Shape Of Stiffeners Research Articles

Corrected method for scaling the dynamic response of stiffened plate subjected to blast load

Test on a small scaled model is an effective approach to predict the dynamic response of full scale structure under blast loadings. However, the geometric dimensions of specimens cannot simply comply with complete geometrical similarity due to manufacture or test restrictions. It would result in the difference structural performance between the full and small scaled models. This paper proposed a corrected similarity relationship of the dynamic behaviour between prototype and replica of stiffened plates subjected to blast load, in which both the thickness of the plate and the configuration (cross-sectional shape) of stiffeners are distortedly scaled-down (double distorted geometric scaling factors). Firstly, based on the mesh convergence study and comparing with results from experimental tests, a numerical method in predicting the confined blast load and dynamic response of structure was verified, which provides a reliable means to determine the dynamic behaviour of stiffened plate designed by the corrected similarity criterion of this paper. Then, the influence of altering the stiffener configuration on the dynamic response of stiffened plates was analysed and on the basis of it, a criterion for scaling the stiffener is proposed to help design a stiffener-distorted model from prototype structure. In addition, a method for scaling the double-parameter distortedly small scaled model is proposed to predict the dynamic response of the prototype. Finally, two sets of examples of both the small size and prototype stiffened structures subjected to blast load were analysed by using the presented method. It is shown that the replica developed by applying the present method is able to accurately predict the behaviour of the full-size stiffened plates, even when the thickness of the plate and the configuration of the stiffeners are distortedly scaling down with different factors.

Simultaneous modeling and structural analysis of curvilinearly stiffened plates using an isogeometric approach

This paper aims to study the buckling and bending analysis of curvilinearly stiffened plates by using an isogeometric approach. First-order shear deformation theory is adopted to model the behaviors of stiffened plates. Based on the employed approach, it is easy to model stiffeners with different sizes and layouts, since the degrees of freedom for the whole structure are integrated into those of the original plate leading to a relatively low computational cost. The performance of the proposed approach is validated via a couple of benchmark problems available in the literature, and the effect of different parameters including bending stiffness, relative mass, cross section, and shape of stiffener on the buckling and bending behavior of curvilinearly stiffened plates is investigated. The results show the relative high accuracy of this method using fewer degrees of freedom for stiffeners, which is beneficial in optimization procedures.

Stiffened concrete-filled steel tubes: A systematic review

Abstract The behavior of concrete filled steel tubular (CFST) elements with different types of stiffening measures has been wildly investigated during the past two decades through experimental, analytical, and numerical approaches. The previous studies highlighted the importance of the presence of internal and external stiffeners to enhance the structural performance of CFST elements under different loading conditions. In this paper, a systematic methodology is proposed in order to rigorously review the current knowledge in literature about stiffened CFSTs. The reviewed studies include tests of static axial compression, pure bending and combined of static loading actions as well as the cyclic behavior and the fire resistance. A coherent taxonomy regarding the research of stiffened CFSTs is proposed based on the loading conditions besides their cross-sectional shape and type of stiffeners. The study also presents a number of practical applications of stiffened CFSTs in different engineering projects. Finally, concluding remarks, current research gap and future research directions on stiffened CFST are provided and discussed.

Experimental and numerical analysis of stiffened curved plates as bottom flanges of steel bridges

This paper deals with the experimental and numerical evaluation of the buckling behaviour and ultimate resistance of stiffened transversally curved panels subjected to uniform axial compression. Furthermore, a verification procedure for curved stiffened panels is proposed that gives a good estimation of the maximum loads obtained from experimental and numerical tests. The procedure is in line with the design methodology of EN 1993-1-5, accounting also for panel curvature. Nine large-scale tests were performed on longitudinally and transversally stiffened plates made of high strength steel, namely S500 and S700. They were subjected to compressive stresses up to collapse. The nine specimens comprised of flat and curved plates that differed in material grade and geometric parameters, such as panel thickness, aspect ratio, size and shape of stiffeners. The effects of different parameters on the plate's resistance to pure compression are discussed. Moreover, a numerical model built in the general-purpose code ABAQUS is presented and verified against the test results regarding initial stiffness, ultimate resistance and failure mode. Numerical simulations (FEA), based on the test panel geometry, the measured initial geometric imperfections and elasto-plastic material characteristics from tensile tests, demonstrate very good agreement with experimental results.

An alternative approach for modal analysis of stiffened thin-walled structures with advanced plate elements

Nowadays, many vehicles and buildings are built using the structural concept of stiffened structure, in order to achieve greater strength with relatively less material. In the present work, a plate finite element with advanced higher-order kinematic field is proposed for the free-vibration analysis of stiffened thin-walled plate structures. A novel approach is introduced to simplify the modelization and assembling phase for the analysis of stiffened structures. The mechanical continuity between skin and stiffener deformed geometry is automatically verified with the present approach. On the basis of the Principle of Virtual Displacements, Equivalent-Single-Layer and Layer-Wise models related to linear up to fourth order variations of the unknown variables in the thickness direction are treated. The Mixed Interpolated Tensorial Components (MITC) method, in conjunction with the Finite Element Method (FEM), is employed to contrast the shear locking effect. Various stiffener shapes are considered for the assessment of the approach: T shape, double-T shape and Z shape. Several numerical investigations are carried out to validate and demonstrate the accuracy and efficiency of the present plate finite element for the modal analysis of stiffened structures, comparing the present results with those from classical finite element formulations based on solid elements available in commerical software.

Welding Distortion Characteristics of Door Openings According to Changing Shape of Stiffener

Welding Distortion Characteristics of Door Openings According to Changing Shape of Stiffener

Characterization and structural performance of hybrid fiber-reinforced composite deck panels

This paper presents the experimental and analytical investigation on the behavior of hybrid fiber-reinforced composite deck made up of glass and jute fibers embedded in vinyl ester matrix. Finite element evaluation of the flexural performance of the composite decks was carried out using ANSYS, FE software. It was observed that analytical evaluation underestimates the value of deflection of deck panels 1 and 2 by 10.91% and 18.57%, respectively, when compared to the experimental results. However, the value of strain obtained by FEA is appreciably higher than that observed during the experiment. The analytical evaluation of deck panels was further extended to HYFRP and GFRP (glass fiber-reinforced polymer) decks with varied cross sections obtained by changing the location and shape of stiffeners. The specifications stipulated by Ohio Department of Transportation (ODOT), USA, for FRP decks were used for evaluating the performance of deck panels. The values of maximum deflection and strain experienced by the deck panels with stiffeners at the web-flange joint were found to be less than that of deck panels provided with stiffeners at the center of top flange of each cellular unit. Out of the various configurations examined, the performance of decks with V-shaped stiffeners and combination of U- and V-shaped stiffeners at top and bottom web-flange joint were found to be best with substantially lower deflection and strain.

Hybrid Optimization of Curvilinearly Stiffened Shells Using Parallel Processing

With the advances being made in additive manufacturing, it is becoming increasingly possible to fabricate a broad class of complex-shaped designs for practical applications. This manufacturing capability has allowed structural designers to implement the use of bio-inspired curvilinear stiffeners for achieving better designs of stiffened plate and shell structures. Curvilinear stiffeners have proven to be useful over straight stiffeners in some applications for achieving better structural efficiency. A framework has been developed that employs a hybrid optimization technique of using particle swarm optimization for stiffener shape optimization and gradient-based optimization as implemented in MSC.NASTRAN SOL 200 for optimization of stiffener cross section and shell thickness. Parallel processing has been used to save extensive wall-clock time. The framework has been employed for optimally designing cylindrical shells/panels stiffened by arbitrarily placed stiffeners, the motivation being lighter-weight fuselage and space launch vehicle designs. Structural optimization results have been presented for the optimal design of stiffened shells with the objective of weight minimization for shells subjected to both buckling and stress constraints. Optimization studies show that both the stiffener placement and the stiffener geometric curvature influence the shell buckling load, which can help to decrease the structural weight by optimizing the cross-sectional dimensions for stiffeners and panel thickness. In this paper, cylindrical shells, stiffened by four stiffeners, placed arbitrarily, are studied under compression and shear load cases. It is seen that arbitrarily placed curvilinear stiffeners lead to a potential 13% weight saving as compared to the use of equally spaced straight stiffeners when designed for the compression load case.

Buckling and Postbuckling of Concentrically Stiffened Piezo-Composite Plates on Elastic Foundations

This research presents the modeling and analysis for the buckling and postbuckling behavior of sandwich plates under thermal and mechanical loads. The lay-up configurations of plates are laminated composite with concentric stiffener and surface mounted piezoelectric actuators. The plates are in contact with a three-parameter elastic foundation including softening and/or hardening nonlinearity. Several types of grid shapes of stiffeners are studied such as ortho grid, angle grid, iso grid, and orthotropic grid. The equations of structures are formulated based on the classical lamination theory incorporating nonlinear von-Karman relationships. The stress function and Galerkin procedure are applied to derive explicit formulations of the equilibrium paths. New results are introduced to give the influences of voltage through the thickness of piezoelectric actuators, different stiffeners, and nonlinear elastic foundations.

Microwave near-field and far-field imaging of composite plate with hat stiffeners

Composite stiffened structures that are widely used in engineering inevitably produce various defects in manufacturing and service. In order to detect them, a microwave nondestructive testing platform is built in this paper, which simply combines near-field and far-field microwave scanning imaging. 0.4 mm metal hole, 0.5 mm and 1 mm inclusions and 0.1 mm thick debonding are detected by high resolution microwave near-field imaging. Internal poor resin infusions defects in 39 mm thick hat stiffener are detected by high penetration microwave far-field imaging. Far-field microwave images the shape and internal structure of stiffener by adjusting stand-off distance. Detection of the fiber wrinkling defects demonstrates the effectiveness of combining near-field and far-field imaging methods, saving 95% of the scan imaging time. Feature-based image stitching technique is adopted to obtain the full-size image of the large stiffened composite structure.

Effect of sequence and stiffener shape on welding distortion of stiffened panel

Welding is extensively used in industries for the assembly of different products including ships, automobiles, trains, bridges etc. Welding distortion is usually a source of dimensional imprecision in assembly and higher manufacturing costs. So, it is of crucial importance to predict and minimize welding-induced distortion by improving the quality of the welded structure. The purpose of this research is to reduce the distortion in large ship panels. The study uses two methods. First, distortion prediction by thermal elastic plastic FE analysis is employed to estimate the inherent deformations of different SM490A steel welded joints. Then, the welding process of a large ship panel is elastically analyzed on the basis of the theory of inherent strains. The elastic analysis reveals some distortions on the edge and inside of the panel. The distortions can be minimized by changing welding sequence of panel stiffeners to symmetrical welding of type B and changing shape to L-stiffener as well as changing stiffener material to the SM570.

Experimental and analytical study of steel slit shear wall

A steel slit shear wall has vertical slits and when it is under lateral loads, the section between these slits has double-curvature deformation, and by forming a flexural plastic hinge at the end of the slit, it dissipates the energy on the structure. In this article, Experimental, numerical and analytical analyses are performed to study the effect of slit shape and edge stiffener on the behavior of steel slit shear wall. Seismic behavior of three models with different slit shapes and two models with different edge stiffener shapes are studied and compared. Hysteresis curves, energy dissipation, out of plane buckling, initial stiffness and strength are discussed and studied. The proposed slit shape reduces the initial stiffness, increases the strength and energy dissipation. Also, edge stiffener shape increases the initial stiffness significantly.

Fatigue life enhancement of automobile wheel disc considering multi-axial stresses based on critical plane approach

We report an optimization procedure of automobile steel wheel fatigue life enhancement considering multi axial stresses based on critical plane approach via Design of experiments (DOE), Response surface methodology (RSM) and reflective Newton methodology. The wheel disc stiffener shape was optimized by defining seven parameters of the stiffener shape (design factors). Central composite design of experiments theory was used to select a minimum but sufficient combination of the design factors, FEM analysis was used to compute the stresses in the disc wheel under cornering load for each design factor combination. To verify the FEM modeling, we conducted an experimental fatigue test. The stress components variation for any arbitrary direction of loading were estimated and the multi axial fatigue and critical plane approach were used to evaluate the margin to fatigue damage. We found that stress components for only three radial loading directions of the rotating force are required to obtain sufficiently accurate stress histories at critical point and critical direction. A clear method was introduced regarding the correct shear stress range selection on critical plane. The RSM, a quadratic surface, was fitted to analytical results regarding the mentioned models. To verify the accuracy of the fitted surface, the responses at the design factors combinations were calculated via the identified quadratic model and compared to the FEM analysis results. Optimum value of design factors was obtained through reflective Newton method which led to generation of the refined wheel stiffener shape. The proposed method for determining the stress components could be used in any similar rotating parts such as wheel hub, brake disc, brake drum, etc.

Flutter Analysis of Laminated Curvilinear-Stiffened Plates

This paper proposes the use of curvilinear stiffeners as a mechanism to control supersonic panel flutter. To account for transverse shear deformation, the plate and stiffeners are modeled according to the first-order shear deformation theory and Timoshenko beam theory, respectively. The Chebyshev polynomials are the basis of the deflection and rotation functions in the Ritz method. The aeroelastic load is formulated according to the first-order high-Mach-number approximation to linear potential flow theory. The minimum potential energy and Hamilton’s principle are used to solve the problem. Plots of frequency versus aerodynamic pressure and damping versus aerodynamic pressure are used to determine the critical aerodynamic pressure, and hence to predict flutter of various isotropic and composite, stiffened, and unstiffened plates. The results for the flutter of straight-stiffened plates are validated through comparison with published papers. Several numerical examples are discussed, for which parametric studies for the shape and number of stiffeners and fiber orientation are performed. The flutter mode shapes are also presented. The present study attests that the critical dynamic pressure can be enhanced, and flutter can be successfully suppressed by changing the stiffener’s shape and fiber orientation.

Performance and Stability Analysis of Sub-stiffening for Mechanical Buckling and Post Buckling: A Selective Study

The recent work is a selective study of different types and shapes of stiffeners and sub-stiffeners. The aim is to get an optimum design model of the sub-stiffened panels. We provide a variety of parameters to enhance the stability performance of sub-stiffened panels. We correspondingly perform the numerical study under ABAQUS 6.13 using the RIKS algorithm in the object of defining the critical loads for both buckling and post-buckling; the ultimate strength load represents the initial structure damage. Comparing to a linear sub-stiffened panel, the simulation results show that the grid and curvilinear sub-stiffening can improve the stability performance.

Buckling analysis of unitized curvilinearly stiffened composite panels

Innovative manufacturing technology has led to the fabrication of complex shape and multi-functional structures by using the concept of integrated and bonded unitized structural components. To study the stability behavior of such structural designs, this paper presents an efficient finite element buckling analysis of unitized stiffened composite panel stiffened by arbitrarily shaped stiffeners. A first-order shear-deformation theory is employed for both the panel and the stiffeners. Displacement compatibility conditions are imposed at the panel-stiffeners interfaces. To obviate remeshing when the stiffener shape changes, the stiffeners’ geometry and displacement are expressed in terms of those of the panel middle surface through compatibility conditions that make use of the interpolation polynomials employed in the finite element method. To accommodate any shaped stiffeners, a generalized geometry parametrization tool is developed to parameterize the shape of the stiffeners including the stiffener placement and the stiffener geometric curvature. Convergence and validation studies using the present method for the buckling analysis of stiffened isotropic and composite panels are conducted to illustrate the accuracy of the present method. Parametric studies show that the stiffener placement, the stiffener geometric curvature, the stiffener depth ratio (height-to-width ratio) and laminates fiber ply orientation influence both the plate bucking load and the correspond buckling mode shape. The tailoriability of the stiffeners shape and the laminates fiber ply orientation provides an enhanced design space in the structural design for improving the structural stability.

A parametric investigation on the hysteretic behaviour of CFT column to steel beam connections

The results of a numerical investigation pertaining to the hysteretic behaviour of concrete filled steel tubular (CFT) column to I-beam connections are discussed in detail. Following the verification of the numerical results against the available experimental tests, the nonlinear finite element (FE) analysis was implemented to evaluate the effects of different parameters including the column axial load, beam lateral support, shape and arrangement of stiffeners, stiffness of T-stiffeners, and the number of shear stiffeners. Pursuing this objective, an external CFT column to beam connection, tested previously, was selected as the case-study. The lateral forces on the structure were simulated, albeit approximately, using an incremental cyclic loading reversal applied at the beam tip. The results were compared in terms of hysteretic load-displacement curves, stress distributions in connection, strength, rotation, and energy dissipation capacity. It was shown that external T-stiffeners combined with internal shear stiffeners play an important role in the hysteretic performance of CFT columns to I-beam connections.

원전 금속단열재의 구조 건전성 강화를 위한 설계 방안

The goal of this paper is to investigate structural integrity factors of RMI(reflective metal insulation) to confirm the design requirements in nuclear power plant. Currently, a glass wool insulation is using now, but it will gradually be replaced with the reflective metal insulation maded by stainless steel plates. The main function of an insulation is to minimize a heat loss of vessel and pipes in RCS(reactor coolant system). It has to maintain structural a integrity in nuclear power plant life duration. In this study, the structural integrity analysis was carried out both multi-plate and outer shell plate by using a static analysis and experimental test. First, inner multi-plate has a self support structure for being air space. Because the effect of total static weight in multi-layer plate is low, a plate collapse possibility is not high. Considering optimum thin plate pressing process, it has to pre-check the basic physical properties. Second, the outer segment thickness and stiffener shape are verified by the numerical static analysis, and sample test for both type of panel and cylindrical pipe model.

DESIGN OPTIMIZATION OF BOX TYPE GIRDER OF AN OVERHEAD CRANE

Double bridge girder overhead cranes are used for heavy duty applications in theindustry. In this paper a detailed parametric design optimization of the main girder of box type isperformed for a 150Ton capacity and 32m long span crane, after its basic design using availabledesign rules. Design optimization is performed using detailed 3D finite element analysis bychanging the number, shape and location of horizontal stiffeners along the length of the girder andnumber and location of stiffeners along the vertical direction to control any possible buckling, withminimum possible weight and for safe stress and deflection. Optimization is performed in twosteps. In the first step, keeping plates thickness constant different types and number of stiffenersare added and optimized geometry is found. In the second step, the best geometry of the first stepis further optimized for maximum allowable bending stress by changing thickness, height andwidth of the box girder with minimum possible weight. Effect of added stiffeners is highlighted incontrolling its buckling.

Parameter-free method for the shape optimization of stiffeners on thin-walled structures to minimize stress concentration

This paper presents a parameter-free shape optimization method for the strength design of stiffeners on thin-walled structures. The maximum von Mises stress is minimized and subjected to the volume constraint. The optimum design problem is formulated as a distributed-parameter shape optimization problem under the assumptions that a stiffener is varied in the in-plane direction and that the thickness is constant. The issue of nondifferentiability, which is inherent in this min-max problem, is avoided by transforming the local measure to a smooth differentiable integral functional by using the Kreisselmeier-Steinhauser function. The shape gradient functions are derived by using the material derivative method and adjoint variable method and are applied to the H1 gradient method for shells to determine the optimal free-boundary shapes. By using this method, the smooth optimal stiffener shape can be obtained without any shape design parameterization while minimizing the maximum stress. The validity of this method is verified through two practical design examples.