Axial Compression Experiments Research Articles

Axial compression performance and optimum design of round-cornered square CFST with high-strength materials

This study investigates the axial compressive behaviour and optimum design of round-cornered square concrete-filled steel tubes (CFST) with ultra-high performance concrete (UHPC) and high-strength steel (abbreviated as RSUCFST). 11 RSUCFST specimens are designed with various steel strength grades, steel thicknesses and cross-sectional sizes for axial compressive experiments. The results show that the RSUCFST stub columns typically experience shear, mid-height buckling, multiple local buckling and weld failures. The load-displacement curves are quantitated into 5 types based on different confinement indices. Utilizing appropriately thicker and higher-strength steel tubes could likely better match the inner UHPC in designing RSUCFST stub columns, while simply enlarging the cross-sectional size considerably improves the ultimate bearing capacity but weakens the ductility of RSUCFST. The optimum steel ratio (αsc) of 0.09–0.4, width-to-thickness ratio (B/t) less than 45(235/fy)0.5 and confinement index (ξ) of 1.0–2.5 are recommended for RSUCFST stub columns by considering axial compressive behaviour, material efficiency and current code suggestions. Lastly, an analytical predicting model of axial bearing capacity of RSUCFST stub column is proposed according to the confinement in round-cornered square cross-section and well validated by experimental results.

Local buckling behaviour of welded I-section steel stub columns with longitudinally profiled steel plates under axial compression: Testing, modelling and design

The use of welded I-section steel members with longitudinally profiled (LP) steel plates is becoming popular in structures, and such members are manufactured with variable thickness to accommodate the loading distributions in practical construction. Compared with the constant thickness steel plates, the use of LP steel plates is more susceptible to local buckling at the thinner end. However, there was no study that reported the local buckling behaviour of such members. Furthermore, existing design codes do not provide any design guidance for calculating the strength of such steel members. In this paper, a total of sixteen welded I-shaped section stub columns with LP and constant thickness steel plates under axial compression were tested to study the local buckling behaviour of such members. The initial geometric imperfections of all specimens were measured using 3D laser scanning technology prior to the axial compression experiments. A nonlinear finite element (FE) model was also established, and validated against the corresponding experimental results, which showed a good agreement both in terms of ultimate strength and failure modes. An extensive parametric study including 130 FE models was conducted using validated FE models. To evaluate the feasibility and reliability of the existing design provisions for steel members with constant thickness steel plates, the test and numerical results were compared against design strength predicted from the existing design provisions. Upon comparison, the existing design formulas in Chinese Standard (GB 50017–2017), American Specification (ANSI/AISC 360–10) and European Standard (BS EN 1993-1-5) are found to be generally conservative when calculating the strength of such members with LP steel plates. New design formulas are proposed, in which the modified normalized slenderness ratio and enhancement coefficient are applied to the existing design provisions.

A sinusoidal beam lattice structure with negative Poisson's ratio property

In this study, a three-dimensional (3D) beam lattice structure (BLS) with negative Poisson's ratio (NPR) effect is proposed by applying sinusoid-shaped beams. The finite element model of the BLS is established, and its sample is manufactured through selective laser sintering (SLS) technology. The axial compression experiment and simulation are performed to investigate the compression characteristics of BLS. BLS bends to one side in the later stages of compression. It can be concluded that the BLS possess strong NPR effect and excellent energy absorption performance. In addition, the effects of compression direction, amplitude and wavenumber on the compression characteristics of BLS are further analyzed. These BLSs exhibit significant anisotropic features, and they often show the deformation modes of S- and <-shaped. When the loading directions are z- and y-axes, these BLSs have more obvious NPR effect and better energy absorption characteristics compared with those of the x-axis. In addition, it is also found that the minimum values of PR (MPR) of these BLSs often appear in the initial stages of compression, and the maximum values of Poisson's ratio (PR) usually appear around the end of compression. In summary, the BLS has excellent mechanical properties and broad application prospects.

Experimental and numerical studies of concrete-filled corrugated steel tubular column under axial compression

This paper proposed a novel composite structure of concrete-filled corrugated steel tubular column with polygonal steel tubes (CFCST-PST), which consisted of concrete and multi-cell steel tubular column, includingpolygonalsteeltubesandcorrugatedsteelplates. This new column enables the confinement of multi-cell steel tubular column to the core concrete in addition to preventing local buckling of the tubes. To investigate the axial compression mechanical properties of the column and the capabilities of polygonal steel tubes, a concrete-filled corrugated steel tubular column with square steel tubes (CFCST-ST) was designed and fabricated as a comparative specimen. Axial compression experiments and finite element studies (FEM) were carried out on both CFCST-PST and CFCST-ST specimens. Through the previous research, it was found that CFCST-ST has better ductility and higher bearing capacity, while the corrugated plate with higher lateral stiffness, so that concrete is well restrained. In this paper, research had revealed that CFCST-PST effectively expands the strongly confined area of core concrete, as compared to CFCST-ST. A detailed discussion of the strain development of the corrugated plates was presented in order to demonstrate the confinement effect. Finally, the method of confining stress homogenization was used to establish formulas for calculating the axial compression load capacity of CFCST-PST for engineering purposes.

Hierarchical-level failure analysis for CFRC lattice stiffened panel

A hierarchical-level failure analysis method from carbon fiber reinforced composite (CFRC), unit-cell lattice to lattice stiffened component was developed to predict the failure load of lattice stiffened panels. A nondestructive method was applied to identify the composite parameters of lattice ribs. Axial compression experiments were carried out to reveal the failure pattern and load of unit-cell lattice and lattice-stiffened panels. Compared with the standard unidirectional laminate strength, these component failure analyses suggest knock-down factors (KDFs) to include the attenuation effect of the rib node intersection. The failure loads of CFRC lattice stiffened panels were predicted by the KDFs. The research lays a good foundation to design and manufacture large-sized CFRC lattice structures.

Axial compression behavior of strength-gradient composite stub columns encased CFST with small diameter: Experimental and numerical investigation

In order to investigate axial compression behavior for strength-gradient composite stub columns encased concrete filled steel tube with small diameter (SGCC), the axial compression experiments of 13 SGCCs and 1 reinforced concrete (RC) stub column were carried out. The influence regularities of height-width ratio, confinement index (θ), stirrup ratio per unit volume (ρv) and axial compressive strength of core concrete on the failure modes, load–displacement curves and load–strain curves of SGCCs were explored. The results showed that SGCCs mainly exhibited three failure modes under axial compression, including shear failure, central crushing and punching failure. By increasing θ and ρv approximately, SGCCs could exhibit ductile failure instead of brittle failure. The deformations of steel tube, longitudinal steel bars, and concrete for SGCCs maintained coordinated during the loading process. Compared with ordinary RC column, the ultimate bearing capacity (Nu) of SGCCs under axial compression was almost doubled. Based on the experimental results, 30 finite element (FE) models were designed to obtain the influence regularities of various parameters on Nu of SGCCs. Applicability of existed design code to predict Nu of SGCCs was also evaluated. Finally, a novel calculation formula for Nu of SGCCs considering constraint effect of stirrups and steel tubes could be proposed, which were in good agreement with the experimental results.

Modular technique to construct lightweight CFRP lattice structures

Carbon fiber reinforced polymer (CFRP) lattice structures are ultralight but stiff and strong. A modular technique based on tubular textiles was proposed to design and made CFRP lattice structures with different unit cell topologies. Foam-filling technique was applied to strength the modular lattice structure (MLS). The out-of-plane compression behavior and energy absorption performance of these MLSs were investigated by axial compression experiments. Modular and foam filling techniques remarkably improve the energy absorption performance through changing the crushing mode from local bucking to progressive folding and can increase the specific energy absorption (SEA) at a level of 66%. Meanwhile, MLSs have much greater compression strength than traditional foams and honeycombs.

Axial Compression Behaviors of Columns Fabricated from Bamboo Oriented Strand Boards

Due to the low specific strength of bamboo oriented strand boards compared with the commonly used wooden building materials, reasonable and novel cross-section designs of bamboo columns fabricated from bamboo oriented strand boards as structural members were investigated. An axial compression experiment was carried out on full-scale bamboo columns to characterize the ultimate behaviors under a concentric load. The ultimate bearing capacities of solid, hollow and five-core columns of the same height were not obviously different from each other. The columns with a larger slenderness ratio showed lower ultimate loads and higher axial deflections. The short columns experienced failure due to material crushing, and the long columns experienced a combination of material crushing and inelastic buckling. The empirical equations for predicting the ultimate bearing capacity for wooden columns showed applicability for bamboo columns. Non-linear finite element modeling analyses were carried out to validate the experimental results, and a satisfactory agreement was found in the failure modes and ultimate bearing capacity.

Study on the splitting and expansion–splitting modes of thin-walled circular tubes under axial compression

In this paper, the deformation and energy absorption of thin-walled circular tubes in splitting and expansion–splitting modes are investigated by experiments and theory modeling. First, axial compression experiments of both steel and aluminum alloy tubes were conducted. The results show that the initial peak force in splitting mode could be reduced by increasing the number of initial cracks, and the steady force and the stroke efficiency of tubes could be greatly improved by introducing splitting deformation to the expansion mode in series. Afterwards, theoretical models for these two modes are developed by considering the stress coupling and stress equilibrium, which can well predict the experimental results. Based on the theoretical models, it is found that the initial peak force increases with the decrease of the number and the length of the initial cracks. However, when these two parameters are smaller enough, the initial peak force will not increase. In expansion–splitting mode, the splitting effect can weak the force induced by the expansion deformation, and there is a critical expansion die angle to make the steady force minimum. Moreover, the plastic dissipation is always larger than the tearing dissipation, while the friction dissipation can account for the largest proportion when the expansion die angle is small.

Mechanical performance of marine concrete filled CFRP-aluminum alloy tube columns under axial compression: Experiment and finite element analysis

This study presents the mechanical performance of marine concrete filled carbon fiber reinforced polymer (CFRP)-Aluminum alloy tube columns (CFRP-CFAT) through axial compression experiment and finite element analysis. 18 specimens were tested including 3 marine concrete filled aluminum alloy tubes (CFAT) and 15 CFRP-CFATs. The effects of the CFRP pasting position (outer and inner CFRP) and the number of CFRP layers were investigated. The typical failure pattern of specimens without inner CFRP was waist drum failure of aluminum alloy tube and concrete crushed, aluminum tube and concrete of specimens with inner CFRP were shear failure, the CFRP of all specimens was fractured. CFRP and aluminum alloy tube have fine deformation coordination performance. With the confinement of CFRP, the ultimate bearing capacity and energy absorption capacity of CFRP-CFATs were increased by up to 60.0% and 37.3%, respectively, also effectively inhibited the damage development of specimens. Moreover, a finite element model was developed, a parametric study was carried and a model for calculating the ultimate bearing capacity of CFRP-CFAT was proposed. The simulated results and calculated results were consistent with experimental results.

Fire performance of superabsorbent polymers protecting cold-formed steel walls with high load ratios

Superabsorbent polymers (SAPs) have great potential in the fire protection of steel structures due to their high absorbency and water-holding capacity. In this paper, SAP is applied to the full-scale cold-formed steel (CFS) wall studs to investigation the fire performance of the CFS walls. An axial compression experiment of CFS wall specimen at ambient temperature and three experiments at elevated temperature were conducted. Meanwhile, considering the effect of thermal expansion load, the actual load of CFS walls may increase significantly under fire condition. Hence, the load ratio of the specimens was 0.85 in the fire experiments. The specimens use an autoclaved lightweight concrete (ALC) board and calcium-silicate (CS) board as the face and base layers of sheathings, respectively. The effect of SAP insulation material, high load ratios and thermal expansion load on the fire resistance of walls are discussed. The results indicate that SAP insulation materials can improve the structural and insulation performance of CFS walls under fire exposure. This is because the dehydration and heat absorption process of the SAP insulation material removes the heat inside the wall cavity, maintaining the maximum temperature of the wall studs below 140 °C. Hence, the fire resistance time (FRT) is extended by 41 min after using the SAP insulation material. In addition, neither a high load ratio nor SAP insulation material changes the failure mode of the wall studs. For the present specimens at ambient and elevated temperature, local buckling was identified on the whole section of stud ends. However, the SAP insulation material will change the fire-induced failure position of wall studs. Specimen W3 with SAP insulation material fails at the top of the studs. Furthermore, a thermal expansion load will significantly speed up the fire-induced structural failure of CFS walls with a high load ratio. The FRT of specimen W4 decreases by 79 min after considering the effect of thermal expansion load.

Multi-Camera Digital Image Correlation in Deformation Measurement of Civil Components with Large Slenderness Ratio and Large Curvature.

To address the limitations of conventional stereo-digital image correlation (DIC) on measuring complex objects, a continuous-view multi-camera DIC (MC-DIC) system and its two forms of camera arrangement are introduced. Multiple cameras with certain overlapping field of view are calibrated simultaneously to form an overall system for measuring the continuous full-surface deformation. The bending experiment of coral aggregate concrete beam and the axial compression experiment of timber column are conducted to verify the capability of continuous-view MC-DIC in deformation measurement of civil components with large slenderness ratio and large curvature, respectively. The obtained deformation data maintain good consistency with the displacement transducer and strain gauge. Results indicate that the continuous-view MC-DIC is a reliable 3D full-field measurement approach in civil measurements.

The dynamic axial compression of FRC with high-speed translated θ-pinch plasma

A novel field reversed configuration (FRC) axial compression experiment with high-speed translated θ-pinch plasma was conducted in the Keda Mirror with AXisymmetry device. The translated north FRC was decelerated and compressed by an oncoming θ-pinch plasma stream, and the dynamic process was revealed by a 2D magnetic probe array. The FRC separatrix length is compressed to one-third of the initial value while the radius expands by ∼57%, resulting in the ∼16% increase in the electron temperature and ∼26% in the density, which matches the calculation from an adiabatic compression model. The good agreement is explained by the fast compression and particle supplementation owing to the compression with plasma. The results reported in this work may contribute to the understanding of electron heating in collision-merged FRC and provide a new compression method for the magneto-inertial fusion concept.

Compressive behavior of double-skin composite walls considering local buckling and post-buckling effect

This paper presents axial compressive experiments of double-skin composite walls (DSCWs) with novel dumbbell-shaped connectors (DSCs) and traditional headed studs. The effects of the wall thickness, material strength, and diameter and number of the headed studs on the axial behavior of the DSCWs were analyzed. The failure modes of the specimens included the local buckling of the steel plates and compressive crushing of the concrete. The buckling position was between two adjacent rows of connectors. The experimental results demonstrated that the denser the arrangement of the connectors and the larger the diameter of the headed studs, the higher the critical buckling stress and axial bearing capacity of the specimens. The compressive stress–strain relationship of the steel material was determined considering the buckling and post-buckling behaviors of steel plates. According to the superposition principle, the theoretical load–displacement relationships of the five specimens were calculated, and the theoretical curves were in good agreement with the experimental results. The calculation formula for the axial bearing capacity of the specimens was introduced with some simplified assumptions, and the average value of the experiment/calculation ratio was 96.14%. ABAQUS software was used to simulate the DSCW specimens, and the failure modes of the models were in good agreement with the experiments. The average value of the experiment/simulation ratio for the peak load was 98.77%. Based on the verified benchmark model, the effects of four parameters on the compressive behavior of DSCWs were analyzed.

Morning glory-inspired lattice structure with negative Poisson's ratio effect

Negative Poisson's ratio (NR) structures have compression-contraction properties. Many studies have focused on the NR effect of artificially designed microstructures, but very few studies have been conducted on biomimetic NR structures. In this study, inspired by the geometric features and living habits of a plant called morning glory, a biomimetic lattice structure is proposed. A finite element model of the morning glory-inspired lattice structure (MGS) was established and the sample was prepared by 3D printing. Axial compression experiments and simulations were performed, and the MGS exhibited the characteristics of light weight, efficient energy absorption, and the NR effect. The mechanisms of the NR and compression force characteristics were analyzed in detail. In addition, many MGS models have been proposed, based on various connection modes of cells. The effects of the cell distance and cell connection modes on the compression behavior of the MGS were further studied. It was found that the energy absorption efficiency and NR effect of the MGS deteriorated with an increase in vertical cell spacing, and the energy absorption efficiency and NR effect of the MGSs tended to contradict each other. Furthermore, the minimum NR (MNR) values obtained for W5MG and F6MG were –1.509 and –1.480, respectively. In summary, the MGSs have broad application prospects.

Femoral periprosthetic fracture treatment using the Ortho-Bridge System: a biomechanical study

BackgroundWe undertook a comparative biomechanical study of type B1 fractures around femoral prostheses following cemented hip arthroplasty using the Ortho-Bridge System (OBS) and a locking compression plate/locking attachment plate structure (LCP + LAP). We aimed to investigate the biomechanical characteristics and advantages of the OBS compared with LCP + LAP when treating this fracture type.MethodsAn OBS fixation model was designed based on OBS and LCP + LAP fixation characteristics. The LCP + LAP combination (Group A) and three different OBS combinations (Groups B, C, and D) were used to fix a B1 fracture model with a femoral periprosthetic fracture. Axial compression and torsion experiments were then performed using simple and comminuted fracture models. The axial compression failure experiment was carried out, and the model stiffness during axial compression, torsion angle in torsion test, and vertical load in the final failure test were collected.ResultsWhen simulating simple oblique fractures, no significant difference was found among the four groups in terms of stiffness in the axial compression experiment (P = 0.257). The torsion angle of the LCP + LAP system was significantly higher compared with the OBS system (P < 0.05). When simulating a comminuted fracture, the experimental data for axial compression showed that the rigidity measurements of the three combinations of the OBS system were higher compared with the LCP + LAP system (P = 0.000) and that the torsion angles of three combinations of the OBS system were smaller compared with the LCP + LAP system (P < 0.05). In the axial compression failure test, the fixed failure mode of the LCP + LAP system was the destruction of the contact cortex at the fracture site, whereas the failure modes in the three OBS combinations involved fracture around the screws above the osteotomy and destruction of the contact cortex at the fracture site.ConclusionsThe findings revealed that the OBS produced superior biomechanical outcomes compared with LCP + LAP, especially for the bridging two-rod dual cortex. According to the performance observed after model axial compression destruction, the OBS was fixed and provided greater stress dispersion, which might make it more suitable for facilitating early functional movement and avoiding the failure of internal fixation.

On multiscale tension-compression asymmetry in skeletal muscle

Skeletal muscle tissue shows a clear asymmetry with regard to the passive stresses under tensile and compressive deformation, referred to as tension-compression asymmetry (TCA). The present study is the first one reporting on TCA at different length scales, associated with muscle tissue and muscle fibres, respectively. This allows for the first time the comparison of TCA between the tissue and one of its individual components, and thus to identify the length scale at which this phenomenon originates. Not only the passive stress-stretch characteristics were recorded, but also the volume changes during the axial tension and compression experiments. The study reveals clear differences in the characteristics of TCA between fibres and tissue. At tissue level TCA increases non-linearly with increasing deformation and the ratio of tensile to compressive stresses at the same magnitude of strain reaches a value of approximately 130 at 13.5% deformation. At fibre level instead it initially drops to a value of 6 and then rises again to a TCA of 14. At a deformation of 13.5%, the tensile stress is about 6 times higher. Thus, TCA is about 22 times more expressed at tissue than fibre scale. Moreover, the analysis of volume changes revealed little compressibility at tissue scale whereas at fibre level, especially under compressive stress, the volume decreases significantly. The data collected in this study suggests that the extracellular matrix has a distinct role in amplifying the TCA, and leads to more incompressible tissue behaviour. Statement of significanceThis article analyses and compares for the first time the tension-compression asymmetry (TCA) displayed by skeletal muscle at tissue and fibre scale. In addition, the volume changes of tissue and fibre specimens with application of passive tensile and compressive loads are studied. The study identifies a key role of the extracellular matrix in establishing the mechanical response of skeletal muscle tissue: It contributes significantly to the passive stress, it is responsible for the major part of tissue-scale TCA and, most probably, prevents/balances the volume changes of muscle fibres during deformation. These new results thus shed light on the origin of TCA and provide new information to be used in microstructure-based approaches to model and simulate skeletal muscle tissue.

Mechanical Behavior of Cross-shaped Partially Encased Composite Columns under Axial Compression

The mechanical properties of two cross-shaped PEC columns were investigated by an axial compression experiment. The experimental results showed that when the cross-shaped PEC columns were destroyed, the concrete was crushed and the flanges were locally buckled. Based on the experimental parameters, the ABAQUS software was used for finite element simulation, and the results of the finite element analysis agree well with the test results. To prevent concrete cracking and flange local buckling in the cross-shaped PEC column, a transverse link connection method was presented. The finite element simulation demonstrates that this method improves the ultimate carrying capacity and ductility of the columns. The effects of link spacing, link diameter, flange width-to-thickness ratio, and limb width ratio are also investigated.

Biomechanical study of embracing and non-embracing rib plates.

The study was carried out to explore the biomechanical properties of embracing and non-embracing rib plates. Forty-eight adult cadaver rib specimens were divided randomly into six groups: three fixation model groups were made using embracing plates (two pairs of equals on both sides of the broken end), and the other three groups were fixed with a pre-shaped anatomical plate (three locking screws on each side of the end were equally spaced). The biomechanical properties of these models were analyzed using non-destructive three-point bending tests, non-destructive torsion experiments, and destructive axial compression tests. In this study, the gap of fracture ends was widened in embracing plate group in the non-destructive three-point bending experiment. No change in the fracture ends was detected in the pre-shaped anatomical plate group. The bending stress of the pre-shaped anatomical plate group was significantly enhanced at the 2-12 mm displacement points (p < 0.05). Moreover, there was no significant difference in torque noticed between the two groups in the torsion experiment (p = 0.082). In the destructive axial compression experiment, the load index of the two groups were higher than the normal physiological load, suggesting that both materials could provide sufficient strength for rib fractures. The pre-shaped anatomical plate displayed more reliable attachment in terms of stability, bending, and load. Our results indicated that the embracing plate has the advantage of fretting at the fracture end.

Machine learning prediction of mechanical properties of braided-textile reinforced tubular structures

Braided-textile composites have been applied in various engineering fields and used for high-efficiency energy absorbers to meet different loading requirements. However, it’s difficult to accurately forecast the mechanical properties of these braided-textile composites based on theoretical method, which is a big obstacle to the precise design of the energy-absorbing structure. In this research, carbon fiber reinforced composite (CFRC) tubular structures were fabricated by two-dimensional braided textiles, and 160 groups of orthogonal axial compression experiments were carried out.Axial compression behaviors of CFRC tubular structures, including peak force, mean crushing force, energy absorption, specific energy absorption, elastic modulus and other relevant parameters, were tested and collected in a database. The feed forward back propagation (FFBP) algorithm based on artificial neural network (ANN), as an algorithm with high convergence accuracy in machine learning (ML), was adapted to build a prediction model to forecast the overall axial compression properties of those CFRC tubular structures uncollected in the database. By a series of error analyses, the ML method was proven to have high accuracy in predicting the relevant mechanical properties within the range of orthogonal design groups. Although the relative error of marginal sample data (especially single-layer tubes) is large, the mean absolute error (MAE) of training set and test set is only about 5% and 10%, respectively. Our work demonstrates the potential of machine learning methods in predicting the overall mechanical properties and guiding the design of composite materials.