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In this paper, an approximate solution using layer-wise theory for the vibration analysis of rotating laminated cylindrical shells with ring and stringer stiffeners under axial load and pressure is presented. The cylindrical shells are stiffened with uniform interval and it is assumed that the stiffeners have the same material and geometric properties and cylindrical shell reinforced by outer stiffeners while stiffeners are treated as discrete elements. The equations of motion are derived by the Hamilton’s principle. In deriving the governing equations three-dimensional elasticity theory are used and the study includes the effects of the Coriolis and centrifugal accelerations and the initial hoop tension. The layer-wise theory is used to discretize the equations of motion and the related boundary conditions through the thickness of the shells. The edges of the shell are restrained by simply supported boundary conditions. The presented results are compared with those available in the literature and also with the FE results and excellent agreement is observed. Finally, the results obtained include the relationship between frequency characteristics of stiffened cylindrical shell and different geometry of stiffeners, stiffener type, rotating velocities, amplitude of pressure and amplitude of axial load.

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Eccentrically braced frames (EBF) by covering the advantages of moment-resisting frames (MRF) and concentrically braced frames (CBF) have been used as seismic load resisting systems in buildings for more than two decades. In eccentrically braced frames (EBFs), the link beams transmit bracing forces through themselves into the columns and other bracings and, in the end, create dominant forces in the bracings. Link beams, similar to ductile fuses, in addition to avoiding bracing buckling, attract earthquake energies. In EBF system, failure and yielding should happen in the link beams, and other members of the structure must remain in elastic behaviour. On the other hand, link beams prevent transmitting of more forces to the other members by yielding, therefore, these link beams are so important. Typically, the link beams, which are relied upon for energy dissipation through inelastic deformation, have had a wide-flange or I-shaped cross-section that requires lateral bracing to prevent lateral torsional buckling. This has limited the use of eccentrically braced frames in bridge piers and towers, as lateral bracing is difficult to provide in those situations. Tubular cross-sections of link beams have substantial torsional stability, making them less susceptible to lateral torsional buckling than I-shaped cross-sections in eccentrically braced frames, and may thus not require lateral bracing.Web of I-shaped cross-sections because of having clamped boundary conditions in its four sides than web of tubular cross-sections that have simply supported boundary conditions in its four sides, having advantage. Web buckling of link beams in eccentrically braced frames cause rapid strength and stiffness degradation, and this significantly impedes the energy dissipation capabilities of the system. Web stiffeners can be used to delay web buckling beyond a certain rotation level.Stiffener spacing of link beam is of important causes for the delay of web buckling. Stiffener spacing is based on the boundary condition of web that is between the flanges and the stiffeners. In this study, link beams with different tubular and I-shaped cross-sections in non-elastic limits are investigated and has been tried by changing link beams stiffeners array cause increasing the distances and decreasing the dimensions of them. For this purpose nonlinear finite element software and AISC-2005, loading protocol are used.The numerical result ofdifferent link beams models indicate that tubular and I-shaped cross-sections if having same geometric profile, I-shaped cross-sections have higher rotation capacity because ofbetter performance of their web, this increasing is approximatelly twice. So study of results indicate that new arraying of stiffeners of tubular link beam inceases the distances of them approximatelly 30% and decreasing the dimensions of them approximatelly 15% anddoesn’t have any bad effect on rotation angle capacity of them. An investigation of the effect of stiffener dimensions indicated that stiffeners dimensions if having minimum area and moment of inertia requirements don’t effect on rotation angle capacity.

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Tubular cross-sections of link beams have substantial torsional stability, making them less susceptible to lateral torsional buckling than I-shaped cross-sections in eccentrically braced frames, and may thus not require lateral bracing. Web of I-shaped cross-sections because of having clamped boundary conditions in its four sides than web of tubular cross-sections that have simply supported boundary conditions in its four sides, having advantage. In this study, link beams with different tubular and I-shaped cross-sections in non-elastic limits are investigated and has been tried by changing link beams stiffeners array cause increasing the distances and decreasing the dimensions of them. For this purpose nonlinear finite element software and AISC-2005, loading protocol are used.The numerical result of different link beams models indicate that tubular and I-shaped cross-sections if having same geometric profile, I-shaped cross-sections have higher rotation capacity because of better performance of their web. So study of results indicate that new arraying of stiffeners of tubular link beam inceases increasing the distances and decreasing the dimensions of them and doesn’t have any bad effect on rotation angle capacity of them. An investigation of the effect of stiffener dimensions indicated that stiffeners dimensions if having minimum area and moment of inertia requirements don’t effect on rotation angle capacity.

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In this study, nonlinear bending analysis of ring-stiffened annular laminated composite plates is studied. A discretely stiffened plate theory for elastic large deflection analysis of uniformly distributed loaded is introduced. The governing equations are derived based on a first-order shear deformation plate theory (FSDT) and large deflection von Karman equations. The numerical results are obtained using the dynamic relaxation (DR) method combined with the central finite difference discretization technique. For this purpose, a FORTRAN computer program is developed to generate the numerical results. In order to verify the accuracy of the present method the results are compared with those available in the literatures and ABAQUS finite element package as well. The computer code can handle symmetric, unsymmetrical and general theta-ply schemes. The effects of the plate thicknesses, different ratio of outer to inner radius, depth of stiffener, boundary condition and laminates lay-up are studied in detail.

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Exact and numerical solution of eccentrically stiffened panels in the industry is a major step forward in the design of these structures. This paper presents an analytical approach to investigate the nonlinear stability analysis of eccentrically stiffened thin FG cylindrical panels on elastic foundations subjected to hygro-thermo-mechanical loads. The stiffeners are assumed to be spiral-type. The panel has the initial geometrical imperfection. The material properties are assumed to be temperature-dependent and graded in the thickness direction according to a simple power law distribution. The elastic foundation is considered based on Winkler and Pasternak proposed model. Governing equations are derived basing on the Lekhnitsky smeared stiffeners technique and classical shell theory incorporating Von Karman-Donnell geometrical type nonlinearity. Explicit relations of load–deflection curves for FG cylindrical panels are determined by applying stress function and Galerkin method. The effects of angel of stiffener, different dimensional parameters, volume fraction index, initial geometrical imperfection, the stiffness of elastic foundation and moisture concentration on the postbuckling of FG panel are investigated. Also effects of temperature gradient through the thickness and effects of different boundary conditions are investigated for thermo-mechanical loading. The obtained results are validated by comparing with those in the literature.

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Eccentrically braced frames (EBF) by covering the advantages of moment-resisting frames (MRF) and concentrically braced frames (CBF) have been used as seismic load resisting systems in buildings for more than two decades. In eccentrically braced frames (EBFs), the link beams transmit bracing forces through themselves into the columns and other bracings and, in the end, create dominant forces in the bracings. Link beams, similar to ductile fuses, in addition to avoiding bracing buckling, attract earthquake energies. In eccentrically braced system, failure and yielding should happen in the link beams, and other members of the structure must remain in elastic behaviour. On the other hand, link beams prevent transmitting of more forces to the other members by yielding, therefore, link beams are so important. Typically, the link beams, which are relied upon for energy dissipation through inelastic deformation, have had a wide-flange or I-shaped cross-section that requires lateral bracing to prevent lateral torsional buckling. This has limited the use of wide-flanges or I-shaped cross-sections in bridge piers and towers, as lateral bracing is difficult to provide in those situations. Tubular cross-sections of link beams have substantial torsional stability, making them less susceptible to lateral torsional buckling than I-shaped cross-sections in eccentrically braced frames, and may thus not require lateral bracing. Long link beams due to providing proper conditions for the openings performances have architectural advantages. Nevertheless, the behaviour of long link beams within sever seismic loads is not comparable to short link beams in stiffness, strength, rotation capacity and energy dissipation capacity, i.e. it is at lower level. Therefore, using long link beams is not recommended in buildings and particularly besides the columns. In this study, a method is presented for arraying the stiffeners of long tubular link beams to improve the behavior of long tubular link beams in eccentrically braced frames. Long link beams at the distance of 1.5b from both ends of the link beams make flange buckling. Now if this distance strength by any way, the flange buckling delay and the rotation capacity of link beams are increased. For this purpose in this investigation, the stiffeners have been used in the middle of the flange vertically in this diatance and the link beam web has been considered as a stiffener that its distance from the middle stiffeners of link beam flange is 0.5b. In long tubular link beams when the middle stiffeners of the link beam flange do not present, Tension-Field will not create and link beam flange will buckle because of moment. When the middle stiffeners of the link beam flange present at its both ends, then Tension-Field will be created. In this investigation, the formulas presented for determining the stiffener sizing of long tubular link beam flange. In this investigation, non-linear dynamic behavior for 6-stotories eccentrically braced frames with different two length of link beams (shear-flexural and flexural), tubular cross sections with two arraying of stiffeners under the influence of three records of far-fault and three records of near-fault are studied. The result of investigations indicates that flange stiffeners of long tubular link beams have important influence in decrease of displacement demand of eccentrically braced frames that approximately 19% for far fault earthquake records and 32% for near fault earthquake records.

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Structures designed to resist moderate and frequently occurring earthquakes must have sufficient stiffness and strength to control deflection and prevent any collapse. Since stiffness and ductility are generally two opposing properties; it is desirable to devise a structural system that combines these properties in the most effective manner without an excessive increase in the cost. Steel structural systems including moment resisting and concentrically braced frames have been widely used to resist earthquake loads. Concentrically Braced Frames (CBFs) have high stiffness, and due to the probable buckling of their diagonal members, are not ductile enough. Versus, Moment-Resisting Frames (MRFs) have adequate ductility as their beam sections can undergo inelastic deformations. However, due to the low stiffness of moment frames, the construction costs will be increased. In recent decades, steel shear panels are utilized as one of the lateral resistant systems, in Steel Plate Shear Walls (SPSWs), and the link beam of steel frames with eccentric bracing to achieve the aim of shear performance and keep the adjacent members in the elastic range. The Tubular frame is one of the common lateral resistant systems in which the columns are placed in close spaces and connected through deep MRF beams around the building perimeters. Based on the new design codes, the minimum limit of span-to-depth ratio (7 for moderate moment-resisting frames and 5 for special moment-resisting frames) is not satisfied at tubular system. So the idea of Shear Resisting Frames (SRFs) with non-prismatic beams connected by a shear fuse in the middle of the span was proposed as one of the alternatives. Using SRFs remove these limitations and increase the energy dissipation capability. In this new concept, the shear force in the beam is considered as the displacement-controlled component of the system. Similar to eccentrically braced frames (EBFs), the link is tuned as a sacrificial component so that the seismic energy is dissipated by shear yielding in a small segment in the middle of the beam. According to the stiffeners layout, lateral loading capacity in SRFs usually is achieved through buckling strengths or post- buckling capacity resulted from tension field action or load carrying capacity from the yielding of the web plates. So stiffeners play a crucial role in the lateral loading capacity of shear resisting frames and have a significant effect on the energy dissipation capability. Following this issue, the effect of transverse stiffeners with different layouts and placements (various spaces and two or one-sided arrangement) on the seismic performance parameters (response modification factor, overstrength factor and rotation capacity of link beam) of steel shear frames with different link length ratios where all of them are controlled with shear behavior, are evaluated by finite element cyclic and pushover analysis. At the end, an optimum space is proposed for different link length ratios and the response modification factors and overstrength factor of multi-story shear resisting frames including 3, 5, 7, 9, 10, 15, and 20-story for a specific link length ratio are presented. Also for facilitating the modeling process of multi-story SRFs in SAP2000 software, modeling parameters and acceptance criteria were extracted from cyclic and monotonic curves. Finally, pushover curves from SAP2000 were compared to ABAQUS to validate these parameters. At the end, a 25-story building with two different lateral resisting systems including tubular frame and SRFs were compared.

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The plate girders used in bridges usually have a deep and relatively thin web, therefore, the buckling of the web is one of the important factors in the design of such girders. While the limit state of web buckling dominant design, Longitudinal and transverse stiffeners are used to increase cross-sectional strength. The location of stiffeners in flat girders has been extensively studied, which has led to the most effective placement for longitudinal and transverse stiffeners. In the case of curved beams in the plan is not as extensive as in the case of flat girders, especially in the case of longitudinal stiffeners in the asymmetric section.
Summarized herein is a study that explored single span, horizontally curved, plate girders having a yield stress of 50 ksi (345 MPa) to investigate their flexural behavior as a function of the position of a single longitudinal stiffener at various locations along the depth of the web. The studies were conducted using ABAQUS with the girder cross-sections under high vertical bending moment and low shear. As a result of these studies, recommendations are made for positioning longitudinal stiffeners on horizontally curved:
-Placement of longitudinal stiffener at distances D/4, D/5, D/6 from the compression flange can control the flexural buckling of the web.
-Among the above-mentioned locations, the location of the longitudinal stiffener at a distance of D/4 from the compression flange has the best shear response in the beam. Therefore, in this study, the optimal location of the longitudinal stiffener at a distance of D/4 from the compression flange.

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Due to the increasing population and lack of construction space, the use of high-rise buildings around the world is inevitable, so the use of sections with high strength to weight ratio that take up less space has been considered by researchers. One of the sections that has been considered by researchers and engineers to achieve this goal is composite columns, especially steel filled with concrete (CFT). These columns use the advantages of steel and concrete both and also have advantages such as eliminating column formwork in construction, providing complete enclosure conditions for concrete, preventing concrete parts from collapsing and tearing from the steel profile of the column and delay. The buckling of steel sheaths due to the presence of concrete is more common than other composite columns. CFTs also have higher strength, lateral stiffness and ductility than reinforced concrete columns of the same dimensions. The use of external stiffeners for replacement with continuity plates has been considered by researchers and design engineers and various forms have been proposed so far. The results of previous research have shown that external stiffeners are a good alternative to continuity plates.
In the present study, the behavior of steel frames with Hollow Steel Sections(HSS) and Concrete Filled Tube(CFT) Columns has been investigated. After launching the test setup and locating the displacement meters and dynamometers, the structure is subjected to cyclic loads according to the defined loading protocol. Three samples of two-opening and two-story frames with hollow box columns (HSS), concrete filled box (CFT) and concrete filled box with horizontal reinforcement nets have been evaluated experimentally and different parameters Their strength, ductility, hardness, energy absorption and cyclic behavior have been studied. In addition, the impact of the presence of concrete and horizontal reinforcement nets has been evaluated. On the other hand, in order to investigate the effect of using external stiffeners and horizontal bar mats in the frame, all connections of the two-story frame of the present study selected of this type. The results show that the use of concrete has improved the strength of connection due to the reduction of the buckling of the column plates, but the ductility has decreased. External stiffeners are used in all specimens, and as expected, the plastic hinge is moved into the beam, providing the idea of strong column-weak beam. In another part of the research, the behavior of the CFT frame and The presence of horizontal bar networks of the panel zone, which shows its effect of it in improving the behavior of the frame. The use of concrete in steel sections increases the strength of the frame, but since it is used in frames with CFT columns, beams with weaker sections show little reduction or little increase due to the use of concrete properties in pressure and Steel is in tension. On the other hand, the presence of concrete reduces the buckling of the column plate. In addition, the box-shaped sections around the concrete cause the concrete to be enclosed and ultimately increase the strength and energy absorption of the structure.

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The Concrete-filled Steel tube columns known as CFT are also called composite columns. These columns consist of steel tube which is filled with concert. Their advantages in comparison with reinforced concrete and steel columns have made their usage more prevalent in high rise buildings. In order to analyze the statistic behavior of concrete-filled Steel tube columns, the ABAQUS was used. For studying the stiffener effect, reinforced and non-reinforced concrete usage, and cohesion ratio between steel and concrete, 16 columns were modeled. They were three meters in length with a pinned support at each extreme end. The results indicated that using stiffener increases the load-bearing capacity of the filled columns to about 8 to 10 percent more than the hollow ones. Comparing the eight other models, the columns using reinforced concrete have a 10 to 28 percent load-bearing capacity more than columns filled with non-reinforced concrete. Furthermore, the columns with 100 percent cohesion ratio had an 8 to 16 percent load-bearing capacity more than the columns with 20 percent cohesion ratio

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Abstract
Steel shear walls have been used in various buildings as a system to resist lateral loads. The special advantage of this type of wall is its good malleability, high initial hardness, and high energy consumption power. But due to its special geometry, the steel shear wall undergoes buckling in the elastic range. To prevent steel sheet buckling in steel shear walls, there are two general solutions: using metal stiffeners or using concrete cover that is connected to steel sheet through shears. Based on this research, a solution has been proposed to improve the seismic performance of modern steel-concrete composite shear walls. The composite steel shear wall is a modern lateral bearing system consisting of a steel sheet with a reinforced concrete cover, which is connected to the sheet from one side or both sides by clips. In the composite steel shear wall, the reinforced concrete cover, by restraining the steel sheet and preventing its buckling, increases the shear capacity of the steel shear wall to the point of yielding in shearing inside the plate instead of tension in the direction of the tensile field. The composite steel shear wall, while increasing the shear capacity of the system, increases the resistance of the panel against destructive factors such as corrosion, fire, impact, explosion, and other cases and causes a reduction of more than 25 to 50 percent in the consumption of steel in medium and large buildings. In the new composite steel shear wall system, a distance is created between the concrete cover and the boundary beams and columns. Tests on conventional and modern composite steel shear walls show that the modern system has little damage compared to the conventional system. From nonlinear static analysis using the finite element method and with the help of ABAQUS software, the influence of the geometric characteristics of steel stiffeners on the seismic performance of the modern steel-concrete composite shear wall has been investigated. After modeling the steel-concrete composite shear wall and validating the numerical model with laboratory results, the effect of parameters such as the number of stiffeners, the type of arrangement, including vertical, horizontal, diagonal, and combined, on the maximum bearing capacity of the composite shear wall, ductility coefficient, additional strength, energy consumption, compressive damage of the concrete hardener, and failure modes have been investigated. The results of this research show that the use of T-shaped steel stiffeners and their arrangement have a significant effect on the bearing capacity of steel-concrete composite shear walls and cause the overall buckling of the steel sheet to become local buckling between the stiffeners. The use of diagonal stiffeners increases the capacity of steel shear walls by 25%. The ductility factor and added strength factor of the steel frame with diagonal stiffeners are about 39 and 124% higher than the ductility factor and added strength factor of the base sample without the use of stiffeners, respectively. The use of diagonal stiffeners in composite shear walls compared to composite shear walls without steel stiffeners increases energy consumption by about 18%. The use of T-shaped steel diagonal stiffeners in composite shear walls compared to composite shear walls without steel stiffeners causes a significant reduction in the damage and failure of the concrete stiffener.