Stiffening Ribs Research Articles

Seismic design of extended stiffened end-plate joints in the framework of Eurocodes

Bolted extended stiffened end-plate beam-to-column joints are widely used in seismic resistant steel frames. The flexural behaviour of this type of joints is crucial in order to guarantee an adequate seismic response. Eurocode 3 part 1–8 provides design rules and analytical models to predict the mechanical behaviour of the joints. Eurocode 8 provides additional design rules for seismic resistant joints, contradicting some requirements of Eurocode 3. In addition, in Eurocode 3 the influence of the rib stiffeners on the flexural response of this type of joints is not clearly accounted for. In this paper the criticisms of current versions of Eurocode 3 and Eurocode 8 are discussed and design criteria for seismic resistant extended stiffened end-plate beam-to-column joints are proposed. In addition, the results obtained from parametric finite element simulations are presented in order to support the discussion and to validate the design procedure.

Cyclic behaviour of low-yield-point steel shear panel dampers

In this paper, a new type of low-yield-point steel BLY160 is applied in the metallic shear panel damper device. To intensively investigate the seismic behaviour of the dampers, reversed cyclic loading tests are conducted to four groups of specimens, with the loading conditions and dimension parameters as test variables. The influences of the width-thickness ratio and corner perforation of the panel, the stiffening rib size and the cyclic load history are analysed. Through the experimental performance of test subassemblies, such as the hysteretic load-displacement loops, skeleton curves, deformation behaviour and failure modes, the earthquake mitigation effects of the damper devices are evaluated. In particular, conspicuous work-hardening is observed in the condition of cyclic deformation under both constant amplitude and increasing amplitudes loading. Contributed by the cyclic hardening of the low-yield-point steel, the energy dissipation capacities of the tested damper devices are approximately 1.5–2.5 times higher than that of a steel panel made of equivalent elasticity and perfectly plastic material. The complicated hysteretic performance with significant strain hardening can be accurately simulated by the kinematic-isotropic combined hardening model proposed in this paper, which incorporates the loading history effect by using the memory surface concept. The validity of the numerical model is verified by the comparison of the predicted cyclic behaviour and test responses.

Free Vibration Analysis of Integrally Stiffened Plates with Plate-Strip Stiffeners

We investigated the natural frequencies and mode shapes of a freely vibrating, integrally stiffened and/or stepped plate. The stiffeners used here were plate-strip stiffeners as opposed to the normally employed rib stiffeners. Both the plate and stiffeners were analyzed using the first-order shear deformation theory. The deflections and rotations were assumed as a tensor product of Timoshenko beam functions, chosen appropriately according to the given boundary conditions. Unlike Navier and Levy solution techniques, the approach used in this paper can also be applied to fully clamped, free, and cantilever supported stiffened plates. The governing differential equations were solved using the Rayleigh–Ritz method. The development of the stiffness and the mass matrices in the Ritz analysis was found to consume a huge amount of CPU time due to recursive integration of Timoshenko beam functions. An approach is suggested to greatly decrease this amount of CPU time, by replacing the recursive integration in a loop structure in the computer program, with the analytical integration of the integrand in the loop. The numerical results were compared with the solutions available in the literature as well as the commercially available finite-element software ABAQUS®, and the results were found to be highly satisfactory.

Experimental Research and Finite Element Analysis on Setting Stiffening Rib of Corner Joints in Gabled Frames

In order to clear constructional design of corner joint, it is necessary to further investi-gate mechanical property of corner joint in gabled frames. Through static test and finite element software analysis of comparing the panel zone with and without inclined stiffener. Some conclusions are given in the article. The load displacement curves show that the capacity of oblique nodes installed within stiffening rib components is enhanced i.e. 40% more than those without stiffening rib nodes. The results reveal that in the gabled frames, the corner node with the inclined stiffening rib can improve the bearing capacity of the specimens. When the extraterritorial flange is tension, the erection of the inclined stiffening rib can prevent structural failure and improve effectually the ductility of the structure.

Numerical Study on Ultimate Behaviour of Bolted End-Plate Steel Connections

Bolted end-plate steel connections have become more popular due to ease of fabrication. This paper presents a three dimension Finite Element Model (FEM), using the multi-purpose software ABAQUS, to study the effect of different geometrical parameters on the ultimate behavior of the connection. The proposed model takes into account material and geometrical non-linearities, initial imperfection, contact between adjacent surfaces and the pretension force in the bolts. The Finite Element results are calibrated with published experimental results ''briefly reviewed in this paper'' and verified that the numerical model can simulate and analyze the overall and detailed behavior of different types of bolted end-plate steel connections. Using verified FEM, parametric study is then carried out to study the ultimate behavior with variations in: bolt diameter, end-plate thickness, length of column stiffener, angle of rib stiffener. The results are examined with respect to the failure modes, the evolution of the resistance, the initial stiffness, and the rotation capacity. Finally, the ultimate behavior of the bolted end-plate steel connection is discussed in detail, and recommendations for the design purpose are made.

Optimized bio-inspired stiffening design for an engine nacelle

Structural efficiency is a common engineering goal in which an ideal solution provides a structure with optimized performance at minimized weight, with consideration of material mechanical properties, structural geometry, and manufacturability. This study aims to address this goal in developing high performance lightweight, stiff mechanical components by creating an optimized design from a biologically-inspired template. The approach is implemented on the optimization of rib stiffeners along an aircraft engine nacelle. The helical and angled arrangements of cellulose fibres in plants were chosen as the bio-inspired template. Optimization of total displacement and weight was carried out using a genetic algorithm (GA) coupled with finite element analysis. Iterations showed a gradual convergence in normalized fitness. Displacement was given higher emphasis in optimization, thus the GA optimization tended towards individual designs with weights near the mass constraint. Dominant features of the resulting designs were helical ribs with rectangular cross-sections having large height-to-width ratio. Displacement reduction was at 73% as compared to an unreinforced nacelle, and is attributed to the geometric features and layout of the stiffeners, while mass is maintained within the constraint.

Sandwich panels with high performance concrete thin plates at elevated temperatures: numerical studies

Performance of conventional load-carrying sandwich structures made of concrete can be improved by the use of high performance concrete (HPC) plates of thin sections (30 mm), linked by shear connectors ensuring the composite behaviour of the structure. This paper proposes the application of a coupled heat and mass transfer (HMT) model to HPC thin plates to study their behaviour at elevated temperatures, predicting temperature and pore pressure distributions. The same model was applied to a sandwich structure including thin plate, stiffening rib, and insulation layer. A last simulation concerned HMT modelling and elastic stress analysis with non-linear temperature effects of a full size loaded sandwich wall, qualitatively assessing the location of critically stressed zones. Modelling output was compared to published experimental results. The model reproduced experimental temperature recordings satisfactorily, except phase changes of water at low heating rates. It was suggested that the function governing moisture evolution with temperature and pressure should be updated for HPC. Pore pressure was found critical for sandwich structures due their higher temperatures. Adding polypropylene (PP) fibres for pressure release is recommended. Stress analysis showed the stiffening rib assumes the major load-carrying role. The thin plate was found largely sensitive to heat, its thermal bowing restrained by shear connectors creating high localised tensile stresses. It was suggested to anchor the shear connectors in the ribs. Geometric discontinuities were also found critical; therefore separation of rib and plate is advised for hazardous situations such as fire events.

Topology Optimization in Aircraft and Aerospace Structures Design

Topology optimization has become an effective tool for least-weight and performance design, especially in aeronautics and aerospace engineering. The purpose of this paper is to survey recent advances of topology optimization techniques applied in aircraft and aerospace structures design. This paper firstly reviews several existing applications: (1) standard material layout design for airframe structures, (2) layout design of stiffener ribs for aircraft panels, (3) multi-component layout design for aerospace structural systems, (4) multi-fasteners design for assembled aircraft structures. Secondly, potential applications of topology optimization in dynamic responses design, shape preserving design, smart structures design, structural features design and additive manufacturing are introduced to provide a forward-looking perspective.

Conceptual design and structural analysis of the CFETR cryostat

CFETR (China Fusion Engineering Test Reactor) is a new tokamak device, one important component of which is cryostat and it is now under designing by China national integration design group. The CFETR cryostat is a large single-wall vacuum-tight container surrounding the tokamak basic machine, which consists of top dome-shape lid, two cylindrical sections with circumferential stiffening ribs and bottom flat head. It shall provide a vacuum environment (10−4Pa) for the operation of the superconducting coils and all the loads that derive from cryostat itself and inner components should be transferred to the floor of tokamak pit. In this paper, two schemes of cryostat were proposed and then the structural analyses including seismic response analysis, elastic stress analysis and buckling analysis were performed to validate the conceptual design of CFETR cryostat. Based on the analysis results, it can be inferred that the cryostat II has a higher stiffness and stability. The structure of cryostat I needs to be improved against buckling and it is more difficult to manufacture for cryostat II due to its complex curved surface compared with cryostat I. Finally, the structural analysis for base section was performed and the design of main support was proved to be feasible. The design of CFETR cryostat has not been finalized and structural optimization still need to be proceeded based on the analysis results.

ANALYSIS OF RUBBER FORMING PROCESS OF FIRE BARRIER FROM TITANIUM CP2 ALLOY FOR AW 139 HELICOPTER

This paper presents conditions of forming products from titanium sheets by means of rubber stamping method. After introducing the issues connected with these elements manufacturing for aviation industry, considering standards and legal regulations, technological problems occurring during forming deep stiffening ribs. The results in the characteristic curvatures and distortion in the final products were generated in the process heterogeneous internal stress state. The Authors aimed at explaining and presenting of solutions limiting occurrence of chosen shape faults, which disqualify these products application in aviation industry. The proposed solutions significantly reduced the incidence of these unfavorable phenomena. The modified method of rub ber stamping of firewall from titanium alloy CP-2 sheet was successfully implement ed in manufacturing conditions of PZL Swidnik.

The Stress–Strain State of a Ribbed Cylindrical Shell Interacting with an Elastic Foundation Under Short-Term Loads

A method for analyzing the stress-strain state of a ribbed cylindrical shell that interacts with an elastic foundation under dynamic axisymmetric loading is presented. The effect of the duration of loading and the parameters of the foundation on the deflection and bending moments of the shell is analyzed Introduction. The effect of the ambient medium on the vibrations, stability, and stress-strain state of shells under dynamic loading was addressed in many studies (5-17, 19, etc.). A literature review indicates that the dynamics of ribbed shells interacting with the ambient medium is of interest. In the present paper, we will use the Pasternak model (4) and the Winkler model to describe the ambient medium as an elastic foundation. 1. Problem Formulation. Basic Equations. Below, we will analyze the stress-strain state (SSS) of a ribbed closed cylindrical shell under short-term loads distributed over its surface. The shell interacts with an elastic foundation that prevents the normal displacements of the shell and the rotations of its mid-surface about a circumferential coordinate line. Let the longitudinal stiffening ribs (stringers) be arranged regularly and the shell be hinged at the ends. To solve the problem, we will use the classical theory of shells and rods (1) and the energy method. The total potential energy of the disturbed elastic system and the kinetic energy are given by

Transmission loss of orthogonally stiffened laminated composite plates

Sound transmission through laminated composite plates reinforced by two sets of orthogonal stiffeners is investigated theoretically. A layerwise shear deformable theory is used to model the vibration of the laminated composite face-panel; A governing equation of I section composite beam is introduced, which accounts for the extensional, flexural, torsional and their coupling effects. The Euler-Bernoulli beam theory and torsional wave equation are employed to describe the flexural and rotational motions of the rib stiffeners, respectively. The technique of Fourier transform is applied to solve the governing equations resulting in infinite sets of simultaneous algebraic coupled equations, which are numerically solved by truncating them into a finite range insofar as the solutions converge. The accuracy of the numerical solutions is checked by comparing the present model predictions with existing literature. The validated model is subsequently employed to quantify the effects of the spacing of the stiffeners and the stacking geometry of the laminated composite face-panel and stiffeners on sound transmission through the structure. It is demonstrated that both the stiffener spacing and the stacking geometry have significant influences on the sound transmission loss across the structure. The proposed theoretical model successfully characterizes the process of sound penetration through stiffened laminated composite plates, which should be much helpful for the practical design of such structures with acoustic requirements.

Research on Rib Stiffener Distribution and Ultimate Strength of Steel Tubular Tower’s K-Joint

The method of calculating K-joint’s ultimate strength given by “Code for design of steel structures” GB 50017-2003 requires that, the angle θ between K-joint’s chord and brace is no less than 30°. While, due to the request of electric gap or transmission line corridor, the angle of steel tubular tower’ K-joint in power transmission line have to be designed less than 30° sometimes. In order to solve the engineer problem, rib stiffener were usually added to K-joint structure. 3 kinds of new rib stiffener to directly-welded K-joint of steel tubular tower were designed, and numerical simulation was made to study the structures’ performance under load and ultimate bearing capacity. With new-designed rib stiffener, K-joint’s stress distribution in weld jointing area, where usually bear stress badly, is improved obviously. Stress concentration is eliminated, and maximum stress is lowered. It is suggested that, in the case of exceeding code’s suggest range, k-joint structure must be reinforced to increase intensity, and the 3 format of rib stiffeners can improve the structure’s stress distribution and ensure the security of the structure.

Experimental Research on Seismic Behavior of Wall Component with Double Steel Plates and Infill Concrete

In order to study the seismic performance of wall component with double steel plates and infill concrete,three wall components with double steel plates and infill concrete were tested.The deformation performance and failure modes were observed under low cyclic lateral loads with high axial compression ratio.Valuable results were obtained for the hysteretic curves,skeleton curves,rigidity degeneration,ductility and energy dissipation capacity.The results indicate that Stud spacing is the key factor to prevent local buckling of steel plate, Steel plate and concrete stress as a whole;Setting stiffening rib, can improve the overall stiffness, bearing capacity and ductility, but had little effect on delaying wall cracks.

A new method for evaluating Borgonovo moment-independent importance measure with its application in an aircraft structure

The moment-independent importance measure proposed by Borgonovo, which is defined as the average shift between the unconditional and conditional probability density functions (PDFs) of model output, is widely used to evaluate the influence of input uncertainty on the entire output distribution. And how to exactly and efficiently estimate the PDFs remains a crucial and challenging problem. In this paper, a novel PDF estimation based method is proposed to efficiently evaluate the moment-independent index. Firstly, the PDF of the model output is obtained based on the concepts of maximum entropy, fractional moment and high dimensional model representation. Secondly, the Nataf transformation is utilized to estimate the joint PDF of the output and input variable. Finally, the index can be easily computed using the generated correlated standard normal samples. Thus the importance measure can be calculated with high efficiency and accuracy using this proposed composited method. Several examples are employed to demonstrate the advantages of the proposed method. Meanwhile, the importance analysis of a stiffening rib of the wing leading edge in a certain aircraft also verifies its good engineering applicability.

Transverse Ribs Affect the Stability of Steel-Concrete Composite Box Beams

The paper uses the finite element method to the specific structure of the linear buckling analysis to study the steel - concrete buckling coefficient changes when the changes and adjustments in the case of composite box girder structure different density transverse stiffening ribs buckling coefficient bracing spacing, Thus obtained that the almost linear relationship between the change in distance between the transverse stiffening ribs and buckling coefficient. Meanwhile get when bracing spacing when a valid range, coefficient of variation of buckling structure is not particularly obvious. Which is to adjust the spacing and lateral bracing number of stiffening ribs provide a space.

Study on the Ultimate Bearing Capacity of Concrete Filled Steel Square Tubular Short Column with PBL

Aiming at the specific concrete filled square steel tubular short column stiffened with PBL under axial compression load, considering about the useful effect of the PBL shear connectors, the mechanical behavior of PBL stiffening ribs was analyzed. Through the analysis of the effective restriction-area and ineffective restriction-area of core-concrete, introduce into the effective constraint coefficient of concrete. The ultimate bearing capacity was deduced based on the unified strength theory, with some influencing factors analyzed as well. Compared with the test results in relevant documents, they coincided well with each other. The result shows that the formula which is deducted from the unified strength theory has good applicability and the solution will show its positive impact in the related fields.

Bolted Ribs Analysis for the ITER Vacuum Vessel using Finite Element Submodelling Techniques

The ITER Vacuum Vessel (VV) primary function is to enclose the plasmas produced by the ITER Tokamak. Since it acts as the first radiological barrier of the plasma, it is classified as a class 2 welded box structure, according to RCC-MR 2007. The VV is made of an inner and an outer D-shape, 60mm-thick double shell connected through thick massive bars (housings) and toroidal and poloidal structural stiffening ribs. In order to provide neutronic shielding to the ex-vessel components, the space between shells is filled with borated steel plates, called In-Wall Shielding (IWS) blocks, and water. In general, these blocks are connected to the IWS ribs which are connected to adjacent housings.The development of a Finite Element model of the ITER VV including all its components in detail is unaffordable from the computational point of view due to the large number of degrees of freedom it would require. This limitation can be overcome by using submodelling techniques to simulate the behaviour of the bolted ribs assemblies. Submodelling is a Finite Element technique which allows getting more accurate results in a given region of a coarse model by generating an independent, finer model of the region under study.In this paper, the methodology and several simulations of the VV bolted ribs assemblies using submodelling techniques are presented. A stress assessment has been performed for the elements involved in the assembly considering possible types of failure and including stress classification and categorization techniques to analyse the critical sections. In particular, studies to optimise the number of bolts on each specific VV area have been developed to assess the compliance with RCC-MR 2007 requirements. It is shown as well that the submodelling technique is a powerful tool to avoid the current computational limitations.

On the Deflexion of Anisotropic Structural Composite Aerodynamic Components

This paper presents closed form solutions to the classical beam elasticity differential equation in order to effectively model the displacement of standard aerodynamic geometries used throughout a number of industries. The models assume that the components are constructed from in-plane generally anisotropic (though shown to be quasi-isotropic) composite materials. Exact solutions for the displacement and strains for elliptical and FX66-S-196 and NACA 63-621 aerofoil approximations thin wall composite material shell structures, with and without a stiffening rib (shear-web), are presented for the first time. Each of the models developed is rigorously validated via numerical (Runge-Kutta) solutions of an identical differential equation used to derive the analytical models presented. The resulting calculated displacement and material strain fields are shown to be in excellent agreement with simulations using the ANSYS and CATIA commercial finite element (FE) codes as well as experimental data evident in the literature. One major implication of the theoretical treatment is that these solutions can now be used in design codes to limit the required displacement and strains in similar components used in the aerospace and most notably renewable energy sectors.

Simulation Analysis of K Node on UHV Transmission Tubular Tower

Layout for K node of steel tubular UHV transmission tower is analyzed in systematic and all-sided with finite element calculation in this paper. The recommendation is that as no applicable formula is available at present, existing specification can still be used for calculation but with a safety margin of more than 10%. K node connected in intersecting welding manner with appropriate stiffening rib will improve the stress, gender more uniformed stress distribution, and effectively reduce stress concentration. Welding connection features smaller displacement and maximum stress and more uniformed stress distribution relative to plug-in connection, therefore it is recommended to be used for K node with slope.