Influence of web holes on the axial compressive buckling behavior of LQ550 high-strength cold-formed steel columns with web stiffeners

Experimental investigation into the axial compressive buckling behavior of LQ550 cold-formed channel columns with web openings

The development of SUV electric vehicles requires a crash box system that is able to reduce deformation more effectively than conventional hollow designs that tend to be unstable when subjected to high-energy impacts. This study compared the performance of three crash box models, namely hollow, lattice 3D-printed core, and lattice with internal divider wall using ANSYS Explicit Dynamics simulation. The main parameters analyzed include the folding pattern of collapse and maximum deformation as indicators of structural stability. The simulation results showed that all models were in concertina deformation mode, but the stability levels differed significantly. The crash box hollow recorded the largest deformation of 47,579 mm, while the divider-less lattice model decreased to 38,899 mm. The lattice configuration with divider walls is the most superior design with a minimum deformation of 31,098 mm, as well as a more symmetrical and controlled fold pattern. These findings confirm that the integration of the lattice structure, especially with the internal divider is capable of increasing rigidity and inhibiting axial buckling without significant mass gain. Further research is recommended evaluating lattice topology variations and experimental tests as verification of numerical results.

This article investigates the free vibration and axial buckling of sandwich cylindrical shells with anti-tetrachiral auxetic core and laminated composite face sheets using third-order shear deformation and Donnell’s shell theories. By applying Hamilton’s principle, the equations of motion are extracted, and the natural frequencies and buckling loads for various boundary conditions are obtained using Fourier series and state-space methods. A homogenization-based approach is utilized to calculate the mechanical properties of the anti-tetrachiral core. The results are validated with available data from prior studies and through finite element simulations. Numerical studies are presented to investigate the influence of geometric parameters of the anti-tetrachiral cell, boundary conditions, and face sheet lay-ups on the natural frequencies and buckling loads. Findings reveal that while the geometric parameters of anti-tetrachiral auxetic cells significantly affect the natural frequencies (up to six-fold) and buckling loads (by nearly two orders of magnitude) in single-layer anti-tetrachiral auxetic shells, the Poisson’s ratio remains constant near −1. However, in sandwich shells with composite face sheets, these geometric variations have milder influence on both natural frequencies and buckling loads. Moreover, the auxetic core reverses the trend of natural frequency variations in different cross-ply laminated shell configurations compared to non-auxetic ones.

Abstract This study investigates the axial compression buckling and post-buckling behavior of carbon fiber-reinforced composite hat-stiffened panels under room temperature dry (RTD) and elevated temperature wet (ETW) conditions. Comparative analysis shows that hygrothermal aging has a minimal effect on the initial buckling load, with an average reduction of approximately 1.2%, but significantly reduces the post-buckling load-carrying capacity, with an average failure load decrease of about 8.3%. Strain measurements indicate that skin buckling occurs first, followed by stiffener instability, ultimately leading to global structural failure. Although the overall failure mode remains unchanged under hygrothermal conditions, the aging environment considerably accelerates damage propagation, causing the structure to reach catastrophic failure at an earlier stage.

The increasing adoption of back-to-back built-up cold-formed steel (CFS) channel columns in construction is attributed to their lightweight nature, versatility in shape fabrication, ease of transportation, cost efficiency, and enhanced load-bearing capacity. Additionally, the incorporation of web openings facilitates the integration of electrical, plumbing, and heating systems. These built-up sections are widely utilized in wall studs, truss elements, and floor joists, with intermediate screw fasteners strategically positioned at regular intervals to prevent the independent buckling of channels. Based on 18 experimental tests, this study demonstrates an excellent correlation between finite element analysis and the experimental results, confirming the accuracy of geometrically and materially nonlinear finite element modeling in predicting the axial buckling strength of built-up short columns. Furthermore, the design standards of the American Iron and Steel Institute and Australian/New Zealand Standards were found to underestimate the axial load capacity by approximately 12.5%. The primary objective of this research is to investigate the influence of various hole configurations, both with and without stiffeners, on the axial performance of built-up short CFS channel columns. A total of 180 finite element models were developed, examining four different unstiffened and edge-stiffened hole configurations, validated against experimental results from plain webs. The findings reveal that web holes and edge stiffeners significantly impact axial load-bearing capacity, while the specific shape of the openings has a negligible effect. Specifically, introducing a hole at the centroid of each web results in an approximate 8.5% reduction in axial load capacity in the absence of edge stiffening. However, the incorporation of stiffeners around the perforations mitigates this reduction and enhances both structural efficiency and load-bearing capacity. These results highlight the critical role of edge stiffening in optimizing the structural performance of perforated built-up CFS columns.

A Comprehensive Experimental and Numerical Analysis on Free Vibration and Axial Buckling Behavior of Hybrid Composites

Abstract Large bending and axial compression are two typical load conditions that cause axial buckling in buried oil and gas pipelines. A numerical simulation model is established using nonlinear finite element software to compare the buckling response characteristics of pipelines under these two types of loads and to explore the applicability of the current standards “Oil and Gas Pipeline Systems” (CSA Z662-2011) and “Seismic Technical Code for Oil and Gas Transmission Pipeline Engineering” (GB/T 50470-2017). The influence of different parameters on buckling is analyzed. By comparing the ultimate compressive strains obtained from simulations under various conditions with the ultimate compressive strains calculated using the recommended formulas in CSA Z662-2011 and GB/T 50470-2017, it is found that the results from CSA Z662-2011 and GB/T 50470-2017 are not conservative for the axial compression model but are conservative for the bending loading mode. The ultimate compressive strain of the pipeline under axial compression load is always smaller than that under bending load. Based on the simulation results, an analytical formula for calculating the ultimate compressive strain of the pipeline with higher accuracy is obtained. The research results can provide guidance for pipeline engineering design and construction.

Effect of residual stress on the axial buckling behaviour of the hydraulic-formed bellows

Torsional and axial buckling analysis of bio-inspired helicoidal laminated composite cylindrical shells

Effects of cutouts on the axial buckling strength of steel thin-walled cylindrical shells

Abstract This work experimentally investigated how ultraviolet (UV) aging affects the buckling properties of polymer-based intraply hybrid composites reinforced with nanoparticles (NPs) and varied in weight ratios. The nanoclay reinforced intraply carbon/aramid/epoxy composite samples with six different weight ratios of nanoparticles (0, 0.5, 1, 1.5, 2, 3%) were subjected to axial and lateral buckling tests after 250 h and 500 h of UV aging. At the end of the study, SEM images were taken for both buckling types and the damage patterns of the composite materials were analyzed. Considering the unaged samples, the critical buckling load (Pcr) of hybrid composites with NP reinforcement reached the highest values for 1% wt, with increases of 22.28 and 25.98% for the axial and lateral buckling test, respectively. The addition of more particles by weight resulted in a gradual decrease in the Pcr for both buckling tests. The Pcr decreases for axial and lateral buckling tests of unaged samples with 3 wt% nanoparticle reinforcement were found to be 8.18% and 25.43%, respectively. Experimental results showed that the buckling features of intraply samples changed due to both UV exposure and the addition of NPs. Furthermore, as UV exposure time increases, the Pcr for each weight ratio increased for both buckling types. Considering the UV effect, the axial Pcr increased by 32.07% and 40.89% in 1%wt particle reinforced samples after 250 and 500 h of UV aging, respectively. Similarly, an increase of 32.65% and 42.32% in lateral Pcr was observed in 1%wt particle reinforced samples after 250 and 500 h of UV aging, respectively. Finally, SEM images revealed matrix cracks, fiber breakage, debris, microbuckled fiber, and delamination mode failure morphologies.

Reinforced concrete (RC) columns are the vital part of building structures and play an important role in the stability and safety of the entire building under axial compression load. In this study, the buckling performance of layered RC columns made of NC, LWC and containing thermo-stone aggregate replacements was studied experimentally. Eighteen square and circular RC columns with different layer arrangements—LNN, LNL, and NNL—were tested under axial loading. Results showed that the NNL and LNN geometry performed better than the fully LWC columns in terms of axial compression and buckling. More precisely, square NNL columns with 25% thermo-stone replacement can attain an axial load capacity of 339.13kN, that represents a value 21.6% larger than the same fully LWC column (278.85kN). Similarly, layered circular columns with 50% thermo-stone replacement (CR-7 and CR-8) recorded 290.5–290.8kN, compared to 245.9kN for the fully LWC counterpart (CR-6). Deflections ranged from 3.75 mm in NC columns to 5.23 mm in layered LWC columns. Square columns consistently exhibited higher buckling resistance than circular ones due to their greater moment of inertia. The findings highlight that strategically placing NC in the middle and upper layers enhances structural performance while maintaining weight reduction.

The incorporation of carbon nanotubes (CNT) into a polymer matrix has opened up exciting possibilities for creating Nano-composite materials with exceptional mechanical properties. In this study, the buckling behavior of a reinforced polymer plate mixed with CNTs is investigated. Various factors, such as the plate’s shape and the elastic base, are examined for their effects on behavior. The investigation is grounded in scientific rigor, drawing upon several theories that address plate behavior. Specifically, the high-order theory, which accounts for transverse shear effects and the parabolic distribution of transverse shear stresses across the plate thickness, is employed. By analyzing the critical buckling load, the interaction between different types of carbon nanotubes within the polymer matrix and the elastic medium is explored. The model’s governing equations, derived from Hamilton’s principle, allow for the prediction of the critical loads associated with axial compression buckling. Notably, it is found that the parabolic distribution, coupled with the Winkler—Pasternak elastic foundation, renders the plate less flexible compared to scenarios without an elastic foundation. This insight leads to a crucial enhancement in the critical buckling load. The significance of incorporating carbon nanotubes in polymer matrices to achieve nanocomposite materials with exceptional properties is underscored. The scientific foundation upon which this study rests provides valuable insights for designing robust and efficient structures.

ABSTRACT This paper presents experimental investigation of the axial behaviour of built-up (BU) (I-section) cold-formed steel doubly-symmetric channel with single-/double-layer sheathing on both sides configuration. Fifteen (15) monotonic concentric axial compression tests were performed on 7-BU sections with single-layer sheathing, 7-BU sections with double-layer sheathing, 1-BU section stud without sheathing. The experiments aim to enumerate ultimate axial strength, buckling interactions, failure pattern and strength enhancement due to sheathing for BU section stud members. The novelty of the study is that, for the first time an attempt is made to investigate the axial behaviour of single-/double-layer sheathed BU section panels using seven different sheathing boards. Results indicate large range of deformation behaviour, with local-global and distortional-global interaction buckling phenomena. Failure is also observed due to failing of screws in specimens with sheathing of thickness ≥ 9 mm and modulus of elasticity > 6400MPa. Also, for the first time, efficacies of four semi-analytical methods based on rational extension of direct strength method (DSM) are presented. Results suggest the insufficiency of current AISI design specifications, whereas predicted results obtained using the new modified DSM methodology are within the adequate variation range as the adopted methodology considers desired buckling interaction. The efficacy of the recommended design methodology is verified through reliability analysis.

Abstract As a lesson learned from the Fukushima nuclear accident, the importance of accident mitigation for Beyond Design Basis Events (BDBEs) is recognized. Excessive earthquake is a typical BDBE. During such events, the Fast Reactor Vessel (FRV) is vulnerable to buckling. The safety goal of FRV under excessive earthquake is to achieve a stable post-buckling state. Our previous study on bending buckling confirmed a global response stability under horizontal vibration. As a parallel study, this paper focuses on axial compression buckling under vertical vibration. Shaking table experiments using thin-walled cylindrical models (R/t=260) are carried out. Similar methodology is applied to investigate the buckling and post-buckling behavior. It is found that axial compression buckling shares an extensive similarity with bending buckling in both buckling mode and post-buckling behavior. Similar global response stability is confirmed due to phase-inverse phenomenon. After buckling, buckling failure becomes stable and does not progress further even when an intense input amplitude is continuously applied. The vibrational load acts as a displacement-controlled load in the out-of-phase domain such that immediate collapse is prevented. Most input energy is dissipated in hysteresis loops rather than being carried by the mass. These mechanisms are independent of input waveform and can be applied to an arbitrary seismic input. In addition, a conservative limit displacement for global response stability is identified. Moreover, the effect of the input frequency ratio, the initial geometrical imperfection and the gravitational force on the post-buckling behavior are clarified.

Buckling behavior of thin-walled cold-formed steel latticed column with lacings under axial compression

Investigating the Effect of Porosity and Pore Shape on Porous Polymer Structure Under Axial Compression and Buckling Behaviour

Steel circular hollow section (CHS) members are widely utilized as axial force-resisting structural members in civil engineering structures. The buckling strength under axial loads is one of the critical parameters to determine the performance of the steel CHS members, which is significantly affected by the discreteness introduced by geometries, material, and initial imperfections. However, the reduction factor employed in the modern design codes (i.e. Chinese codes and EC3) only accounts for the reduction caused by all kinds of discreteness and does not reflect the impacts of every single discreteness and imperfection. To fill the gap, this paper proposed an interpretable machine-learning method to provide the probabilistic axial buckling strength of steel CHS members prediction result in a distribution form with the consideration of detailed discreteness. The model to predict the nominal axial buckling strength of steel CHS members was first developed utilizing ten machine learning algorithms after sufficient numerical simulations, where the numerical model was verified using test results. The artificial neural network (ANN) was selected for developing the prediction model due to its highly reliable performance in testing. The developed ANN models were further interpreted utilizing Shapley Additive exPlanations (SHAP) to determine the interrelationship of different parameters. Then, the probabilistic axial bucking strength prediction model was established based on the developed ANN models, where the Latin hypercube sampling method was applied to address the discreteness of geometries, material, and initial imperfections. The generated probabilistic axial bucking strength prediction model’s effectiveness was verified by the evidence that the machine learning prediction results can highly match the numerical results' probability density function and the result from codes while significantly reducing the computation time. Finally, the design parameters’ impact on the axial buckling strength’s discreteness was evaluated using the global sensitivity analysis (GSA) method. The result shows that the discreteness of design parameters substantially influences the distribution of the axial buckling strength of the steel CHS members and the proposed prediction model can provide an accurate probabilistic distribution prediction.

The failure of synthetic small-diameter vascular grafts has been attributed to a mismatch in the compliance between the graft and native artery, driving mechanisms that promote thrombosis and neointimal hyperplasia. Additionally, the buckling of grafts results in large deformations that can lead to device failure. Although design features can be added to lessen the buckling potential, the addition is detrimental to decreasing compliance (e.g., reinforcing coil). Herein, we developed a novel finite element framework to inform vascular graft design by evaluating compliance and resistance to buckling. A batch-processing scheme iterated across the multi-dimensional design parameter space, which included three parameters: coil thickness, modulus, and spacing. Three types of finite element models were created in FEBio for each unique coil-reinforced graft parameter combination to simulate pressurization, axial buckling, and bent buckling, and results were analyzed to quantify compliance, buckling load, and kink radius, respectively, from each model. Importantly, model validation demonstrated that model predictions agree qualitatively and quantitatively with experimental observations. Subsequently, data for each design parameter combination were integrated into an optimization function for which a minimum value was sought. The optimization values identified various candidate graft designs with promising mechanical properties. Our investigation successfully demonstrated the model-directed framework identified vascular graft designs with optimal mechanical properties, which can potentially improve clinical outcomes by addressing device failure. In addition, the presented computational framework promotes model-directed device design for a broad range of biomaterial and regenerative medicine strategies.