نشریه آنالیز سازه - زلزله
سال شانزدهم شماره 4 (زمستان 1398)

Concrete is one of the main materials used in the construction industry and there are disadvantages to the conventional method of using steel, which reduces the breakage and concrete failure. Today, the spread of the science of applying polymeric materials to overcome these disadvantages has quickly taken its place in concrete ingredients. These materials can produce stronger concrete with greater flexibility and a smoother surface and can increase concrete resistance to erosion, impact and corrosion. In this research, using Geogrid, which is a family of geosynthetics, the tensile strength of concrete increased by 15%. Because it is used as a solid with very low risk, the geogrid is placed at different distances from the neutral warp. Based on the results of the experiments and according to the diagrams obtained from the geogrid experiments, if utilized as a semi-solid in the tensile region, the geogrids will result in the equal distribution of stresses and will have a better effect on increasing tensile strength. Of course, using a combination of steel and geogrid in the tensile region and according to the geogrid characteristics, it is easier to achieve a soft failure (tensile failure), which is the best type of failure for concrete structures.

Based on numerous studies, using weak and fragile building materials such as traditional brick due to their high weight, low strength, and low ductility during earthquake will cause the most casualties and losses. Observations from past earthquakes indicate that many structures have undergone remarkable damage even in moderate earthquakes. Low ductility and strength, high weight and severe strength degradation under seismic loads are responsible for these buildings failures. In this paper, behavior of a modern reinforced composite gypsum panel is evaluated and compared with corresponding panels made with traditional materials. The cheap and accessible basic materials used for making these panels result in favorable performance including a significant increase in the tensile and compressive strength as well as providing panels with integrity. So that when it breaks down, its particles do not disintegrate. In order to determine the basic mechanical properties of such panels, numerous standard tensile, compressive, and shear tests have been performed on various panel specimens at the materials laboratory of the faculty of mechanical engineering, Sharif University of Technology. Considerable ductility, strength, energy dissipation capacity, minimum cost, and fast construction are among the features of the proposed panel. Applying the finite element simulation, the buckling force of these composite gypsum panels were determined, which shows high buckling capacity. Subsequently, parametric studies were performed to evaluate the effects of openings on the behavior of these panels as load-bearing walls. The results of experimental tests for this type of panel presented that tensile strength is 4.3 Kg/Cm2 and compressive strength of panel is 18 Kg/Cm2, which are more considerable in comparison with the other traditional masonry materials.

Nowadays, the requirements of designing structures based on low weight and high strength in structural engineering science, have increased the possibility of unwanted and destructive vibrations in these systems. Also, using of computer softwares for modeling alone cannot accurately predict the dynamic behavior of structures. For this reason, a fundamental approach to experimental techniques was developed and made progress in the field of modal analysis. In recent years, modal analysis has been applied as a tool to determine and enhance the dynamic properties of structures. The vibrational modes obtained from the modal analysis, are useful for understanding the behavior of the structure correctly. Modal analysis is also used in modal time history analyzes and quasi-dynamic analysis of response spectrum. An important point in modal analysis is that when using modal analysis there are two types of analytical models named special vector state and Ritz vector state. Finding the best method for modal analysis of structural responses is very important in modal analysis, so far no comprehensive studies have been conducted to date. Considering the importance of this issue, in this study the evaluation of the accuracy between the two modes of vectors (Ritz) and (Eigen) in modal analysis is done. It is concluded that the modal analysis of Eigen vector is more accurate than Ritz vector and the results of Eigen modal              analysis are closer to reality.

In recent years corrosion of steel reinforcement in concrete has been recognized as one of the most important reasons for early damage in reinforced concrete structures. In marine environments, the release of ion chloride and ion sulfate into concrete resulted in corrosion, are the major cause of dameges and shortening the useful life of reinforced concrete structures. Because concrete is weak in tension and it is cracked due to the operation loads, chlorine ions can easily enter concrete through these cracks, causing corrosion of the rebars. Therefore, the fibers can reduce the corrosion of the bars in concrete by delaying of cracking or reducing the crack width as well as silica fume Pozzolan can decrease the rebars corrosion through reduction of  penetration of liquids. Accordingly, in the present study 5 concrete compositions were made. Silica fume pozzolan was added to the concrete mixtures by replacing 10 wt.% of the cement and Barchip fibers with values ​​of 2.5, 3.5 and 5 kg/m3 were added to the concrete mixtures. In order to evaluate the mechanical properties, compressive and flexural strength tests, and for concrete durability, special electrical resistance and half-hour water absorption tests were performed. The results show that silica fume is effective in decreasing of half-hour water absorption and increasing of the specific electrical, compressive and flexural strength of concrete, and the combined application of silica fume and Barchip fibers enhances the flexural strength of concrete up to 65%. There is also a decrease in electrical resistance and an increase in compressive strength and half-hour water absorption by the addition of Barchip fibers to the concrete composition containing silica fume

Progressive collapse is a phenomenon that begins with initial local damage, due to unusual loading or design and construction errors, and leads to collapse of a large part or the entire structure. Of course, the progressive collapse phenomenon will rarely occur during the useful lifetime of the structure. However, this issue can cause a lot of financial and life damage, thus it has become a major challenge in structural engineering. In this study, the structural models were steel plate shear wall with different configuration and moment frame systems with 5, 10 and 15 stories, which were designed in SAP2000 V.19 software two dimensionally according to code regulations and then the nonlinear dynamic analysis was performed in finite element ABAQUS software. The Alternate Path Method (APM) is used according to UFC4-023-03 guideline in this study, which is the most economical and rational method. Considering the displacement and rotation values of the members due to the column removal and the frame ductility, and failure damage indices, the most important results indicate that the probability of occurrence of progressive collapse due to the corner column removal of the 5-story moment frame is more critical than other frames and also, a proper and similar performance was observed due to the corner column removal in steel plate shear walls with the configurations examined

Low–velocity foreign object impact damage is one of the most important issues in composite materials used in military and civil structures. Fiber composites are strong sheets, which are subjected to impact loads, to reduce the damage of the impact using hard resins. In this research, low-speed bullet impact to six beams with FGM layering whose modulus of elasticity in the beam thickness varies from ceramic to metal and the response of the beams to low velocity impact has been investigated by finite element method using Abacus software. The strain, displacement and tension of the beam have been analyzed in two modes of the last layer of the metal and ceramic – metal. A comparison of displacement, tension and strain diagrams along the length of the beam for the six beams has been made. It was observed that the higher the properties of the metal than the ceramic, the higher the amount of displacement and tension and the strain in the beam decreased with increasing degree of ceramic properties compared to the metal.