Shape Of Stiffeners Research Articles

Test Analysis of Stiffened T-Stub Connections

To investigate the effect of stiffener on the stiffness and strength of T-stubs, 3 T-stub connections without stiffeners and 6 stiffened T-stub connections with varied shape and thickness of stiffeners were tested monotonically. The load carrying capacity, relative deformations of endplates and strains on the stiffeners and endplates were measured. The load-deformation curves of the connections and load-strain curves were presented. The test results showed that the commonly used stiffeners in current Chinese practice often yield or/and buckle prematurely. And the stiffener designed by the method can meet the requirement in CECS102-2002, which demands that the stiffener should be able to force the extended portion of endplates from clamped-free boundary to plates fixed on two adjacent boundaries.

補強材のレイアウトを考慮した船体構造最適化に関する研究

The optimization of the ship structure with design variables of the plate thickness and the shape of stiffener is a popular study filed. But, the optimization of the structure with the design valuables of the number and the position of stiffners are necessary for obtaining a better optimal solution. Therefore, the optimization with theses design valuables is performed in this paper. The optimization with theses design variables needs a lengthy calculation time because recreating FEM models and re-analyzing must be performed. In order to overcome this problem, the calculation method for evaluation of the strength of structures without recreating FEM models and the method of reducing calculation amount of FEM are proposed. There is another problem in optimization part. Since the number of stiffeners is changed the number of design variables may vary during an optimization process. In order to solve this problem, an effective optimization method for this problem is proposed. The structure which imitate a double hull part of oil tanker is selected for target of optimization. These proposed methods are applied to this optimization model and their effectiveness an verified.

Hybrid GAを用いたスティフナーを有する大型構造物の最適化に関する研究

An optimization technique using the hybrid GA for large structures in which a lot of stiffeners are attached is proposed in this paper. The object function is the mass of structure and the design variables are the number and the position of stiffeners, the shape of stiffener and the thickness of plate. These design variables make a combinational optimization problem for which genetic algorithm is effective. However, this optimization problem includes the position of stiffener and the thickness of plate which are kinds of continuous design variables. A lots of bits are needed for expressing continuous design variables by strings of genetic algorithm in order to have reasonably small increments of them, which results in a large calculation amount. In order to overcome this problem, a hybrid GA is introduced in this paper. Hybrid GA is optimization method which combines GA with another optimization technique which handles continuous design variables. The relation among the thickness of plate, the span of stiffeners attached on the plate, the deflection and the stress of plate are introduced in order to predict suitable design variables in this added optimize technique. The proposed optimization method makes it possible to optimize continuous design variables, the position of stiffeners and the thickness of plate,with small calculation amount. Several selected problems are solved to show the capacity and validity of the proposed method.

3307 補強材の本数及び位置を最適化するための計算手法に関する研究(OS5-6 設計と最適化6,OS5 設計と最適化)

The optimization of the large structure with the layout of stiffener is considered by a new calculation method in this study. Many number of stiffener are attached to large structures. Optimization of the large structures with design variables of plate thickness and shape of stiffener is performed. However, in order to obtain a better optimal solution, the optimization of the structure with design variable of number of stiffener and allocation of stiffener is required. But, the optimization of structure with design variable of the number of stiffener and allocation of stiffener is not performed. There are two problems. The first problem is the FEM model. FEM models need some nodes at allocation of stiffener as a characteristic of FEM. When number of stiffener and allocation of stiffener are changed by the process of the optimization of the structure, number of nodes and allocation of nodes of FEM model is also changed. Therefore, in order to ensure consistency of mesh, it is necessary to remake FEM model. In order to optimize structural, it is necessary to examine many propositions for design. However it is difficult to create and analyze the proposition for design of many numbers in restricted time. The second problem is the optimization method. When the number and allocate of stiffeners are changed, the stricture is modified and the number of design variables is changed. The optimization problem with changed number of design variables cannot be optimized by standard optimization methods. The methods of solving these problems are examined.

端部スチフナ補剛を施したH形断面梁の塑性変形能力

The H-shaped beams reinforced by the horizontal stiffeners at the beam end can be expected improvements in the plastic deformation capacity. The purpose of this paper is to show plastic deformation capacity of the H-shaped beams and to clarify the optimal stiffener shape. For this purpose, authors conduct cyclic loading tests on the several parameters ( length of the beam, thickness of the web and length, width and thickness of the stiffener ), and confirm the distinction of plastic deformation capacity related to the stiffener shape. Furthermore, in addition to the loading tests, by using the numerical analysis and the energy method, authors fix the required rigidity and the required length of stiffeners according to the demanded performance.

Optimum Design of Curvilinear Stiffened Panels with Stiffening Beams

The paper presents a framework for design and optimization of curvilinear stiffened panels with any cross-section shape of stiffener. Within this framework, the weight of stiffened panel applied complex loads, is minimized under the constraints of structural responses include global buckling, maximum stress and crippling. Then, a stiffened panel with two blade curvilinear stiffeners is optimized using this framework, and the optimum performs better than another existing design. Finally, it is concluded that stiffening beam is suitable for simulate stiffener sustains part of applied load directly.

흙댐 제체의 보강재 설치에 따른 월류붕괴 지연효과

현재 국내 저수지의 대부분(99.1 %)은 흙댐으로 이러한 형식은 건설비용이 저렴하고 다른 시공보다 시공성이 용이하여 많은 저수지 건설에 채택되었다. 그러나 흙댐은 월류 침투 현상에 취약하여 설계 홍수량을 초과한 홍수 발생 시 붕괴가능성이 높은 단점이 있다. 본 연구에서는 수리실험을 통해 이러한 흙댐 제체에 월류 붕괴가 발생할 경우에 대하여 제체 사면에 설치한 L형 T형 <TEX>$L^*$</TEX>형의 보강재 형태에 따른 붕괴 양상 변화를 분석하고, 무보강 제체에 비하여 보강재 설치 제체에서 붕괴지연으로 인한 피해감소 효과를 분석하였다. 그 결과 붕괴부에서 발생하는 흐름이 보강재와 충돌하여 분산됨으로 인해 에너지 감세효과를 갖게 되어 토사의 침식속도가 감소하고 이에 따른 붕괴발달 속도가 지연되는 현상이 관찰되었다. 이러한 연구결과에 따라 보강재의 붕괴지연효과를 무보강 제체와 비교할 경우, 붕괴 발생에서 붕괴종료까지 약 1.73~2.29 배의 시간지연이 발생하였으며 첨두 유출량의 감소효과가 나타났다. 저수지 제체 붕괴는 붕괴부의 급속한 발달로 인해 이를 긴급히 보수하는 시간이 부족하여 큰 피해로 이어지게 된다. 사면에 보강재를 설치한 경우 제체 붕괴 지연효과로 인하여 긴급보수시간 및 인명구조시간의 확보가 가능하며, 첨두유출량 감소로 댐 하류부의 피해를 감소시키는 효과가 있어 저수지 붕괴에 대한 비상대처계획 수립시 기초자료로 활용할 수 있을 것으로 판단된다. Most embankment of the reservoirs (99.1 %) have been constructed in the earth filled type in Korea because the construction of this type is less expensive and simpler than others such as concrete one. However, it has to be reinforced the slope to prevent the breach due to overtopping or piping under unexpected flood conditions. This study has been analyzed the retardation effect using three types (L, T, <TEX>$L^*$</TEX> shape) of stiffener in order to reinforce embankment when they are collapsed by overtopping flow. Experimental results showed that L-type stiffener is the most effective in delaying the breaching of embankment and reducing the soil erosion when compared with others. The reinforced embankment breaching showed that time delay was occurred about 1.73 to 2.29 times and the peak flowrate was reduced compared to non-stiffener embankments due to energy dissipation by collision and less soil erosion. The embankment breaching mostly leads to major damages because of the lack of repair time. Thus, since these stiffeners can resist the rapid breach, it would be possible to earn the time to emergency repair and lifesaving, as well as reduction of damages of embankment in downward region with decreasing peak flowrate. Results from this study would be used for the basis when establishing the emergency action plan for the reservoirs on the verge of hazard.

2408 固有振動問題に対する補強リブ付きシェル構造の形状最適化手法

This paper presents a shape optimization method for the natural vibration problem of stiffened thin-walled or shell structures. The boundary shapes of stiffeners are determined under the condition where the boundary is movable in the inplane direction to the surface. The design problems deal with eigenvalue maximization problem and volume minimization problem, which are subject to a volume constraint and an eigenvalue constraint respectively. The both optimization problems are formulated as distributed-parameter shape optimization problems, and the shape gradient functions are derived using the material derivative method and the adjoint variable method. The optimal free-boundary shapes are obtained by applying the derived shape gradient functions to the H^1 gradient method for shells, which is a parameterfree shape optimization method proposed by one of the authors. Several design examples are presented to validate the proposed method and demonstrate its practical utility.

어레이 안테나 장착을 위한 단순화된 주익 구조의 복합재 모자형 보강재 최적설계

정찰 및 감시를 위한 어레이 안테나가 내장된 날개는 컷아웃이 수반되기 때문에 구조성능이 저하된다. 본 논문에서는 단순화된 복합재 날개에 어레이 안테나 탑재시 안테나성능 저하와 날개구조 성능 저하를 최소화할 수 있는 복합재 모자형 보강재의 두께에 대해 최적설계를 수행하였다. 최적의 모자형 보강재 형상 선정을 위하여 모자형 보강재의 웹 경사도와 플랜지의 길이에 변화를 주어 상용 유한요소해석 프로그램을 이용하여 구조 해석을 수행하였다. 복합재 모자형 보강재형상에 대하여 응력과 좌굴에 대한 구속조건으로 상용 최적화 프로그램인 VisualDOC와 상용 유한요소해석 프로그램을 이용하여 최적화를 수행하여 보강재의 두께를 결정하였다. The structural performance is degraded in case of embedding the array antenna for reconnaissance and surveillance into the wing skin structures. In this paper, the optimal design for the thickness of composite hat-shaped stiffener which is reinforced embedded array antenna on the simplified composite wing box was conducted. To select the basic shape of hat-shaped stiffener, structural analysis was carry out using the commercial finite element analysis program while changing the web slope and flange length of hat-shaped stiffener. The optimal thickness of the composite hat-shaped stiffeners was determined by using commercial optimization program such as VisualDOC and commercial FEA program with considering stresses and buckling constraints.

Demand on Stiffeners in Stiffened Extended End-Plate Connections

The paper reports a study on the effect of stiffeners on stiffness and strength of T-stubs to find out the strength and stiffness demand on stiffeners. The tensile capacity of triangular stiffeners is first analyzed and is compared with that of a long rectangular one, an efficiency factor formula is proposed. A triangular stiffener with length-to-width ratio of 2:1 is suggested be used in practice. By requiring stiffened T-stubs have a similar strength and rigidity to the unstiffened T-stub having 41% percent thicker endplate, it is found that the stiffener must be able to transmit 85% of the total tension force, based on this requirement, the stiffener thickness is determined. Three unstiffened T-stub connections and six stiffened T-stub connections with 1:1 and 2:1 triangular stiffeners were tested monotonically. The load carrying capacity, relative deformations of endplates and strains on stiffeners and endplates were measured. The load-deformation curves of the connections and load-strain curves were presented. The influences of different shapes of stiffeners on loading resistance and rotational stiffness characteristic of stiffened T-stub connections were evaluated. The test results showed that the short stiffeners in current Chinese practice yield or/and buckle prematurely, and the stiffeners designed by the proposed method in this paper are able to change the extended portion of endplates from one side clamped to 2 panels fixed on two adjacent sides.

Multidisciplinary optimization of a stiffened shell by genetic algorithm

Vibration analysis of simply supported rotating cross-ply laminated stiffened cylindrical shell is performed using an energy approach which includes variational and averaging method. The stiffeners include rings and stringers. The equations are obtained by Rayleigh-Ritz method and Sander’s relations. To validate the present method, the results are compared to the results available in other literatures. A good adoption is observed in different type of results including isotropic shells, rotating laminated shells, stiffened isotropic shells and stiffened laminated shells. Then, the optimization of parameters due to shell and stiffeners is conducted by genetic algorithm (GA) method under weight and frequency constraints. Stiffener shape, material properties and dimensions are also optimized.

Collision Analysis of Ship Side

Structural design of ships against collision requires prediction of the extent of damage to stiffened plates subjected to impact. In ship structures, stiffened plates are furnished with vertical or horizontal stiffeners to sustain conventional loads such as shearing, bending and local buckling. The consideration of collision in ship structural design is especially important for tankers where accidents may cause serious environmental pollution. In predicting the extent of collision damage, FE modeling of stiffened plates using ABAQUS software is applied to demonstrate different collision scenario. Typical stiffened plates of tankers in service with different configurations of stiffeners are used to examine absorbed energy in each case. The aim of this paper is to examine the stiffener shape that absorbs more deformation energy.

Analysis and optimization of externally stiffened crush tubes

Nonlinear finite element analysis is used to investigate the quasi-static axial collapse response of cylindrical tubes which are externally stiffened by multiple identical rings. The rings divide the long tube into a series of short thin-walled tubes. It is assumed that the size and shape of integral stiffeners are controlled through a machining process. The effects of various geometric parameters such as wall thickness, ring spacing, ring thickness and width on the collapse response, crush force and energy absorption of monolithic, integrally stiffened steel tubes are studied and used as a general framework for a design optimization study. Through design and analysis of computer experiments, global metamodels are developed for the mean crush force and energy absorption, using the radial basis function approximation technique. Using both single- and multi-objective design optimization formulations, optimum designs for different response characteristics are found. The crush mode in the form of progressive collapse or buckling is found to heavily depend on the ratio of stiffener spacing to stiffener height as well as the ratio of wall thickness to stiffener thickness. The optimization results show the viability of externally stiffened tubes as efficient energy absorbers.

Optimum Vibration Control Design of a Light Weight Structure in Wide Frequency Domain

Although there are many studies on vibration reduction of a panel by making use of constrained viscoelastic materials, there is almost no research on vibration reduction for light weight paddle throughout the low to high frequency domains whose dynamic properties might be affected by the weight and rigidity of constrained viscoelastic damping materials. There is also little work on optimizing both parameters of constrained viscoelastic materials and light reinforced structural materials simultaneously. In this research, above-mentioned lightweight structure such as a solar paddle of a small satellite is of interest. For a lightweight structure like a solar paddle, the use of vibration control devices is not practical because of its cost and increase of mass, and then large modification of structure is not also practical. Furthermore, large response in high frequency domain is very critical for such structures from the viewpoint of fatigue. The objective of this research is to propose an optimum vibration control design method applicable throughout low to high frequency domains by considering parameters of the thickness, pasting regions for the constrained viscoelastic materials, and the position and cross section shape of stiffener simultaneously by making use of Response Surface Method (RSM) and Genetic Algorithm (GA). Through the design of a solar paddle of a small satellite, the effectiveness of the proposed method was demonstrated in comparison with other four methods including a conventional way.

Multiobjective optimization of orthogonally stiffened cylindrical shells for minimum weight and maximum axial buckling load

In the present research, the weight and axial buckling optimization of orthogonally stiffened cylindrical shells is carried out by the Genetic Algorithm. Constraints include two nondimensional functions of weight and buckling load in such a way that the stiffened shell has no increase in the weight and no decrease in the buckling load with respect to the initial unstiffened shell. In analytical solution, the Rayleigh–Ritz energy procedure is applied and the stiffeners are treated as discrete members. The optimization is implemented for shells with simply supported end conditions stiffened by four shapes of stiffeners including rectangular-, cee-, I-, and hat-shaped ones. The results show that the I-section and rectangular-section stiffeners are, respectively, the most and the least efficient in designing stiffened cylindrical shells for minimum weight and maximum critical axial buckling load.

Influence of longitudinal stiffeners on elastic stability of girder webs

In this paper, linear buckling analyses of plates with longitudinal stiffeners having various shapes and positions and subjected to axial force, in-plane bending and shear are developed. The aim is to give some new practical insights about the shape and optimum position of longitudinal stiffener in webs when axial force, bending moment and shear act. By means of a comprehensive numerical investigation, some practical issues for buckling phenomena in stiffened plates, taking into account (a) dimensions and shape (square and rectangular) of the plate, (b) dimensions and shape of the stiffener (with open and closed cross-sections), (c) location of the stiffener, and (d) load configuration (uniform compression, pure bending, combinations of axial compression and bending, and shear) are developed.

Compressive Strength of Stiffened Plates With Imperfections: Simple Design Equations

The behavior and ultimate compressive strength of stiffened plates with imperfections have been investigated in this paper using a nonlinear finite element method. The imperfections considered consisted of initial deflection and residual stresses. Several types of initial deflections were investigated, including those that may initiate stiffener column buckling and stiffener tripping. Extensive parametric study was conducted in order to systematically determine the impact of these initial imperfections on the ultimate compressive strength of stiffened plates of various geometric properties and stiffener shapes. The objective of the study was to develop simple design equations for determining ultimate strength based on finite element parametric study. The developed algebraic equations reflect the impact of imperfections on ultimate strength. A Perry-Robertson type equation was developed to incorporate the influence of the imperfections. It was found that under certain conditions a hybrid type mode of failure was necessary to accurately represent the behavior of stiffened plates with imperfections, in addition to the usual plate and stiffener failure modes. It was also found that column buckling type initial deflection is the most important form of imperfection.

Free vibration and buckling response of hat-stiffened composite panels under general loading

The paper presents finite element free vibration and buckling analysis of laminated hat-stiffened shallow and deep shells using arbitrarily oriented stiffener formulation. Modified approach for modelling the curved stiffener is implemented using necessary transformations. A simplified stiffener formulation is presented to accommodate various shapes of stiffener shapes in developing the rigidity matrix for the finite element formulation. Investigation has been carried out on free vibration and buckling analyses of laminated composite stiffened shell structures with laminated open section (rectangular or ‘T’ shaped) and closed section (‘hat’ shaped) stiffeners. Parametric study on the hat-stiffened panels for the free vibration and buckling analyses confirms that the closed section stiffener being torsionally rigid is found to show better performance over open section stiffeners.

Optimization of layout and shape of stiffeners in 2D structures

The problem of layout and shape optimization of stiffeners in plates loaded in plane and in bending Kirchhoff’s plates is considered in the paper. Two types of reinforcement are analyzed here, namely introduction of elements made of stiffer material like fibers or beams and introduction of ribs. The problem of minimization (maximization) of arbitrary objective functional of displacements, strains, stresses or reactions with constraint imposed on the structure cost is considered. Using adjoint method, expressions for sensitivities with respect to introduction of stiffeners are derived and on this basis conditions of modification are formulated. In order to find optimal reinforcement, heuristic algorithm is proposed in the paper. At first, using information from sensitivity analysis, initial localization of a new fiber or rib is determined. Next, in order to correct their positions and to determine other parameters characterizing stiffened structure standard optimization is performed. Usually, optimal position of the stiffener only a little differs from the initial position. Numerical examples illustrate applicability of the method.

Postbuckling Failure Behaviours of Hat-Stiffened Composite Panels with Different Bonding Methods

Postbuckling failure behaviors and strength were investigated in compression tests of the hat stiffened composite panels manufactured with different bonding methods and different stiffener section shapes. The skin-stiffener separation loads, separation failure behaviors and final collapse loads were different with respect to bonding methods and stiffener shapes. As the separation failure was initiated early and propagated larger area, collapse loads and structural performance of the panels decreased. The test results showed that the co-curing with or without adhesive film and open type stiffeners were most beneficial for the postbuckling strength.