Edge Stiffeners Research Articles

Enhanced ACLD treatment using stand-off-layer: FEM based design and experimental vibration analysis

The main disadvantage of active constrained layer damping treatment is the reduced transmissibility of active forces. This problem can be solved up to certain extent by using edge anchors. These edge anchors or stiffeners increase the transmissivity of forces only at very high feedback gains but decrease the effectiveness of passive constrained layer damping (PCLD) treatment. The efficiency of the passive constrained layer damping treatment can be improved drastically by adding the stand-off-layer (SOL) between the viscoelastic layer and the base beam. This technique has additional advantages as well. Firstly, it increases the viscoelastic strain so that more energy is dissipated via viscoelastic layer. Secondly, it enhances the effect of active forces and moments even without using edge anchors because the shear modulus of the SOL is in the range 10 8–10 9 N/m 2. Hamilton’s principle in conjunction of finite element method is used to derive the equations of motion. The complex eigenvalue is developed and solved numerically by using simple proportional feedback control strategy. Results are compared with ordinary active constrained layer damping (ACLD) treatment in order to highlight the effectiveness of the proposed technique. Validity of the proposed treatment has also been verified experimentally.

Stiffness of Douglas-fir lumber: effects of wood properties and genetics

Because stiffness (modulus of elasticity (MOE)) is important for structural wood products, breeders and silviculturists seek to efficiently measure and improve this trait. We studied MOE in a 25-year-old progeny test of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) using field-based tools (ST300 and HM200) to measure stress wave MOE of standing trees and logs. We measured density, static bending MOE, and transverse vibration MOE on 2 × 4s, and density, SilviScan MOE, and SilviScan microfibril angle on small clearwood samples. Bending MOE had moderate to strong phenotypic and genetic correlations with stress wave MOE of trees and logs, transverse vibration MOE of 2 × 4s, and the densities of 2 × 4s and basal wood discs but was weakly correlated with the numbers and sizes of knots. The best lumber grade had the highest bending stiffness and smallest edge knots. Bending stiffness had a strong positive correlation with the density of small clearwood samples and a moderate negative correlation with microfibril angle. Compared with microfibril angle and edge knots, path analyses indicated that density had the strongest direct effect on bending MOE. We recommend that breeders measure and select for stress wave velocity to improve bending stiffness in Douglas-fir. Genetic gains can be increased by including wood density, but genetic selection for fewer or smaller knots will be ineffective.

Stiffener Requirements to Prevent Edge Buckling

Steel connection elements such as gusset plates and coped beam webs feature unsupported edges that are sometimes stiffened to prevent buckling. The stiffener requirements for structural elements with large aspect ratios are well established. However, for typical connections with an aspect ratio of ½ to 2, the existing requirements may not provide accurate results. The results from 123 elastic finite element models were analyzed to determine the stiffness requirements for edge stiffeners with smaller aspect ratios. A design procedure based on a simplified model is proposed as a starting point for stiffener design.

Energetics of highly kinked steps edges

We have determined the step edge free energy, the step edge stiffness and dimensionless inverse step edge stiffness of the highly kinked < 010> oriented step on a (001) surface of a simple square lattice within the framework of a solid-on-solid model. We have found an exact expression for the step edge free energy in the case that only nearest neighbour interactions are taken into account. At low temperatures the dimensionless inverse step edge stiffness reduces to the universal value 1 2 2 . However, with increasing temperature the dimensionless inverse step edge stiffness increases. Incorporation of an attractive next-nearest neighbour interaction leads to a suppression of the dimensionless inverse step edge stiffness. For a non-zero next-nearest neighbour interaction the dimensionless inverse step edge stiffness even vanishes at zero temperature.

Evaluation of Direct Strength Method for CFS Compression Members without Stiffeners

The axial compressive strength of the cold-formed steel (CFS) members with edge or intermediate stiffener is affected by interaction of local, distortional and overall buckling. In order to overcome the tedious and time consuming nature of the traditional Effective Section method of evaluating strength of such members, direct strength method (DSM) has been advanced recently. However, the DSM has not been adequately evaluated for calculating the strength of compression members (such as tubular, plain channel, and I-sections) consisting of only stiffened and unstiffened elements, without either lip stiffener or intermediate stiffener. These members experience interaction of only local and overall buckling before failure. In this paper, results of a study on the suitability of DSM to evaluate the compressive strength of plain channel, I and rectangular tubular members is presented. Extensive experimental data in literature and additional data generated using currently accepted effective width method (based on better estimate of local buckling stress evaluated considering element interaction), are used in this study. It is found that DSM can be used to evaluate strength of such members also.

Unified Element and Section Approach to Design of Cold-Formed Steel Structures

Slender open-section cold-formed steel members that contain flanges with edge stiffeners may buckle in different modes and with mode interactions. The element design approach (effective width method) has been shown to produce unconservative capacity predictions for a particular class of such members. This paper presents a modification to the effective width method derived from an investigation of the fundamental behavior of edge stiffened flange elements and sections that contain them. The modified element design approach is validated against the results of 913 compression and bending members collected from the literature, where all section and member buckling modes and interactions were evident. A section design approach is also presented which is directly in line with the element approach. The unified element and section approach is shown to provide accurate and reliable design solutions for cold-formed steel compression and flexural members. Proposals for the North American specification for cold-formed steel structures are presented.

An answer to an important controversy and the need for caution when using simple models to predict inelastic earthquake response of buildings with torsion

AbstractThis paper presents evidence that the extension of conclusions based on the widely used simplified, one story, eccentric systems of the shear‐beam type, to actual, nonsymmetric buildings and consequent assessments of the pertinent code provisions, can be quite erroneous, unless special care is taken to match the basic properties of the simplified models to those of the real buildings. The evidence comes from comparisons of results obtained using three variants of simplified models, with results from the inelastic dynamic response of three‐ and five‐story eccentric buildings computed with detailed MDOF systems, where the members are idealized with the well‐known plastic hinge model. In addition, a convincing answer is provided on a pertinent hanging controversy: For frame‐type buildings, designed in accordance with the dynamic provisions of modern codes (such as EC8 or IBC2000), which allow reduced shears at the stiff edge due to torsion, the frames at the flexible sides are the critical elements in terms of ductility demands. Copyright © 2009 John Wiley &amp; Sons, Ltd.

A displacement potential-based numerical solution for orthotropic composite panels under end moment and shear loading

The elastic behavior of an orthotropic composite panel is analyzed under the influence of an end moment as well as shear loading. The panel is rigidly fixed at one of its ends, and the fibers are assumed to be directed along its length. An efficient finite difference computational scheme, based on the displacement potential formulation, is used to analyze the present mixed boundary value elastic problem. The effects of several important issues, for example, the panel aspect ratio, edge stiffening, and fiber reinforcement, on the elastic field are investigated. Solutions are presented mainly in the form of graphs and the predicted deformed shape. Finally, the reliability and superiority of the present computational scheme is discussed in comparison to the corresponding finite element predictions. A list of symbols can be found on page 1003.

Fatigue Performance of Sandwich Beams With Peel Stoppers

Abstract: This paper concerns a newly developed peel stopper for sandwich structures, which may be embedded as a core insert or an edge stiffener. The major purpose of the peel stopper is to prevent large debonds/delaminations between face sheets and core in sandwich structures in the case of failure. Experimental investigations of conventional sandwich beams and beams furnished with peel stoppers, under static and fatigue loading conditions, and with temperature monitoring, were conducted. The experimental programme included investigation of crack initiation and propagation, as well as of fatigue endurance of conventional and modified sandwich beams. The results showed that although the peel stoppers did not significantly influence the fatigue life of the sandwich beams, they were exceptionally effective in re‐routing the crack propagation away from the face–core interface. Moreover, one of the two peel stopper designs presented prevented face–core debonding/delamination and total failure of the sandwich beams.

A New 2D Local Vibrational Model for Unidirectional Clamped—Clamped Sandwich Structure with Edge Stiffeners

Flexural vibration of a clamped—clamped, three-layer, one-span sandwich, unidirectional structure composed of isotropic layers is considered in the article. A new single series model of the 2D problem, obtained within the local theory of linear elastodynamics, is presented. Very realistic boundary conditions at edges of the structure, which correspond to the engineering solution with the edge stiffeners, are introduced and satisfied. Eight eigenfrequencies of the structure for two sets of input data are calculated, according to the new model, and compared with numerical and experimental results existing in the literature. A detail comparative analysis of the results is done and some conclusions are presented.

Global minimum cost design of a welded square stiffened plate supported at four corners

This paper presents the application of a refined version of the original Snyman–Fatti (SF) global continuous optimization algorithm (Snyman and Fatti, J Optimiz Theory Appl 54:121–141, 1987) to the optimal design of welded square stiffened plates. In particular we investigate square plates of square symmetry subjected to uniformly distributed normal static loads, supported at four corners, and stiffened by a square symmetrical orthogonal grid of ribs. Halved rolled I-section stiffeners are used welded to the base plate by double fillet welds. Profiles of different size are used for internal and edge stiffeners. A cost calculation method, developed by the first two authors and mainly used for welded structures (Farkas and Jarmai 2003), allows for the computation of cost for different proposed designs of the welded stiffened plates. The cost function includes material, welding as well as painting costs, and is formulated according to the fabrication sequence. Design variables include base plate thickness as well as the dimensions of the edge and internal stiffeners. Constraints on stress in the base plate and in stiffeners, as well as on deflection of edge stiffeners and of internal stiffeners are considered. For this purpose the Snyman–Fatti (SF) global unconstrained trajectory method is adapted to handle constraints of this type. For control purposes a particle swarm optimization (PSO) algorithm is also applied to confirm the results given by the SF algorithm. Since the torsional stiffness of open section stiffeners is very small, the stiffened plates are modelled as a torsionless gridwork. We present an algorithm for calculating the moments and deflections for torsionless gridworks with different number of internal stiffeners, using the force method.

Photogrammetry measurements of buckling modes and interactions in channels with edge-stiffened flanges

With the advent of flange edge stiffeners and higher-strength steels producing thinner structural sections, additional complexities in buckling modes and their interactions has arisen. A number of authors have demonstrated that the use of flange edge stiffeners may result in the interaction of buckling modes, which may be detrimental to the strength of the section. However, the exact behaviour of such interactions and how they may be accounted for in design is not yet fully understood. One reason for this has been the lack of sufficiently detailed data of the transverse buckling deformations, which may involve displacements in different buckling modes and with different relative magnitudes. This paper presents the results of channel sections with simple flange edge stiffeners tested under pure compression. A 3D photogrammetry system was used in order to accurately capture the full-surface transverse buckling deformations of the flanges and webs. The detailed buckling results are used to describe and explain the fundamental behaviour of flanges and webs, particularly with respect to interactions of buckling modes. Comparisons of the test results with the recently modified effective width method and the direct strength method are discussed.

Explicit Buckling Analysis and Design Equations for Composite Plates under Compression with Free Reinforced Edges

AbstractIn the present contribution, the buckling problem of compressively loaded symmetrically laminated orthotropic composite plates with free reinforced edges is studied [1]. Starting from the exact transcendental elasticity solution of the problem, a straightforward criterion for the determination of the minimum bending stiffness EImin of the edge stiffeners is presented that allows for the determination of EI such that no global buckling of the plate and flange occurs. (© 2008 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Experimental and numerical investigation on cold-formed steel C-section flexural members

This paper presents an experimental and numerical investigation on the bending strength and behavior of cold-formed steel C-section flexural members with upright, inclined and complex edge stiffeners. A total of 24 specimens that divided into 12 tests including 6 pure bending tests and 6 non-pure bending tests have been conducted. Local buckling, distortional buckling and interaction between local and distortional buckling were observed in the tests. The experimental results show that the edge stiffener and buckling mode have great influence on member’s bending strength. Comparison of the bending strengths under the two bending states show that the bending strength under non-pure bending is higher than which under pure bending, but the increased magnitude is related to the buckling modes. Moment gradient effect has only a minor influence on local buckling, but has great influence on distortional buckling. The tests were simulated by finite element program of ANSYS and the simulated results show good agreement with the experimental results in terms of bending strength and buckling mode.

Design of uniformly compressed edge-stiffened flanges and sections that contain them

Recent developments in the section approach to the design of cold-formed steel structures have led to design rules that address sections with edge-stiffened flanges, where the edge stiffeners give rise to the distortional buckling mode. However, the element approach to design (effective width method) remains unable to deal with this mode of buckling, and has been shown to routinely provide unconservative design capacities for such sections. This paper provides design rules for edge-stiffened elements that may be used in conjunction with the existing element approach in specifications, in order to determine the capacity of sections with edge-stiffened flanges in compression. The design rules are developed from an extensive analysis of the fundamental behaviour of plates simply supported on three sides with the remaining (longitudinal) edge stiffened with an edge stiffener. When used in conjunction with the effective width method they are shown to provide excellent agreement with tests of sections that contain edge-stiffened flanges in compression, thus removing the unconservatism in current specifications.

Pseudo‐dynamic test of a full‐scale CFT/BRB frame—Part II: Seismic performance of buckling‐restrained braces and connections

AbstractThis paper is Part II of a two‐part paper describing a full‐scale 3‐story 3‐bay concrete‐filled tube (CFT)/buckling‐restrained braced frame (BRBF) specimen tested using psuedo‐dynamic testing procedures. The first paper described the specimen design, experiment, and simulation, whereas this paper focuses on the experimental responses of BRBs and BRB‐to‐gusset connections. This paper first evaluates the design of the gusset connections and the effects of the added edge stiffeners in improving the seismic performance of gusset connections. Test results suggest that an effective length factor of 2.0 should be considered for the design of the gusset plate without edge stiffeners. Tests also confirm that the cumulative plastic deformation (CPD) capacity of the BRBs adopted in the CFT/BRBF was lower than that found in typical component tests. The tests performed suggest that the reduction in the BRB CPD capacities observed in this full‐scale frame specimen could be due to the significant rotational demands imposed on the BRB‐to‐gusset joints. A simple method of computing such rotational demands from the frame inter‐story drift response demand is proposed. This paper also discusses other key experimental responses of the BRBs, such as effective stiffness, energy dissipation, and ductility demands. Copyright © 2008 John Wiley &amp; Sons, Ltd.

Research on cold-formed steel columns

The paper summarises research on cold-formed steel columns performed by the author. Cold-formed steel members are either cold-rolled or brake-pressed into structural shapes. As a result, cold-formed steel open sections are usually singly-point- or non-symmetric. The most common types of singly-symmetric sections are channel and angle. The research focused on cold-formed steel open sections, such as plain and lipped channels, channels with simple and complex edge stiffeners as well as plain and lipped angles, and unequal angles. In addition, cold-formed steel built-up closed sections with intermediate stiffeners were investigated. Both experimental and numerical investigations into the strength and behaviour of cold-formed steel columns were conducted. The column strengths obtained from these investigations were compared with the design strengths obtained using various international standards for cold-formed steel structures. Furthermore, the behaviour and design of cold-formed steel lipped channel columns at elevated temperatures were also investigated. The paper also summarises the design recommendations for cold-formed steel columns.

Structural Health Monitoring with Piezoelectric Wafer Active Sensors for Space Applications

Ultrasonic guided waves inspection using Lamb waves is suitable for damage detection in metallic structures. This paper will present experimental results obtained using guided Lamb waves to detect flaws in aluminum specimens with design features applicable to space applications. Two aluminum panels were fabricated from a variable-thickness aluminum top plate, with two bolted I-beams edge stiffeners and four bonded angle stiffeners. Artificial damages were introduced in the two panels: cracks, corrosions, and disbonds. The proposed investigation methods used bonded piezoelectric wafer active sensors to excite and receive Lamb waves. Three wave propagation methods were used: pitch-catch, pulse-echo, and the embedded ultrasonic structural radar. In addition, we also used a standing-wave damage detection technique, the electromechanical impedance method. The paper will present in detail the salient results from using these methods for damage detection and structural health monitoring. Where appropriate, comparison between different methods in detecting the same damage will be performed. The results have demonstrated the ability of piezoelectric wafer active sensors working in conjunction with guided Lamb waves to detect various types of damages present in complex geometry structures typical of space applications.

Load-carrying capacity and energy absorption of thin-walled profiles with edge stiffeners

The paper presents results of the study into plastic mechanisms (collapse behaviour) of short stub thin-walled profiles with edge stiffeners under compression. The aim of the study was to investigate an applicability of such profiles as energy absorbers. Solutions of other researchers and the author are presented. The new plastic mechanism solution for hat-section column is derived.

Experiments on channel columns with inclined simple edge stiffeners under compression loading

In order to investigate the compression behavior of pin-ended cold-formed channel columns with inclined simple edge stiffeners, a total of 30 pin-ended cold-formed channel columns with three sections (sloping lip stiffener turned at 45°, 90°, and 135° to the flange, respectively) and three different lengths (500 mm, 1 250 mm, and 2 000 mm) were tested. It was found that the inclination angles and loading positions have an obvious effect on compression ultimate load-carrying capacities and failure modes. All three sections have certain post-buckling strength, and the failure modes of most of the specimens contained distortional buckling. The capacity of the specimens with 45° inclined angle for bearing compression is appreciably higher than the other two types of specimens with 90° or 135° inclined angles at the same negative eccentricity, but obviously lower than the other two at the same positive eccentricity. Furthermore, tests were simulated by finite element analysis. Results from the analysis are in great agreement with the experimental data.