Search Results (59)

Thin plates are widely used and can be subjected to combined loads that trigger elasto-plastic buckling. Often, these plates are perforated, which significantly changes their mechanical response. This study investigates six perforation geometries (elliptical, longitudinal hexagonal, transverse hexagonal, longitudinal oblong, transverse oblong, and rectangular) and their influence on the ultimate buckling stress of perforated plates under biaxial compression and lateral pressure. Three plates with a distinct width b and length a ratio (b/a) and five unperforated plate volume and perforation volume ratios (ϕ) are analyzed using finite element analysis in ANSYS^®, combined with Constructal Design, Exhaustive Search, and the Technique for Order Preference by Similarity to an Ideal (TOPSIS). Perforation geometry is shown to be a decisive parameter: elliptical perforations are the most efficient, limiting strength loss in rectangular plates with b/a = 1/3 and ϕ = 0.025 to about 6%, while oblong perforations cause reductions of up to 14%. In square plates (b/a = 1), elliptical perforations preserve more than 98% of the original strength for ϕ ≤ 0.05 and over 90% at ϕ = 0.20. TOPSIS results highlight configurations that balance small reductions in ultimate buckling stress with up to 23% lower maximum deflection, providing practical design guidelines. Full article

To enhance the structural performance of concrete-filled steel tube (CFST) columns, various strengthening techniques have been proposed, including the use of internal steel stiffeners, external wrapping with carbon fiber-reinforced polymer (CFRP) sheets, and embedded steel elements. However, the behavior of concrete-filled stainless-steel tube (CFSST) columns remains insufficiently explored. This study numerically investigates the axial performance of square CFSST columns internally strengthened with embedded I-section steel profiles under biaxial eccentric loading. Finite element (FE) simulations were conducted using ABAQUS v. 6.2, and the developed models were validated against experimental results from the literature. A comprehensive parametric study was performed to evaluate the effects of several variables, including concrete compressive strength (f_cu), stainless-steel yield strength (f_y), the depth ratio between the stainless-steel tube and the internal I-section (D_st/D_si), biaxial eccentricities (e_x and e_y), and tube thickness (t). The results demonstrated that the axial performance of CFSST columns was most significantly influenced by increasing the D_st/D_si ratio and load eccentricities. In contrast, increasing the concrete strength and steel yield strength had relatively modest effects. Specifically, the ultimate axial capacity increased by 9.97% when the steel yield strength rose from 550 MPa to 650 MPa and by 33.72% when the tube thickness increased from 3.0 mm to 5.0 mm. A strength gain of only 10.23% was observed when the concrete strength increased from 30 MPa to 60 MPa. Moreover, the energy absorption index of the strengthened columns improved in correlation with the enhanced axial capacities. Full article

Widely employed in diverse engineering applications, stiffened steel plates are often subjected to biaxial compressive loads. Under these conditions, buckling may occur, initially within the elastic range but potentially progressing into the elasto-plastic domain, which can lead to permanent deformations or structural collapse. To increase the ultimate buckling stress of plates, the implementation of longitudinal and transverse stiffeners is effective; however, this complexity makes analytical stress calculations challenging. As a result, numerical methods like the Finite Element Method (FEM) are attractive alternatives. In this study, the Constructal Design method and the Exhaustive Search technique were employed and associated with the FEM to optimize the geometric configuration of stiffened plates. A steel plate without stiffeners was considered, and 30% of its volume was redistributed into stiffeners, creating multiple configuration scenarios. The objective was to investigate how different arrangements and geometries of stiffeners affect the ultimate buckling stress under biaxial compressive loading. Among the configurations evaluated, the optimal design featured four longitudinal and two transverse stiffeners, with a height-to-thickness ratio of 4.80. This configuration significantly improved the performance, achieving an ultimate buckling stress 472% higher than the unstiffened reference plate. In contrast, the worst stiffened configuration led to a 57% reduction in performance, showing that not all stiffening strategies are beneficial. These results demonstrate that geometric optimization of stiffeners can significantly enhance the structural performance of steel plates under biaxial compression, even without increasing material usage. The approach also revealed that intermediate slenderness values lead to better stress distribution and delayed local buckling. Therefore, the methodology adopted in this work provides a practical and effective tool for the design of more efficient stiffened plates. Full article

Significant progress has been made in the low-temperature toughness and crack resistance of polypropylene fiber-reinforced composites. However, there is still a gap in the research on damage evolution under freeze–thaw cycles and complex stress ratios. To solve the problem of durability degradation of traditional rubble masonry in cold regions, this paper focuses on the study of polypropylene fiber-mortar-masonry blocks with different fiber contents. Using acoustic emission and digital image technology, the paper conducts a series of tests on the scaled-down polypropylene fiber-mortar-masonry structure, including uniaxial compressive tests, three-point bending tests, freeze–thaw cycle tests, and tests with different stress ratios. Based on the Kupfer criterion, a biaxial failure criterion for polypropylene fiber mortar-masonry stone (PPF-MMS) was established under different freeze–thaw cycles. A freeze–thaw damage evolution model was also developed under different stress ratios. The failure mechanism of PPF-MMS structures was analyzed using normalized average deviation (NAD), RA-AF, and other parameters. The results show that when the dosage of PPF is 0.9–1.1 kg/m³, it is the optimal content. The vertical stress shows a trend of increasing first and then decreasing with the increase in the stress ratio, and when α = 0.5, the degree of strength increase reaches the maximum. However, the freeze–thaw cycle has an adverse effect on the internal structure of the specimens. Under the same number of freeze–thaw cycles, the strength of the specimens without fiber addition decreases more rapidly than that with fiber addition. The NAD evolution rate exhibits significant fluctuations during the middle loading period and near the damage failure, which can be considered precursors to specimen cracking and failure. RA-AF results showed that the specimens mainly exhibited tensile failure, but the occurrence of tensile failure gradually decreased as the stress ratio increased. Full article

Thin plates are commonly used in mechanical structures such as ship hulls, offshore platforms, aircraft, automobiles, and bridges. When subjected to in-plane compressive loads, these structures may experience buckling. In some applications, perforations are introduced, altering membrane stress distribution and buckling behavior. This study investigates the elasto-plastic buckling behavior of perforated plates using the Finite Element Method (FEM), Constructal Design (CD), and Exhaustive Search (ES) techniques. Simply supported thin rectangular plates with central elliptical perforations were analyzed under biaxial elasto-plastic buckling. Three shapes of holes were considered—circular, horizontal elliptical, and vertical elliptical—along with sixteen aspect ratios and two different materials. Results showed that higher yield stress leads to higher ultimate stress for perforated plates. Regardless of material, plates exhibited a similar trend: ultimate stress decreased as the aspect ratio dropped from 1.00 to around 0.40 and then increased from 0.35 to 0.25. A similar pattern was observed in the stress components along both horizontal (x) and vertical (y) directions, once the y-component became considerably higher than the x-component for the same range of 0.40 to 0.25. For longer plates, in general, the vertical elliptical hole brings more benefits in structural terms, due to the facility in the distribution of y-components of stress. Full article

Traditional fiber-reinforced polymer (FRP) retrofit methods can restore the strength of reinforced concrete columns well, but stiffness is also partly restored. To increase the initial stiffness of retrofitted columns, this study investigated the seismic behavior of retrofitted resilient reinforced concrete (RRC) columns that were retrofitted by different methods, including high-strength mortar retrofit, carbon fiber-reinforced polymer (CFRP) retrofit, and CFRP and steel plate retrofit. In addition, the effect of the axial load was also considered. Quasi-static tests were conducted twice on five specimens, i.e., before and after repairing. The first test was used to create earthquake damage, and the second test was used to compare the seismic behavior of the retrofitted columns. The experimental results indicated that the CFRP retrofit method, whether with a steel plate or not, can restore the lateral resistance capacity well; furthermore, the drift-hardening behavior and self-centering performance were well maintained. The residual drift ratio of the CFRP-retrofitted column was less than 0.5%, even at a drift ratio of 3.5%, and less than 1% at the 6% drift ratio. However, the initial stiffness was only partly restored using the CFRP sheet. The introduction of steel plates was beneficial in restoring the initial stiffness, and the stiffness recovery rate remained above 90% when CFRP sheets and steel plates were used simultaneously. The strain distribution of the CFRP sheet showed that the steel plate did work at the initial loading stage, but the effect was limited. By using the steel plate, the CFRP hoop strain on the south side was reduced by 68% at the 6% drift ratio in the push direction and 38% in the pull direction. The axial strain of CFRP cannot be ignored due to the larger value than the hoop strain, which means that the biaxial stress condition should be considered when using an FRP sheet to retrofit RC columns. Full article

The presence of mixed-mode stresses, combining both opening and shearing components, complicates fatigue life estimation when applying the Paris law. To address this, the crack path, along with Mode-I (opening) and Mode-II (shear) components, was numerically analyzed using Fracture Analysis Code (Franc2D) based on the linear elastic fracture mechanics (LEFM) approach. Accordingly, fatigue life and stress intensity factors (SIFs) under various biaxial loading ratios (λ) were calculated using the Paris law and compared with available data in the literature. The results show that crack growth is primarily driven by the Mode-I component, which exhibits the largest magnitude. Thus, the Mode-I stress intensity factor (K_I) was adopted for the numerical integration of the fatigue life equation. Furthermore, the influence of normal and transverse loads (σ_y and σ_x, respectively) on the crack path plane and SIF was examined for λ. The analysis revealed that lower λ values led to faster crack propagation, while higher λ values resulted in extended fatigue life due to an increased number of cycles to failure. The comparison demonstrated good agreement with reference data, confirming the reliability of the proposed modeling approach over a wide range of biaxial loading conditions. Full article

Q345 steel is usually used on structures working under high temperature where creep deformation could endanger their structural integrity. In order to support the application of steel structures made of Q345 under high temperature, a fracture analysis on defective Q345 steel in the process of small-scale creep crack propagation has been performed. Three-dimensional finite element models with a semi-elliptical surface crack have been established, and the crack propagation process of Q345 steel has been simulated at 400 °C. The constraint effect near the crack tip in the process of creep crack propagation has been analyzed using the J-A₂ two-parameter method in which the influence of the crack aspect ratio, loading level, and biaxial loading ratio was studied. The previously developed constraint-based R6 procedure was adopted to assess the structural integrity of the cracked structure under small-scale creep conditions. The results showed that small-scale creep crack propagation behavior exhibits great influence on both crack tip fields and a constraint effect near the crack tip. The increase in the biaxial loading ratio, loading level, and aspect ratio of the crack could lead to an increase in the J integral, an enhancement of the constraint effect, and a decrease in the safe area in the failure assessment diagram for the cracked structure in the process of small-scale creep crack propagation. Full article

The size of ships has increased considerably in recent decades. This growth impacts the stress magnitude in the bottom hull plates, which constantly suffer from biaxial compression and lateral water pressure, potentially leading to buckling. Adding stiffeners is an effective alternative to increase mechanical buckling resistance if placed in a proper way. Several researchers have investigated the influence of stiffeners on plates under different loading conditions. However, the behavior under combined biaxial compression and lateral pressure has not yet been widely explored. This work aims to verify and validate a computational model to analyze the elastoplastic buckling of plates under biaxial compression and lateral pressure, applying it in a case study to define the ideal geometric configuration to increase ultimate buckling resistance, using the constructal design method and exhaustive search technique. In this study, a portion of the volume from a reference plate without stiffeners was converted into stiffeners to determine the optimal geometry for maximizing ultimate buckling resistance. The numerical model was verified and validated, and the case study identified the optimal plate configuration with five longitudinal and four transverse stiffeners, with a height-to-thickness ratio of 8.70, achieving a 284% increase in ultimate buckling resistance compared to the reference plate. These results highlight the importance of geometric evaluation in structural engineering problems. Full article

This study investigates the traditional coal pillar support methods employed in double-roadway excavation of high-mining-height longwall faces, specifically those with widths ranging from 20 m to 30 m. It highlights that these methods not only result in substantial coal pillar loss and low recovery rates but also create conditions for stress concentration due to inadequate dimensions, thereby increasing the risk of accidents. Based on the engineering context of the Jinjitan Coal Mine’s 113 and 111 working faces, this paper optimizes coal pillar dimensions through theoretical calculations and Flac3D numerical simulations, with the results indicating that the optimal coal pillar width is 12 m. Analysis of a 12 m inter-roadway coal pillar focuses on the bearing characteristics of auxiliary transport roadways and coal transportation roadways. Five different reinforcement schemes are examined, including (no support, conventional anchor reinforcement, presser anchor cable through reinforcement, constant-resistance large-deformation anchor cable through reinforcement, and a combination of presser with negative Poisson’s ratio (NPR) constant-resistance large-deformation anchor cable support). The findings reveal that in the investigation of the reinforcement mechanism for the 12 m wide coal pillar, employing NPR constant-resistance large-deformation anchor cables alongside presser anchor cables effectively mitigates the compression deformation caused by dynamic loading disturbances from the overlying rock layers. This approach not only dissipates energy but also transforms the coal pillar from a biaxial stress state to a triaxial stress state. The reinforcement scheme successfully reduces the peak stress of the coal pillar from 68.5 MPa to 35.3 MPa, significantly enhancing both the peak strength and residual strength of the coal pillar, thereby ensuring the stability of the inter-roadway coal pillar and the safe recovery of the working face. Full article

Accurately determining the mechanical properties of complex materials is a key challenge in structural analysis, especially when using the finite element method (FEM). While homogeneous materials can be modeled with relative ease, heterogeneous materials such as composites or biological tissues with multiphase compositions pose significant difficulties due to the variability in their internal structures. The most used approach is numerical homogenization, which allows for the estimation of effective material properties by combining the characteristics of individual phases; however, this technique may not always be feasible, especially for materials with irregular or unknown phase distributions. This paper proposes an original methodology that combines non-destructive experimental testing with an inverse finite element modeling to extract the anisotropic elastic properties of quasi two-dimensional structures such as membranes and plates. The method involves modeling the component using membrane or plate finite elements, but managing a global stiffness matrix expressed analytically. While geometric information is incorporated in the global stiffness matrix, the material properties, specifically the components of the anisotropic elasticity matrix, remain unknown. The experimental data, comprising force and displacement measurements, are used to solve a nonlinear system, allowing for the identification of the material’s constitutive properties via numerical computation. To validate this approach, two experimental setups were conducted. The first involved a hyperelastic neoprene membrane, subjected to various biaxial preloading conditions, while the second focused on PLA plates produced through additive manufacturing including both homogeneous and reinforced variants. In both cases, the method successfully captured the full anisotropic elastic response, yielding accurate estimates of Young’s moduli, Poisson’s ratios, shear modulus, and orthotropy system orientation, in agreement with independent mechanical tests. This combined approach offers a practical and efficient solution for determining the elastic properties of complex materials, particularly in cases where traditional homogenization techniques are impractical or inadequate. Furthermore, this method can be a versatile tool for evaluating the damaging and aging effects on materials subjected to cyclic loading or those with irregular and complex internal structures. Full article

This study substantiates the need for direct tensile strength testing of shotcrete and fiber-reinforced shotcrete, rather than relying on indirect methods, to accurately reflect material performance under biaxial stress conditions when used for structural reinforcement. Experiments on field specimens confirmed that tensile strength values derived through direct testing differ significantly from those calculated based on compressive strength. The study presents a new testing methodology with optimized specimen dimensions (32, 40, 50, and 82 mm diameter cylinders with length-to-diameter ratios of 3.0) to mitigate eccentricity effects, ensuring normal-section failure. Results show that tensile strength values for fiber-reinforced shotcrete with brass-coated fibers (13–15 mm length, 0.3–0.5 mm diameter, 30 kg/m³ dosage) reached 68 MPa, compared to 60 MPa for standard shotcrete, while basalt-fiber reinforcement (6 mm length, 1% by weight) resulted in 42 MPa. The initial modulus of elasticity for unreinforced shotcrete was 280 × 10³ MPa, with fiber reinforcement slightly increasing this value to 287 × 10³ MPa. The findings support a direct approach to testing, providing a foundation for developing predictive methodologies for fiber-reinforced shotcrete properties based on reinforcement type and dosage. These results are essential for applications such as seismic strengthening, where accurate tensile characteristics are critical for performance under dynamic loading. Full article

This study presents a detailed analysis of a fatigue test campaign in order to identify different crack patterns. It was conducted on 6061-T6 aluminum tubular specimens featuring an internal diameter of 10 mm and different thicknesses (2, 3 and 4 mm). These specimens were subjected to cyclic tensile loads with a load ratio of R = 0.1, utilizing a sinusoidal load function at a frequency of 3 Hz. The investigation examines the crack growth rates, the stress intensity factor, and the final and intermediate fracture zones by applying overloads in some cases. The differences with two-dimensional specimens and the importance of this study for the interpretation of results with biaxial loading states are highlighted. The different states of crack growth detected are analyzed using artificial vision techniques. The differences between the exterior and interior faces of the specimen are revealed, and a series of states prior to the formation of the radial crack front expected in these specimens are identified. Full article

In the present study, the mechanical response and deformation behavior of a Mg AZ31 plate with different types of pre-twins was systematically investigated under biaxial tension along the normal direction (ND) and transverse direction (TD) with different stress ratios. The results show that significant hardening was observed under biaxial tension. The yield values in the direction of larger stress values were higher than those under uniaxial loading conditions, and the solute atom segregation at twin boundaries generates more obvious strengthening effect. Noting that, for TRH (with cross compression along the rolling direction (RD) and TD and annealing at 180 °C for about 0.5 h) sample, the strength effect of the RD yield stress ${\mathsf{\sigma }}_{\mathrm{RD}}:{\mathsf{\sigma }}_{\mathrm{ND}}$ = 2:1 was higher than that of the ND yield stress under stress ratio ${\mathsf{\sigma }}_{\mathrm{RD}}:{\mathsf{\sigma }}_{\mathrm{ND}}$ = 1:2. There is a complex competition between twinning and detwinning under biaxal tension along the ND and TD of the pre-twinned samples with the variation in the stress ratio along the TD and RD. The variation in the twin volume fractions for all samples under biaxial firstly decreases and then increases with a higher stress ratio along the ND. As for the TDH sample (precompression along the TD and annealing), the changes of the twin volume fraction were lower than that of the TR sample (cross compression along the TD and RD). However, the amplitude of variation in twin volume fraction of the TRH sample is higher than that of the TR sample. This is because the relative activity of detwinning decreases and that of twinning increases, as the ND stress mainly leads to the growth of pre-twins and the TD stress often promotes detwinning of primary twins. With a higher stress ratio along the ND, the activity of twinning deformation increases and that of detwinning decreases. Full article

Four-pile caps made from concrete are essential elements for the force transfer from the superstructure to piles or pipes. Due to the difficulties in carrying out full-scale tests and all the instrumentation involved, the use of numerical models as a way to study the mechanical behavior of these elements presents itself as a good alternative. Such numerical studies usually provide useful information for the update and improvement of normative standards and codes. The concrete damaged plasticity (CDP) constitutive model, which combines damage and plasticity with smeared-crack propagation, stands out in the simulation of reinforced concrete. This model is composed of five parameters: dilatation angle (ψ), eccentricity (ϵ), ratio between biaxial and uniaxial compressive strength (σ_bo/σ_co), failure surface in the deviator plane normal to the hydrostatic axis (K_c), and viscosity (μ). For unidimensional elements, the values of the CDP parameters are well defined, but for volumetric elements, such as concrete pile caps, there is a gap in the literature regarding the definition of these values. This fact ends up limiting the use of the CDP on these structural elements due to the uncertainties involved. Therefore, the aim of this research was to calibrate two numerical models of concrete four-pile caps with different failure modes for the evaluation of the sensitivity of the CDP parameters, except for ϵ, which remained constant. As a result, the parameters σ_bo/σ_co and K_c did not significantly influence the calibration of the force × displacement curves of the simulated structures. Values of ψ and μ equal to 36° and 1 × 10⁻⁴, respectively, are recommended for “static” analysis, while for “quasi-static” analysis, ψ values ranging between 45° and 50° are suggested according to the failure mode. The results also showed to be sensitive to the constitutive relation of concrete tensile behavior in both modes of analysis. For geometric parameterization, the “static” analysis is recommended due to the lower coefficient of variation (3.29%) compared to the “quasi-static” analysis (19.18%). This conclusion is supported by the evaluation of the ultimate load of the numerical models from the geometrically parametric study compared to the results estimated by an analytical model. Full article