Local Buckling Research Papers - Academia.edu (original) (raw)

Построен эффективный вычислительный алгоритм, позволяющий находить расчетные длины стержневых элементов рамных конструкций. Для каждого элемента формируется матрица реакций со стороны отбрасываемой части системы и, с учетом этих реакций, решается задача о собственных значениях уравнения продольного изгиба стержня. При поиске собственных значений напряженное состояние системы фиксируется. Решение точное. Продемонстрировано высокое быстродействие алгоритма.

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- Local Buckling

The local buckling behaviour and ultimate cross-sectional strength of tubular elliptical profiles in compression
is examined in this study through numerical modelling. The numerical models were first validated
against previous experimental data with good agreement observed, enabling an extensive
parametric study to be performed. A total of 270 elliptical sections were simulated in order to examine
the influence of cross-section aspect ratio, geometric imperfections and local slendernesses. The obtained
ultimate capacities, load–deformation responses and failure modes are discussed. It was found that for
lower cross-section aspect ratios the behaviour of the elliptical hollow sections (EHS) was similar to that
of cylindrical shells across a number of metrics; however, as the aspect ratio increased, more plate-like
stable postbuckling behaviour was observed. Imperfection sensitivity was found to decrease with
increasing slenderness and aspect ratio. The influence of the shape of the initial imperfection on the
strengths of the EHS columns was also assessed and was found to be generally limited. Finally, a design
method has been proposed for Class 4 EHS members that reflects the reduction in capacity due to local
buckling with increasing slenderness, but also recognises the improved postbuckling stability with
increasing aspect ratio; the proposals were shown to provide safe and accurate predictions for the
strengths of the EHS columns with nondimensional local slendernesses up to 2.5 and aspect ratios from
1.1 to 5.0.

- by Finian McCann
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- Tubular Steel, Steel Structures, Slender structure, Local Buckling

Local buckling is a failure mode commonly observed in thin-walled structural steel elements. Even though its effect on their behaviour at ambient temperature conditions is well documented and incorporated in current design codes, this is not the case when such elements are exposed to fire. This paper focuses on the occurrence of local buckling in steel members at elevated temperatures by conducting a thorough review of the literature. Experimental data (over 400 in total) gathered from 16 different sources are presented for both hot-formed as well as cold-formed elements made from different cross-sectional geometries (rolled or welded H-sections, box sections, channels etc). The effect of local buckling (and the various parameters that influence it) on the failure temperature is discussed based on the collected experimental evidence. Finally, the methods (numerical modelling and proposed analytical expressions) used by different authors to understand this phenomenon for steel members exposed to fire are discussed.

Steel structural elements with web-tapered I cross section, are usually made of welded thin plates. Due to the nonrectangular shape of the element, thin web section may be obtained at the maximum cross section height. The buckling strength is directly influenced by lateral restraining, end support and initial imperfections. If no lateral restraints, or when they are not effective enough, the global behavior of the members is characterized by the lateral torsional mode and interaction with sectional buckling modes may occur. Actual design codes do not provide a practical design approach for this kind of elements. The paper summarizes an experimental study performed by the authors on a relevant number of elements of this type. The purpose of the work was to evaluate the actual behavior of the web tapered beam-columns when applying different types of lateral restraints and different web thickness.

Laminated structures find many applications in various engineering fields namely aerospace, bio-medical, civil, marine and mechanical engineering due to easy handling, good mechanical properties and low fabrication cost. Laminated plates with round holes and other openings are extensively used as structural members in aircraft design. These holes are act sometimes as access holes, holes for hardware to pass through, or in the case of fuselage, windows and doors or simply used to reduce the weight of the structure. These laminated structures are often subjected to load in one or more direction in cycles or as intermittent load. Thus there is need to study the failure of these components under bi-axial loading with the view to optimize the shape and lay of the components so as they give maximum service and more life. In this paper bi-axial testing machine is developed to determine bucking load of different materials. Experiments are carried out on cross ply composite under various buckling loads on the bi-axial testing machine. The theoretical results, analytical and experimental results are compared with each other. It is observed that the strength of Bakelite composite plates is higher than glass epoxy laminated composite plate. So Bakelite is more suitable than glass epoxy.

In this paper, a generalised complex finite strip method is proposed for buckling analysis of thin-walled cold-formed steel structures. The main advantage of this method over the ordinary finite strip method is that it can handle the shear effects due to the use of complex functions. In addition, distortional buckling as well as all other buckling modes of cold-formed steel sections like local and global modes can be investigated by the suggested complex finite strip method. A combination of general loading including bending, compression, shear and transverse compression forces is considered in the analytical model. For validation purposes, the results are compared with those obtained by the Generalized Beam Theory analysis. In order to illustrate the capabilities of complex finite strip method in modelling the buckling behavior of cold-formed steel structures, a number of case studies with different applications are presented. The studies are on both stiffened and unstiffened cold-formed steel members.

Infill panel is the first element of a building subjected to blast loading activating its out-of-plane behavior. If the infill panel does not have enough ductility against the loading, it breaks and gets damaged before load transfer and energy dissipation. As steel infill panel has appropriate ductility before fracture, it can be used as an alternative to typical infill panels under blast loading. Also, it plays a pivotal role in maintaining sensitive main parts against blast loading. Concerning enough ductility of the infill panel out-of-plane behavior, the impact force enters the horizontal diaphragm and is distributed among the lateral elements. This article investigates the behavior of steel infill panels with different thicknesses and stiffeners. In order to precisely study steel infill panels, different ranges of blast loading are used and maximum displacement of steel infill under such various blast loading is studied. In this research, finite element analyses including geometric and material nonlinearities are used for optimization of the steel plate thickness and stiffener arrangement to obtain more efficient design for its better out-of-plane behavior. The results indicate that this type of infill with out-of-plane behavior shows a proper ductility especially in severe blast loadings. In the blasts with high intensity, maximum displacement of infill is more sensitive to change in the thickness of plate rather the change in number of stiffeners such that increasing the number of stiffeners and the plate thickness of infill panel would decrease energy dissipation by 20 and 77% respectively. The ductile behavior of steel infill panels shows that using infill panels with less thickness has more effect on energy dissipation. According to this study, the infill panel with 5 mm thickness works better if the criterion of steel infill panel design is the reduction of transmitted impulse to main structure. For example in steel infill panels with 5 stiffeners and blast loading with the reflected pressure of 375 kPa and duration of 50 milliseconds, the transmitted impulse has decreased from 41206 N.Sec in 20 mm infill to 37898 N.Sec in 5 mm infill panel.

Sandwich construction is increasingly used as wall and roof cladding for building structures. Typically, a cladding panel may consist of two plane or profiled metal faces with a foamed plastic core. The core may be polyurethane, polyisocyanurate, polystyrene or phenolic resin. When such a panel is subject to static loading due, for instance, to wind, snow or temperature gradient, one face is compressed and becomes liable to local buckling. If this face has a trapezoidal or similar profile the failure mode is similar to that for profiled steel sheeting, though the failure stress is enhanced by the presence of the core. The compressed face element first forms a series of buckling waves which increase in amplitude in the postbuckling phase. Failure takes place when one buckle in the region of maximum bending moment cripples.
In light gauge steel applications, the conventional design treatment for this phenomenon utilises the concept of effective width. In order to investigate the extension of the effective width concept to plate elements supported by plastic foam material, a series of tests were undertaken on foam-filled steel beams. This paper describes these tests and their interpretation in terms of an enhanced effective width formula.

Local buckling in floor beams has been one of the important observations in several fire events in steel buildings such as World Trade Center Tower 7 and large-scale fire experiments such as Cardington in UK. Utilizing three dimensional finite element methods for complex geometry and nonlinear behavior of such connections, local buckling of the web followed by the buckling of the lower flange is observed to occur in early stages in fire, which causes instability to the floor system, and a reduction in the connection strength. To fully capture the behavior of floor systems, one needs to be able to predict such buckling behavior of the beam. This paper contributes to such knowledge by investigating the local buckling of floor beams at elevated temperatures using nonlinear finite element models. The results are compared to AISC provisions of plate buckling under ambient and elevated temperatures.

- by Serdar Selamet
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- Structures and Fire Engineering, Steel Structure, Local Buckling

The paper is dealing with numerical research of the post-buckling behavior and the ultimate strength of welded I-shaped plate girders subjected to patch loading. This load case appears during the incremental launching stage of bridges in which many cross-sections are exposed to forces that will not appear during the bridge normal operation. The finite element analysis considering the influence of patch load length and different initial geometrical imperfections on the ultimate load is presented. Results for longitudinally unstiffened and stiffened girders are compared. The combined action of the longitudinal stiffener and larger patch load lengths can significantly increase the ultimate capacity. The most unfavorable ultimate strengths of longitudinally stiffened girders are obtained using initial geometrical imperfections that correspond to the deformed shape at collapse.

- by Sasa Kovacevic
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- Steel Structure, Buckling, Local Buckling, Patch Loading

Abstract An experimental research considering the behavior and ultimate strength of longitudinally stiffened plate girders subjected to localized edge loading in the plane of the web, a load case usually referred to as patch loading, is presented. Based on a literature review, the limitations of previous investigations are listed, which proved the need for additional experimental research. Part I of this research includes the main experimental test results, originally given in (Markovic, 2003 [1]), while in Part II the finite element modeling, verification of numerical models as well as results of an extensive parametric study will be presented. The driving force for performing this experimental campaign was to investigate the influence of patch load length on the ultimate capacity of longitudinally stiffened girders since this parameter has not been systematically studied. The influence of patch load length is thoroughly analyzed and results concerning the influence of longitudinal stiffeners are elaborated. The experiments are described in detail and the main conclusions of the experimental investigation are presented. It may be concluded that there is a significant influence of the length of patch load on the behavior and ultimate strength of the girders. The combined influence of increased patch load length and longitudinal stiffener can significantly increase the patch load resistance of plate girders. It can be concluded that the ultimate load of stiffened girders follows the ultimate strength of unstiffened ones under small patch load lengths. When a specific applied load length is reached, an appreciable strengthening effect can be obtained.

An efficient computational algorithm was constructed, which allows finding the buckling lengths of the rod elements of frame structures. A matrix of reaction from the side of the truncated part of the system is formed for each element and the problem of the eigenvalues of longitudinal bending equation of the rod is solved. When searching for eigenvalues, the stress state of the system is fixed. The solution is exact. High speed of algorithm is demonstrated.

- by Eugene B R I T V I N
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- Local Buckling

This paper investigates theoretically the compressive load-carrying behaviour of geometrically imperfect web-core sandwich plates. Slender plates, which first buckle globally, are considered. The study is carried out using two approaches, both solved with the finite element method. The first is the equivalent single-layer theory approach. First-order shear deformation theory is used. The second approach is a three-dimensional shell model of a sandwich plate. Plates are loaded in the web plate direction. Simply supported and clamped boundary conditions are considered with a different level of in-plane restraint on the unloaded edge. The results show that the behaviour of the sandwich plate is qualitatively equal to the isotropic plate of the same bending stiffness for deflections lower than the plate thickness. As the deflections increase, the lower in-plane stiffness of the sandwich plate results in lower post-buckling strength. Local buckling of face plates in the post-buckling range of the sandwich plate further reduces the structural stiffness.

Purpose-The purpose of this paper is to present an improved temperature-dependent constitutive model for steel that accounts for local instabilities of slender plates using an effective stress-based method. This model can be easily implemented for use with Bernoulli beam finite elements (FEs) in the fire situation. Design/methodology/approach-The constitutive model is derived by calibration on parametric numerical analysis on isolated plates subject to buckling at different elevated temperatures. The model is implemented in the FE software SAFIR and validation is performed against experimental and shell element analysis results. Findings-A constitutive model based on an equivalent stress method is proposed as an efficient way to consider local buckling in steel members exposed to fire. The proposed stress-strain-temperature relationship is asymmetric and is modified in compression only, by reducing the proportional limit, the yield stress and the strain at yield stress. The reduction of these parameters depends on the plate's boundary conditions, slenderness and temperature. The validation of the proposed model shows good agreement over a range of profile dimensions, temperatures and steel grades. Research limitations/implications-The model is still giving conservative results for large compressive load eccentricities. An enhanced model is under development to improve the predictive capability under large eccentricities. Practical implications-The proposed model, easily implemented into any finite element software, allows using fibre type (Bernoulli) beam FEs for modelling structures made of slender sections. This has major practical implications as beam elements are the workhorse used for simulating the behaviour of structures in fire. This model, thus makes it possible to simulate large structures with slender steel sections at a limited computational cost. Originality/value-The paper presents a novel steel constitutive model based on an innovative approach to capture local buckling at the material level using an equivalent stress approach. The theoretical development, validation and perspectives for future improvements are presented.

- by julio florez-lopez
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- Nonlinear Analysis, Local Buckling

In order to design a steel member subjected to a bending moment and an axial load, there are an infinite number of possible solutions I- or H- steel cross-sections, the doubly-symmetric solution being just one of them. This paper presents a procedure to obtain the optimal steel cross-section from the infinite number of possible solutions. The process is based on the Reinforcement Sizing Diagrams employed in reinforced concrete strength design. The procedure looks for any type of solution regarding compact or non-compact steel sections. All aspects related to local instabilities will be taken into account, as well as special considerations in order to address the global instabilities associated with the slenderness of the steel element.

- by Enrique Montes
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- Structural Optimization, Steel Structures, Local Buckling

PhD Thesis Of Dr Mohammed Rahif Hakmi

At ambient temperature, estimations of the post-buckling strength of steel plates (web and flanges) in wide-flange beams are based on the assumption that the stress at the edge of the plate equals the yield stress of the material. At elevated temperatures, however, material behaves in a nonlinear manner beginning at very small strains. This work presented in this paper has shown that at elevated temperatures, the ultimate buckling load occurs when stresses at the plate edge are smaller than the yield stress, which is typically defined at large strains such as 2%. Hence, the current expressions for plate buckling strength at ambient temperature cannot be directly applied at elevated temperature. By taking into account the nonlinear behavior of steel at elevated temperatures, we propose a new post-buckling strength equation for webs and flanges in wide-flange beams that correlates well with finite element studies at elevated temperatures.