Constructal design, finite element method and exhaustive search are applied to analyze different arrangements of steel plates with Rectangular or trapezoidal Stiffeners. As performance parameters, the maximum deflection and maximum von Mises stress are considered. A non-stiffened plate adopted as reference is studied together with 25 plates with Rectangular Stiffeners and 25 plates with trapezoidal Stiffeners. The results show that trapezoidal Stiffeners are more effective in minimizing the maximum deflection in comparison with Rectangular Stiffeners. However, regarding the minimization of stress, the Rectangular Stiffeners normally present better performance. When both performance parameters are concomitantly considered, a slight advantage of 4. 70% for Rectangular geometry is identified.

Given any structure, we seek to find the solution of mechanical problem as precisely and efficiently as possible. Within this condition, the BEM is robust and promising development, standing out in the analysis of cases with occurrence of large stress gradients, as in problems of fracture mechanics. Moreover, in BEM the modeling of infinite means is performed naturally, without the use of approximations. For methods involving domain integration, such as FEM, this is not possible, as models with high number of elements are usually adopted and their ends are considered flexible supports. This paper deals with the development of numerical models based on the BEM for mechanical analysis of stiffened domains. In the modeling of hardeners, immersed in a medium defined by the BEM, we tried to use both the FEM, already present in the literature, and the BEM 1D, being a new formulation. The objective was to perform the coupling of BEM with FEM and BEM 1D for elements of any degree of approximation, evaluating both isotropic and anisotropic medium. In addition, a complementary objective was to verify the effects of the adoption of different discretization and approximation degrees on the Stiffeners. However, the coupling with the BEM 1D leaded to more stable results and better approximations. It was observed that the FEM results were instable for many results, mainly in the quadratic approximations. When the approximation degree rises, the methods tend to converge to equivalent results, becoming very close in fourth degree approximation. Lastly, it was observed stress concentration in the Stiffeners ends. In these regions, the discretization and the approximation degree have large influence to the numerical response.

In this research, in order to investigate the effect of the piezoelectric patch which is used as a sensor or actuator in rotating flexible structures such as a helicopter blade, the free vibrations of the rotating Rectangular sheet with and without the piezoelectric patch have been presented. First-order shear deformation theory is considered for plate displacement and piezoelectric field. Considering the effect of Coriolis acceleration, centrifugal acceleration and centrifugal in-plane forces, the equations of motion are derived from Hamilton's principle and the electromechanical couple equation is obtained from Maxwell's equation. For piezoelectric, two electrical conditions, open circuit and closed circuit, which are used in sensors and actuators, respectively, have been considered. The equations are discretized with the help of the numerical method of generalized differential squares and the matrices of inertia mass, eccentricity, Coriolis and stiffness matrix are obtained. Natural frequency values for beam and rotating plate have been compared in Abaqus software. Also, the values obtained from the numerical solution in MATLAB have been verified with articles and ABAQUS, which have high accuracy. The effect of parameters such as hub radius, rotation speed, sheet thickness, aspect ratio, piezoelectric patch thickness and applied voltage on the natural frequency of the system has also been investigated.

Web of plate girders in bridges are usually reinforced by welded transverse Stiffeners in order to improve their shear capacity. Due to problems associated with field welding and fatigue, welded Stiffeners are not suitable for retrofitting existing bridges. Bolted Stiffeners are a practical alternative for strengthening girders that are expected to experience shear stresses in excess of their design shear capacity. This paper presents the results of an analytical study into behavior of plate girders with bolted transverse Stiffeners. Based on this study new requirements are developed for design of such girders.

The web of plate girders in bridges are usually reinforced by welded transverse Stiffeners in order to improve their shear capacity. Due to problems associated with field welding and fatigue, welded Stiffeners are not suitable for retrofitting existing bridges. Bolted Stiffeners are a practical alternative for strengthening girders that are expected to experience shear stress in excess of their design shear capacity. This paper presents the results of an analytical study into behavior of plate girders with bolted transverse Stiffeners. Based on this study new requirements are developed for designing of such girders.

In this research, web stability of plate girders with diagonal Stiffeners has been studied. For theorical study of stability of plate girders with diagonal Stiffeners same rules have been employed which are implied in studying the web stability of plate girders with vertical Stiffeners. For obtaining the buckling factor k, Lusas software has been used. With regard to obtained formulas and tests results, it has been found that where diagonal Stiffeners are used, the shear post-buckling strength of web which in turn is a result of the existing tension field action is higher than the case where vertical Stiffeners are used. Thus by using diagonal Stiffeners, the thickness of plate girder's web can be reduced which will cause economy. It should be noted that in this case, the force in diagonal Stiffeners will be higher than that of vertical Stiffeners, but the increase in weight of Stiffeners is less than decrease of the weight of web plate due to employment of diagonal Stiffeners.

Many tubular joints commonly found in offshore jacket structures are multi-planar. Investigating the effect of loaded out-of-plane braces on the values of the stress concentration factor (SCF) in offshore tubular joints has been the objective of numerous research works. However, due to the diversity of joint types and loading conditions, several quite important cases still exist that have not been studied thoroughly. Among them are internally ring-stiffened multi-planar XT-joints subjected to axial loading. In the present research, data extracted from the stress analysis of 81 finite element (FE) models, verified using experimental test results, was used to study the effects of geometrical parameters on the chord-side SCFs in multi-planar tubular XT-joints reinforced with internal ring Stiffeners subjected to two types of axial loading. Parametric FE study was followed by a set of the nonlinear regression analyses to develop four new SCF parametric equations for the fatigue analysis and design of axially loaded multi-planar XT-joints reinforced with internal ring Stiffeners.

This study aims to enhance the performance of explosion-proof doors by analyzing the structure, arrangement, and features of their Stiffeners. Numerous numerical models were developed to assess how the above parameters affect the performance of Rectangular doors under blast loads. The modeled doors consist of Stiffeners on their inner face that help them absorb energy and reduce displacement. An optimization process was also carried out to determine the best number and thickness of Stiffeners that can minimize displacement while optimizing steel consumption. The analysis revealed that using a non-parallel stiffener can decrease the displacement of the door's center by about 30% while maintaining the same weight. Moreover, the optimal number of Stiffeners depends on their thickness. If the thickness of the stiffener is less than 25% of the door panel's thickness, seven Stiffeners should be used. If the thickness is between 25% to 40%, five Stiffeners are optimal. When the thickness ranges from 40% to 60%, three Stiffeners are sufficient, and if the thickness is greater than 60%, one stiffener will provide the best functionality for the explosion-proof door.

Concrete Filled Double Steel Tubes are mostly used in bridge piers, tall buildings, offshore and coastal structures and power transmission towers. Finite element analyses via ABAQUS software have been performed aiming to evaluate the strength, ductility and plastic deformation of CFDST columns with different hollow ration and Stiffeners configurations. According to analyses results more strength and high ductility levels can be provided decreasing the composite section hollow and increasing Stiffeners thickness. More stiffener plates with larger dimensions result in more strength and stiffness in composite columns due to increase in concrete confinement and adjoint interaction of steel and concrete. It also raises plastic deformation level of the columns and postpone the local buckling.