Search Results (97)

Channels with three standard symmetrical sections and one asymmetric section are mounted as cantilever beams with the web oriented vertically. A classical solution to the analysis of stress in each thin-walled cantilever channel is provided using the principle of wall shear flow superposition. The latter is coupled with a further superposition between axial stress arising from bending and from the constraint placed on free warping imposed at the fixed end. Closed solutions for design are tabulated for the net shear stress and the net axial stress at points around any section within the length. Stress distributions thus derived serve as a benchmark structure for alternative numerical solutions and for experimental investigations. The conversion of the transverse free end-loading applied to a thin-walled cantilever channel into the shear and axial stress that it must bear is outlined. It is shown that the point at which this loading is applied within the cross-section is crucial to this stress conversion. When a single force is applied to an arbitrary point at the free-end section, three loading effects arise generally: bending, flexural shear and torsion. The analysis of each effect requires that this force’s components are resolved to align with the section’s principal axes. These forces are then considered in reference to its centroid and to its shear centre. This shows that axial stress arises directly from bending and from the constraint imposed on free warping at the fixed end. Shear stress arises from flexural shear and also from torsion with a load offset from the shear centre. When the three actions are combined, the net stresses of each action are considered within the ability of the structure to resist collapse from plasticity and buckling. The novelty herein refers to the presentation of the shear flow calculations within a thin wall as they arise from an end load offset from the shear centre. It is shown how the principle of superposition can be applied to individual shear flow and axial stress distributions arising from flexural bending, shear and torsion. Therein, the new concept of a ‘trans-moment’ appears from the transfer in moments from their axes through centroid G to parallel axes through shear centre E. The trans-moment complements the static equilibrium condition, in which a shift in transverse force components from G to E is accompanied by torsion and bending about the flexural axis through E. Full article

Cold-formed steel (CFS) channel beams are increasingly used as primary structural elements in modern construction due to their lightweight and high-strength characteristics. To accommodate building services, these members often feature perforations—typically circular and unstiffened—produced by punching. Recent studies indicate that adding edge stiffeners, particularly around circular web openings, can improve flexural strength. Extending this idea, attention has shifted to hexagonal web perforations; however, limited research exists on the bending performance of hexagonal cold-formed steel channel beams (HCFSBs). This study presents a detailed nonlinear finite element (FE) analysis to evaluate and compare the flexural behaviour of HCFSBs with unstiffened (HUH) and edge-stiffened (HEH) hexagonal openings. The FE models were validated against experimental results and expanded to include a comprehensive parametric study with 810 simulations. Results show that HEH beams achieve, on average, a 10% increase in moment capacity compared to HUH beams. However, when evaluated using current Direct Strength Method (DSM) provisions, moment capacities were underestimated by up to 47%, particularly in cases governed by lateral–torsional or distortional buckling. A reliability analysis confirmed that the proposed design equations yield accurate and dependable strength predictions. Full article

Flexure-based linear stages have become prevalent in precision engineering; however, most designs suffer from parasitic shifts that degrade positioning accuracy. Conventional solutions to mitigate these parasitic motions often compromise support stiffness, reduce motion range, and increase structural complexity. This study presents a novel family of flexure-based rectilinear-motion stages using coupled n-RRR planar parallel mechanisms, achieving extremely low parasitic shifts while addressing the forementioned limitations. Four design variants are selected and analyzed via Finite Element Method (FEM) simulations, evaluating parasitic shifts, stroke, and support stiffness. The most precise configuration, a 4-RRR rectilinear stage having kinematic chains coupled via two Watt linkages, exhibits a lateral shift smaller than 0.258 µm and an in-plane parasitic rotation smaller than 12.6 µrad over a 12 mm stroke. Experimental validation using a POM prototype confirms the high positioning precision and support stiffness properties. In addition, a silicon prototype incorporating thermally preloaded buckling beams is investigated to reduce its translational stiffness. Experimental results show a translational stiffness reduction of 98% in the monostable configuration and 112% in the bistable configuration (i.e., negative stiffness), without support stiffness reduction. These results highlight the potential of the proposed mechanisms for a wide range of precision applications, offering a scalable and high-accuracy solution for micro- and nano-positioning systems. Full article

This study investigates the flexural performance of desert sand concrete-filled steel tube (DS-CFST) members through experimental validation and finite element modeling (FEM). An extensive database of square and circular CFST specimens subjected to pure bending was analyzed to validate an ABAQUS-based FEM. Parametric studies evaluated the influence of steel yield strength, steel ratio, stirrup confinement, and desert sand replacement ratio (r) on ultimate bending moment, stiffness, and failure modes. The results indicated that steel yield strength and section geometry significantly affected bending capacity, while desert sand substitution (r ≤ 1) had a negligible impact on capacity, reducing it by less than 3%. The FEM accurately predicted buckling patterns, moment-curvature relationships, and failure modes. New design formulas for predicting ultimate bending moment and flexural stiffness were proposed, demonstrating superior accuracy (mean error < 1%) compared to existing design codes (AIJ, AISC, GB). This study highlights that DS-CFST members, particularly circular sections, offer robust flexural performance, with enhanced ductility and uniform stress distribution. The findings underscore the potential of using desert sand as a sustainable material in concrete-filled steel tube structures without compromising structural integrity. Full article

This paper presents a novel algorithm, Variable Spacing and Extrusion (VaSE), designed to optimize the infill pattern of material extrusion (ME) 3D-printed parts for specified mechanical performance while ensuring manufacturability. The algorithm adjusts deposition spacing and width across layers to achieve functionally graded infill distributions derived from input density maps. First, the variable line spacing algorithm is implemented by normalizing the weighted density distribution. Errors in between the desired density and the density from the line spacing are corrected with a varying extrusion width algorithm. Two application scenarios are demonstrated with the proposed VaSE algorithm. First, beam samples are optimized for flexural stiffness and tested under three-point bending, showing a 10.8–19.2% stiffness increase compared to homogeneous infill, except at low (25%) volume fractions, where local buckling dominated failure. The second scenario involves maximizing the frequency of the first three modes of beams under an induced vibration. The optimized beams, taken straight from a topology optimization algorithm performed in the ANSYS 2023 finite element software, were compared to the beams that were instead put through the VaSE algorithm after the topology optimization. While all manufactured beams underperform relative to simulation, the VaSE-optimized beams show substantial frequency gains (34–63% for the first mode, 0.82–65% for the second mode) over purely geometry-based designs, with the exception of high-mass-fraction beams. These findings highlight the significance of the VaSE algorithm in enhancing mechanical performance and extending the design space of ME additive manufacturing beyond conventional homogeneous infill strategies. Full article

The flexural buckling failure is a relatively common instability phenomenon in rock slopes both at the small and large scale. It poses a serious threat to the normal operation and maintenance of nearby infrastructure and the life and property safety of surrounding residents. A profound understanding of the deformation and failure mechanism of flexural buckling, as well as the development of quantitative approaches for buckling stability analyses, are of great significance for the risk identification and control of buckling landslides. This study combines the literature relevant to flexural buckling of rock slopes by systematically reviewing the research progress and trends from 1970 to 2023, following the research path of “triggering mechanism → analysis methods”. Based on this proposition, the intrinsic and triggering factors that influence the deformation process of flexural buckling failure in dip rock slopes are detailed and clarified. Then, the main progress achieved in physical, analytical, and numerical modelling regarding the stability and run-out analysis of buckling landslides is comprehensively introduced. Finally, this study provides some outlooks for future research and practice in the field of buckling landslides. Full article

To study the mechanical properties of asymmetric K-shaped square tubular joints with built-in stiffening rib lap joints, axial tensile tests were carried out on one K-shaped joint without built-in stiffening ribs and four K-shaped joints with built-in stiffening ribs using an electro-hydraulic servo structural testing system. The effects of the addition of stiffening ribs and the welding method of the stiffening ribs on the mechanical properties were studied comparatively. The failure mode of the K-shaped joint was obtained, and the strain distribution and peak displacement reaction force in the nodal region were analyzed. A finite element analysis of the K-shaped joint was carried out, and the finite element results were compared with the experimental results. The results showed that the addition of transverse reinforcement ribs and more complete welds shared the squeezing effect of the brace on the chord. Arranging more reinforcing ribs in the fittings makes the chord more uniformly stressed and absorbs more energy while increasing the flexural load capacity of the fittings’ side plates. The presence of a weld gives a short-lived temperature increase in the area around the crack, and the buckling of the structure causes the surface temperature in the buckling area to continue to increase for some time. The temperature change successfully localized where the structure was deforming and creating cracks. The addition of the reinforcing ribs resulted in a change in the deformation pattern of the model, and the difference occurred because the flexural capacity of the brace with the added reinforcing ribs was greater than that of the side plate buckling. Full article

This review investigates interlayer hybrid fiber composites for wind turbine blades (WTBs), focusing on their potential to enhance blade damage tolerance and maintain structural integrity. The objectives of this review are: (I) to assess the effect of different hybrid lay-up configurations on the damage tolerance and failure analysis of interlayer hybrid fiber composites and (II) to identify potential fiber combinations for WTBs to supplement or replace existing glass fibers. Our method involves comprehensive qualitative and quantitative analyses of the existing literature. Qualitatively, we assess the damage tolerance—with an emphasis on impact load—and failure analysis under blades operational load of six distinct hybrid lay-up configurations. Quantitatively, we compare tensile and flexural properties—essential for WTBs structural integrity—of hybrid and glass composites. The qualitative review reveals that placing high elongation (HE)-low stiffness (LS) fibers, e.g., glass, on the impacted side reduces damage size and improves residual properties of hybrid composites. Placing low elongation (LE)-high stiffness (HS) fibers, e.g., carbon, in middle layers, protects them during impact load and equips hybrid composites with mechanisms that delay failure under various load conditions. A sandwich lay-up with HE-LS fibers on the outermost and LE-HS fibers in the innermost layers provides the best balance between structural integrity and post-impact residual properties. This lay-up benefits from synergistic effects, including fiber bridging, enhanced buckling resistance, and the mitigation of LE-HS fiber breakage. Quantitatively, hybrid synthetic/natural composites demonstrate nearly a twofold improvement in mechanical properties compared to natural fiber composites. Negligible enhancement (typically 10%) is observed for hybrid synthetic/synthetic composites relative to synthetic fiber composites. Additionally, glass/carbon, glass/flax, and carbon/flax composites are potential alternatives to present glass laminates in WTBs. This review is novel as it is the first attempt to identify suitable interlayer hybrid fiber composites for WTBs. Full article

This paper presents an experimental and numerical investigation of the axial compression behavior of perforated cold-formed steel upright profiles commonly used in pallet racking systems. The primary objective is to examine how slenderness influences the failure modes and load-bearing capacity of these structural elements. Three column lengths, representative of typical vertical spacing in industrial rack systems, were tested under pin-ended boundary conditions. All specimens were fabricated from 2 mm thick S355 steel sheets, incorporating web perforations and a central longitudinal stiffener. Experimental results highlighted three distinct failure mechanisms dependent on slenderness: local buckling for short columns (SS-340), combined distortional–flexural buckling for medium-length columns (MS-990), and global flexural buckling for slender columns (TS-1990). Finite Element Method (FEM) models developed using ANSYS Workbench 2021 R1 software accurately replicated the observed deformation patterns, stress concentrations, and load–displacement curves, with numerical results differing by less than 5% from experimental peak loads. Analytical evaluations performed using the Effective Width Method (EWM) and Direct Strength Method (DSM), following EN 1993-1-3 and AISI S100 specifications, indicated that EWM tends to underestimate the ultimate strength by up to 15%, whereas DSM provided results within 2–7% of experimental values, especially when the entire net cross-sectional area was considered fully effective. The originality of the study is the comprehensive evaluation of full-scale, perforated, stiffened cold-formed steel uprights, supported by robust experimental validation and detailed comparative analyses between FEM, EWM, and DSM methodologies. Findings demonstrate that DSM can be reliably applied to perforated sections with moderate slenderness and adequate web stiffening, without requiring further local reduction in the net cross-sectional area. Full article

A generalized buckling solution for anisotropic laminated composite fixed–free columns under axial compression is developed using the critical stability matrix. The axial, coupling, and flexural equivalent stiffness coefficients of the anisotropic layup are determined from the generalized constitutive relationship through the static condensation of the composite stiffness matrix. The derived formula reduces down to the Euler buckling equation for isotropic and some special laminated composites. The analytical results are verified against finite element solutions for a wide range of anisotropic laminated layups yielding high accuracy. A parametric study is conducted to examine the effects of ply orientations, element thickness, finite element type, column size, and material properties. Comparisons with numerical results reveal a very high accuracy across the entire parametric profile and a linear correlation between the percentage error and a non-dimensional condensed parameter is extracted and plotted. Full article

The double crystal monochromator (DCM) is a spectrometer in synchrotron radiation beamlines, and its stability directly impacts the quality of the emitted light. In order to meet the requirements of the fourth generation of synchrotron light sources, researchers have designed a DCM using an active control method to ensure stability by actively compensating for crystal displacement through voice coil motors. The active control method imposes high demands on the vibration isolation performance of the DCM frame. In response to external excitation characteristics, this paper proposes a quasi-zero stiffness (QZS) isolation system based on a compressed buckling beam structure. Random vibration simulations using finite element analysis revealed that, under different operating conditions, the 3σ displacement of the core part of the DCM is maintained at the nanometer level. Moreover, this paper presents a calculation method based on elastic potential energy to establish force equilibrium equations for negative stiffness and analyzes stress distribution in the beam during vibration using the derived deflection curve. Validation through finite element simulations confirms the method’s accuracy in calculating negative stiffness and stress distribution. Because of the structural similarities, some of the results of this paper can be applied to the study of negative stiffness honeycomb materials. Full article

Cold-formed steel (CFS) unsymmetrical angles are increasingly used in structural applications such as portal frames, roof trusses, and transmission towers. However, research on built-up face-to-face unsymmetrical CFS angle columns (FFUACs) with stiffeners remains limited. This study addresses this gap by presenting the findings from six experimental investigations on intermediate FFUACs connected using intermittent screw fasteners. The results offer insights into failure deformation patterns and load-axial shortening behaviour. A nonlinear finite element (FE) model was developed to account for material and geometric nonlinearity, with experimental results used for validation. This study contributes 166 new data points, including six experimental tests under concentric compression and 160 finite element analysis (FEA) results focused on the compressive strength of FFUACs. Additionally, this study evaluates the performance of existing design guidelines based on the direct strength method (DSM). The DSM strength predictions were found to be less conservative for stub FFUAC specimens that failed due to local buckling and more conservative for short FFUAC specimens that failed due to a combination of local and flexural buckling. A revised DSM methodology is proposed to address these discrepancies. Full article

Stiffened steel corrugated shear walls (SSCSWs) have achieved extensive applications in building structures and serve as efficient lateral force-resisting members. Single-side-stiffened steel corrugated shear walls (SS-SCSWs) are more flexible in terms of their structural configuration compared to conventional SSCSWs because this novel structural member effectively reduces wall thickness and simplifies the construction process. In this paper, numerical analyses were carried out to investigate the shear elastic buckling and resistant behavior of SS-SCSWs. A formula for the equivalent flexural stiffness of single-side stiffeners was given based on theoretical analysis. The elastic buckling and elastoplastic analyses of SS-SCSWs were carried out by finite element (FE) models to determine the value of the equivalent flexural stiffness coefficient. Meanwhile, the elastic and elastoplastic transition stiffness ratios of single-side stiffeners were proposed to predict the minimum stiffness required for the stiffener to provide sufficient constraint. The accuracy of the above formulas was verified by calculating the shear elastic buckling loads, the ultimate shear resistance, and the out-of-plane displacements of the SS-SCSWs. Furthermore, parametric analyses were performed to reveal the influences of the aspect ratio and plate thickness on shear resistance capacity. The equivalent flexural stiffness coefficients in both the elastic and elastoplastic analyses were determined to be 0.45 and 0.7, respectively, through curve fitting. The results indicated that the theory of BS-SCSWs could accurately predict the shear elastic and elastoplastic behavior of SS-SCSWs after modifying its expression for flexural stiffness. Consequently, the modified theoretical formulas were demonstrated to be suitable for SS-SCSWs in practical designs. Full article

This study investigates the effectiveness of polyether block amide (PEBA) thermoplastic elastomeric nanofibers in reducing low-velocity impact damage across three carbon fiber composite lay-up configurations: a cross-ply [0°/90°]2s (CP) and a quasi-isotropic [0°/45°/90°/−45°]s (QI) lay-up utilizing unidirectional plies, and a stacked woven [(0°,90°)]4s (W) lay-up using twill woven fabric plies. The flexural strength and interlaminar shear strength of the composites remained unaffected by the addition of nanofibers: around 750 MPa and 63 MPa for CP, 550 MPa and 58 MPa for QI, and 650 MPa and 50 MPa for W, respectively. The incorporation of nanofibers in the interlaminar regions resulted in a substantial reduction in projected damage area, ranging from 30% to 50% reduction over an impact energy range of 5–20 J. Microscopic analysis showed that especially the delamination damage decreased in toughened composites, while intralaminar damage remained similar for the cross-ply and quasi-isotropic lay-ups and decreased only in the woven lay-up. This agrees with the broad body of research that shows that interleaved nanofibers result in a higher delamination resistance due to toughening mechanisms related to nanofiber bridging of cracks. Despite their ability to mitigate delamination during impact, nanofibers showed limited positive effects on Compression After Impact (CAI) strength in quasi-isotropic and cross-ply composites. Interestingly, only the woven fabric composites demonstrated improved CAI strength, with a 12% improvement on average over the impact energy range, attributed to a reduction in both interlaminar and intralaminar damage. This study indicates the critical role of fiber integrity over delamination size in determining CAI performance, suggesting that the delaminations are not sufficiently large to induce buckling of sub-layers, thereby minimizing the effect of nanofiber toughening on the CAI strength. Full article

An experimental study of cold-formed thin-walled steel unequal-leg angles (CFTWS-ULAs) under axially oriented pressure is presented in this paper. Firstly, the initial imperfections and material properties of the angle specimens were measured in detail. The angle specimens were tested under fixed-ended conditions. The results of the experiments showed that the angle specimens with small slenderness ratios were susceptible to local buckling, the angle specimens whose legs had high slenderness ratios and low width–thickness ratios were found to easily suffer from the occurrence of flexural buckling, and the angle specimens whose legs had high width–thickness ratios were found to easily suffer from the occurrence of interactive buckling between local buckling and flexural buckling. The finite element analysis of the ULAs was conducted using ABAQUS6.14 finite element software by creating a model. The buckling modes and ultimate bearing capacities of the test specimens were compared, and the finite element analysis verified that the established model built using the finite element is credible and subsequent parametric analysis was performed. The slenderness ratio had the most significant impact on the ultimate bearing capacities of the unequal-leg angles, as indicated by the analysis results. When the width–thickness ratio and the width ratio of the legs fell within a specific range, the ultimate bearing capacities of the unequal-leg angles increased as the width–thickness ratio and the width ratio of the legs increased. Finally, the comparison results showed that the design strengths predicted by the specifications were very conservative, because the local buckling and torsional buckling were calculated at the same time. Therefore, a recommendation was proposed that the calculation of the load-carrying capacity of an unequal-leg angle should ignore torsional buckling. Full article