Modares Civil Engineering journal
Year:2021 | Volume:21 | Issue:2|Papers Count:17

Roller compacted concrete (RCC) is a Portland cemented concrete mix with zero slump and dense aggregate dispersed by conventional machinery in asphalt concrete and compacted by rollers. No need for reinforcement and dowel bars, easier implementation, relatively less cost, no need for a finisher, and less shrinkage cracking are the main advantages of this type of pavement over the other rigid pavements. Low skid resistance and uneven surface are the main limitations of roller-compacted concrete. According to manual 354 (Guidance for Design and Implementation of Roller Compacted Concrete pavement of Road in Iran), its application is limited to urban streets and parking lots with low speed. To overcome this limitation and improve the skid resistance of RCC, casting a thin layer of concrete with high skid resistance immediately after implementation and compaction of RCC has been suggested. In the present study, this kind of two lift concrete pavement (2LCP) mechanical and fracture properties were evaluated and compared with typical single lift concrete pavements. Therefore, a thin layer of plain concrete and polypropylene fiber reinforced concrete with a relative thickness of 30% of total pavement thickness has been cast of RCC pavement. The main objectives of casting a layer of fiber Reinforced concrete on RCC are providing an even surface with high skid resistance and improving the flexural and cracking resistance of these composed systems. Compressive strength and mode I fracture tests were performed on samples after 28 days of curing. In the two-lift concrete pavement system, to prevent cold joints between the layers, the layers' differential implementation times were limited to 30 minutes. The results showed that due to the lower water to cement ratio, plain concrete's compressive strength is higher than roller-concreted concrete. Also, the addition of polypropylene fibers to plain concrete reduces the compressive strength of concrete slightly. In two-lift concrete specimens, replacement of plain concrete or fiber reinforced concrete by 5 cm with roller concrete does not decrease flexural strength than a single layer of RCC. Like single-layer specimens, the use of fibers in the upper layer does not increase the specimens' flexural strength. The fracture energy of the roller compacted concrete is slightly higher than normal concrete in single layer concrete pavement, but the addition of polypropylene fibers increases the specimens' fracture energy considerably. Similar to compressive strength, the bending strength of normal concrete is greater than roller-compacted concrete. In two lifts concrete specimens, replacement of plain concrete with roller-compacted concrete reduces the fracture energy, but the use of fiber-reinforced concrete in the upper layer compensates fracture energy reduction. As a general conclusion, it can be stated that replacement of plain concrete and fiber concrete with roller-compacted concrete in two lifts specimens had no significant adverse effect on flexural strength and fracture strength of the specimens compared to single-layer roller compacted. It’, s possible to implement roller compacted concrete for the high-speed street and highway with the bottom layer in two-lift concrete pavements.

Retaining walls have many applications of geotechnical activities, the most important of which is the control of lateral soil pressure. There are several methods for restraining retaining walls, including mechanical restraints buried in the soil. In this paper, the performance of the retaining wall restrained by single-plate and double-plate restraint under constant strain loading, which includes the load-bearing capacity of the wall, horizontal displacement and the effect of loading heel distance to wall height, is investigated. The effect of the mentioned cases on the shape of the wedge rupture has been observed by particle image velocimetry (PIV) method. Taking into account the scale coefficient of 0. 1 and applying static loading in plane strain conditions, the test chamber with dimensions of 120 cm in length, 50 cm in width and 80 cm in height has been modeled and constructed. One side of the chamber is covered with 2 cm thick Plexiglas to observe the performance of the wall against the test variables. The chamber is filled with poorly graded sandy soil (SP) of Sufyan region of East Azerbaijan province with a specific weight of 16. 67 kN / m3 and an internal friction angle of 28 °,and a constant density in the form of dry precipitation. The mechanical loading system consists of a loading jack coupled with a digital display and a load cell with an accuracy of 0. 1 g placed on the ground, which can be measured by rotating the loading shaft at each stage, the amount of force applied to the loading heel and also The opening of the jack is measured by a displacement gauge with an accuracy of 0. 1 mm. Accordingly, the lowest horizontal displacement and the highest bearing capacity are related to the control of two plates with the same surface. The first step is without load and the first image is formed from the soil surface without deformation. This work was continued in a total of 7 steps until reaching a settlement of 35 mm of the loading heel, followed by shooting at the end of each loading stage. Accordingly, the lowest horizontal displacement and the highest bearing capacity are related to the double plate with the same surface. Decreasing the ratio of loading heel distance to wall height has shown more load-bearing capacity and less horizontal displacement in the wall. According to the analysis of PIV results, the particle strain at the critical slip surface is obtained in double plate inhibitions smaller than the single plate inhibition, and by reducing the ratio of loading heel distance (D) to wall height (H), the amount of soil particle strain has increased significantly (the performance of the retaining wall has weakened) and by increasing the ratio of loading heel distance to wall height, the effect of inhibitory plates in control Horizontal displacement and increased bearing capacity (retaining wall performance has been improved). In this regard, by reducing the ratio of loading heel distance to wall height, the restraint behavior of single and double plates has become more similar and their effect on wall performance has been observed with a slight difference in the strain of soil particles.

Metal faced Polyurethane/Polyisocyanurate sandwich panels are used in construction sites and temporary accommodation especially after destructive events such as flooding and earthquake, that a clear example was the temporary settlement of earthquake victims after earthquake occurrence in the Kermanshah province at November 2017. However, flammability of polyurethane foam core of these panels and the higher risk of fire in these types of buildings, highlight the importance of assessing fire performance of these panels. In this study, fire performance of several types of metal faced sandwich panels with PUR/PIR foam core produced in the country, was evaluated by reaction to fire and fire resistance tests. The reaction to fire behavior of foams was also evaluated separately. The results showed that the polyurethane foam was not fire retarded and met reaction to fire class F,but the poly-isocyanurate foam depicted a better fire behavior and met fire class E. Fire resistance tests were performed on common types of sandwich panels in the temporary buildings with two different execution details including a steel sheet fixed to the joint position in the panels and the other, fireproof paint and their fire performance was compared to unprotected panel. According to the results, deformation of the joint in sandwich panel is the main disadvantage and it is very critical in real fire due to flame spread through the joints which is critical in a real fire incident, when evacuating the occupants and acting fire brigades. Hence, protection of the joints by insertion of a protective sheet, increases fire resistance and improves the integrity by increasing the time by 40 minutes compared to the unprotected panel. Finally, fire safety recommendations were provided for the safe use of these panels in temporary buildings.

Reliability analysis, considering the randomness of geometry, materials, and loading variables, is a proper guide for structural design in engineering. The stochastic finite element method is used to analyze the structural systems, concerning uncertainty in random parameters of structures. Solving the equations of stochastic finite element leads to the calculation of all possible structural responses taking into account all the random variables of the structural system and loads. Because of the uncertainty effect on the response of structural systems, reliability analysis seems essential. However, due to the limitations of the classical methods of reliability analysis, there is a need to calculate the reliability index based on the probability density function of response in structures. In this study, by combining the perturbation method and the change –,of –,variable method and without the limitation of the statistical type of random distribution of random variables, the probability density function of response is calculated. By calculating the probability density function of the static response of the structures, as a result, the probability of failure and the reliability index are obtained directly. It is obvious that the accuracy of the result of the stochastic finite element analysis depends on the random field element meshes. For this purpose, the distributed random field is discretized over the number of elements of equal length in structural members for each random variable. In the stochastic finite element method, due to the uncertainty of the characteristics of random variables in the structure, it is necessary to define a correlation function between a random variable in different elements. The reliability index is considered as a measure of convergence by considering the scale of fluctuations and the correlation function of random variables in adjacent elements in structure. In each number of elements, the structural reliability index is calculated directly by using the explicit probability density function of static response and the structural resistance function to converge on a certain number of elements. In this study, the stochastic finite element analysis is performed in linear static mode for a simple beam and a cantilever column. The variables of geometry, materials, and loading are also considered randomly with real statistical distributions according to the literature review. As can be expected from the deterministic finite element method, as the number of elements increases and the meshing is smaller, the reliability index increases. Considering the lower scale of fluctuations for random variables makes the reliability index converge to a larger value. However, on a larger scale of fluctuations convergence occurs in a smaller number of elements due to the greater correlation of random variables in adjacent elements. Additionally, the results of the probability density function of the static response with the explicit method compared to those of the Monte Carlo simulation method show a better match. The advantage of using the reliability index as a measure of convergence in meshing the configuration of limited random components is taking into account all the possible structural responses instead of using the average structural response in the design of structures.

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 the connections of SMRFs have been developed by some researchers to resolve the ductility problem in the connection of rigid beam to column in SMRFs. Circular pipe steel damper (CPSD) proposed as a type of steel damper can indicate and mainly dissipate the seismic energy through its inelastic deformation. Among steel dampers such as shear panel damper, the advantage of CPSD is to resiste applied load in all directions. Under cyclic loading, the circular shape of CPSD can change to elliptical shape which causes an extra energy in its absorption capacity. The previous studies 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 the cross section can enhance the behaviour of pipe steel damper (PSD). In this study, the ellipse PSD (EPSD) (or the ellips of cross section) was proposed for improving the performance of 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) was assessed subjected to cyclic loading in the ABAQUS software. It is noted that the proposed EPSD has the same weight in comparison with that of the common CPSD. The results of the assessment shown that 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 subjected to cyclic loading was compared. The results of the comparison revealed that the EPSD in the rigid connection increased to about 63% of the total dissipated energy. Due to the distribution of stresses in more area of the EPSD, the strength of the proposed damper increased. Finally, the performance of a rigid beam to column connection equipped with the proposed EPSD and the welded connection subjected to cyclic loading was compared. The results of this study demonstrated that the rigid connection equipped with the proposed EPSD colud withstand a large number of cycles of loading until the failure. Therefore, the proposed EPSD can be used instead of welded connection in SMRFs. In the future studies, it is proposed that the best geometry shape of the PSD subjected cyclic loading can be found in the framework of an optimization problem.

The Dez dam, with a volume of 3. 3 billion cubic meters and 203 meters height, was built with the aim of generating hydropower, flood control and meeting agricultural demands. With the loss of about 700 million cubic meters of dam reservoir capacity due to sedimentation and approaching the level of sediments to the power plant intake, as well as increasing downstream water demand and reducing the reservoir inflow due to the upstream development projects, the optimal operation of the Dez Dam has faced problems. In order to overcome these problems, a plan to increase the height of the dam has been proposed. On the other hand, the Ghadir water supply project with design discharge of 24 cms for transferring water from the dam reservoir to some cities of Khuzestan province is underway. So far, the effects of these projects on the water level variations and thermal regime changes in the dam reservoir have not been studied. In this paper, first by using the two-dimensional CE-QUAL-W2 hydrodynamics and water quality model, the sensitivity analysis, model calibration and confirmation for simulation of water level, thermal profile and total dissolved solids was performed. Then, the effect of Ghadir project in the thermal regime as well as water level changes in the wet and dry conditions, before and after dam heightening while reducing and not reducing the reservoir inflow has been studied. By performing model sensitivity analysis, it was found that the model showed the highest sensitivity respectively to the shading parameter and empirical coefficients a, c and b with the sensitivity index values of 3. 25, 2. 58, 2. 34 and 1. 23, respectively. After the sensitivity analysis, the model was calibrated for water level, temperature and total dissolved solids. The results showed that the calibration mean absolute error of water level, temperature and TDS was 9 cm, 0. 79 °, C and 15 mg/l, respectively. On the other hand, by examining the effect of power plant and Ghadir project on thermal stratification, it was observed that the thermal profiles do not experience a significant change due to the inability of the shear forces to overcome the buoyant forces. Also, by evaluating the effect of Ghadir project while reducing the reservoir inflow on the water level in different hydrological conditions, the positive effect of implementing the Dez Dam heightening plan to reduce the effects of water transfer and the possibility of continuous operation of the dam reservoir, Appeared. In this regard, in the hydrological conditions of 2014, which is an average of the hydrological conditions, the decrease in reservoir inflow and operation of the Ghadir project, leads to decrease in the water level of 10. 68 meters and 7. 8 meters, respectively. By comparing the water level in the conditions of increasing and not increasing the height of Dez Dam in dry and wet periods, improvement of about 50% and maximum improvement, respectively, in maintaining the minimum operational water level in the conditions of increasing the dam height can be seen. Therefore, in case of non-implementation of the Dez Dam heightening project, operation of Ghadir project to supply drinking water to parts of Khuzestan province will face a serious challenge.

The interaction between soil and geosynthetics has great importance in engineering work, especially in design and stability analysis of geosynthetic-reinforced geotechnical structures. In recent decades, several laboratory methods have been performed to properly understand the interaction between soil and geogrids, including pullout test, large-scale direct shear test. Although factors such as the geometry of the reinforced soil system and its construction process may affect the interaction properties between the soil and the geosynthetic, these properties are strongly influenced by the physical and mechanical properties of the soil and the geometrical and mechanical properties of the geosynthetic. Pullout test determines the geosynthetic pullout resistance, which is an important design parameter in relation to the internal stability of geosynthetic-reinforced geotechnical structures, and allows the measurement of displacements throughout the specimen during the pullout testing. Pullout force refers to the tensile force required to create an external sliding of geogrid embedded in soil mass. The tensile strength of the reinforcement consists of the frictional resistance on the surface of the longitudinal and transverse members of the geogrid and the passive resistance that is mobilized against the transverse members. Although fine-grained soil is recommended in the design of geosynthetic-reinforced soil structures, many geosynthetic-reinforced soil structures are constructed using soil containing a fine percentage. Therefore it is important to investigate the effect of fine grains on the stability and performance of such soil structures under different loading conditions. Geosynthetic-reinforced soil structures are sometimes affected by cyclic loads due to traffic and train crossings, vibration of industrial machinery, wave and earthquake. In this study, by performing static and multistage pullout tests, the static and post-cyclic pullout behavior of a uniaxial geogrid manufactured in Iran under the brand GPGRID80/30 is presented. The tests were carried out on a large scale pullout box with a dimension of 90 × 50 × 50 cm and with a constant rate and multi-stage procedures on three different soil types including clean sand, sand containing 10 and 20% fine silt and three effective vertical stresses of 20, 40 and 60 kPa. Results show that geogrid static pullout resistance increases with increasing effective vertical stress in all three different soil types. Also, the increase of silt in the sandy soil resulted in an increase in the monotonic maximum pullout resistance at effective stress of 20 kPa. The geogrid behavior in all three soils for 20 kPa vertical effective stress was strain softening and for the 40 and 60 kPa vertical effective stress the geogrid pullout behavior was strain hardening. However, 10% increase in silt content leads to a slight decrease in monotonic pullout resistance and a 20% increase resulted the slight increase in monotonic pullout resistance of geogrid at vertical stress of 40 and 60 kPa. As the amount of silt content increased, the effect of cyclic loading on post-cyclic resistance increased, especially in vertical effective stresses of 40 and 60 kPa. Also, at effective stress of 20 kPa, the geogrid post-cyclic resistance decreased in all three sands, sand containing 10% silt and sand containing 20% silt relative to its corresponding monotonic pullout resistance.

One of the most popular lateral load resisting systems is the concentric bracing. However, despite the unique advantages of the system, it has irregular and unstable hysteresis cycles because of differences in compressive and tensile strength. Hence, many studies are devoted to improve these braces to achieve an ideal symmetric elastoplastic behavior which has resulted in construction of Buckling-Restrained Braces (BRB). BRBs, although have a much better seismic performance than ordinary bracing, have a main disadvantage (similar to conventional bracing) of producing large nonlinear displacements due to their low stiffness, and consequently they have potential to form soft story. Recently, Strongback Bracing System (SBS), which is a combination of a zip system and an elastic truss system, has been introduced. SBS actually includes two types of features: a rigid elastic truss to tie story drifts over the height of the structure, and a conventional bracing system to dissipate energy. Therefore, this system can prevent or delay probability of soft story by controlling the distribution of floor displacements and the nonlinear demand of the structure. However, the studies conducted on this system are limited, and to the best of the author’, s knowledge performance of this system with BRB configuration under seismic sequences is not yet investigated. In this paper, seismic performance of the SBS system is investigated and compared with the BRB one. First, behavior of these systems are studied under main shock. Next, seismic sequences are applied on the structures to better understand the behavior of SBS frames compared to BRB. For this purpose, three 4-8-and 12-story frames were designed with two SBS and BRB systems. BRB elements were used as inelastic braces of SBS system. Nonlinear static analysis was conducted to evaluate the seismic parameters of the structures such as response modification factor and overstrength factor. Also, nonlinear time-history analysis was performed to find maximum and residual response of the structures. In the next step, a fragility analysis was conducted using IDA to estimate performance of the structures under mainshock and seismic sequence for different performance levels. 3 performance levels were selected for SBS and 4 performance levels for BRB which show the elastic to global collapse of the structures. The results of static analysis showed that the SBS system has a uniform distribution of displacement in the height of the structure, which prevents the formation of soft story. In all analyses, SBS showed a superior performance, especially in 4 story structure. Also, SBS frames showed higher response modification and overstrength factors. Results of dynamic analysis showed that the 4-story SBS structure was much less vulnerable to seismic sequences compared to the BRB one. However, the performance of SBS system decreases with increase in the height of the structures, such that 12-story frame experienced large deformations and collapsed under lower seismic demands than BRB frame. This was due to buckling of some elements in rigid truss which led to concentration of demands in these elements. Therefore, more stringent provisions are needed for design of taller structures with SBS system.

Classic one-way shear design provisions began with 45 degrees truss analogy introduced by Ritter and then rectified by addition of a concrete contribution term (Vc) which was basically based upon the results of some academic tests of simply supported RC beams with concentrated loadings. There are some strong evidence and examples that this empirical approach and the difference between its experimental base and the effective mechanisms in many of existing applications can be disastrous. Shear failure of reinforced concrete falls in the category of brittle and undesirable failure modes and has caused unrectifiable incidents in structures and infrastructures throughout the world. Some of such examples are the shear failures observed in the event of Kobe earthquake, shear failure of US air force warehouse, fatal highway bridge failure in Laval, Canada, and damage of Sleipner offshore platform. After such observations, there have been some good efforts in development of methods based on the physical description of main mechanisms influencing the shear behavior of RC members and especially RC panels under in-plane stresses that led to development of theoretical approaches such as modified compression field theory (MCFT), softened truss model (STM), and critical shear crack theory (CSCT). These theories made some breakthrough in nonlinear analysis of RC structures and become the basis for shear design in some of advanced codes like AASHTO LRFD, fib model code and CSA. Due to the complex nature of shear behavior in reinforced concrete, consensus in this field has not been reached among researchers, yet. In this study, through a parametric study on shear capacity of reinforced concrete panels based on Local Stress Field Approach (LSFA), and assumption of a thorough and compatible physical description, an efficient method for shear capacity analysis of reinforced concrete members is introduced. The principal effecting input parameters in parametric study were selected randomly within a reasonable range in the n-dimensional space of variables. These variables included: ratio of longitudinal stress to shear stress, ratio of longitudinal reinforcement, yield stress of longitudinal reinforcement, characteristic strength of concrete, maximum aggregate size, transverse reinforcement amount, and yield strength of transverse reinforcement. The remaining input parameters, like concrete tensile strength, fracture energy, rebar size, etc. were picked reasonably, in accordance with main parameters. Using an immense and strong experimental database of reinforced concrete slender beams failed in shear alongside with a database of reinforced concrete panels failed under in-plane loads, it is shown that the proposed method is a reliable, simple and easy to use approach that possesses high accuracy in calculation of shear capacity of slender reinforced concrete beams with or without transverse reinforcement, in comparison with existing reputed methods, and leads to safe and economic designs. Continuous transverse reinforcement (CTR) with a rectangular or polygonal shape is a relatively new technique that has been introduced in order to accelerate and facilitate the construction of RC structures. Studies show that rectangular continuous transverse reinforcement can improve the shear behavior and shear capacity of reinforced concrete beams, although existing shear design provisions, even the most advanced ones, are unable to predict this enhancement in capacity. It is shown that the proposed method is able to predict the aforementioned improved shear capacity of reinforced concrete beams with rectangular continuous transverse reinforcement.

In this research, the seismic response of offshore wind turbines, considering the interaction of saturated soil-pile-structure, has been investigated using numerical method of finite element. OpenSees software has been used to consider the conditions of soil saturation and pore water pressure changes. Due to the existence of soil constitutive model in OpenSees, such as the PDMY model and coupled u-p elements, it has a good ability to model saturated soil and pore water pressure changes. For numerical verification, a centrifuge test carried out by Yu et al. was used. This test was carried out on an offshore wind turbine with tripod foundation, with a height of 13 meters and three piles, 0. 5 in diameter and 3 meters in length with a triangular arrangement, and the response of the turbine tower and pore water pressure variations under the earthquake load have been investigated. In this experiment, blades, hub and Nacelle were simplified as a rigid mass on top of wind turbine tower and so large moment caused by the earthquake load was modeled on the foundation. For simulation and creating numerical model, only one half of the system was modeled using symmetry boundary condition. Soil 3D continuous medium was modeled through coupled u-p formulation correlated to saturated porous medium using PDMY constitutive model that has the ability to simulate sandy soil behaviour under cyclic loadings in drained and undrained condition. The model consisted of 14288 nodes and 12420 coupled u-p 3D elements for saturated soil part. Nonlinear beam-column elements were used for pile parts. For simulating actual size of pile cross-section, rigid beam elements perpendicular to the longitudinal axis of the piles were used. Actually these rigid elements were beam-column type that their stiffness is 10000 times larger than the stiffness of pile elements. One node of this elements was connected to the pile and the other node was tied to the soil node with same location through equal DOf constraint. Each pile with 3 meter in length consisted of 12 nonlinear beam-column elements. For half pile 65 rigid elements and for full pile 104 rigid elements was used to simulate actual size of pile cross-section. Wind load on tower is estimated by equation provided in DNV standard. Also the thrust force (force applied by the wind on the rotor of turbine) is calculated through the previous study (Leite) and using Manwell equation. Wave load is calculated by Morison equation and the kinematics of water particles are simulated by Airy wave theory (linear wave theory). After passing the verification stage, through the parametric study, the effect of other environmental loads (wind and wave load) and peak ground acceleration (PGA) on the seismic response of the offshore wind turbine are investigated. The results showed that in seismic analysis of offshore wind turbines, the interaction of environmental loads should be considered, and the Superposition Principle can not be easily applied. It was also found that the relationship between the peak ground acceleration and the turbine tower response is nonlinear. On the other hand, by increasing the PGA, the effect of soil-piles interaction on the ru ratio increases.

Dam reservoirs are constructed in order to flood control, reserve and provide water for downstream use, energy production and/or recreational purposes. Sedimentation is one of the most important operational conflicts in the world,surface run-off water erodes and carries the sediments on their route to the downstream all the time. Because sedimentation in reservoirs would reduce its useful volume, to reserve and retain the present reservoirs and to minimize the dissipation of reservoir volume because of sedimentation is very important. As a result, presentation of an appropriate method for increasing the efficiency of pressurized sediment flushing could be a significant way in increasing the useful lifetime of dams and also in surviving the pools with less water wasting. In this manner, using some hybrid method for increasing the efficiency of sediment flushing could be highlighted. At present, the efficiency of sediment flushing from outlet gates is very low. In this paper, a new method to increase the efficiency of sediment flushing is presented in which a structure namely SFM structure consisted of two parallel piles rows is installed on reservoir bed at the upstream of outlet gate. In this experimental research one to six pairs of piles with a permeability of 37. 5% in two parallel rows at distances of 4, 8, 16 and 24 cm from each other were installed. The water flow will exit through the outlet gate after passing among the piles. Redirection of streamlines around the piles and also passing the flow along the corridor will cause some horseshow and wake vortices and also will cause the situation so as the sediments will rise and start to move. This will make the streamlines to interact and the proportional velocity of water to increase along the corridor and as a result, it is anticipated that more sediments will flush from the outlet gate and the flushing cavity volume will expand toward upstream. In this research it is noted that the SFM structure to be applicable and easy to construct inside a full-scale reservoir,so despite Madadi et al (2016), there is no ceiling on top of the columns because in prototype scale construction of such huge roof is not applicable. Because the maximum velocity gradient is normal to the outlet gate based on flow hydrodynamics, the arrangement of the columns is proposed to be perpendicular to the gate axis. Uniform non-cohesive sandy aggregates with a mean size of 0. 67 mm were utilized as packed sediment in the reservoir. The results showed that the flushed sediment from the reservoir increases by 261% when the SFM structure with corridor width of 8 cm is utilized compared to that of the reference test (without SFM structure). Based on economic considerations and results of the present study (direct and indirect costs of piles construction) one can see that the four pairs of piles with permeability of 37. 5% and row distances of 2Do (L/Do=2) is the most optimum case among the tested cases of SFM structure in increasing the efficiency of sediment flushing around and through outlet gate in reservoirs. Considering the results, the SFM structure is an applicable structure and further investigations should be performed in order to find its design charts.

There are some Innovative methods to control the damage caused by seismic loads, and one of them is to concentrate the damages on the designated region or members. The reduced beam section connection, also known as the dogbone connection, is a promising option for improving the ductility of steel beam to column moment connections, especially in high-risk regions. By symmetrically trimming the width of the beam flanges over a discreet length in the vicinity of the beam ends, a ductile fuse can be created to accommodate the inelasticity that is required for seismic energy dissipation while is not only protecting the beam to column connection but also prevent causing the catastrophic and progressive collapse of the structure. This paper's emphasis is the performance of the steel portal frame with RBS connections based on detail provided by AISC specification. The concentration of plastic deformations in the RBS region under cyclic load causes intensified stresses that accumulate damage. The prediction of ductile damage and fracture is one of the most important challenges in many engineering applications. Damages in a structure are caused by material degradation due to initiation, growth, and coalescence of microcracks/voids in a real-life material element from monotonic, cyclic/fatigue, or dynamic/explosive impact loading. The damage evolution law describes the rate of degradation of the material stiffness once the corresponding initiation criterion has been reached. In this study, the ductile damage model presented for steel is used. Damage Initiation parameters and damage evolution rules were obtained based on standard tensile test from literature and software procedure analysis. A coupon model has been established based on the standard tensile test to evaluate the ductile damage model. Also, to validate the steel portal frame with the RBS connection model two-step has been considered. In the first step, the global response of the steel moment frame was validated based on Wakabayashi's test. Also validation of the RBS connection model was checked based on Pachoumis experiments in the next step. Then, according to AISC 360 steel and AISC 341 steel, a steel moment frame design with RBS connection was designed. By selecting and extracting a single-span portal frame, the effect of considering damage was investigated by finite element analysis. Initial geometrical imperfections were determined using the AISC 360 Recommendation for out-of-plumbness, out-of-straightness, and localized geometrical defects. The cyclic displacement amplitude followed the loading protocol in the ATC-24. The study results show in the elastic region the behavior of the frame remains unchanged before the frame reaches the high amplitude cycle. But gradually, with increasing cycles, the size of the hysteresis loop and ultimate resistance became smaller. Thereby, if the aim is to focus on the load levels that lead to large localized plastic deformations, it is critical to consider the damage parameters to improve the reliability of the results. Measurement of the area below the graph in the last loading cycle shows that the dissipated energy in the two cases without vertical load and with a vertical load on the columns is decreased by 2. 6% and 4. 1%, respectively. The continued deterioration of the RBS region due to damage spreads leads to complete frame failure, which is not properly predicted when damage parameters are ignored.

Heavy metals are considered as one of the most important environmental threats, especially for aquatic ecosystems, due to their toxicity, stability, widespread distribution and bioaccumulation in the food chains. Urban runoff is the main non-point source of heavy metal emissions to receiving environments, which its quality and evaluation is particular importance. The major part of Tehran’, s surface runoff, especially the northern and eastern catchment, is transferred to the southern areas by drainage network and affects receiving environment including surface water, groundwater and sensitive ecosystems such as Band-e-Alikhan wetland. The aim of this study was to investigate the content of heavy metals in urban runoff and compare the efficiency of the index of Iran’, s surface water resources quality toxic parameters with the Contamination Index, heavy metal evaluation index and Heavy metal pollution index. For this purpose, sampling was performed from the outlet of Tehran’, s Sorkheh –,Hesar catchment during three flood events in 2018-19 and the concentration of Arsenic, Iron, Lead, Zinc, Cadmium, Chromium, Copper, Manganese, Molybdenum and Nickel were measured by ICP-MS. Iron, Manganese, Zinc, Lead, Copper, Chromium, Nickel, Arsenic, Molybdenum and Cadmium had the highest abundance in all samples, respectively The values of the index of Iran’, s surface water resources quality toxic parameters, Contamination Index, heavy metal evaluation index and Heavy metal pollution index were in the range of 5. 5 to 68. 2, 9. 6 to 74. 4, 83. 2 to 192. 7 and 8. 8 to 23. 7, respectively. The contamination index indicated that all samples were in the highly contaminated class, while according to the and heavy metal evaluation index and Heavy metal pollution index indices, 67 and 86 percent of the samples were highly contaminated, respectively. Also, the index of Iran’, s surface water resources quality toxic parameters values showed that 70 percent of the samples are in very bad quality class, and the other samples are in bad quality class. In general, a comparison of the results of the studied indices indicate that most of the samples were polluted. The results of the present study showed that the studied indices presented similar results in determining the contamination status of most samples. The results of Spearman's rank correlation coefficient showed strong correlation (0. 775-0. 999) between all of four indices in runoff, Which confirmed the similar behavior of the indices in determining the contamination status of the samples. In more detail, comparing the values of the indices with each other showed that their response to a significant increase in the concentration of elements is different. So that, the changes in the value of the Iran’, s surface water resources quality toxic parameters gradually decrease with increasing the concentration of elements and its value is fixed in very high levels of pollution, but the values of the other three indices increase linearly with increasing the concentration of elements. Comparison of the results of the indices for the runoff quality assessment, showed that index of Iran’, s surface water resources quality toxic parameters had the highest affinity with the pollution index, Heavy metal pollution index and heavy metal evaluation index, respectively, which shows the appropriate efficiency for evaluating these streams. Thus the index is suitable for evaluation of heavy metal contamination in urban storm-water runoff due to high separation of pollution degree and less susceptibility to very high concentrations. It is recommended that, more elements in a wide range of concentrations should be considered in order to performance evaluation of the indices in future researches.

In this paper, a crack detection method is presented to detect Euler-Bernoulli beams containing arbitrary number of transverse cracks. The proposed method uses the time domain signal of the free vibration response to provide the position and depth of cracking of the Euler-Bernoulli beam that is modeled with a modified stiffness using the Spring model, with high accuracy and precision. The time history responses used in this paper are nodal computational accelerations at certain points of the beam exposed to impact load. The acceleration of the nodes is calculated with the Newmark beta method at the edge of the elastic beam`s superelements. Initially, using the computational time history of the damaged beam and the analytical model of the Euler-Bernoulli beam, the objective function of the failure detection problem, to be optimized by particle swarm algorithm, is defined and, intensity and location of transverse cracks are calculated by solving the optimization problem in Matlab environment. In order to determine the accuracy of the proposed method, three beam samples with different cracks and loadings are considered. In the first sample, the crack supposed to be in the superelements of beam and the beam considered to be with four elements as superelements. The second one has ten elements and same loading as previous. The third one has twenty elements and the loading is on the second element. All of the loadings are impulse loads. The comparison of the results of a four elements beam with the primitive conditions shows that accuracy of the deducted results were exactly matched. For the ten element beam, the results were satisfying but in the twenty element beam with asymmetric loading, obtained results indicate imprecise match. To determine the accuracy of the developed model in real environmental conditions, different percentages of noise were added to the data of all three samples. These noise addition to data, contain 1, 3, 5 Percentages of noise. The results show that the model presented in the presence of noise also provides accurate results and the model is not sensitive to the presence of noise in the data applied to three samples. Considering different number of elements in each sample, no convergence was observed, Also the results were not sensitive to the location of impact load applied on the samples. The results of this study indicated that asymmetric cracking and loading variation are very effective in predicting beam failure. The results also indicate that variable reduction is very effective on the accuracy of results. Having more cracks and therefore more elements to analyze will yield to less accurate results. To lessen these inaccuracies, it can be practical to achieve better results by assuming the location of crack is constant in the element length if the depth of crack be the matter of importance. The number of iterations that have been executed, indicate that the pace of convergences in the developed process is less than when PSO deployed solely. This speed rate for obtaining results makes the developed method practical for solving crack detection problems in structures.

Steel cylindrical silos are key storages in many industries. They can be composed of flat or corrugated sheets. To construct these structures, steel sheets may be welded or bolted to each other. This study addresses steel welded silos with flat sheets. Different loads, such as, filling and discharge loads, wind load, seismic load and thermal loads should be considered in design of silos. Nevertheless, during the life cycle of a silo, filling and discharge of particulate solids exert the most frequent loads on the silo walls. Due to larger values of discharge pressures as compared with those of filling pressures, discharge loads are primarily considered for structural design of silos. Due to small wall thickness, buckling resistance is of vital importance in steel silos design. Ensiled materials exert normal pressures and frictional tractions on silo walls. Accordingly, during discharge process, meridional buckling resistance of shell walls concurrent with internal pressures should be assessed. It is well known that buckling strength is very sensitive to geometric imperfections in shell structures. In welded silos, the most regular and well-defined imperfection is local depressions existing in circumferential welded joints due to the plate rolling process and shrinkage of the weld. The assumed shape given for this type of imperfection in the literature were adopted throughout the paper. Eurocode as the most advanced and pioneering standard on the design of steel silos, provides a hand design procedure for buckling evaluation of steel silos under discharge loads. To assess the procedure, a full suite of computational shell buckling calculations was performed with special emphasis on the effect of aforementioned geometric imperfection. A slender, an intermediate slender and a squat silo were considered for the assessments. Linear elastic Bifurcation Analysis with Imperfections (LBIA) and Geometrically and Materially Non-linear Analysis with Imperfections (GMNIA) were carried out for each structure. Sample silos were loaded in accordance to the pressure distribution proposed in the Eurocode. By assuming strake’, s height of 2 meters, uniform depressions were simulated in circumferential welded joints of each silo. Three different Fabrication Quality Classes (FQCs) denoted by FQC A, B and C in a descending order from Excellent to Normal Class were introduced in the Standard. The imposed depression amplitudes were calculated in accordance to FQCs of the silos. Considering the results obtained, the LBIA buckling modes show several circumferential buckling waves at the first welded joint of each silo from the base. Lowering the FQC leads to the decrease in number of circumferential waves and to the development of buckling waves at the location of second and third welded joints. Nevertheless, the more sophisticated GMNIA analyses predict elastic-plastic buckling mode in the form of diamond pattern concentered at the first welded joint of the silos from the base, irrespective of selected FCQ. However, for the slender silo the two upper welded joints are also interact during buckling. With respect to the design buckling resistance ratios (rRd) obtained by hand calculations and through non-linear analyses, the former method has predicted rRd values in the range from 13% to 32% lower than those of GMNIA. Therefore, hand design procedure of Eurocode produced satisfactory results, without high conservatism. However, more researches on this issue can enhance the reliability of conclusions made with respect to the Eurocode provisions.

Seismic loading in seismic prone countries is very important and the lack of enough attention can make irreparable damages to structures and non-structural elements. Dissipating earthquake energy just by using elastic capacity of structure will increase the dimension and weight of structural elements such as column, beam, walls,and therefore the cost of building will increase. Incoming seismic energy should be dissipated in plastic process and in this process, structure must remain stable. Shear wall is widely used because of its suitable behavior against seismic loading and good ability of energy dissipation. Sometimes it is inevitable to avoid openings in shear walls due to architectural considerations. Providing enough ductility in these shear walls is a difficult job because of stress concentration around of voids. The other problem of using shear walls is plastic deformations that make the structures useless. One way of improving ductility and self-centering ability of shear walls is using smart materials. Shape memory alloys are one of the newest smart materials that have two important behaviors,mainly known as memory effect and superelasticity. Removing the residual deflection after unloading of elements made by shape memory alloys by heating is called memory effect. Superelasticity in SMAs results in returning the elements to their initial shape after unloading without having any residual displacement. Good corrosion resistance, good fatigue behavior and weldability are the other positive behaviors of shape memory alloys. In this paper the improvement of the shear walls ductility and self-centering ability with using shape memory alloys in superelastic phase is investigated. Shape memory alloys can withstand up to seven percent of strain without any residual deformation. In this paper shear walls modeled by shear-flexure interaction multi-vertical-line-element-model (SFI-MVLEM). This model was implemented in the Open System for Earthquake Engineering software (OpenSees). Considering interaction between shear and flexural response in shear walls has made this element superior. Superelastic reinforcement bars were embedded in plastic hinge of boundary elements, coupled beam and walls web separately. Shear wall modeled by using SMA in boundary element, coupled beam and walls web called SMAB, SMAC and SMAW respectively. To examine the effects of these alloys on energy dissipation capacity and self-centering ability of the shear walls, structure were evaluated in cyclic analysis. Place of using SMAs on shear wall in very important and can influence widely on shear wall so most optimized place of using SMAs in shear wall should recognized. Two case of optimization considered in this analyze. In first one, best place is a place that using SMAs on it causes minimum energy dissipation reduction and maximum residual displacement removing. In second one, best place is the place that causes maximum residual displacement removing with minimum usage of SMAs. In order to find the influence of SMAs on ductility of shear wall, pushover analysis was used. Using SMAs in boundary elements of shear walls made maximum increasing in ductility of shear wall but the best place for using SMAs for optimization of usage of SMAs is walls web. Based on the results, with using shape memory alloys, ductility of shear walls was increased and its residual deformation and energy dissipation capacity was decreased. The best place of using SMAs in shear wall is coupled beam for optimization of energy dissipation and residual displacement and for optimization SMA usage is walls web.