فهرست مطالب سیروس یوسفی خاتونی

Buckling of thin-walled structures is an important issue. Thin wall shells have many applications. The refinement of fuel and fluid storage tanks is very valuable. The important points of the thin-walled cylindrical shells are the little thickness of the shell relative to the other dimensions of these structures. This feature places the instability issue as a determining factor in the behavior of these structures. Due to the low thickness and compressive strength of the field, the forces on the shell of these structures are more likely to be buckling. Researchers have always tried to increase the buckling strength of thin-walled cylindrical shells by recognizing the behavior of different types of materials and their geometry types, thus maximizing the use of existing structures. The conventional method is to use steel rings to retrofit steel cylindrical shells. However, the use of this method according to the conditions of the workshop and that the structure may be load-bearing and carrying flammable liquids is due to the use of welding with fire hazards and practically there will be no use of this method in these structures. So according to the above topic, in this research, the benefits of using CFRP as new materials have been considered. In this paper CFRP rings are used to replace steel reinforcement rings. Here, the use of these materials has been investigated for the reinforcement of thin-walled cylindrical shells under uniform lateral pressure. This type of loading is generally caused by the discharging of cylindrical shells and reservoirs. In this paper, CFRP rings were used as reinforcement against the buckling of thin-walled steel cylindrical shells and at certain locations at shell height. Five specimens have been manufactured and used for testing. The first experimental specimen is without ring reinforcement. The second and third specimens have a reinforcing ring in the middle of specimen high. The number of CFRP layers in the XC2 specimen is half the XC3 specimen. The fourth and fifth specimens have two reinforcing rings in one third and two-thirds of the height of the specimens. The number of CFRP layers is based on the results obtained from the nonlinear numerical analysis. The number of layers is chosen so to stop CFRP ring buckling. The external uniform pressure is used as specimens loading by employing a vacuum pump. ABAQUS software has been used for nonlinear analysis. The results of the experiments show that the CFRP rings greatly increase the buckling and post-buckling strength of the thin-walled shells. Therefore, the use of CFRP rings is being proposed as an alternative method for the reinforcement of these structures. experimental results show that the XC5 specimen, which has two CFRP rings, has the highest buckling strength compared to other specimens. The results show that buckling strength of cylindrical shells increases with increasing number of rings and number of layers. In this research, theoretical relations, as well as the code relations of the United Kingdom and the European :union:, have been used to assess the obtained results and a good agreement achieved.

Steel shear walls has been noticed against wind and earthquake lateral loads about high buildings in the last three decades. This modern phenomenon is growing rapidly worldwide so that system have been employed highly in construction of new buildings and seismic upgrading of existing buildings in some countries such as USA and JAPAN. That is a very simple system from viewpoint of implementing and there isn’t particular complexity. High strength and ductility are main advantages of these systems. Current paper has investigated comparatively behavior of steel shear walls made of smooth and corrugated sheets. Also the paper has assessed push-over curves and cyclic binding. According to this result of the research, corrugated steel shear walls have lower ductility than smooth shear walls. The research also founded that despite the high strength of corrugated sheets in low displacement, behavior of flat shear walls is more stable than corrugated shear walls. On the other hand flat steel shear walls attract energy more than corrugated shear walls. Therefore using of flat shear walls is recommended in high seismic regions. In this research, 18 samples of flat steel shear walls and corrugated shear walls were modulated. In all models, panels height were 3 m and panels span were 3, 4 and 5 m. the thickness of sheets in the samples were 3, 4 and 5mm. According to results of the research: 1- Corrugated sheets are unstable and unpredictable in high thinness. In the low displacements occurs a mutation state, so it distinguishes the corrugated and flat shear walls behavior. 2- At low displacement, a corrugated sheet bears greater load than a flat sheet. 3- In a constant thickness for thinner corrugated sheets is increased the mutation rate and its behavior becomes more non-uniform. 4- Despite of the fact, pynchyng phenomenon appears in all samples, but all samples behavior is stable and significant energy attraction is observed.