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Buckling instability refers to a significant limit on the structures with I-section members, which causes severe decreasing of critical buckling load. Many mechanisms and techniques have been developed to increase the loading capacity of I-section structures, e.g., using composite materials or changing web geometry. This study aims at theoretically investigating the effect of geometry on the buckling capacity of wood composite I-beams with sinusoidal corrugated web. Experiments and numerical simulations are carried out to validate the theoretical predictions. The presented model is also reduced to flat web to validate with an existing study. Good agreements are observed from the validations. Parametric study is conducted to indicate the effects of web geometry on the critical buckling load. A significant increasing of buckling load (minimum 17.7%) is obtained between flat and sinusoidal web I-beams. Sensitivity study is carried out to evaluate the influences of web thickness, beam length and beam height on the loading capacity of sinusoidal I-beams. Optimal design is conducted to investigate the impact of the ratios of wavelength-to-beam length ( a L ) and wave amplitude-to-flange width ( A T ) on the critical buckling load and volume of wood corrugated I-beams. The findings in this study can be further used as guidance for the design of composite I-beams with sinusoidal corrugated web. [ABSTRACT FROM AUTHOR]

Many authors in the literature agreed that the flow theory of plasticity either fails to predict buckling or overestimates plastic buckling stresses and strains of plates and shells while the deformation theory succeeds in forecasting buckling and provides estimates that are more in line with the experimental results. Following a previous study by the same authors focused on compressed cylinders, the present work aims to investigate the reasons for the discrepancy between the flow and deformation theory predictions in the case of cylinders subjected to combined axial tensile load and increasing external lateral pressure. To this end, geometrically nonlinear finite-element calculations of selected cylindrical shells using both the flow theory and the deformation theory of plasticity have been conducted, and the results are compared with some accurate physical test results and with numerical results obtained by other authors using the code BOSOR5. It is found, contrary to common belief, that very good agreement between numerical and test results can be obtained in the case of the flow theory of plasticity. The reasons underlying the apparent plastic buckling paradox are discussed in detail. [ABSTRACT FROM AUTHOR]

Abstract: The structural behaviour of elliptical hollow sections has been examined in previous studies under several loading conditions, including pure compression, pure bending and combined uniaxial bending and compression. This paper examines the elastic buckling response of elliptical hollow sections under any linearly varying in-plane loading conditions, including the most general case of combined compression and biaxial bending. An analytical method to predict the elastic buckling stress has been derived and validated against finite element results. The predictive model first identifies the location of the initiation of local buckling based on the applied stress distribution and the section geometry. The critical radius of curvature corresponding to this point is then introduced into the classical formula for predicting the elastic local buckling stress of a circular shell. The obtained analytical results are compared with results generated by means of finite element analysis. The comparisons between the analytical and numerical predictions of elastic buckling stress reveal disparities of less than 2.5% for thin shells and, following an approximate allowance for the influence of shear, less than 7.5% for thick shells. [Copyright &y& Elsevier]

Abstract: This paper describes a series of compression tests of circular hollow steel (CHS) sections and circular concrete-filled tubular (CFT) sections. The diameter to thickness ratios of the test specimens ranged 45–140. This range was set to investigate the effect of local buckling in the circular steel skin on the ultimate strength of CFT columns. The confining effect against filled-in concrete was also studied. A squash load formula for CFT stub columns is proposed to account for the post-local-buckling strength of steel skin. The ultimate strength of steel skin was predicted by a kind of Direct Strength Method (DSM). The proposed DSM does not require the computation of the effective area of the steel skin, but uses the gross area of the steel skin and the design strength formula based on various test results. The compressive strength formula of the filled-in concrete accounting for the strength ratio of steel skin to filled-in concrete is also proposed to consider the increase in compressive strength of the filled-in concrete, due to the confining effect of the steel skin. The design strengths of CFT columns were compared with the test results for verification. [ABSTRACT FROM AUTHOR]

Abstract: Modern procedures for the design of shell structures against buckling have their basis in analytical studies of axisymmetric shell geometries under the very simple load cases of uniform compression, external pressure and torsion. Studies of more complex but realistic stress states were based on prebuckling analyses using either membrane theory or linear bending theory because even these involved considerable mathematical complexity. As a result, only limited conclusions for practical design could be drawn and the effects of geometric nonlinearity could not be assessed. With recent advances in computing power and nonlinear finite element programs, it is now possible to undertake nonlinear analyses of complex load patterns that would have been very difficult to do only a decade or so ago. A number of practical load cases lead to a strip of pressure down one meridian, of which the best known ones are probably wind on tanks, eccentric discharge in silos, local thermal differentials, and partial fluid filling of a cylinder. This paper explores some of the rather unexpected stress patterns and modes of buckling that are predicted to develop in thin-walled cylindrical shells under such unsymmetrical strips of normal pressure. The results of a parametric study are presented to show the influence of the circumferential spread of the pressure strip on the structural behaviour. It is shown that the structural response to such loads may be very different, depending on whether the load acts inward or outward, and whether geometric nonlinearity and geometric imperfections are also included in the assessment. [Copyright &y& Elsevier]

Abstract: This paper first time presents an analytical investigation on the nonlinear postbuckling of imperfect eccentrically stiffened thin FGM plates under temperature and resting on elastic foundation using a simple power-law distribution (P-FGM). Both of the FGM plate and stiffeners are deformed under thermal loads. The formulations are based on the classical plate theory taking into account geometrical nonlinearity, initial geometrical imperfection, temperature-dependent properties and the Lekhnitsky smeared stiffeners technique with Pasternak type elastic foundation. By applying Galerkin method and using stress function, effects of material and geometrical properties, temperature, elastic foundation and eccentrically stiffeners on the buckling and postbuckling loading capacity of the eccentrically stiffened FGM plate in thermal environments are analyzed and discussed. Some results were compared with the one of the other authors. [Copyright &y& Elsevier]

Abstract: A series of stub column tests on complex sections with intermediate stiffeners is presented in this paper. Initial geometric imperfections and material properties of the test specimens were measured. It is shown that the intermediate stiffeners could effectively enhance the local buckling stress of thin-walled sections. The test strengths are compared with the design strengths calculated using the direct strength method in the North American Specification and Australian/New Zealand Standard for cold-formed steel structures. It is shown that the direct strength method using finite strip method to obtain the buckling stresses is very conservative. Therefore, finite element method was used to predict the elastic buckling stresses. It is shown that the design strengths calculated using direct strength method based on the buckling stresses obtained from finite element analysis results generally agree with the test results well. [Copyright &y& Elsevier]

Abstract: An analytical investigation of the buckling/wrinkling behavior of GFRP webs in cell-core sandwiches subjected to combined in-plane shear and bending stresses is conducted. Web–core panels are modeled as long orthotropic plates stabilized by a relatively thick layer of elastic foam. The boundary condition of the plate is defined according to the interaction between the webs and face sheets in the presence of the core material by applying a series of numerical analyses using the three-dimensional finite element modeling. Two approaches are adopted to predict the wrinkling behavior. The first is to predict the buckling/wrinkling of webs subjected to combined shear and bending loads using a mixed-mode interaction formula. In the second approach, the wrinkling behavior of web–core panels is treated as a biaxial compression–tension local buckling problem. The developed approaches are applied to predict the wrinkling loads of thin-walled webs in GFRP cell-core sandwich beams designed for the GFRP cell-core sandwich roof of the Novartis Campus Main Gate Building constructed in Switzerland. [Copyright &y& Elsevier]

Abstract: Fire safety has become an important part in structural design due to the ever increasing loss of properties and lives during fires. Conventionally the fire rating of load bearing wall systems made of Light gauge Steel Frames (LSF) is determined using fire tests based on the standard time–temperature curve in ISO834 (ISO 834-1, 1999 [1]). However, modern commercial and residential buildings make use of thermoplastic materials, which mean considerably high fuel loads. Hence a detailed fire research study into the fire performance of LSF walls was undertaken using realistic design fire curves developed based on Eurocode parametric (ENV 1991-1-2, 2002 [2]) and Barnett's BFD (Barnett, 2002 [3]) curves using both full scale fire tests and numerical studies. It included LSF walls without cavity insulation, and the recently developed externally insulated composite panel system. This paper presents the details of finite element models developed to simulate the full scale fire tests of LSF wall panels under realistic design fires. Finite element models of LSF walls exposed to realistic design fires were developed, and analysed under both transient and steady state fire conditions using the measured stud time–temperature curves. Transient state analyses were performed to simulate fire test conditions while steady state analyses were performed to obtain the load ratio versus time and failure temperature curves of LSF walls. Details of the developed finite element models and the results including the axial deformation and lateral deflection versus time curves, and the stud failure modes and times are presented in this paper. Comparison with fire test results demonstrate the ability of developed finite element models to predict the performance and fire resistance ratings of LSF walls under realistic design fires. [Copyright &y& Elsevier]

Abstract: This paper summarises an investigation carried out to predict the structural behaviour of CFRP-strengthened cold-formed steel lipped channel columns−more specifically, it addresses the applicability of the provisions of Eurocode 3 (EC3) and the AISI Specification (AISI-DSM, direct strength method), both developed for cold-formed steel members, to estimate their load-carrying capacity. It is worth noting that EC3 and AISI-DSM adopt different approaches to perform this task: while the former is based on the “effective width” concept, the latter may adopt the “Direct Strength Method”. First, the most relevant aspects related to the experimental and numerical investigations carried out to obtain “exact” column collapse loads are briefly presented. Then, an extensive numerical study is performed, which is intended to evaluate the benefits of CFRP-strengthening for different CFRP ply configurations, number of CFRP plies and steel yield stresses. After proposing different methodologies to extend the application of the EC3 and AISI-DSM design provisions to CFRP-strengthened cold-formed steel columns, the estimates provided by them are compared with the experimental values. On the basis of these comparisons, some concluding remarks are drawn concerning the merits and shortcomings of extending the domain of application of the current EC3 and AISI-DSM design approaches, so that they may cover also CFRP-strengthened lipped channel columns. [Copyright &y& Elsevier]

An experimental study was conducted to evaluate the compressive behavior of damaged circular hollow section (CHS) steel columns repaired by carbon fiber-reinforced polymer (CFRP) or high-strength grout. A total of 22 specimens, including bare steel specimens, CFRP repaired specimens and grout repaired specimens were tested under axial compression loading. The design parameters are the amount of loss in wall thickness, extent of damage along tube height, and the damage angle around the circumference. Two promising retrofit techniques, external wrapping of CFRP and grouted jacket, were adopted here. The repairing efficiency was assessed in terms of the above-mentioned retrofit techniques and design parameters. A finite element (FE) analysis was also performed and analyzed with test results. The failure modes are presented together with load-shortening and load-strain behavior of specimens. The results indicate that the behavior of damaged CHS steel columns can be effectively rehabilitated by either CFRP or grout jacketing. The local buckling of the internal steel tube was either delayed by fibers or suppressed by the surrounding grout, leading to an improvement both in compressive strength and deformation capacity. It was also found that grouted jacket repair generally shows an overwhelming strength enhancement over the CFRP wrapping method except for specimens with 90° damage around circumference, which shows a delay of the restraining effect. A parametric study was eventually undertaken to fully understand the influences of design parameters on columns' compressive characteristics. [ABSTRACT FROM AUTHOR]

In this paper, a new type of multi-planar slope change joint (abbreviation SCJ) in a new type of long span transmission tower is presented. Difference between the new tower and regular ones lies in the tower leg. In the new tower, each leg is a built-up column constituted with four steel tubes. The SCJ is a complicated multi-planar connection in the tower. Three-dimensional loading of the joint was achieved in the experiment. Detailed configuration of the SCJ and the experimental system were introduced. Finite element models of the SCJ were established and validated against experimental results. Experimental and numerical analysis results, under different cases, indicated that the joint zone was within the elastic bearing capacity. Buckling failures appeared in the upper or lower tubes. Then parametric studies were carried out to study different factors that may have influence on the ultimate load. Axial load distribution among the four lower tubes in the joint was also analysed. Finally, some joint design recommendations were proposed. [ABSTRACT FROM AUTHOR]

Abstract: Analytical approach used for critical load determination is based on Ritz energy technique in which two factors are crucial for the accuracy of results. First factor is deflection function. Herein, double Fourier series are used to represent buckled shape of the plates under arbitrary external loads. The second and the most important factor is adoption of adequate realistic stress distribution within plate prior to buckling. Based on the Baker&Pavlović&Tahan and Pavlović&Liu investigations, exact stress distributions were introduced herein. In that way, with the adequate deflection functions and precise stress distribution, Ritz energy method can produce highly accurate results. Through several examples for the plates with different boundary conditions, for which available literature offers very few analytical solutions, accuracy of the presented analytical approach is proved. Results obtained by analytical approach are reaffirmed by numerical finite-element runs. [Copyright &y& Elsevier]

Abstract: A numerical study on the elastic buckling behaviour of simply supported cylindrically curved panels, with longitudinal edges unconstrained and loaded edges constrained, including the influence of curvature, aspect ratio and loading type (from pure compression to full in-plane bending) is presented in this paper. Subsequently, an extension of rules for internal plated members’ critical stress calculation from EN 1993-1-5 is proposed that takes into account the effect of curvature. The proposed approach, based on the numerical results, gives a safe but accurate estimate (lower bound) for the elastic critical stress. [Copyright &y& Elsevier]

Abstract: Cutting roll-formed steel lipped C-sections may produce different extent of cross section distortion along the lengths of the sections and may lead to additional initial geometric imperfections. Ten stub columns cut from two different sections were tested under axial compression. Flanges of the stub columns experienced distortional mode of failure, whereas the webs showed signs of local buckling failures. Ultimate compressive strengths obtained from the test results were 75–77% of the strengths estimated based on BS5950:Part 5. This indicates that geometric imperfections caused by cutting may significantly reduce the ultimate strength of stub columns. [Copyright &y& Elsevier]

This paper examines the load bearing capacity of medium-length steel cylindrical shells with a circular cutout under the action of axial compression. Numerical simulations were performed for a radius-to-thickness ratio ( R / t ) ranging from 100 to 500, and an imperfection parameter ( α ) of between 1 and 4. Structural steel and the behavior of perfect plastic material were considered within the scope of the study. The investigation includes the influence of the cutout size and number, radius-to-thickness ratio. The paper also contains a comparison between theoretical predictions, ABAQUS ® FE results and experimental data for axially compressed cylinders. A reasonable correlation was obtained between numerical predictions and experimental tests. Details relating to the experimental procedure and FE model are provided. A parametric study was conducted to propose empirical equations, estimating the limit load of cylindrical shells as a function of geometry ( R / t , α and cutout number) and material properties ( E , v and σ y ). Empirical formulas were produced, fitting a surface plot using the Least Square method, for both the perfect shell structure (reference shell load) and the limit load reduction factor ( ϕ ). All variables in the empirical formula were normalized. A stochastic error analysis was used as a tool to measure how the results of proposed equations approach the FE predictions. Finally, based on experimental and numerical results, formulas are presented to calculate the limit load of medium-length shells with and without circular cutouts having a discrepancy not exceeding ± 10 % regarding error analysis. [ABSTRACT FROM AUTHOR]