Given the sensitivity of axially-loaded cylinder buckling to geometric imperfections, the advent of additive manufacturing provides a compelling platform to assess subtle changes in initial ...configuration from an experimental perspective. The cylindrical form is ubiquitous in many load-bearing contexts, from soda cans to submarines to rocket fuel tanks. Despite the relative simplicity of the shape, it is striking how the assessment of buckling loads continues to pose strong challenges to the designers of these load-bearing components, often in a situation where weight-saving is a key constraint. Furthermore, this type of buckling typically corresponds to a sudden, severe, catastrophic event, and in addition to posing serious consequences in practice, this also presents challenges for those conducting high-fidelity experiments, especially in terms of repeatability. Any conditions that deviate from a pristine cylindrical shape, and purely axial loading, are the root-cause of the buckling variability. Typically, the slight deviations from the pristine (perfect) conditions are somewhat random and unpredictable in nature. 3D-printing now provides the experimentalist with the ability to produce cylindrical specimens to a very high degree of geometric fidelity, thus allowing a degree of control of the form of subtle geometric imperfections. This paper focuses attention on a specific form of deviation from a pristine cylindrical shape, in which the longitudinal sides follow a mild cosine wave form. The amplitude of this shape is varied (in both directions, i.e., inwards and outwards), and its effect on both the buckling load and buckling mode shape assessed experimentally, using the outcome of finite element analysis as a guide.
•Uses 3D-printing to produce high-resolution cylinders, including subtle prescribed initial geometric imperfections.•Experimental testing to verify two interesting features in cylinder buckling.•The experimental studies were motivated by observations in finite element analysis.•Good qualitative agreement between theory and experiment.
Austenitic stainless steel is an excellent construction material for structures required to withstand accidental loads such as seismic and/or fire events due to its appropriate mechanical properties, ...including high ductility, considerable strain hardening and good fire resistance. In recent years, a considerable amount of research has been devoted to the understanding of the structural performance of single isolated stainless steel members. However, new trends in the design philosophy moving from current member-based methods to direct system-based approaches will require more experimental evidence on more complex structural systems such as frames, which are currently scarce. With the aim of contributing to the advances in this field, one of the first known extensive experimental programmes on austenitic stainless steel frames is presented in this paper. The experimental programme comprised several sub-programmes, in which the performance of stainless steel structures at different levels was investigated. This paper describes a series of tests on austenitic stainless steel cross-sections and members, which were utilized in the planning and analysis of the subsequent frame tests. The paper also outlines the complex experimental set-up adopted for the stainless steel frame tests, including the implemented loading schemes, auxiliary elements and instrumentation, through a detailed explanation of the different issues encountered in the process of their definition. The knowledge gained and the experiences reported in this paper could assist researchers in planning similar experimental programmes.
•An experimental programme on austenitic stainless steel RHS is described.•Tests on coupons, stub columns, beams and columns are presented.•An experimental set-up for frame tests is presented.•Load schemes and protocols for frame tests are defined and discussed.•Auxiliary arrangements for frame tests are described.
Beams with sinusoidal web opening are alveolar beams manufactured from a single web cut, which lead to the production of higher I-sections and with a better strength-to-weight ratio when compared to ...the I-sections from which they originated. There are few studies in the literature about this I-section type, especially in relation to their behavior regarding global stability and Lateral Torsional Buckling (LTB) strength. Bearing in mind the importance of understanding the behavior of alveolar beams with sinusoidal openings in relation to LTB, an extensive parametric study was carried out through numerical analysis in the commercial finite element software ABAQUS. The study was performed with 10 I-sections of the IPE type, with lengths ranging from 6 m to 32 m. In addition, initial imperfections were considered, such as residual stresses and geometric imperfections. With the parametric study results, it was possible to evaluate the main existing analytical procedures, both for the determination of the LTB elastic critical moment, as well as the LTB ultimate moment. The adequacy of standard procedures (AISC; Eurocode 3 and AS4100) was evaluated, as well as analytical procedures present in the scientific literature for determining the LTB ultimate moment. Through the achieved results, it was possible to analyze the behavior of different adaptation methods for the calculation of the elastic critical moment in sinusoidal alveolar beams, as an alternative to the traditional double-T approach. Furthermore, it was found that the AISC-360 standard is unsafe in the case of actions applied to the upper flange, even though this is the most common condition in engineering projects.
•Buckling and Post-buckling numerical analyses are performed in AngelinaTM beams.•Several approaches to determining the I-section geometric properties were evaluated.•Alternative approaches to double T section were verified.•The average section approach can be a good alternative.•The LTB behavior of standard procedures for AngelinaTM beams was studied.
•Effect of cut-out size on buckling capacity of the shell is a function of its imperfection magnitude.•Long rectangular cut-out along longitudinal direction exhibits higher buckling load Pu for ...perfect and imperfect shells than other orientations.•Loss of flexural stiffness at cut-out cross-section leads to early buckling of imperfect shells with large circumferential opening.•FRP strengthening is effective in resisting pre-buckle deformations i.e. lip opening as well as alleviating stress concentration effects, leading to increase in Pu especially for large longitudinal cutouts.•Elliptical cut-outs exhibit higher Pu than rectangular cut-outs with different corner radii for imperfect bare shells.•Photo-frame stiffening around cut-out with large overlap width and thin stiffener is beneficial for perfect shells and thick stiffener is beneficial for imperfect shells.•Stiffener around cut-out is relatively more effective than FRP strengthening to compensate the loss of flexural resistance at cut-out cross-section.
This paper presents a detailed buckling study on FRP strengthening of metallic cylindrical shells with different geometric imperfections and centrally located unstiffened and stiffened cut-outs. Initially, bare and FRP strengthened aluminium cylindrical shells have been manufactured. Geometric imperfections have been measured and implemented in the numerical model. Interfacial bond quality has been assessed by two different non-destructive techniques. The buckling response of bare and FRP strengthened shells have been numerically simulated and validated with respective experiments. Subsequently, the difference in buckling response between FRP strengthened and bare aluminium shells with variations in cut-out’s size, orientation, shape, and corner radius has been analysed for unstiffened cut-outs. The effect of increase in stiffener’s thickness and overlap width for photo-frame type stiffening of rectangular cut-outs with and without closure has been investigated. The study has revealed interesting observations. (1) Effect of cut-out size on buckling capacity of the shell is a function of its imperfection magnitude. For shells with large initial imperfections, introducing a cut-out as well as with increase in its size, relatively smaller drop in buckling capacity is found; while shells with small initial imperfections resulted in a steep and large drop in buckling load even with a small cut-out size. (2) FRP strengthening is more effective for shells with cut-outs compared to shells without cut-outs, as it increases the flexural stiffness of shell against asymmetric buckles’ initiation and resists outward lip opening along longitudinal edge of cut-out. (3) For shells with large initial imperfections, elliptical cut-outs offer higher buckling resistance than rectangular cut-outs with varying corner radius but with FRP wrapping, rectangular cut-outs with rounded edges exhibit the best buckling performance. (4) In the case of shells with stiffened cut-out, both with or without closure, FRP strengthening is effective only for shells with smaller initial imperfections. Further findings and observations are discussed and concluded.
The behavior of structural steel frames is significantly influenced by the presence of structural and geometric imperfections. The structural imperfections, namely, the residual stresses, are ...generated during most manufacturing processes involving material deformation, heat treatment, machining or processing operations. As the residual stresses, the geometric imperfections are fundamental in the analysis of critical buckling and post-buckling behavior of thin-walled structures. These initial imperfections can be captured using the second order inelastic analysis, also known as advanced analysis. In the modern steel design codes, e.g., European code EC3, Australian code AS4100, North American Code AISC360-16 and Chinese code GB50017 the development of advanced numerical analyses is allowed to predict the behavior of steel and composite frames. However, the random nature of the shapes and magnitudes of the initial imperfections results in difficulties in developing these analyses. Therefore, this paper presents an assessment of the influence of structural imperfections, namely, the residual stresses, and geometric imperfections on the Lateral Distortional Buckling (LDB) strength of steel–concrete Composite Beams (SCCB). The basis of the research is a thorough comparison between numerical and experimental results. Several residual stress patterns found in the literature have been implemented in numerical simulations of four different tests on SCCB subjected to uniform hogging moment. In addition, a sensitive analysis of the geometric imperfection values, namely, the initial bending, was developed. The post buckling numerical analyses were developed with the ABAQUS software. The analysis shown in this work shall help the choice of the initial imperfections on future numerical simulations on SCCB.
•Post buckling numerical analyses are performed in steel-concrete composite beams.•Residual stresses have great influence in the LDB strength.•Differences between experimental and numerical results were verified.•Initial imperfections that provide the best and worst approximation have been determined.
This paper presents a series of validated finite element (FE) models geared to parametrically examine the effects of initial web out-of-flatness imperfections on the shear strength and behavior of ...steel plate girders under pure shear. The prototype girder models are based on field measured imperfection shapes and magnitudes, with variations in web slenderness (93, 109, and 118) and panel aspect ratio (0.89, 2.02, 2.22, and 2.29). Additional model cases are analyzed by incorporating idealized eigenmode shapes and scaled to web out-of-flatness tolerance limits per AASHTO/AWS D1.5. The FE strength results are compared against various code-based nominal shear strength predictions. The following key findings are derived: (1) field measured and eigenmode imperfections exhibit similar shear behavior and deformation response throughout all shear mechanism stages; (2) the yield mechanism of a stiffened web panel in shear is negligibly impacted by the initial imperfections of the web and is triggered by second-order flexural bending from in-plane shear-induced compression; (3) an initial imperfection with an eigenmode shape and a maximum magnitude ranging from d/300 to d/600 (where d equals to the least panel dimension) can suitably approximate the shear strength of plate girders when compared with field measured imperfections; and (4) code-based nominal shear strength predictions demonstrate to be conservative for web panel aspect ratios ≥2.0.
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•Effects of initial web out-of-flatness imperfections on shear strength are studied.•Finite element modeling based on panel extension models was utilized.•Effects of field-measured imperfections are similar to those of eigenmode shapes.•First positive eigenmode with a peak magnitude of d/300 to d/600 is recommended.•Code-based predictions are unconservative for a/D=0.89 but conservative for a/D≥2.0.
Concrete-filled steel tubular (CFST) truss is a type of composite structure with CFST chords and hollow tubular braces. CFST trusses have been increasingly used in large-scale structures such as ...towers, bridge girders, piers and arch ribs. The compression and flexural behaviour of CFST trusses are greatly improved compared to hollow tubular trusses due to the concrete infill in chords. With the complex configuration, nonlinear material interaction and sophisticated construction process, initial imperfections may largely affect the strength and stability of a CFST truss structure. Relevant studies in the past mostly focused on one single type of imperfection with assumed magnitude in CFST member whilst in reality a variety of combinations of steel and concrete imperfection exist. This paper develops a nonlinear analysis formwork with the reliability analysis of CFST truss with random imperfections based on on-site measurement data and Monte-Carlo (MC) simulations. Advanced nonlinear finite element analysis (FEA) that can account for the material interaction and confinement in CFST trusses is established and validated by reported test data. The flexural behaviour of CFST trusses with deterministic and probabilistic initial imperfections are evaluated and compared, based on which the reliabilities and related system resistance factors in regards to random initial imperfections are proposed.
•We presented finite element analysis on CFST truss with initial imperfection taken into consideration.•We conducted sensitivity analysis of CFST truss with random initial imperfection based on Monte-Carlo simulation.•We conducted reliability analysis and presented resistance factors for CFST truss with random initial imperfection.
Initial thickness imperfections of thin membranes due to manufacturing are inevitable and commonly observed. This paper presents an experimental and numerical investigation on how thickness ...imperfections affect the wrinkling of stretched membrane structures. With the measured data from a limited number of samples, we model the uncertain deviation of membrane thickness from that of a perfect geometry as a non-probabilistic bounded field with spatial dependency. After representing the bounded field as a linear function of a reduced set of uncertain coefficients by using a series expansion, the effect of thickness imperfections on the membrane wrinkling is investigated. To this end, the upper and lower bounds of out-of-plane displacements for membranes with initial imperfections are evaluated by a mathematical programming. The proposed wrinkling evaluation problem is then solved efficiently by using the Kriging-based optimization algorithm, with validation done by Monte Carlo simulation. The results show that initial thickness imperfections play a critical role in the wrinkling behavior of membranes.
In this article the effect of a rectangular cutout on the buckling behavior of a thin composite cylinder was investigated using numerical and experimental methods. To verify the finite element ...results, a limited number of tests was carried out on perforated and non-perforated glass/epoxy cylinders with 90/−23/23/90 layups. In the numerical analysis, linear and nonlinear approaches were employed to study the effect of initial imperfections on the buckling of the cylinders. Several key findings including the effects of cutout size and orientation, and the mutual effects of the cutout and initial imperfections on the buckling behavior were investigated in detail.
In the presence of cutouts, the effect of initial imperfections on the buckling load is a function of the cutout size. In cylinders with rectangular cutouts, buckling analysis revealed that a rectangular cutout in the circumferential direction causes around 8% more reduction in the buckling load than the same cutout in the axial direction. Also, numerical findings illustrated that elastic stress concentration factors for the circumferential cutouts are much greater than those for the axial cutouts; thus premature failure around the cutout will trigger earlier buckling in the cylinder with circumferential cutouts.
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