<p>Buckling and postbuckling of plates and stiffened panels are considered. Computational models for direct calculation of the response are developed using large deflection plate theory and energy principles. Deflections are represented by trigonometric functions. All combinations of biaxial in-plane compression or tension, shear, and lateral pressure are included in the formulations. The procedure is semi-analytical in the sense that the incremental equilibrium equations are derived analytically, while a numerical method is used for solving the equation systems, and for incrementation of the solution.</p><p>Unstiffened plate models are developed both for the simply supported case and for the clamped case. For the simply supported case the material types considered are isotropic elastic, orthotropic elastic, and elastic-plastic. Two models are developed for analysis of local buckling of stiffened plates, one for open profiles and one for closed profiles. A global buckling model for stiffened panels is developed by considering the panel as a plate with general anisotropic stiffness. The stiffness coefficients are input from the local analysis. Two models are developed for combined local and global buckling, in order to account for interaction between local and global deflection. The first is for a single stiffened plate, and uses a column approach. The second is for a stiffened panel with several stiffeners.</p><p>Numerical results are calculated for a variety of plate and stiffener geometries for verification of the proposed model, and comparison is made with nonlinear finite element methods. Some examples are presented. For all models, the response in the elastic region is well predicted compared with the finite element method results. Also, the efficiency of the calculations is very high. Estimates of ultimate strength are found using first yield as a collapse criterion. In most cases, this leads to conservative results compared to predictions from finite element calculations. </p>

Because of their high strength to weight ratio, stiffened steel plates are often used in light structures where plates are placed into compression. The stability of steel plates stiffened with longitudinal tee-shaped stiffeners and subjected to uniaxial compression or combined axial compression and out-of-plane bending formed the basis for this research project. The research was conducted to develop a simple approach to assess the post-buckling behaviour of stiffened steel plates and provide a limit states design procedure that accounts for the post-buckling stability in the assessment of the resistance factor. The behaviour of stiffened plates was investigated using a finite element model that had been validated through comparison with test results. An exhaustive parametric study, including 1440 finite element analyses, was conducted to investigate the strength and behaviour of stiffened steel plates. A virtual work model was developed to explain the effect of the formation of a plastic hinge mechanism on the post-buckling strength and behaviour. Combined with the numerical results, the theoretical model confirms that the plastic hinge mechanism can cause a sudden loss of capacity. The required lateral deflection for a plastic hinge development can be calculated using the virtual work model for prediction of the unstable behaviour. Based on a better understanding of the behaviour of stiffened steel plates, a set of design equations were developed to calculate the strength of stiffened steel plate subjected to compression in the direction of the stiffener and out-of-plane bending. The proposed design equations were compared with current design guidelines through a comparison of the design approaches with the finite element analysis results. The proposed method showed much better accuracy than the current design approaches. A reliability analysis was conducted to provide appropriate resistance factors for limit states design. Due to the complexity of the design formulas, the Monte Carlo simulation technique was used to generate the statistical distributions of the predicted strength. The second-moment method was used to calculate the resistance factors for different values of safety index. The resistance factor varied from 0.90 to 0.65 for values of safety index from 2.5 to 4.5, respectively. / Structural Engineering

Buckling and postbuckling of plates and stiffened panels are considered. Computational models for direct calculation of the response are developed using large deflection plate theory and energy principles. Deflections are represented by trigonometric functions. All combinations of biaxial in-plane compression or tension, shear, and lateral pressure are included in the formulations. The procedure is semi-analytical in the sense that the incremental equilibrium equations are derived analytically, while a numerical method is used for solving the equation systems, and for incrementation of the solution. Unstiffened plate models are developed both for the simply supported case and for the clamped case. For the simply supported case the material types considered are isotropic elastic, orthotropic elastic, and elastic-plastic. Two models are developed for analysis of local buckling of stiffened plates, one for open profiles and one for closed profiles. A global buckling model for stiffened panels is developed by considering the panel as a plate with general anisotropic stiffness. The stiffness coefficients are input from the local analysis. Two models are developed for combined local and global buckling, in order to account for interaction between local and global deflection. The first is for a single stiffened plate, and uses a column approach. The second is for a stiffened panel with several stiffeners. Numerical results are calculated for a variety of plate and stiffener geometries for verification of the proposed model, and comparison is made with nonlinear finite element methods. Some examples are presented. For all models, the response in the elastic region is well predicted compared with the finite element method results. Also, the efficiency of the calculations is very high. Estimates of ultimate strength are found using first yield as a collapse criterion. In most cases, this leads to conservative results compared to predictions from finite element calculations.

No description available.

Statistical Energy Analysis (SEA) is one of the methods in literature to estimate high frequency vibrations. The inputs required for the SEA power balance equations are damping and coupling loss factors, input powers to the subsystems. In this study, the coupling loss factors are derived for two and three plates joined with a stiffener system. Simple formulas given in the literature for coupling loss factors of basic junctions are not used and the factors are calculated from the expressions derived in this study. The stiffener is modelled as line mass, Euler beam, and open section channel having double and triple coupling. Plate is modelled as Kirchoff plate. In the classical SEA approach the joint beam is modelled as another subsystem. In this study, the beam is not a separate subsystem but is used as the characteristics of the joint and to calculate the coupling loss factor between coupled plates. Sensitivity of coupling loss factors to system parameters is studied for different beam approaches. The derived coupling loss factors and input powers are used to calculate the subsystem energies by SEA. The last plate is joined to the first one to simulate the fuselage structure. A plate representing floor structure and acoustic volume are also added. The different modelling types are assessed by applying pressure wave excitation. It is shown that deriving the parameters as given in this study increases the efficiency of the SEA method.

The Element Free Galerkin (EFG) method, which is based on the Moving Least Squares (MLS) approximation, is developed here for vibration, buckling and static analysis of homogenous and FGM plate with curvilinear stiffeners. Numerical results for different stiffeners configurations and boundary conditions are presented. All results are verified using the commercial finite element software ANSYS® and other available results in literature. In addition, the vibration analysis of plates with curvilinear stiffeners is carried out using Ritz method. A 24 by 28 in. curvilinear stiffened panel was machined from 2219-T851 aluminum for experimental validation of the Ritz and meshfree methods of vibration mode shape predictions. Results were obtained for this panel mounted vertically to a steel clamping bracket using acoustic excitation and a laser vibrometer. Experimental results appear to correlate well with the meshfree and Ritz method results. In reality, many engineering structures are subjected to random pressure loads in nature and cannot be assumed to be deterministic. Typical engineering structures include buildings and towers, offshore structures, vehicles and ships, are subjected to random pressure. The vibrations induced from gust loads, engine noise, and other auxiliary electrical system can also produce noise inside aircraft. Consequently, all flight vehicles operate in random vibration environment. These random loads can be modeled by using their statistical properties. The dynamical responses of the structures which are subjected to random excitations are very complicated. To investigate their dynamic responses under random loads, the meshfree method is developed for random vibration analysis of curvilinearly-stiffened plates. Since extensive efforts have been devoted to study the buckling and vibration analysis of stiffened panel to maximize their natural frequencies and critical buckling loads, these structures are subjected to in-plane loading while the vibration analysis is considered. In these cases the natural frequencies calculated by neglecting the in-plane compression are usually over predicted. In order to have more accurate results it might be necessary to take into account the effects of in-plane load since it can change the natural frequency of plate considerably. To provide a better view of the free vibration behavior of the plate with curvilinear stiffeners subjected to axial/biaxial or shear stresses several numerical examples are studied. The FEM analysis of curvilinearly stiffened plate is quite computationally expensive, and the meshfree method seems to be a proper substitution to reduce the CPU time. However it will still require many simulations. Because of the number of simulations may be required in the solution of an engineering optimization problem, many researchers have tried to find approaches and techniques in optimization which can reduce the number of function evaluations. In these problems, surrogate models for analysis and optimization can be very efficient. The basic idea in surrogate model is to reduce computational cost and giving a better understanding of the influence of the design variables on the different objectives and constrains. To use the advantage of both meshfree method and surrogate model in reducing CPU time, the meshfree method is used to generate the sample points and combination of Kriging (a surrogate model) and Genetic Algorithms is used for design of curvilinearly stiffened plate. The meshfree and kriging results and CPU time were compared with those obtained using EBF3PanelOpt. / Ph. D.

No description available.

<p>A large rectangular industrial duct consists of plates stiffened with parallel wide flange sections. The plates along with stiffeners acts to resist the pressure loads and to carry other loads to the supports. The behaviours of the components of large industrial ducts are significantly different from the behaviours on which the current design methods are based on. Investigation presented herein deals with the design methods for spacing stiffeners, proportioning stiffeners and calculating shear resistance of side panel.</p> <p>Current method of spacing stiffeners is based on large deflection plate theory. A parametric study was conducted on dimensionless parameters identified in order to benefit from membrane action in partially yielding plate for spacing stiffeners. Design equations were established in terms of dimensionless pressure, plate slenderness and normalized out-of-plane deflection for three cases namely; 0%, 16.5% and 33% of through thickness yielding of the plate. Results show that approximately 50% increase in stiffener spacing when yielding of 16.5% of thickness is permitted.</p> <p>Under suction type pressure load, the unsupported compression flange and restrained tension flange lead to distortional buckling of the stiffeners. The current methods do not address distortional buckling adequately. A parametric study on dimensionless parameters governing the behaviour and strength of stiffened plat panels was conducted. The study indicated that the behaviour and strength of the stiffened panels could be a function of web slenderness and overall slenderness of the stiffener. The study also identified the slenderness limit of stiffener web for which the stiffener reaches the yield moment capacity. This study demonstrated the conservatism of current method. Finally a method was established to calculate the strength of stiffened plate panel subjected lateral pressure.</p> <p>Side panels adjacent to the supports transfer large amount of shear to the supports and, in addition, resist internal pressure. Currently the design of side panels for shear is based on the methods used for the web of fabricated plate girders. The behaviour and the characteristics between the web of plate girder and the thin side panels are significantly different. A parametric study was conducted on dimensionless parameters identified. It was concluded that the plate slenderness dominates the normalized shear strength of stockier side panels. The aspect ratio and plate slenderness influence the normalized shear strength of slender side panels. Design methods to calculate the shear strength of side panels were proposed.</p> / Doctor of Philosophy (PhD)