Search Results (951)

Advancing rapidly in modern bridge engineering technology, through concrete-filled steel tubular (CFST) arch bridges have achieved widespread application in transportation infrastructure development. Nevertheless, vehicle fires occurring in complicated operational settings may rapidly escalate into major disasters. Fires in oil tankers are particularly dangerous for the safety of bridges. This study examines the fire resistance of through concrete-filled steel tubular (CFST) arch bridges exposed to tanker truck fires. The study formulates a detailed model utilizing Fire Dynamics Simulator (FDS) to simulate fire scenarios, elucidating the spatial temperature distribution characteristics within arch bridge structures. A three-dimensional finite element model established in ABAQUS (Abaqus 2024, Dassault Systèmes Simulia Corp, Providence, RI, USA) is employed to simulate structural responses by analyzing the mechanical behavior of key components under different fire conditions. Practical fire resistance design recommendations for extreme tanker truck fire scenarios are ultimately proposed. Numerical results demonstrate that structural components near the fire source (such as transverse bracings, hangers, and fire-exposed arch surfaces) experience significantly higher temperatures than other regions. Notable temperature gradients developing along hangers and arch ribs in fire-affected zones are observed, while substantial cross-sectional temperature gradients occurring in these components under tanker truck fires reveal their damage evolution mechanisms. The fire exposure scenario at the quarter-point of the midspan is identified as the most critical fire exposure scenario for through CFST arch bridges under tanker truck fires. Under this extreme scenario, the deflection on the fire-exposed side of the global structure exhibits a significant three-stage distribution characteristic: an initial ascending phase around 0–800 s, followed by a sharp descending phase during 800–1100 s, and then a stabilization trend. A fire resistance limit criterion based on component failure (t_f3 = 853.43 s) is established, and a global fire resistance limit assessment methodology for through CFST arch bridges under extreme tanker truck scenarios is proposed. Full article

Equipment failure is the leading cause of industrial operational disruption, with unplanned downtime accounting for up to 11% of manufacturing revenue, highlighting the need for effective proactive maintenance strategies, such as protective sensors that can detect potential failures in critical equipment before a functional failure occurs. However, sensors are also subject to hidden failures themselves, requiring periodic failure-finding inspections. This study proposes a novel integrated multimethodological approach combining discrete event simulation, Monte Carlo, optimization, risk analysis, and multicriteria decision analysis methods to determine the optimal inspection period for protective sensors subject to hidden failures. Unlike traditional single-objective models, this approach evaluates alternative inspection periods based on their risk-informed overall values, considering multiple conflicting key performance indicators, such as maintenance costs and equipment availability. The optimal inspection period is then selected considering uncertainties and the intertemporal, intra-criterion, and inter-criteria preferences of the organization. The approach is demonstrated through a case study at the leading Portuguese electric utility, replacing previous empirical inspection standards that did not consider economic costs and uncertainties, supported by an open, transparent, auditable, and user-friendly decision support system implemented in Microsoft Excel using only built-in functions and modeled based on the principles of probability management. The results identified an optimal inspection period of 90 h, representing a risk-informed compromise distinct from the 120 h interval suggested by cost minimization alone, highlighting the importance of integrating organizational preferences into the decision process. A sensitivity analysis confirmed the robustness of this solution, maintaining validity even as the organizational weight for equipment availability ranged between 35% and 82%. The case study shows that the proposed approach enables the identification of inspection intervals that lead to quantitatively better maintenance cost and availability outcomes compared to empirical inspection standards. Full article

A precast concrete sandwich panel (PCSP), consisting of inner and outer wythes, an insulation layer, and connectors, relies heavily on the shear behavior of these connectors, which governs the structural performance of the entire system. Owing to their low thermal conductivity, excellent durability, and high strength, fiber-reinforced polymer (FRP) connectors offer strong potential for widespread application. This study introduces a novel cross-shaped FRP rod connector designed to provide improved anchorage performance, bidirectional shear resistance, and ease of installation. However, concern remains about the specific influence of embedment depth, outer-wythe thickness, and insulation-layer thickness on its shear performance. Moreover, no calculation model for shear capacity or shear–slip model has been established considering the shear-bending interaction within the connector. To evaluate its shear behavior, six groups of push-out tests were conducted, with key parameters including embedment depth, outer-wythe thickness, and insulation-layer thickness. The specimens exhibited two primary failure modes: connector fracture and concrete anchorage failure. The measured shear capacity per connector ranged from 5.63 kN to 14.19 kN, increasing with longer embedment depths, decreasing with increasing insulation thickness, and showing no clear dependence on outer-wythe thickness. Guided by test results and the Hashin failure criterion for composite materials, analytical formulas to estimate the shear capacity of FRP connectors were developed. The mean ratio of calculated to experimental values is 0.97, with a standard deviation of 0.06, indicating good agreement between the predicted and measured shear capacities. Furthermore, a theoretical shear–slip model was established. The correlation coefficients between the experimental and calculated load–slip curves for all specimens are greater than 0.98, indicating a high consistency in curve shape and variation trend. Full article

Effective monitoring and early warning of the instability of anti-slide piles in loess landslides depend on identifying the precursory signs of anti-slide pile failure. The acoustic emission (AE) characteristics of concrete anti-slide piles under cyclic loading were studied by using the model box test of the loess landslide–pile system. Cyclic graded loading simulates natural landslide sliding. The synergistic relationship between AE signal characteristics and pile bending moment is established, which reveals the evolution law from micro-damage to macro-damage. The results show that (1) AE ringing count and energy count change in the same way, first stable and then a sudden increase. The evolution of AE dominant frequency and amplitude experiences four stages: low frequency and low amplitude (initial damage), high frequency and low amplitude (stable development), medium frequency and high amplitude (accelerated development), and low frequency and high amplitude (failure). Each stage obviously corresponds to the change in bending moment. (3) The significant increase in the proportion of low-frequency AE energy effectively indicates that the landslide–pile system has entered the state of accelerated deformation and instability, which provides a quantifiable, real-time early warning criterion. This study verifies the feasibility and effectiveness of acoustic emission technology in anti-slide pile damage monitoring and landslide early warning and provides a new technical way for the precursor’s identification and early warning of anti-slide pile instability. Full article

Swarm unmanned surface vehicles (USVs) have been increasingly explored for maritime defense and security operations, particularly in scenarios requiring the rapid detection and interception of multiple attackers. The target detection reliability and defender–target assignment stability are significantly crucial to ensure quick responses and prevent mission failure. A key challenge in such missions lies in the assignment of targets among multiple defenders, where frequent reassignment can cause instability and inefficiency. This paper proposes a novel ETA-hysteresis-guided reinforcement learning (RL) framework for continuous multi-target hunting with swarm USVs. The approach integrates estimated time of arrival (ETA)-based task allocation with a dual-threshold hysteresis mechanism to balance responsiveness and stability in multi-target assignments. The ETA module provides an efficient criterion for selecting the most suitable defender–target pair, while hysteresis prevents oscillatory reassignments triggered by marginal changes in ETA values. The framework is trained and evaluated in a 3D-simulated water environment with multiple continuous targets under static and dynamic water environments. Experimental results demonstrate that the proposed method achieves substantial measurable improvements compared to basic MAPPO and MAPPO-LSTM, including faster convergence speed (+20–30%), higher interception rates (improvement of +9.5% to +20.9%), and reduced mean time-to-capture (by 9.4–19.0%), while maintaining competitive path smoothness and energy efficiency. The findings highlight the potential of integrating time-aware assignment strategies with reinforcement learning to enable robust, scalable, and stable swarm USV operations for maritime security applications. Full article

The validity and accuracy of photoplethysmography (PPG)-based wearable heart rate (HR) monitors remain debatable. This study aimed to determine the concurrent validity of HR records from a wide range of contemporary PPG monitors across the full spectrum of exercise intensities and running conditions. Ten well-trained male endurance athletes performed several incremental maximal aerobic (IMA) tests and high-intensity interval training (HIIT) sessions while wearing a Polar H9 chest strap, as the reference criterion; 16 PPG-based heart rate monitors were tested (Amazfit Fit5; Apple Ultra and SE; Garmin 35, 45, 235, and 935; Polar M200, M430, OH1, Vantage M, Vantage V, Vantage V3, and Verity Sense; Galaxy Watch 5, Suunto 3 Fitness). The results showed excellent ICC (>0.90) versus the reference device across IMA and HIIT tests. Overall, the ICC decreased, and magnitudes of error increased (BIAS, SEM, and CV) as the intensity increased. Moreover, lower ICC values and greater BIAS, SEM, and CV were observed during the HIIT compared to the IMA test. Nevertheless, notable differences between devices were observed in magnitude of errors, accuracy, data loss, and read failures. In conclusion, PPG-based HR monitor validity is device-dependent and therefore exercise data from running training and competitions should be interpreted with caution. Full article

The Trepponti bridge in Comacchio (Italy) is a significant masonry landmark characterised by a complex geometry. Its structure comprises five irregularly connected segments, creating pronounced geometric discontinuities. Accurately modelling this configuration is challenging due to the highly complex mechanical behaviour of masonry. This study presents a robust computational strategy for the nonlinear structural assessment of such heritage bridges. The methodology integrates a parametric meshing environment (PoliBrick plugin) with nonlinear finite-element analysis in Straus7. An initial discretisation is generated through PoliBrick, undergoes geometric optimisation to produce an analysis-ready model. The bridge is homogeneously modelled and meshed through macro-blocks obeying a Mohr–Coulomb failure criterion. Material parameters are defined according to the LC1 knowledge level stipulated by the Italian structural code. Differential settlement scenarios are simulated by imposing controlled vertical displacements on individual and paired piers. This approach enables evaluation of structural displacement, stress distribution, and crack propagation. The analyses reveal a markedly asymmetric structural response, identifying two specific piers as critical vulnerable elements. The proposed framework demonstrates that parametric meshing effectively reconciles accurate geometric representation with computational efficiency. It offers a practical tool for guiding the conservation and safety evaluation of irregular vaulted masonry bridges. Full article

Concrete structures in western saline soil regions are subjected to extreme environments with coupled dry-wet cycles and high concentrations of erosive ions such as Cl⁻, SO₄²⁻, and Mg²⁺, leading to severe degradation of mechanical properties. This study employed a simulated accelerated, high-concentration solution (Solution A, ~8× seawater salinity) similar to the composition of actual saline soil to perform accelerated dry-wet cycling corrosion tests on ordinary C40 concrete specimens for six corrosion ages (0, 5, 8, 10, 15, and 20 months). For each age, three replicate cube specimens were tested per property. The changes in cube compressive strength, splitting tensile strength, prism stress–strain full curves, and microstructure were systematically investigated. Results show that in the initial corrosion stage (0–5 months), strength exhibits a brief increase (compressive strength by 11.87%, splitting tensile strength by 9.23%) due to pore filling by corrosion products such as ettringite, gypsum, and Friedel’s salt. It then enters a slow deterioration stage (5–15 months), with significant strength decline by 20 months, where splitting tensile strength is most sensitive to corrosion. Long-term prediction models for key parameters such as compressive strength, splitting tensile strength, elastic modulus, peak stress, and peak strain were established based on grey GM(1,1) theory using the measured data from 0 to 20 months, achieving “excellent” accuracy (C ≤ 0.1221, p = 1). A segmented compressive constitutive model that considers the effect of corrosion time was proposed by combining continuous damage mechanics and the Weibull distribution. The ascending branch showed high consistency with the experimental curves. Life prediction indicates that under natural dry-wet cycling conditions, the service life of ordinary concrete in this region is only about 7.5 years when splitting tensile strength drops to 50% of initial value as the failure criterion, far below the 50-year design benchmark period. This study provides reliable theoretical models and a quantitative basis for durability design and life assessment of concrete structures in western saline soil regions. Full article

During the hammer riveting of aircraft composite wing trailing edges, issues such as unclear damage mechanisms resulting from the continuous impact loading of composite materials, difficulty ensuring connection strength, and issues with damage control remain unresolved. This study investigates the dynamic impact load transfer mechanism during hammer riveting, establishes a model which maps the correlation between impact loads and rivet plastic flow, and develops a composite material VUMAT subroutine (a user-defined material subroutine in Abaqus/Explicit) based on the 3D Hashin failure criterion. A progressive damage simulation model for composite materials subjected to multiple hammer riveting operations is constructed. Based on mechanical analysis, a double-sided countersunk rivet with a support structure is proposed to suppress damage during composite hammer riveting. Simulation and experimental analysis demonstrate that, compared to conventional rivets, the new rivet effectively reduces contact stress (by up to 32.29%). Damage zones are concentrated at the straight hole and at the junction between the straight and countersunk holes. Furthermore, damage modes are simplified to matrix compression and tensile stress, with their respective proportions decreasing by 16.7% and 25.9%. Full article

To address the synergistic stability evaluation of coal pillars and caving deposits in room-and-pillar mining of nearly vertical coal seams, this study takes the 101 Coal Mine (104th Regiment, Xishan Area, Urumqi, Xinjiang) as the engineering background. It combines physical similarity simulation and theoretical analysis to explore the synergistic bearing mechanism of coal pillars and caved deposits. Based on limit equilibrium theory, a combined instability criterion considering roof mudstone’s bending-toppling and shear-sliding is established; the Rankine earth pressure theory is modified, and a stability coefficient K_s (reflecting synergistic bearing effect) is proposed to realize quantitative evaluation of goaf stability. A model experiment simulates the mining of a 73° nearly vertical coal seam. Results show the roof instability mode (under coal pillars and caved deposits) is equivalent to anti-dip slope’s toppling-sliding composite failure. Experimental and theoretical results agree well, verifying the model’s rationality and applicability. This study provides a theoretical basis and analytical method for calculating the synergistic stability of coal pillars and caving deposits in nearly vertical coal seams. Full article

Reinforced concrete structures constitute a fundamental component of modern construction; however, the execution process is highly susceptible to construction errors that may reduce the safety and durability of structural elements. Despite numerous studies addressing failures and degradation mechanisms, there is a lack of methods enabling quantitative, multi-criteria assessment of the significance of individual execution errors. The aim of this article is to identify, evaluate, and prioritize execution errors occurring during the construction of reinforced concrete structures, considering their impact on safety, durability, and repair costs. A hybrid decision-making model combining the fuzzy WINGS and fuzzy TOPSIS methods was developed to enable the assessment of execution errors under uncertainty. The scientific novelty of this study lies in the application of a hybrid fuzzy approach to the evaluation of construction errors in reinforced concrete works, allowing for the simultaneous consideration of criterion importance and the intrinsic ambiguity of expert judgments. Fuzzy WINGS was used to determine the criterion weights, while fuzzy TOPSIS facilitated the development of error rankings. Within the reinforcement-related errors, the most critical were the following: insufficient concrete cover (0.89), non-compliant reinforcement layout (0.82), and reinforcement discontinuity (0.81). Among formwork errors, the highest importance was assigned to exceeding permissible geometric deviations (0.94), while for concreting errors, the most significant were discontinuity of concreting (0.35) and improper technological joints (0.34). The proposed model provides a practical decision support tool for technical supervision, quality management, and risk assessment in reinforced concrete construction. Due to the universal structure of the hybrid fuzzy WINGS–fuzzy TOPSIS methodology itself, the approach may also be adapted in future research to other decision-making problems, should their nature justify the use of fuzzy multi-criteria methods. Full article

L360QS pipeline steel, due to its high toughness, high strength, resistance to sulfide stress cracking, and resistance to hydrogen-induced cracking, is increasingly being used in pipeline network construction. Its fracture behavior is a critical factor for safe operation in mountainous steep-slope environments, but it has not yet been widely studied. Therefore, this paper conducts extensive experiments on the ductile fracture of L360QS pipeline steel. The tests employed standard tensile, notched tensile, shear, and compression specimens, covering a stress triaxiality range from approximately −0.33 to 0.92. The study combined Ling’s iterative method to establish an elastoplastic constitutive model considering post-necking behavior, and incorporated it into finite element models to extract the average stress triaxiality and equivalent plastic strain at the moment of fracture initiation for each type of specimen. Based on the extracted data, a piecewise ductile fracture model was established: a simplified Johnson–Cook criterion is used in the high triaxiality range, while an empirical function is used to describe fracture behavior in the medium, low, and negative triaxiality ranges. The model was validated using a train–test split approach, predicting fracture displacements for an independent test set of specimens. The results showed all prediction errors were within 5%, demonstrating the model’s high accuracy. Furthermore, a Spearman correlation analysis quantified the influence of geometric factors, revealing that notch curvature has the strongest monotonic relationship in controlling average stress triaxiality and fracture strain. The fracture model established in this paper can accurately predict the fracture behavior of L360QS pipeline steel and provides a reliable basis for failure prediction and safety assessment under complex service conditions (such as mountainous steep slopes). Full article

Additive Manufacturing (AM) using Fused Layer Modelling (FLM) often results in polymer components with limited and highly anisotropic mechanical properties, exhibiting structural weaknesses in the layer direction (Z-direction) due to low interlaminar adhesion. The main objective of this work was to investigate and quantify these mechanical limitations and to develop strategies for their mitigation. Specifically, this study aimed to (1) characterize the anisotropic behavior of unreinforced Polycarbonate (PC) components, (2) evaluate the effect of continuous, unidirectional (UD) carbon fiber tape reinforcement on mechanical performance, and (3) validate experimental findings through Finite Element Method (FEM) simulations to support predictive modeling of reinforced FLM structures. Methods involved experimental tensile and 3-point bending tests on specimens printed in all three spatial directions (X, Y, Z), validated against FEM simulations in ANSYS Composite PrepPost (ACP) using an orthotropic material model and the Hashin failure criterion. Results showed unreinforced samples had a pronounced anisotropy, with tensile strength reduced by over 70% in the Z direction. UD tape integration nearly eliminated this orthotropic behavior and led to strength gains of over 400% in tensile and flexural strength in the Z-direction. The FEM simulations showed very good agreement regarding initial stiffness and failure load. Targeted UD tape reinforcement effectively compensates for the weaknesses of FLM structures, although the quality of the tape–matrix bond and process reproducibility remain decisive factors for the reliability of the composite system, underscoring the necessity for targeted process optimization. Full article

Under the dual challenges of energy supply demand imbalance and the efficient operation of underground gas storage (UGS) facilities, this study investigated the mechanical behavior of reservoir rocks and optimal production pressure differential in a depleted gas reservoir in China under multi-cycle injection-production. For the first time, we reveal the mechanical degradation mechanism of hydration and cyclic fatigue for three typical lithologies in depleted sandstone reservoirs. Rock mechanics tests were conducted to analyze the effects of lithology, water saturation, and cyclic loading on mechanical properties, and appropriate failure criteria were evaluated. The main findings are as follows: (1) Under a confining pressure of 45 MPa, the peak strength of fine sandstone was the highest at 160.13 MPa, and the peak strength of argillaceous sandstone was the lowest at 114.92 MPa. The strength increased approximately linearly with confining pressure. (2) Increasing water saturation significantly weakened rock strength, particularly in argillaceous sandstone due to hydration effects. At 45% water saturation, its strength decreased by 37.38%. while Young’s modulus and Poisson’s ratio remained relatively unaffected. (3) Rock strength progressively degraded with the number of loading cycles. Siltstone showed the most significant degradation, with a strength reduction of 28.50% after 200 cycles. The damage induced by cyclic loading was less severe than that caused by hydration. (4) Among five failure criteria evaluated, the Mogi–Coulomb criterion demonstrated superior predictive capability by incorporating three-dimensional principal stress effects, showing closest agreement with the experimental data. We further established a depth-dependent production pressure differential profile and proposed a lithology-specific injection-production strategy. These findings provide theoretical foundations for optimizing injection-production strategies and sand control measures in depleted reservoir UGS systems. Full article

This paper addresses the problem of decision-making support for the modernization of distributed automated control systems (ACS) in power engineering by proposing an integral quality criterion that combines similarity-driven Markov process modeling with geometric programming. The methodology transforms the transition rate matrix of a continuous-time Markov chain (CTMC) into a matrix polynomial, enabling the derivation of normalized similarity indices and the development of a criterion-based model to quantify relative variations in system quality without requiring global optimization. The proposed approach yields a generalized criterion model that facilitates the ranking of modernization alternatives and the evaluation of the sensitivity of optimal decisions to parameter variations. The practical implementation is demonstrated through updated state transition graphs, quality functions, and UML-based architectures of diagnostic-ready evaluation modules. The scientific contribution of this work lies in the integration of similarity-based Markov modeling with the mathematical framework of geometric programming into a unified criterion model for the quantitative assessment of functional readiness under multistate conditions and probabilistic failures. The methodology enables the comparison of modernization scenarios using a unified integral indicator, assessment of sensitivity to structural and parametric changes, and seamless integration of quality evaluation into SCADA/Smart Grid environments as part of real-time diagnostics. The accuracy of the assessment depends on the adequacy of transition rate identification and the validity of the Markovian assumption. Future extensions include the real-time estimation of transition rates from event streams, generalization to semi-Markov processes, and multicriteria optimization considering cost, risk, and readiness. Full article