Search Results (41)

This study investigates the axial compression behavior of square reinforced concrete (RC) columns confined by a novel type of rectangular closed basalt fiber-reinforced polymer (BFRP) tie fabricated using a continuous filament winding method, and hybrid steel–BFRP configurations. The proposed ties were developed to overcome common limitations of conventional FRP stirrups, such as reduced tensile strength at bent regions and premature rupture. A total of five RC column specimens were tested under monotonic axial loading: one reference specimen with conventional steel ties, two specimens with BFRP ties spaced at 45 mm and 90 mm, and two hybrid specimens combining steel and BFRP ties. Experimental results showed that the steel-confined column achieved the highest peak axial load of 1793.2 kN and an ultimate strain value of 1.12. The specimen with closely spaced BFRP ties (45 mm) reached 94.7% of the peak load of the steel-confined specimen and exhibited over 137% higher axial strain capacity. The hybrid specimen with two interleaved BFRP ties achieved the highest confinement effectiveness ratio of 1.306. The findings demonstrate that the proposed BFRP ties offer a structurally viable and corrosion-resistant alternative to steel ties, particularly when used in hybrid systems. This research contributes to the development of durable, high-performance confinement strategies for RC columns in seismic and aggressive environmental conditions. Full article

The present study investigates the influence of the configurations of anchor bolts and stiffeners on the monotonic response under moment conditions in the major axis and compression force of partial-strength exposed column base plate connections in order to ameliorate their response, limiting the number of welded details. Parametric finite element simulations were performed based on models calibrated against experimental results available from the recent literature. The results show the efficiency of the investigated configurations, namely, (i) the presence of rib stiffener results in high stiffness and strength with a reduction in ductility; (ii) the linear pattern of anchor bolts (e.g., rectangular distribution) is characterized by the limited contribution of the outer anchor bolts to the overall resistance of the connection; (iii) the trapezoidal pattern of the anchor bolts exhibit a better mechanical performance as well as their efficiency; and (iv) the increase in compression force influences the mechanical response of the base connection with an increase in both resistance and rigidity until the column is stable against the moment–axial force interaction. Full article

In order to study the microstructure evolution of polytetrafluoroethylene–copper (PTFE-Cu) composites under compression load and reveal the molecular dynamics mechanism of deformation failure, three PTFE-Cu composites with different densities (3.0 g/cm³, 3.5 g/cm³, 4.0 g/cm³) were prepared in this study. The crystallinity of PTFE in each sample was determined via differential scanning calorimetry (DSC). The quasi-static compression mechanical properties test was carried out to analyze the effect of PTFE crystallinity on the macroscopic mechanical response of the composites. It is found that the crystallinity of the three PTFE-Cu composites was 43.05%, 39.49% and 40.13%, respectively, showing a non-monotonic trend of decreasing first and then increasing with an increase in copper powder content. The elastic modulus and yield strength of the material are negatively correlated with the crystallinity. The failure mode is the axial splitting failure and the composite morphology of axial splitting failure and shear tearing. Finally, the molecular dynamics simulation method is used to reveal the microstructure evolution and deformation failure mechanism of PTFE-Cu composites under compression load from the atomic scale, which provides a theoretical basis and experimental support for understanding the mechanical properties of PTFE-Cu composites. Full article

Monotonic axial compression tests were carried out on 16 steel fiber-reinforced concrete (SFRC) columns confined by rectangular spiral stirrups. The impacts of stirrup spacing, stirrup strength, concrete strength, and cross-sectional aspect ratio on the peak load, ductility, and failure mode of these columns were analyzed. The test results demonstrate that steel fibers significantly mitigate the spalling of the concrete column’s protective layer through their bridging effect. Small spacing and high-strength spiral stirrups effectively confine the core concrete, enhancing the bearing capacity and ductility of concrete columns. Concrete strength exhibits a positive correlation with the confinement effect. However, as concrete strength increases, the rate of improvement in the confinement effect decreases. At peak compressive stress, the high-strength stirrup may not reach its yield state. Based on the test results, a method for calculating stirrup stress under the peak stress of confined concrete is proposed. A “coupling restraint coefficient” is proposed, and a constitutive model for HRSS confined steel fiber reinforced concrete is developed, considering the coupled effect of effective confinement forces in different directions. Comparative analysis shows that the constitutive model established in this paper agrees well with the experimental results and demonstrates good applicability. Full article

This paper explores the development of 3D-printed self-sensing Ultra-High Performance Concrete (UHPC) by incorporating graphite (G) powder, milled carbon microfiber (MCMF), and chopped carbon microfiber (CCMF) as additives into the UHPC matrix to enhance piezoresistive properties while maintaining workability for 3D printing. Percolation curves were established to identify optimal filler inclusion levels, and a series of compressive tests, including quasi-static cyclic, dynamic cyclic, and monotonic compressive loading, were conducted to evaluate the piezoresistive and mechanical performance of 29 different mix designs. It was found that incorporating G powder improved the conductivity of the UHPC but decreased compressive strength for both mold-cast and 3D-printed specimens. However, incorporating either MCMF or CCMF into the UHPC resulted in the maximum 9.8% and 19.2% increase in compressive strength and Young’s modulus, respectively, compared to the plain UHPC. The hybrid combination of MCMF and CCMF showed particularly effective in enhancing sensing performance, achieving strain linearity over 600 $\mu \epsilon$. The best-preforming specimens (3G250M250CCMF) were fabricated using 3 wt% of G, 0.25 wt% of MCMF, and 0.25 wt% of CCMF, yielding a maximum strain gauge factor of 540, a resolution of 68 $\mu \epsilon$, and an accuracy of 4.5 $\mu \epsilon$ under axial compression. The 3D-printed version of the best-performing specimens exhibited slightly diminished piezoresistive and mechanical behaviors compared to their mold-cast counterparts, yielding a maximum strain gauge factor of 410, a resolution of 99 $\mu \epsilon$, and an accuracy of 8.6 $\mu \epsilon$. Full article

FRP-confined gangue aggregate concrete partially filled steel tubes (CGCPFTs) can not only effectively enhance the performance of coal gangue concrete, but also fully exploit the elastic-plastic mechanical behavior of the steel tubes. However, research on theoretical models that can describe their mechanical properties is yet to be conducted. To fill this gap, theoretical models for structural design and analysis were proposed for CGCPFTs. For the analytical model, based on the available experimental data, a prediction method for the stress–strain behavior of the gangue aggregate concrete in CGCPFTs, which is confined only by FRP and partly confined by both FRP and the steel tubes, was first proposed. Additionally, the condition for the synergetic deformation of the two confined states of gangue aggregate concrete within the CGCPFT was proposed. Based on the condition, an iterative incremental process was developed which subsequently allows for the theoretical calculation of the load–displacement curve for the CGCPFT under monotonic axial compression. For the design model, by introducing the constraint contribution coefficient of the steel tube, the existing closed-loop calculation formula for the stress–strain relationship of FRP-confined concrete was revised. Furthermore, by expressing the axial and lateral stresses of the steel tube as a unified circumferential effect on the concrete, the calculation methods for the ultimate strength and strain in the closed-loop formula were redefined, thus achieving the prediction of the stress–strain behavior of CGCPFTs. The comparison with the test data obtained by the author and their team revealed that both the analysis and design models could provide accurate predictions. Full article

Concrete structures such as bridge decks and road pavements are subjected to repetitive loading and are susceptible to fatigue failure. A simplified stress–strain analysis method that can simulate concrete behavior with a sound physical basis, acceptable prediction precision, and reasonable computation cost is urgently needed to address the critical issue of high-cycle fatigue in structural engineering. An equivalent fatigue constitutive model at discrete loading cycles incorporated into the concrete damaged plasticity model (CDPM) in Abaqus is proposed based on fatigue damage evolution. A damage variable is constructed from maximum fatigue strains, and fatigue damage evolution is described by a general equation whose parameters’ physical meaning and value range are identified. With the descending branch of the monotonic stress–strain curve as the envelope of fatigue residual strength and fatigue damage evolution equation as shape function, fatigue residual strength, residual stiffness, and residual strain are calculated. The equivalent fatigue constitutive model is validated through comparison with experimental data, where satisfactory simulation results were obtained for axial compression and flexural tension fatigue. The model’s novelty lies in integrating the fatigue damage evolution equation with CDPM, explicitly explaining performance degradation caused by fatigue damage. The proposed model could accommodate various forms of concrete constitution and fatigue stress states and has a broad application prospect for fatigue analysis of concrete structures. Full article

This study analyzes the nonlinear seismic behavior of cluster-connected prefabricated shear walls under varying axial compression ratios. The investigation focuses on the connectivity of shear wall segments assembled using cluster connections rather than separate walls connected by beams. Using the finite element software ABAQUS, this study simulates monotonic horizontal displacement loading to evaluate the yield strength, peak strength, and deformation capacity of the shear walls. The results demonstrate that the horizontal load-bearing capacity of the shear wall significantly improves with an increase in axial compression ratio, while the axial compression ratio also influences ductility. The numerical simulations are validated against experimental data, confirming the accuracy of the model. These findings provide essential insights for optimizing the seismic design of precast shear walls. Full article

Background and Objectives: Osteoporosis renders the use of traditional interbody cages potentially dangerous given the high risk of damage in the bone–implant interface. Instead, injected cement spacers can be applied as interbody devices; however, this technique has been mainly used in cervical spine surgery. This study aimed at investigating the biomechanical behavior of cement spacers versus traditional cages in lumbar spine surgery. Materials and Methods: Destructive monotonic axial compression testing was performed on 20 human cadaveric low-density lumbar segments from elderly donors (14 f/6 m, 70.3 ± 12.0 y) treated with either injected cement spacers (n = 10) or traditional cages (n = 10) without posterior instrumentation. Stiffness, failure load and displacement were compared. The effects of bone density, vertebral geometry and spacer contact area were evaluated. Results: Cement spacers demonstrated higher stiffness, significantly smaller displacement (p < 0.001) and a similar failure load compared to traditional cages. In the cage group, stiffness and failure load depended strongly on bone density and vertebral height, whereas failure displacement depended on vertebral anterior height. No such correlations were identified with cement spacers. Conclusions: Cement spacers used in lumbar interbody stabilization provided similar compression strength, significantly smaller failure displacement and a stiffer construct than traditional cages that provided benefits mainly for large and strong vertebrae. Cement stabilization was less sensitive to density and could be more beneficial also for segments with smaller and less dense vertebrae. In contrast to the injection of cement spacers, the optimal insertion of cages into the irregular intervertebral space is challenging and risks damaging bone. Further studies are required to corroborate these findings and the treatment selection thresholds. Full article

This research suggested natural hemp fiber-reinforced ropes (FRR) polymer usage to reinforce recycled aggregate square concrete columns that contain fired-clay solid brick aggregates in order to reduce the high costs associated with synthetic fiber-reinforced polymers (FRPs). A total of 24 square columns of concrete were fabricated to conduct this study. The samples were tested under a monotonic axial compression load. The variables of interest were the strength of unconfined concrete and the number of FRR layers. According to the results, the strengthened specimens demonstrated an increased compressive strength and ductility. Notably, the specimens with the smallest unconfined strength demonstrated the largest improvement in compressive strength and ductility. Particularly, the compressive strength and strain were enhanced by up to 181% and 564%, respectively. In order to predict the ultimate confined compressive stress and strain, this study investigated a number of analytical stress–strain models. A comparison of experimental and theoretical findings deduced that only a limited number of strength models resulted in close predictions, whereas an even larger scatter was observed for strain prediction. Machine learning was employed by using neural networks to predict the compressive strength. A dataset comprising 142 specimens strengthened with hemp FRP was extracted from the literature. The neural network was trained on the extracted dataset, and its performance was evaluated for the experimental results of this study, which demonstrated a close agreement. Full article

In order to explore the horizontal joint connection performance of the innovative tooth groove connection and vertical reinforcement lapping in the reserved hole, five horizontal joint specimens were designed and constructed in this paper. Through the combination of monotonic horizontal load tests and finite element simulation analysis, the effects of axial compression ratio, vertical reinforcement connection degree, reserved hole type, mortar strength, and tooth groove depth on the horizontal joint connection performance of innovative tooth groove connections and vertical reinforcement lapping in reserved holes were comprehensively analyzed and discussed. The results indicated that the specimens were subjected to penetration failure at the tooth groove joint, but the vertical reinforcements and UHPC in reserved holes can effectively transfer the stress, ensuring satisfactory connection performance. With the increase in axial compression ratio and vertical reinforcement connection degree, the joint connection performance enhanced gradually, while the reserved hole type had little effect on the joint connection performance. In addition, it was found that increasing the mortar strength and the tooth groove depth can significantly improve the peak bearing capacity through finite element analysis. Finally, the optimization design suggestions for this innovative tooth groove connection and vertical reinforcement lapping in the reserved hole were given considering factors such as joint connection performance and construction assembly. Full article

To investigate the seismic behaviors of novel steel-reinforced concrete composite frames prestressed with bonding tendons (PSRCFs), 15 groups of PSRCF specimens were designed with the following main parameters: the cubic compressive strength of high-strength concrete (f_cu), the axial compression ratio of frame columns (n), the slenderness ratio of frame columns (β), the steel ratio of angle steel (α), the span–height ratio of frame beams (L/h_b), and the prestressing degree (λ). Based on the modified concrete constitutive model proposed by Mander and the prestressing effect applied by the cooling method, the finite element models of PSRCFs were established by using ABAQUS software, the static analysis on the frame structures under the combined actions of axial forces and horizontal loads was carried out, and the monotonic load–displacement curves were explored. By comparing with the skeleton curves obtained by the experimental hysteretic curves, the rationality of the modeling method was verified. The PSRCFs had good mechanisms of strong columns and weak beams. Based on this, the influences of different parameters on the seismic behaviors such as hysteretic curves, skeleton curves, stiffness degradations, energy dissipation capacities, and ductility of the specimens were investigated. The results show that the hysteretic curves of the PSRCFs are full and have no pinch phenomenon. The ultimate load and the stiffness degradation of specimens can be improved significantly by increasing α, and on the contrary, the ultimate load and stiffness degradation decreased by increasing β. The ductility of the specimens decreased gradually with the increasing β and n. The energy dissipation capacity of the specimens decreased with the increasing β. The trilinear model of the skeleton curves and the restoring force model of PSRCF_S were established by statistical regression, which agree well with the numerically simulated results. These can provide theoretical support for the elastoplastic analysis on this kind of PSRCF structure. Full article

The motivation to design a more efficient and compact aircraft engine leads to a continuous increase in overall pressure ratio and decrease in the stage number in compressors. Compared to the traditional multi-stage compressor, a single-stage ultra-high-pressure-ratio centrifugal compressor with a pressure ratio higher than 10.0 can significantly improve the engine’s power-to-weight ratio and fuel economy with a reduced structure complexity. Thus, it has great potential to be adopted in the compression system of advanced aero engines, such as turboshaft engines, in the future. However, the highly narrow Stable Flow Range (SFR) of ultra-high-pressure-ratio centrifugal compressors is a severe restriction for engineering applications. This research focuses on the aerodynamic performance of a ultra-high-pressure-ratio centrifugal compressor, and three-dimensional simulation is employed to investigate the effect of Self-Recirculating Casing Treatment (SRCT) on the performance and stability of the centrifugal compressor. Firstly, the parametric model of SRCT is established to investigate the effect of geometry parameters (rear slot distance and rear slot width) on the aerodynamic performance of the centrifugal compressor. It is concluded that SRCT improves the compressor’s SFR but deteriorates its efficiency. Also, a non-linear and non-monotone relationship exists between the SFR and rear slot distance or width. Then, the flow mechanism behind the effect of SRCT is explored in detail. By introducing the SRCT, an additional flow path is provided across the blade along the circumferential direction, and the behavior of the shock wave and tip leakage flow is significantly changed, resulting in the obviously different loading distribution along the streamwise direction. As a result, the mixing and flow separation loss are enhanced in the impeller flow passage to deteriorate the efficiency. On the other hand, the blockage effect caused by the mixing of slot recirculation and mainstream flow near the impeller inlet increases the axial velocity and reduces the incidence angle below the 90% spanwise section, which is considered to effectively stabilize the impeller flow field and enhance the stability. Full article

The design of intersecting nodes in high-rise oblique mesh structures is a critical issue. The existing research on the intersecting nodes of oblique meshes mainly focuses on plane intersecting nodes and monotonic axial compression loads. The plane intersecting nodes cannot consider the contribution of the node’s out-of-plane angle and floor beam to the node’s out-of-plane stiffness in actual structures. In this paper, numerical analysis using ABAQUS was conducted to investigate the mechanical performance of space intersecting nodes of oblique meshes (OMSIN) under cyclic axial tension and compression loads, to provide a reference for the engineering application of oblique mesh structures in seismic regions. Six parameters were considered: the space intersecting angle, the plane angle symmetry coefficient, the plane intersecting angle, the out-of-plane constraint restraint, the steel content of the cross-section, and the concrete strength. The study showed that changes in the thickness of the steel tube wall are unfavourable for the uniform transmission of stress. Increasing the space intersecting angle significantly weakened the seismic performance, and the space angle affects the failure mode of the node. Asymmetric arrangements of the upper and lower plane angles caused nonlinear development of out-of-plane. The ultimate load and overall compressive stiffness of the specimen were positively correlated with the plane angle, and vertical constraints should be applied to the node position of components with plane angles greater than or equal to 70°. The out-of-plane constraint was a key factor affecting the seismic performance of the node, and it was proportional to the ultimate load of the component. In structural design, if the aim is to improve the mechanical performance of the component by increasing the steel content, more enormous out-of-plane constraints should be set to control plane external displacement strictly. The concrete strength is proportional to the ultimate axial load and axial stiffness, and its influence on the mechanical performance in the axial tension direction is not significant. Finally, a dimensionless skeleton curve model of the node was established. The existing formula for the bearing capacity of CFST columns was fitted to obtain the calculation formula for the axial yield and ultimate load of the OMSIN under cyclic loads. Full article

The construction of high-rise oblique grid buildings requires a large amount of concrete. To save resources, an oblique grid of intersecting nodes composed of steel outer tubes and steel fiber, recycled concrete inner tubes (OGSFRCIN) has been proposed. ABAQUS is used to study the mechanical properties of the nodes under axial pressure, accounting for the effects of six parameters: the oblique angle, the thickness of the stiffening ring, the thickness of the connecting plate, the concrete strength, the recycled aggregate replacement rate, and the steel fiber content. The results show that the oblique angle, connecting plate thickness, concrete strength, and steel fiber content significantly affect the ultimate bearing capacity of specimens. The reinforcing ring thickness has a significant effect on the evolution of lateral displacement. It is not advisable to use components with a replacement rate of 100% recycled aggregate in engineering practice because of insufficient lateral stiffness and ultimate strength. The specimen’s out-of-plane displacement is tightly restricted when the connecting plate’s thickness is greater than or equal to 10 mm. In practical engineering, the connecting plate and reinforcing ring thickness should not be less than 10 mm, and the recommended steel fiber content is 1.0% to 2.0%. Through the analysis of the mechanical properties of the OGSFRCIN under monotonic axial compression and reciprocating axial tension and compression loads, it can be seen that OGSFRCIN have good mechanical properties and can be applied in engineering practice. Here, the modified formulas for calculating the bearing capacity of OGSFRCIN are put forward. Full article