نشریه آنالیز سازه - زلزله
سال چهاردهم شماره 2 (تابستان 1396)

Concrete as the most commonly used materials in the construction is of particular importance and according to structures retrofitting in various lateral forces to reduce human and economic damage, light and its impact are considered on a variety of structures. Concrete with lower density can lead to lighter structures in a way that using concrete with specific gravity of less than 1900 Kg/m3 and compressive strength more than 17 MPa in reinforced concrete structures is considered by many design engineers. Using of Sawdust in mix design of concrete is one way to reduce the density of concrete. In this research the percentage replacements of sand by sawdust were (0%, 15%, 25% and 35%). The size of test sample concrete adopted was 100x100x100 for compressive strength and 200x100 for tensile strength. The samples were removed from their moulds after 24 hours and allowed to cure 7,14 and 28 days. The results show that 25% Sawdust replacement of Sand with the compressive strength of 19MPa and density of 1904 is the optimal choice.

The analysis and design of structures based solely on the elastic behavior of the members and the lack of attention to the plastic behavior in tolerating of the lateral forces leads to noneconomic design. All the regulations in the world, a special coefficient, called the building's coefficient of behavior, which is calculated to reduce the earthquake forces is considered and allows the designer to analyze the elastic structure under reduced forces and design based on its results. The magnitude of this coefficient in the earthquake regulations is based primarily on the observations of the performance of various building systems in past strong earthquakes and based on engineering judgments. Accordingly, many researchers have expressed concern about the lack of reasonable coefficient of behavior, based on research studies and computational backing in earthquake regulations, and emphasized on the correction of these coefficients based on scientific studies. By studying the results of dynamic analysis on the studied structures in two types with behavior factor 6 and behavior 7, it was shown that increasing the coefficient of behavior can play a very important role in the Seismic response. The coefficient of behavior in the building does not have a significant effect on the horizontal displacement of the structure. Because in the buildings of one and four story, according to the 2800, the effect of twisting is not considered, and because of this, the coefficient of behavior in the buildings of one and four floors does not have much effect on the earthquake force.

The design of structures against wind and earthquakes due to losses caused by these phenomena in different countries is very important. Designing of tall buildings should be have comprehensive and complete against the forces of wind and earthquake. Earthquake is one of the world's natural phenomena, so that in recent years the human losses during 1947 and 2005 have been announced about 550 thousand people worldwide. The main goal of this study is to investigate the behavior of resistant reinforced concrete core in high-rise building of the tube in tube system with stairs against earthquakes in building with 100 meters height and 25 floors under the influence of three Accelerogram Bam, Tapas and Northridge via SAP2000 software. Base shear, roof displacement and column axial force compared together. The results of the research showed that modeling stepping on the coordinates of the center of mass has not made a significant change, but rigidity center has mainly changed due to stiffness of stair slab. Also high-rise building's seismic response affected by the earthquake Accelerogram type

Hyperbolic structures are grid-based space structures. The shape of the structures is similar to a square with fillet edges. If the mid-point of the square sides is connected in orthogonal x and y directions, the “+” shaped configuration remains at its position if the edges become even more curved and their elevation (z coordinates) do not change. Nonetheless, the elevation of the remaining points changes and form the hyperbolic structure. The application of hyperbolic structures is in covering long-span. In this study, a particular hyperbolic structure is optimized both in terms of shape and size. The Charged System Search (CSS) algorithm is used to carry out the optimization. Subsequently, optimization results are compared with corresponding results from the genetic algorithm method.

Recent earthquakes, the severe structural damage that ensues and modifications incorporated into building codes call for retrofitting of structures more than ever. A viable method is utilizing composite Fiber Reinforced Polymer (FRP). This system was initially used to the flexural strengthening of RC beams. In this study, a RC beam, one of the primary structural elements, is investigated in a commercial finite element software, ABAQUS; ten RC beams with FRP sheets used in different shapes and positions (the area of sheets is equal in different cases) are studied under torsional loading. Results showed that strengthening the mid portion of the FRP provides better results and incorporation of FRP sheets delays the ingress of diagonal shear cracks in faces of the RC beams which in turn increases the torsional moment capacity and reduces shear stresses in faces of the RC beam.

In this paper a new method for crack detection in structures based on first three mode frequencies and modal strain energies using least square support vector machine has been proposed. Since the mode shape vectors are equivalent to nodal displacements of a vibrating structure, therefore in each element of the structure strain energy is stored. The strain energy of a structure due to mode shape vector are usually referred to as modal strain energy (MSE) and can be considered as a valuable parameter for crack identification. Also, change of natural frequencies is effective, inexpensive, and fast tool for non-destructive testing. So, the proposed method uses the first three natural frequencies and modal strain energies as the input parameters and crack states as output to train the least squares support vector machine model.

The design and evaluation of concrete gravity dams will be studied in the present study. The case study consists of a comparison between old research methods and new ones. In the present case, an analysis of concrete gravity dams with different water levels influenced by earthquake will be presented. The subject of the study is a concrete gravity dam project by Rolling Compact Concrete (R.C.C), which is to be located 30 kilometers away from the South East of Sanandaj named Jaweh. It would be the second R.C.C dam made in Iran. The data used in the study is collected from detective. One of the investigation methods is a simplified one by Chopra and Feneves, which is based on a pseudo dynamic method. The new investigation method is conducted on the basis of finite element. Abaqus and Cadam Softwares are based on finite element method as well. This essay investigates the effect of linear behavior of concrete gravity dam with different water levels on rigid and flexible foundation. Afterwards the effect of non-linear behavior of concrete gravity dam on tensil cracking will be investigated and cracking seems directions will be studied by three earthquake accelerators.