نشریه سازه و فولاد
سال چهاردهم شماره 29 (پاییز 1399)

The study includes an analytical approach to the issue of improving the seismic performance of the frame tube resistant skeleton. In this regard, the use of large-scale zipper elements in resisting skeleton of structures is investigated. Add a configuration of these elements only on the lower floors of structures can be a positive effect on reducing the parameters of the dynamic response of combined frame tube structures. Reduction of inter story drift and permanent drift, Creating downward trend in absolute acceleration and relative velocity graphs of the center of mass, Reducing non-linear rotation of panel zones, Represents the better performance in the skeletal configuration of a prototype tall frame-tube structure. Three 30-story building of frame tube skeleton and two configurations in combination with large-scale zipper elements selected and designed. A set of nonlinear analysis for side loading of these structures are done based on a choice of five powerful earthquake records. The presence of high-energy pulses and extensive acceleration spike with a combination of high speed pulses in selected time history records, is characterized by the modelling of near-fault ground motions. The skeleton of selected structures is designed based on the sixth and tenth National Building Regulations and the 2800 (Fourth Edition). Evaluation of the results showed that presence of large-scale configuration Zipper-Elements in the lower decks, Create an integrated behavior mechanism and the continuity of the seismic performance in tall building rigid skeleton. Showing the stable structural dynamic behavior of structures, particularly in large velocity pulse range, Along with reducing drift parameter, are the most important characteristics of such infrastructure in resistant skeleton tall buildings.

Due to Inappropriate performance of the moment welded connections in the Northridge earthquake in 1994, different details for moment connections was proposed to make more ductile response against earthquake loading. Using Post-tensioned (PT) connections in steel moment frame was approach to achieve to more ductile response that different methods for these connections have been proposed by the researchers. Experimental investigation demonstrated that post-tensioned connections to have strength, stiffness and proper self-centering ability and high energy dissipation capacity if used energy dissipating element. In this study, we used three types of structures with the number of 15, 10, 5, stories to study the progressive collapse. Nonlinear analysis of structures has been performed by OPENSEES software. The analytical results show that the failure of columns located in the corner of the plan has more intense effect on structures. Also, with increasing number of stories, the vertical displacement decreases in the connection above the removed column, which indicates that redistributing the unbalanced gravity loads due to column removal in structures with a greater number of stories is better. In the 5 and10 story special moment frame in the corner column removal scenario rotation of the beam adjacent the removed column is beyond the corresponding rotation of the life safety performance level, whereas the value of rotation in PT frame is significantly less than level of life safety performance

Y-shaped steel braces one of the systems is the lateral load. These braces, despite having the performance good architecture and resistance and hardness acceptable, they are not ductility. The use of dampers, such a rotary friction damper can increase their ductility capacity. The purpose of this paper is to evaluate the seismicity of y-shaped braces with rotary frictional damper. For this purpose, a frame of a floor and a span with y-shaped brace was selected and evaluated in two cases with and without rotary frictional damper. In evaluating these two frame, the stiffness, strength and energy absorption were considered. The results show that the strength and stiffness in the case with the damper decreases by 20% and 35%, but the energy absorption increases by 50%.

Eccentric braces are lateral load-resistant systems that have high plasticity and suitable stiffness due to the inelastic behavior of the link beam. Urban structures are mainly in the category of intermediate structures. In this category of structures, the force transmission is in the form of shear and bending, and both factors govern the behavior of the structure. Near- fault records have a less effective duration than far- fault records and have one or more long-range impact pulses and high periodicity. In this article, the seismic behavior of these frames under near-fault earthquakes is investigated with the variation of link beam length with the help of the ABAQUS finite element method and Perform 3D software. For this purpose, two dimensional models of EBF with 7- story and considering 3 different eccentricity/length ratio of (1,1/9,2/8) for each frame with different behaviors of link beam are modeled.  Finally, by comparing the effect of link beam length on the final behavior of the frames with earthquakes specific frequency content, it’s resulted that by increasing link beam length Parameters such as stiffness and strength of link beam under symmetric cyclic load are reduced and Parameters such as Maximum shear and acceleration of stories in near-fault earthquakes for 7- story frames are decreased and also maximum drift of the frames are proliferated. In addition, the average of total dissipated inelastic energy decreased with the increasing of the link beam length.

In the steel plate shear wall, the thin steel plate is connected to the boundary elements, Therefore, forces transfer from the panel to the columns and increase the required cross sectional area of the columns. Separating the steel panel from the columns, reduces the seismic demands on the columns and prevent from the premature failure of the columns and the collapse of the entire structure. However, this technic decreases the lateral resistance of the system, therefore in such a case, using high yield steel (HYS) for the panel or utilizing a thicker steel plate may be required. In this paper, the seismic behavior of the steel plate shear walls connected to frame beams only (SSW-BO) is studied through nonlinear finite element analysis by ABAQUS software. After validating the numerical model against available experimental results, the effect of the edge stiffeners on the behavior of SSW-BO is explored. Based on the results, changing the edge stiffener cross section does not influence the seismic behavior, the stiffness, the lateral resistance and the dissipated energy of SSW-BO if the stiffeners are not connected to the top and bottom beams. However, connecting the stiffeners to the beams, drastically improve the seismic behavior and hysteretic characteristics of SSW-BO. It should be noted that, in such a case, greater forces may apply to the beams which should be considered in the seismic design of these members.

The importance of geometric and material nonlinear analysis in trusses is not deniable. Furthermore, everyone knows the importance of closed-form solution to the behavior of structures. However, the solution volumes make this type of analysis impossible or very difficult for most structures. Closed-form solution only for a few simple trusses, with geometric and material nonlinearities, can be obtained. Elastic analysis of trusses is widely performed by the methods, such as, the finite element scheme. So far, researchers have proposed many approaches for truss nonlinear analysis. New techniques are validated by the benchmark problems. In this view, it is important to have an explicit solution for this purpose. In this paper, some simple two and three-dimensional trusses are analyzed analytically. This study considers both large deformations with elastic-plastic behavior simultaneously. The behavior of material is assumed to have a bilinear diagram. The strain energy function is obtained in terms of the Green strain. Equilibrium equations are satisfied by minimizing total energy. At the point, in which determent of the tangent matrix becomes zero, structural instability is found. The load-displacement graph is obtained by analyzing the strain of the truss members in the stable range of the equilibrium path. It is important to know that the multi-relational function of the equilibrium path of each truss can be applied to test the accuracy of new nonlinear analysis techniques.

Nowadays, with the advancement of the building industry, new structural systems are introduced by researchers. Despite the fact that modern systems have many advantages, they suffer from a common problem that is the lack of sufficient knowledge and experience for designers and executors in how to design and implement them as well as the need for new materials and skilled labors. In the present study, a new structural form was proposed that has both the benefits of modern systems and does not require much new technical knowledge. The system (LBF) consists of hot-rolled box section columns that are arranged at short distances from each other to which square beams are connected. All sections are hot rolled and joints are made by welding so that the implementation problems are rare and the need for skilled labors is obviated. In this paper, had been introduced the components of this construction form. Then, behavior of this connection evaluated with using the Abaqus software and experimental under monotonic loads. The obtained results indicate that this construction form has the potential to be used in regions with low hazard of earthquakes and with low-rise buildings.
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