فهرست مطالب جواد مشهدی

The purpose of this study is to present a new method of plate damage detection using the wavelet-based contourlet transform method. The contourlet transforms developed based on the Wavelet transform is a new two-dimensional transform that overcomes the limitations of the wavelet transform. The wavelet-based contourlet transform is a new family of contourlet transforms with the same two-step characteristic introduced from the same filter banks, radial, and angular decomposition. This method is used in plate damage detection for the first time. In the first step, the plate using the wavelet transform is decomposed into four sub-bands. Then, a radius decomposition with eight bands in each sub-band of the initial image is introduced using one of the directional filter banks. The radius decomposition in different directions is known as the advantage of this method in comparison with the wavelet transform. This advantage is observed in images with curved lines. In this method, the change in the elastic modulus is considered as damage in plates. The fundamental mode shape of intact and damaged plates is first obtained from the structural frequency analysis. Then, the location, shape, and approximate size of damage are obtained by applying this transform to the responses of the structure.

Nowadays, non-linear analysis of structures has become an attractive matter and appears necessary for most structural engineering applications, whereas tendency for more accurate structural analysis has increased by many engineers. In general, nonlinear analysis is divided into two main parts: geometrical and material nonlinearity. In some cases, both nonlinear types are used simultaneously in the analysis process. In this paper, a new Incremental-iterative method for the analysis of truss structures, including both geometric and material nonlinearity behavior, is proposed. Nonlinear equilibrium equations are solved using an Incremental-iterative method based on the displacement control process. The basis of geometric nonlinear process is based on rotational formulation and material nonlinearity is based on tracing the stress-strain relationship for post-buckling behavior of the truss members. In this proposed method, it is assumed that the magnitude of the displacement increment vector to the size of the total displacement vector at the beginning of each load increment, is a fixed value. Based on this idea and thinking, the corresponding equations are written and a new formulation has been developed based on the displacement control scheme, as, by employing a specified displacement, the corresponding load will be obtained. Using fixed incremental displacement algorithm, this paper, proposed a novel method that has a possibility of passing the limit points in the case of highly nonlinear behavior state. The proposed method, is able to pass the limit points including snap-through and snap-back. Some examples are provided for the proposed method and by solving them, the efficiency of the proposed algorithm is examined. A limit point refers to the turning point for the equilibrium path of a structure, which can be further considered as the transition point from stable to unstable equilibrium states or vice versa. In analysis of such structures, the simple incremental iterative methods unable to pass this limit points. The simple incremental iterative methods couldn’t trace the equilibrium path after the limit points. For resolving such disadvantages, advanced analysis methods have been developed numerical examples demonstrate the feasibility and accuracy of the proposed algorithm, to be highly suitable in predicting nonlinear response of structures with multiple limit points and snap-back points, and trace the equilibrium path accurately. The results show that the method developed in this paper, traces the equilibrium curve as well as the modified arc-length method with a small difference. In spite of the fact that the procedure herein explained is only implemented for truss structures, it is possible to generate the proposed method for other structures. This paper is organized as follows. In the first section, we will have a brief review of nonlinear analysis of trusses, including both geometric and material nonlinearity. A literature review is done and a number of available methods in this field is describe. In the second section we explained the basic concepts in nonlinear analysis. The third section geometric and material nonlinear behavior of trusses are reviewed. Section four is allocated to implementation of proposed method for nonlinear analysis. In section five, the validity of the proposed method is illustrated with some examples.

Progressive collapse is the collapse of all or a large part of a structure precipitated by damage or failure of a relatively small part of it. These efforts tended to focus on improving redundancy and alternate load paths, to ensure that loss of any single component would not lead to a general collapse. To avoid of progressive collapse in structures, some criteria have been considered by regulations that after elimination of a member, structure should have ability to bear applied loads and transfer them to other members using substitution paths. In this study, the effect reinforced concrete slab in performance of steel moment resisting frame in progressive collapse was investigated.in this research a part of roof with structural members and connections were modeled and effective parameters of slab to increase structure capacity and crack propagation path due to corner, lateral and middle column elimination, were evaluated. In modelling, the effects of rebar, concrete strength and slab thickness on strength in different cases of column elimination were investigated. Results showed that moment resisting frame with composite slab have more capacity to bear loads due to column elimination in comparison with frame without composite slab. Also, the rate of increasing strength depends on location of column in the plan.