Search Results (788)

The response modification factor R is a fundamental parameter in seismic design, linking the elastic demand expected under strong ground motion to the reduced forces used in practice. It reflects the capacity of well-detailed structures to dissipate energy through stable inelastic behavior while maintaining sufficient strength, stiffness, and deformation capacity to prevent collapse. Accordingly, R directly influences design base shear, member forces, reinforcement demands and expected seismic performance. It is prescribed by seismic codes as a single typology dependent value, although analytical evidence indicates that its magnitude varies systematically with structural configuration. Therefore, this study decomposes R for twelve reinforced concrete moment-resisting frame archetypes that combine three heights (4, 8, and 14 stories) with four span configurations (1–4 spans) over a constant 12 m plan length. All frames are designed per ACI 318-19 and ASCE/SEI 7-22 for the Pedernales, Ecuador, subduction-zone seismic hazard. The response modification factor R is evaluated through a component-based decomposition that separates the effects of ductility, overstrength, and redundancy—namely the capacity ductility ${\mu }_c$, the demand ductility ${\mu }_d$, the overstrength $\Omega$, and a geometric redundancy index ${\rho }_g$, using bilinearized pushover analyses. Dynamic verification, used here as a consistency check, is explicitly restricted to the low-rise class (four-story frames) through nonlinear response-history analysis under eleven spectrum-matched ground-motion records; results for the 8- and 14-story frames are therefore pushover-based only. To bracket the inelastic reduction capacity, a demand-based companion factor $R^{*}$ is reported and defined as the demand-based counterpart of R, providing a capacity-oriented estimate R and a demand-oriented companion estimate $R^{*}$. R ranges from 3.80 to 14.56, whereas $R^{*}$ ranges from 1.82 to 7.63. The component ranges are the capacity ductility ${\mu }_c=6.04$–$11.50$, the demand ductility ${\mu }_d=3.04$–$5.98$, the overstrength $\Omega =1.19$–$1.38$, and the geometric redundancy index ${\rho }_g=0.485$–$1.000$. Capacity ductility saturates in taller frames (about $\sim 12\%$ variation). In addition, $\Omega$ and ${\rho }_g$ exhibit a mechanical trade-off that challenges the independence assumption implicit in the multiplicative decomposition. Dynamic results corroborate the pushover-implied demand only for the low-rise class; no extrapolation to taller frames is claimed. Overall, the findings motivate configuration-sensitive analytical calibration as a prerequisite for any future normative discussion on R. Full article

Mass-timber rocking-wall systems are designed to limit residual deformation by concentrating lateral response in controlled uplift, recentering, and replaceable energy-dissipation mechanisms. Full-scale shake-table records provide a rare opportunity to evaluate this design concept using reproducible physical descriptors rather than isolated peak-response quantities. The public NHERI TallWood two-story mass-timber rocking-wall experiment is reanalyzed using fourteen sequential earthquake records, measured table accelerations, floor and roof accelerations, and instrumented deformation channels. A physics-informed workflow extracts input-intensity, transfer-function, coherence, modal-frequency, equivalent-damping, residual-deformation, self-centering, and deformation-weighted inertial-demand descriptors. An experiment-updated equivalent elastic Abaqus model converts selected identified states into three-dimensional displacement and stress-transfer fields. The identified dominant frequency decreases from approximately 2.11 Hz in the initial low-level event to approximately 0.70 Hz after the final maximum-level excitation, corresponding to a frequency-squared stiffness-loss index near 0.89. Despite this pronounced modal softening, measured residual deformation remains small in absolute terms, and the self-centering index remains moderate to high over most of the sequence. The results indicate that the tested system evolves mainly through changes in contact, uplift, diaphragm compatibility, and interface stiffness rather than through a conventional cumulative plastic-damage mechanism. The descriptor set and calibrated finite-element visualization provide a transferable basis for comparing future mass-timber shake-table datasets and for linking open experimental repositories, modal identification, and finite-element state visualization in performance-based seismic assessment of low-damage timber buildings. Full article

Glass-transition-driven shape memory polymers are promising materials for 4D printing because their thermally activated transition enables programmed deformation and recovery without relying on melting or crystallization-driven switching. In this study, PDMS-MMA-modified photocurable networks were designed for vat photopolymerization-based 4D printing by varying PDMS-MMA content and switching monomer structure while maintaining a fixed TMPTMA crosslinker content. The resin formulations were prepared using tert-butyl acrylate (tBA) or isobornyl acrylate (IBOA) as switching monomers, PDMS-MMA as a flexible mobility-regulating segment, and TMPTMA as a multifunctional crosslinker. The effects of formulation composition on printability, network formation, thermal stability, thermomechanical transition, mechanical properties, and shape memory behavior were systematically investigated. FT-IR analysis confirmed effective photocuring of the acrylate/methacrylate networks, while rheological evaluation showed that resin viscosity depended on monomer structure and PDMS-MMA content. DMA results revealed thermomechanical transition, although some formulations exhibited broad tan δ responses due to network heterogeneity and distributed segmental relaxation. Based on resin printability, printed-part resolution, and relatively well-defined tan δ transitions, T-15 and I-15 were selected as representative formulations for quantitative shape memory evaluation. Shape memory testing was conducted under force-control mode because stable strain-controlled programming was not achievable for the printed specimens. Both T-15 and I-15 exhibited high shape fixity over two programming–recovery cycles. I-15 showed stable recovery behavior with recovery ratios of 91.51% and 95.87%, whereas T-15 showed apparent over-recovery with recovery ratios exceeding 100%, likely due to residual stress release during reheating. Overall, these results demonstrate that thermally activated shape-memory performance is governed not only by the nominal transition temperature but also by the coupled effects of PDMS-mediated segmental mobility, switching monomer structure, mechanical integrity, and elastic energy storage within a fixed crosslinked network framework. Full article

During the meshing process of plastic gears, inhomogeneous thermal deformation is prone to occur due to the coupling effect of frictional heat generation and material thermal sensitivity, leading to contact misalignment on tooth surfaces. Traditional modification designs mostly rely on empirical approaches or merely compensate for static elastic deformation, which cannot adequately address thermo-mechanical interactions. In this paper, an active modification method based on the identification of thermal deformation regions is proposed. First, a thermo-structural coupling finite element model of polyoxymethylene (POM) gears is established, taking into account the temperature-dependent modulus. The steady-state temperature field is obtained through ANSYS 2024 R1 simulations, and its accuracy is verified against experimental measurements. Subsequently, the thermal deformation distribution is acquired by coupling the structural field. The cumulative deformation energy function is introduced, and the modification length is objectively determined as L = 0.35 mm by adopting the extreme point of the second derivative of the normalized cumulative energy. Three modification strategies, namely linear modification, Walker curve modification, and Mingchuan curve modification, are designed. Simulation results demonstrate that all three strategies effectively reduce the thermal deformation, steady-state temperature, and contact pressure of the gears, among which the Walker curve modification exhibits the best performance. After modification, the maximum thermal deformation is reduced by 44.14%, the maximum contact pressure by 16.2%, and the maximum steady-state temperature by 9.5%. The proposed method transforms thermal deformation from a “passive response” into an “active design input”, verifies the feasibility of thermally driven modification, and thereby establishes a quantifiable thermally adaptive modification approach for plastic gears. Full article

Thermal/environmental barrier coatings (T/EBCs) have become a notable research field for the development of high-performance thermal protection coatings. The mechanical properties are essential for T/EBCs, which determine the functionality, reliability and durability of coatings. The Yb₄Hf₃O₁₂ TEBCs were prepared by atmospheric plasma spraying using nanostructured spherical feedstocks and the nanomechanical properties of the Yb₄Hf₃O₁₂ coatings were characterized by nano-indentation in this work. Results indicate the elastic indentation work (W_e) is 16.06 ± 1.45 nJ and the plastic indentation work is 28.62 ± 6.87 nJ for nanostructured Yb₄Hf₃O₁₂ coatings. The ratio of plastic work to total deformation work during indentation as the energy dissipation parameter (η) is 0.63 ± 0.05 for nanostructured Yb₄Hf₃O₁₂ coatings and it can be preliminarily inferred that the Yb₄Hf₃O₁₂ coating may possess favorable erosion resistance, although direct erosion testing is needed for confirmation. Full article

Additively manufactured composite architected discs offer a potential route for producing lightweight semi-finished blanks that can subsequently be shaped by conventional forming processes. However, the relationship between infill architecture, feature size, and deep-drawing formability remains poorly understood. This study investigates the deep-drawing response of material-extruded short-fibre-reinforced polymer composite discs by combining experimental tests and finite element simulations. Four infill strategies, namely perforated body, re-entrant, square and triangular, were first compared at drawing depths of 10 and 20 mm. The perforated body and re-entrant geometries were successfully formed at 10 mm, whereas only the perforated body withstood 20 mm without macroscopic failure. A second campaign focused on perforated discs with hole diameters of 2.5, 5, 7.5 and 10 mm. All configurations were drawable at 10 mm, while the 2.5 mm case failed at 20 mm. Statistical analysis confirmed that hole diameter significantly affected both retained cup height and side-hole aspect ratio. At 20 mm, larger holes reduced local ovalization but increased elastic recovery, leading to lower retained cup height. FEM simulations were used as an interpretative first-order model. They supported the experimental trends by comparing deformation modes, tensile/compressive stress redistribution, forming energy and strain localization. The results show that the formability of architected composite blanks is governed not only by material volume or porosity but by the ability of the internal architecture to accommodate deformation through a suitable balance between local stiffness and geometric compliance. These findings provide design-oriented guidelines for the development of additively manufactured architected blanks intended for hybrid additive–forming manufacturing routes. Full article

To explore the effects of internal unloading and lateral stress on rockburst behavior in deep hard rock roadways, rockburst simulation tests were executed utilizing a self-developed internal unloading apparatus. A miniature camera was employed to monitor and record the rockburst evolution process of surrounding rock following internal unloading. Results demonstrate that the rockburst process primarily consists of four stages: the quiet stage, the buckling deformation stage, the rock fragment exfoliation stage, and the V-shaped notch formation stage. As the lateral stress increases from 15.2 MPa to 26.7 MPa, the vertical stress corresponding to the initial failure (σ_zi) increased from 64.00 MPa to 74.00 MPa, the fractal dimension of rock fragments decreases from 2.4033 to 2.3459, and the rockburst severity decreases. Under high lateral stress conditions, rock bearing capacity is comparatively high, making it less prone to rockbursts. However, more elastic strain energy accumulates inside the surrounding rock. Consequently, once a rockburst occurs, its intensity is notably greater than that subjected to low lateral stress. This suggests that increasing the lateral stress exerts a strengthening effect on the surrounding rock of the roadway. Numerical simulations were performed to study the crack evolution laws within the surrounding rock. Studies have revealed that internal unloading induces both shear and tensile cracks, but mainly tensile cracks. As the lateral stress increases, the number of shear and tensile cracks induced by internal unloading increases. The internal unloading triggers rock damage, leading to a strength-weakening effect. It becomes more pronounced as lateral stress increases. By comprehensively comparing the effects of internal unloading and lateral stress, the initial failure vertical stress increases with rising lateral stress, demonstrating an overall strength-strengthening effect induced by increasing lateral stress. Therefore, the strength-weakening effect resulting from internal unloading is weaker than that resulting from increasing lateral stress. Full article

Mechanical damage remains a major constraint in low-damage harvesting and handling of the Korla fragrant pear, owing to its cultivar-specific bruise-sensitive traits (BSTs), namely its thin peel, crisp flesh, smooth epidermis, and high bruise sensitivity. This review synthesizes evidence from the Korla fragrant pear, other pear cultivars, apple, and related fresh produce to clarify damage mechanisms and engineering strategies for damage control. The reviewed studies show that injury is mainly governed by impact energy, compression load, contact stiffness, friction, fruit velocity, spacing, and transfer trajectory. Quasi-static compression and drop-impact tests provide essential thresholds, including elastic modulus, rupture force, absorbed energy, bruise area, and bruise volume, but Korla-specific data remain insufficient. Nondestructive techniques are complementary: RGB machine vision supports rapid surface screening, hyperspectral imaging improves early bruise detection, X-ray computed tomography quantifies internal bruising, and scanning electron microscopy verifies cellular damage mechanisms. FEM and DEM can predict stress distribution, deformation, collision behavior, and equipment-induced injury when calibrated with cultivar-specific parameters. Overall, apple- or general pear-based technologies require recalibration before application to the Korla fragrant pear. Future work should establish Korla-specific damage thresholds and validate detection, simulation, and conveying systems under real orchard and packing-line conditions. Full article

Fractures are widely developed in deep coal-mine surrounding rocks. They weaken the load-bearing capacity and energy-storage capacity of rock specimens, which may induce surrounding-rock deformation, roof collapse, and other hazards. Current studies on fractured rock masses mainly focus on a single parameter, such as fracture number or fracture dip angle. However, their coupled effects remain unclear. Integrated analyses of mechanical behavior, crack propagation, and energy evolution are also limited. In this study, uniaxial compression simulations of intact sandstone, single-fracture sandstone, and double-fracture sandstone were conducted using PFC^2D. The effects of fracture number and fracture dip angle on mechanical properties and failure characteristics were investigated. The results show that fractures reduced the peak stress and modulus of elasticity. A stronger weakening effect was observed with increasing fracture number. With increasing fracture dip angle, both peak stress and modulus of elasticity showed a V-shaped trend. The minimum peak stress occurred at 15°, while the minimum modulus of elasticity occurred at 45°. Sandstone failure was mainly dominated by tensile cracks. At 15°, the total crack number was the lowest, with 932 and 818 cracks for single-fracture and double-fracture specimens, respectively. Energy analysis showed that increasing fracture number reduced elastic strain energy and promoted dissipated energy. The weakest energy-storage capacity was observed at 30°. Overall, fracture number and fracture dip angle jointly controlled strength degradation, crack propagation, and energy evolution. This study provides a reference for fracture–damage assessment and disaster prevention in deep coal-bearing sandstone. Full article

This study comprehensively evaluates the mechanical properties, shrinkage behavior, and durability of concrete prepared with limestone- and granite-manufactured sands under standard-curing and steam-curing conditions. The results indicate that limestone-manufactured sand concrete consistently exhibits superior compressive strength and splitting tensile strength across all curing ages, outperforming granite-modified counterparts. The introduction of granite-manufactured sand significantly degrades these mechanical properties, with deterioration intensifying as granite content increases. Dynamic elastic modulus and damping ratio analyses reveal that limestone-based concrete maintains the highest dynamic stiffness and lowest energy dissipation under both curing regimes, suggesting fewer internal defects. In contrast, granite incorporation reduces the dynamic elastic modulus and increases the damping ratio, reflecting structural deterioration and enhanced energy loss. Drying shrinkage tests demonstrate that limestone concrete achieves the lowest shrinkage deformation throughout the testing period, even under steam-curing conditions. Conversely, granite addition markedly elevates shrinkage, particularly under steam-curing conditions, leading to compromised volumetric stability. Durability assessments highlight that manufactured sand concrete exhibits higher capillary absorption, electrical flux, and porosity, attributed to inherent material defects and the surface characteristics of manufactured sand. Granite-modified concrete further weakens interfacial shear strength between aggregates and cement paste, indicating poor interfacial bonding. Steam curing exacerbates microstructural defects, emphasizing the need to optimize curing protocols. The findings propose strategies for enhancing manufactured sand concrete performance: improving interfacial adhesion between aggregates and cement paste, rationalizing supplementary material dosages, and refining steam curing regimes. These measures offer potential pathways to develop high-performance manufactured sand concrete with balanced mechanical and durability properties. Full article

Brittle geomaterials such as coal and rock are prone to unstable failure under high stress and dynamic disturbances, where rapid release of stored elastic strain energy can trigger dynamic disasters. Polyurea, a high-strength and high-ductility elastomer, can form a continuous flexible coating on the surface of coal/rock to regulate their deformation–fracture behavior. Here, uniaxial compression tests were performed on coal specimens coated with polyurea layers of different thicknesses (0–1.25 mm). Acoustic emission (AE) and digital image correlation (DIC) were jointly employed to characterize macroscopic deformation, microcrack evolution, fracture-mode transition, and energy partitioning. The results show that polyurea provides passive lateral confinement that suppresses lateral expansion and shifts macroscopic failure from brittle splitting to progressive ductile damage. AE-based AF–RA analysis indicates that thicker coatings increase the normal stress and shear resistance along potential fracture planes, promoting a microfracture transition from shear-dominated to tension-dominated cracking. Energy analysis demonstrates that the coating enhances pre-peak energy dissipation via coordinated deformation with the coal, while thicker coatings (≥1.00 mm) exhibit pronounced post-peak elastic tensile deformation to absorb and buffer fracture-released energy, impeding the instantaneous energy release typical of bare coal. Moreover, the elastic energy index shows that polyurea markedly reduces impact tendency, with an appropriate thickness stabilizing specimens from strong to weak/non-impact propensity. These findings clarify the coupled confinement–fracture–energy regulation mechanisms of polyurea coatings and provide quantitative guidance for coating-thickness design to mitigate dynamic failure hazards in brittle materials. Full article

Near-fault pulse-like ground motions (NFPLGMs) impose concentrated energy demands that can severely damage bridges, yet their scarcity and the influence of structural parameter uncertainties are often neglected in seismic fragility assessments. This study proposed a synthesis method for NFPLGMs by superposing low-frequency pulse components (extracted via the Gabor wavelet transform and low-pass filtering) with high-frequency stochastic components based on an evolutionary power spectrum. A three-span reinforced concrete bridge was modeled in OpenSeesPy, and Incremental Dynamic Analysis (IDA), together with a quadratic response surface model, were used to plot seismic fragility curves. The damping ratio (ξ), elastic modulus of steel reinforcement (E_s), yield strength of steel reinforcement (f_y), diameter of longitudinal reinforcement (D), and peak ground acceleration (PGA) were treated as random variables. Sensitivity indices were computed using Monte Carlo sampling (n = 10,000). Results show that ξ most strongly affects the displacement ductility ratio of the bridge pier (u_d) (variation of up to 32.6%), while E_s dominates the shear deformation of the bridge bearing (d) (variation of up to 43.8%). Neglecting structural parameter uncertainties overestimates median PGA thresholds (m_R) for different damage states by 1.5%–36.1%, and replacing NFPLGMs with ordinary ground motions overestimates seismic capacity by 1.7%–36.6%. The bridge bearing is consistently more vulnerable than the pier, with a collapse probability of 0.9566 at PGA = 1.0 g. These findings highlight the necessity of incorporating both NFPLGM characteristics and structural parameter uncertainties into bridge seismic fragility assessment. On the other hand, when seismic retrofitting of bridges is carried out using coating materials, priority should be given to more vulnerable components, such as bridge bearings, to improve the utilization efficiency of limited resources. Full article

Free vibrations of axially moving beam-like nanostructures have been investigated in recent years; however, vibrations of moving nanochassis traveling over a surface with arbitrarily small irregularities have not been displayed yet due to some complexities in modeling. To address this challenge, a nonlinear, nonlocal surface energy-based composite beam-like model is established to fairly accurately capture the nanochassis’ vibrations. The nanocar consists of a composite-like nanochassis and the ends’ wheels, where the nanochassis is modeled by an appropriate beam model and the wheels are simulated as rigid solid elements that are attached to the beam’s ends. Both differential- and integral-based formulations are presented, and their nonlinear stiffness, as well as the procedure for capturing the nonlocal elastic field, is carefully explained using the assumed mode approach. For several particular cases, the predicted results by the suggested models are verified with those of several analytical solutions, and reasonably good agreements are achieved. Beyond the aforementioned comparison studies, the possible instabilities of the nanochassis that travels over a straight route were also identified and explained under a small deformation regime. Through conducting a fairly comprehensive parametric study, the roles of amplitude and frequencies of the harmonic route, axial velocity, length, diameter, nonlocality, surface energy, and geometrical nonlinearity on maximum deformations and internal forces are examined comprehensively. This study could be considered as basic scrutiny for the nonlinear analysis of more complex traveling nanostructures over arbitrarily shaped surfaces. Full article

ETFE cushions are applied to building facades in a wide range of geometric forms and sizes. However, information on how cushion geometry and dimensions affect bulging behavior, thickness and area values, structural strength, thermal conductivity, and energy performance remains limited. Therefore, this study investigates cushion typology in eight geometries (isosceles and equilateral triangle, square, rectangle, rhombus, pentagon, hexagon, circular) with side lengths or radius values between 1 and 10 m, covering 115 variations. Geometric/physical mathematical area calculations, the parabolic dome model, elastic plate bending theory, the empirical thickness model, and thermal-resistance and degree day-based energy calculation approaches are used to obtain planar area, inflated curved surface area, maximum and average thickness, R and U values, and heating, cooling, and total energy consumption for each typology. The use of AI in numerical calculations provides fast and efficient design solutions in architecture and enables various geometric and performance scenarios to be produced rapidly. Circular, hexagon, and pentagon cushions lower U values and provide energy savings due to their high bulging capacity and deformation homogeneity; square, rhombus, and rectangle cushions show medium-level performance; isosceles and equilateral triangles limit energy savings because they produce higher U values. In conclusion, an increase in average bulging thickness and characteristic length reduces the number of cushions required to cover the facade, decreases the U value, reduces total heating and cooling energy consumption, and improves thermal performance. When a facade is covered with cushions of different geometries and sizes, it provides up to approximately 99.24% energy savings. Full article

Rock pillars in deep underground mines are subjected to complex stress environments. The combined effects of in situ stress and cyclic disturbances from mining activities lead to a redistribution of the surrounding rock mass stress field, which readily triggers instability and failure, posing severe threats to mining engineering safety. To investigate the damage mechanism of cyclic loading on rock and its weakening effect on the bearing capacity of mine pillars, this study takes limestone as the research object. A series of uniaxial compression tests were conducted on limestone specimens subjected to triaxial cyclic pre-damage, complemented by numerical simulations to further characterize the energy and deformation evolution of the damaged limestone under cyclic loading conditions. The findings are as follows: (i) Triaxial cyclic tests on limestone show that both the input energy and dissipated energy follow similar trends, decreasing rapidly in the initial stage before stabilizing. The elastic strain energy remains largely constant, with most of the input energy being stored as elastic strain energy. Under constant stress levels and cycle numbers, increases in confining pressure and frequency reduce the rock’s input energy, elastic strain energy, and dissipated energy. (ii) The peak stress of damaged limestone exhibits a positive correlation with the pre-damage confining pressure and cyclic frequency, while it decreases with an increasing number of cycles. Higher confining pressure and frequency raise the input energy, elastic potential energy, and dissipated energy at the peak stress point. (iii) Deformation and failure in damaged limestone originate from the development and propagation of localized deformation zones. Increased lateral displacement within these zones promotes the formation of macroscopic fractures. Due to significant structural heterogeneity inside the localized areas, the evolution of deformation energy is influenced by regional characteristics. (iv) Simulation results indicate that the uniaxial compressive failure of limestone involves the accumulation and propagation of micro-scale tensile cracks, which ultimately coalesce into macro-scale shear fracture surfaces. During uniaxial loading of pre-damaged limestone, newly generated cracks predominantly initiate around pre-existing cracks, with only a limited number distributed randomly. Their peak intensity shows a positive correlation with the pre-damage confining pressure. Full article