دکتر محمد کارکن

Dams are one of the vital components of human societies and one of the strategically important assets of any society with a significant role in the sustainable development of the country. In this research, the damage caused by the blast of a double curvature arch concrete dam has been evaluated according to the mean velocity and frequency caused by the blast in the near-field. The model of the material used is the numerical simulation include the explosives, air, water, and concrete, which has been modeled. The problem-solving method used to apply the blast in modeling is Load Blast Enhanced. Using this method, the propagation of the pressure wave caused by the blast and finding the critical points of the dam body against the blast have been investigated. Then, the structural responses and the dam damage characteristics in different blast scenarios have been investigated according to the change in the blast depth, the distance from the concrete dam body, and the blast load. Also, by using vibration parameters such as peak velocity summation (PVS) and mean frequency (MF), the combined spectrum has been evaluated and proposed as a way to design a blast-resistant dam and find a safe standoff distance in case of emergency. Finally, two PVS-MF spectra have been suggested according to the charge weight and their distance for optimal and useful classification of dam damage according to three modes: slight, moderate, and severe, for initial and critical evaluation.

In this paper, a high-order eight-node element based on the analytical response of the governing differential equation is proposed for the analysis of plane structures. The formulation of the proposed element is based on the Hellinger-Reisner mixed functional and the analytical response of the compatibility equation governing plane problems. It is worth noting that in order to formulate finite elements with the Hellinger-Reisner functional, two independent stress and displacement fields are required. For this purpose, Airy stress functions are first made available by the analytical solution of the compatibility equation. By utilizing these stress functions, the stress field within the element is obtained. Also, the quadratic displacement field of the isoparametric element is used for intra-element displacement. By applying the Hellinger-Reisner mixed functional and stationary of this functional relative to the independent stress and displacement fields, the stiffness matrix, and the element node force vector are made available. Finally, with various numerical tests, the accuracy and efficiency of the proposed element are evaluated. These tests prove the high accuracy of the proposed element in the analysis of plane structures.

Several hazards often affect the stability of structures, and when designing and analyzing the structure, this should be considered. With increasing seismic strength of the structure, the strength of the structure increases against other forces, such as the explosion force. One of the most commonly used building design systems for lateral loads is the use of a cross bracing system. Using cross braces with friction damper can have more damping and energy absorption compared to cross braces without friction damper; it will behave better in big bangs. In this paper, the effect of cross braces with a friction damper and no friction damper on the performance of concrete structures against explosive force has been studied. For this purpose, the displacement and relative displacement of the floors in different modes of loading of the explosion have been calculated. Finally, the results show the effect of friction damper on reducing lateral displacement and relative displacement of the floors, so that in the structure with the damper compared with the structure without a damper, the lateral displacement and relative displacement of the floors significantly decreased. Studies show that adding a friction damper to the structure increases the stiffness of the structure, so the frequency of the structure is reduced.

In this paper, a new 2-node element is proposed for free vibration and buckling analysis of symmetrically laminated beams. The element’s formulation is based on first order shear deformation theory (FSDT). For this aim, the deflection and rotation field of the element is selected from third and second order functions, respectively. Moreover, the shear strain is assumed to be constant along with the element. By establishing the total strain energy in the element and stationary with respect to shear strain, the explicit form of the shape functions of deflection and rotation fields of the proposed element, are obtained. It should be mentioned, by decreasing the element’s thickness, these shape functions are approach to the Euler-Bernoulli shape’s functions and the shear locking problem does not occurred in the element. By utilizing the obtained shape functions, the explicit form of the stiffness matrix are calculated for the element. On the other hand, by using the governing equation of the free vibration and buckling of the beam, the explicit form of the translation and rotary mass matrices, and geometric stiffness matrix of the element are obtained. Finally, several numerical tests fulfill to assess the robustness of the developed element. For this purpose, free vibration and buckling analysis of symmetrically laminated beams with different boundary conditions and aspect ratios, are performed. The results of the numerical tests demonstrate high accuracy and efficiency of the proposed element for free vibration and buckling analysis of laminated beams.

Most structures experience large deformations under applied loads. Due to the deforming of geometry of structures, geometrical nonlinear analysis is needed. The co-rotational method is a simple and practical technique for nonlinear geometrical analysis. In this technique, unlike other nonlinear methods, is supposed the strain of the element to be small. The aim of this research is to develop a new co-rotational method for geometrical nonlinear analysis of two-dimensional truss structures based on small strains. A co-rotational method makes the separation of rigid body motion and small strains possible for a truss element. Therefore, global and local coordinate systems are utilized. Linear stiffness matrix of two-node element is used for small strains in local coordinate systems. Then, by writing co-rotational equations, transformation matrix is introduced for this element. The transformation matrix is used to calculate tangential stiffness matrix and element node force vector in global coordinate systems. At the end, the accuracy of the proposed method is evaluated by numerical tests. These tests confirm high accuracy of the proposed element for geometrical nonlinear analysis of twodimensional truss structures.