جستجوی مقالات مرتبط با کلیدواژه « شکل پذیری » در نشریات گروه « عمران »

This study aims to assess reinforced concrete moment frames designed at varying ductility levels within a typical reinforced concrete structure, from a reliability perspective. The article explores the probabilistic methods for designing different ductility levels in the current Iranian Concrete Code, focusing on reliability. Specifically, a three-story concrete moment frame structure, designed to low, medium, and special ductility levels as per the Iranian code, is studied. The reliability analysis encompasses uncertainties in loading, dimensional parameters, and evaluating structural performance functions such as floor drift and acceleration. The study utilizes horizontal earthquake components specified by the FEMA P-695 standard to analyze earthquake record uncertainties. Furthermore, a comparison of the reliability index and probability of failure for each performance function is used to assess failure uniformity. The findings reveal a maximum probability of failure in collapse damage state of approximately 9%, 5%, and 2% for low, medium, and special ductility frames, respectively.

In recent decades, different structural systems have been proposed to make tall buildings with suitable seismic performance. According to the art of architecture roll, especially in tall structures, and its effect on the taking attention of tourists and international investors, engineers turned towards systems that compose suitable structural performance with beauty. One of these systems is called diagrid structural system. In this paper after reviewing a number of researches conducted in this field, beside the study of seismic performance, coefficient of behavior of these types of structures are calculated by static nonlinear analysis method using SAP2000 structural analysis software. In this research, 9 structure models with the number of floors 18, 36 and 54 were modeled with three angles of 50.2, 67.4 and 74.5. By examining the results, it was observed that the mean coefficient of behavior for 18, 36 and 54 story models is about 2.70, 3.00 and 3.85 respectively. also, the results shows that using the diagrids by angles of 67.4 and 74.5 degrees, the value of stiffness is increases, and the displacement of the roof floor and the it's period decrees, also the structure is more economical in terms of material consumption, so the optimal angles should be this range, which more flexibility is created in the plan and elevation of the structure.

Generally, elevated tanks of liquid storage are designed for higher seismic forces than buildings due to their ductility and low energy absorption capacity. So that for a tank with low ductitlity, its base shear coefficient is about 6 to 7 times larger than the base shear coefficient of a ductile building and for a tank with high ductility, this ratio is about 3 to 4 times higher than all standards. In standard 2800, the fourth edition for elevated tanks of liquid storage behavior coefficient 2 and 3 is considered. In standard 2800, the fourth edition for air tanks of liquid storage behavior coefficient 2 and 3 is considered. In the publication, No. 38 coefficients of behavior for elevated tanks are presented in accordance with the standard 2800. The results showed that in standard 2800, the ratio of the base shear coefficient of the tank to the base shear coefficient of the ductile building in the relatively high risk zone for tanks with behavior coefficients of 3 and 2 in short periods was 3.5 and 5,25, respectively, while this value was obtained in No. 38 publications 4 and 6, respectively. The results also showed that the ratio of base shear coefficient of tanks to buildings in short periods for both behavior coefficients and four soil types in publication No. 38 was 14% higher than the results of the fourth edition of standard 2800

It is now known that the behavior of any structural system during an earthquake is largely determined by its energy dissipation capacity through ductile behavior. And shows the degree of nonlinear behavior of the structure. In this paper, in order to compare the bending frames from the economic point of view and the effect of ductility on the amount of consumable materials, conventional reinforced concrete bending frames with different ductility and with different number of 6 and 12 floors have been selected as representatives and observing all criteria. Aba are designed for each group. After proper typing and observing the executive points and preparing executive plans, the amount of consumable materials (concrete and steel) has been determined and all costs have been estimated according to the existing price list (2009).These costs only include the cost of materials used in the construction of beams, columns and foundations, and the cost of roof and other structural costs are not included because changing the type of ductility has no effect on other costs and only in the design of beams, columns and Foundations are effective.

In general, shear reinforcement in reinforced concrete beams typically involves the use of stirrups. However, substituting stirrups with continuous rectangular spiral reinforcement can enhance construction efficiency and lower costs. Meanwhile, the adoption of fiber-reinforced concrete in concrete structures is on the rise due to its distinctive properties. To address the tensile and shear vulnerabilities of concrete, reinforcing it with fibers is a viable solution. This study explores the experimental replacement of stirrups with continuous rectangular spiral reinforcements in both traditional concrete and steel fiber-reinforced concrete (SFRC) beams. Three beams were subjected to static loading tests: the first beam, referred to as ST-NC, featured stirrups and normal concrete as a reference; the other two beams incorporated continuous rectangular spiral reinforcements with normal concrete (SP-NC) and steel fiber-reinforced concrete at a 0.75% volume fraction (SP-F0.75). The experimental findings indicate that the beam reinforced with continuous rectangular spiral reinforcements and fiber concrete exhibits improved shear resistance, energy absorption, and ductility compared to the normal concrete beam and the reference beam. The beams with continuous rectangular spiral reinforcements, using normal concrete and steel fiber-reinforced concrete, demonstrated a 23.8 and 46.5% increase in shear capacity, respectively, compared to the reference beam. Additionally, energy absorption in SP-NC and SP-F0.75 beams increased by 69 and 158%, respectively, compared to the reference beam. The ductility of the continuous rectangular spiral reinforcement beam with normal concrete and steel fiber-reinforced concrete is 0.87 and 1.17 times that of the reference beam, respectively. Notably, the results reveal a reduction in the ductility of the SP-NC beam compared to the reference beam, and the addition of 0.75% by volume of fibers to the concrete resolves this ductility weakness in the SP-NC beam. These findings underscore the advantages of employing continuous rectangular spiral reinforcements in beams constructed with steel fiber-reinforced concrete, as proposed in this study

Reinforced-Concrete Shear Wall (RCSW) is a common lateral resisting system especially in mid and high-rise structures. This popularity among engineers is due to high ductility and in-plane stiffness of the RCSWs. RCSWs have shown good performance as seismic load-bearing systems in past earthquakes. However, the main disadvantage of RCSWs is the crushing of concrete at the foot of the wall and as a result the buckling of the reinforcement in this area, which makes it difficult and, in some cases, impossible to repair after the earthquake. As a solution, using Buckling-Restrained Brace (BRB) as boundary elements at the base of the RCSWs is proposed and investigated in this research. For this purpose, two sets of 6 and 12-storey structures with conventional RCSW and BRB-RCSW as lateral resisting system were designed, and their seismic response were assessed through static (monotonic and cyclic), dynamic Nonlinear Time History (NLTH) and Incremental Nonlinear Dynamic Analyses (NIDA). The results indicate improved structural performance and an increase of response modification factor from 4.4 in conventional RCSW to 5.47 in RCSW-BRB. Furthermore, the proposed system prevents the induced damage at the foot of the RCSW while the replaceable BRBs act as the fuses, increasing the resiliency of the structure. So that the behavior factor of the frame equipped with buckling-restrained braces increased by 30 percent in the 6-story building and 20 percent in the 12-story building.

In previous earthquakes, many steel frames suffered damage to their ordinary rigid moment beam-to-column connections. As a result, the use of multi-level control systems in structures has gained attention from engineers in recent years. The main idea in this system is to combine two separate control systems with different stiffness and strength, thus creating dual seismic behaviors. In this study, a two-level friction-yielding damper passive control system is presented for beam-to-column connections, and its cyclic behavior is evaluated using nonlinear static analysis with the finite element method using ABAQUS software. The evaluation results demonstrate that the performance of the samples improves with an optimal ratio of length to thickness. This improvement is reflected in increased stability and area of the hysteresis curves, ultimately leading to higher energy absorption. Additionally, the hysteresis curves indicate a ductile behavior for the proposed damper in the moment connection. Moreover, the obtained hysteresis curves show that the system reliably dissipates energy at different earthquake levels, satisfying the seismic criteria for special moment resistant connections based on the AISC code. The proposed damper serves as an energy dissipating device, effectively dissipating energy at different levels of earthquakes by facilitating slip and yielding, thereby controlling the seismic response of the structure.

This paper describes the development of a ductile fuse system to reduce Seismic demand in steel frames with knee element connections. In these types of structures, connections often require reinforcement to withstand the tensile capacity of the brace to comply with the capacity design process.To overcome this problem, it is necessary to think of a solution to prevent the premature failure of the connection.For this purpose, in this research, different models of ductile fuses consisting of a reduced cross-sectional area are placed on the brace of the knee element in a braced frame.The fuses are designed to reduce the tensile capacity of the knee element braces to the capacity of the joints. The results show that the braced frame with fuse can be used to reduce the seismic load demand to the connections sufficiently, to prevent the strengthening of the connection caused by the application of capacity design principles. It was also observed that the properly designed fuse system in braced frames shows a stable hysteretic response under cyclic loading and maintains sufficient ductility with a reasonable reduction in the compressive strength of the braced members. Also, the results showed that the failure of all samples occurs in the fuse, and as a result, by using the fuse, it is possible to use the full capacity of the connection and brace. Finally, based on the results of the study, the best fuse models that creates both Sufficient ductility and compressive strength to an acceptable level were identified for design applications.

The flexural performance of steel fiber reinforced concrete (SFRC) is significantly influenced by fiber properties such as fiber quality, shape, aspect ratio, orientation, and distribution. Digital image processing is an optical and non-contact measurement method that can determine the extent of sample size and deformation under any loading conditions. In this paper, eight reinforced concrete beams with and without steel fibers were selected, including four separate groups containing different volumetric percentages of steel fibers, designed and loaded with four-point bending test in accordance with the rules of ACI 318-19 design regulations. The first group consisted of two ordinary concrete beams as reference samples and six other concrete beams reinforced with steel fiber with a percentage of 0.5, 1.0, and 1.5%. Different longitudinal reinforcements (one state of minimum reinforcement and one state of maximum reinforcement in accordance with the provisions of the design regulations) were examined and analyzed in these specimens. Strain gauges were installed on the longitudinal bars to measure the strain during the loading process. Experimental results showed that the loads, flexural strength, ductility, and energy absorption of fiber-reinforced concrete beams were improved compared to similar conventional concrete beams. The highest ductility ratio among the samples made with tensile reinforcement was observed in the beam with a minimum longitudinal bar and 1.0% of fibers. The ductility of this sample was 30% higher than the similar non-fibrous sample with minimum longitudinal tensile reinforcement. The results showed that the ratio of ductility of the sample with maximum tensile reinforcement was decreased up to 46% compared to the companion beam with minimum tensile reinforcement. Significant increases in flexural strength, equal to 16, 23, and 29%, respectively, were observed in beams with minimum tensile reinforcement and containing steel fibers 0.5, 1.0, and 1.5%.

Regarding the dependence of ductility response in structural components on their ability to keep stability after yielding of the material, in this paper, the influence of change in tangential modulus of work-hardening part of stress-strain response, was observed on the load carrying capacity and plastic buckling response of stainless-steel tubular columns. To keep cost-effectivity in the research, the objective of the study was followed by FE modeling, which was verified by simulation of plastic buckling in an experimental specimen with D/t=60, made of duplex stainless-steel. For all components of the models, S4R elements were used and both material and geometrical nonlinearity were included in the models. To conduct deformation of the columns according to the experimental observations, an initial imperfection equal to t/100 to combination of first three mode shapes of the columns was imported. The material stress-strain response after yield point was determined for the model by a multilinear curve according to the tensile stress-strain curve, obtained experimentally. The main parameters for comparison of the FE model and experimental observation were force-displacement curves. The FE study was extended by modeling of stainless-steel columns with various D/t ratios in range of D/t=30-120. Two main parameters comprised of energy absorption capacity and deformation of the column related to yield of the section and collapse threshold (e/g) were compared to the columns with various D/t ratios.According to force-deformation curves, by decrease of D/t ratio, the energy absorption capacity increased considerably for the columns, for example the energy absorption capacity and e/g ratio increased by 12% and 12%, respectively for comparison of the columns with D/t=60 and D/t=30, however, e/g ratio for the columns of D/t=120 and 100 were less than two, categorized as a force-controlled column. Two models with D/t=30, 60 were selected to follow the objective of the study. The work-hardening response of the material was approximated by two linear segments, the first by a tangential modulus equal to E=7.9 GPa and the second was by the tangential modulus equal to E=2.4 GPa. The influence of change in tangential modulus through a range between 0-200% was observed on the structural parameters related to ductility, comprised of energy absorption capacity up to collapse threshold and deformation of column at the collapse threshold. The results showed different reaction of the columns with different D/t ratios, increase of tangential modulus at the first work-hardening part was more significant than increase of the influence by the later part of the work-hardening response for the column of D/t=60, however an inverse effect was observed for the column of D/t=30, i.e. the influence of tangential modulus at the later part was more significant for this column. By doubling the tangential modulus of earlier part of the work-hardening response, the energy absorption capacity and e/g ratio for the column of D/t=60 increased by 26% and 46%, respectively. By doubling the tangential modulus of later part of work-hardening response, the energy absorption capacity and e/g ratio for the column of D/t=30 increased by 111% and 71%, respectively. The results showed significant parts of work-hardening response of duplex stainless-steel, to be exploited for development of ductility in the tubular columns.

The ductility coefficient is used to calculate the ductility strength coefficient and then the response modulation coefficient R. The modulus of response R is used in seismic loading standards to reduce the amount of forces due to the nonlinear behavior of structures in earthquakes. They have become inseparable in seismic design, because they have good use and performance due to earthquake force. In recent decades, in order to reduce the problems caused by conventional methods, studies on energy dissipation systems have been conducted in valid world regulations, including FEMA and ASCE regulations, one of which is attenuator systems, dampers. Visco is elastic, which is inactive in the control systems. In this study, while getting acquainted with viscoelastic dampers, in order to investigate the effect of viscoelastic dampers on seismic vibration response and ductility reduction coefficient, a 6-story structural model in two modes without dampers and with 2D damping with soft concrete bending frame in soft SeismoStruct software has been modeled that the results of this study show that the incorporation of visco-elastic dampers leads to a reduction in roof floor displacement and base shear. The studied structures showed that the proper efficiency of these systems in reducing the vibration response of the structures.

In the present study, the cyclic behavior of steel plate shear wall of a three-story steel frame equipped with added damping and stiffness (ADAS) dampers was evaluated. In this study, with the aim of investigating and improving the performance of the steel plate shear wall against lateral forces, the proposed dampers were applied in the distance between the columns and the steel plate shear wall infill plates. The parameters studied include the thickness of the damper sheet (8, 10, 12, 14 and 16 mm) and the thickness of the infill plate (3, 4, 5 and 6 mm) respectively. Evaluation of cyclic behavior of steel plate shear wall was performed using finite element method via ABAQUS software and the loading protocol based on ATC-24 was applied. In order to verify, the experimental specimen was simulated by ABAQUS software and it was observed that the experimental specimen and the finite element model are in good conformation and the finite element model can be applied to study and compare the parameters considered in this study such as energy dissipation, strength, stiffness and ductility. The results showed that as the thickness of the damper sheet increased, the energy consumption in the steel plate shear wall system increased from 12 to 66 percent compared to the model without dampers. Also, by reducing and increasing the thickness of the infill plates in the second and third floors compared to the model without dampers, we saw an increase in energy consumption from 52 to 64 percent compared to the model without dampers, which indicates the good performance of the dampers. The strength of the steel plate shear wall system increased from 2.40 to 3.14 times by considering different thicknesses for the damper compared to the model without damper, and further by considering the infill plates for the steel plate shear wall system. We saw an increase in strength from 2.30 to 2.81 times compare to the model without damper. The stiffness level of each steel plate shear wall model was investigated and compared, and we saw an increase in stiffness from 76 to 99 percent compared to the model without damper. Also, considering the thickness of different infill plates for the steel plate shear wall system, the stiffness increased from 82 to 98 percent compared to the model without damper. As the thickness of the damper sheets increased, the ductility increased from 2.32 to 2.55 times compare to the model without damper. Also, considering the thickness of different infill plates for the steel plate shear wall system, we saw an increase in strength from 2.29 to 2.55 times compare to the model without damper. Further, by examining the hysteresis curves and the hysteresis damping ratio of different models, it was evident that the models equipped with dampers are significantly superior to the models without dampers, and as the thickness of the dampers increased, the area under the curve of each model increased. As a result, the larger this level is, it indicates that the member is more malleable and has the ability to absorb more energy. Finally, the performance of the proposed dampers was investigated along with the damper failure mechanism. The results showed that ADAS dampers with their special deformations, significantly increase energy consumption and make the steel plate shear wall more malleable and by absorbing a large amount of energy they reduced the force applied to the main components and prevented the destruction of the steel plate shear wall.

Staggered truss system is one of the types of lateral bracing systems in steel structures. In this system, lateral forces are transmitted through the rigid floor diaphragm between adjacent trusses. The columns of the staggered truss system are placed only in the outer walls and the middle columns are removed. Hence, a large open space without columns is achievable, which is architecturally appropriate. In this paper, the effect of geometric characteristics of staggered truss systems such as the ratio of the opening length, the type and arrangement of the side trusses in seismic performance is investigated using ETABS software. For this purpose, the ability of the analytical model was first validated to estimate the available experimental results. It was observed that the analytical result is in good agreement with the results of the Experimental model. Then, by examining several different models, the effect of the length of the middle opening was investigated on the seismic parameters of the Staggered truss system. The results showed that the ratio of the length of the middle opening is very important in seismic performance; So that this ratio can have a direct effect on the ductility and stiffness of the structure. Finally, the effect of truss type used in side openings was evaluated on the best span ratio based on the best level of seismic performance. In this paper, three types of structures are used: short, medium and high.

The great depth of the deep beams allows the opening in the web. Openings in deep beams are intended for the passage of pipes and installation ducts. The presence of openings in the web cuts the members of the tie and strut in the equivalent truss and reduces the load-bearing capacity and ductility of the beam, which can even cause rupture. One solution to this problem is to use FRP reinforcing strips. In this research, the effect of FRP reinforcement sheets on the bearing capacity of deep concrete beams with rectangular opening has been investigated. For this purpose, reference laboratory samples were modeled and validated by finite element method with Abaqus software, then a number of parameters that may affect the response of the deep beam, such as the number, dimensions and distances of openings, were selected and kept constant. Other parameters, the response of the beam to its changes were examined. The results showed that the samples with BOX shaped reinforcement sheet had less bearing capacity than U-shaped reinforcing sheet. Also, samples with U-shaped FRP sheet have 38% more load capacity than sample without sheet and 13% more than BOX sheet. By comparing the reinforced specimens in terms of ductility and coefficient of behavior, it was found that the U-shaped reinforcing sheet has better performance.

Fiber Reinforced Polymers (FRP) are often used for structural repairs to improve the strength and ductility of the structures. Previous studies have shown that utilizing active confinement in concrete structures can improve the seismic behavior of concrete columns under pressure. In this study, the behavior of concrete columns actively confined by AFRP fibers was investigated under the combined effects of axial compressive and cyclic lateral loads. Two concrete columns were actively confined by AFRP strips. In addition, a non-confined column (SCR) was utilized as a control specimen. Then all specimens were tested under axial and lateral cyclic loading. Experimental results showed that the ultimate compressive strength and axial strain of specimens with active confinement are improved compared to the SCR specimen. Also, due to the increased number of small cracks in the specimen, a higher extent of energy was absorbed under the applied loading. The loading protocol caused no rupture in the AFRP strips, and no shear crack and brittle failure in the specimens were observed.

The main purpose of this study was to evaluate the vulnerability of steel shear walls using brittleness curves. To achieve this goal, the amount of ductility and damage index of several sample frames reinforced by steel shear wall are evaluated by modeling and performing nonlinear static and dynamic nonlinear analyzes, and damage index control based on ductility is introduced as a performance acceptance criterion. Seismic performance was evaluated using IDA incremental dynamic analysis and fragility curves were obtained using displacement and ductility index. According to the results, a relationship between performance levels and damage index is presented, which indicates the probability of passing performance levels in each of the structures. Damage index for each model was calculated by extracting increasing curves, as a result of which other structural characteristics such as stiffness, ductility and yield point of the structure can be obtained. The advantage of this method and the introduction of fragility curves based on damage index is determining the ductility parameter based on the structural criteria of the structure. Based on this, the strength of each structure can be calculated according to the yield displacement of the structure.

In order to prevent damage caused by earthquakes in different types of structures including concrete structures, various methods are used by structural engineers considering terms of design and working conditions. This research aimed to evaluate the performance of these structures in different conditions and evaluate their impact on the structural behavior coefficient. For this purpose, ABAQUS finite element software has been utilized to model a concrete moment frame with one span in one floor equipped with simple concrete slab, spherical and cubic hollow slabs in different conditions.

It is now known that the behavior of any structural system during an earthquake is largely determined by its energy dissipation capacity through ductile behavior. And shows the degree of nonlinear behavior of the structure.In this paper, in order to compare bending frames from the economic point of view and the effect of ductility on the amount of consumable materials, conventional reinforced concrete bending frames with different ductility and with different number of 6 and 12 floors are selected as representatives and observing all criteria. Aba are designed for each group. After proper typing and observing the executive points and preparing executive plans, the amount of consumable materials (concrete and steel) has been determined and all costs have been estimated according to the existing price list (2009). These costs only include the cost of materials used in the construction of beams, columns and foundations, and the cost of roof and other structural costs are not included because changing the type of ductility has no effect on other costs and only in the design of beams, columns and Foundations are effective.

One of the most important components in steel structures is their joints. It is a matter of correct design of steel members, especially fittings. Since the beam flange is not connected to the column flange in the side plate connection system, all the vulnerabilities and uncertainties of the brittle behavior of conventional joints that in the full penetration welding behavior of the beam flange to the column wing are eliminated. Today, the use of composite sections filled with concrete has been widely considered in many structures. One of the steel joints that has been proposed in the past years is the use of side plates, which to some extent guarantees the linear behavior of the connection spring. In this research, the behavior of side joints with side panels in composite steel and concrete frames has been investigated. Thus, after ensuring the modeling process by validating a steel connection in Abacus software, a U-shaped steel beam composed of a CFT column with a side plate is modeled and parameters has been investigated.The effects of compressive strength of concrete were also investigated. The results showed that except for the diameter of the screws, other factors affect the strength, hardness and ductility . Increasing the width of the plate has increased the strength, stiffness, ductility and energy absorption. By decreasing the d / t ratio of the column, the strength, stiffness and energy absorption are increased and the ductility is reduced. As the compressive strength of concrete increases, the amount of strength, stiffness, ductility and energy absorption increases. The arrangement of the screws, the diameter of the screws, the d / t ratio of the beam and the addition of the thickness of the side plate do not have much effect on the strength, stiffness and ductility and energy absorption of the joint.

Masonry walls are one of the main load-bearing elements against lateral forces. Because brick walls and vertical and horizontal beams in this type of buildings are used as a support for the roofs and to withstand gravity load and also as a shear wall to withstand seismic load. These methods also include reinforcement using FRP fibers, fiber-reinforced concrete and shotcrete. One of the most important methods of strengthening this type of walls, which is considered due to climatic conditions and the production of materials in Iran, is the use of brick wall reinforcement using surface concrete, which has been the subject of several laboratory studies. . In this research, the numerical study of coiled masonry wall reinforced using surface concrete and steel belt network as one of the methods of masonry wall reinforcement using finite element method has been investigated. Therefore, in this research, by numerical modeling of six samples of coiled masonry wall using finite element method by ABAQUS finite element software, three samples as reinforced masonry and three samples as reinforced masonry have been subjected to increasing load. . By examining the method of strengthening the masonry wall reinforced with surface concrete, the capacity as well as the ductility of this type of wall will be evaluated and compared with unreinforced samples.