جستجوی مقالات مرتبط با کلیدواژه « Concrete Shear wall » در نشریات گروه « فنی و مهندسی »

The present research investigates the strain demand of boundary elements of concrete shear walls reinforced with hybrid steel-composite rebars. In this regard, the numerical model of an existing full-scale sample has been done in VecTor-2.0 software and the results has been validated. Then, parametric studies were carried out for different values of the hybridization ratio where the cyclic response, maximum force, secant stiffness, single-cycle energy, displacement recovery index and strain values of the rebars are extracted. The results show that the combination of steel and composite rebars improves the hysteresis response of shear walls, maintains the post-yield strength, and increases the secant stiffness for lateral drifts over 1.9%. Also, this technique leads to a self-centering behavior minimizing the seismic damage. Hybridization with the combination ratio rh≥0.2 provides strength and maintains the stability of the wall. Increasing the hybridization ratio higher than rh=0.3 only results in an increase in the strength with no residual displacement change. For walls with a low rebar hybridization ratio, the cyclic strain-displacement curves are asymmetric, but the behavior becomes symmetric and the maximum steel strain is reduced by 50% by increasing the ratio. The expansion in the steel strain cycles is insignificant for low hybridization ratios. However, it becomes more apparent with the increase of composite rebars. The effective straining height of the steel in the basic model is equal to half the length of the shear wall, but with the addition of composite rebars, this height increases up to 80% of the wall length, which indicates the yield distribution of the steel in a wider area of the member when it is hybridized with composite.

So far, various elements have been introduced for modeling concrete shear walls, which are classified into two general categories: microscopic and macroscopic. Compared to microscopic elements, macroscopic elements have less degrees of freedom and therefore require less time for analysis. This is the main advantage of these elements. In this article, a special type of macroscopic elements called Multiple-Vertical-Line-Element-Model (MVLEM) is used to model the concrete shear wall. These elements simulate the behavior of simple shear walls well, but when the opening is embedded in the wall, it does not work satisfactory. In this article, the modified MVLEM is used to model the concrete shear wall with asymmetric openings. For this purpose, an experimental concrete shear wall with asymmetric openings was selected and verified using the microscopic finite element method in Abaqus software. After validation, the shear wall was subjected to macroscopic modeling in Abaqus software. In this model, a method for macroscopic modeling of the coupling beam was proposed, which is based on the moment distribution diagram in the beam. When the wall is subjected to lateral loading, due to its geometric shape, the amount of moment on one side of the beam is almost zero and on the other side it is maximum. In simple concrete shear walls under lateral load, the amount of moment at the top of the wall is zero and at the bottom is maximum too. Therefore, the coupling beam can be considered as a simple shear wall. In the shear wall with asymmetric openings, the coupling beams are modeled as simple shear wall whose base is connected to the main wall. After modeling the coupling beam, three different methods were proposed to connect this beam to the main body of the wall. This research includes a microscopic wall with asymmetric openings, three macroscopic walls. The main difference between the macroscopic walls is in the way of connecting the beam to the shear wall, which is based on the difference in the stiffness of the connection. In order to check the accuracy of the proposed models, macroscopic and microscopic walls were subjected to static and quasi-dynamic loading. Based on the results of the aforementioned analyses, the models showed acceptable behavior. The amount of connection stiffness caused the behavior of macroscopic models to be different from each other. Based on the results, as the stiffness of the beam to the wall increases, the bearing capacity and elastic stiffness of the model increases and the ductility decreases. The degree of stiffness of the connection also affects the cyclic behavior of the wall. In such a way that the higher the stiffness of the connection, the greater the loss of carrying capacity is observed in cyclic loading. In the model whose stiffness is higher than the other models, it experiments a large resistance drop in the ninth and tenth cycles. In the model whose stiffness is less than the others, less drop is observed and it shows a soft behavior. The model in which the connection stiffness was in the middle level showed the most accuracy compared to other models.

Permanent deformation after an earthquake increases the cost of the retrofit and even the implementation of the rehabilitation plan. A resisting system to control the lateral forces due to earthquakes is to use shear walls with good energy dissipation capability. Permanent deformation and cracking in the border and critical areas of the wall after relatively strong earthquakes leads to a decrease in the seismic performance of the wall. In this research, the responses and cyclic behavior of concrete shear walls under the cyclic loading protocol are investigated. For this purpose, using OPENSEES software platform, concrete shear wall modeling based on SFI-ΜVLEM method or wall modeling using multiple vertical elements based on the macro fiber method has been studied. The main models analyzed in this study include 2 concrete walls with steel rebars and memory alloy (SMA) with different dimensions and arrangement of reinforcements and innovative concrete wall with separate border elements in the form of concrete columns made of engineered concrete (ECC) and SMA rebars.  Validation of the models was based on previous studies. After validation of the initial models, the parametric study of the models was performed in order to investigate the effects of the dimensions of the boundary areas, the type and arrangement of the reinforcements and the amount of gravitational forces on the shear walls in the models. The results obtained from the outputs show that the use of SMA materials in the boundary areas of the wall has a significant effect on the self-centering behavior of the wall and the energy dissipation of the shear wall is reduced by using SMA materials.

Today, in building structures, concrete shear walls are widely used due to their desirable ductility and high energy dissipation. The presence of openings in the concrete shear wall changes the behavior of the wall and also creates new members in the wall, so the presence of openings in the wall behavior is very effective. Among the components of shear wall are the base walls and interface beams. A connecting beam is a beam that connects two shear walls created by an opening. The base of the wall is the vertical part of the wall that is bounded between the opening and the edge. Therefore, in this study, the behavior of eccentrically open concrete shear walls that have been reinforced by steel sheets has been investigated. In this research, a sample of concrete shear wall with eccentric opening with the name of reference sample has been validated in ABAQUS software. According to the definition of ACI318-14, one wall base is in the dimensional range of the wall and the other is in the dimensional range of the wall base. The samples were reinforced using vertical, horizontal and diagonal steel sheets simultaneously (in RCSW15 to RCSW20 samples) and in them different parameters such as increasing bearing capacity, strength, hardness, ductility and energy dissipation were studied. . In the RCSW15 and RCSW16 models, only the reinforcement around the opening is done by vertical and horizontal steel sheets. In the RCSW17 sample, horizontal, vertical and diagonal sheets are used simultaneously. The RCSW18 uses horizontal and vertical sheets in the opening corner. In the RCSW19 model, horizontal and diagonal sheets are used to reduce strain on the heel of the wall. In the RCSW20 sample, reinforcement is performed by horizontal and vertical sheets in order to increase the bending and shear capacity. Sample loading is lateral and cyclic. Among the reinforced designs of RCSW20 sample, the best design was selected because this design increased the final strength of the structure by 127.3%, increased the maximum strength by 13.42% and increased the crack resistance by 22.53%. It also increased the amount of energy consumed by 16.8%.

Reinforcement of structures with concrete moment frame system by submitting metal damper with optimal cross section has been done in the present study. To investigate the effect of damping on the behavior of the structure, the structural system with the proposed damper was compared with three types of bearing systems of different structures of concrete moment frame, concrete shear wall and bracing with different number of floors 8, 14 and 20. In this study, 4 groups of concrete structures were studied and compared in terms of lateral bearing system, including medium concrete moment frame with behavior coefficient (R = 5), medium concrete moment frame with shear wall with medium ductility, concrete moment frame with Medium ductility with EBF steel brace and Medium ductility concrete moment frame with EBF steel brace Equipped with yielding metal damper. The studied structures have building frames with dimensions of 25 x 25 meters, which are modeled on 8th, 14th and 20th floors. Each dimension of the structure in the plan has 5 openings with lengths of meters. In modeling structures with dampers, four types of dampers modeled with 4, 6, 8 and 10 flowing plates in the damper have been used. By comparing them, it has been determined that the damping with 10 flowing plates has better performance and the results of that structure in Comparison with other systems was used. In 8-story models, the maximum final displacement in the brace was 17% higher than in the damper. The 8-story structure with dampers not only withstood the highest shear but also had the best performance compared to other systems. The results show that in structures with a low number of floors, the use of the system with the proposed damper is more appropriate and in medium structures, the shear wall system has a better performance.

Due to the earthquake prone region in Iran and the need of strengthen structures against lateral loads which one of the important elements used in the structure are the shear walls. The use of concrete shear wall structural system, due to the hardness and maximum resistance, high energy absorption and the building movement control are suitable system against the lateral load of the building. If the shear wall and boundary elements are homogeneous, in other words they are similar,  the problems are much less, but it happens that such structures are not made of one, for example, the type of the shear wall is concrete and the type of the boundary elements are steel or the opposite. One of the uses of concrete shear wall is its simultaneous use with steel frame, which consists of shear wall, boundary columns and level-level beams. The way of connecting these walls to boundary are very important. Therefore, knowing the behavior of these structures is important. In this research, the shear wall of the concrete type and its connection to steel frame will be studied and investigated. For this purpose, first a 10-floor structure along with a steel frame system with concrete shear wall was modeled in Etabs software, in order to determine the beam dimensions, columns, wall and the amount of the longitudinal and transverse reinforcements of the concrete shear wall. Then, a wall from the first floor is selected with boundary elements to be modeled in Abaquse software in 4 different types of boundary elements and how to connect the steel frame to the concrete wall and compare the resistance and the type of the wall failure under pushover and hysteresis load. The models which are made are as following: A_ Buried column in concrete shear wall. B_ Half-buried column in concrete shear wall. C_ Buried column in concrete shear wall by attaching the welding of transverse shear wall reinforcement to the column flange. D_ Buried column in concrete shear wall by connecting bolt shear wall transverse reinforcement to the column flange. From the results of the analysis of the models that are made in the abacus software, can be concluded; the shear wall model with buried column and bolt connection of transverse reinforcement are shown that have more resistance than other models of connection, that the reason for this can be found in strong bolt connection, which makes the steel border element more involved  in the tolerance of the seismic loads. Also, the model with the half-buried columns showed less resistance than the other models of connection, where the unconfined in the boundary elements zone and less participation of the steel element in this condition can be known for this reason. Also, the maximum resistance and displacement of the models in hysteresis analysis were lower than pushover analysis.

One of the approaches to passive defense is to protect important buildings against progressive collapse. Progressive collapse is a phenomenon that happens in a building due to the removal of some structural members. In this research, the progressive collapse of a 26 story residential building in Tehran was studied by the alternative load path (ALP) method according to UFC 4-023-03. Several independent column and shear wall removal scenarios were adopted from the first floor. Nonlinear dynamic analysis was performed with SAP2000 software according to UFC to evaluate the bridging ability of the building on the remained members. Plastic joints in beams and columns were defined in special moment frames according to the instructions ASCE41-17 and FEMA356. Also, the shear walls were modeled by the multi-layer shells method and the mid column equivalent method. The results showed that correct relocation of the shear walls in a dual system within building guidelines leads to appropriate resistance to progressive collapse.

The arrangement of the centers of mass, resistance and stiffness has a great influence on the stability of the structure and its behavior against the moderate and strong earthquakes. In this study, three structural models with 6, 9 and 12 stories with dual bending system of intermediate steel frame coupled with concrete shear walls in three types of regular, irregular with stiffness and resistance eccentricity has been modeled using finite element software and fragility curves are depicted for different structural performance levels. Survey results showed that at immediate occupancy (IO) performance level the structure is still in the linear region and the probability of exceeding from collapse prevention (CP) performance level in the stiffness eccentricity model is higher compared to other models. Also, the probability of exceeding from the CP performance level in the resistance eccentricity model is higher than the other models because the structure arrives at the plastic region.

Iran is located in a region that has critical conditions in terms of seismicity, so structures designed in the country must be resistant to lateral loads. Reinforced concrete shear walls are the most common systems resistant to the lateral loads of wind and earthquake in the structures. One of the types of shear walls is the shear wall with openings, which are created for mechanical and architectural reasons. The presence of these openings in the shear wall causes changes in the ultimate resistance, changes in the behavior of the force distribution, and changes in the failure mechanism. Due to the fact that some shear walls are designed using old regulations that these regulations do not provide the ductility of the shear wall, so due to the incompatibility of the seismic design of these regulations with the new regulations, it is necessary to repair and strengthen these walls. Due to the fact that the effect of the wall with opening and reinforced with special flexural frame at a relatively high height was not studied in previous studies, so in this study, by studying the behavior of this type of frame, the coefficient of behavior of this type of system was evaluated. In this study, the concrete shear wall was added as a reinforcement to the flexural frame of the special reinforced concrete in two heights of 8 and 12 storeys, which were pre-designed, then circular, rhombic and rectangular openings were created in the walls and compared with each other. The results of the analyses present that the strength and behavior coefficient of the structure decrease with the opening of the wall, which is different for openings with different shapes. At the same level analysis,  circular-shaped openings and among all openings, openings with half the original dimensions exhibited the best performance, indicating that the smaller the dimensions of the openings, the higher the structural strength.

One of the effective factors in the designing process of buildings is how to control and manage the seismic force to achieve the optimal seismic resistance while maintaining proper ductility. In this regard, the application of various bracing systems in the construction of high-rise buildings, such as steel and concrete shear walls is a common solution. Therefore, in this research, once considering the soil-structure interaction and again without considering the impact of this interaction on two 10 and 15-story structures, different models of ABAQUS software were presented in the presence of steel and concrete shear walls. The nonlinear analytical method was investigated. For this purpose, by modeling the structures mentioned in the software, the effect of using steel and concrete shear walls was analyzed in terms of the impact of soil-structure interaction and without it. The results of modeling for 10-story structures showed that the performance of the structure with steel shear wall is better than concrete shear wall. In addition, the results obtained for the 15-story structure showed that the performance of this structure with steel shear wall was better than concrete shear wall. In general, the results present that the steel shear wall exhibits better behavior than the concrete shear wall. In general, it was found that by taking into account the soil-structure interaction in the modeling performed for both types of structures, the outputs are closer to reality.

In this research, numerical modeling and evaluation of the using new smart alloys in concrete shear wall structures is investigated via finite element method. For this purpose, two 5-story concrete shear walls, one of which is without opening and the other is with openings, are modeled in Abaqus software. In these shear walls, steel and shape memory reinforcement with different percentages were installed in these walls. Then, the results of seismic behavior analysis after installing members made of shaped-memory alloys in reinforced concrete shear wall with interface joint beams are presented. The obtained results are compared with the response of shear wall structures without these members. There are no shape memory bars in the reference shear wall and all its reinforcement is made of steel. The finite element method is a technique which widely used in this field of study. Utilizing this type of analysis and comparing the behavior between single shear wall and shear wall by using shaped-memory alloys, improving seismic behavior and dramatically reducing final and lasting deformation in shear wall structure with shape memory alloy are monitored. In static loading, similar results were observed, indicating the elimination of permanent deformation by these alloys

One of the challenges that threaten buildings today is the discussion of the progressive devastation caused by earthquakes and fires. In most seismic and explosive events, most of the casualties have been caused by the demolition of buildings compared to any other direct impact; therefore, ensuring the sustainability and non-demolition of buildings is of primary importance. However, even if properly designed ductile buildings are exposed to certain undesirable features, they will suffer extensive damage. Therefore, it is necessary to apply the principles of earthquake and explosion resistant design in three different levels of structural forms, building plans and ductility for all buildings. This can cause problems for structures designed on the basis of current regulations during severe earthquakes and even lead to total demolition. In other words, any weaknesses in the design or implementation of the components may lead to the progressive failure of structures during the loading of an explosion or earthquake. Pop-up shear walls in concrete buildings are designed due to architectural limitations. These walls are less resistant than conventional shear walls, but they increase the structural ductility. Although the design of such walls is based on valid regulations and regulations, it is not considered progressive failure and in cases where the structure does not have the necessary resistance to progressive damage, reinforcement is required. The Progressive Damage Issue in Concrete Shear Wall Structures, which form the basis of the present study, examines the effect of reinforcement percentage (ρ) on the progressive failure. Progressive failure has not been investigated so far, considering the importance of this issue in this study, we investigate the effect of parametric change of reinforcement percentage (ρ) on the behavior of concrete structures under progressive failure. At the end of the study, the results showed that the effect of increasing the percentage of reinforcement (ρ) on reinforced concrete structures under an explosive load and progressive failure would improve the performance of the structures.

Due to architectural reasons and constraints on the plan structure, openings such as doors, windows, and Installations ducts have been created on the concrete shear wall. It causes some changes in behavior, stiffness, load capacity and failure mechanism of specimens. In this paper, ABAQUS software is used for finite element modeling and investigating on parameters. In order to verify the results of this software, a scaled six stories wall with two bands of openings are modeled in ABAQUS software and compared with experimental results. After verification, parameters of opening area and position, bands of opening coupling, beam dimensions and diagonal reinforcement are investigated by nonlinear finite element method.
Results further confirm that if dimensions of opening do not change the failure mechanism of the wall, the opening position will be more effective than the opening area. In specimens with two bands of opening, making a ratio of lateral pier length to middle pier length more than 50%, increaseas effective compressive area and coefficient correlation and thus the sample has reached its maximum load capacity. The comparison of results also showed that a specimen with coupling beam height to height floor ratio of 0.52, the use of diagonal reinforcement on the coupling beam and putting up them in the base wall can be a suggestion for appropriate design of concrete shear wall with an opening.

Nowaday, with the proliferation of terrorist attacks on buildings in the world, a close examination of the behavior of structures under blast loads is a necessity. Pressure caused by the explosion of one of the most destructive loads that the structure may experience. Since the existing structures are usually designed to the common gravity and seismic loads, it is necessary to investigate their performances under blast loadings. In this study, analytical studies have been done for 2D structural models of concrete flexural frame and shear wall Partially Buried system with different number of stories 2 and 5. structures assessed based on the UFC 3-340-02 guidelines for 1000 kg TNT blast from 20 meters, the software SAP 2000 Design and nonlinear dynamic analysis have been. In order to loading, pressure values obtained from the explosion's blast wave, shock waves and pressure from the calculated reflection and As well as air blast wave parameters, including speed wavefront, period and wavelength explosion was determined and pressure graph - time of the explosion is offered. After analysis, The plastic hinge rotation, the formability and the highest axial force, shear force and bending moment occurred members, as well as maximum displacement, velocity and acceleration absolute floor level roof for all models will be investigated.

Shape Memory Alloys (SMA) are smart and novel materials that exhibit variable stiffness and strength associated with their different polycrystalline phases. The Shape Memory Effect (SME) and Superelastic Effect (SE) are two distinct properties that make SMA a smart material. Shape memory effect (free recovery effect) means that a large (pseudo-) plastic deformation can be reversed by heating. If the going back is prevented by, e.g., concrete, a stress in the SMA results (constrained recovery effect) [1]. A Superelastic SMA can restore its initial shape spontaneously even from its inelastic range upon unloading.
The specific objective of this study is to investigate the effect of ordinary and pretension SMAs with memory effect behavior in concrete shear walls separately. For this purpose, we analyzed concrete shear walls with different percent of SMAs and steels under monotonic loading in ABAQUS Finite element. Two different concrete shear walls, one reinforced with ordinary SMA together with steel rebars and the other with pretension SMA with steel rebars, have been analyzed. The seismic behavior of the two concrete structure models has been compared in terms of their load against displacement.