Modares Civil Engineering journal
Year:2019 | Volume:19 | Issue:3 |Papers Count:17

One of the usual methods for river banks protection is using spur dike structures that if properly designed and executed, in addition to controlling erosion, It leads to the rehabilitation of rivers margin valuable lands. Spur dikes affect the streamlines and it make changes in the velocity and direction of the flow, leading to major changes in the bed topography around the spur dike as well as the beaches. Recognizing and directing these changes will lead to the River Affordable Planning in the desired areas. In the present study, the effect of the Deflecting open gabion spur dike, attracting and repelling on the bed topography of the flow path and flow pattern has been investigated. ADV was used to measure flow velocity in different directions. This velocity meter is submitted by transmitting waves of 10 or 16 MHz frequency from a transmitter to a sample size of 6 mm in diameter and 3 mm in diameter at a distance of 5 cm from the transmitter and receiving waves by receiver antennas measures the velocity of particles within the sampling volume. The device has the ability to measure the distance from the floor inside the water. Therefore, taking into account the baseline level, the measured distance at each point was deducted from the base value and the scouring of that point was obtained. In these experiments, the Froude number was fixed at 0. 26. Also, the depth of flow in the set of experiments is 14. 6 cm, which is extracted according to the discharge rate and the displacement threshold formula. The experiments were carried out in such a way that after the equilibrium of the bedding and scouring harvest, the flow pattern was started using the ADV device. In this review, the performance of the spur dikes will be compared with the impervious spur dike. The results show that by decreasing the porosity of the spur dikes, the mainstream deviation and the intensity of the secondary flows around the spur dike have increased, which increases the topographic changes of the bed and creates larger cavities around the spur dike. As the erosion rate increases around the spur dike, sedimentation on the edges increases. in all three types of spur dikes, with increasing porosity, the dimensions of the scour hole are reduced. By increasing the porosity of the spur dike, the flow velocity from the pores of the spur dike increases, which reduces the difference in the flow rate from the headland and the flow through the pores of the spur dike and reduces the ability to carry flow sedimentation. In a spur dike with 50% porosity, bed topography changes occurred in a very small area around the spur dike and focused on the nose, while for a spur dike with zero porosity, the topography of the bed, depending on the type of spur dike, is several times the length of the spur dike, in Channel length and width occurred. The attracting spur dike has created much less variation in the flow pattern due to the way it is placed in the path of flow, and therefore the bed topography is less influenced by the presence of the spur dike.

In recent years, damage identification of structures becomes more attractive for researchers in order to quantify the condition of structural system during service life. Moreover, identifying the damage location and severity is very important after disasters such as earthquake and terrorist attak. Structures can also be damaged by normal activity such as corrosion, aging, fatique, wind, waveload, etc. Therefore, the structural health monitoring is an emerging field to ensure good performance of structures. In this paper, identification of the location and severity of damages in structures are studied by analytical method using artificial bee colony optimization (ABC). In the analytical method, the mass and stiffness matrices of structure can be determined by the finite element procedure. Considering the stiffness matrix of healthy structure and that of the damage structure, the location and severity of the damage can be determined. It is assumed that the global mass matrix remains unchanged after the damage occurs in the structure. The natural frequencies and mode shapes of damaged structure can be obtained by measurement. In the study, the damage characteristics are known. Then by applying the eigenvalue equation, the stiffness matrix is determined for damaged structure. Finding the location of damage is introduced as an inverse problem. The conventional methods are very expensive and time consuming, while meta-heuristic methods are capable to solve complex optimization problems. Swarm intelligence algorithm introduces the collective behavior of social insects colonies to solve optimization problems. Artificial bee colony algorithm is an evolutionary computing method, which was developed, based on the intelligent foraging behavior of honeybee swarm. Each food source is considered as a possible solution. The location and quality of the nectar from the flower is related to the damage properties and fitness function, respectively. The dimension of every artificial employed bee is equal to the number of member of the structure. Then quality value of the food source is evaluated by the fitness function. The best fitness value is memorized in each search. When the fitness value is improved after a predefined iteration, the new possible solution will be considered. In the ABC process, the number of food source, the limit and the maximum cycle number are three control parameters. In the optimization problem, applying a proper objective function is one of the indispensable part of the process. Since the structural damage detection is a highly nonlinear problem, a proper objective function can detect the damage accurately and quickly. There are various methods for damage detection, which generally can be classified into two categories, static and dynamic method. Because of the efficiency of the dynamic method, the objective function is selected based on the dynamic technique, which utilizes the eigenvalue problem. In the mathematical equation of the objective function, the mass and stiffness matrix of healthy structure is defined by finite element method. The natural frequencies and mode shapes obtained by the measurement or modeling the structure. The stiffness matrix of damaged structure is determined with the optimization algorithm to minimize the objective function. In a measurement test, the used sensors cannot detect all of the degrees freedom of a structure, therefore the obtained information in measurement include a limited number of frequencies or mode shapes. In addition, to avoid a time consuming process, it may be decided to utilize only a limit number of frequencies obtained by the measurement. The system equivalent reduction expansion process (SEREP), which is an accurate and efficient technique of model reduction, is utilized in the paper. Moreover, the damage detection is examined through three numerical examples, plane and space truss and palne frame, each one has two damage scenarios, which include noisy measurement data. The results indicate that the proposed method is a powerfull procedure to detect damages in structures.

Force-based seismic design, as the conventional earthquake resistant design philosophy, is going to be replaced with probabilistic performance-based design methodology. Through this method, induced damages against various levels of strong ground motions, play a dominant role. Seismic-induced damages are characterized by probabilistic damage functions, namely fragility curves. Fragility curves show the probability of exceeding damage levels (i. e. limit states) conditioned on strong ground motion intensities (i. e. Intensity Measures). Amongst well-known limit states (such as Immediate Occupancy, Life Safety and Collapse Prevention) for which the structure is to be checked, sidesway collapse limit state is of the greatest importance owing to the large amount of triggered losses during past earthquakes. Incremental Dynamic Analysis (IDA) method is the most popular method to achieve fragility curves for variuos limit states. Through this methodology, the structure is affected by increasing levels of ensemble of strong ground motions. For each ground motion, the intensity which causes the instability of finite element model of the structure presents the collapse points. Fitting log-normal probability distribution to the achieved intensities presents collapse fragility curves. The structure is to be checked against sidesway collapse in such a way that the probability of collapse for design-level seismic hazard is less than the pre-defined allowable probability. Optimization of structures is aimed to present the topology, shape of structures and size of structural sections in such that minimum target function (mostly the structural weight) is achieved, while variuos design constraints are satisfied. Size optimization of structural members has been accomplished through previuos researches applying gravity and equivalent lateral forces while seismic effects are taken into consideration. Besides to achieve the optimum structures applying the physical effects of earthquakes, number of researches applied time history analysis of structures against one earthquake record or mean of number of earthquake records. To involve the effects of uncertainties regarding strong ground motions, probabilistic damage margins must be included in the optimization constraints. To achieve this goal, in this paper, weight optimization of structres considering probabilistic constraints (represented by the target collapse probability) is investigated. To achieve an efficient algorithm, the collapse fragility curve of structure is predicted by trained neural network. The network is trained based on incremental dynamic analysis of simulated models of samped structures. Besides probabilistic constraint regarding collapse probability margin, maximum normal stress and inter-story drift ratio (as the deterministic constraints) are involved. Deterministic constraints are calculated by matrix analysis of the structure. The neural networks are trained to predict mean and standard deviation values of collapse fragility curves assuming modeling parameters as input neurons. Genetic algorithm is applied to solve the optimization problem for which the collapse probability for population of structures is predicted through the trained neural network. Finally, the effects of target collapse probability on the achieved optimum weight are examined. Achieved results show that the probabilistic constraint governs the optimization problem if the target probability of collapse is less than 10%. Beyond this value, deterministic constraints, which are the maximum normal stress and interstory drift ratio governs the optimum weight of the sampled structure.

Increasing builders waste of autoclaved aerated concrete (AAC) require new concepts for future recovery processes. There are two main aspects, underlining this basic necessity for developing AAC recycling models. Environment protection ranks first because of the risk of groundwater pollution by compounds leached out from AAC waste during its deposition. The second aspect is raw materials preserving because of the high content of the valuable potential recyclable calcium-silicate-hydrate phase 11 Å tobermorite (5CaO 6SiO2 5H2O) besides pure quartz and minor aluminate. In general the main constituents of AAC amount around 40– 50 wt-% for tobermorite and approx. 30– 40 wt-% for quartz. The tobermorite phase is causing the AAC strength and forms hydrothermally at 180– 200 ° C and 10– 12 bar pressure during autoclaving from the raw materials lime, quartz, and water. Minor parts of aluminum powder for pore-forming and small amounts of cement and anhydrite for better handling of the AAC-green bodies are the further additives of the AAC raw materials mixture. The high silicate content, as well as the valuable calcium parts, display AAC waste as an interesting raw material for zeolite formation as known from the treatment of fly ashes and slags. According to their outstanding properties zeolites are used in sorption techniques, catalysis, molecular sieving, and ion exchange processes, and in previous studies, we already could show zeolite hydro sodalite formation beside hydrogarnet and other valuable calcium-and sodium aluminosilicates applying NaAlO2 as an aluminum source in the reaction mixture. Those previous syntheses were performed in water and under low alkaline (1 m NaOH) and low acid (1 m citric acid) conditions. This mild reaction milieu was found to be responsible for relatively low AAC conversion rates and the formation of multiphase products. In reference, the aluminum source NaAlO2 was added to the AAC always before the leaching reactions were performed. In contrast, the presented study investigates leaching of pure AAC in stronger alkaline media of 4– 8 m NaOH and the combination with acid treatment, before the aluminate is added for the final crystallization process. This procedure is expected to be much more effective to synthesize uniform zeolite products at 100% AAC conversion rates, as shown in the following experimental study. Autoclaved Aerated Concrete (AAC) used in low-rise buildings and infilled frames as a structural member. One of the weaknesses of AAC is low mechanical strength. In addition, AAC blocks absorb water of mortar which can lead to executive problems. In this paper, the effect of silica fume, zeolite and granulated blast furnace slag (7%, 14% and 21% by weight of cement) was investigated on improving mechanical properties and water absorption of AAC. The compressive and tensile strength tests and water absorption test was conducted on 10 x 20 cm cylindrical and 10 x 10 x10 cm cubical specimens. The results showed that pozzolanic materials can improve mechanical properties and water absorption of AAC. The compressive strength for AAC mixes containing silica fume, zeolite, and granulated blast furnace slag, increased up to 184%, 200%, and 172% compared with AAC control mix. In addition, the use of pozzolanic materials with the ratio of 21% by weight of cement improved tensile strength of AAC up to 25%. Generally, silica fume, zeolite and granulated blast furnace slag in different replacement levels decreased water absorption up to 50%, 45%, and 35%, respectively.

The members of concrete structures may need to be retrofitted for various reasons, including poor quality of materials, design errors, structural changes, non-compliance with the requirements of design codes and also losing cover concrete due to rebar corrosion. Steel jackets, concrete jackets and fiber reinforced polymers can be mentioned as commonly used retrofit methods for concrete members. There are also several methods for retrofitting concrete columns that have lost their concrete cover. Using concrete jacket has some disadvantages, such as a significant increase in the weight of structure, increasing the element dimensions and the required time for the implementation of the rehabilitation. On the other hand, steel jackets have various difficulties in implementation stage. In this study, specimens of square concrete columns that have lost their cover concrete due to rebar corrosion have been investigated and have been retrofitted by combining a number of methods. These methods include the use of a new concrete layer and the wrapping of columns with carbon fiber. Combining these methods will result in the enhanced performance of the rehabilitation technique since these methods will cover the deficiencies of each other. It is expected that these combined methods will result in increased load capacity, energy absorption and ease of forming. Therefore, in this study, the combined effect of carbon fibers and high performance concrete layer is investigated. The combination of high compressive strength of this type of concrete and high tensile strength of carbon fibers can be used to increase the axial load capacity and energy absorption of square concrete columns. The variables of this study include the type of cover concrete (UHPC, UHPFRC and SCM) and the number of layers of carbon fiber (one or two layers). The total number of specimens in this study was 42, of which 6 were control specimens, 6 were damaged control specimens and 30 were damaged specimens, which were retrofitted with cover layer and carbon fiber. All of the specimens are placed under uniform axial load. The results of the experimental study show that in the retrofitting of the square column, it is better to use the UHPC coating layer. While it is better to use a self-compacting mortar as a coating layer in retrofitting the circular column. Retrofitted columns have significant increase in strength and energy absorption capacity compared to the control columns. The least effect was seen for the columns retrofitted with the coating layer of ultra-high performance fiber reinforced concrete (UHPFRC), which showed an increase by 33% and 85% in terms of strength and energy absorption with respect to the control columns. The greatest effect was seen in the columns retrofitted with self-compacting mortar coating layer with two layers of carbon fiber, which increased the strength and energy absorption by 210 and 480%, respectively. Also, the results show that because the confinement effect in the circular sections is uniform and the entire concrete is effectively confined, the effect of the type of concrete on the coating layer is reduced. A numerical study on a real-dimension column was carried out to verify the results of the laboratory tests and also in order to allow the experimental results from small-sized samples be extended to large-scale columns. The results showed that by increasing the column dimensions, the carbon fiber confinement effect is significantly reduced.

Engineering problem related to Expansive soils is their changes in volume by moisture. This soil tends to expand by absorbing water, so if they are not allow to expand and constrained pressure swelling pressure will create. Swelling pressure can cause settlement and damage to structures which are supported by this soil. There are different solutions for overcoming on this problem but utilizing of Geofoams (EPS) is one of the most innovative approaches. In this paper, the results of tests were conducted on buried flexible pipe which supported by geofoam in the expansive soil are presented. In these experiments, two boxes have been used in such a way that a smaller box is placed inside a larger box and space between two box was filled by water. Flexible pipe and geofoam (EPS) were located in the center of small box and then expansive soils were poured around the geofoam (EPS) and flexible pipe. The expansive soil which was used in this research was sodium bentonite. Sodium bentonite expands when wet, absorbing as much as several times its dry mass in water. Because of its excellent colloidal properties, it is often used in drilling mud for oil and gas wells and boreholes for geotechnical and environmental investigations. The property of swelling also makes sodium bentonite useful as a sealant, since it provides a self-sealing, low permeability barrier. It is used to line the base of landfills, for example To investigating the influence of geofoam (EPS) in reduction of the swelling pressure and displacement was purpose of this experimental study. Four tests were done on flexible pipe, in the first test, flexible pipe was buried in expansive soil alone and in other tests geofoam (EPS) was used. Geofoams which used for protection of buried pipe, have 4 mm, 20 mm and 40 mm thickness respectively. each test was conducted in 32 days, because after 32 days the dial gage did not show any changes. By comparison on the values of obtained swelling pressure and displacement, it became clear that using a geofoam (EPS) with thickness of 4mm and 20mm can decrease swelling pressure and displacement up to 50 and 80 percent, respectively. Also value of swelling pressure and displacement reduction for test with 40 mm thickness geofoam (EPS) was negligible. So it was found that increasing in geofoam (EPS) thickness can partially reduce swelling pressure and displacement of expansive soil, however, there is no direct correlation with increaseing the geofoams thickness.

Wave run up elevations and wave overtopping rate are two important parameters in design of coastal structures specially in definition of their crest elevation. Wave run up in contribution with wave breaking generates local turbulences as well as large deformations around free surface profile. Smoothed Particle Hydrodynamic (SPH) method as a powerful Lagrangian method in modeling free surface flows is based on particle methods and can be used for modeling large deformation of surface boundary. This model has been modified via considering bed friction force and it is applied in this study to evaluate wave run up values. Two modifications i. e. stepped and smoothed approaches are introduced to implement bed shear stress in weakly compressible SPH models. Dam break flow and wave run up over different beach slopes are modeled and the results are compared with experimental and analytical data. It is concluded that considering the bed friction force is less important in dam break flows than in wave run up models that neglecting bed shear stress as a common practice in SPH methods can generate significant errors. These errors can be diminished efficiently by means of the introduced methods. The improvement rate, however, depends on slope geometry as well as wave condition and it is more sensible in simulating sliding waves over bed slope during run up phenomenon than breaking waves with considerable wave momentum. In the latter case, the wave momentum dominates the process and the bed friction force is not able to resist against the wave force and the the wave profile is consequently less dependednt on the bed friction value. By the way, the reslts have been yet improved and 40% error has been decreased to 7% in this case. In the former case with the limited wave run up values, however, the improvement is more noticeable and 90% error of the unmodified methods has been decreased to 6% using the modified SPH method. The results show that the wave run up will be modified using the bed friction force. Meanwhile, both the introduced method i. e. smoothed and stepped exertion of bed friction forces, results in nearly same wave profile because the total force is equal in both schemes. The only difference is the distribution pattern of the force between particles located near the friction boundary that leads to different distribution of particle velocities. Smoother velocity profile can be resulted in case of using transitional application of bed shear force which is moe comtaible with the natue while the stepped insertion of bed friction force may lead to numerical errors too. In spite of better result of the smoothed method, the implementation of the stepped method is easier and needs less numerical efforts. In addition, parallel processing using graphical processing units (GPU) are utilized to increase the efficiency of the modified model. The efficiency of GPU in comparison with CPU is evaluated and computational costs of different numerical steps are analyzed. It is observed that calculation of forces is the main time consuming step and using GPU can speed up the modified model significantly.

Structural damage not only changes the dynamic characteristics of the structure, but also it may lead to complete destruction of the structure in some cases. Since early identification of damage can prevent such catastrophic events, structural health monitoring and damage detection has absorbed the attention of the civil, mechanical and aerospace engineers in the last decades. An effective health monitoring methodology not only can provide information about the global serviceability of the monitored structure, but also it can help the engineers to prepare cost-effective rehabilitation programs based on the obtained details about the health of the structure and its members. Different methods have been proposed for structural damage identification and estimation. Vibration-based methods consider the changes in the structural modal parameters, like natural frequencies and associated mode shapes, and/or their derivatives, like modal flexibility and residual force vector, for damage identification and quantification. Considering their acceptable sensitivity to widerange of structural damages, vibration-based methods are considered as one of the most practical approaches for structural fault prognosis. Employing vibration parameters to define the damage detection problem as a model updating problem, is one of the well-known strategies that can return both the damage location and extent in different types of engineering structures. Such methods can be solved with optimization algorithms to find and report the structural damage in terms of the global extremums of a damage-sensitive objective function. In this paper a new model updating approach for health monitoring and damage localization and quantification in engineering structures is presented. At first, a damage-sensitive objective function, which is based on the error function between the modal data of the monitored structure and its analytical model, is proposed. This objective function is formulated by means of the point-by-point matching strategy to minimize the difference between two models. Modal natural frequencies and the associated mode shape vectors are directly fed to the objective function and this can result in an easy assessment methodology to check the convergence rate of the function. Moreover, in such a case, the objective function uses the sensitivity of both these parameters for damage identification. The proposed inverse problem is solved using Moth-Flame Optimization (MFO) algorithm which has been inspired form spiral convergence of moths toward artificial lights. From mathematical point of view, updating the position of the moths with respect to the flames – which are the best solutions obtained during iterations– , reduces the probability of being trapped in the local extremum points and also, ensures the convergence of the algorithm to its global optimal solution. The applicability of the method was evaluated by studying different damage patterns on three numerical examples of engineering structures: a seven-story shear frame, a simple beam with 10 elements, and a planar truss with 29 elements. In all these studies, damages were simulated as reduction in the stiffness matrix of the damaged elements. Different issues, like noise effects, were considered and their impacts on the performance of the proposed method were investigated. Furthermore, comparative studies were carried out to discuss the advantages and drawbacks of the introduced method as well as the employed techniques. The obtained results indicate that the method is an effective strategy for vibration-based damage detection and localization in engineering structures.

Marl is a combination of clay and calcium carbonate which its carbonate content is between 35 to 65 %. Marl soils have variable characteristics and their engineering behavior may be highly different in dry and saturated conditions. Such soils suffer from falling, swelling, divergence, and loss of resistance when exposed to water and moisture. Marl deposits have higher erosionability than other deposits due to the structural nature such as the presence of destructive particles and chemicals (carbonate Calcium, Gypsum, Anhydrite and Salt). Palygorskite and sepiolite are clayey minerals forming the marl soil, which leads to instability, load capacity reduction and swelling in the soil. Microstructural study of soil stabilization of the Southern Marl using lime and Nano-SiO2. Using additives such as lime, cement and nanoparticles is one of the methods for soil chemical modification. The present study investigates the effect of lime and Nano-SiO2 on the engineering properties of marl soil and the formation of new compounds due to the stabilization process. The soil used in this study was the marl sample of the west of the Bandar Abbas l on the northern margin of the Persian Gulf. In this area, natural and artificial slopes are instable. Also, extensive failures in many of geotechnical projects such as failure in the foundations, tensile cracks and slopes on the roads have been reported. The structure and minerals of the marl soil can be considered as the main cause of such problems. Observations indicate that most of failures have occurred after rainfall. Based on the Unified Soil Classification System (USCS), Marl is a clay with low compressibility (CL) in which 95% passed through the No. 200 sieve. The hydrated lime used in this study was passed through the No. 100 sieve. The pH of lime is 12. 81. In this regard, after determining the geotechnical properties of Marl soil, the improvement of engineering properties of the samples stabilized with different percentages of lime and Nano-SiO2 has been evaluated at the end of the treatment period. In order to identify present minerals in the soil and investigate the formation of calcium silicate hydrate compounds in the reaction of soil with lime and Nano-SiO2, the XDR test was conducted. Also, SEM was used to evaluate the impact of adding lime and Nano-SiO2 on the structure and morphology of the soil. The results showed that the presence of Nano-SiO2 in the limestone system led to the uniform distribution of cement (C-S-H) compounds in the soil. Based on the results, with increasing the treatment time, lime participation in pozzolanic reactions was increased, also the results obtained from the Atterberg limits test showed a diminution in the paste limit of the marl sample with increasing lime and Nano-SiO2 values. Based on the results of the Atterberg limits, compared to the outline of stabilization with increasing lime, the presence of Nano-SiO2 in the process of stabilizing with lime led to 4 units' reduction of the plastic limit. Based on the results of the present study, the stabilized marl soil showed best geotechnical properties in the presence of 6% of lime and 0. 7 % of Nano-SiO2.

The Geological hazard and the lack of appropriate underground investigation have always made the design and construction of underground works a risky affair. As a consequence a larger safety factor should always be considered for underground works compared to similar surface constructions. During excavation of a tunnel and by the opening a cavity the flow lines of stress field in the soil or rock mass are deviated and are channeled around it to create a zone of increased stress around the walls of the excavation. This channeling of the flow stresses or arch effect ensures that the cavity is stable and will last over time. Depending on the size of stresses created and the strength and deformation properties of the ground, arch effect can be produced in three states. In first state arching is close to the profile of excavation, when the ground around the cavity withstands the deviated stress flow around the cavity well, responding elastically in terms of strength and deformation. For second state, arching is far from the profile of the excavation, when the ground around the cavity is unable to withstand the deviated stress flow and responds an elastically-plasticizing and arch effect forms far from walls of the excavation. In the last state arching is not produced at all, when the ground around the cavity is unable to withstand the deviated stress flow and responds in the failure range producing the collapse of the cavity. The stability of tunnel can be determined and optimized through numerical modeling by finding stresses around tunnel and face movement. The gradual reduction of horizontal stress from the tunnel face during the excavation process leads to the formation of deformation on the ground surrounded tunnel. Face Extrusion is the first response of environment to the excavation process. Extrusion appears on tunnel face and along the longitudinal axis of the tunnel and its geometry could be symmetric or asymmetric. This phenomenon depends on the resistance and properties of the advance core, arch effect and the main stress area exposed to the tunnel. In the present study a part of the Tehran Metro Line 7 tunnel in analyzed. The selected part for modeling locates in 0+900 to 0+1000 meters from the beginning of the southeast of line 7. Using geotechnical reports, the soil properties are selected and an elasto-plastic stress-strain behavior is considered for soil. All numerical modellings are done by finite difference method using in Flac 3D software. Based on results of numerical modelling the relationship between the stresses of the tunnel face and its extrusions are investigated and the results are presented in the form of confinement stress-extrusion curve or “ tunnel characteristic curve” . The characteristic curve is plotted under dimensionless axes and it is observed that these non-dimensional curves are placed on each other under special conditions for different tunnels i. e. there is only one characteristic curve for tunnels with different geometry. Conditions for unique characteristic curve are also presented here.

Seismic design in current codes is elastic and the nonlinear behavior is only incorporated indirectly. Structures which are designed by these codes are subjected to large excessive inelastic deformations under heavy earthquakes, which could lead to undesirable response or even collapse of the structure. Although elastic methods have been satisfactory in the past, public demands are leading design procedures to higher levels of performance, safety and economy. So due to the above mandate, performance based design is suggested for the seismic design. Performance based design is defined as a design procedure in which the structure performs in a predefined manner under different levels of loading. Therefore, in order to determine structure behavior under different loading, analytical models are needed to predict structural components behavior. In many buildings, steel moment frames are used as lateral loading system. In the steel moment frames buildings, connections play an important part in seismic performance and ductility of the structure. On the other hand, I-beam sections with box columns sections are widely used in steel moment frames. As a result, it is of great importance to predict these type of connections’ behavior for the deformations in the nonlinear range. For feasibility of modeling of structural components considering stiffness and strength deterioration, relations are needed to correlate hysteresis model parameters to physical and geometrical factors, which practically determine deterioration. To obtain these relations, sufficient experimental results are required to calibrate deteriorating hysteresis model parameters. However due to the lack of enough experimental results for each particular connection, numerical models with acceptable accuracy could be used instead, and the obtained results can be used to calibrate the parameters. Considering the importance of I-beam to box column connections utilizing top and bottom plates and introducing these connections in the tenth code of Iranian national building regulations, and the WFP connections in FEMA-350 and AISC as one of the accepted connections, specifying the relations that determine the deterioration behavior of this type of connection is of particular importance. Thus the aim of this research is to propose relations in order to predict the behavior of the I-beam to box column moment connection. For this reason, WFP connections that were previously designed and tested by few researchers are used as the benchmark and verification samples. Essentially, the purpose is to propose relations to predict the behavior of these connections under cyclic loading considering all modes of stiffness and strength deterioration. The proposed relations made be simple and practical so that can be used in the design of structures. Hence, the simplified model of the concentrated plastic hinge can be used for both beam ends. To determine the behavior of these hinges under uniform cyclic loading, the Ibarra-Krawinkler hysteretic model is used. Deterioration model parameters are calibrated by using the results from numerical analysis and the intended relationships are represented by nonlinear regression. In conclusion, the detoriation model developed for WFP connections of I-beam to box column can provide efficiently for acceptance criteria of moment frames and can be used in special moment frames.

Global water scarcity and air pollution by greenhouse gases have amplified the need to use of unconventional water and environmental friendly materials in the concrete industry. Because of its proximity to the Caspian sea, the geological conditions and hydrogeological characteristics of the northern and western regions of Golestan province, groundwater in this area is very salty. On the other hand, due to lack of access to good quality surface water in most of the months, civil and construction activities in this area are always challenging. Accordingly, the present study was conducted to investigate 120 treatments (including three levels of water quality including tap water, briny grounwater and mixture of equal ratio of tap water and briny grounwater), four levels of zeolite (including 0, 10, 20 and 30 percent of zeolite application instead of cement in the concrete mix design), two levels of cement content (including 250 and 350 kg. m-3) and five curing ages (including 3, 7, 21, 56 and 90 days) in three replications. Considering the considerable types of the experimental treatments in this study and in respect to the lack of statistical analysis in previous studies, the results of this study were analyzed based on a completely randomized design with factorial experiment using analysis of variance (ANOVA) and means comparison (LSD) tests. Averagely, use of briny groundwater resulted insignificant increase in the compressive strength of concrete specimens compared to tap water, while combined water significantly decreased this property, but this reduction was within permissible range 10 percent based on national and international standards. Also, replacement of 10, 20 and 30 percent of cement by zeolite compared to non-zeolite treatment significantly reduced the compressive strength of concrete specimens by 9. 9, 9. 5 and 23. 1 percent, respectively, but the difference between replacement level 10 and 20 percent was not significant. However, Concurrent use of briny groundwater and zeolite up to 20% can be recommended without significantly reducing the compressive strength of concrete. In the cement content of 250 kg. m3, the difference between tap water and combined water treatments was not significant, but the use of briny groundwater resulted significance increase in compressive strength of concrete pieces by 22. 8 and 21. 8 percent compared to tap water and combined water, respectively. In contrast, in the cement content of 350 kg. m-3, the highest compressive strength was obtained in samples made with tap water, briny groundwater and combined water, respectively, and the differences between them were statistically significant. The results showed that due to two-and three-way interaction of these three factors on compressive strength of cement pieces, which means different effects of water quality and application percent of zeolite on different content of cement, the choice of the best application level of zeolite and water type according to the cement content should be selected based on the mix design test in building site. However, using of briny grounwater and zeolite in the concrete mix design, especially in cement content of 350 kg. m-3, without significantly reducing the compressive strength of concrete and even significantly increase of this property in some treatments, is recommended.

Progressive collapse is a particular phenomenon in structures in which all or a part of the structure is collapsed due to a local damage or fracture in a limited part of the structure. This phenomenon is often triggered by an accident such as an explosion in the structure and then progresses for reasons other than the proper redistribution of forces between other members of the structure. In this phenomenon, failure is often triggered by an accident such as an explosion in the structure and then progressed to other parts of the structure due to some reasons such as inappropriate redistribution of forces between the other structural members. In recent years, study on progressive collapse in structures has been increasingly taken into account and a number of different researches have been conducted on this topic. One of the issues discussed in this regard is the impact of structural systems on the potential for progressive collapse in buildings. One of the most common types of building structures is reinforced concrete buildings that are also widely used in Iran. In these buildings, various types of structural systems such as “ moment-resisting frames systems” , “ bearing wall systems” , “ dual systems include moment-resisting frames and shear wall” , etc. are used. Choosing an appropriate system to have more safety against a premature failure requires knowledge of the behavior of these systems against this phenomenon. Proposing and choosing an appropriate structural system to have more safety against the progressive collapse, taking account economic considerations, requires having sufficient knowledge of the behavior of these systems against this phenomenon. In this paper, an attempt has been made to compare the behavior of various structural systems of reinforced concrete structures against the progressive collapse. In this regard, after literature review on the researches and existing standards/codes provisions related to this issue, nine reinforced concrete frames different in structural systems or number of stories have been modeled and the behavior of these frames has been investigated. These frames consist of 3, 7, and 10-story frames, as well as three structural systems: “ Intermediate reinforced concrete moment frame” , “ special reinforced concrete moment frame” and “ Intermediate reinforced concrete moment frame + Intermediate reinforced concrete shear walls” . The loading and design of these frames is done in two ways: taking into account the criteria for progressive collapse, without taking into account these criteria. In the design of the structures with the aim of preventing a progressive collapse, the UFC-4-023-03 regulations have been used and these structures have been evaluated under different column removal scenarios. Finally, the provisions for linear and nonlinear analysis presented in this code are also compared. The results show that in terms of the ability to withstand the loads on the structure after column removal and also economic considerations, “ Intermediate reinforced concrete moment frame” have better behavior than other structural systems studied in this paper. Moreover, in the studied structures, it is determined that the UFC-4-023-03 regulations, in the nonlinear analysis method, has been provided more conservative criteria compared with linear analysis.

Proper operation of gated spillways, which plays an important role in safety of dams during flood event, remains as a prominent challenge. Although telecommunication networks used in flood warning systems facilitate flood management by dams to some certain level but accurate prediction of both the magnitude and timing of peak flood flows with few days of lead time is not still possible. Therefore, operation of gated spillways may mostly benefit from the observed reservoir water level and observed flood discharges in the upstream gagging stations. In Iran, many of river-reservoir systems face severe floods every year. Most of these reservoirs are operated based on engineering judgments of dam personnel and static policies such as rule curves, which are not proper formulated for flood events with various return periods. In this study, we proposed a rule curve for operation of gated spillways using sequential approach and its performances was compared with previously developed operation policies. For this purpose, nine stages as critical control levels were assigned and spillway gate openings associated with each critical level were determined for Mahabad Dam, located in northwest of Iran, as the case study of this research. Each control level was related to given percentage of the design flood volume. When using the proposed rule curve, as a critical control level is reached, the discharge through the spillway and related opening of its gate are accordingly increased. The gate openings associated with each critical water level were optimized using a real coded Genetic Algorithm (GA). This attitude or policy of nine-stage operation includes an appropriate algorithm for determining critical levels, development of operational models spillway gates, calculation of gate opening in each stage, and applying the model to the case study of Mahabad dam. This study adopts the nine stages approach for which nine control levels and gate openings are determined by GA. As it mentioned before, the nine critical levels should be placed in flood retention reservoir between initial water surface elevation and maximum water surface elevation. So, it will have crucial role to determinate gate opening spillway during flood events, and increase of flood storage in the flood retention reservoir. This model was employed to route a flood with the same return period of design spillway flood through Mahabad reservoir. The performance of the proposed rule curve was then assessed by determining the amount peak flow discharge reduction. The results of the case study shows superiority of the proposed rule curve over previously developed operation policies for flood control in Mahabad Dam. One of the main advantages of the proposed methodology is that for using the proposed rule curve not flood forecast data is needed and therefore, it can be considered as a reliable tool for operation of gated spillways when there is no flood warning system in the upstream basin. The future studies can be focused on testing the proposed algorithm on other reservoirs. In the cases of dams with large flood control volumes, critical control levels can also be considered as decision variables of the GA optimization model.

Flooding of rivers is accompanied with a threat on the population living on their floodplains and on the neighboring settlements. Accurate modeling of such flows is thus imperative to assess flood risks, perform real-time flood routing, or estimate the impact of a mitigation schema. The converging of the compound channel causing the flow become even more complicated. The flow patterns in converging compound channel and free-surface profile has been simulated by using RSM turbulence model and VOF method, respectively. The comparison of the experimental results including longitudinal free surface profiles, depthaveraged velocity distribution and the ratio between floodplains and total discharge confirmed that the numerical simulation can be used to model the flow pattern in converging compound channel. Furthermore, Absolute Percentage Error (APE) for each of these parameters was amounted to 3. 25%, 4. 66% and 9. 72%, respectively. Respectto the numerical simulation capability in anticipating the flow field parameters, we investigated the effect of relative depth on the flow patterns in a converging compound channel. Moreover, the flow parameters including velocity distribution, depth-average velocity, secondary flows, ratio between floodplain and total discharge, bed sheer stress and energy dissipation were investigated in different relative depths h* (0. 1, 0. 2, 0. 3, 0. 4 and 0. 5). By evaluating and comparing the flow results in the different relative depths, we came to conclusion that the longitudinal-average velocity in the main channel increased as the cross section was narrowed. However, the longitudinal-average velocity in the floodplains decreased in the relative depths of 0. 1 and 0. 2 as the cross section was narrowed. In contrast, this parameter increased in the relative depths of 0. 3, 0. 4 as well as 0. 5 the floodplains narrowed. Velocity gradient between the main channel and floodplains in the relative depth of 0. 1 was strong and in the relative depth of 0. 5 was insignificant. In the smaller shallow depth, this velocity gradient has been resulted in secondary flow in the cross section of converging compound channel. Accordingly, in the relative depth of 0. 1 and 0. 2 four cells of secondary flows were formed and in the relative depth of 0. 3 just two cells of secondary flowswere formed. The secondary flows in the relative depths of 0. 4 and 0. 5 was eliminated. Convergence in the length of main channel get the discharge conveyance copacity of floodpland to decrease. furthemore by decreasing the relative depth the capability of floodplains to conveance the discharge was significantly dicreasead. This decrease was evident in the depth of 0. 1 in which the ratio between floodplain and total discharge was amounted to 2. 52%. Sheer stress in channel bed increased when the relative depth of the main channel increased and the maximum amount of bed shear stress was happened at end of the channel. On the other hand, in the floodplains, this parameter decreased along with the converging in the lower relative depths (0. 1, 0. 2) and for the other relative depths the bed sheer stress increased along with converging. In channel inlet the maximum and minimum amount of energy dissipation was resulted at the relative depth of 0. 1 and 0. 5 repectively.

With rapid rise in development of urban districts, a ferocious demand for water-collecting urban sewer systems is inevitable. In fact, flexible sewer collecting systems and drainage systems should be developed for controlling sewage and runoff, respectively. In the case of underground, conducting water flow properly through high vertical distances needs reliable criteria design for dissipating flow energy. Vortex structure is taken into account as one of the economical infrastructures which can be used to eradicate destructive impacts of inflow over a drop with invert elevation. In the current investigation, a physical model, made of Plexiglas segments, was set up to study hydraulic performance of vortex drop structure in terms of flow energy dissipation efficiency (FEDE). 144 experiments were conducted and analyzed by means of full factorial method (FFM). Results of dimensional analysis demonstrated that Froude number (Fr), ratio of drop total height to shaft diameter (L/D), and ratio of sump depth to shaft diameter (Hs/D) were considered effective variables on the FEDE. Hence, a regression based equation in form of a quadratic polynomial was proposed to estimate FEDE variable. Experiments aims were to investigate simultaneous effects of approach flow Fr, L/D, Hs/D on the FEDE. Results of experiments indicated that FEDE variable had downward trends with an increase in Fr variable and additionally, FEDE has gone through upward trends with an increase of L/D and Hs/D ratios. Increase in ⁄ , which causes remarkable effect of wall friction on vortex flow, leads to increase in FEDE in the structure. Moreover, observations showed that decrease in inlet discharge for smaller Froude number results in more rotations of vortex flow in vertical shaft than flow with larger discharges for larger Froude number. This causes reduction of FEDE due to increase in inlet discharge. In addition, shown that in the structures with smaller ⁄ ( ⁄ ), the reduction effect of on the FEDE is more. With respect to positive effects of sump depth range ( ⁄ ) on FEDE and flow patterns observed in the entrance outlet tunnel, range ( ⁄ ) can be replaced by ⁄ range (0. 7-1) proposed Zhao et al. [11]. In addition, the results showed that the interaction of and Hs/D on the FEDE in the structure is not significant. For Q between 9. 7 and 27. 1 l/s, formation of hydraulic jump in tangential inlet was not occurred and flow was drained freely to drop shaft. Additionally, water surface in tangential inlet was lower than that of approach channel. In the outlet part of vortex structure, flow hitting the baffle leads to relatively significant increase in flow elevation top of the baffle in comparisons with other parts. Moreover, for constant values of Q and Hs/D ratio, flow elevation over the baffle has increased with an increase in L/D ratio, while for constant values of Q and L/D ratio, flow elevation has plummeted with an increase in Hs/D. Observations of experiments indicated that baffle-hitting flow accelerated without existence of sump at the base of drop shaft. Then caused to detaching flow and consequently occurrence of cavitation increased.

Thin-walled cylindrical steel silos are susceptible to instability under wind pressure when they are empty or only partially filled. Steel silos are widely used for storage of particulate solids. They are an integral part of many industries. They are almost always constructed from many short cylindrical shells of different thicknesses as the stress resultant on the wall progressively increases towards the base. Silos may be composed of flat or corrugated sheets. Different stiffening methods are employed in the design of these structures. The use of horizontal stiffening rings in the circumferential direction or vertical stiffeners along the meridional direction of the cylindrical shell are two paractical strengthening strategies. This paper investigates numerically the wind buckling behavior of three steel silos. They are composed of flat sheets with stepped walls with multiple discrete steps in thickness. No stiffeners are used in the silos. In order to cover the main aspect ratios mentioned in Eurocode, three different silos were considered. The dimensions were chosen to have similar capacities for storage containers. The steel silos were designed by global numerical analysis using geometrically and materially non-linear analysis with imperfections (GMNIA) for the discharge loads according to Eurocode for wheat as the ensiled material. The vertical and circumferential distributions of wind loading were adopted from Eurocode. Two proposed circumferential pressure distributions for an isolated silo and a silo in a group were taken into consideration. Where the silo does not have a closed roof, an additional uniform value of internal underpressure coefficient should be considered, thus increasing the net stagnation inward pressure on the silo walls. The effects of additional inward pressure on a vented silo with a small opening were specially explored through the paper. Therefore, a total of four different load cases were examined in this paper: isolated load case and grouped load case, each of them for silos with closed roof and for vented silos. Two types of analyses were undertaken for the wind buckling assessment of the silos: the linear elastic bifurcation analysis (LBA) and the geometrically and materially non-linear analysis (GMNA). However, due to small wall thickness, the material non-linearity did not take place in non-linear wind buckling analyses (GMNA=GNA). The buckling mode obtained from LBA, characterized by one meridional half-wave and several circumferential half-waves of decaying sinusoidal form on the upper windward side of the silos. The GMNA buckle modes represented an approximately similar meridional half-wave found from LBA eigenmodes. Neverthless, in the circumferential direction, non-uniform buckle half-waves were expanded almost all around the silo walls with decaying amplitudes on the leeward side. More circumferential halfwaves were formed in the grouped load case in both LBA and GMNA, as well. According to non-linear load-deflection curves, the buckling in all load cases was of snap-back type. The curves showed more non-linear charecteristics in group load case. Moreover, in general, the wind buckling resistance of silos under grouped load case was less than isolated load case. Finally, silos with closed roof compared with vented silos with a small opening, exhibited about 40% more wind buckling resistance.