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The semi arid mountain ,due to climatical ,hydrological and topographical properties ,represents vulnerable base for the occurrence of landslides.The deep stream bed and streamflow in long beds ,main triggering factors materials wall of valleys to slides events.In study region ,as a semi arid region ,was occurred many landslides ,because these landslides events changing the hydrological properties of valleys and amount of load sediment.In this study ,by using of geological and topographical maps ,sampling of soil and field work ,analysied the valleys landslides.The result of this study show that, all of failures and landslides are related to rate of drainge density ,specials depended to drainage density of deep beds , related to rate the changing of ratio of Ds/Dd ,also related to changing R .When increases the rate of slope angle ,then increases probably of the landslides occurrence on unconsolidated materials .

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Stream erosion is one of important cause for the increase amount of sediment .Countless factors plays important role as a single or in set,when acts as erosion's factors on stream beds or on slopes and delivers materials in streamflow.Aggradation and degradation landforms and changing shape of longitudinal profiles of rivers at time,are evidences of these operation.The shape of longitudinal profiles gives important information about processes .By use of the regression analyses ,explained and interpreting of shape of longitudinal profiles and to compare many rivers with each other is possible.Evolution valleys defines rate of erosion at bed of rivers or basin.In this articles ,analyses erosion at longitudinal profiles of rivers concern to valleys and basin and area zonation with many type of erosion in study area .The results of this study show that,Garangoo basin settles in mature stage and medium erosionis prevail.

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The northern and southern borders of Mishow- Dagh mountainous chain (northwest of Iran) include zones with ideal characteristics for optimum development of alluvial fans. The alluvial fan development in this area is related to environmental factors such as tectonic activities. In this study, we discussed to what extent tectonics affect the peculiarities in the sedimentary processes occurring in the fans on different sections of the study area (37 Quaternary alluvial fans in four groups), thus causing geomorphological anomalies in them. For this object, we analyzed the main morphological features of the fans and their drainage basins, as well as some of their constitutive elements. We then focused on the connection zone between the fans and their drainage basins. Finally, we analyzed the possible relations between the different parameters of the drainage areas and the fans. All of these analysis were based on interpretation of geological, topographical, areal photos and satellite images and as well as field studies. The results showed that tectonics play a double role; On the one hand, there have been recent displacements in the zone occupied by the drainage areas, as well as between the basement and the basins in which the fans accumulate and, on the other hand, tectonic activity is responsible for the more intense subsidences in the northern and southern plains of the study area, which gives rise to significant differences in the rate of creation of accommodation space between some sectors and others. Generally, Quaternary tectonic activities have caused changes in sweep angle, longitudinal and fan cross profiles, segmentation, head incision, development of erosional gullies, uplift of Quaternary sediments, formation of telescopic alluvial fans, structure of fans and elongation of drainage basins, slope changes on mountain fronts, positive allometry in fan areas and drainage basin relations, and development of new sedimentary basins.

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The landslide events on the slope of mountains catchment is the result of the activity of many processes and also the effects of many factors, such as litology, slope, land use, amount of precipitation, fault, road and stream. These factors play an important role on the landslide events in mountain region, but in a particular site ,a special factor always plays the major role on these events so that determining of this factor in the prevention action is of great importance .In Garangoo,s catchment, which has special differences in term of litological and geological characteristics and also in terms of the shape of connection between human and environment, the differences in these characteristics ,causes of the landslide events to be different. In this paper, regardeding the distribution of the landslides on nine map layers of the agents, map was event frequency calculated and special factor was selected on triggering of the landslide events ,by using a the determination of special factor method. In the final stage, using Arc/View was zonate the potential vulnerability area with the related landslide events. This calcution and zonation map showed that volcano ash and marl, that old and large landslides have been occurrend over these materials, are favorable areas for the landslides occurrence. On the other parts of Garangoo,s catchment, irrigation planting ,with disturbance outcome on the slope, has become the major triggering factor on the landslides occurrence.

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Methyl tertiary-butyl ether (MTBE) One of the gasoline additives used to increase octane and reduce greenhouse gas emissions, MTBE can enter the human blood flow through different ways including inhalation, oral and skin contact. Human carbonic anhydrase is one of the metalloenzymes that is found in almost all living organisms and has been extensively studied and many diseases are associated with carbonic anhydrase. In this study, the effect of MTBE proximity with human carbonic anhydrase II enzyme on enzyme activity was investigated by visible-ultraviolet spectroscopy and changes in enzyme Tm at different concentrations of MTBE were reported. In addition, the structural changes of the enzyme in the presence of MTBE were examined by intrinsic fluorescence spectroscopy. The results show that the enzyme activity in the presence of MTBE is inhibited by liner-complex mechanism. The results of intrinsic fluorescence spectroscopy of the enzyme show changes in the structure of the enzyme in the presence of MTBE. Also, following the binding of MTBE to the enzyme, the thermal stability of the enzyme is reduced and it becomes sensitive to temperature changes.

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The physical and chemical properties of soil are very different.‌In addition to influences on these properties, these elements also indirectly or directly affect the soils erosive sesitivity.The changes of soil properties is very rapid on the length of slopes. Due to rapid changes, the attention on the impacts these changes on erosive soils is very important. Planners must pay due attention to these properties and also be concerned at soils characteristics at all projection. Texture, structure, rate of organic carbon, EC, pH and moisture of soil, may affect the fertility and erosion of soils. The study area, is located on the northwest slopes of Sabalan mountain, from 38˚.15' to 38˚.30' N, and from 47˚‌.00' to 47˚.38' E between Ahar and Meshkinshar. In this paper, we studied soils erosive properties in relation to the slope elements. The results suggested that slope elements have a major and detrimental role on the chemical and physical properties of soil, erosion and gulling.

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Expansive soils are found in many parts of the world particularly in arid and semi-arid regions. They are considered a worldwide problem as they cause extensive damage to civil engineering structures. As a result, a clear understanding of the behavior of such soils is required for the effective design of structures and infrastructures on these soils. Researchers have demonstrated various methods to reduce expansive soils swelling potential, with one being soil treatment. In this paper an experimental program was developed to study the treatment of an expansive soil using mechanical and chemical techniques. Two different types of artificial fiber consisting of polyethylene (bar shaped) with a diameter of 0.3mm and polypropylene (tape shaped) with a width of 3mm were used in order to randomly reinforce soil samples with various fiber contents of 0.5%, 1% and 1.5%; and fiber lengths of 10, 20 and 30mm. Chemical treatment was carried on using lime and cement as soil stabilizers with various percentages of 5%, 8% and 10%; for curing times of immediate, 3 and 7 days. Uniform and repeatable moist-compacted soil samples were prepared by static compaction at a chosen moisture content and dry density less than the optimum water content and maximum dry density from standard proctor compaction tests. Free swelling and swelling pressure tests were conducted using a one-dimensional oedometer apparatus. In addition multiple regression equations with 3 and 2 independent variables were developed based on experimental results. The proposed multiple regression equations present an understanding of the variation of free swelling and swelling pressure as a function of swelling time, fiber or chemical stabilizer content and fiber aspect ratio (fiber length divided to fibers diameter or width) or curing time for various values. Experimental results and statistical analysis indicated that soil treatment with artificial fibers and chemical stabilizers can indeed reduce swelling potential in expansive soils. Reduction of free swelling and swelling pressure in samples randomly reinforced with artificial fiber was seen to be dependent on fiber content, fiber length and fiber shape, where tape shaped fibers showed more reduction in free swelling and swelling pressure thus being more effective compare to bar shaped fibers. Furthermore reduction of free swelling in samples treated with chemical stabilizers were seen to be a function of percentage of chemical stabilizer and curing time with cement showing to be more effective compare to lime. In addition chemical stabilizers proved to be more effective in reducing soils swelling potential compare to artificial fibers. The suggested regression equations can predict and estimate the free swelling curve, final free swelling and swelling pressure for various swelling time, fiber or chemical stabilizer content and fiber aspect ratio or chemical stabilizer curing time with accuracy and a high degree of agreement between experimental and predicted values. Also, the regression equations can aid the performance of a sensitivity analysis which indicates the importance of each independent variable (fiber or chemical stabilizer content, fiber aspect ratio or chemical stabilizer curing time) in estimating final free swelling and swelling pressure.

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The treatment of wastewater generated from acrylonitrile butadiene styrene (ABS) resin manufacturing industry have a great importance due to its high chemical oxygen demand (COD) and some other toxic substances. Activated carbon adsorption, chemical oxidation and biodegradation are the most conventional methods to the treatment of ABS effluents. Among them, the biological treatment as an environmentally friendly technology is highly regarded in the bio treatment and biotransformation of the toxic compounds of ABS wastewater to the intermediate and final compounds such as CO2 and water. This study was conducted to evaluate the performance of an activated sludge system for pretreating ABS manufacturing effluents. The wastewater pretreatment plant is consisted of 3 fine screens, a grit chamber, an equalization basin, dissolved air floatation (DAF) system, an activated sludge reactor and a final clarifier. This system was operated to reduce the TSS and COD values in the effluent in order to obtain to interior discharge permits to the central wastewater treatment utility operated by Tabriz petrochemical complex. Four runs weighed average sampling was conducted during 6 months according to the standard methods of the examination of water and wastewater. The parameters including COD, BOD5, TSS, TDS, sulfate, total kjeldahl nitrogen (TKN), ammonia-N, nitrate-N, alkalinity, cyanide, phosphate and pH were measured in wastewater samples according to the standard methods. The concentrations of acrylonitrile, acrylamide and acrylic acid in wastewater samples were determined using gas chromatography (GC) equipped with flame ionization detector (FID) with capillary column. Microbial structure of activated sludge was also evaluated using R2A, PCA and Nutrient Agar culture media as well the biochemical standard tests. According to the results, at surface loading rate of 2.76 m3/m2.h applied to DAF, the COD and TSS removal efficiencies of 24 and 43% were obtained, respectively. The ratio of BOD5/COD in the influent was 0.57 indicated the moderate biodegradability of ABS wastewater. In addition, the COD and BOD5 removal efficiencies in biological reactor were 59 and 68% respectively, at the organic loading rates (OLR) of 0.79 ± 0.06 kgCOD/m3.d. Totally, the COD, BOD5 and TSS removal efficiencies in the pretreatment system were 80, 90 and 88%, respectively. In addition, at the acrylonitrile loading rates of 0.067 ± 0.008 kg ACN/ m3.d, the removal efficiency of acrylonitrile was 91% which 26% of that has occurred in the biological reactor. Also, the removal efficiency of cyanide was 97% which only 4% of that has occurred in the biological reactor. Twenty bacterial strains were isolated and identified from the activated sludge samples. Among the isolated bacterial strains, four strains include Alcaligenes sp. Pseudomonas sp. Bacillus sp. and Moraxella sp. were identified as heterotrophic nitrifiers. Based on the results, the nitrifier bacteria have played an important role in the degradation of acrylonitrile in the biological activated sludge system. The results of parameters analysis, performance evaluation and microbial assessment revealed the satisfactory performance of COD removal as well nitrification. However, it seems that a significant portion of the volatile organic compounds (VOCs) are removed from the influent wastewater by stripping.

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Nonlinear behavior is a common feature of all real-world systems. However, for the sake of simplicity, a linear model is often used in the controller design procedure. Nevertheless, the neglected nonlinear dynamics could degrade the performance of controller drastically. This study presents a new method of designing a model predictive controller (MPC) for a class of nonlinear systems. In the proposed method, an MPC is first designed in state space based on a linear model and then modified by using modal series to compensate for the effect of the neglected nonlinear dynamics in the linear model. Because the proposed controller adjusts a linear controller instead of designing a new one, it can be easily applied in industries to modify controllers that have been designed based on linear models. In addition, its computational burden is much less than that of nonlinear MPC methods. In this study, the proposed technique is used to control two real-world systems, and the results of its application are discussed.

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Increasing pollution levels due to rapid industrialization and urbanization are now causes of major concern in industrializing countries. Petroleum and chemical processes are responsible for many emissions both into the air. Equipment leaks in chemical and petroleum processing industries are responsible for significant amount of emissions. Even if each individual leak is generally small, it is the largest source of emissions of volatile organic compounds (VOCs) from petroleum industries and chemical manufacturing facilities. Styrene and Acrylonitrile are two major components in the streams of ABS plant of Tabriz Petrochemical Complex which is expected to be released to the atmosphere through various sources such as equipment leaks and tank venting. In the first step of this study the major sources of pollutants emission in the ABS plant were identified considering the PDF and PID of the plant. Then the emission rate of each source was estimated using the emission factors presented by USEPA. An emissions factor is a representative value that attempts to relate the quantity of a pollutant released to the atmosphere with an activity associated with the release of that pollutant. Emission factors are powerful tools for policy makers as they can be used to relate emissions and concentrations. In the last step, the estimated emission rates were used as the input of Industrial Source Complex Short-Term Version 3 (ISCST3) model to predict the ground level concentration of Styrene and Acrylonitrile around the ABS plant. The ISCST3 is steady-state Gaussian plume model which can be used to assess pollutant concentrations from a wide variety of sources associated with an industrial complex. The model is generally applicable for near-field (within 10 km) impact assessment of air pollutant in meteorologically and topographically uncomplex conditions. Among the 54 pumps, 23 compressors and other equipments of the plant, 11 pumps, 8 compressors and 6 storage tanks were identified as the emission sources of considered pollutants. The emission rates of pumps and compressors were estimated using the emission factors presented in AP-42 document of USEPA. The emission estimation of Styrene and Acrylonitrile from six storage tanks has been done using USEPA standard regulatory storage tanks emission model (TANKS 4.0.9a). The emission software program TANKS is developed using emission factors presented in AP-42. The results showed that the compressors are the significant sources of considered pollutants which release about 586 g/day Styrene and 2506 g/day Acrylonitrile to the atmosphere. The emission rate of Styrene and Acrylonitrile from pumps were estimated 36 g/day and 94 g/day, respectively. The results of using TANKS model indicated that Styrene and Acrylonitrile emission rates are 7 g/day and 22 g/day, respectively. The estimated emission rates were used as the input of ISCST3 model to find the ground level concentrations of considered pollutants around ABS plant. The results showed that the maximum level of Styrene was 646 µg/m3 which is below the Reference Concentration (Rfc). In the case of Acrylonitrile the maximum level of estimated concentration was 272 µg/m3 which is higher than Rfc. The implementation of a leak detection and repair (LDAR) program or modifying/replacing leaking equipment with “leakless” components were recommended to reduce the emissions from equipment leaks of ABS plant.

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In the design process of a moment resisting frame (MRF), the principle of weak–beam and strong–column should been considered because the plastic hinge occurs in the beams. This mechanism is caused that the frame has capable of dissipating significant energy and remain stable in the inelastic region. Hence, the stability is defined as the ability of the frame to maintain its elastic level of resistance throughout the entire inelastic range of response. Using this principle, plastic hinges can be develop in the beams adjacent to the connections and usually very close to the column face. This mechanism allow cracks caused by the plastic hinging. The cracks can also propagate into the connection core region, and initiate a brittle failure mechanism. Furthermore, the mechanism has been not established in many existing MRFs designed based on the previous codes. Hence, the methods have been proposed and developed in order to relocate the plastic hinge away from the column face. Fiber Reinforced Polymer (FRP) has been used as a strengthening solution of beam–column connections and successfully reported for retrofitting existing structures. In fact, the use of a web–bonded FRP retrofitting system can control the mechanism of plastic hing and provide the strong–column weak–beam concept. Due to the many advantages, such as high strength, low weight, endurance and convenience, Carbon Fiber–Reinforced Polimers (CFRPs) have been widely used in strengthening concrete structures.
However, the strength and stiffness of CFRP are severely reduced at elevated temperatures, which will affect the strengthening effect seriously.
In this study, six schemes of strengthened concrete beam–column connection using CFRP are proposed and the seismic performance of the strengthened connection is investigated. In order to achieve this purpose, seven scaled–down RC exterior joint of a typical ordinary MRF are chosen and modeling this strengthened connection is implemented in the general finite element program, ABAQUS software. In the finite element model of strengthened concrete beam–column connection, the concrete is modeled using the damaged plastic model. The sheets of CFRP are also considered as the elastic and orthotropic model. These schemes of strengthened concrete beam–column connection are tested under moderately monotonic/cyclic loads. In order to verify the finite element model of the connection, the analysis results of this model is compared with the experimental investigation on the external beam–column connection repaired strengthened using CFRP. The results demonstrates the verification of the finite element model. The selection of the best scheme of strengthened concrete beam–column connection using CFRP is based on the improvement of the seismic performance of connection such as the load–carrying capacity, the energy absorption, the initial stiffness and changing failure mechanism of connection. The nonlinear results show that the proper layout of CFRP sheets can increase the load–carrying capacity, the energy absorption and the initial stiffness of connections. Furthermore, the proposed schemes of strengthened concrete beam–column connection are caused that the failure is relocated from the column face and located in beam. Therefore, the proposed best scheme of strengthened concrete beam–column connection using CFRP can be recommended and utilized in the practical projects of concrete structures.

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Introduction: Petrochemical industry is one of the major industries playing significant role in the economy of Iran. In general, petrochemical effluents contain various contaminants including suspended solids, organic matters, oil and grease, metal salts, sulfide, ammonia, hydrocarbons, cyanides, volatile organic compounds (VOCs) and other toxic substances. In most of petrochemical complexes, wastewaters are treated by activated sludge process along with the oil/water separation systems as a pretreatment. Since the performance evaluation of wastewater treatment plant is required to assess the effluent quality, to meet higher treatment requirement and to know the feasibility of handling higher hydraulic and/or organic loadings, this study was conducted to evaluate the performance of a full-scale petrochemical wastewater treatment plant.
Materials and methods: Wastewater treatment system consists of a screening unit, an API, an equalization basin, coagulation and flocculation, DAF system, aeration tanks, primary and secondary clarifier and filtration. The treatment plant was designed to treat the wastewater generated from different units of petrochemical complex with reuse purposes of treated effluent. To evaluate the performance of the treatment plant, 12-h composite flow weighted samples were carried out in 4 days within 6 month and were analyzed for COD, BOD5, TDS, TSS, phenol, cyanide, oil, ammonia and TKN in accordance to standard methods. Microbial structure of activated sludge was also evaluated. Overall performance of the plant and the performance efficiency of each unit were calculated.
Results: According to the results, the actual average influent flow was significantly lower than the average design flow based on the long-term data and our measurements. This increases the hydraulic retention time (HRT) in all units in the WWTP. Based on the results, the values of COD, BOD5 and TSS in the influent and effluent were 1319±230, 967±491 and 227±174 mg/l and 73.6±19.6, 33.6±25.9 and 6.4±5.9 mg/l respectively. The ratio of BOD5/COD was calculated about 0.58 indicates a good potential for biodegradability of the wastewater. The results also revealed that 68.5% removal of COD and 81.9% removal of BOD5 have been occurred in preliminary and primary units while; these units are usually designed for the elimination of oil and suspended solids as well as the equalization of quantitative and qualitative parameters of the influent. At an organic loading of 0.48±0.15 kg/m3.d the removal efficiencies for COD and BOD5 in biological unit were calculated about 37 and 46% respectively. The mean value of MLSS within the biological reactor was 1463 mg/l. In addition, the mean plus standard deviation values of MLSS measured in returned activated sludge (RAS) were 2323 ± 1080 mg/l. According to the daily average concentrations of COD in the effluent of the WWTP, in some cases within the study period, the COD values were exceeded from national discharge standards. Microbial analysis showed that among the isolated bacterial strains, the genus belonging to Alcaligenes, Pseudomonas, Bacillus and Moraxella as heterotrophic nitrifying bacteria was identified as predominant strains in biological unit.
Conclusion: Based on the results, in 64% of our measurements (135 days from 209 days of study period), the daily average effluent COD values were above national guidelines for surface water discharge (60 mg/l). In 3% of the time during the study period, the daily average values of COD in the effluent were more than 200 mg/l. The results also indicated that the average effluent concentration of oil was significantly higher than the expected design value.

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Controlling the maximum acceleration and displacement of the roof within the acceptable range is important and essential. In order to control structures, a number of control systems have been introduced that are categorized into four system including active, passive, semi active and hybrid system. One of the most used passive systems is the tuned mass damper system which is placed on the roof of structure for controlling the behavior of building. In addition, the optimization of structures subjected to the earthquake load is an essential task for the safe and economic design of structures. It must be noted that earthquakes are random phenomena and the precise prediction of forthcoming events is a hard task. However, in seismic design codes, the static and modal seismic methods for the seismic design of structures are adopted by the design spectrum produced based on previous earthquakes. Hence, in order to overcome this problem, the concept of critical excitation as a robust method has been presented and developed to generate worst–case critical excitations. The critical excitation method have been presented in the framework of an optimization problem to maximize the structural responses subjected to some constraints. In this paper, an effective method is presented to determine the optimum values for the parameters of the tuned mass damper system subjected to critical earthquakes. The critical earthquakes are unique and are computed based on the dynamical properties of the structure. For this purpose, based on the obtained information from the past occurred earthquakes the critical earthquakes of a ten story shear building are established subjected to the constraints. The constraint scenarios include some computable properties of the ground motion such as energy, peak ground acceleration an upper bound Fourier amplitude spectrum. In fact, in this stage, to compute the critical earthquakes an inverse nonlinear constraint optimization problem must be solved for each time step. Then, the building equipped by a tuned mass damper system at roof of the structure (controlled building) is considered and the optimal design of tuned mass damper subjected to critical earthquakes are implemented. The maximum absolute displacement and acceleration of the roof are considered as the objective functions. Finally, among the computed earthquakes, one of them which produces the maximum objective functions is selected as the critical earthquake. In the optimization procedure, the mass, damping and stiffness of the tuned mass damper (TMD) system are adopted as the design variables. Multi-objective particle swarm optimization method is used to optimize the parameters of the tuned mass damper system. Since, the optimal design of the tuned mass damper system is presented as a multi-objective optimization problem, a set of optimal solutions are obtained. Numerical examples demonstrate the ability and efficiency of the proposed method in the optimal design of the tuned mass damper system subjected to the critical earthquakes. In addition, the numerical results show that the maximum absolute values of the displacement and acceleration of the roof efficiently decreases when the building is controlled by the optimum tuned mass damper system. Also, the results show that the severe earthquake needs a bigger mass for tuned mass damper in order to control the displacement and acceleration of the roof.

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In this paper, the viscous fingering instability in miscible Newtonian fluid displacements is studied experimentally. Studying the results of this instability have widely application in oil extraction from ground bed oil reservoirs to the ground surface. In order to be more actualized results, a porous media with transparent walls and compact structure of spherical glass beads is constructed, that have close permeability to ground bed. The main purpose of this study is to investigate the effects of viscosity ratio, flow rate and Blake dimensionless number on the quality of growth and the shape of the fingers, also their effect on important physical parameters including the mixing length, sweep efficiency and noise growth to base state. The results showed that with increasing the viscosity ratio, instability and number of finger branches increases and more tiny fingers are formed. Also, increasing the viscosity ratio increases the mixing length and decreases the sweep efficiency. Likewise, with increasing the flow rate, it was observed that the number of wide fingers Increased and fingertips tend to spread. Furthermore, by studying the results it was found that increasing the flow rate, increases the sweep efficiency, but have No tangible effect on the mixing length. Also, the results show that increasing the Blake decreases the mixing length and increases the sweep efficiency.

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The staggered-truss system has been proposed as a lateral load resisting system in the structural steel framing for high-rise buildings, which was developed in Massachusetts Institute of Technology in 1960s. The system consists of a series of storey-high trusses spanning the total width between two rows of exterior columns and arranged in a staggered pattern on adjacent column lines. the system has the columns only on the exterior walls of the building, the usual interior columns are omitted. Thus, the staggered-truss system can provide a full width of column-free area. In the system, the role of energy absorption and endurance of inelastic deformations is responsible for the special segment of truss, so that the ductility of structure is provided by the development of plastic hinges in this region. Although, in the special segment of truss an opening near the center of span must be provided to permit a width and height of sufficient proportions which is used as a corridor. Hence, the effects of this opening must be investigated in the performance of this system. In this study, the effects of the special segment length and its strengthening pattern on the seismic performance of staggered-truss system are investigated. In order to achieve this purpose, an 8-storey steel staggered-truss system with a 1/8-scaled studied in work of Zhou et al. [14] is selected and considered subjected to the low cyclic loading. First, the finite element (FE) model of this structure, in which both the material and geometric nonlinearity, is provided in ABAQUS software, and the validation of the model is controlled by experimental and numerical study and of Zhou et al. [14]. The results of modeling this structure show that the FE model of this structure has appropriately accuracy. Then, the seismic performance of the system is evaluated by considering the various lengths of the special segment and the proposed strengthening patterns in the special segment. The results of the evaluation show that the use of special segments with great length make the entire structural capacity is not fully utilized. Hence, when the large opening is required the regions must be properly strengthened. In this study, different patterns of the special segment, including strengthening of chords, strengthening of vertical members of the special segment and the strengthening pattern proposed by the Manual Number 14 of AISC code are investigated. Since the plastic hinges are usually formed at the chords of the truss, the strengthening of chords has the greatest effect on increasing the initial stiffness and strength of structure. Instead of the strengthening of the total length of the chord, a part of both ends of the special segment is also strengthened, so that its performance is as same as that of the strengthening of the total chord. It is noted that the strengthening of the special segment is one of the ways to increase the initial stiffness and resistance structure, but this strengthening must not omit the performance of the fuse in the truss system, and the conditions of strong beam and weak column are provided. Based on the FE analytical results, the suggestions of this study can be considered for the design of staggered-truss system.

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The high ductile of steel moment-resisting frames (SMRFs) during earthquakes has been challenged due to the brittle fractures of their welded (rigid) beam to column connections. Consequently, SMRFs have suffered severe damages and have produced collapse in main structural members (such as beams and columns). During previous years, energy dissipative devices in connections have been developed by researchers to resolve the ductility problem in rigid beam to column connections of SMRFs. Slit steel damper (SSD) as one of these devices contains a plate or a standard section with a number of slits in its web. The damper can dissipate the seismic input energy with inelastic deformation absorption and also prevent seismic energy transmission to the main structural members (such as beam and column). Due to the uniform strut width of SSD, stress concentration at the end parts of the damper struts is produced and unbalanced distribution of von-Mises stresses along the struts is shown. Furthermore, slit dampers are commonly fractured in the end parts of its struts. The low participation of the middle parts of struts in the energy dissipation is caused. Henec, finding the best shape of slits has been attracted by researchers. In this study, new geometry shape of SSD was proposed for improving rigid beam to column connections of steel structures. For investigating the performance of the proposed damper, the behavior of a rigid connection with the common and proposed SSD was assessed subjected to monotonic and cyclic loads in ABAQUS software. The proposed SSD has the same weight in comparison with that of the common SSD. The results of assessment was shown that in the proposed SSD reducing the width of damper slits in two its ends and increasing its middle parts improved its seismic performance in comparison with that of the common SSD. The proposed damper in comparison with common one subjected to shear load can effectively contribute to about 41% of the total dissipated energy. Furthermore, using the proposed damper in a rigid beam to column connection subjected to cyclic loading can effectively contribute to about 51.8% of the total dissipated energy. The performance of the proposed SSD shows that first, the middle part of strip treat like fuse and the suitable ductility provide. Then, the maximum stresses transfers to the top and bottom of strips. Due to the distribution of stresses in more area, the strength of the proposed damper increases. Therefore, withstanding a large number of loading cycles until the failure in this proposed damper, it can be used instead of welded connection in SMRFs.

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The high ductile of steel moment-resisting frames (SMRFs) during earthquakes has been challenged due to the brittle fractures of their welded (rigid) beam to column connections. Consequently, SMRFs have suffered severe damages and have produced collapse in main structural members (such as beams and columns). During previous years, energy dissipative devices in connections have been developed by researchers to resolve the ductility problem in rigid beam to column connections of SMRFs. Circular pipe steel damper (CPSD) proposed as a type of steel damper can indicate and dissipate seismic energy mainly through inelastic deformation. Among steel dampers such as shear panel damper, the advantage of CPSD is to resiste applied load in all direction. Under cyclic loading the circular shape of CPSD can change to elliptical shape which causes an extra energy in its absorption capacity. The previous study indicated that the stress concentration was high at both ends in the loading direction. The maximum stress was also observed at lower ends in the direction of loading. Henec, finding the best shape of cross section can enhance the behaviour of pipe steel damper (PSD). In this study, ellipse PSD (EPSD) was proposed for improving rigid beam to column connections of steel structures. For investigating the performance of the proposed EPSD, the behavior of a rigid connection with the common slit steel damper (SSD) SSD was assessed subjected to cyclic load in ABAQUS software. The proposed EPSD has the same weight in comparison with that of the common CPSD. The results of assessment were shown that in the energy dissipation of the proposed EPSD and CPSD subjected to cyclic load is equal to 11.11 kJ and 9.11 kJ, respectively. Thus, the proposed damper in comparison with CPSD can effectively contribute to about 22% of the total dissipated energy. The distribution of stress in the proposed EPSD in comparison with that of CPSD was also uniformly caused in the hight of EPSD. Furthermore, the performance of a rigid beam to column connection equipped with the proposed EPSD and SSD in subjected to cyclic loading was compared. The results revealed that EPSD in the rigid connection increased to about 63% of the total dissipated energy. Due to the distribution of stresses in more area, the strength of the proposed damper increases. Finally, the performance of a rigid beam to column connection equipped with the proposed EPSD and the welded connection in subjected to cyclic loading effectively was compared. The results demonstrated that the connection equipped with the proposed EPSD colud withstand a large number of loading cycles until the failure. Therefore, the proposed EPSD can be used instead of welded connection in SMRFs.

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