2024-03-29T02:54:35+04:30 http://mcej.modares.ac.ir/browse.php?mag_id=624&slc_lang=fa&sid=16
624-11597 2024-03-29 10.1002
Modares Civil Engineering journal MCEJ 2476-6763 10.22034 2015 15 1 Concrete Open Arch Bridge Optimization majid pouraminian Abstract: Arch bridges are generally considered widely as esthetically pleasing bridges and its different variations can be found from both historical and modern times all over the word. Arch bridges can be divided into several different types by different definition. One possibility to divide them is through the spandrel. Spandrel can be open or closed. When it is open, there are usually columns to transmit the loads from the deck to the arch. The purpose of this study is to determine the optimum design of arch longitudinal no prismatic single-cell section. In this study, Cetina Bridge, which is a long span open reinforced concrete arch bridge spanning Cetina river canyon near the town of Trilj. The arch is of span 140m with a rise of 21.5 m, giving rise-to-span ratio of 1/6.5. The FE model of the Cetina open spandrel arch bridge was constructed using the Ansys. The main span and columns was simulated with Beam4, and element solid45 was used for reinforced concrete non prismatic single cell arch. For definition of arch geometry in longitudinal sections, parabolic conic functions are employed. In this present work the optimum design is carried out by taking total material volume of substructure of bridge as objective function. Substructure includes of column and reinforced concrete arch. Height of skewback abutment, Height of crown of arch, back and soffit radii of arch and position of crown respect to global axes are considered as design variables. The distance between the columns is assumed constant and equal to 21.6 m in optimization process. Also the cross sections of column are not taken as design variables. Instead of this, cross section of piers is selected proportionally with these of application project. During problem formulation most of practical design variables and constraints are considered. Three type of design constraints were taken into account: stress constraints of arch, transversal displacement constraints of arch crown and geometric constraint. Initially, a program is developed in MATLAB in order to generate coordinate of nodes, then is taken finite element software ANSYS for modelling the geometry of an arch dam. Finally, the optimization technique is performed by Simultaneous Perturbation Stochastic Approximation (SPSA) algorithm. Shape optimization for each of the arch web thickness to be examined (i.e. t_w=0.3-0.5m ). The following, some of important conclusions are drawn from the present work: It is concluded that SPSA can be effectively used in the shape optimization of the bridges. The total reinforced concrete volume obtained in this study is 23% less than the application project. For each t_w, the optimum arch geometry is obtained, when the volume of the arches and columns is minimized. Minimum volume of substructure achieved for t_w=0.35m with 1131 m3 . Keywords: long span; Open Arch Bridge; SPSA algorithm; Finite Element Analysis; substructure; shape optimization; long span Open Arch Bridge SPSA gradient based algorithm substructure shape optimization 2015 5 01 1 9 http://mcej.modares.ac.ir/article-16-11597-en.pdf
624-2748 2024-03-29 10.1002
Modares Civil Engineering journal MCEJ 2476-6763 10.22034 2015 15 1 Behavior of steel unbonded brace in seismic strengthening of reinforced concrete buildings Alireza Mortezaei One of the strengthening methods in reinforced concrete frame buildings is improving seismic behavior of such structures by means of steel bracing. When influenced by compressive stresses, traditional steel braces would buckle and are free of any ductility. As a result, efforts in order to restrain buckling problem for steel braces has led to creation of steel unbonded brace. In these braces, Eulerian buckling of central steel core is controlled by placing in a steel tube full of mortar. In this paper, RC buildings of 6, 12 and 18 stories are first designed based on standard 2800 and then controlled based on the rehabilitation regulation and the third edition of standard 2800. After analyzing and in order to improve seismic behavior, these buildings are strengthened by the use of common braces and steel unbonded braces and the columns of braced frames are also reinforced by concrete jacket. Totally, 42 models were analyzed by nonlinear static analysis (pushover analysis). The results indicate that structures with traditional braces have weakness in high level of drifts due to buckling of compressive braces and the energy absorption in 12 and 18 stories structures is even lower than non-strengthened structures. Nevertheless, this defect is removed by applying unbounded braces because of somehow identical behavior in extension and pressure as well as utilizing total capacity of these kinds of brace. Also, in comparison with structures with traditional braces and non-strengthened structures, a high level of energy absorption will be obtained. One of the strengthening methods in reinforced concrete frame buildings is improving seismic behavior of such structures by means of steel bracing. When influenced by compressive stresses, traditional steel braces would buckle and are free of any ductility. As a result, efforts in order to restrain buckling problem for steel braces has led to creation of steel unbonded brace. In these braces, Eulerian buckling of central steel core is controlled by placing in a steel tube full of mortar. In this paper, RC buildings of 6, 12 and 18 stories are first designed based on standard 2800 and then controlled based on the rehabilitation regulation and the third edition of standard 2800. After analyzing and in order to improve seismic behavior, these buildings are strengthened by the use of common braces and steel unbonded braces and the columns of braced frames are also reinforced by concrete jacket. Totally, 42 models were analyzed by nonlinear static analysis (pushover analysis). The results indicate that structures with traditional braces have weakness in high level of drifts due to buckling of compressive braces and the energy absorption in 12 and 18 stories structures is even lower than non-strengthened structures. Nevertheless, this defect is removed by applying unbounded braces because of somehow identical behavior in extension and pressure as well as utilizing total capacity of these kinds of brace. Also, in comparison with structures with traditional braces and non-strengthened structures, a high level of energy absorption will be obtained. Unbonded bracing buckling-restrained bracing pushover analysis Seismic behavior energy absorption 2015 5 01 9 23 http://mcej.modares.ac.ir/article-16-2748-en.pdf
624-10857 2024-03-29 10.1002
Modares Civil Engineering journal MCEJ 2476-6763 10.22034 2015 15 1 Optimum patterns for arch dam shape design in highly seismic zones shaghayegh rashidinia Mohammdtaghi Ahmadi One of the most important issues in arch dam design, is optimum shape design of the dam body in such a way that both safety and economical constraints could be satisfied. The aim of this research is the introduction of some patterns for optimum arch dam shape in seismic zones and the identification of the optimum shape trends in proportion to physical and geometrical parameters of each specific site. Method of research includes parametric and statistical calculations on several arch dam sites samples. Thus optimization procedures are performed on dams with different heights, canyon widths, canyon shape types (V-shape or U-shape), and foundation moduli of deformation. Studying the resulting optimized arch dams shapes, certain trends of design variables is deduced in order to achieve optimum shape of the dam body when site specification changes. These trends are showed in graph forms. Resulting rules can be used as arch dam design guidline. One of the most important results of this study is the increasing trend in the thickness design variables in the central cantilever and abutments with the increase of the foundation modulus of elasticity. These rules can be used as guidelines for dam shape design. One of the most important issues in arch dam design, is optimum shape design of the dam body in such a way that both safety and economical constraints could be satisfied. The aim of this research is the introduction of some patterns for optimum arch dam shape in seismic zones and the identification of the optimum shape trends in proportion to physical and geometrical parameters of each specific site. Method of research includes parametric and statistical calculations on several arch dam sites samples. Thus optimization procedures are performed on dams with different heights, canyon widths, canyon shape types (V-shape or U-shape), and foundation moduli of deformation. Studying the resulting optimized arch dams shapes, certain trends of design variables is deduced in order to achieve optimum shape of the dam body when site specification changes. These trends are showed in graph forms. Resulting rules can be used as arch dam design guidline. One of the most important results of this study is the increasing trend in the thickness design variables in the central cantilever and abutments with the increase of the foundation modulus of elasticity. These rules can be used as guidelines for dam shape design. One of the most important issues in arch dam design, is optimum shape design of the dam body in such a way that both safety and economical constraints could be satisfied. The aim of this research is the introduction of some patterns for optimum arch dam shape in seismic zones and the identification of the optimum shape trends in proportion to physical and geometrical parameters of each specific site. concrete arch dam optimum geometrical shape Optimization dam design 2015 5 01 23 35 http://mcej.modares.ac.ir/article-16-10857-en.pdf
624-11262 2024-03-29 10.1002
Modares Civil Engineering journal MCEJ 2476-6763 10.22034 2015 15 1 Pounding response of adjacent buildings with non-equal height under near-fault strong ground motion Moein Rezaei Balouchi Reza Saleh Jalali In this paper a simple model of one and two-storey adjacent buildings excited by the horizontal and vertical components of fault-normal pulse and fault-parallel displacement with different magnitudes and time lags has been considered. In the considered model each storey consist of a rigid beam connected to two axially rigid mass-less columns by nonlinear rotational springs and linear rotational dashpots. For determination of the pounding force the non-linear viscoelastic model has been chosen. In this model, a non-linear spring following the Hertz law of contact is applied together with an additional non-linear damper, which is activated during the approach period of collision in order to simulate the process of energy loss taking place mainly during that period. The ground motion is described by fault-normal pulse and fault-parallel permanent displacement, and their amplitudes and duration are selected consistent with the variables that describe near-fault motions. An important physical characteristic of the selected pulse and displacement is large initial velocity associated with onset of these motions and it is proportional to the stress drop on the fault. It is assumed that the buildings are near the fault and that the longitudinal axis of the buildings (x-axis) coincides with the radial direction (r-axis) of the propagation of waves from the earthquake source so that the absolute displacements of the bases of columns because of the wave passage are different. It is further assumed that the ground motion can be described approximately by linear-wave motion. It is assumed that the excitations at all bases have the same amplitude but differ in terms of phase. The phase difference (or time delay) between the input ground motions depends on the length of the buildings and the horizontal phase velocity of the incident waves. The system of equations of motion has been solved by the fourth-order Runge-Kutta method because of its self-starting feature and the long-range stability. For the considered models the results indicate: (1) for nonlinear behavior of material the impact force tends to increase of maximum relative displacement and permanent deformation specially in the second storey (2) the maximum impact force and the minimum distance required to avoid pounding of adjacent buildings under fault-normal pulse are many times larger than those induced by fault-parallel displacement (3) material nonlinearity reduces the maximum impact force and the minimum distance required to avoid pounding significantly, respect to the linear case. Also in nonlinear case the maximum impact force occurs at d>0, while for linear case it happens at d=0 (4) the time delay in ground motion can increase 1.5 to 2 times the maximum impact force and the minimum distance required to avoid collision. The horizontal component of the ground motion is predominant in this magnification and the effects of the vertical and rocking components of ground motion are negligible. Pounding near-fault ground motion forward directivity fling-step adjacent buildings 2015 5 01 35 46 http://mcej.modares.ac.ir/article-16-11262-en.pdf
624-8658 2024-03-29 10.1002
Modares Civil Engineering journal MCEJ 2476-6763 10.22034 2015 15 1 Remediation of BTEX-contaminated groundwaters by Nano scale zero-valent Iron based PRBs Nader Shariatmadari Nasser Asadi Seyfar Saeid Saeidijam Ali Akbar Heshmati Benzene, toluene, ethylbenzene and xylenes, commonly referred to as BTEX, are critical monoaromatic environmental contaminants around the World, of which the major aromatic contaminants in gasoline pose serious environmental health problems. Leaking tanks or ruptured pipelines pollute soil and groundwater with these compounds. Because of their polarity and very soluble characteristics, these compounds will be able to enter the soil and groundwater systems and cause serious contamination problems and threats to the public safety and environment. One of the most promising ground water remediation technologies is the use of permeable reactive barriers (PRBs) packed with reactive material to intercept and decontaminate plumes in the subsurface. The concept of PRBs is rather simple. Reactive material is placed in the subsurface to intercept a plume of contaminated groundwater which must move through it as it flows, typically under its natural gradient. As the contaminant moves through the Reactive material, reactions occur that alter it to less harmful or immobile species. The PRB is not a barrier to the groundwater, but it is a barrier to the contaminant. The key advantage of a reactive barrier is the passive nature of the treatment. That is, for the most part, its operation does not depend on any external labor or energy inputs. Once installed, the barrier takes advantage of the in situ groundwater flow to bring the pollutants in contact with the reactive material. The reactive material used in the barrier may vary depending on the type of contaminants being treated. The most common reactive agent used to date has been granular iron. For contaminants of unknown treatability or media of unknown reactivity, addressing these issues will involve laboratory studies using both batch and column techniques. As for any remedial technology, it is imperative to fully understand the factors that can result in either effective implementation and successful remediation or failure to achieve the remedial design objectives. Iron nanoparticles are increasingly being applied in soil and grounwater remediation and hazardous waste treatment. Nearly two decades after iron nanoparticle was first proposed, the iron nanoparticle technology is at a critical point of its development process. Extensive laboratory studies have verified that nanoscale iron particles are effective for the treatment of a wide range of common groundwater pollutants such as chlorinated organic solvents, organochlorine pesticides, polychlorinated biphenyls (PCBs), organic dyes, and various inorganic compounds. Numerous field trials have also demonstrated the favorable prospective for in situ remediation. Nonetheless, there are still substantial knowledge gaps on many fundamental scientific issues. In this Experimental study, A series of laboratory experiments in various temperatures and contaminant concentrations were conducted on Nano sized zero-valet iron (nZVI) to determine its removal efficiency as PRB reactive materials against BTEX compounds in saturated Kaolinite clays, And the initial Concentration of BTEX is reduced to 60%. Obtained results may provide required data in groundwater remediation PRB systems design. BTEX PRB nano zero-valent Iron permeable reactive barriers ground water remediation 2015 5 01 47 57 http://mcej.modares.ac.ir/article-16-8658-en.pdf
624-170 2024-03-29 10.1002
Modares Civil Engineering journal MCEJ 2476-6763 10.22034 2015 15 1 Investigation of Web sidesway buckling phenomenon in Steel Girders In previous experiments, practice and in some condition of loading, geometry and support configurations, a type of instability has been observed in which tension flange moves laterally which it has been addressed in design codes as “web sidesway buckling”. Web sidesway buckling is a case of instability that it was observed in beam with restrained top flange and no constraint for bottom flange. Primary studies and experiments show that web sidesway buckling is due to both local instability in the web just under loaded zone and global instability of tension flange along length of the girder. In the present paper, a concise study has been carried out on behavior and the mechanism of this instability occurrence in web sidesway and how to evaluate loading capacity of the girders in the light of experiments, then a simple model which is a modification on the existing model has been proposed. Experimental work has been conducted to investigate the effect of tension flange on the load capacity of beams. The specimen's dimensions were adjusted in order to show web sidesway buckling. In addition, the supports configuration was made compatible with this instability. The objectives of the experiment were to obtain; mechanism of instability initiation, deformation pattern, effect of tension flange width and nonlinear deformations underneath the loading point. A closer view in load-displacement behavior of test specimens shows at first, loading accompanies lateral displacement due to imperfection and then rate of displacement reduces. After reaching to maximum load, girder has still capacity for load carrying but with excessive lateral displacement in tension flange. The results of experiments also show that web sidesway buckling generally accompanied by local buckling or crippling of the web under loaded zone. Deformation initiates with lateral movement of tension flange. Then local buckling and yielding occur, and finally, web sidesway buckling develops along the beam length. From this time onwards, load capacity is approximately constant. Furthermore, it can be seen that the rate of lateral displacement is directly dependent on width of tension flange. On the other hand, the results from design equations of design codes for estimating load capacity of girders against web sidesway buckling are too conservative in comparison to the proposed model. The critical load is affected by tension flange clearly, and occurrence of this type of instability is credible in other sections such as T- shape beam but in a lower critical load with respect to the I-shape sections. Also the results from the new model are in good agreement with that of experimental data. Finally, • It seems that only the existence of an area in the web affected by a tension stress field do not cause web sidesway buckling and transformation of tension stress field into compression field determents on initiation of instability. web sidesway buckling Instability tension flange steel beam Critical load 2015 5 01 56 73 http://mcej.modares.ac.ir/article-16-170-en.pdf
624-1373 2024-03-29 10.1002
Modares Civil Engineering journal MCEJ 2476-6763 10.22034 2015 15 1 Bio-electrochemical reduction of nitrate from wastewater using graphite-coated multi-walled carbon nanotubes Abas rezaee Due to extensive usage of nitrogenous fertilizers and discharge of industrial and domestic wastewater, nitrate contamination of water is becoming a main environmental concern. High levels of nitrate in drinking water causes serious health problems such as methemoglobinemia in infants and gastric cancer. Because of such health problems, nitrate removal from water is urgent and has been a hot topic over the recent years. Various technologies such as the ion exchange, reverse osmosis, electrocatalytic, adsorption, electrodialysis and biological process, have been used to eliminate nitrate ion from water and wastewater. Nevertheless, these methods have several drawbacks such as high installation and maintenance costs, difficult operation, brine production, membrane fouling, further treatment, slow process and carbon source requirement. A large number of investigators thus have focused on the reduction of nitrate by the electrochemical process usually because of its efficiency, very low sludge production, small area occupation and facile operation. Integration of electrochemical and biological processes as bioelectrochemical systems has been recommended to overcome the potential problems. In bioelectrochemical denitrification, denitrifying microorganisms make use of hydrogen generated at the cathode by the electrolysis of water as an electron donor to reduce nitrate into nitrogen gas. Autohyrogenotrophic denitrifying bacteria commonly adhere to the cathode surface and make a biocathode. Therefore, Cathode electrode material is one of the major factors that affecting in the bioelectrochemistry efficiency. Cathode material can directly affect to denitrifying bacteria attachment, hydrogen production, electron transfer and electrical conductivity. Bioelectrochemical process can be used to eliminate nitrate through a catholic reduction process. Carbon material has high mechanical strength and a rough surface which is ideal for the formation of biofilm as compared with metal materials. However, carbon materials are difficult to apply in large scale processes due to high electrical resistivity that tend to increase electrode ohmic losses. Hence, carbon electrodes are supported by a conductive material current collector such as carbon nanotubes and metallic materials. Carbon nanotubes have a good biocompatibility with bacteria and have not shown negative effect on biofilm formation. It had been reported that carbon nanotubes can facilitate transfer of electrons between bacteria and electrode in bioelectrochemistry. The aim of this study is bio-electrochemical removal of nitrate from wastewater using carbon nanotubes immobilized in cathode. This study has been done in a bathe scale bioelectrochemical rector with a two chambers. Considering that nitrate reduction done in biocathode, carbon nanotube used in cathode for increasing nitrate removal. The effects of pH, current density and retention time were evaluated for nitrate removal in a bio-electrochemical reactor.The highest nitrate reduction rates were occurs in neutral pH and current density of 15 mA/cm2. Furthermore, at current density of 15 mA/cm2 and retention time of 8 hours, the bioelecterochmical system can reduce the nitrate levels to below the environmental standard.The results showed that multi-wall carbon nanotube as cathode modifier increase the nitrate reduction efficiency about 14 persent. The use of multi-wall carbon nanotube can increased biofilm formation and therfor the reduction time for achieving to nitrate standard was reduced. Bioelectrochemical Nitrate Denitrification Carbon nanotubes 2015 5 01 57 65 http://mcej.modares.ac.ir/article-16-1373-en.pdf
624-12274 2024-03-29 10.1002
Modares Civil Engineering journal MCEJ 2476-6763 10.22034 2015 15 1 Evaluation of mixed mode fracture resistance of different asphalt concretes-An Experimental study mohammadreza mohammadaliha Mohammadhossein Rezaiefar Hassan Fazaeli Asphalt cracking is one of the major distress and deterioration modes of pavements of roads especially in the cold regions. Different types of cracks such as top-down, reflecting and alligator cracks are usually observed in the asphalt pavements. These cracks may be initiated due to improper construction and implementation of paving process, daily or seasonal cyclic thermal loads and mechanical traffic loading induced by moving vehicles. Consequently, the investigation of crack growth behavior in the asphalt overlays is an important issue for design, construction and maintenance of roads and highways. Due to the applied thermal and mechanical stresses, the cracks initiated in the asphalt layers may often experience different deformations including mode I(tensile or opening), mode II (shear or sliding) and any combinations of opening-shearing deformations (i.e. mixed mode I/II). Fracture toughness is a key fundamental parameter for investigating the crack growth behavior of cracked bodies. From the other hand, since asphalt mixtures are composite materials composed of aggregate, binder and air void, their fracture behavior might be affected by the asphalt characteristics specifications. Hence in this research the influences of asphalt characteristic specifications (including the type and size of aggregates, bitumen type, air void content and the mixture composition) is investigated experimentally on the mixed mode fracture toughness of different asphalt mixtures. For conducting the fracture toughness experiments, semi circular bend (SCB) specimens containing a vertical edge crack and subjected to asymmetric three-point bend loading was used. In order to study the influence of mixture characteristic specifications on the value of fracture toughness, two aggregate types (i.e. limestone and siliceous), two aggregate sizes (with nominal maximum aggregate sizes 19 mm and 4.75 mm), two binders (60/70 and 85/100) and two air void percentages (i.e. 4% and 6%) were considered for manufacturing asphalt mixtures. The SCB specimens were then tested under two different loading mode mixities (i.e. Me = 0.8 (mixed mode condition with dominantly tensile deformation) and Me = 0.38 (mixed mode condition with dominantly shear deformation) at -15oC. The load-displacement curves for the whole samples were linear which revealed the linear and elastic behavior of asphalt mixtures at the tested low temperature. Thus, the corresponding values of fracture toughness (KI, KII and Keff) were determined using the obtained fracture loads and the available formula. The experimental result showed that the mixed mode cracking resistance of asphalt mixtures is significantly affected by their properties. Analysis of results indicated that the specimens containing 4% air void (i.e. with the more compacted mixtures) show greater resistant against cracking than the asphalt specimens containing 6% air void. Meanwhile by increasing the maximum aggregate size the fracture toughness is also increased. Mixtures made of limestone aggregates and softer binders had more fracture toughness. Analysis of results also showed that when the contribution of mode II deformation is increased, the influence of air void and aggregate size on the fracture toughness of tested asphalt mixtures becomes negligible. Asphalt concrete Fracture toughness Semi circular bend specimen (SCB) Mixed mode I/II Low temperature Cracking 2015 5 01 73 85 http://mcej.modares.ac.ir/article-16-12274-en.pdf
624-9630 2024-03-29 10.1002
Modares Civil Engineering journal MCEJ 2476-6763 10.22034 2015 15 1 The Simulation of Mullins’ Effect in Load-Displacement Hysteresis Loops of Fiber-Reinforced Elastomeric lsolators Hamid Toopchi-Nezhad This paper briefly reviews Fiber Reinforced Elastomeric Isolators (FREIs) as a relatively new type of elastomeric bearings. In comparison with conventional Steel Reinforced Elastomeric Isolators (SREIs) that are reinforced with steel plates, FREIs utilize fiber fabric layers as the reinforcement material. The fiber reinforcement is employed to prevent the lateral bulging of elastomer layers when the bearing is subjected to vertical compression. Fiber reinforced isolators are categorized in two groups, namely, “bonded-“ and “unbonded-“ FREIs, depending on the boundary conditions at top and bottom surfaces of the bearing. The main objective of this paper is to simulate the lateral load-displacement hysteresis loops of unbonded-FREIs. In an unbonded-FREI, no bonding is provided between the bearing and its top and bottom contact supports. As such, shear forces are transferred via friction at the contact surfaces. When an unbonded-FREI is deformed laterally, portion of its contact surfaces roll off the contact supports, and the bearing exhibits a specific deformation called “rollover deformation”. As a result of rollover deformation, the effective lateral stiffness of the bearing is decreased significantly. This in turn improves the seismic isolation efficiency due to the increased base isolated period of bearing. The ultimate lateral displacement in an unbonded-FREI may achieve when the originally vertical faces of the bearing contact top and bottom supports. Lateral load-displacement response in an unbonded-FREI is characterized with a gradual softening (due to rollover deformation) that is followed by a stiffening behavior at the ultimate stage of lateral bearing displacement. Under a cyclic excitation, the response characteristics of the bearing during the first load-cycle are different than the subsequent cycles of the same load amplitude. This phenomenon that is specific to elastomeric materials is known as Mullins’ effect. In this paper an extended Bouc-Wen model is developed to simulate the lateral load-displacement hysteresis loops of unbonded-FREIs. The model captures the gradual softening and ultimate stiffening behavior in the load-displacement curve of the bearing, and addresses the Mullins’ effect in the simulation of hysteresis loops. The proposed model comprises two simultaneous coupled equations which employ six constant coefficients altogether. To determine these coefficients, the model is fitted to experimentally-evaluated load-displacement hysteresis loops of prototype bearings. The experimental loops are obtained from cyclic shear tests that are conducted on the bearing while it is subjected to constant vertical compression. In order to account for Mullins’ effect, an individual set of coefficients corresponding to unscragged loops (the first cycle of each displacement amplitude) are evaluated. The second set of coefficients is attributed to scragged response (subsequent cycles of each displacement amplitude) of the bearing. To simulate the load-displacement hysteresis loops, the proposed model switches between the first and the second set of coefficients depending on the unscragged or scragged state of the elastomer, respectively. A constraint is imposed on the model to assure its continuity when the model coefficients are alternated. Comparison between analytical and experimental results (shake-table test data) indicates that the proposed model is accurate in dynamic response simulation of the unbonded-FREIs studied in this paper. Fiber Reinforced Elastomeric Isolators Hysteresis Loops Mullins’ Effect Bouc-Wen Model Time history analysis 2015 5 01 86 96 http://mcej.modares.ac.ir/article-16-9630-en.pdf
624-7830 2024-03-29 10.1002
Modares Civil Engineering journal MCEJ 2476-6763 10.22034 2015 15 1 Investigation of stress reduction in sandy soils during saturation Arash Pourjafar Reza Mahinroosta Abstract:If dry cohesionless soil material is saturated, stress reduction will occur in the soil mass, followed by sudden deformation,which is called collapse settlement. In this research, effect of saturation on the shear strength parameters of sandy soils and effective factors on collapse behavior of this material has been investigated by triaxialshear device. First of all, preliminary tests were performed in order to prepare physical properties of sandy soils including: grain-size analysis, specific gravity, maximum and minimum densities. After providing soil samples with specific relative densities, dry and saturated triaxialtests were carried out in different confine pressures to evaluate shear strength parameters of these materials. In order to investigate the stress reduction of material due to saturation, triaxial tests were done initially on dry samplesand shearing continued until a proposed stress level; keeping constant axial strain, samples were saturated until a period of time and shearing was continued again to reach failure in the wet state. In this way, effect of diverse factors such as confining pressure, shear stress level, relative density, initial moisture content and size of particles on the stress reduction of sandy material were investigated.Abstract:If dry cohesionless soil material is saturated, stress reduction will occur in the soil mass, followed by sudden deformation,which is called collapse settlement. In this research, effect of saturation on the shear strength parameters of sandy soils and effective factors on collapse behavior of this material has been investigated by triaxialshear device. First of all, preliminary tests were performed in order to prepare physical properties of sandy soils including: grain-size analysis, specific gravity, maximum and minimum densities. After providing soil samples with specific relative densities, dry and saturated triaxialtests were carried out in different confine pressures to evaluate shear strength parameters of these materials. In order to investigate the stress reduction of material due to saturation, triaxial tests were done initially on dry samplesand shearing continued until a proposed stress level; keeping constant axial strain, samples were saturated until a period of time and shearing was continued again to reach failure in the wet state. In this way, effect of diverse factors such as confining pressure, shear stress level, relative density, initial moisture content and size of particles on the stress reduction of sandy material were investigated. time and shearing was continued again to reach failure in the wet state. In this way, effect of diverse factors such as confining pressure, shear stress level, relative density, initial moisture content and size of particles on the stress reduction of sandy material were investigated.Abstract:If dry cohesionless soil material is saturated, stress reduction will occur in the soil mass, followed by sudden deformation,which is called collapse settlement. In this research, effect of saturation on the shear strength parameters of sandy soils and effective factors on collapse behavior of this material has been investigated by triaxialshear device. First of all, preliminary tests were performed in order to prepare physical properties of sandy soils including: grain-size collapse settlement sand saturation triaxial test Shear Strength 2015 5 01 97 108 http://mcej.modares.ac.ir/article-16-7830-en.pdf
624-6728 2024-03-29 10.1002
Modares Civil Engineering journal MCEJ 2476-6763 10.22034 2015 15 1 Simulation of Sediment Transport at Straight channel and Lateral Intake narges nazari In this paper, the Lagrangian tracking of individual particles was performed at the straight channel and the lateral intake. This study is conducted for the aim of investigation of Discrete Phase Model )DPM (for simulation of tracking of individual sediment particles and also estimation of the rate of bed load at the entrance of intake related to the main channel. The Reynolds stress transport model )RSM) of the FLUENT software was used for evaluating the turbulent flow characteristics. The study was conducted in two parts. At the first part, the particle movement was simulated in the straight channel for evaluating of the model operation. The comparison of numerical results (predicted) and experimental data (measured), which were done for this purpose, confirmed numerical simulation. In the second part, sediments movement pattern in lateral intake from straight direction investigated from quantitative and qualitative views and compared with available experimental data. The qualitative analysis of sediments movement showed a shape of wedge liked sand bar forms by bed load at the entrance of lateral intake. The quantitative comparison of the predicted and measured Qs (ratio of the bed load discharge in lateral intake to the bed load in main channel) shows predicted values were more than the measured values. In this paper, the Lagrangian tracking of individual particles was performed at the straight channel and the lateral intake. This study is conducted for the aim of investigation of Discrete Phase Model )DPM (for simulation of tracking of individual sediment particles and also estimation of the rate of bed load at the entrance of intake related to the main channel. The Reynolds stress transport model )RSM) of the FLUENT software was used for evaluating the turbulent flow characteristics. The study was conducted in two parts. At the first part, the particle movement was simulated in the straight channel for evaluating of the model operation. The comparison of numerical results (predicted) and experimental data (measured), which were done for this purpose, confirmed numerical simulation. In the second part, sediments movement pattern in lateral intake from straight direction investigated from quantitative and qualitative views and compared with available experimental data. The qualitative analysis of sediments movement showed a shape of wedge liked sand bar forms by bed load at the entrance of lateral intake. The quantitative comparison of the predicted and measured Qs (ratio of the bed load discharge in lateral intake to the bed load in main channel) shows predicted values were more than the measured values. from quantitative and qualitative views and compared with available experimental data. The qualitative analysis of sediments movement showed a shape of wedge liked sand bar forms by bed load at the entrance of lateral intake. The quantitative comparison of the predicted and measured Qs (ratio of the bed load discharge in lateral intake to the bed load in main channel) shows predicted values were more than the measured values. Sediment Particle Lagrangian Approach Fluent lateral intake 2015 5 01 109 119 http://mcej.modares.ac.ir/article-16-6728-en.pdf
624-10027 2024-03-29 10.1002
Modares Civil Engineering journal MCEJ 2476-6763 10.22034 2015 15 1 Investigating the intergranular interaction to define the equivalent steady state Many studies have been focused on soil-related problems so far. These may include consolidation, soil settlement, or swelling for clayey soils. However, before some incidents like liquefaction phenomena had been recognized, sands were not defined as a sort of problematic soil. After some liquefaction and flow failure took place during Niigata and Alaska earthquakes in 1964, comprehensive studies were carried out to explain sands behavior under various situations. One of the most crucial factors that can affect soil behavior is fines content and their types. Many investigations have been conducted on behavioral characteristics of clean and silty sands since liquefaction first observed in these kinds of soils. Most of studies suggest that sand liquefaction potential boosts with an increase in silt content until a threshold value and after that it starts to decline as silt content increases. Most of the studies conducted so far have mainly focused on clean sand or its mixtures containing non-plastic fines with not much attention paid to the soil mechanics of the critical state of clayey sands. The reason for this neglect might have been the misconception that plastic properties in clay prohibit flow behaviors and liquefaction. However, the studies of Northridge 1994, Kokaeli 1999, Chi Chi 1999, and Niigata 2004 earthquakes have indicated that notable settlements occur in soils containing considerable amounts of clay, resulting in great destruction. The researchers have emphasized that more detailed investigations are needed to determine the critical state behavior of clayey sands The steady state line or critical state line is one of the main factors used in the critical state topics. It is used for investigating the variation of liquefaction potential, calculating state parameters and also determining the parameters affecting on the collapse or state boundary surface shapes. Sand skeleton void ratio, equivalent void ratio and the interaction of sand and fines are being the main subjects of sand critical state behavior researches. In this paper the possibility of equivalent steady state line is investigated to order to reach a unique frame work for interpretation the critical state behavior of clayey sands. The inter granular interaction of coarse and fine grains and the fine communication in inter granular contacts are investigated to reach the equivalent void ratio. An appropriate and useful relation is presented to calculate the fine contribution percent in inter granular contacts and so the equivalent void ratio trough performing numerous cyclic triaxial on different combination of sand and clay, evaluating the variation of liquefaction resistance and finally mathematical analysis the results. Increasing the fine content has increased the instability of combinations. Also it has been shown that the different steady state lines can be converted to a one equivalent steady state line using the proposed relation. The latter means that it would be possible to predict the steady state line of every optional mixture of sand and fine trough performing some tests just on clean sand. In order to certificate the proposed relation, it has been verified based on some previous researches. Steady State Line Cyclic Triaxial Equevalent void ratio 2015 5 01 119 130 http://mcej.modares.ac.ir/article-16-10027-en.pdf
624-10152 2024-03-29 10.1002
Modares Civil Engineering journal MCEJ 2476-6763 10.22034 2015 15 1 The Role of Ductile Behavior of Connection Elements on Seismic performance of CBF morteza naghipour Seyyed Salimbahrami Marzieh Nemati Nonlinear behavior of members and their connections during earthquake caused ductility in buildings. Also increasing the number of resisting elements of structure reduces cost of repair and reconstruction in bending structures. In contrast, the concentrically brace frames do not have sufficient ductility But their vulnerable members are limited, thus their reconstruction were much less expensive than bending frames. In order to overcome concentrically brace frames disadvantages and they providing good ductility for them, Extensive research has been conducted in the past two decades by researchers. Several methods have been proposed by various researchers which were resulted in increasing the ductility of concentrically brace frames. In this research, a new type of energy dissipation elements was introduced. This dissipation consists of a ring which increased the ductility and earthquakeenergy absorption and can be used in braced frames. Also, during an earthquake, it has depreciates significant portion of input energy by entrance to non-linear phase and forming flexural plastic hinges, so it prevent entrance of other members to non-linear phase and buckling of brace members. In order to increase the capacity of this member, a box was used that connected to the ductile ring by two plates. By increasing the diameter, rate of ductility decreased. However increasing the thickness would enhance the ductility. Stresses and deformations were been studied by using the finite element under cyclic loads. Obtained hysteresis curves indicate that the introduced element can be act as an energy absorbing member and also act as a fuse to control the buckling of brace, while providing to the required ductility. Pushover analyses for determining the seismic demand of structures and especially in earthquake engineering based on performance, it has been considered by many researchers. General basis of this method is a nonlinear mathematical model of the structure was under a lateral load pattern and this lateral load increases at a constant rate until the structure reaches a predetermined target displacement. This target displacement was measured at a control point. During the ascending increase in lateral load, resistance and stiffness of structural components were corrected at each step according to predefined nonlinear. Also performance of this ductile element was investigated in 2D concentrically brace frames under Pushover analyses. Obtained results from pushover analysis indicated that ductile element can decrease base shear force and also increase ductility of structure. The obtained results indicate that installation or replacement of steel ring in proposed connection was easily possible with low cost and high speed. Furthermore, nonlinear static analysis obtained results reflects the lower base shear force for braced frame with proposed element compared to braced frames without proposed element Which results in Cutting down construction and foundation strengthening costs of building. At the end, results of Pushover analysis of concentrically braced systems can be mentioned. High behavior coefficient of structural braced systems with proposed element represents suitable performance and ductility of proposed element in building. Concentrically Brace Ductile Rings Finint Element Pushover 2015 5 01 131 143 http://mcej.modares.ac.ir/article-16-10152-en.pdf
624-9937 2024-03-29 10.1002
Modares Civil Engineering journal MCEJ 2476-6763 10.22034 2015 15 1 Stress path effect on wetting behaviour of unsaturated soils One of the most important behavioral aspect of unsaturated soil is, engendered deformation due to wetting. Numerous research works exist in the literature concerning wetting behaviour of unsaturated soils. However the majority of them have been done in oedometric conditions. The oedometric apparatus, despite its simplicity, presents a certain limitations. In fact in this apparatus lateral deformation is zero, Also in the its classical form, confining pressure cannot be controlled and pore water pressure and matric suction measurement are not possible. Therefore, the effect of stress path cannot be studied. These limitations are not relevant in the triaxial apparatus. On the other hand, there is a few study concerning stress path on wetting behaviour of unsaturated soils. In the present study, using a special triaxial apparatus, influence of stress path on wetting behaviour of an unsaturated sand-fine mixture, for two level of initial deviator stresses and different initial suctions, was studied. The selected soil is composed of 60% sand, 25% clay and 15% silt. This soil is non plastic and according to Unified Soil Classification System, it is classified as silty sand (SM). The specimens were prepared using the moist tamping method. The purpose of using static wet compaction as opposed to dynamic compaction is to obtain a more homogenous specimen in terms of density and shear strength. Before applying wetting process, two types of conventional stress paths were induced on soil specimens,. The first stress path was coincided with k0 lines. For obtaining the oedometric condition using triaxial apparatus, the area of specimen was kept constant by augmentation of confining pressure incrementally. In the second stress path, first, specimen was isotropically consolidated, then axial stress was increased, while confining stress was maintained constant during loading process. Two groups tests including low and high levels of initial deviator stress state were considered in this study. For every group, the level of initial stress exerced on specimens, before wetting step, was similar. All of specimens were in equilibrium regarding to pore-air and pore-water pressures. Pore-air pressure was kept constant equal to 250 kPa for all of specimens. During wetting process external loadings, applied on specimens, were constant, while matric suctions was decreased incrementally due to change in water content. There are several conclusions deduced from this study. Difference between observed deformations in consolidation phase (before wetting) for two stress paths depends on the level of deviator stress, so that for low level of deviator stress this difference is insignificant. However for high level of deviator stress, this difference is considerable. Engendered deformation during wetting for a given stress path depends essentially on the levels of matric suction and deviator stress at the start of wetting, so that, deformation due to wetting increase with increasing in initial suction or initial deviator stress. Based on the measured axial and volumetric strains during wetting phase, in the axisymmetric triaxial conditions, lateral strain was calculated. The obtained results indicate that lateral strain is considerable, therefore, evaluation of wetting effect in oedometric conditions underestimates deformation field unsaturated soil stress path wetting triaxial test 2015 5 01 143 155 http://mcej.modares.ac.ir/article-16-9937-en.pdf
624-925 2024-03-29 10.1002
Modares Civil Engineering journal MCEJ 2476-6763 10.22034 2015 15 1 Prediction of collapse potential of soils using Artificial Neural Network Collapsible soils are soils that compact and collapse after they get wet. The soil particles are originally loosely packed and barely touch each other before moisture soaks into the ground. As water is added to the soil in quantity and moves downward, the water wets the contacts between soil particles and allows them to slip past each other to become more tightly packed. Water also affects clay between other soil particles so that it first expands, and then collapses like a house of cards. Another term for collapsible soils is "hydrocompactive soils" because they compact after water is added. The amount of collapse depends on how loosely the particles are packed originally and the thickness of the soil that becomes wetted. Collapsible soils consist of loose, dry, low-density materials that collapse and compact under the addition of water or excessive loading. These soils are distributed throughout the southwestern United States, specifically in areas of young alluvial fans, debris flow sediments, and loess (wind-blown sediment) deposits. Soil collapse occurs when the land surface is saturated at depths greater than those reached by typical rain events. This saturation eliminates the clay bonds holding the soil grains together. Similar to expansive soils, collapsible soils result in structural damage such as cracking of the foundation, floors, and walls in response to settlement. Collapsible soils may be suspected in undeveloped areas that have young, accumulating sandy and silty soils in dry areas. The soils may be confirmed to be collapsible through engineering testing. These tests include study of seismic waves through the soils, rates of drilling through the soils (blow counts), and testing undisturbed soil samples obtained by careful drilling for compaction after wetting. In this study, the ability of Artificial Neural Networks (ANN) has been investigated to determine the collapse potential of soils. Therefore, different samples of collapsible soil have been collected from an area (Zahedan plain). General tests were performed on the samples in the laboratory and 130 samples of collapsible soil from different depths and locations were recorded in the database. The collapse potential tests (One-dimensional collapse test) was carried out on the samples and with the aim of further investigations, the grain size distribution, specific gravity, atterberg limits and strength properties of the samples were performed. In the later stages, the collapsible samples data were prepared for the artificial neural networks input. After the network training process and the subsequent learning, some network models have been selected under experiments, which include six inputs and one output. According to the predicted results, it was indicated that the correlation between experimental and predicted data by the ANN is 95%. Furthermore, the results show that artificial neural networks can predict collapse potential of soils, also the calculations and required tests will be reduced due to their simple use and inexpensive tests. Collapsible soil Collapse Potential Modeling Artificial Neural Networks (ANN) 2015 5 01 155 165 http://mcej.modares.ac.ir/article-16-925-en.pdf
624-11039 2024-03-29 10.1002
Modares Civil Engineering journal MCEJ 2476-6763 10.22034 2015 15 1 Performance-based design optimization under the set of earthquake records using the uniform deformation theory Reza Karami Mohammadi Performance-based design optimization (PBDO) is a relatively new concept in structural seismic design optimization. One of the PBDO methods which has been introduced in recent years is the optimization based on the uniform deformation theory. This method is quite different from other optimization techniques and formed based on the concept of structural performance and uniform distribution of deformation demands in the structure subjected to the seismic excitation. The aim of this method is to assign specific sections to elements such that all of the elements can reach their allowable deformation capacity during the earthquake. According to this theory, inefficient material is gradually shifted from the strong to weak areas leads to a uniform deformation (ductility) state at the end of a repetitive process. Although the base of this theory and proposed algorithm is to attain a uniform state of deformation in the whole structure, but the allowable limit of deformation values defined in PBD codes is not constant for all of structural elements. Additionally, in these codes, some actions of structural elements may be controlled by deformation and some controlled by force. Therefore, by considering the acceptance criteria of PBD codes, it is not possible to reach a uniform deformation state in the whole structure. Hence, in this paper uniform distribution of demand capacity ratio (DCR) is considered instead of uniform state of deformation. Historical review of applying this methodology shows that researchers mostly have used it to the optimum design of the structures under the earthquake records separately. Since earthquakes are random by nature, it is unlikely that the same earthquake ground motion will be repeated at some future time. This reveals that design based only one earthquake is insufficient and it is necessary to consider several earthquakes in checking the dynamic responses of a building. This paper presents an algorithm to PBDO of steel moment frames under set of ground motion records using the basic concepts of the uniform deformation theory. The proposed method consists of two phases. In the first phase of the search, to enhance the convergence rate, the search space of design variables is assumed to be continuous. Additionally in this phase of the search, only the deformation-controlled elements may vary. In the Second phase of the search, first for each structural element groups, the nearest discrete section to the imaginary section achieved in the first phase is identified and selected and then the structure is analyzed again and the DCRs are controlled. In this phase, acceptance criteria for both deformation and forced-controlled elements are supposed to be satisfied. Efficiency of the proposed algorithm is demonstrated in the optimum design of two baseline steel moment frames under a set of ground motion records. Results indicate that the proposed algorithm has a high speed to reach the optimum solution. The results are also compared with the optimum designs obtained by pushover analysis. It is shown that the optimization based on the pushover analysis results higher frame weight than time history analysis. Structural optimization performance-based design Uniform deformation theory Nonlinear time-history analysis pushover analysis 2015 5 01 165 175 http://mcej.modares.ac.ir/article-16-11039-en.pdf