نشریه مهندسی عمران مدرس
سال نوزدهم شماره 2 (خرداد و تیر 1398)

The purpose of this study is to develop the previous proposed analytical model by the first and second authors for short links, so it can be used for all kinds of links including short, intermediate, and long links. Eccentrically braced frames (EBF) offer high lateral stiffness because of their braced configuration while also providing high ductility and energy dissipation. They are widely used as a lateral-force resisting system for multi-story buildings located in seismic areas. The key components of the EBF system include columns, collector beams, braces and active links. The active links are designed to provide ductility and energy dissipation through yielding under design basis earthquakes, while all other structural members are designed to be stronger than the links and stay in elastic range. The link is defined by a horizontal eccentricity between the intersection points of the two brace centerlines with the beam centerline. Sufficient analytical model which can accurately predict the inelastic performance of the links is needed to perform reliable nonlinear analyses of EBFs. Analytical models that are used to study the inelastic seismic response of the EBFs usually reflect the anticipated behavior of the different frame elements. Links are modeled as inelastic elements with concentrated end flexural and shear hinges. Beams outside of the link, braces, and columns are typically modeled as elastic beam-column elements, because no inelastic behavior is anticipated in design. Ricles and Popov proposed an analytical model for short links. Ramadan and Ghobarah replaced the sub-hinges with translational and rotational springs and proposed a new model. Both models had incorrect shear stiffness so that the shear stiffness of model was half the link shear stiffness. Richards and Uang corrected the shear stiffness of the model proposed by Ramadan and Ghobarah, and proposed a new analytical model for short links. Koboevic et al. proposed an analytical model based on the results of experimental test performed by Okazaki and Engelhardt, regardless of the fact that the actual measured dimensions of sections were different from the standard dimensions of sections. To account for this issue, despite of what is said in their paper, the strain-hardening ratio was set to 0.0045. For this reason, the shear stiffness of their proposed model was incorrect and the predicted shear forces are 15 to 24 percent more than the experimental shear forces. Ashtari and Erfani showed that available analytical models do not predict very well the maximum shear forces and deformations too, and proposed an analytical model which can accurately predict both maximum and intermediary values of shear force and deformation of short links. To the authors’ knowledge, currently there are only suitable analytical models for short links. In this study an analytical model which can accurately predict both maximum and intermediary values of forces and deformations for short, intermediate, and long links, is proposed. The parameters of model are established based on test results from several experiments on links and EBFs. Comparison of available test results with the hysteresis curves obtained using the proposed analytical model established the accuracy of the model. The proposed model is recommended to be used to perform inelastic analyses of EBFs.

One of an effective and economical solution in order to weir efficiency is using nonlinear weirs, Which can cause  the increase of the flow over weir by changing in geometric plan and increasing in weirs length in fixed widths of the channel . in this research, the hydraulic performances of  the piano-key weirs has been simulated by FLOW-3D and also it has been validated by the laboratory data. In the following, the discharge coefficient (Cd) has been measured and evaluated with the creation of single and double circular orifice on the heel of weir ( , For the different water head and in relation to without dimension parameters    .
Findings shown with the expansion orifice diameter, discharge coefficient of combined weir -with the maximum opening  - is increasing between 0.5 to 6% in comparison to without orifice piano-key weir., besides, with the rise in the high of single orifice ,which has a fixed diameter, the discharge coefficient is reducing between 0.5 to 3%. From the other side, the usage of double orifices decreases the discharge coefficient in comparison to the single type at the same opening size, in a way that by increase in the distance of orifices, at first, it faces to the rising trend and then by reaching to   it starts revising. Finally, an equation is provided for the estimation of the discharge coefficient by benefiting without dimension parameters with   .

Results of traffic assignment models are the main output of transportation planning studies and decision making for future developments is based on these results. Therefore, accuracy of these models is very important. Despite the mentioned importance, comparing the models and their solving methods to estimate actual traffic volume and network performance measures is rarely considered in previous studies. The traffic assignment process has started from the simplest methods like All-or-Nothing, then it has developed using the rules and supplement assumptions such as Wardrop principles and finally it has evolved by concepts such as Fuzzy theory. Traffic assignment models can be categorized by various factors into several groups: deterministic vs. stochastic, congestion considering vs. unconstrained capacity and being equilibrium or not. The main goal of this paper is a comparative and quantitative analysis of various traffic assignment methods to estimate the observed traffic volumes. In this regard, the main questions that this study seeks to answer is as follows: 1- Do the results of various traffic assignment methods have a significant difference in terms of overall network indices? 2- Is there a significant difference in the accuracy of traffic volume estimation in various traffic assignment methods? In this study various traffic assignment methods such as All-or-Nothing, Incremental, Stochastic, User Equilibrium, Stochastic User Equilibrium and System Optimum have been examined. To compare the results of traffic assignment methods, in addition to estimated link volumes, various performance measures such as vehicle-kilometers traveled, vehicle-hours traveled, fuel consumption and air pollutants emission are also used. In this regard the city of Qazvin is selected as a case study. This city has more than 400 thousands inhabitant, near 46 square kilometers area, 113 traffic analysis zone (TAZ) and its network has 2300 directional links and 1200 nodes. The results of applying these methods in Qazvin city network show that various traffic assignment methods based on User Equilibrium, despite different assumptions, have no significant difference in estimating the overall network performance measures as well as estimating traffic volume in links (correlation between estimated and actual link volumes using all of these models is approximately 0.88). But the other methods, which do not consider equilibrium assumption and volume-delay functions, produce different results (correlation between estimated and actual link volumes using all of these models is approximately 0.70). Although estimated link volumes in some of traffic assignment models are significantly different, overall network performance measures are approximately the same. In all of assignment models the differences between estimated and actual link volumes in average are high which are not negligible (approximately 20 percent). In addition to high average error in estimating link volumes, the distribution of these errors has significantly high standard deviation (approximately 20 percent). In spite of different and complicated assumptions, models and solving algorithms in various traffic assignment methods, on basis of Kolmogorov-Smirnov (K-S) test results, the distribution of links volume estimation error is not significantly different. According to this fact, it seems that should be careful in using the results of traffic assignment models to compare and assess minor network improvement alternatives, such as changing conventional streets function to pedestrian streets, upgrading intersections to interchanges, cross section widening, traffic signals optimization and changing traffic direction in streets.

Local scour around bridge pier is one of the important problem in bridge stability against water flow that is created due to hole scour around bridge pier and castrates its stability. So as, providing methods for control and scour reduction around bridge pier have very importance. Yet different methods have been proposed for preventing and reducing the local scouring around the bridge pier. Use of Submerged Vanes is one of the methods that researchers are interested in. Submerged plates are thin rectangular structures that because of having angle with the flow direction, is created high pressure and low pressure region on both sides. These structures create a secondary vortex and change the flow pattern in the river bed and as a result, change the sediment and scour transmission. Submerged vanes performance to reduce the bridge pier scouring the sediment movement around the vanes due to the downward flow in front of them, are affected by the layout of the plates. These vanes are designed in cross section of the channel and fixed with a little angle relative to flow direction perpendicularly on bed. In this research, submerged vanes were used to reduce the local scour around the single bridged pier located in bend head. Effective variables in this study were vanes overlapping length, space of submerged vanes from bridge pier center and space of submerged vanes from each other perpendicular state on flow direction. For this purpose, a cylindrical bridge pier to diameter 5 cm in the laboratory was performed with a sharp bend 180 degree with central radius to channel width ratio equal 2, a width 1 meter and height 90 cm with straight direction length of bend upstream 6.5m and straight direction length of bend downstream 5m in clear water conditions( u)⁄u_c =0/98 with water discharge of 70 liters per second and depth 18cm. The submerged vanes were Plexi Glass with width 1.5 equal pier diagonal (7.5cm), thickness equal 20% pier diagonal and located in 25 angle relative to horizon with height of out of bed 4.5cm (submergence percent 0.75) with sitting vanes center in the middle of channel (50% channel width from inner shore, with overlapping length (Lcv) 80 and 100% and intervals of submerged vanes from each other perpendicularly on flow direction 5 and 10cm (Lvv/D)=1.2 in position 83 and 79.5 degree from beginning of the bend (interval equal 5 and 7.5 pier diameter toward upstream from located pier site) (Lvp/D=5, 7.5). According to the results of this study, the 20 percent reduction in the overlapping length of the submerged vanes decreases the depth of the scour hole around the bridge pier about 30 percent. Also use of submerged vanes, is transferred location of maximum scour depth to a place near than pier and limited width of scour hole around pier. Furthermore, submerged vanes limit sedimentation region to 0-12% channel width from inner shore and in 70-127 degree from the beginning of the bend. Minimum and maximum scour in hole around pier with submerged vanes is created 0.53 and 0.65 equal flow depth in the beginning of the bend in V80-5-2 and V100-7.5-1 Tests, respectively. The discussion about the results of this research is from the other parts of this article.

In this paper, due to the role of the catenary action of the structural members in large deformations and transfer of additional loads due to the middle column removal is important to prevent the catastrophic event of progressive collapse, a simulation method is introduced using 3D numerical finite element method (FEM). This method is simple, reliable and very suitable for predicting the response of RC members to the failure level. For verification of numerical model, two series of specimens tested experimentally by previous researchers have been used. The first series include the beam-column subassemblages under a middle column removal senario for comparing and displaying the numerical modeling capabilities in the prediction of three levels of performance including flexural, compressive arc and catenary action and the second series include a set of concrete beams rienforced with hybrid combinations of steel and fiber Reinforced polymer (FRP) bars. Comparisons between the load-displacement curves obtained from experimental data and numerical results of both series of specimens reveal the high accuracy of the proposed simulation method. In the following of research, based on validated numerical models, the effect of FRP bars in combination with steel reinforcement on the performance of beam-column subassemblages under progressive collapse and the effect of mechanical properties and their arrangement in concrete beams section on the strength and ductility and catenary action are investigated.

Nowday, slab track is widely used in the world as railway supresturture because its advantages in comprison with conventioanl ballasted railway superstureure. So, design and analysis process of railway slab track is one the main issues in recent researches.  One of the main factor in the design and analysis of slab track is distrubtion of vertical load on longitudinal direction of the track (load distribution factor). In this paper, a 2D numerical model is developed in FORTRAN to investigate the effect of slab track properties on the load distribution factor. In this model, the slab track is comprised of rail, fastening system, concrete slab, elastic layer, concrete base and subgrade. Rail, concrete slab and concrete base are modeled as two nodeded beam element and fastening system, elastic layer and subgrade are simulated as spring element. According to the elements stiffness matrices, slab track stiffness matrix is developed. A wheel load is applied on the rail (in the middle of the model). Based on the two noded beam element shape functions, load vector of the model is developed. The equlibrium equation of the model is solved and load distribution factor is derived. To investigate the validity of the results obtained from the model, a comparsion is made between results obtained from the model and those of ABAQUS as a commercial finite element software. Rail displacement, concrete slab displacement, concrete base displacement and load disribution factor obtained from the ABAQUS are compared with those of the model developed in this paper and a very good agreement was illustrated between results. A parametric study was performed to investigate the effects of rail flexural rigidity, fastening system stiffness, concrete slab flexural rigidity, elastic layer stiffness, concrete base flexural rigidity and subgrade stiffness on the load distribtion factor. The results obtaine from the parametric study indicate that as the slab track element stiffness or flexural rigidity is decreased, the load distribution factor is decreased and vertical load is distributed widely in the longitudinal direction of the track. Rail pad stiffness has the maximum effect on the load distribution factor reletive to the other parameters. As the rail pad stiffness is changed from lowest to highest magnitude, the load distribution factor is varied from 0.3 to 0.7. The results obtained in this research indicate that propeties of lower slab track elements have lower effects on the load distribution factor compared to the upper slab track elements. So when the flexural rigidity of the concrete slab is changed from low to high, load distribution factor is changed from 0.52 to 0.54. Moreover, when the elastic layer stiffness, concrete base flexural rigidity and subgrade stiffness are changed from low to high, the load distibution factor are almost unchanged and is roughly 0.54. This shows that elastic layer stiffness, concrete base flexural rigidity and subgrade stiffness do not have any significant effects on the load distribution factor. So when a model is developed to calculate the load distribution factor and dcrease of analysis computation cost, elastic layer stiffness, concrete base flexural rigidity and subgrade stiffness could be ignored in the model.

Semi-supported steel shear walls (SSSW) are a new lateral resisting system whose plates do not have any direct connection to the main columns of structure. Instead, they are connected to secondary columns which do not carry the gravity loads. The applied lateral loads may create overturning moment on the middle storeys. The ultimate shear capacity of the SSSWs in presence of the overturning moment has been reasonably determined with an analytical procedure. It was finalized with some applicable interaction curves between the ultimate shear capacity and the overturning moment which can be used for analysis and design of this system. In addition, some experimental studies have been conducted to find an insight for the cyclic behavior of this system. As the elastic buckling of wall plate always occurs at the low levels of lateral loads, the system stays in a relatively large region of elastic post-buckling. In this region, the geometrical nonlinearity with linear material behavior appear in the wall plate. Thus, the storey shear force has a linear variation versus the lateral displacement until the first point of wall plate is yielded. Perhaps solution of the Von-karman plate equations is the best approach to find an analytical vision for the elastic stiffness of the SSSWs. These equations are described with two coupled nonlinear fourth order differential equations. The mentioned equations have been widely solved for many plates which are under combinations of different in-plane and out of plane loads and various boundary conditions and imperfections. In this study, the Galerkin method was employed in a semi analytical procedure to solve the Von-karman plate equations for the wall plate of SSSW system in a middle storey. This solution leads to achieve the displacement field of the SSSWs at the different levels of lateral loads until the first point of the wall plate is yielded. Thus, the linear variations of the in-plane displacement versus the lateral load will be obtained. Since the ultimate capacity has been previously measured, then an ideal elasto-plastic curve can be obtained for this system. The wall plate is supposed as a thin plate whose parallel edges have two different boundary conditions: two simply supported and two stiffened free edges where the wall plate is connected to the storeys beams and the secondary columns respectively. A sine monomial is considered as the deflection function which is satisfied the boundary conditions. Then, an algorithm is analytically developed to find the out of plane deflection of plate and the two-dimensional elasticity is used to determine the in-plane displacement of plate. The obtained results are compared with those of FE analysis and the suggested algorithm can be programmed in usual computers. The results show that some parameters such as the wall plate dimensions, the geometric properties of secondary columns (i.e. cross sectional area, moments of inertia), the storey shear force and yield stress of wall plate effect on the end point of elastic post-buckling. But, the slope of this region is independent from the variation of overturning moment and section of secondary columns.

Construction of hydraulic structure on dispersive soil created a lot of problems such as piping or internal erosion. Since it is not economical to change dispersive soil with non- dispersive soil, therefore, it is very important to improve the erosion resistance of soils using appropriate and cost effective techniques. This research is intended to study the effect of adding nano-clay on erodibility of dispersive soil. The nano-clay (montmorillonite) has been used as a modern and eco-friendly additives for controlling internal erosion in dispersive soils. To conduct this research, dispersive soil has been treated with four different percentages (i.e. 0, 0.5, 1, 1.5 and 3 % by weight of the parent soil) of nano-clay. The Variables taken into account are the curing time (i.e. 1, 2, 7, 14 and 28 days) and the mixing percentages. Erodibility parameters were obtained by the Hole Erosion Test (HET) in different hydraulic gradients (i.e. 7.05, 7.96 and 11.05). It is found that increase in nano-clay content is increasing the resistance of dispersive soil to erosion. The optimum amount of nanoclay in reducing erosion for samples of one day curing time was obtained 1% and the erosion index rate was 4.33. For 2 and 7 days curing times the  optimum amount of nanoclay was observed equal to 1.5% and the index of erosion rate was 4.85 and 4.72, respectively. It was also observed that in larger hydraulic gradients, the effect of nanoclay in reducing erosion is more. Also, increasing nano-clay addetive changed plastic index properties of soil.

Concrete is the most used building material in the world. Many studies have targeted concrete due to its numerous benefits over other building materials. Being a moldable and rather cheap building material, it has provided good motives for engineers to further investigate the mechanical and microstructural properties of concrete with the incorporation of different kinds of additives. To do so, waste materials admixtures were suggested into the matrix to lessen the amount of cement through cement replacement as Pozzolanic mineral admixtures. These admixtures are used in concrete to enhance the mechanical properties. Waste materials not only reduces the cement content but enhances the qualities of concrete such as mechanical and the microstructural properties. However, only limited amounts of replacement were suggested. In this research, a new waste material is introduced to use in concrete as a pozzolanic material. In this paper, for the first time, Pistacia Atlantica Ash is used into the matrix of concrete to reduce the amount of cement and then, the effects of Pistacia Atlantica Ash on the concrete are investigated. Pistacia atlantica is a species of wild pistachio tree. In Iran, it is called Baneh or Van.
Fruit of Pistacia Atlantica is collected from the Saghez city located in north Kurdistan, Iran. The fruit of Pistacia Atlantica is first burned at 500 ºC for 3 hours. Then, Pistacia Atlantica Ash is sieved. Cement is replaced Pistacia Atlantica Ash. To do so, 5, 10, 15 and 20% Pistacia Atlantica Ash is admixed in the concrete samples. The Water to cement (W/c) ratio are kept constant at 0.45 for the entire mixes. Amount of aggregates are kept constant for all series of mixes. All of the samples are cured in water.
Four design mixes of Pistacia Atlantica Ash separately are casted for compression tests, slump, modulus of elasticity, ultrasonic pulse velocity (UPV), and microstructural properties. The compressive strength of samples at ages of 7, 14, 28, and 90 days are recorded. Cement replacement with Pistacia Atlantica Ash decreased the early age compressive strength. However, the compressive strength in the specimens increased in the course of time. The target compressive strength of control samples is set to be 39MPa at 28 days. Compressive strength of samples with 20% Pistacia Atlantica Ash is improved up to 18.3% at 28 days.
 One of the major findings is that concrete that incorporates twenty percent of Pistacia Atlantica Ash weight of cement showed better mechanical properties. Concrete slump in the specimens are considerable decreased comparing to the control samples. The replacement of Pistacia Atlantica Ash with cement increased the elastic modulus. Also, scanning electron microscopy (SEM) results showed that admixing Pistacia Atlantica Ash led to improvement in the microstructure, and pozzolanic behavior of mixtures. The results from microstructural analysis are conclusive that C-S-H formation increased when of Pistacia Atlantica Ash is added to the samples. In general, the results are conclusive that the addition of 20% Pistacia Atlantica Ash enhances the properties of concrete such as compressive strength modulus of elasticity and density of microstructure.

Nowadays, reinforced concrete structures are widely being constructed all over the world and some of them need to be strengthened for variety of reasons such as poor design, damages caused by earthquakes, etc. Nowadays, engineering attitude toward demolition and renovation of structures have been changed to retrofitting and upgrading. By retrofitting, the structural reliability increases and saves both time and cost. In some of special cases that the structure can not be demolished and rebuilt, retrofitting plays an important role. The columns of the structures are one of the main elements that are subjected to axial, shear forces, and bending moments, and their strength and ductility have an important impact on their seismic capacity. Different methods are used for strengthening of columns. These methods include concrete jacketing, steel jacketing and composite jacketing (FRP). Among the various retrofitting methods of reinforced concrete columns, steel jacketing is one of the methods used to strengthening of RC structures, especially for confining RC columns with rectangular and square cross sections. Steel cage is a type of steel jacket and because of its effectiveness, ease of use, light weight and the availability of material, it has become an affordable, effective, economic and simple option. This method involves the use of four longitudinal angle steel profiles fixed to the corners of the RC columns, to which some transverse steel strips are welded. The gap between steel cage and column is filled with cement or epoxy mortar. Different parameters affect the behavior of the column reinforced with steel cage. Studies carried out on this strengthening method have mostly focused on the axially loaded columns. The parameters have been studied are the number of steel strips, the size of the steel strips, the size of the steel angels, the thickness of the steel strips, the yield stress of the steel of the cage, the compressive strength of the concrete used in the column, and, finally, the use of capitals in the beam-column connection joint zone. Capitals are welded to the steel cage and located at each end of the cage, loads applied to the beam are transmitted to the steel cage through the capitals. Loads from an upper floor of the building are also transmitted to the cage through the beam via the capitals. Current study investigates the behavior of RC columns strengthened with steel cage under axial force and bending moment. In this regard, the strengthened RC column with steel cage was modeled using finite element method using ABAQUS software and calibrated by experimental results obtained from other laboratory research works. Then, the parameters affecting the behavior of the strengthened columns were examined. The results of this study show a good agreement with experimental results and demonstrate a considerable increase in the ultimate axial force and bending moment.

Water shortage and wastewater discharge into environment have led to significant research in the field of environmental engineering for developing high efficient, fast, and cheap wastewater treatment. In recent years, advanced oxidation processes (AOP) have been subjected to significant attention for wastewater treatment due to feasibility of the process in mild reaction conditions, requiring low cost equipment, and short time of the process. Electro-Fenton process addresses the potential drawbacks of Fenton reaction including transportation of H2O2 and regeneration of ferrous ions which act as catalyst. In the present study, ZSM-5 catalyst was synthesized by hydrothermal technique and promoter was introduced through wet impregnation method. Ir-ZSM-5 catalyst w::as char::acterized by XRD, FE-SEM, BET, FT-IR and NH3-TPD techniques. The XRD patterns revealed the high crystallinity for the both parent and Ir impregnated ZSM-5 catalysts. FE-SEM images showed micro-spherical morphology. N2-adsorption-desorption confirmed mesoporous structure for the synthesized catalyst including 321.1 and 327.3 m2/g specific surface area for the parent and Ir-ZSM-5 catalysts, respectively. FT-IR spectrum confirmed formation of ZSM-5 zeolite and also revealed presence of surface hydroxyl groups. NH3-TPD revealed that acidity of the impregnated ZSM-5 catalyst was increased due to interaction of Ir with zeolite structure. Acidimetric-alkalimetric titration determined pHPZC for the parent and Ir-ZSM-5 catalysts equal to 3.6 and 3.9, respectively. Catalytic performance of Ir-ZSM-5 catalyst for removal of methylene blue (MB) from wastewater in heterogeneous electro-Fenton like reaction was evaluated. Different operation conditions were tested including concentration of catalyst, pH of wastewater solution and applied current between graphite electrodes. The results showed that Ir-ZSM-5 catalyst had acceptable performance in near neutral pH level due to the improved adsorption of MB molecules on Ir-ZSM-5 structure. The stable catalytic activity resulted from formation of no sludge related to active phase. Detected OH groups at the surface of the catalyst attained positive charge at pH<phpzc and negative charge at pH>pHpzc which influenced the adsorption capacity of the catalyst at different pH levels through electrostatic adsorption of ionized MB molecules on the catalyst. Blank test using no amount of Ir-ZSM-5 catalyst led to only 77% MB removal which was attributed to anodic oxidation on the surface of the graphite electrodes. Increasing applied current led to the improved MB removal owing to the faster degradation of the sacrificial graphite anode. The optimum operational conditions for the proposed system were pH=3, 0.2 gL-1 of Ir-ZSM-5 catalyst and 100 mA applied current which resulted in the highest MB removal (100%). The reusability test of the catalyst was carried out by 3 consecutive runs at the optimum conditions. After each run, the used catalyst was regenerated at 550 °C to remove the adsorbed organic molecules due to adsorption of either MB or its oxidation intermediates. The regenerated catalyst showd the high catalytic performance with insignificant change of the removal efficiency as result of the high crystallinity and specific surface area of the synthesized catalyst. A pseudo first order kinetic was proposed for the reaction of removal which fitted the experimental data with the high correlation factor. The results confirmed the high potential of the heterogeneous electro fenton-like process for wastewater treatment.</ph

Concrete -filled steel tube are widely used today in many civil engineering structures. The advantage of steel members is their high tensile strength and ductility and, on the other hand, concrete members have high compressive strength. Composite members combine steel and concrete, which have positive properties of both materials. In members under compressive loading, circular tube columns, for a given cross section area, have the large uniform bending strength in all directions in comparison to other cross-sections. Filling the pipe with concrete will increase the ultimate strength of the member without significantly increasing costs. On the other hand, the concrete in the tube delays the local buckling of the pipe wall. In this type of section, the outward buckling will reduce the amount of confinement, ductility and ultimate strength.
Subsea and offshore marine structures are mainly made of hollow steel circular sections, where water pressure reduces their load carrying capacity. By converting these sections to concrete filled tube, external pressure can improve the behavior by increasing the confinement. This paper tries to investigate the effect of external pressure on the ultimate strength of CFT, so that the use of this kind of composite sections in construction and retrofitting of marine structures would be investigated. This paper tried to evaluate the effect of lateral pressure on improving the behavior of concrete-filled steel tubes (CFT) by conducting laboratory studies. For this purpose, tri-axial testing set up, with capability of 400 bars pressure, was designed and constructed by the authors. Parameters such as lateral pressure, concrete strength and diameter to thickness ratio (D/t) of steel tube were tested.
Concrete with strength of 15 to 45 MPa was cast in pipes of 0.5 to 2 mm thickness and subjected to axial loading under external pressure between 0 and 150 bars. All specimens have a constant diameter of 100 mm and a height of 250 mm and are filled with ordinary concrete. All specimens have a diameter of 100 mm and a height of 250 mm and are filled with normal concrete. To evaluate effect of lateral pressure on the final strength, the ratio of d Parameters such as ultimate strength and failure mode of specimens along with their displacement load diagrams were investigated. Diameter to thickness in some samples was considered higher than the values proposed in the standards. Experimental tests results were compared with the relationships presented in the Eurocode 4 and AISC standards.
According to the calculations, the AISC standard result in conservative numbers compared to the EC4 standard for the ultimate strength of the specimen. External pressure has increased the loading capacity, as well as the ductility of the specimens by preventing the buckling and sudden crushing of the core concrete. Increase in load carrying capacity due to external pressure was up to 91% in some specimen. The effect of increasing on ultimate strength on the lower thickness specimens was significant. In conclusion, results of the experiments showed a significant effect of lateral pressure on the final strength of the CFT with normal concrete.

Investigation of multi-physics problems such as flow-structure interaction (FSI) in free surface is very important in mechanical engineering, whereas numerical simulations of such problems have been widely conducted by researchers. The implementations of CFD in engineering applications are most of the time based on the Eulerian description. In this method, one can focus on flows at a fixed spatial point x at time t and any flow variable Φ is expressed as Φ (x, t). This description has been studied for over fifty years and is clearly understood. Most of commercial codes have been developed by using finite difference, finite element and finite volume approaches. Simulating free surface flow with most Eulerian CFD methods is potentially very difficult as explicit treatment of the free surface is required. Moreover, The problems of most Eulerian and mesh-based numerical methods for complex free surface deformations involves difficulties and complexities of various boundaries remeshing as well as moving boundaries and exact determination of free- surface fluid. Another description of study of CFD is the Lagrangian method where one can follow the history of an individual fluid parameter through the time. In the Lagrangian methods, any flow variable is expressed as Φ (x0, t), where the point vector x0 of the particle at the reference time t = 0. Smoothed Particle Hydrodynamics (SPH) is a meshless and fully Lagrangian method which is able to simulate the FSI problems due to its simplicity and capability, as there is no special treatment needed for the free surface. The current problem in hydrodynamic science and fluid engineering is studied as a complex phenomenon in free-surface flow. Smoothed Particle Hydrodynamics (SPH) is a flexible Lagrangian and meshless technique for CFD simulations initially developed by Lucy (1977) and Gingold and Monaghan (1977) to simulate the nonaxisymmetric phenomena in astrophysics. In recent years, the SPH method has been very popular in fluid mechanics, e.g. multiphase flows,3 heat conduction,4 underwater explosions, free-surface flows, etc. In this method, each particle carries an individual mass, position, velocity, internal energy and any other physical quantity. The Lagrangian nature of SPH would lead this method to be well suited to problems with large deformations and distorted free surfaces. Simplicity, robustness and relative accuracy in comparison with other numerical methods are the main advantages of using SPH.10 Moreover, the SPH method can handle fully nonlinear, multiply-connected free-surface problems and extend computations beyond wave breaking, which need complex treatments in other grid-based methods, e.g. Volume of Fluid (VoF).In this approach the computational domain is formed by a set of particles. Each particle represents macroscopic volume of fluid conveying information about the mass, density, pressure, speed, position and the other parameters related to the nature of the flow. However, the computational cost is a disadvantage of SPH because the time step is small because of the explicit integration scheme in a weakly compressible formulation. This method has been successfully applied to a range of free-surface problems which involve breaking and splashing up There is a choice of SPH formulation in the literature mostly expressed in weakly compressible forms where pressure is obtained from the equation of state In this research, SPH is used to investigate the flow-structure interaction in free surface. First, the simulation of dam break problem on a dry and infinite bed is shown and compared with the experimental data. Then, and after implementing the governing equations, the vibration of a beam is studied. Finally, the dam break problem on an elastic gate is shown. Comparison between the SPH results and available numerical and experimental data shows that the SPH method is useful method for simulating the FSI problem.

Shape and topology optimization have become one of the main researches that is widely used in engineering fields. The purpose of topology optimization is to find an appropriate (optimal) distribution of materials in the design domain so that the shape and number of voids is optimized and the objective function is minimized or maximized. In recent decades, noticeable researches and various topology optimization methods were proposed. The level set method is being used successfully in structural shape and topology optimization. This method is an implicit method for moving interior and exterior boundaries, while these boundaries may join together during the process and new voids may be formed. The structural boundary is illustrated by the zero level set and nonzero in the domain. In the above context, the level set function is used as a switch to distinguish between the two domains present in the computing space. This way of illustration has an important feature by which the domain boundaries can be combined together or divided. By using the solution of Hamilton-Jacobi equation resulting from this function, the domain’s boundary starts to move. The control over movement of this boundary is done by velocity vector of Hamilton-Jacobi equation. Now, in order to use this method in topology optimization, it is sufficient to establish a relationship between velocity vector of Hamilton-Jacobi and shape derivation, which is used for optimizing objective function. It is possible to use standard level set for structural topology optimization.
In this paper, the spherical Hankel basis functions are used to optimize the structural topology using the level set method. The proposed functions are a combination of the first and second kind of Bessel functions fields as well as the polynomial ones in complex space and are derived from radial basis functions. Using the spherical Hankel functions, the dependence of the function of the level set method on the space and time is separated, which results in the transformation of the Hamilton-Jacobian partial differential equation into a conventional differential equation. In this way, the difficulties arising from solving partial differential equations are eliminated, and thus there is no need to re-set the function of the level set method in the optimization process. Further, in order to increase the speed and precision of convergence in creating an optimal design, the classic Lagrange shape functions are replaced with the spherical Hankel ones. The proposed shape functions have some properties such as infinite piecewise continuity, the Kronecker delta property, and the partition of unity. Moreover, since they satisfy all three polynomial fields and the first and second kind of Bessel ones in the complex space, they can be effective in improving the accuracy and speed of convergence, while the classic Lagrange shape functions are able to satisfy only the polynomial function fields. Finally, several numerical examples are presented to study the performance of the spherical Hankel radial basis and shape functions.

The extent of masonry structures and their weaknesses against earthquakes will increase the need for research on new ways of seismic rehabilitation of these structures. Recently, in addition to conventional techniques such as Mesh, Shotcrete, and FRP, new materials such as ECC materials have been considered by the researchers to retrofit the masonry walls. The composite materials of cement base, which is one of the types of cement base materials, due to the presence of fibers in the matrix, has a significantly different tensile strain capacity than that of conventional concrete, so that the range of this parameter for a typical mortar is 0.015%, and for composite materials of ECC is from 0.5 up to 6%. In the present study, the effect of these materials on the performance of the bearing masonry walls with in-plane failure modes including the diagonal tension mode (brittle mode) and the bed-joint sliding mode (the ductile mode) were investigated. The results of the research are based on the numerical method. ABAQUS software was used for numerical modeling. Due to validate the model, the available laboratory information of as-built masonry walls has been used. The as-built masonry walls are half scale. The wall dimensions for diagonal tension mode and bed-joint sliding mode were 1900x1400x110 and 2700x1400x160 mm, respectively. The gravity load of the wall was 0.1 MP. The walls strengthened with 20 mm ECC layers on one and both sides. In one case, ECC layers were joint to the foundation and in other case were not. A change in failure mode of strengthened walls (brittle to ductile) and hardening behavior were the main achievement of this research. If the connection between ECC layers and the foundation is absent, the failure mode of strengthened walls will be toe-crushing and rocking mode. If the connection between ECC layers and the foundation is present, the failure mode of strengthened walls will be toe-crushing and bed-joint sliding mode. Other obtained results showed an effective increase in strength and dissipated energy. The extent of this increase depends on how ECC layer is connected to the foundation. If there is no connection between ECC layers and the foundation, the strength and dissipated energy of walls with diagonal tension failure mode for one-side and both-sides ECC layers will be 2.3 and 3 times, respectively, in comparison with those of as-built masonry walls. Whereas for the bed-joint sliding mode, the extent of wall strength and dissipated energy is 1.4 and 1.8. according to the obtained results and comparing the properties of the wall strengthened by one-side and both- sides ECC layers, a significant difference was not observed, especially in bed-joint sliding mode. Appositively, if there is a connection between ECC layers and the foundation, the strength of walls for one-side and both-sides ECC layers will be 3.5 and 6 times, respectively, in comparison with those of as-built masonry walls. Whereas the dissipated energy of walls will be 3 and 4.5 times. Based on these results, if the ECC layers and the wall foundation are connected, the capacity of strengthened walls will be optimized.

One of the challenges in the field of civil engineering is to mitigate the seismic vibration of structures induced by dynamic loads, such as earthquake and strong wind in order to prevent undesirable damages causing human discomfort and economic consequence. The vibration control systems can be categorized as passive, active and semi-active. In recent years, semi-active control systems demonstrate better control effects than both passive and active systems. Semi-active control devices can behave as passive devices in the event of a power loss, and are therefore more reliable and consume less power than the active systems. In this study, to evaluate the effectiveness of the semi-active tuned mass damper using MR damper and a fuzzy logic controller, the nonlinear model of the nine-story benchmark structure is subjected to earthquake excitation. The semi-active tuned mass damper consists of a 1000 kN magnetorheological damper and the damping force of the MR damper is controlled by the fuzzy logic controller.The Bouc–Wen model is utilized to model the dynamic behavior of the MR damper. For this purpose, the increment dynamic analysis (IDA) is conducted to consider the effectiveness of the maximum acceleration of two near- and far-field acceleration records on the performance of the control systems. Two near-field earthquake acceleration records including Kobe (1995) and Northridge (1994) and two far-field earthquake acceleration records including El Centro (1940) and Hachinohe (1968) are used in this study. To achieve the optimum parameters of tuned mass damper, a numerical search method is used to reduce the displacement of the last floor of the structure. The optimal mass ratio, damping and the frequency of the tuned mass damper of these analysis for this structure are 3.5 %, 10 % and 2 rad/s. Also, this benchmark structure is modeled in OpenSees and the fuzzy inference system was implemented in MATLAB. In order to implement the semi-active control system, it’s necessary to communicate between OpenSees and MATLAB. For this purpose TCP-IP method is used. The displacement and velocity response of the ninth floor of structure equipped with tunned mass damper are considered as the input values for the fuzzy inference system. Furthermore, the required voltage of MR damper in this floor is defined as the output parameter of the fuzzy system. Moreover, the membership functions of fuzzy control are triangle and trapezoidal functions. The obtained results of the FLC are compared with the those of passive controlled structure. Therefore, absolute displacement and acceleration values of the last floor of the structure, the maximum relative displacement and the base shear values are investigate. The results showed that the FLC reduces the maximum last floor displacement, the maximum relative displacement and the maximum base shear by 17.75 %, 15.88 % and 16.85 % as compared to the uncontrolled structure, respectively and also, it reduces those responses by 3.62 %, 1.17 % and 15.76 % as compared to the passive response, respectively. Furtheremore, the fuzzy control system has effective performance than the passive system to decrease the maximum and residual displacement of the stories. On the other hand, the fuzzy control system has a low performance in reducing the maximum last floor acceleration.

In the present paper, the effects of deconvolved earthquake input on the linear and nonlinear seismic response of an existing arch dam in a 3D space are investigated. nonlinearities originate from the opening/slipping of the vertical contraction joints within the dam body. The reservoir–structure interaction is taken into account by the finite element method with the appropriate boundary conditions. The reservoir was assumed to be compressible. The Shahid Abbaspour arch dam was selected for the case study. Finally, the viscous condition at the far-end boundary of the foundation is used to model the radiation effect. A quasi elastic damping model is utilized. The stiffness and mass proportional damping, equivalent to 10% of the critical damping based on the 2Hz and 6Hz frequencies of the dam foundation system, is applied to the structure. Three components of the 1994 Northridge earthquake as maximum credible earthquake are selected as the free field ground motions. The analysis is carried out in two steps. First a deconvolution analysis is performed to adjust the amplitude and frequency contents of an earthquake ground motion applied at the base of the foundation to achieve the desired output ground acceleration at the dam-foundation interface at the different points. Then the calibrated base acceleration history is applied to the foundation base of the dam-reservoir-foundation-system to perform the seismic analysis. Based on the results, spectra of the response at the dam-foundation interface at different points match very closely with the spectra of the horizontal free field ground motions. However, the existing deconvolution procedure does not produce appropriate results for high frequency ground motion records. To overcome such limitation, a modified procedure has been used for vertical earthquake which has led to better convergence. In existing procedure, a correction factor for each frequency is computed using the ratio of the Fourier amplitudes of the reproduced ground acceleration at the dam-foundation interface and free-field ground acceleration signals in a given iteration. The acceleration signal applied at the base of the foundation model is modified using the correction factor for each frequency. In modified procedure, Instead of adjusting the Fourier amplitudes, the response spectra at different frequency are adjusted. It is worth mentioning that the main novelty of the present investigation, is that it takes into account the effects of deconvolved earthquake input in addition to both the joints nonlinearity. According to the analyses, modeling vertical contraction joints leads to a decrease in the maximum value of stensile stress levels through the dam body by 6%. The extreme values of joints opening/sliding experienced by the contact elements located on the upstream face along the crest are 6.3mm and 18.1mm, respectively. The maximum values for joints sliding occurred in vicinity of the abutments. Also, maximum values of joint opening/sliding along the height of the dam body experienced by the contact elements located between the central cantilever and the adjacent ones on the upstream face occurred in crest of the dam body. However, to achieve more realistic results, other factors such as the spatial variation in ground motion, should be considered.

By developing of the consumerism and rapidly progress of industrial and commercial lifestyle in most of the countries, the solid waste production has been growth rapidly in the recent years. The leachate production starts shortly after the production of waste and cause the pollution of environment and especially contamination of the soil. Chemical processes are usually considered as the most effective processes for degradation of soil pollutants. In these processes, the chemical reagents are added to make the desired reactions take place. But it is sometimes necessary to increase the amount of reagents so that the reactions take place completely. This may cause chemical reagents to remain in the soil. Ozone, which acts as a powerful oxidizer, is capable of degrading organic pollutants in a short period of time without producing any toxic residuals. Nowadays ozonation has become one of the most favorable processes in soil remediation technologies. Ozone is used in the treatment of a wide range of pollutants. Due to the high diffusion coefficient of ozone, all of the present pollutants in soil are theoretically available for this oxidant. Since leachate contains a range of organic and inorganic pollutants, ozonation process is therefore can be a useful process in treating soils contaminated with leachate. In this study, application of ozonation process as an ex-situ method on the treatment of composting leachate polluted soil was studied in laboratory scale and in batch mode. Experiments were conducted using a cylindrical Plexiglas reactor with the diameter of 3 cm and the height of 60 cm. Ozone gas was continuously passed through a diffuser at the bottom of the reactor. Ozone generator with 5 g/h nominal capacity was used to produce ozone gas from pure and dry oxygen. Ozone content was measured with a digital ozone analyzer. A rotameter was also applied to measure the volume of gas injected to the reactor. The leachate used in this study has been collected from one of composting plant in north of Iran. The soil used in this study was mainly silica with the particle size of 0.12-0.3 mm. In order to pollute the soil; a certain amount of leachate was well mixed with the soil and then dried to the desired humidity. According to the results the maximum removal of soil organic content was obtained at pH=9 after 120 minutes ozonation with a flow of 200 ml/min. By increasing the initial organic content of the soil, the removal via ozonation has been also increased. In other word the soil with higher initial contaminations has shown better removal efficiencies compared with the one with lower initial pollutants. In this study, the presence of trivalent iron oxide caused 42% increases in soil organic content removal efficiency. In this research applying gas washing technique with acid also greatly enhanced the removal efficiency of ozonation process. According to the conducted experiments, after pre washing of ozone with acid, the removal of soil organic content with nearly 90% increase, reached to 21.2%. The results were also shown that, the change in the type of acid did not have a significant effect on the soil organic matter removal efficiency.