Modares Civil Engineering journal
Year:2019 | Volume:19 | Issue:5 |Papers Count:18

For safe underground excavation, different supporting systems can be used in weak ground conditions. However, rock mass instability does not give opportunity to install an appropriate supporting system. Because, tunnel face collapses and moves suddenly toward into tunnel. Different approaches and methods has been developed to prevail over this condition including sequential excavation of tunnel face, grouting of unstable and loose zones behind the face, using inclined longitudinal elements above tunnel crown prior to excavation known as arch umbrella elements methods, installing a pre-cutting system, and pre-reinforcement of tunnel face by fiber glass longitudinal elements. These methods may be employed either alone or together according to the severity of the problem. Fiber glass dowels are one of the most efficient and economic methods of above mentioned approaches. Fast installation, flexibility in using with other supporting systems … are the other advantages of this pre-reinforcement. Although numerous studies have been conducted to evaluate and quantify the effectiveness of this method, some aspects such as evaluation of the tensile force induced in the dowels has not been studied. In fact, a correct dimensioning and evaluation can be obtained through three-dimensional numerical modelling. Hence, this paper studied numerically the behavior of the longitudinal fiber glass dowels installed uniformly at tunnel face along tunnel axis and may accompanied with the different supporting system i. e. with shotcrete layer as the main supporting system or with arch umbrellas or pre-cutting system as the other pre-support method. The analyses was carried out by FLAC 3D in different weak ground condition, say the class IV in Binyavsky category, subjected to three different in-situ stresses implying tunnel depths. As well, four lateral stress coefficient were chosen in the analyses. The fiberglass forces as well as tunnel center displacements are the output of this simulation. First of all, the obtained results from the numerical simulation in hydrostatic stress condition were verified by one of the previously presented analytical methods, then analyses were extended to non-hydrostatic stress condition. The results showed non-hydrostatic stress causes non-uniform stress and displacements in the face. As a result, the location of critical zones developed in tunnel face. It leads to employ more dowels on those zones. On the other hand, as lateral coefficient increases, the maximum stress of the dowels and strain of tunnel center increases. The maximum strain and stress occur at k0=2. However; critical zone can be developed at the tunnel crown at k0=0. 5. Therefore, with increasing the lateral coefficient, critical zone moves toward the tunnel sides. As well, the best result for the dowels could be seen when they were accompanied with pre-cutting system. It is more highlighted to notice that using dowels in more deep tunnels subjected to great lateral stress (say very squeezing condition) is not sufficient (because they yield) but must be accompanied with other system. Finally, from the results of numerous analyses, mathematical formulations were presented to fast calculate the maximum stress of dowels and strain of the tunnel center in any different condition of weak ground condition.

Nowadays, Steel Plate Shear Wall (SPSW) is considered as a suitable alternative to conventional lateral load resisting systems that used for earthquake resistant design of structures, because of high post buckling strength, significant ductility, stable hysteresis characteristics and high initial stiffness. Also, steel plate shear wall has lighter weight of structures, increased floor area, quicker speed of construction, significant economically affordable and high quality control compared to a traditional reinforced concrete shear walls. Study on behavior of steel plate shear wall began in 1970s with the aim of providing an easy method for the analysis and design. The initial experimental and analytical research clarified varies aspects of seismic behavior of steel plate shear wall, but it is still unknown, because of its complex behavior and design. Although some researches on steel plate shear wall has been done since the early 1980s, the appropriate performance of structures that had steel plate shear wall as lateral load resisting systems in the Northridge, USA (1994) and Kobe, Japan (1995) earthquakes caused researchers and working engineers to investigate and implement the steel plate shear wall system to a greater extent. Analytical and experimental research works and studies, provided primarily in Canadian, US and UK universities on steel plate shear wall considered different facets of the seismic behavior of steel plate shear wall and flourished the essential procedures for its application as an effective lateral load resisting system. However, in order to investigate the performance of steel plate shear wall comprehensively, wide range of nonlinear behavior has to be assessed and predicted and it requires hysteresis models that are capable to consider all deterioration modes. One of the comprehensive analytical hysteresis models is the modified Ibarra-Krawinkler (IK) deterioration model that provides four deterioration models including basic strength deterioration, post-cap strength deterioration, unloading stiffness deterioration and accelerated reloading stiffness deterioration for systems with bilinear, peak oriented and pinching behavior. In this study, by calibrating the modified Ibarra-Krawinkler deterioration model parameters for steel plate shear walls with different properties, some equations are proposed to determine modified Ibarra-Krawinkler deterioration model parameters. First, one of the experimental specimens was modeled and analyzed in ABAQUS software and accuracy of results was measured. Then, 60 number of pinned joints-one story steel plate shear walls with different infill plate thickness and bay length, using two types of steel for infill plate are numerically modeled and analyzed by ABAQUS software. Also, the height of steel plate shear walls was kept constant equal to 3500 mm. Using OpenSees software numerical analysis results, the modified Ibarra-Krawinkler deterioration model parameters are calibrated. Then, by identifying the effective and pertinent factors, some statistical equations are suggested. According to the results, effective parameters on lateral load resisting capacity, elastic stiffness and post capping stiffness were thickness of infill plate and its steel type and ratio of bay length to height of steel plate shear wall. Also according to the results, ratio of bay length to height of steel plate shear wall had more influence on modified Ibarra-Krawinkler deterioration model parameters.

Today, the use of waste tires mixed with soil has been expanded in various geotechnical projects to absorb and reduce the vibration caused by seismic and dynamic loads. Therefore, the objective of this work was to evaluate the dynamic properties of such mixtures prior to practical applications. Given that the different kinds of exterior cyclic loading affect the natural soil, such as earthquakes, high buildings, high speed rails, wave loads, oil tanks, reservoirs and so on, and they demonstrate different wave patterns. So far independent research on the effect of loading frequency on the dynamic properties of the sand-tire mixture has not been carried out. Therefore, in this paper, 1-g shaking table tests were employed to investigate the effect of loading waveform on dynamic properties of sand-tire mixture. A hydraulic shaking table with a single degree of freedom, designed and constructed at the Crisis Management Center of Urmia University, was used to conduct the experiments. Firoozkuh No. 161 sand was used in all the experiments and tire powders were used as a soil reinforcement material. Tire powders are made from discarded tires that have been broken into pieces and sieved by an industrial tire-shredder system. Also, accelerometers were used to measure the acceleration of the input to the sample as well as to record the acceleration caused by the input excitation at different depths of the soil sample. The displacement transducers (LVDT sensors) were also used to measure linear displacement. To record information, all sensors were plugged into a 16-channel dynamic data logger ART-DL16D. Samples were constructed in both unreinforced (pure sand) and reinforced form and with a relative density of zero. In reinforced samples, tire powders were added to the sand with 5%, 10%, 15% and 20% in gravimetric basis. To prepare the sample, a wet tamping method was utilized in both the unreinforced (pure sand) and the reinforced (sand mixed with tire powders) specimens. In this method, first, the sand was mixed with 5% water. Samples were subjected to rectangle, sinusoidal and triangle waveform at constant frequency of 2 Hz and input acceleration of 0. 1g and 0. 3g. The results showed that in all cases, soil samples exhibit the highest shear modulus and damping ratio under rectangle loading. Therefore, the values of G and D for the rectangular waveforms are greater than those of the sinusoidal and triangle waveforms. The shear modulus and damping ratio for the sinusoidal waveforms are marginally greater than those of triangle waveforms. The effect of loading waveform on the damping ratio of the soil at low levels of strain is negligible, but it increases with increasing strain levels. The shear modulus reduced by increasing the tire powder and the highest reduction is observed in the mixture with 10% to 15% of tire powder. By increasing the tire powder, the damping ratio values of samples increased so that the mixture with 20% of the tire powder has the highest damping ratio. In all cases, the shear strain increased by increasing the amplitude of the input acceleration, and as a result, the shear modulus decreased and the damping ratio increased. In addition, with increasing acceleration, the difference between the values of the shear modulus and the damping ratio increases between different loading waveforms.

In recent years, the construction of high-security buildings against the conditions of explosion and fire is a very important issue in the world. Therefore, one of the appropriate strategies in this field is to use steel-concrete composite columns to be used in the core of the concrete column to maintain its durability and stability against high temperatures. This paper studies the impact of temperature rise on the performance of concretefilled double skin tubular steel columns with prismatic geometry. In doing so, a number of columns whose interior core was square, diamond and circularly-shaped and their exterior core was prismatic with a square cross-sectional area increasing with the slope of 2. 1 degrees from top to the bottom, were constructed and exposed to the temperatures of 25, 250, 500 and 700 ° C. Accordingly, the temperature rates up in compliance with ISO-834. Afterwards, all column specimens were subjected to cyclic loads adopted from the ATC-24 loading protocol which proceeded until the specimens failed. Firstly, the 28-day compressive strength of concrete, measured, and steel used is tested under tensile test and the stress and strain characteristics were obtained. The results indicate that although the failure mode of the columns with interior core of square or diamond shape resembles each other, the columns whose interior core was circularly-shaped, experienced more intensive damages compared to the latter specimens. Failure mode of the columns base was developed as a diagonally with degree of 45° by temperature of 500 ° C but at the temperature of 700 ° c, the damages have occurred horizontally at the level of 10 cm from the column base. Moreover, initial stiffness and ductility ratio of the columns with diamond-shaped interior core was approximately 2 times greater than the other columns. in all columns, the maximum damage in the leg area is caused by the maximum anchor in that area caused by 25 to 700 ° C, and with increasing temperature, the central and middle regions are also completely destroyed, so that at 700 ° C in all specimens, concrete is completely crushed in such a way that it has virtually no role in the load-bearing capacity of the column. The destruction of concrete in columns is almost identical in all columns of the inner circle of the circle, squares and diamond. In general, the load-bearing capacity of the columns decreased by about 50 % after 15 cycles at a temperature of 700 ° C after 9 or 12 cycles, and the loading process was halted. In the meantime, the columns of the inner circle of the circle had broken out earlier than the other columns and did not have proper functioning. also in the diamond-shaped columns, the rupture process and the severe reduction of the carrier capacity are initiated at 500 ° C, indicating that this column does not indicate that this column is due to heterogeneous geometrical distribution at the height of the column. Generally, in all columns, at 25 to 500 ° C after 15 cycles and at 700 ° C after 9 or 12 cycles, the load capacity of the columns dropped by about 50% and the loading process was stopped.

The formation of a vortex at the mouth of power plant intake is one of the unfavorable hydraulic phenomena that occur during dewatering of dams. More precisely, the formation of vortex flows in the openings of the intake disturbs the proper functioning of the intake structure. vortices cause problems such as oscillating in the system, reducing turbine output, increasing hydraulic losses in the intake openings, entering the air and particles into the intake pipe and eventually reducing its efficiency. In recent years, various scholars have conducted extensive studies on the phenomenon of vortex. In the meantime, research has been carried out experimentally using mechanical devices and less attention has been paid to the natural phenomena existing on the level of reservoirs of dams and their impact on the vortex. One of the most important natural phenomena that occurs in the reservoir of dams is the waves that can affect the vortex. In this research, with the aim of investigating the effect of waves on the vortex, numerical simulation of waves in the openings of vertical intake has been studied in various vortex formation conditions. In this regard, three class of vortices A, B and C were simulated in numerical model and the results were investigated after dealing with waves. To simulate the flow in the vertical intake, the model designed by Sun and Liu was used. This model is designed in a cylindrical shape with four rectangular inlets, with a vertical intake located at the center and end of the cylinder. In the present study, the model was studied in three-dimensional and two-phase mode, so that numerical simulation of vortex and wave can be investigated with this approach. In order to reduce the computational time to solve the equations, Euler's method was chosen and the turbulence was simulated using the LES model in STAR-CCM Software. After sensitivity analysis, 3 mm grid dimensions were selected. For computational mesh domain, a Cartesian coordinate was used and the free surface was considered using the VOF method. Accordingly, after formation of three classes of vortices A, B and C in the numerical model, three waves with a/d ratio of 2. 6%, 1. 3% and 0. 3% were generated and the effect of their collisions on vortices was analyzed. The amplitudes of the waves are determined in relative proportions of the reservoir water's height and are not far from reality. The results showed that the waves reduced the components of tangential, radial and axial velocity. According to the results, the maximum component of the tangential velocity at the time of the presence of waves is reduced by about 14%, 19% and 23%, respectively, in the class A, B, and C vortices. The radial velocity component is also reduced by about 9%, 13% and 18% for the A, B, and C vortices, respectively. The maximum axial velocity was also reduced to 26%, 13%, and 23% for class A, B, and C vortices, respectively. According to the simulation results, the decrease rate with decrease decreasing wave amplitude, which means that smaller waves can lower the velocity components and thus weaken the vortex flow.

The increase of population and demand for water, agriculture and energy cause rapid increase construction of the dam has been. Moreover, the increase of dam height to increase storage and estimate the need for water cause increase the velocity of water over the spillway has been. Spillways, chutes and bottom outlets are important hydraulic structures for dam safety. Due to high velocities combined with low pressures, cavitation damages may occur on chute bottom and cause major damages or endanger the dam stability. Damage experience for flows in spillway tunnels and chutes indicates that damage becomes significant when water velocities exceed 30m/s, this velocity or head can be considered as the borderline for high velocity or high head flows. Introducing air to high-speed flow is necessary to prevent pressure reduction and its events such as cavitation. It is possible to protect spillway surfaces from cavitation damages using aerator devices. Usually, the air entering the flow is not reached to the bed chute. It is necessary to install the first aerated according to topographic conditions and cavitation index at the appropriate location. By determining the process of changing the air concentration of the bed, the distance between the two aerators can be determined. The air in the flow causes the compression and damping that cause Bursting bubbles. In result, the damage caused by cavitation is reduced. So cavitation investigations will be necessary and need to reduce and prevent cavitation damages. The length of the flow jet has a fundamental role in determining the distance between two aerators. With increases the length of the jump, the contact surface of the upper and lower layers of the jet is in more contact with the air and affects the amount of air entering the flow. The absorbed air is removed from the flow after the Jet collision. By determining the minimum concentration of air in the bed, an optimal distance between the two aerations can be selected to prevent cavitation damage. Select the minimum air concentration of bed is based on the relationship provided by Wood (1983). It means that the concentration of average air in the stream is higher, which causes the flow of bulking and requires taller walls for the sides of the shut Which is not economically feasible. The variation in the air concentration of the bed can only be considered as a function of the length of the jump flow and the upstream heights. Creating a suitable duct for providing A negative cavity pressure Lead to better performance that causes increases the distance between aeration. So use of aerators in suitable places and the entrance of air to water flow is a most effective way to reduce this damage, therefore in this study, an equation has been derived to estimate the distance between two aerators base on 1200 data of 90 experiments with R2 more than 0. 84. Results of the present study with distance aerators of the Azad dam based on the minimum air concentration of bed have been compared and investigated.

In this paper, a new boundary element analysis for the modeling of two-dimensional potential problems is proposed. The boundary element method is reformulated here based on spherical Hankel elements for the purpose of approximation of the state variables of the Poisson and Laplace differential equations (potentials and fluxes). Spherical Hankel function is obtained by combing Bessel function of the first (similar to J-Bessel ones) and second (also called Neumann functions) kind so that the properties of both mentioned functions will be combined and result in a robust interpolation tool. The interpolation functions of the boundary element method are obtained using the enrichment of the spherical Hankel radial basis functions. To this end, the expansion of a function in which only the spherical Hankel radial basis functions approximations are used have been given polynomial terms. Generally, radial basis function (RBF) is an efficient tool in finding the solution of non-homogeneous partial differential equations. Its main idea is the expansion of nonhomogeneous term by its values in interpolation nodes, based on Euclidean norm that leads to obtaining a particular solution. Although the J-Bessel RBF contains the features of the first kind of Bessel function, it usually cannot represent the full properties of a physical phenomenon. Therefore, using the combination of the first and second kind of Bessel function in complex space (Hankel function) may lead to more accurate and robust results. In other words, the solution of Bessel equation can be referred as a prominent usage of both first and second kind of Bessel, which shows that using them together may result in more accuracy and robustness. The aforementioned discussion brings this matter to mind whether it is possible to present RBFs that benefit from both Bessel functions of the first and second kind. Therefore, by the idea of combining spherical Hankel in imaginary space, enrichment of them for a three-node element in the natural coordinate system is explained in this paper. Moreover, the algebraic manipulations and formulations are reduced because of profiting from the advantages of complex number space in functional space. It is also possible for the proposed shape function to satisfy both Bessel function fields and polynomial functions, unlike classic Lagrange shape functions that only satisfy the polynomial function fields. Moreover, the proposed shape functions benefit from the infinite piecewise continuous property, which does not exist in the classic Lagrange shape functions with limited continuity. The spherical Hankel function of the first kind has a strong singularity in its imaginary part, the spherical Neumann function. This issue results in the fact that when the Euclidean norm tends to zero, the limit does not exist. In the following, an extra term with power n  1 is applied to remove this singularity. After the elimination of the singularity, the limit state of coinciding source point and field point is calculated. In the end, to demonstrate the accuracy and efficiency of the proposed shape functions, several numerical examples are solved and compared with the analytical results as well as those obtained by classic Lagrange shape functions. The numerical results show that the proposed Hankel shape functions represent more accurate solutions, using fewer degrees of freedom, in comparison with classic Lagrange shape functions.

Dynamic properties of structures, such as natural frequency, shape modes, and damping ratios, play a decisive role in structure behavior against dynamic loads like earthquakes. Determining the earthquake forces imposed on structures based on the design spectra is one of the utilization of these properties. Other applications of these features could be utilized to update the finite element model, detect potential damage in structures, long-term health monitoring of structures, and evaluating the safety of structures after heavy loading. Therefore, accuracy and reducing the cost of extracting these properties would have a significant role in improving the efficiency and consequently of the useful life of structures. In other word, the more accurate of structural dynamic properties means, the more accurate determination of the seismic response of the structures. These properties depend on a great deal of detail, such as material behavior and the geometry of the structure, which could not be easily simulated in analytical models. So, performing seismic tests on structures is the most reliable method for obtaining these properties. Determination of these properties have been done in a variety of ways. However, various methods have been developed in many studies to extract these quantities by image processing. The aim of this article is presenting a novel approach to increase the accuracy of remote sensing by image processing. Therefore, the current paper is an attempt to apply the average method to improve efficiency as a cheaper method for obtaining the dynamic properties of structures. For this purpose, a cantilever aluminum beam and a Threestory frame with additional mass have been considered, and the commercial camera captures the vibration of the structure. The extracted displacements of each four points on the edge of the specimen are recorded as the input signals of the system. With two numerical derivatives of these displacements, the acceleration of the structure is obtained. Peak survey method utilized to extract natural frequencies, damping ratios, and mode shapes of the each selected point. The averaging method applied to calculate the final properties of the structure. At last, the results are compared with the values obtained from the acceleration sensors embedded on the structure and the finite element results. Then the accuracy and error of the algorithm are evaluated. However, these results could be utilized as the input information in the health-monitoring of the structures. The results show that the novel method did not improve the accuracy of the first three natural frequencies modes of vibration in comparison with the standard method for the cantilever beam. It is also observed that the new method wouldn’ t make a significant difference in the calculation of damping ratios of the system. On the other hand, although the existence of cables and sensors would reduce the accuracy of image processing and recorded displacements, the new algorithm improves the estimation of the first three shapes modes. In the same way, the same function was performed for the Three-story frame structure. Although its natural frequencies did not change for the first three modes of vibration, the mode shapes are closer to the values obtained from the accelerometer sensors.

Activated sludge process is commonly utilized for the treatment of wastewater with the benefits of high efficiency and easy operation. However, during the biological treatment of wastewater, huge amounts of waste biomass (called as “ waste activated sludge (WAS)” ) are inevitably generated in the process. The WAS should be treated in order to reduce the water content of raw WAS, transform the highly putrescible organic matter into stable or inert organic and inorganic residue, and finally condition the residue to meet disposal acceptance regulations. But, WAS treatment and disposal, representing 50– 60% of the total operating costs of the wastewater treatment. WAS is produced in massive volumes; specifically, more than 25, 000 tons of WAS is produced in Iran per year. Anaerobic digestion is one the most applicable methods in WAS stabilization due to its ability to reduce WAS volume and produce biogases. A mixture of primary and secondary sludge (WAS) passes through anaerobic digestion, but this process is more difficult for WAS than primary sludge. However, the hydrolysis stage limits anaerobic WAS digestion. To optimize the general process of WAS anaerobic digestion and increase hydrolysis performance, it would be possible to pre-treat WAS by various mechanical, thermal, chemical, and biological methods. In this research the influence of ultrasonic bath pre-treatment was studied to observe the effects of ultrasonic density and sonication time on WAS solubilisation. The charactristics of ultrasonic wave producer was surface area of 240×137 mm2, frequency of 40 kHz, power of 265W. Increases in soluble chemical oxygen demand and soluble polysaccharide concentration, as well as the decrease in volatile suspended solids, indicate that pre-treatment could cause WAS solubilisation. The cavitation produced by ultrasound waves radiation breaked down the bacterial cell wall and released the intracellular substances into an aqueous phase. Since polysaccharide is one of the main parts of extracellular polymeric substances (EPS), a polysaccharide concentration increase in the solution indicated that ultrasonication disintegrates WAS floc and the EPS value reduced in biological flocculation. Increases in ultrasonic density and sonication time caused more solubilisation, stronger cavitation arised with an increase in ultrasonic density and with increased ultrasonic density; more floc structure disintegration was achieved in less time. The best Pre-treatment efficiency was achieved in ultrasonic density 0. 53 W/mL and 20 min. sonication time and it caused 20% increase in biogas production and 24% volatile suspended solids solubilisation compared to the control sample. The volatile solids after anaerobic digestion of pre-treated sludge also decreased. Increament in ultrasonic density and snication time had direct relation with volatile solids reduction. The best volatile solids efficiency was achieved in ultrasonic density 0. 53 W/mL and 20 min. sonication time and it caused 48% decrease in volatile solids Given the change in WAS, electrical conductivity with ultrasonic bath pre-treatment, in addition to other tests like chemical oxygen demand and volatile suspended solids, electrical conductivity could also effectively assess WAS solubilisation.

Increasing water in the slope layers induced the failure of slopes. . Water is the most important factor in most of the slope stability analysis. Although water does not directly lead to the slopes displacement, but is an important factor for the following reasons: (1) water increases due to rainfall and snow melt will lead to increasingslope weight. (2) Water can change the angle of slope (angle of slope is an angle that slope is stable in this angle). (3) Water can be absorbed or excreted by minerals are available in the soil. After adding the water, the weight of the rock and soil increases. (4) Water can dissolve the cement between the seeds and cohesion between the seeds is lost. In this paper, the feasibility of using piles to stabilize layered earth slopes were studied. A set of physical modeling of foundations was performed adjacent to layered slopes. The deformation pattern and shear strains of soil near slope and below surcharge load were studied. For this purpose, a comprehensive set of tests and numerical analysis were undertaken on different slope models. In each step of loading, digital image of deformed soil was captured and image processing was applied with GeoPIV software for investigation of soil deformation on slope and below the footing. the effect of pile and saturated conditions effects on improvement ratio (safety factor of stabilized slope with pile / safety factor of the slope stability without piles), bearing capacity of foundations, slope stability and slip surface shape in layered slope were investigated. The results show that the slip surface of layered slopes differs depending strongly on the installed pile positions and layered saturation conditions. In consideration of the model tests and numerical analysis results, it is found that, when clayey layer was near ground surface, changes in clayey layers water content significantly affected on slip surface and layered slope stability. Consideration of slipe surface shape for different layers saturation canditions, it is found, saturation of below layers which is located below the slip surface, has not significant effects on slope stability and slip surface shape. But with increasing upper layers water content, large volume of soil were failed. Experimental and numerical results show, for stable slope before applied surcharge load or before water content increases, critical slipe surface occurred in front the installed pile. But for unstable slope, critical slip surface positions depend on layers saturation and soil properties and occurred in front or behind or in upper and lower part of pile. In general The critical slip surface location dependent on water table level conditions and location of pile. Also from the experimental and numerical results it is found, the optimum location of pile for increasing bearing capacity of foundation which is located on slope crest, is near slope crest and maximum magnitude of Bearing capacity ratio ((bearing capacity of reinforced slope/ bearing capacity of non-reinforced slope)(BCR)) was obtained when piles installed near slope crest. Also optimum location of pile for increasing slope stability are found near mid of slope. A close agreement between the experimental and numerical results in Failure mechanism and the critical values of the studied parameters is observed.

Bridge failure is a common phenomenon all around the world. Bridges are one of the most important structures which are under attention from many years ago. Bridge is a structure to cross over obstacles such as rivers or valleys. Investigation of scouring in water structures especially in bridges is absolutely important in river engineering. Failure of several structures in all over the world are usually due to structural consideration and giant scales on piers. Created procedure of scouring by group of piers are more complicated than one single pier. Increasing the resistance of bed materials and decreasing the power of erosion factors are the ways to stand against local scouring. To decrease the power of erosion factors (horseshoe and wake vortex), equipment such as collars, submerged vanes and etc. are being used. This study was conducted with freshwater on cylindrical piers. The experiments were with a constant discharge during 6 hours in hydraulic laboratory of Ferdowsi University of Mashhad. In order to perform this study was used a channel that width, height and length were respectively equal to 0. 3, 0. 4 and 10 meters. In this research, Sands with median diameter of 0. 72, special gravity of 2. 65 grams per cubic centimeters and geometric standard deviation of 1. 12 are used in the experiments. Range of flow rate was from 8 to 18 Liters per second. An adjustable weir in the downstream regulates the water depth in the channel. The area for conducting the experiments in the channel has one meter length and 10 cm bed height, which is 6 meters away from the beginning of the channel. Scouring procedure of downstream pier was investigated base on flow velocity. Results show that depth of local scouring of downstream pier can be categorized in 4 zone based on flow velocity: 1-No scouring occurrence zone, 2-Synchronized scouring zone, 3-Transitional zone, and 4-Deviance zone. Following previous investigations, effects of application of rolled cable over piers on reduction of scouring around two piers and zones of downstream pier (zones related to velocity) were examined. In this study, the efficiency of using rolled cable around the piers as one way of controlling and reducing local scouring, to decrease scouring is investigated. Results show that rolled cable, scouring will decrease. In fact, rolled cable around the piers will decrease the power of down flow, horseshoe and wake vortexes. Results show that scouring was reduced around piers due to application of rolled cable. So that cable at its best state reduces the maximum scour depth by 50 percent for downstream pier in the situation distance 3D and 54 percent for downstream pier in the situation distance 5D. Reduction of scouring depth of downstream pier was less than upstream piers. Scouring depth of downstream pier with rolled cable was 7 and 26 percent reduced in comparison with piers (No rolling cable was used) located at 3D and 5D from it. Because of scouring reduction as consequences of rolled cable, downstream zones were significantly changed that finally caused synchronized zone removal.

In this paper hydraulics and flow structure over the rectangular piano key weirs with different heights have been studied experimentally and numerically and effects of different fillet shapes on hydraulic performance are investigated. Experiments are conducted in a one meter width flume. Models of the tested weirs are made from PVC Plates in 3 different heights and with the same L/W ratios equal to 5. Discharge coefficient curve for wide range of heads over height ratio for 3 different weir heights are determined and effect of triangular, half round and oval fillets on increasing of discharge coefficient are investigated. In this research, the chosen range for ratio of head over height is in good agreement with ratio which has been used to design of prototype weirs. Large triangular and oval shaped fillets have significant effects on improvement of performance of the piano key weirs. Main effect of fillets is more uniformly distribution of the flow streamlines over the downstream part of the side crest. In second part of this paper, one and half-key piano key weirs with oval noses and without any nose (net) have been numerically modeled using Flow-3D model. Discharge coefficients of one of the numerically simulated rectangular models is compared with derived discharge coefficient curve from physical model. Convergence of inflow and outflow of numerical model has been controlled. Satisfactory correspondence presents between the experimental and numerical studies. Discharge distribution over the crest of the normal PKW and the weir equipped with oval fillet are compared. Result showed that due to uniformly distribution of the streamlines, the fillet notably increases flow rate at the downstream part of the side crest. Results of numerical simulations are exported to Tecplot software, in order to visualize the flow streamlines at different parts of the studied weirs. The weir with oval fillet affects the flow streamlines in three positions: the near bead streamlines of the weir with oval fillet, have less lateral diversion when they reach beneath the overhang of the outlet keys. In other word, streamlines pass this region more smoothly rather than normal PKW. As a result, the fillet decreases the local head loss, when the flow enters the inlet keys. Streamlines of the mid depth level show less contraction at the entrance and middle of the inlet keys. Consequently, lower velocity of the flow along the inlet keys, helps to more evacuation of the flow from side crests. Finally, streamlines release more uniformly from downstream part of the side crest. These phenomena results low submergence level at the middle of the outlet keys. The outlet keys are the brake of nonlinear weirs. By decreasing the submergence level of the outlet keys, flow from the side crests discharge more freely from inlet to the outlet keys.

Drought is an integral part of natural hazards. It usually occurs gradually and without any warning. Moreover, this phenomenon is usually created over time and does not disappear quickly. Recently, some factors such as climate variability and the impact of climate change have influenced drought frequency and intensity in many parts of the world. Various definitions have been provided for drought but in general the lack of water resources in a specific period in a geographical area is considered as drought which implies this phenomenon as a regional hazard. IRAN is located in an arid and semi-arid region in which it experiences drought frequently. There are different types of drought such as meteorological, hydrological, agricultural and socialeconomic. These types are differentiated based on the influential factors which are rainfall, river flows, soil moisture, and social-economic consequences. There are many indices proposed for measuring drought severity; among them Standardized Precipitation Index (SPI), Palmer Drought Severity Index (PDSI) and Surface Water Supply Index (SWSI) could be mentioned. Each of these indices has its own pros and cons and is suitable for a particular type of drought. Therefore, knowing the types of drought can provide a better understanding of shortages and their characteristics. Various factors are utilized for measuring these indices including precipitation, reservoir storage, discharge, temperature and potential evapotranspiration. In this study the three main aforementioned indices were first calculated for Aharchay watershed, located in East Azerbaijan province. Next based on combining these three indices with another two important parameters, groundwater level and solar radiation, a combined drought index is developed and calculated for the studied region. Considering the fact that the aforementioned parameters and indices have different level of importance in combined index, different weights based on the expert opinions (subjective approach) and the level of variation (objective approach) are assigned to the parameters considering how critical each parameter is in the overall drought analysis. This combined index demonstrated various climatic, hydrological and agricultural aspect of the region. In the next step, bivariate analysis of the two variables, intensity and duration, is carried out using copula. This is done by first checking the dependency between intensity and duration using Pearson, Spearman, and Kendall correlation coefficients. Second, various copula functions were fitted such as Gaussian, T, Clayton and Gumbel functions. Third, based on the Ordinary Least Square (OLS) and test, the best copula functions were used. Lastly, based on the chosen copula the joint probability distributions were obtained. Two cases named “ OR” and “ AND” were defined for joint probability of the two variables and different return period curves were drawn. The results showed that the most severe drought in this watershed occurred in June 2004. Moreover, by assessing correlation coefficient between the considered indices it is shown that analysis of the drought in a region based solely on one index would neglect other imperative aspects in drought determination which necessitates a more integrated indicator. Furthermore, in bivariate analysis, return periods of “ AND” cases were more than “ OR” case. The results of this study could be utilized in preparedness and monitoring drought.

The tubular structures are having the capability of resisting wind and earthquake loads with the exterior tube system. Tube systems consist of closely spaced exterior columns and deep beams around the plan that provides sufficient rigidity and stability for tall/high-rise buildings. Another advantage of the tubular system is the significant reduction of the building materials and increasing the architectural space in the internal plan. The mentioned cases have increased the popularity of this kind of structural system. But the most important problem in the tube system is the shear lag. Shear lag is the non-uniform distribution of axial stress on the face columns when the tube system is subjected to lateral loads. Shear lag can occur in any box-shaped structural system that is loaded laterally. Shear lag increases structural displacement, limiting the use of maximum structural capacity and causing warping of the floors. The purpose of this research is to study the effects of shear lag on the tube system and find how to reduce shear lag. In order to do this, a tubular structure is analyzed and designed based on the Capacity Design Approach and Performance Base Design based on LATBSDC, ASCE 7-16, and AISC 360-10. To evaluate the seismic performance of the tubular structures, the Nonlinear Dynamic Procedure (NDP) for two ground motion intensity levels based on LATBSDC is used. Nonlinear dynamic response analyses for two earthquake ground motion intensities done and acceptability criteria demonstrated. In the next step shear lag in the designed structures is investigated. Also, the relationship between shear lag and the stiffness of the peripheral beams is studied. The result shows that increasing peripheral beam stiffness is not a good way to reduce the effects of shear lag because of economic issues. Also, other proposed methods, such as the addition of core or internal tubes, are not a suitable solution to reduce the effects of shear lag, given the high cost they impose on the project. Due to the development process and the effect of shear lag on tubular structures, adding two-bay X-braces to one-fifth of the height of the structure in lower floors have been proposed to reduce the effects of shear lag. In order to calculate the shear lag, the column's axial stress distribution in the tubular structure is considered as the basis and compared with the column's axial stress distribution in the two-bay X-braced tube system. The proposed tube system and tube system have been analyzed by different levels of earthquakes and compared for performance purposes. In all the analysis and evaluations carried out in this study, the performance and behavior of the proposed systems were better than the tubular structure. With the addition of two-bay X-braces to one-fifth of the height of the tube structure in lower floors, the stress in the corner columns has been significantly reduced. Also the proposed system has been able to significantly reduce the shear lag. Therefore, in order to reduce shear lag and achieve proper behavior in tube systems, it is recommended to use the proposed systems in this study.

Maintenance and repair of structures during the life of the structure is inevitable. Therefore, using a repair material that have the ability to re-service in a longer time is necessary. Today, produce a repair material that has a complete bond with the damaged element and makes it economical based on the available materials in the country is necessary. On the other hand increasing the quantities of waste materials, scarcity of land-filling space and because of its ever increasing cost, recycling industrial waste materials has become an attractive proposition to disposal. One of these by-products is waste foundry sand. Waste foundry sand that contains resin, coal powder and bentonite which are solvable in the water and leads to environmental pollution. Therefore, industry owners are looking for a solution to the problem of organic waste due to pressure from environmental organizations. One of these solutions is dumping of construction waste in cement products such as concrete, mortar and grout. In this research, with the aim of reaching mortar and grout with good performance and durability, as well as up to 40 MPa compressive strength of 28 days, the initial mixture ratios were determined and the final mixture was determined by making laboratory samples and correction of ratios. 5 mixtures for mortar and 5 maixtures for grout. In the mixtures for all mortar and grout samples, the ratio of water to cement is fixed at 0. 4 and the cement content of the mortar samples is 650 kg/m 3. Natural sand mortar samples have been replaced with 10, 15, 20 and 25 percent waste foundry sand. The amount of cement for grout samples is 1100 kg / m3. In grout mixtures, 10, 15, 20, and 25 percent of sand have been replaced by waste foundry sand (WFS). The results indicate that replacing WFS reduces the workability of mortar and grout. The compressive strength of the mortar samples is reduced by replacing different amounts of WFS at the age of 7 and 28 days. Mortar with 20% replacement of WFS, is the optimum percentage of waste sand in the mortar. However, the compressive strength of the grout samples increases by replacing 10% casting sand. By increasing the replacement value by more than 10%, the compressive strength decreases. Based on various studies in concrete, ultrasonic velocity test (as a non-destructive test) is used to estimate the compressive strength, which has a linear correlation between ultrasonic wave velocity and compressive strength. But the results of this study showed that the non-destructive test of ultrasonic waves does not have the ability to estimate the compressive strength and the flexural strength of the mortar. This result was also observed in Grout samples. Therefore based on the results of this research the ultrasonic velocity test does not have the capability to estimate the compressive and flexural strength of mortar and grout. Despite the decrease in the mechanical properties of the mortar by replacing WFS, the water absorption of the mortar containing this material has decreased, which is up to 15%. But by increasing the replacement percentage by up to 25%, the volumetric absorption of the samples of the grout decreases.

Natural rivers are rarely in direct flow because of regulating energy grade-line, and usually have a curved path to which it is referred to as "meandering channels". After the appearance of meandering rivers, with the passage of time and lateral movement of the meanders, the external bending progression and the sinusoidal or curvature is increased. In meandering channels, the curvature of the meandering sections with a dimensionless number can be defined as the sinusoidal which is the ratio of meander length of main channel to the floodplain length. By increasing sinusoidal slope number, flow velocity and river discharge capacity decrease. As a result, the risk of flood has increased significantly and during floods the water level exceeds to the bankfull and then enters to the floodplains. In this case, due to the interaction between higher velocities in the main channel and the lower velocities in the floodplains and the momentum transfer between these two regions, the flow profile is constantly changing. In this research, the hydraulic characteristics of flow including the depth-averaged velocity, the water surface profile, longitudinal velocity distributions, ratios of transverse to longitudinal velocities in the central axis of the main channel and the mean velocity and flow rate of the main channel along the meandering compound channel have been investigated numerically, regarding the change in the sinusoidal ratio for six types of channels with different sinusoidal ratios. In order to investigate the effect of sinusoidal ratio in meandering compound channels on the hydraulic characteristics of the flow, the FLOW3D software is used. So that, the turbulence model with experimental data have a better compliance. for this purpose, two RNG and k-ε turbulence models were then used and the performance of these two models were investigated to simulate the important hydraulic characteristics of the flow, such as the flow velocity, and it was determined that the RNG turbulence model has a better accuracy than the k-ε turbulence model. In the following, this model was introduced as a final turbulence model for numerical simulations. Numerical simulation results show that by increasing the sinusoidal ratio of channel from 1 to 1. 641, the mean velocity of the main channel section is decreased by 54% on average and the flow rate of the main channel decreases by the average of 38%. Also, by increasing the sinusoidal ratio, the maximum depth-averaged velocity, Ud, decreases from 0. 55 m/s to 0. 38 m/s, and the maximum free surface height of the water rises from 0. 305 m to 0. 332 m in the outer bend of the CS1 cross section. By increasing the sinusoidal ratio causes the ratio of the transverse velocity to be increased longitudinally in the central axis of the main channel, so that its value in the most critical state reaches from zero to 0. 4. As the sinusoidal ratio increases, the maximum length velocity moves towards the right side floodplain (internal bend) and decreases its value. So that by increasing the sinusoidal ratio from 1 to 1. 641, the maximum longitudinal velocity 0. 55 m/s to 0. 42 m/s and its position moves from the centerline of the main channel to the inner bend over the depth of the main channel overflow.

The presence of halite karst systems in dam reservoirs can be one of the crucial sources of pollutants for the water resources. Karstic regions are those with dissolving caves. If the dam is constructed in the regions with reactive rocks it is likely to be endangered by karst phenomenon, dissolution and corrosion of current waters. construction of dams and reservoirs in these formations are associated with high risk. A comprehensive and accurate understanding of the salt dissolution processes facilitates the description of salt karst formations dissolution process in dam reservoirs. This research was performed based on three bases: field studies, experimental investigation and numerical modeling. For determination of dissolution coefficient, the physical model of the reservoir was built in the form of the trapezoidal channel and samples of salt rock in the reservoir were used in the physical model of karst formation. This model was implemented in different conditions and the results of dissolution amount and salt concentration were measured for different time scales. At the next stage, the physical model was simulated in the numerical model for determining of dissolution coefficient. The numerical model ran with different dissolution coefficients and results were compared with experimental results. With this comparison and adaptation of results, the dissolution rate of halite karst determined and then used in the numerical simulation of the main reservoir. With simulation of main reservoir using dissolution coefficient obtained from laboratory study, the effect of salt karst formation on the reservoir’ s water quality was analyzed. The influences of effective parameters such as dissolution rate, air temperature, discharge and relative humidity on the water quality of dam reservoir were studied along with carrying out a wide range of sensitivity numerical analysis. To this purpose, a versatile finite volume tool ‘ MIKE’ was used. Using the experimental study and numerical simulation and implementation of results, the dissolution coefficient of salt karst formation was calculated about 0. 2 cm/h. Numerical model results showed that early months of operation were not critical to the project and salt concentration in reservoir was in the range of 0. 8 to 0. 9 of allowable limit. But considering the changes occurring in the reservoir’ s conditions, the process of salinity distribution increases and salt concentration increases with time. By comparing the salt concentration in reservoir and numerical model, it was found that the average error percentage of concentration values was about 13. 65 percent and the numerical model showed the values lower than the reservoir in most times.   The sensitivity analysis of parameters affecting the salinity distribution showed that these parameters have a significant impact on salinity distribution and salt concentration in the reservoir. It was found that with 10 percent changes in studied parameters, dissolution rate with 21%, air temperature with18%, discharge with 21. 1% and relative humidity with 6. 1% caused changes in salt concentration of reservoir. According to the results, it is evident that dissolution rate and discharge were the most important factors that influence the behavior of salinity distribution in the dam reservoir.

Nowadays, one of the main problems of human being is the protection of the environment against the presence of waste materials. Every year millions of tires are discarded, thrown away or buried all over the world. One of these waste materials, waste tires are. Wired tires are made of rubber particles and steel fibers. Past research has shown that rubber particles and recycled steel fiber from waste tire, can be used in concrete. This type of steel fibers can have a positive effect on the mechanical properties of concrete. Rubber particles in concrete reduce the compressive strength. In some studies, it has been shown that rubber particles increase or decrease the abrasion resistance of concrete, and even the size of the rubber particles also affect the abrasion resistance of concrete. In this research, simultaneous application of powder and crumb rubber, wire and recycled steel fibers from waste tire in concrete mixture, has been investigated to study the abrasion and compressive strengths and unit weight of concrete. In this research, in 12 mixing designs, replacing of powder and crumb rubber with sand to the amount 9%, 13. 5%, 18%, 22. 5% and 27% by volume of sand and adding 0. 5% by volume of wire and recycled steel fibers from waste tire has been used. In all designs, the cement cutie is 380 and the ratio of water to cement is 0. 47 constant. In this research, different samples are compared with the control sample. Compressive strength were performed after 7 and 28 days. Also, abrasive resistance and weight per unit volume were performed after 28 days. The results of the experiments show that rubber particles with a fine gradation will have a better impact on the abrasion resistance. But this is not so that about compressive strength and it reduces more resistance. Based on the results, adding 0. 5% recycled steel fibers with a length ratio to high diameter to concrete containing 9% of powder and crumb rubber, reduction in compressive strength improves and cause increased abrasion resistance. But the adding steel wire to concrete containing powder and crumb rubber reduces the abrasion resistance. Use the powder and crumb rubber with 0. 5% recycled steel fibers, reduces the compressive strength and by increasing the amount of powder and crumb rubber, reduction of resistance will be more. The abrasion resistance of concrete containing powder and crumb rubber with with 0. 5% recycled steel fibers is increased relative to the control concrete. By increasing the powder and crumb rubber content, the abrasion resistance increases, but this upward trend occurs to a certain percentage of powder and crumb rubber replacement with sand, and then the percentage of increasing abrasion resistance decreases. By increasing the powder and crumb rubber, weight loss will be increased. From this perspective, it causes the lightness of concrete which can be the advantage of using these waste materials in concrete. The abrasion resistance of concrete containing 9% of powder and crumb rubber with 0. 5% recycled steel fibers has increased up to 37. 5% relative to the control concrete.