mohammadtaher kamali

The electromechanical coupling behavior of composite piezoelectric materials plays an important role in various industries. Therefore, it is necessary to investigate and study the propagation and scattering of waves in such materials in order to understand their properties and dynamic behavior. in this study, using an exact analytical method, electromechanical fields due to the scattering of plane waves by a piezoelectric spherical particle with spherical isotropic embedded in an unlimited isotropic polymer matrix has been studied. In the present formulation, there is no restriction on the range of the frequency of the incident wave. The dynamic stress concentration factors and the dynamic electric displacement concentration factor at the piezoelectric particle-matrix interface were calculated. Subsequently, the effect of the frequency of the incident wave on the maximum values of the dynamic stress concentration factors and maximum value of the dynamic electric displacement concentration factor as well as their appurtenant locations for shear and longitudinal waves compared

In this paper, a three-dimensional solution with mixed layerwise formulation is presented for multi-layer composite plates with arbitrary geometry and boundary conditions.  In this study, the displacement field the out-of plane stresses are considered as a sum of a series of functions with unknown coefficients. The boundary conditions and the continuity of the displacement field and the traction stresses between the layers are exactly satisfied. Equilibrium and compatibility equations are also applied using the Reissner's variational principle. The results show that the mixed formulation has faster convergence than displacement based formulation, and provides more accurate values of interlaminar stresses.

In this study, a semi-analytical method based on the Reisner's mixed formulation is presented for the elastic analysis of anisotropic homogeneous solids with an edge or interior crack. In this method, the displacement and the stress fields are represented as the sum of a known function and a finite series of functions with unknown coefficients. The functions are constructed in such a way that the displacement discontinuity across the crack faces and the exact singular behavior of the stress field at the crack tip are captured, moreover all essential and natural homogeneous and inhomogeneous boundary conditions are satisfied exactly. The equilibrium and the compatibility equations are also applied with the desired accuracy using the Reissner's variational principle. Solution of the variational equation leads to a set of linear algebraic equations in terms of the unknown coefficients. After computing of the unknown coefficients, the displacement and the stress fields are obtained and subsequently the stress intensity factors (SIFs) and crack opening displacement (COD) are calculated. The results show that computing of SIFs has high convergence rate and the results of the proposed approach are in good agreement with those of the analytical solutions reported in the literature.

In this paper, the behavior of connection of steel beams to circular concrete columns is investigated analytically and experimentally. In the experimental part, two exterior connections of steel beam to circular concrete column (RCS) are tasted. In the first specimen, based on the design guide of composite structures (ASCE 1994), transvers reinforcement in the column with the minimum spacing of 25mm is used to prevent compressive failure of concrete at the top and bottom of the steel beam. In the second specimen, the spacing of transvers reinforcement in the column at the top and bottom of the beam increased to 75mm which is the maximum allowable value in columns. Moreover, for strengthening the column at the top and bottom of the beam, carbon fiber reinforced polymer (CFRP) sheets are used. The experimental and analytical results show that the connections of both specimens are ductile and have great strength in high drift .The reinforcement of the second specimen using CFRP sheets improves the ultimate strength by 13%. Also, the ductility of the reinforced specimen is increased. As a result, the use of FRP sheets can be good alternatives for complex connections of steel beams to concrete columns. Also, both experimental specimens were modeled by Abaqus software, and the load- displacement relationships of the specimens were obtained and compared with the test results. The comparison shows that the analytical model can predict the behavior of the connections, appropriately.

In the steel frames, beam-column connections are traditionally assumed to be rigid or pinned, but in the steel frames, most types of beam-column connections are semi-rigid. Recent studies and some new codes, especially EC3 and EC4, include methods and formulas to estimate the resistance and stiffness of the panel zone. Because of weaknesses of EC3 and EC4 in some cases, Bayo et al. proposed a new component-based method (cruciform element method) to model internal and external semi-rigid connections that revived and modified EC methods. The nonlinear modelling of structures plays an important role in the analysis and design of structures and nonlinear static analysis is a rather simple and efficient technique for analysis of structures. This paper presents nonlinear static (pushover) analysis technique by new nonlinearity factor and Bayo et al. model of two types of semi-rigid connections, end plate connection and top and seat angles connection. Two types of lateral loading, uniform and triangular distributions are considered. Results show that the frames with top and seat angles connection have fewer initial stiffness than frames with semi-rigid connection and P-Δ effect more decreases base shear capacity in the case of top and seat angles connection. P-Δ effect in decrease of base shear capacity increases with the increase of number of stories.