فصلنامه مدل سازی در مهندسی
پیاپی 21 (تابستان 1389)

Quasi static push-over analysis is widely utilized to evaluate nonlinear behavior and ultimate capacity of offshore platforms against environmental wave loading. In reality the forces imparted by the waves traversing the structure, are dynamic loads. If these lateral dynamic loads are to be used in push over analysis, they can provide a more precise estimation of the maximum load that can be resisted by the structure compared to the value derived using quasi static approach. Other parameters that have effect on determination of the ultimate capacity of platforms are the platform structural configuration and its supporting conditions. In this paper, a comprehensive technique within a dynamic push-over analysis for jacket offshore platforms is provided. In the analyses performed herein, the ultimate capacity of a sample platform with two bracing configuration, and with different supporting conditions has been evaluated by using static and dynamic push-over analysis.

The Discussion of optimization of reinforcement elements in stabilizing rock slopes, due to the huge cost of such operations and problems caused by landslides and slope instability due to the lack of adequate reinforcement, has been always considered for researchers in the field of Geomechanic and Geotechnic. Therefore in this study the optimal distribution of reinforcement elements on the rock slopes which has the risk of instability in this study has been considered and new methods of reinforcing the required level or DRD method has been used. The purpose of this study is to provide a rational process for the optimum distribution of reinforcing elements that required in unstable rock slopes and especially critical zones. In this method, rock slope has been divided according to geometrical properties and for each zone with regard to geometrical and Geomechanical layer's properties, the coefficients and finally the Influence coefficients matrix is obtained. Also, according to finite element method and numerical modeling of displacement of each zone and then the displacement ratio matrix of divided zone is obtained. Eventually, within a matrix operation, DRD values for each zone obtain and distributions of reinforcement elements are done based on these values. In order to be practical, distribution of optimized reinforcement elements in rock slopes of Siah Bishe Dam has been evaluated.

Because of wide applications of composites at low temperatures, mechanical properties of glass fiber-reinforced epoxy have to be assessed at low temperatures. Experimental or analytical investigation on the tensile failure behavior of glass/epoxy laminated composite with/or without stress concentration subjected to thermo-mechanical static loadings at low temperatures has not been done yet. In the present work, a finite element model was developed to perform the progressive failure analysis of quasi isotropic composite plates at room temperature and -60°C. In this model Hashin failure criteria was used to detect possible failures. Quasi-isotropic laminates with stress concentration was selected. Full characterization of UD composite at -60°C was performed by a set of experimental tests. These results were used as input data for finite element model. The load is increased step by step. For each given load, the stresses (mechanical and thermal) are evaluated and the appropriate failure criterion is applied to inspect for possible failure. For the failed element, material properties are modified according to the failure mode using a non-zero stiffness degradation factor. Then, the modified Newton–Raphson iteration is carried out until convergence is reached. This analysis is repeated for each load increment until the final failure occurs and the ultimate strength is determined. The present method yields results in a reasonable agreement with the experimental data at room temperature and -60 ºC. The effect of low temperature on the failure mechanism of the plates was also determined.

Pavement analysis is an important field in pavement engineering, because of its causes on pavement behavior and obtaining more accurate equations for it. By science developing, many pavement analysis softwares have been developed which most of them are based on Multi-Layer Theory and a few work based on Finite Elements Method (FEM). Lots of input, spending much time in modeling process and to be unable to running more than one pavement modeling in a time are their main deficiencies. Artificial Neural Networks (ANN) as one of artificial intelligence algorithms has a lot of advantages such as low input numbers, reducing considerable time in the modeling process, multi pavement modeling at a time. In this article, after modeling verification, simulated an artificial neural network based on 384 models which were modeled by finite elements software and found a back propagation ANN with 8-10-2 combination with sigmoid transfer function which was the optimum network for the network.

Water resources developments and the future planning need the management tools which would be capable to simulate the complicated systems in order to support decisions making. The main objective of this method of simulation is its simplicity and rapid learning of system behavior in present and future. System dynamics is a feedback –based object- oriented simulation approach which represents complex dynamic systems in a realistic way and also allows the involvement of users in model development. By this way, the confidence in modeling process increases. In this study, a dynamic model of Damghan dam (located in Semnan province) has been developed. The aim of this study is to determine the effect of different operation policies on the behavior of reservoir in supplying downstream demands until 2030. For this purpose, eight scenarios proposed. Among them, three scenarios give the best results in supplying the downstream demands. It is revealed that the application of suitable policies can provide the present demands and also the future developments. In this study, the dam height is optimized considering the suitable supply for downstream demands.

After the 1994 Northridge and 1995 Kobe earthquakes and the extensive damage in moment resisting connections side plate connection was introduced. This connection is able to hold plastic hinge far from the beam-column connection and has sufficient strength and ductility so plastic hinges can form in beams. The structure is expected to withstand large deformations resulting from lateral loads, this property of structures is defined as ductility. In order to include ductility in structure analysis and also to use entire capacity of the structure, the conception of R-factor is used in linear analysis. To evaluate the ductility and R-factor of a structure, use of nonlinear analysis is inevitable. In the present study models of dual systems with side plate connections, various types of bracing, different braced spans and lateral load distribution patterns has been nonlinearly analyzed using PERFORM-3D at different heights (4, 8 and 12 stories). Then using Uang method ductility, extra resistance and behavior factor of the models were obtained and compared. On the basis of this study, the side plate connection increases R-factor and as the number of bracing increases, R-factor increases as well. Studying chevron, diagonal and X bracing indicates that R-factor is the greatest for diagonal bracing and smallest for chevron bracing. Comparison of uniform, triangular and modal lateral loading patterns indicates that R-factor reaches its highest value for triangular lateral load distribution and the lowest value is obtained through triangular loading pattern.

Classical modal testing of large structures such as bridges, towers and building is encountered with some problems such as exciting the structure and noisy environment. Therefore, researchers have proposed some new methods for identification of dynamic properties by measuring only the responses of structure. In this paper, one of the well-known methods entitled Frequency Domain Decomposition (FDD) is considered numerically and experimentally. The finite element method was used to conduct a model of a six stories building. The model was excited by random forces in a simulated test and modal parameters of the building were estimated. Also, the sensitivity of the results to the location and the type of excitation and measurement noise has been evaluated. To consider the FDD method experimentally, a clamped-clamped beam has been used. The classical and operational modal tests have been conducted on the beam and the modal parameters were estimated. The results of numerical and experimental studies show the effectiveness and accuracy of the FDD method in identification of modal parameters of structure.