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The design of earthquake-resistant structures and the reduction of damages caused by them have always been considered. One of the ways to reduce earthquake vibrations in steel frames is to use cable braces. In addition, one of the ways to improve the behavior of the structure against seismic loads is the use of dampers. In this research, magnetorheological damper and cable brace are used simultaneously. To check the effectiveness of the proposed system, four steel frames including, a steel frame without cables and dampers, a steel frame with cable braces, a steel frame with magnetorheological dampers and, a steel frame with cable braces along with magnetorheological dampers, which have one-span and two spans, were selected and the behavior of this frame Assuming different conditions, under nonlinear static lateral load and seismic loads, it has been checked in SAP2000 software. By examining the results obtained from the nonlinear static analysis of the case of a one span, it is concluded that the steel frame with cable brace and magnetorheological damper reduces the lateral displacement of the frame and often the internal forces of the beam and column more than other frames. gives by examining the results of the time-history dynamic analysis of one-span and two-span conditions, it is concluded that the proposed system reduces the lateral displacement of the frame and the internal forces of the beam and column more than other frames in most of the investigated earthquakes. In other words, using the proposed systems improves the performance of the structure against lateral loads.

 

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A variety of numerical methods were developed for the wave propagation analysis in the field of structural health monitoring. In this framework, meshless methods are suitable procedure for the analysis of problems such as damage initiation and its propagation or the fracture of materials. In this study, Hermit-type radial point interpolation method (HRPIM) is investigated for the numerical modeling of flexural wave propagation and damage quantification in Euler-Bernoulli beams using MATLAB. This method employs radial basis function (RBF) and its derivatives for interpolation which leads to Hermitian formulation. The evaluation of performance and capability of HRPIM is based on the comparison between the captured HRPIM ang benchmark signals using the root mean square error (RMSE) and reflection ratio from damage. The algorithm of damage quantification is the analytical solution which relates the reflection ratio to the damage extent. In this study, Gausian-type RBF is utilized and the number of field nodes, the size of support domain, shape parameters of RBF, the number of polynomials in the interpolation formula, the arrangement of background cells and the number of Gaussian points in damage length are the effective parameters on results. Based on the evaluation, the acceptable values and range of theses parameters are presented for correct modeling.

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The detection of changes in the dynamic behavior of structures is an important issue in structural safety assessment. Deployment and servicing of marine and coastal structures such as piers in the marine environment with constantly changing, requires understanding the dynamic behavior of these structures to prevent possible damage. Among the factors of uncertainty in understanding the dynamic performance of piers is uncertainties related to semi-rigid connection of deck to piles. According to this fact that the main mass of the structure is on deck, the connection of deck to piles is very important. In this study, experimental and numerical model of beach piers were studied. A Test on experimental modal analysis was performed to determine the response of structures. A numerical model of the structure prepared and theory of modal analysis was performed on it. Then, based on the finite element model updating of structure approach, identify and determine the percentages of semi-rigid connections. Results show this fact the connection isn’t fully rigid. According to the present method can be compared to determine the percentage of semi-rigid connections and prepare the finite element model with more adaptable to the experimental model. Updated results with this method were very close to the real model.

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Various researches have been performed regarding the deterioration and behavior of fabrics made from carbon, glass and aramid in different environmental conditions. Carbon fibers reinforced polymer (FRP) are very corrosion resistant. The CFRP laminates are extremely useful in very corrosive atmospheres, such as marine and aggressive chemical atmospheres. They have been advanced over the years because of their high strength, light weight, long-term durability and high resistance to deterioration. The very thin (0.2 - 0.4 mm) laminates are very easy to apply and can be applied in cross directions without any difficulty. Environmental conditions impact on the bond strength of FRP-to-concrete has sparsely been investigated. The sources of CFRP bond deterioration can originate from alkaline attack and thermal expansion. Alkaline attack occurs at the interface of the concrete and a CFRP laminates with the resulting damage to the matrix of the CFRP laminates. Also, alkali aggregate reaction can lead to the destruction of concrete elements. However, studies in this field are not enough and for externally bonded FRP materials, no such long term test results are available yet. Severe corrosion damage can often be prevented by a correct treatment of the structure against chemical influences or aggressive environmental effects. Methods such as the externally bonded reinforcement (EBR), despite of their advantages, have a problem known as the premature debonding of FRP from concrete substrate. In this method the surface of concrete is sanded and cleaned. After the preparation of the surface, the layer of epoxy is applied uniformly on the surface of concrete. Then, FRP is installed on the surface and saturated with epoxy. In other hand, a new strengthen method is the externally bonded reinforced on grooves (EBROG) method that consists of grooves on the surface of concrete. In this method, grooves with a proper length, width and depth are catted on the concrete surface; then the concrete surface and the grooves are cleaned with an air pressure. Later, grooves are filled with an appropriate epoxy. At the end, FRP sheets are installed with a proper epoxy on the concrete surface. In this paper, the effect of environmental conditions, including three alkaline environments with temperatures of 〖 23〗^° C, 〖40〗^° C and 〖60〗^° C, was investigated on the bond strength of FRP-to-concrete. The specimens were strengthened with two methods: EBR and EBROG. Samples were kept in environmental conditions for 3000 hours. Single-shear tests were conducted to evaluate the bond behavior of FRP-to-concrete. Experimental results showed that the specimens strengthened by the EBROG method - in the alkali environment with different conditions - experienced up to 50 % higher than ultimate bond loads compared with the specimens which were strengthened by the EBR method. In the EBR method, the bond failure mode changed from concrete delamination in laboratory condition to epoxy-concrete interface separation in alkali immersion with different temperatures. On the other hand, in the EBROG method environmental conditions had not effect on the mode of failure and more than 90% of specimens experienced FRP rupture. As a whole, the alkali environment caused a sudden drop in the bond strength of FRP-to-concrete substrate.