Position Of Stiffeners Research Articles

Fracture Analysis of Stiffened Panels Under Combined Tensile, Bending, and Shear Loads

The objective is to present the formulation of numerically integrated modified virtual crack closure integral technique for concentrically and eccentrically stiffened panels for computation of strain-energy release rate and stress intensity factor based on linear elastic fracture mechanics principles. Fracture analysis of cracked stiffened panels under combined tensile, bending, and shear loads has been conducted by employing the stiffened plate/shell finite element model, MQL9S2. This model can be used to analyze plates with arbitrarily located concentric/eccentric stiffeners, without increasing the total number of degrees of freedom, of the plate element. Parametric studies on fracture analysis of stiffened plates under combined tensile and moment loads have been conducted. Based on the results of parametric,studies, polynomial curve fitting has been carried out to get best-fit equations corresponding to each of the stiffener positions. These equations can be used for computation of stress intensity factor for cracked stiffened plates subjected to tensile and moment loads for a given plate size, stiffener configuration, and stiffener position without conducting finite element analysis.

Free Vibration Analysis of Composite Hat-stiffened Panels By Method of Finite Elements

Free vibration analysis of laminated composite plates/shells stiffened with ‘open’ and ‘closed’ type sections as stiffeners have been carried out in the present investigation. The plate/shell has been analyzed using eight noded isoparametric shell elements and the stiffeners have been modeled using three noded isoparametric curved beam elements. There is no restriction on the positioning of stiffener elements within a shell element. The stiffness and mass matrices of the stiffener and plate/shell elements are calculated irrespective of the stiffener position within the shell element. A unified formulation describing the rigidity matrix of laminated stiffeners having open (rectangular, ‘T’, ‘L’, and ‘I’ shaped) and closed type (hat or box shaped) sections has been presented. Free vibration analysis of laminated plates/shells with open and closed section stiffeners have been analysed using the method of finite elements. Numerical results for the free vibration analysis solved by the present formulation are presented and compared with published results.

Buckling and vibration of stiffened plates subjected to partial edge loading

The buckling and vibration characteristics of stiffened plates subjected to in-plane partial and concentrated edge loadings are studied using finite element method. The initial stresses are obtained considering the pre-buckling conditions. Buckling loads and vibration frequencies are determined for different plate aspect ratios, edge conditions and different partial non-uniform edge loading cases. The non-uniform loading may also be caused due to the supports on the edges. The analysis presented determines the stresses all over the region for different kinds of loading and edge conditions. In the structural modelling, the plate and the stiffeners are treated as separate elements where the compatibility between these two types of elements is maintained. The vibration characteristics are discussed and the results are compared with those available in the literature. Buckling results show that the stiffened plate is less susceptible to buckling for position of loading near the supported edges and near the position of stiffeners as well.

Optimum Stiffener Layout for the Reduction of Vibration and Noise of Gearbox Housing

Dynamic excitation from the gears generates vibration modes in the gearbox which causes radiation of unwanted structure-borne noise. To reduce the noise as well as the vibration, the stiffened plate construction is frequently used for the housing, where the rib stiffener layout is the key to this design. In this paper, the most effective position of stiffeners in order to reduce the vibration and noise radiation is searched and discussed. The analysis considers first a plate fixed at edges and excited at its center, and then a simplified rectangular gearbox excited at the shaft bearing locations. The housing of a simplified single-stage gearbox is modeled by triangular finite shell elements. It is excited by a set of harmonic forces which are applied at the bearing positions. The rib stiffener is modeled by beam elements, and its optimum layout is searched by a genetic algorithm. The vibration energy is adopted as the objective function to be minimized for the design for low vibration. On the other hand, the radiated sound power is the objective function for low noise. Although the noise is caused by the vibration, the optimum stiffener layout to realize low noise is not always identical to the layout that yields low vibration because of the difference in radiation efficiency. This is numerically clarified first from the viewpoint of the vibration mode of a plate. In the case of the design for the gearbox housing concerned, the vibration mode which causes the difference in radiation efficiency is not presented. Consequently, the optimum stiffener is placed along the line from the point of excitation to a fixed point, which reduces the vibration deflection of the faces with bearings as well as the in-plane displacement of the bearings.

Nonlinear FE analysis of longitudinally stiffened girder webs under patch loading

The ultimate load behavior of longitudinally stiffened girder webs under patch loading is studied here by means of a nonlinear finite element analysis. Large-deflection effects and initial shape imperfections are taken into account. The influence of the slenderness of the directly loaded web panel on the patch loading capacity is studied in depth, together with the size of the loaded flange. In addition, the influence of stiffener rigidity is also analyzed. This study was aimed at finding an optimum position of longitudinal stiffeners for patch loading. Currently, designers use the value recommended for bending, i.e. one-fifth of girder depth. The results presented here show that a stiffener located closer than one-tenth of the girder depth significantly increases the load carrying capacity of the plate girder due to a decrease in the slenderness ratio of the web panel between the loaded flange and the longitudinal stiffener.

Transient Analysis of Composite Cylindrical Shells with Ring Stiffeners

The theoretical method is developed to investigate the effects of ring stiffeners on free vibration characteristics and transient response for the ring stiffened composite cylindrical shells subjected to the impulse pressure Loading. In the theoretical procedure, the Love's thin shell theory combined with the discrete stiffener theory to consider the ring stiffening effect is adopted to formulate the theoretical model. The concentric or eccentric ring stiffeners are laminated with composite and have the uniform rectangular cross section. The modal analysis technique is used to develop the analytical solutions of the transient problem. The analysis is based on an expansion of the loads, displacements in the double Fourier series that satisfy the boundary conditions. The effect of stiffener's eccentricity, number, size, and position on transient response of the shells is examined. The results are verified by comparison with FEM results.

Optimum design of welded stiffened plates loaded by hydrostatic normal pressure

The optimal positions of horizontal stiffeners are computed considering the condition that the base plate parts, having equal thicknesses and loaded by bending moments, should be stressed to yield strength. The trapezoidal stiffeners are designed for bending using the stress and local buckling constraints. The optimal number of stiffeners is determined on the basis of material and fabrication cost calculations. It is shown by a numerical example that the nonequidistant stiffener arrangement gives 22% weight and 16–18% cost savings.

Estimation of Layerwise Elastic Parameters of Stiffened Composite Plates

For the first time, an investigation of stiffened and unstiffened multilayered composite plates has been conducted to determine the material property parameters of the plate as well as the stiffener from numerically simulated experimental modal data and finite element predictions, using model updating techniques. The problem is formulated as a global minimization of the error function, defined by the difference in undamped eigenvalues as well as mode shapes, as predicted from the finite element modeling compared to that obtained experimentally. The parameter estimation problem is solved using an iterative gradient-based minimization algorithm, which can start from any randomly selected set of initial parameters. The position, physical properties, and orientation of stiffeners create considerable variations in the modal properties as compared to the bare plates of similar construction. This makes each of the stiffened plate problems rather unique. A few simulated examples are presented, and the methodology is found to be robust, even in the presence of random noise.

ESTIMATION OF IN-PLANE ELASTIC PARAMETERS AND STIFFENER GEOMETRY OF STIFFENED PLATES

An investigation on stiffened plates has been conducted for the first time to determine the elastic parameters as well as the cross-sectional dimensions of rectangular stiffeners from experimental modal data and finite element predictions, using model-updating technique. The problem is formulated as a global minimization of the error function, defined by the difference in modal properties as predicted from the finite element modelling to that obtained “experimentally”. The parameter estimation problem is solved using an iterative-gradient-based minimization algorithm and can start from different randomly selected set of initial parameters. The Levenberg–Marquardt algorithm has been implemented to minimize the error function. Proper bounds are realistically chosen for the selection of the initial values of the parameters. The position, physical properties and orientation of stiffeners create considerable variations in the modal properties as compared with the bare plates of similar construction. This makes each of the stiffened plate identification problem rather unique. The position of stiffeners as well as its orientation makes certain measurement points more suitable for comparing analytical and experimental mode shapes. The optimum measurement set of co-ordinates, which can be used for the purpose of identification, is thus case specific. The geometrical properties of stiffener cross-section also affect the modes. Inclusion of different sets of modes in noisy environment and the differences in the estimated parameters are studied. A few simulated examples are presented to investigate the uniqueness and convergence of results. The methodology is found to be very accurate and robust.

EVOLUTIONARY OPTIMIZATION OF MECHANICAL STRUCTURES

In this paper an optimization method for mechanical structures, based on a combination of genetic algorithms and neural networks (NN), is discussed. The NN is used as an approximation of the finite element analysis. Three examples show that using these methods in order to optimize mechanical systems is an efficient way. Examples presented are optimization of the position of dampers on beams, optimization of the position of stiffeners on plates or shells, and optimization of the damping by viscoelastic material constraints.

Tests of Profiled Steel Decks with V‐Stiffeners

The size and position of intermediate stiffeners in the compression flanges of thin‐walled profiled steel decks exert a strong influence on the dominant buckling mode of the flange. The ability of the deck to provide both high load‐carrying capacity before the onset of elastic buckling and a high ultimate‐load capacity may therefore be affected. A program of tests to determine the effectiveness of intermediate stiffeners in controlling buckling modes is undertaken. A series of specimens are loaded in pure bending resulting in various buckling waveforms prior to ultimate failure through a plastic collapse mechanism. The experimentally determined buckling stresses are found to be comparable with studies performed using a finite‐strip numerical analysis in which both local, and distortional buckling modes are predicted. A simplified design procedure for distortional buckling is proposed. The existing design procedure for local buckling in the Australian Standard AS1538‐1988 is confirmed.

Computer-aided design of hydraulic press structures

Hydraulic presses represent 3-D complex structures for which an exact analytical method of stress and deformation analysis is cumbersome and time-consuming. In order to reduce core memory requirement and the cost of computation, a simplified plane stress (PS) FEM model for a 918 kN hydraulic press structure (welded frame) has been identified for its analysis. The patterns of deformations and stresses are in fair agreement with those obtained by 3-D analysis. Although the PS model of analysis is not valid for obtaining actual values for complex structures, it has been used in making a comparative study of the behaviour of the structure. The factors considered are fillet, edge cutting, provision of openings, change in position of stiffeners and eccentric loading.

Optimization of Stiffening Rings' Position in Welded Tubular X-Joint

Summary Experimental results are presented to show that the position of the stiffening rings in welded tubular X-joints has a great impact on the value of the stress concentration factor (SCF) at the hot spot as well as its location. Preliminary guidelines for an optimal ring position are proposed. proposed. Introduction In offshore structures, such as semisubmersible drilling vessels and fixed platforms, tubular members comprise the main load-carrying components. The platforms, tubular members comprise the main load-carrying components. The design of joints between these tubular members is complicated because the radial flexibility of the tube walls leads to significant stress concentrations. Since many of these structures are subjected to alternating loads, the presence of stress concentrations can lead to an early fatigue failure. Ring stiffeners often are used as a means of reducing the SCF and thus increasing the fatigue life. This has been confirmed by the results of Maeda et al. and Matoba et al. The effect of the position of ring stiffeners on the maximum SCF value and, hence, the fatigue life is, to my knowledge, not available in the open literature. This paper represents a preliminary study of the effect of positioning of both internal and external ring stiffeners on the value and positioning of both internal and external ring stiffeners on the value and the location of the maximum SCF. It should be recognized that this paper is not intended to give a generalized recommendation for the optimal ring position but rather to alert designers and fabricators to the danger of position but rather to alert designers and fabricators to the danger of unoptimized position. Poor positioning of the rings can result in very little improvement in the state of stress as well as the expense and drawbacks associated with welding. Experimental Details The experiments were conducted on welded tubular X-joints with an angle of intersection equal to 900 (this joint also is classified as double-T joint). JPT p. 328