economically vital. The application of concrete pavements has been widely used around the world. Among different type of concrete pavements, Roller Compacted Concrete (RCC) has been recently been used as an alternative to conventional concrete pavements. The advantages of using RCC includes cost saving as a result of the construction method, material availability and the increased pavement placement speed. Appropriate permeability is essential in producing RCC due to lower cement content being used. The purpose of this research work is to enhance the permeability of RCC mixes by replacing certain percentage of cement with pozzolan material namely Silica Fume (SF). As such eight different percentage of SF were added to the RCC mixes and tested for permeability and compressive strength. The test results showed considerably increase in performance in comparison with conventional RCC mixes.