Modares Civil Engineering journal
Year:2021 | Volume:21 | Issue:6|Papers Count:17

In this research, the SSIIM numerical model is investigated to investigate the flow pattern, velocity meters, current strength and turbulence parameters around the pier of the vertical bridge with submerged vanes. The parameters of different overlap length, and the distance of the submerged vanes upstream from the pier of the bridge and from each other in sharp 180-degree bend in the steep-ratio hydraulic radius 2 with a height of 90 cm and a width of 100 cm and a length of straight direction upstream and downstream of the bend respectively 6. 5 m and 5 m, were analyzed. SSIIM software was used to investigate the flow field around the around the cylindrical bridge pier and upstream submerged vanes. The K-ε,turbulence model was also used to solve the Navier-Stokes equations. In order to validate, the results of the simulated model were compared with the available experimental data in the case of submerged vanes located upstream of the bridge pier. The match between the numerical and experimental data indicated the proper performance of the SSIIM numerical model in modeling the flow pattern in the problem under study. The results showed that the range of secondary flow power was measured in all models with the presence of upstream submerged vanes from 10. 5 to 12%. Shear stress changes after local scouring were also calculated. The maximum shear stress from the beginning of the bend to near the bend exit was inclined towards the inner bank of the bend and in the bend output range the maximum shear stress was transferred to the middle of the bend and then the second half of the bend. The results also showed that the tangential velocity was increased as the immersion range of the submerged vanes and the pier approached, so that the maximum tangential velocity occurred in the passage through the pier. As the height from the initial bed increases, the maximum positive tangential velocities increase. The results also showed that at the level near the bed, the radial flow is towards the inner bank. The greatest difference in radial velocities, as opposed to tangential velocities, is observed near the bed. The highest changes in the maximum landing number are related to models with submerged vanes at a distance of 7. 5 times the pier diameter, which by changing the distance between the vanes from 1 to 1. 5 times the pier diameter from each other, an increase of 12. 5% And by changing the distance of the submerged vanes to 2 times the pier diameter from each other, it decreases by 11%.

In recent decades, the science of structural health monitoring has played a key role in preventing damage and extending the life of structures. To conduct behavioral assessment, it is desirable to use tools that achieve sufficient accuracy with low cost. The processing of behavioral data requires methods that are able to identify and correctly troubleshoot different levels of damage from existing information. Nowadays, sensors are used to measure the behavior of structures including deformations and displacements and even deflections, but these sensors have some weak points. For example, Risk of damage to the sensor, pointwise and one-dimensional measuring, their data is difficult to analyze and using multiple or high-tech sensors becomes expensive. Optical behavior measurement and close-range photogrammetric operations have recently received attention due to their low cost and good accuracy. This method has some advantages like Indirect contact with objects, highspeed image capture, easy access to convenient digital cameras, low viewing costs, and the ability to process composite and instant data with easy operation. In addition, the high flexibility of this method in measuring accuracy and design capability to achieve predetermined accuracy is an important feature of this tool. Analytical methods are based on rules or equations that provide a clear definition of the problem. These methods work well in the cases which the rules are accurately clear and defined but there are many practical cases for which the rules are not known or it is very difficult to discover that calculations cannot be performed using analytical methods. Neural network is a generalizable model, which is based on the experience of a set of training data and therefore free of explicit law. Neural networks have the ability to collect, store, analyze, and process large amounts of data from numerical analyzes or experiments. Therefore, they have the ability to predict and build diagnostic models to solve various engineering problems and tasks In this paper, an attempt has been made to use this method to measure and troubleshoot laboratory model of a scaled suspension bridge that has a relatively complex behavior. For this purpose, the structure was subjected to uniform static loading in three step levels with three states: healthy and damaged in the deck and cables. Damages were created quite intentionally in the laboratory model, and from the information obtained, a database of bridge behavior in various situations was created. In order to assess the feasibility of using different methods in data processing and troubleshooting, first the data in the database were used in a simple linear method (direct comparison) and training in algorithms of machine learning methods. After that, deliberate damage was done again in the laboratory structure to allow testing the efficiency and accuracy of different methods. Finally, the accuracy, precision, and stability of the data processing methods of the support vector machine and artificial neural network were compared. The results showed that by object bundle justification of two-dimensional optical behaver measurement with close-range photogrammetry, a guaranteed accuracy of 0. 0021 mm could be achieved. Using intensity image processing seems helpful to ease the calculation. Using high number of nodes in hidden layer makes it more difficult and time-consuming to train the neural network. In the first level of processing, the detection of the presence or absence of damage was associated with the complete superiority of neural networks with 100% accuracy and in the second level, the detection of the affected area, depending on the type of processing, the neural network with hyperbolic tangent transfer function archived 93% accuracy and the support vector machine archived 68% of the accuracy.

In a reinforced concrete member, especially in a beam, mechanisms of shear transfer are as follows: 1. The force created in shear bars after diagonal cracks, 2. The shear capacity of the concrete in a part of the compressive region of the concrete with no crack, 3. The forces from the aggregates interlock at the both sides of the crack, 4. The force due to the dowel action of the flexural bars that connect both sides of the crack and create resistance against shear deformation of the crack. Dowel action can be defined as follows: the ability of the longitudinal bars to transfer the force perpendicular to their axis. The distance between the longitudinal axis of the non-deformed parts at both sides of the crack is considered as the deformation of the dowel bar. To be able to analyze and design the reinforced concrete structure members correctly, their behavior must be evaluated under different loadings. The efficiency, accuracy and speed of the structure analysis techniques depend on using suitable behavior models. In reinforced concrete structures, the concrete will be cracked under normal loadings due to its weakness in tension. Therefore, it is important to know the mechanisms of stress transfer in the cracked surfaces to evaluate the response of the reinforced concrete structures. In the recent years, an extensive experimental and analytical study on the effect of longitudinal bars in shear transferring (dowel action) has done. Almost all the models presented the theory of Beam on Elastic Foundation (BEF) as the best way to simulate the behavior of the dowel action. In this model, the subgrade stiffness of concrete is the most important parameter. BEF model is a linear model, because the dowel bar and its surrounding concrete are modeled by a uniaxial element on a row of springs. The advantage of the linear models is that they gather all features of the concrete and the interaction of the concrete-bar in a bearing stiffness coefficient. For this reason, a suitable formulation is required for it to model the beam behavior from the elastic stage to the failure. In the elastic state, the bearing stiffness can be presented as a constant like BEF traditional models. However in the nonlinear state, the stiffness must be a function of displacement to model the failure due to the load. In the present research, an experimental program is followed on the beam-type specimens to identify the behavior of the cracked surfaces under the effect of the shear. Using the test specimens made of ultra-high performance concrete, the shear transferred through longitudinal bar (dowel action) is measured. The shear response of the dowel bar, the subgrade stiffness and the displacements are measured. Furthermore suitable formulations are proposed for the UHPC subgrade stiffness. Based on the results of the tests and using the studies of other researchers, a suitable model is presented for the shear mechanism through the bar in the cracked surfaces of ultra-high performance concrete. The results show the suitable precision of the proposed relations to estimate the dowel displacement-shear curve in the specimens with vertical and inclined cracks.

Hydrodynamically, there is a complex confrontation among the porous obstacles along the flow path and the fluid is significantly important Existence of obstacles in the flow path causes changes in hydraulics and hydrodynamic parameters of the flow. Among the hydrodynamic parameters that change due to the presence of obstacles in the flow path, we can mention the intensity of flow turbulence. Since turbulence is related to the energy dissipation of flow, it has always been important to study this phenomenon. one of the most important issues of river engineering is The construction of obstacles in the fluid path, especially when these obstacles are built at the river crossing. The results of studying the behavior of fluid around porous obstacles can be used in the design of gabion groins, as well as the construction of gabion obstacles in the flow path, to dissipate flow energy. In this study, the flow structure around porous groins on the side of the canal and porous obstacles in the middle of a straight channel with a fixed bed has been investigated in a laboratory. The ADV was used to measure three-dimensional velocities and reynolds stresses around the gabion obstacles with different porosity on the side and middle of the channel The obstacles on the side of the canal act as groins and the obstacles in the middle of the canal act as obstacle consuming the energy of the stream. The velocity was measured at 1265 points for groins and it was measured at 1525 points for obstacles located in the middle of the channel. The results showed that the three-dimensional velocity components decrease with increasing porosity in groins and obstacles. Also, the separation of flow, return flow, . . ., is more severe when the obstacles is in the middle of the channel than when the groin is on the side of the channel wall. Also, the effect of porosity percentage on obstacles is much greater and clearer than on groins. And the intensity of turbulence and the extent of the area have the maximum intensity of turbulence in the obstacles in the middle of the canal is more severe than the groins in the side wall. The maximum amount of kinetic energy for obstacles is somewhat larger than for similar groins. However, the maximum turbulence intensity for the obstacles with porosity percentages of 0, 20, 40 and 60 is about 2. 95, 2. 4, 1. 9 and 1. 6 times the maximum turbulence intensity in the same groin, which is relatively large. Therefore, it can be understood that the presence of a obstacles in the middle of the channel, although it does not cause much change in flow energy, but the presence of obstacles in the middle causes the current energy dissipation up to about 2 times the current energy dissipation behind the groin. and, the process of reducing the intensity of turbulence is slower at higher porosities. Finally, The width of the zone with more turbulence intensity in the cross section for the obstacles with porosity of 0, 20, 40 and 60% is about 2. 3, 2. 1, 2 and 1. 9 times the range in the same groin, respectively. Which in itself indicates a greater depreciation of the flow behind the obstacle.

In stochastic subspace methods, the most important factor influencing the dynamic specifications is the dimensions of the Hankel matrix include the number of rows and columns. Using small matrix dimensions is unlikely to identify existing poles, and selecting very large dimensions not only increases the likelihood of virtual and bias poles but also increases computational costs. In this study, it is intended that the optimal dimensions of the Hankel matrix in the balanced stochastic subspace method be calculated in such a way that in addition to covering the existing poles, it also has a minimum computational cost. For this purpose, the condition number of the Hankel Matrix and Energy Indicator is used in two steps. The steps are as follows: First, calculate the optimal order of each cycle, and then use the optimal order to draw the condition number of the system matrix for different dimensions and calculate the desired dimension from its convergence. To verify the accuracy of the proposed method, the ambient vibration test of the Namin Entrance Bridge has been used. This bridge is located at the entrance of Namin city, 25 km from the center of Ardabil province, Iran, which includes two spans of 27. 10m with a concrete deck. The deck of the bridge is located on beams with I sections, which are 2. 5m away from each other, and the whole set of beams and deck is located on a system of foundations and piles with a diameter of 120cm. This bridge being the only entrance to the city and is exposed to various traffic loads, it was necessary to monitor the dynamic characteristics of the bridge as modal frequencies and damping ratios to evaluate the performance and ensure the health of the bridge structure. According to the numerical analysis and the length of the data (12000), the minimum order and the maximum number of cycles are 22 and 55, respectively. By diverging the curvature of the energy indicator graph, the optimal order is determined in the initial 5-12% of the singular values of cycles. For example, the maximum order of the 6th cycles was obtained, 28-62. Also, from the convergence of the maximum condition number of cycles from the 8th cycle, the optimal dimension was selected 352. In a general summary, it can be said that the use of the energy indicator concept in finding the effective order of the stability diagram has a significant effect on reducing the uncertainty of the extracted results. So that from the three identified stable poles, two poles have been extracted in the effective-order area. Also, using the concept of conditional number to find the optimal dimension of the system was effective, so that by drawing a stability diagram for the 15th cycle, it was found that the identified modal characteristics were not significantly different from the results of the optimal cycle (8th). Finally, the extracted modal properties have an acceptable agreement with the numerical model and frequency domain decomposition method (FDD). The modal frequencies of both methods (FDD & B-SSI) have a good correlation but the damping ratios were very different. In frequency domain methods the damping ratios being very sensitive to the quality of data collection, one can expect that the results of the subspace method are closer to reality.

Occurrence of the nonlinear behavior can be a sign of changes in structural parameters and the presence of damage in systems. This paper presents a method for detecting and quantifying of nonlinearity, as an indication of damage, using the indicators that are extracted from the frequency response functions (FRFs) and Hilbert transform of FRFs, for steel moment frame structural systems. Using time history analysis under selected harmonic ground motions, the results of FRFs for the studied 4-story system are illustrated and discussed. Nonlinear behavior is a result of formation plastic hinges under earthquake loading. FRFs and Hilbert transform of FRFs are extracted from both the linear and nonlinear behavior of 4, 8, and 12-stories steel moment frames under fifteen different earthquake records with different characteristics in their time histories. Some near and far field well-known earthquakes records have been selected for the present study as the ground motions input in time history analysis. Different levels of nonlinearity are determined based on the maximum rotation of hinges in column members of structures equal to 2θ, y, 4θ, y and 6θ, y, in which θ, y is yield limit rotation. The indicators of the studied systems are calculated and evaluated for linear and different levels of nonlinearity based on the mathematical power of changes for FRFs and Hilbert transform of FRFs. The presented indicators are extracted based on the frequency response functions (FRFs) and Hilbert transform of FRFs for the responses of absolute acceleration and relative displacement of stories. The indicators are calculated at the location of acceleration sensors (accelerometer) in four levels of the structural systems, while the formation of plastic hinges in the columns of the structures will occur only at the level of the distance between the adjacent sensors. Three aspects of identifying “, existence”, , “, location”,and “, extent”,of plastic hinge rotation can be investigated for nonlinearity detection. In the present research, it is tried to cover the three aforementioned cases in the extracted indicators and presented results. According to the illustrated results it is concluded that: 1-Comparing harmonic loading results showed that frequency content of ground motions and existence of free vibration data in responses have proper effects on compatibility of FRFs. It is concluded that compatibility of FRFs are related to the frequency content of ground excitations and using the presented indicators are not acceptable for any type of optional loading. 2-The proposed method and calculated indicators have enough accuracy and sensitivity in detecting the “, existence”, , “, location”,and “, extent”,of damage. 3-To identify “, existence”,of damage, using the indicators with higher mathematical power of changes, I Pβ,1j (j: a and d) (β, : 2), more certainty is included. 4-To identify “, location”,of damage, the indicators that are extracted from FRFs of displacement of monitoring stories, I Pβ,1d, can be used. 5-To identify “, extent”,of damage, using the indicators with lower mathematical power of changes, I Pβ,1j (j: a and d) (β, : 0. 5), are more accurate.

Every year, road accidents around the world lead to many losses and damages around the world, the most important factor in the occurrence of these accidents is the human factor. The role of humans in accidents is evaluated from different aspects, which driving anger is one of the most important among them. The issue of driving anger, like all human behavior, has always been very complex. Therefore, different scales have been proposed to evaluate this human behavior, which can be said that the Driving Anger Scale (DAS) is one of the most valid and widely used. For this reason, in recent years, this efficient tool has been translated into various languages around the world and used in different countries. The results of previous studies showed that cultural, linguistic, economic, social, and etc. differences between societies lead to the formation of different structures of this tool. Therefore, before using this useful tool in any research field, at first, its structure in each of the societies should be examined. Therefore, this study intends to evaluate the validity and reliability and find appropriate structure for this scale among Iranian drivers using statistical tools. Therefore, to evaluate the validity of this tool, both exploratory factor analysis (EFA) and confirmatory factor analysis (CFA) were used. The results of exploratory factor analysis considered the six-factor structure is suitable for this scale. Then, the six-factor structure obtained from the exploratory factor analysis stage was compared as two distinct models considering the existence and absence of correlations between subscales as well as a one-factor model of the questionnaire using confirmatory factor analysis. The results of these models showed that the structure of the DAS’, s single-factor model was not appropriate compared to the other two structures and in addition, the best values were related to the six-factor structure without considering the correlation between components. Also, ANOVA test was used to evaluate the effect of age and gender differences on each component of this scale. Based on the results of this test, in general, there are statistically significant differences in driving anger among Iranian participants in terms of age and gender. Young people, meanwhile, scored relatively higher on all six components (discourtesy, traffic obstruction, slow driving, illegal driving, police presence, and hostile gestures) and DAS’, s total score. Also, in terms of significant gender differences, among participants men had higher scores than women in all cases except in the traffic congestion subscale. In addition, the results of correlation analysis showed that there are significant relationships between DAS’, s subscales with Depression-Anxiety-Stress Scale (DASS) and Bass and Perry Aggression Questionnaire (BPAQ) total scores. On the other hand, the relationship between the number of significant accidents with the traffic obstruction subscale, overall DASS and BPAQ scores is significant and the relationship between the number of minor accidents with slow driving subscale and the overall BPAQ score is statistically significant. Finally, according to the results obtained from this study, the Driving Anger Scale (DAS) is a valid and reliable instrument for measuring the anger among Iranian drivers.

Construction on problematic soils, such as soft soils, is usually associated with numerous difficulties. Soil improvement is one of the available solution to encounter the problem in which the geotechnical conditions and the soil's material properties are essentially improved. Reinforcement of soil is usually carried with aim increasing soil's shear strength and reducing the erosion and/or settlement, permeability control and etc. . . . Geosynthetics are made of the polymer materials which are used as reinforcement in geotechnical projects. Geosynthetics, depending on their application, have different types, which can be referred to as geotextile, geogrid, geonet, geomesh, geomembrane, geocell, geocomposite. Considering the mechanical and hydraulic properties of the geosynthetics, they are used in various fields. The suitable design and use of these materials leads usually to significant increase in the factor of safety, performance improvement, and cost reduction in projects when compared with other classical solution. In recent decades, extensive studies have been conducted on the types of Geosynthetics and their function. On the 3D geosynthetics, however, deep studies are of few. In this study, the soil interaction with gridanchor as 3D geosynthetic (G-A) and the effect of various parameters (transverse distance of anchors from each other, joint angle of anchor to the geogrid relative to the horizon, aperture size and normal steress) for gridanchor has been investigated. Also, their performance has been compared with geogrids as 2D geosynthetics (G). In geogrids, the aperture size of geogrid, tensile strength of the samples and normal steress are considered as variables. The Pull out test is considered as the basic experiment to approach the goals of the current studies. According to the variables considered for each type of reinforcement systems, 50 pullout tests have been performed on the samples. Of these, 13 tests were performed as observational tests to ensure the accuracy of the test results. The soil used in this study is poorly graded sand (SP). Gridanchor is a type of geosynthetics that was first used by Mosallanezhad et al. In 2008. The results outcome of tests indicate that the use of Gridanchor and compared with geogrid has a significant effect on increasing the reinforced substrate's pullout load. The effect of normal stress parameters, anchor installation angle and anchor distance from each other on the performance of the gridanchor has been investigated and optimal values have been proposed. If using geogrid in high normal stress, it is better to use geogrid with higher tensile strength. So that if a grid anchor is used in high stresses, it is better that the distance of the anchors from each other is greater than their distance in low stresses. Generally, the use of threedimensional geosynthetics performs better at normal stresses and low displacement.

A vital stage in oil refining is elimination of hydrogen sulfide, which is done by means of sodium hydroxide solution in petrochemical industries, leaving a spent caustic soda (NaOH solution) as the product. In the process, hazardous gases react with sodium hydroxide and hydrogen sulfide solutions and Thiol compounds to form a rich brown to nearly black effluent demonstrating the fragrant toxic components such as methanethiol, enzene, toluene and phenol. Despite all these odorous noxious organosulfur compounds, spent caustic soda leads to environmental problems due to its alkalinity (pH>12), salinity (5-12 wt. %) and high sulfide content (1-4 wt. %). Spent NaOH was registered as industrial dangerous waste in resource conservation and recovery act law. Inefficient and inappropriate management in spent NaOH treatment and disposal causes stability challenges, reduction in energy resources and water security attenuation. Techniques for spent caustics treatment have been neutralization with acid, wet air oxidation, combination of neutralization and Fenton (i. e. electro-Fenton), biologic treatment and ignition each of which would face some limitations. In recent decades, electrocoagulation (EC) has engrossed much attention as an Environmental-friendly and effective process. In addition, the EC process is a potential suitable way for treatment of wastewater with a view to costs and environment. Furthermore, EC offers further advantages as simple operation facilities, small occupying area, dispensability of chemical additives and short treatment time. EC often consists of anodes and DC cathodes a part of which are immersed in wastewater container. Shape, number and configuration of electrodes may be different but rectangular types are preferred. The widespread anodes are iron and aluminum based for their availability, reasonable cost and harmless media. In electrocoagulation, electrolysis takes place to dissolve metal anode (sacrificial electrode) in wastewater. Metal ion flow from sacrificial electrode as coagulant surrounds wastewater particles. After release of Al3+ and Fe2+, the ions react with hydroxide groups and metal hydroxides turn to insoluble agglomerates able to trap contaminants and increase particle size by complexation of electrostatic attraction. In addition, hydrogen gas produced in cathode, allows agglomerates to float on surface. The object of this study is electrochemical evaluation of COD removal from refinery wastewater, specifically refinery spent caustic, using iron and aluminium (anode) and graphite (cathode) electrodes. Therefore, the effect of key variables including electrode arrangement (bipolar-serie, monopolar-serie and monopolar-parallel), anode electrode material (iron and aluminium), using pierced anode electrode and cathode graphitem initial pH (7-11), electrolysis time (0 to 120 minute), current density (15. 6 to 28. 125 mA/cm2) was evaluated. The three parameters of current density, electrolysis time and initial pH has been modeled with design expert software with response surface method (RSM) and central composite design (CCD). Impact of other variables has been investigated with single parameter method. According to the results, the optimum conditions including, parallel mono-polar electrode arrangement, aluminium electrode has been achieved. In designing experiments in accordance with the model provided by the software, quadratic analysis design with R2=0. 96 had a high accuracy in designing the experiment. According to the model analysis and laboratory work, optimum electrolysis time was 116 min, current density was 25 mA/cm2 and initial pH=8 reached COD removal percentage of 85. 1% in vitro and 88. 9% for model.

The science of seismic control of the structures always seeks to reduce and control the destructive effects of the forces which are produced during an earthquake event. However, the yield of the soil under intensified seismic loads can cause some irreversible effects on the structural elements and the structure may withstand the increased moments and the forces for which it is not formerly designed. This unfavorable phenomenon significantly affect the seismic response and performance of the structures, and will ultimately leads to disappearance of all functional goals that are sought to create in the structural design stage by the designer of the structure. In this research, by a relatively accurate three dimensional finite element modeling, from a highrise concrete structure equipped with the active mass damper, and by examining the lesser-known aspects of the problem such as uplift of the foundation and the effects of nonlinear interaction of soil and structure, an attempt has been made to conduct a relatively comprehensive study on the questions of seismic control of structures equipped with active mass dampers due to the nonlinear effects of the underneath soil behavior. For this purpose, time history dynamic analysis was performed on the structural model under the effect of 22 horizontal records of distant basin earthquakes in x and y directions followed by the Appendix A of FEMA P695. The Ibarra model (a reviewed and modified model based on the Clough model) is used for modeling of the hysteresis behavior of concrete materials. The underneath soil is modelled by three springs approach presented in ATC 40 and FEMA 440 with equivalent stiffness based on soil modulus of elasticity and Poisson’, s ratio of three categories (the main C category and upper and lower C and E categories ). To achieve the goal of optimization and evaluation of the active mass damper parameters (consist of tuning ratio, mass ratio and damping ratio), the mass damper spectra method with investigation of changes in structural responses has been used. The Fuzzy theory has been used to calculate the control force of an active mass damper. The results indicate that with respect to entrance of the structure to non-linear zone and its interaction with non-linear behavior of the soil, the efficiency of the active mass damper in uplift control of the foundation decreases, but a good efficiency is observed in the lateral displacement and inter story drift control. By evaluation of the three dimensional analysis results of a nonlinear soil structure system equipped with the active mass damper, the researchers observed that for the set of the recorded earthquake and based on the specifications considered for fuzzy algorithm, the active mass damper has a satisfactory effect in the control of displacements and drifts of the structure, in the amount of almost 15 percent. It was also identified that the active mass damper has a negligible effect on the foundation uplift in the structures which constructed on the hard soil. But when the soil becomes softer, a 3 percent mean decrease is observed in the uplift displacements in foundation.

Structural vibration control has become a controversial topic among researchers today. In recent years passive dampers have been proposed as an effective and reliable method against these vibrations. In this paper, an innovative configuration for steel braced frames using energy dissipaters is presented. The proposed bracing system includes two-level slotted bolted connection (SBC) dampers with slipping performance and a horizontal shear panel system (H-SPS) or eccentrically braced frames (EBF) which is called CS+EBF. The proposed model consists of four structural parts, including horizontal shear link beam, beam, bracing and columns, which other structural components were designed based on the shear capacity of horizontal shear link beam. The brace provides the rigidity of the frame and remains elastic until the end of the loading, like columns and beam. The SBC fuse with frictional movement of the end of the brace in the slot hole and the HSPS fuse with shear yield can dissipate energy at low, medium and severe earthquake levels, respectively, and prevent or delaying the bracing member from buckling. Past experience has shown that dampers designed for an earthquake energy level also start working in low level earthquakes than that level, which has hampered the ability of these dampers to dissipate energy in more severe earthquakes. Therefore, the SBC fuse is considered as an auxiliary fuse in this innovative two-level system to prevent the main fuse from operating in mild earthquakes. Also, the SBC fuse, unlike the yielding fuses after the earthquake, does not need to be replaced and is repaired by applying prestressed load to the connection screws, which distinguishes the proposed twolevel system from other similar systems. The samples are modeled with 1/2 scale and solid elements to achieve accurate results. The proposed configuration and other similar samples, in addition to push over loading, were also subjected to cyclic SAC loading protocol to compare the behavior of the proposed sample and other samples properly. The results obtained in this study indicate that in the push over analysis, in addition to maintaining the strength and stiffness of the proposed sample (CS+EBF), the ductility of this sample compared to other similar singlelevel systems, SCBF and EBF has increased. In addition based on cyclic loading, it was found that two-level proposed system has more ductility and energy dissipation than similar single-level systems and also shows that with increasing shear thickness of shear panel beam, energy dissipation and final strength of braced frame increases. The energy dissipation of the proposed configuration is 88% and 33% higher than that of SCBF and EBF single-level systems, respectively, and the share of energy dissipation of the first fuse (SBC) and second fuse (H-SPS) is 33% and 30% of the total energy dissipated by the CS+EBF2 braced frame respectively.

Liquefaction is the cause of many earthquake-induced failures in loose to semi-dense saturated deposits. Most recently published works have been focused on the liquefaction potential of clean sands. However, the studies on silt and silty sands, particularly the effect of cyclic stress ratio (CSR) on the critical silt content in evaluating sand liquefaction potential with 40% fine grains and more, have received less attention. Hence, the present work attempts to determine the effects of CSR, backpressure, the percentage of non-plastic fine-grain contents, and the effect of pressure on the saturated soil using cyclic triaxial experiment constant confining pressure. Samples were prepared by mixing 161-Firoozkuh Sand with three different silt amounts, including 0, 30, and 60 wt%. The experiment continued by the “, wet tamping method, ”,in which samples were made with a diameter of 5 cm and a height of 10 cm. All samples were compacted under a constant confining pressure of 100 kPa at a relative density of 32%, following the recommendation of ASTM. D-5311. According to the obtained results, with increasing the silt in the sand by 30%, a decrease in liquefaction resistance occurred. However, with a further increase of silt to sandy soil with 60% silt, an increase in liquefaction resistance was observed. This indicates that systematic progress from pure sand to sand with 30% silt led the fine particles of silt to fill the voids between coarser particles of sand. This resulted in reducing the soil drainage capacity during earthquake vibrations or cyclic loading. Therefore, the liquefaction potential increases in these conditions, but the sand-like behavior still prevails up to 30% fine-grained. A further increase beyond 30% changes the soil behavior, and the soil adopts fine-grained behavior, which reduces the liquefaction potential. CSR's effects on liquefaction behavior of all soil samples of this study have been evident that with changes in the CSR, the percentage of fine particles that cause the highest pore water pressure, respectively, change. In this regard, the liquefaction curve equation is presented in the range of sandy to loamy sands. The results showed that by increasing the silt content up to 30%, a decrease in liquefaction resistance occurred, and then a further increase in the silt content caused an increase in the resistance. It was observed that by increasing fine grains up to 30%, the behavior of sand is predominant,however, when the content of fine grains exceeds 30%, the behavior of fine grains and silt is dominant. Collectively, the results show that changes in CSR's value cause a regular change in the percentage of fine particles that cause the highest pore water pressure. On the other hand, the effect of backpressure on the soil skeleton in the saturation state (B-value) of the samples based on liquefaction potential and the resulting strains was insignificant in the sand with 60% silt and somewhat more pronounced in the sand with 30% silt.

Since the development of the construction industry in the field of concrete structures, this material has been known as one of the most commonly used substances in the last century. Extensive use in industries such as bridge construction, dam construction, landscaping, construction structures, and construction of ports, piers and special structures has made concrete a valuable material and made it the center of attention of many researches. But production of Portland cement requires consumption of natural resources such as limestone, fossil fuels and also electrical energy which emit significant amounts of greenhouse gases, resulting in environmental pollution. Therefore, it is better to look for other materials to replace Portland cement. Geopolymers can be a suitable and inexpensive alternative to various types of cement because the raw materials used to produce them are more accessible than that of the conventional cements. Additionally, because geopolymers are produced in lower temperatures, the emission of pollutants such as carbon dioxide produced by cement kilns is prevented. The World Environment Commission has defined the concept of sustainable development as the ability to meet the current needs without compromising the ability of future generations to meet their needs. This definition requires increased consideration of all aspects of a particular industry from the supply of raw materials and energy consumption to reuse or recycling. Therefore, the shortage of low-cost raw materials in the future of cement and concrete industry should be carefully considered. Because in the production of cement, the use of materials based on limestone is common and reserves of limestone are limited, the concrete industry is facing multiple challenges to provide an increasing need for Portland cement. In fact, due to this shortage and increasing production of Portland cement, these goods can only be produced for less than 59 years. In 2011, the world’, s cement production was about 3. 6 billion tons which means that more than 3 billion tons of limestone was needed to produce clinker which illustrated that the limestone reserves were already running low. Geopolymer concrete consists of two main parts: the base material and the activating material. The base material is actually a combination of aluminosilicates, and since natural and synthetic pozzolans are rich sources of such compounds, they can be used as base material. Different forms of Pozzolans such as silica or silica-aluminum materials have little effect or no adhesion value,however, in a very ultrafine form and in the presence of moisture during the chemical reactions with the activating substance at normal temperature, compounds with cementitious properties can be formed. This process is called pozzolanic reaction, and the types of pozzolans that can be mentioned are raw or calcined natural pozzolans such as volcanic ash, and industrial pozzolans such as fly ash, calcite clay, silica fume, iron slag, rice husk ash, etc. Based on the definitions of the activating substance, it can be said that it is an alkaline solution that dissolves aluminum and silicon ions in the base material, and by performing the reaction, it forms the composition of geopolymer paste. The most important activating solutions in the research are sodium hydroxide, potassium hydroxide, sodium silicate, sodium carbonate and potassium silicate, and compared to other alkalis, sodium hydroxide and potassium hydroxide show higher levels of alkalinity.

There are many factors causing damages to a structure, including earthquakes, winds, environmental effects, etc. In order to repair a damaged structure, first its damage locations should be identified. Therefore, the damage identification of structures is considered as an important issue in civil engineering as well as mechanical engineering. Many methodologies have been devised for damage identification of structures, which are generally categorized to destructive and non-destructive cases. As a non-destructive damage identification approach, solving inverse problems for identifying the properties of a damaged structure is one of the popular methods which utilizes an optimization algorithm to minimize an error function in terms of measured strains or displacements. Since an iterative procedure with significant number of structural analyses should be carried out for the optimization process, an efficient numerical method should be employed to reduce the total computational cost. In this paper, the identification of hole in two-dimensional continuum structures is investigated with finite cell method and particle swarm optimization algorithm. The finite cell method is an efficient numerical method for solving the governing equations of continuum structures having geometrical complexity and/or discontinuities, which uses the concept of virtual domain method. The use of this concept makes the mesh generation easier such that the simple structured meshes can be utilized even for the curved boundaries of a structure, and hence mesh refinement is not necessary for the problems like damage detection. The finite cell method uses adaptive numerical integration for the cells including non-uniform material distribution. Accordingly, quadtree integration is utilized for the structural analysis using the finite cell method. Consequently, the computational time is significantly reduced. On the other hand, particle swarm optimization is a well-known meta-heuristic algorithm, and hence it does not require the gradient information of the problem. This population-based algorithm has been inspired by the social behaviour of animals such as fish schooling and birds flocking. The basis of this algorithm relies on the social influence and learning which enable individuals to preserve cognitive consistency. Thus, the exchange of ideas and interactions between individuals can lead them to solve optimization problems like damage detection. This study proposes the finite cell method and particle swarm optimization algorithm for damage detection of plate structures with single hole or multiple holes. As a non-gradient-based method, particle swarm optimization explores the search space to find the coordinates of the existing damage by minimizing an error function. This error function is evaluated by the strains or displacements calculated by the structural analysis utilizing the finite cell method. In order to evaluate the proposed methodology, numerical examples are provided to demonstrate the capability of finite cell method and particle swarm optimization algorithm in damage detection of two-dimensional structures. The first example considers the damage detection of a plate with a single hole, and it also considers the effects of mesh density. The second example employs a plate structure with three holes. The results demonstrate that the proposed methodology, with suitable computational efforts, can successfully be applied to damage detection of these structures.

In this paper, solution of inverse problems in a plane linear elastic bodies are investigated. In recent years, many studies have been conducted to develop effective approaches for damage detection in structural components. The efforts made over the last decades to overcome the mathematical challenges encountered in non-linear inverse problems may be categorized in two procedures: traditional methods, and qualitative methods. Although satisfactory results can be obtained using traditional approaches, they impose long reconstruction times associated with necessity of an accurate initial guess. These schemes require a priori information that may not be necessarily available. Consequently, the mentioned limitations have led to the conceptually distinct class of inverse scattering solutions, known as “, qualitative methods. ”,These methods are based on non-iterative obstacle reconstruction from far-and/or near-field measurements of the scattered field which avoids incorrect model assumption. Qualitative methods may be considered as probe/sampling methods such as linear sampling method, topological sensitivity, factorization method, and point source method, which seek to determine the geometric properties of scatterers. In this regard, the LSM and the FM introduced in the inverse scattering literature of far-field acoustics for the first time, are particularly attractive. This is due to the abilities of these methods to provide accurate reconstruction of the location and shape of the unknown scatterer from measurements of near-or far-field patterns, by monitoring the behavior of the norm of regularized solution. This norm is bounded inside the targets and unbounded elsewhere. Moreover, the most interesting feature of qualitative methods is that they do not require a priori information/assumption on the scatterer and/or the investigation domain. In addition, these methods may handle multiple scatterers as easily as single ones. Furthermore, these methods involve relatively low computational cost and can be applied to various types of defects such as non-convex and not-connected ones. For this purpose, sampling method in frequency domain is introduced for cavity/crack detection in a structural element such as plate. This goal is followed by partitioning the investigated region into an arbitrary grid of sampling points, in which a linear equation is solved. The main idea of the linear sampling method is to search for a superposition of differential displacement fields which matches with a prescribed radiating solution of the homogeneous governing equation in Ω, (D), for each sampling point. Although this method has been used in the context of inverse problems such as acoustics, and electromagnetism, there is no specific attempt to apply this method to identification of crack/cavities in a structural component. This study emphasizes the implementation of the sampling method in the frequency domain using spectral finite element method. A set of numerical simulations on two-dimensional problems is presented to highlight many effective features of the proposed qualitative identification method.