جستجوی مقالات مرتبط با کلیدواژه « Stiffener » در نشریات گروه « عمران »

The I-shaped beam to circular column connections can be constructed by curved cutting of the beam flanges or by installing external diaphragms around the column, which cause both economic and practical difficulties. A practical method proposed for construction of these connections consists of welding a link channel to the circular column and welding the beam to the link channel. As this method is new, the effect of link channel dimensions, I-shaped beam section dimensions, circular column dimensions and the link channel stiffeners on the connection behavior is not known well. Accordingly, this paper presents a FE investigation on the cyclic behavior of I-shaped beam to circular column moment connections with link channel. The main novelty of the research is the parametric evaluation of the affecting parameters, considering the stiffness and strength degradation from ultra-low-cycle fatigue, which is made possible by including ductile damage for metallic materials in ABAQUS software. For this purpose, first, the parameters of the damage model are calibrated by comparing the numerical results with the laboratory data, and then, the connection models are analyzed under a displacement-control quasi-static cyclic loading. Based on the results, the thickness of the link channel plate has the most significant effect on the overall behavior of the connection compared to other link parameters. It is also observed that the link channel stiffeners increase overall stiffness and strength of the connection. However, they cause extension of yielding towards the beam to link connection, and cause rapid growth of plastic strain in this area.

In this research, the effect of the elliptical web reduction, the effect of the radial flange reduction and also the effect of the use of stiffener, on the behavior of beam, on the behavior of connection and on the performance of steel moment frame is studied. By using Finite-Elements Method and 3D elements in ABAQUS, the nonlinear-static analyses of the frame under cyclic loading are carried out and the Von-Mises criterion is checked. The results show that in the beam with no reductions, maximum stresses and strains occur in the web. By reducing the web section of the beam, maximum stresses and strains are transferred to the location of the reduced section. The ratio of maximum strength to the strength at the final step of loading, and also, the value of dissipated energy, show that, in comparison with the connections with radial-shaped reductions, the connections with elliptical-shaped reductions have less strength degradation and more ductility.

Steel shear wall is one of the most suitable common systems for the strength and stability of the structure against lateral loads. In this system, vertical boundary elements around the shear wall, in addition to being part of the lateral load-bearing system, are responsible for bearing the weight of the structure during and after the earthquake, and therefore in designing this system, the border elements are tried to be remained in the elastic state after complete yield of the web plate. Also, to provide uniform stress along the length and height of the wall, vertical and horizontal boundary elements must have high flexural stiffness. Code provisions in this case sometimes lead to the selection of non-economic sections in the beams and columns attached to the wall. In this study, in order to reduce the demand for vertical boundary elements attached to the wall and to make the design economical, vertical and inclined stiffeners are predicted inside the wall. These stiffeners direct the plastic deformations mainly into the wall and away from the columns. To evaluate and compare the behavior of the proposed model, 30 finite element models were studied under lateral monotonic and cyclic loading. The results show that the addition of stiffeners, in addition to increasing the stiffness and lateral resistance of the system, increases the ductility of the lateral bearing system and reduces the required flexural stiffness of horizontal boundary elements.

In the past years, special attention has been drawn to the explosion and its effect on various structures, especially thin-walled structures. One of the most effective factors for changing the behavior of such structures is thermal and shock loads caused by explosions. In the meantime, considering the geometric nature of the shells, which have a wide surface and thinness, as well as their wide application in various industries such as missile industries, nuclear industries, shipbuilding and silo construction, it is necessary to investigate the effect of these loads on the nonlinear dynamic behavior of the shells.  However, knowing the large deformation of such structures under these loads, practical and cost-effective solutions such as strengthening the shells using hardeners are recommended. On the other hand, implementation problems and the possibility of creating an opening in the shells lead to a change in their behavior. In this thesis, using the ABAQUS finite element software, the elastoplastic response of single-curvature steel shells with and without opening and stiffener against blast loads is investigated. For this purpose, the effect of the supporting conditions, the thickness of the single curved shell, the mass of the TNT material, the distance from the place of explosion to the centre of the shell, the curvature of the shell, and the effect of opening and stiffener have been investigated. The results indicated better performance of the shell with the bearing support condition compared to other support conditions. Increasing the curvature of the shell initially led to an increase in displacement and then a decreasing trend. Results of the research indicate that the creation of circular and square openings has reduced the stiffness of the shell, followed by an increase in displacement, and the increase in displacement for square openings is more than circular openings.

Seismic performance is one of the most important factors in designing of structures. Lateral load bearing systems in structures are responsible to transfer lateral loads into the ground. Steel plate shear wall as a load bearing system in structures has some advantages such as easy and fast implementation, being economical, repairable, changeable and applicable on existing structures. Therefore, more research on these systems can help to design and retrofitting of existing structures. There are two general types of steel plate shear wall: stiffened and unstiffened. In this study, it is tried to determine the best geometrical shape of steel plate shear wall in terms of seismic performance. Material volume which are applied in all models are the same in order to compare their seismic performance in an equal circumstances and this is the innovative aspect of this study. Seven different stiffened and unstiffened steel plate shear walls are modeled using FEM in this paper. All models are analyzed with non-linear static analysis and linear incremental and cyclic loading. It is investigated that stiffened models had better performance in terms of seismic behavior in comparison with unstiffened models. These models also had more stiffness, more ductility and they absorb more plastic energy. Proposed models with new and innovative forms had better seismic performance, higher stiffness, higher strength, higher plastic energy absorption and higher ductility compare to usual stiffened models. In addition, these models had controlled out of plane displacement and better stress distribution.

By development of science and technology, new structural systems have been developed and researched. In the last four decades, extensive studies have been done on the application of the steel plate shear wall systems. Steel plate shear walls are made and executed in various shapes. Trapezoidally corrugated steel plate shear wall is a relatively new structural system. In this paper, the effects of position, geometric shape, percentage, distance from the boundary elements and the use of the stiffener around the opening were investigated in the seismic parameters of the trapezoidally corrugated steel plate shear wall system including stiffness, strength, ductility and dissipation energy by using 46 models. The openings were geometrically square, vertical and horizontal rectangular, equal to 10, 14, and 18 percent area of the steel panel. This research was performed analytically using ABAQUS finite element software. The results of the study show that the square-shaped opening has better performance than the rectangular opening in all positions. Also, models with central opening have lower strength, initial stiffness and energy absorption rather than other models. Overall, the best position to create the opening in the corrugated plate is in the middle top of the plate and at the distance of 160 mm from the beam and also in the upper corner of the plate but without distance from the boundary elements. Another result of this research is that by using stiffener around the opening, initial stiffness and strength and energy absorption of the corrugated steel shear wall can increase until 41% and 25% and 24%, respectively. In addition among the different stiffeners, the plate with 60 mm width and 3 mm thickness has the best dimension for the stiffener around the opening.

The perforated steel plate shear wall is one of the different lateral load resisting systems. The steel plate shear wall system contains two rectangular openings, the middle panel between two openings has a major role in the energy absorption. In this paper, considering the middle panel similar to the link-beam of EBF and reviewing the existing theoretical formulas for anticipating the middle panel behavior, a new condition related to the stiffness of web plate and stiffeners, which are located on the surrounding opening is added. The results show that the new added condition helps better identify the behavior of the middle panel and to separate the boundaries of behavior type. In addition, a formula with high accuracy is determined to calculate the shape factor of a section with box-shaped flanges. Furthermore, in accordance with obtained diagrams from triple conditions, the effects of six dimension parameters on the behavior of the middle panel are investigated and the bounds of changing the behavior type of the middle panel are determined. The results of the theoretical study show that the 64% increase in width, 47%, and 32% decrease in height and plate thickness of middle panel respectively and 100%, 14%, and 122% increase in height of web, flange width, and thickness of box stiffeners respectively changed the behavior type of middle panel from flexural-dominant to shear-dominant. These obtained results were calculated only in the case of examining the relevant parameters.

Using Stiffener in steel plate shear wall (SPSW) improves seismic behavior of the system. The transferred force from the steel plate to the peripheral frame is one of challenging topics that discussed by the designers in optimal design of SPSW. Particularly, with the insertion of stiffeners, the amount of transferred force to the columns significantly reduced by the building codes. In this paper, the seismic behavior of a 10-story building with stiffened SPSW investigated in three different design phases. In the first phase, seismic design requirements of American Institute of Steel Construction (AISC) considered with the maximum permissible spacing between the stiffeners. In the second phase, the reductive effects of the building code on transferred forces to the peripheral frame ignored and instead, the minimum required stiffness of peripheral frame considered similar to SPSW without stiffeners. In the third phase, the distance between the stiffeners increased and the optimal design philosophy discussed. In this way, the designer can manage the yielding or buckling of the steel plate. Therefore, the capacity of the floor will be a combination of shear buckling and yield capacity of plate. Plate-Frame Interaction (PFI) theory and finite element tools approved that the peripheral frame design forces and its contribution in seismic behavior of system can vary according to distance of stiffeners.

Functionally Graded Materials (FGMs) are kinds of composite materials that due to the continuity of mixture of constituent materials as Functionally Graded, have more effective mechanical properties. Also, due to some executive needs, make opening and stiffener in shells will be necessary. Therefore, In this paper, the effective parameters on the free vibrations of Functionally Graded plates with opening and stiffener have been studied. In order to do this, ABAQUS finite element software has been used, in the first, the effect of important parameters such as volume fraction index, geometric dimensions and plate support conditions have been analyzed. The results show that the thickness and volume fraction index have the highest and lowest effects, Respectively, on the natural frequencies of each of the FGM plate modes and with the increase of simple support conditions in the edges of the plate (the decrease of fixed conditions), the natural frequency of the plate decreases. In the following, the effect of opening and stiffener on the natural frequencies of the plate has been observed, that Circular opening has a greater effect on the natural frequency of the plate than the square opening, and also the stiffener thickness has a greater effect on The natural frequency of the FGM plate than its height.

In this paper effects of the placement of various stiffeners and opening on the interaction behavior of steel plate shear walls and precast concrete frame, has been investigated. Steel plate shear walls has been bolted to concrete frame, by use of embedded plate in boundary concrete elements. Push over and dynamic analysis under seven earthquake acceleration in ABAQUS software, was done.
The results showed that the proposed connection, by keeping up its stability and strength, showed appropriate function in the route of load bearing of shear wall. Also it was observed that adding steel plate shear wall to concrete frame increased initial stiffness, base shear and dissipated energy 4, 4.3 and 340 times, respectively. The sample with opening in diagonal line and horizontal and vertical stiffeners, had maximum dissipated energy (22% increased). This sample showed the maximum relative displacement (increased 2 times) and minimum base shear force (decreased by 10%). Adding horizontal and vertical stiffeners to simple sample, increased dissipated energy by 16% while, the sample with diagonal stiffeners decreased dissipated energy by 25%. This model showed the minimum relative displacement (decreased by 15%) and maximum base shear force (increased by 7%). Placing the opening at the middle of sides in this model, increased dissipated energy by 35%.

Functionally Graded Materials (FGMs) are kinds of composite materials that due to the continuity of mixture of constituent materials, have more effective mechanical properties which leads to eliminate the interlayer stress concentration. The most common usage of such materials is in thin-wall structures, such as plates and shells. One of the most effective factors in behavior of such structures especially in single-curved shells, thermal loads or Impact loads is caused by explosion. Also, due to some executive needs, make opening in shells and their behavioral changes are important and suggesting solution will be necessary. Therefore, in order to prevent large displacement and resistance improvement, using shells made of FGM and suitable stiffeners, will be suggested. In this study, ABAQUS finite element software has been used to survey the Effect of opening and stiffener on geometric nonlinear dynamical behavior of single-curved FGM shells under the blast loads. In order to do this, the effect of volume fraction index, the effect of different openings and stiffeners has been studied. Results show that by increasing the volume fraction index, the maximum amount of displacement of the shell decreased. Making opening in the center of the shells, has better function in contrast with making opening distribution in the level of shells. By increasing moment of inertia of longitudinal and circular stiffeners, the maximum displacement has been decreased. Also, by utilizing opening distribution and longitudinal stiffeners, the maximum amount of displacement can be reduced.

The behaviour of gusset plates in concentric braced steel frames has been studied. Parameters studied are the thickness and shape of the gusset plate, use of linear and elliptical clearance, non-existence of clearance, edge, longitudinal and internal stiffeners, and use of a single- or double-profile bracing. Analysis has been performed by the three-dimensional non-linear finite element method using the ABAQUS code. Cyclic loading has been used. By eliminating the clearance, the plastic strains in weld between the gusset plate and bracing and plastic strains in the gusset plate are increased. In the weld between the gusset plate and bracing, the existence of any type of stiffeners has increased plastic strains compared to unstiffened gusset plates. In most cases, edge and longitudinal stiffeners have decreased plastic strains of the gusset plate and internal stiffeners have increased them The maximum energy dissipation has belonged to edge stiffeners with an increase of 15.4% compared to unstiffened gusset plates. By decreasing the thickness from 24 mm to 18.8 mm the maximum stress has been decreased by 3.5%. For similar gusset plates, use of single-profile bracing instead of double-profile bracing has not changed the value of maximum lateral load for compressive bracing. In this case, most of variation has belonged to the plastic strains of the weld between the gusset plate and bracing with an increase of 30% in a rectangular plate with a linear clearance and a reduction of 65% in a rectangular plate without clearance compared to a double-profile bracing.

The increasing risks resulted by blast loads in current broad and thin plates necessitate the studies and evaluation of these challenges. Practical and cost-effective solutions such as plates enforcement with stiffener are suggested due to high displacement of structure as a result of applied loads. Moreover, application issues and the possibility of developing opening in plates and thus their change of behavior are considered important issues, for which solutions are suggested in this study. Functionally graded plates (FGM) with a power distribution in the direction of thickness are suggested as a solution to this challenge. Accordingly, the present study assesses parameters related to plates with opening including kind, percentage and the position of opening, the mass amount of explosive material, and the parameters related to plates with stiffener including type, count, arrangement of stiffeners, boundary condition and also the joint effect of stiffener and opening using Abaqus Software. The results indicate that opening decreases the plate hardness which consequently increases the amount of displacement. Plate displacement constantly reduces as a result of increase in opening percentage and hence decrease in the surface on which load is applied. On the other hand, the rectangle shape of stiffener has a better performance due to higher moment of inertia and easier application compared to other shapes. By studying the joint effects of these factors, it can be suggested that developing opening and application of an appropriate stiffener can significantly reduce the amount of plate displacement compared to other types.

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.

Fixity of column base connection plays a major role in overall behavior of steel structures. Several parameters influence the real behavior of the column base connections, among them base plate thickness, anchor bolts and stiffeners details can be mentioned. A nonlinear three dimensional finite element method has been utilized for numerical studying of the behavior of the column base connection. Thickness of the base plate and stiffeners and also sizes and numbers of the anchor bolts were changed in a number of models to determine their effects on the nonlinear behavior of the regular column base connection. It was observed that column base connection characteristics such as its moment-rotation behavior, yielding pattern of base plate and anchor bolts and local stress concentration of the connection elements can be significantly affected by changing any detail of the connecting elements. The effects of each parameter on the behavior of column base connection were categorized and presented in this paper.

The special concentrically braced frame (SCBF) is a common type of steel structural system for resisting lateral loading. This type of system provides the required stiness and strength at relatively low cost. Design codes, based on past research, have recommended some details for connections and braces, in order to ensure suf- cient ductility and energy dissipation capacity in this system for their application in seismic design. In this paper, the behavior of four SCBF specimens with dierent details of connections is studied using experimental and numerical models. They are single story single bay sub-assemblages of frames with a single brace that are subjected to lateral cyclic loads. In the rst specimen, a 2tp straight line clearance at the end of the brace was observed, but, in the second specimen, an 8tp elliptical clearance was provided. In the third and fourth specimens, stieners were installed to provide enough sti- ness for gusset plates, so that they can act as xed ends for braces. The dimensions of the gusset plates in these specimens were naturally dierent. Measures such as stiness, strength, ductility, energy dissipation capacity and equivalent plastic strain are used to compare the behavior of specimens in experiments and nite element analysis. The results show that all specimens satisfy code expectations with regard to seismic performance. For unstiened gusset plates, the accumulation of plastic strain at the corners of the gusset plates and in the middle of the brace results in crack initiation and fracture in specimens in the nal stages of cyclic loading. In stiened specimens, although gussets are smaller, plastic hinges are formed in the middle and at the end of the brace element, but nal cracking and fracture occurs in the middle of the element. In these specimens, higher buckling resistance and lower out of plane displacement of braces are observed.

Concrete Filled Double Steel Tubes are mostly used in bridge piers, tall buildings, offshore and coastal structures and power transmission towers. Finite element analyses via ABAQUS software have been performed aiming to evaluate the strength, ductility and plastic deformation of CFDST columns with different hollow ration and stiffeners configurations. According to analyses results more strength and high ductility levels can be provided decreasing the composite section hollow and increasing stiffeners thickness. More stiffener plates with larger dimensions result in more strength and stiffness in composite columns due to increase in concrete confinement and adjoint interaction of steel and concrete. It also raises plastic deformation level of the columns and postpone the local buckling.

Nowadays steel-concrete composite members have successfully been used in pier، beam and deck of bridges، and column، beam and slab of high-rise buildings. Due to their considerable energy absorption and dissipation capacity، concrete filled steel tubes (CFST) members have gained popularity in bridge and building construction. Composite members not only have many advantages in the structural construction but also make a significant improvement in the behavior of structure compared with reinforced concrete and steel structures. Some of these advantages include: Easy and fast for erection and fabrication، using standard connection، savings in the construction costs، suitable performance against seismic loading، high loading and ductility capacities (with fewer volume). In this study، efficacy of type، number and location of two stiffening methods have been investigated on the flexural، buckling and ductility behavior of composite columns. It was found that stiffener enhances the ductility، absorbing energy، strength and critical buckling load of composite columns in comparison to columns without stiffeners.