Search Results (234)

This article focuses on the research and development of innovative polymer-concrete composites for the manufacture of precision machine tool frames and critical mechanical engineering components. The relevance of this work stems from the need to replace traditional cast iron and cement concrete with materials with superior damping properties and thermal stability. The polymer matrix used in this study was ED-20 epoxy-diane resin, modified with (FAM) furan resin and cured with polyethylenepolyamine (PEPA), which together ensured minimal linear shrinkage (less than 0.5–1%) during polymerization. The focus was on the effect of multimodal filler distribution, including quartz sand, gabbro, and basalt, as well as reinforcing additives such as silicon carbide and fiberglass, on the final performance characteristics of the material. Experimental studies determined the key physical and mechanical parameters of the obtained samples. The results showed that the optimized composition (Smp_001) exhibited compressive strength up to 92.3 MPa, significantly exceeding that of standard high-strength concrete. It was established that the use of silicon carbide and glass fiber promotes the formation of a dense heterogeneous microstructure characterized by extremely low porosity (1.2–2.5%) and record-low water absorption (less than 0.05%). These characteristics guarantee high dimensional stability of the frames during prolonged contact with process fluids and cutting fluids. The scanning electron microscopy (SEM) and (EDS) energy dispersive X-ray spectroscopy methods confirmed the dense packing and high degree of interaction of the polymer matrix with the crystalline phases of the filler. This condition of the interfacial boundaries guarantees stable stress transfer throughout the entire volume of the material, which minimizes the risk of local damage during operation. The study confirmed that the developed material has vibration damping properties 6–10 times more effective than gray cast iron, a critical factor in improving machining accuracy on modern metal-cutting machines. The scientific novelty of the study lies in its substantiation of the synergistic effect of the combined use of basalt fillers and silicon carbide to achieve the precision properties of a structural material. Its practical significance is confirmed by the possibility of producing large-scale parts by casting without the need for complex finishing, opening up new prospects for modernizing the machine tool industry. Full article

Urban stormwater is often viewed as a drainage problem rather than a local water resource, even in areas where runoff capture could simultaneously reduce flooding and promote the reuse of non-potable water. This study develops, installs, and field-tests a decentralized, school-scale stormwater harvesting system that relocates permeable concrete, transforming it from a passive infiltration surface into a purpose-built capture and pretreatment interface. The system integrates a 3 m × 3 m permeable concrete slab with load-bearing sections, an impermeable underlayer to ensure controlled flow, a double-compartment sump for staged sedimentation and hydraulic damping, sequential filtration with sand/gravel and activated carbon, and a 5000 L storage tank. The prototype was implemented at CETis 105 in Querétaro, Mexico, and evaluated during its commissioning and operation in the 2023 rainy season. Field operations demonstrated reduced ponding in the catchment area and a reliable flow of runoff to the pretreatment units. In the sump compartments, apparent color decreased from 221 to 59 Pt-Co, turbidity from 46.8 to 12.9 NTU, and COD from approximately 30–35 to 15–18 mg·L⁻¹, corresponding to approximate pretreatment reductions of 73.3%, 72.4%, and 40–57%, respectively, before post-filtration. Conversely, the elevated pH, electrical conductivity, and total dissolved solids indicated interaction with fresh cementitious materials and dissolved ionic residues during initial operation, highlighting the need for curing, initial washing, and post-filtration verification before declaring compliance with reuse requirements. Therefore, the results support the feasibility of the proposed configuration as a decentralized, low-infrastructure architecture for localized runoff control and pretreatment, while confirming that full reuse validation still requires microbiological and post-filtration evaluation. The study provides a field-proven system design adaptable to school campuses and similar institutional environments for distributed stormwater management and non-potable water storage. Full article

In the classical Stochastic Subspace Identification (SSI) method, mode selection is primarily based on frequency stability, damping stability, and mode shape similarity using the Modal Assurance Criterion (MAC). However, these criteria are often insufficient for reliable modal identification in high-noise environments. This study advances beyond the classical approach by introducing a multi-criteria optimization framework for mode evaluation. In addition to the conventional frequency and damping assessments utilized in the classical SSI method, the proposed approach incorporates a range of supplementary structural metrics. These include Density, Cosine Similarity Difference (CSD), Damping Stability (DS), Spatial Roughness (SR), Mode Shape Complexity (MSC), Signal Energy Coherence (SEC), and Normalized Modal Difference (NMD). These metrics are computed within specifically optimized windows on the stabilization diagram. By integrating spatial, phase, and energy-based characteristics of mode shapes alongside traditional metrics such as the MAC, the method enables a more comprehensive and robust mode selection process that surpasses the limitations of relying solely on frequency and damping stability. Compared to the classical SSI, the optimized window approach provides a significant advantage by enabling the reliable selection of consistent modes by considering the continuity and multi-criteria coherence of modes across window transitions. As a result, the elimination of noise modes and the reliable separation of structural modes are established on a more systematic basis. To achieve this, a two-stage optimization strategy is implemented: the first stage determines the optimal frequency window width and minimum mode count threshold, while the second stage utilizes a Multi-Criteria Decision Making (MCDM) framework based on the Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) algorithm to assign optimized weights to the structural metrics and rank the candidate windows accordingly. As a result, the ideal frequency window is identified based on its TOPSIS score and subsequently validated using the MAC, confirming that the selected window corresponds to reliable structural modes. The framework is validated using long-term in situ measurements from a Roller Compacted Concrete (RCC) dam operating under significant environmental and operational noise. The dataset comprises continuous, high-resolution (200 Hz) vibration recordings collected between 1 July 2023 and 30 October 2024. While the calendar duration is limited to several weeks, the uninterrupted 24 h measurements yield a high-density time-series dataset with substantial information content, enabling a statistically meaningful and robust evaluation of modal identification performance under real-world and noisy conditions. The results reveal that relying solely on traditional selection criteria such as pole density and the MAC can often lead to the identification of spurious modes, particularly in noisy environments. In contrast, the proposed TOPSIS-based multi-criteria decision-making framework incorporates a broader range of structural indicators, balancing frequency, damping, spatial, and energy-related metrics to enhance the consistency and reliability of mode selection. This approach proved effective even under high-noise conditions, successfully distinguishing true structural modes from artificial ones. Application of the TOPSIS method to RCC dam data revealed consistent fundamental frequencies at approximately 5–10 Hz, 10 Hz, and 15 Hz, confirming its robustness and suitability for complex structural monitoring tasks. Full article

During the decommissioning of the BN-350 reactor, the spent nuclear fuel (SNF) was transferred to long-term dry storage in TUK-123 transport and storage cask systems designed for transportation and long-term storage with a design service life of approximately 50 years. The TUK-123 system consists of a UKKh-123 storage package, which is a sealed metal-concrete cask (MCC), and a protective-damping cover (PDC) used only during transportation. Radiation characteristics are a key quantitative criterion for assessing the safety of long-term storage in the absence of direct access to fuel and cask components. This paper presents the results of a computational study of the radiation characteristics of BN-350 SNF under dry storage conditions as of 1 January 2025. Spatial distributions of the ambient dose equivalent rate were determined for normal storage conditions and for accident scenarios involving partial failure of fuel assembly (FA) canisters and fuel redistribution. It was established that in the near-field region, the dose fields are formed predominantly by long-lived fission products and activation nuclides, whereas the neutron contribution is determined mainly by the spontaneous fission of actinides and (α, n) reactions. The results obtained provide a quantitative basis for assessing the radiation safety of long-term BN-350 SNF dry storage. Full article

Top-heavy industrial towers, which carry large, concentrated masses of equipment at upper levels and feature open lower stories, are vertically irregular by design and tend to amplify seismic displacement and acceleration demands near the tower top. Although tuned mass dampers (TMDs) have been studied extensively for buildings, bridges and chimneys, their application to this particular class of slender industrial towers—where production-equipment vibration tolerance, retrofit accessibility and limited downtime drive the design—has received little dedicated attention. This paper reports a focused numerical investigation of seismic response mitigation for a 101.2 m molten-asphalt granulation tower retrofitted with a single pendulum-type TMD. A three-dimensional coupled finite element (FE) model was constructed in ABAQUS using C3D8R solid elements for the reinforced-concrete shaft and T3D2 truss elements for the embedded reinforcement; modal analysis returned a fundamental frequency of 0.912 Hz and a torsional-to-translational period ratio of 0.65, indicating a translational-mode-dominated response. Elastic time-history analyses under the El Centro and Taft records together with a code-spectrum-compatible synthetic accelerogram show that a pendulum TMD with mass ratio μ = 2.5%, tuning frequency offset Δf = 5% and damping ratio ξ = 10%—installed at the uppermost equipment level guided by the modal-displacement criterion—reduces the peak top displacement, peak top acceleration and peak base shear by roughly 23%, 23% and 22%, respectively, in both principal directions. The controlled top acceleration falls comfortably below the 2.94 m/s² operational tolerance of the on-tower melting equipment. To address the rationality of the chosen TMD parameters, a single-variable parametric sensitivity study spanning μ ∈ [1%, 5%], ξ ∈ [5%, 15%] and Δf ∈ [0%, 10%] is performed on an equivalent reduced model that captures the qualitative parameter-response trends; the chosen baseline values lie inside a stable performance plateau and are shown to be a balanced compromise among the three response measures. The principal contribution of the work is, therefore, (i) a complete TMD retrofit framework—modal-based placement, parameter design, coupled FE assembly and multi-record verification—adapted to top-heavy industrial towers, and (ii) qualitative evidence, supported by a sensitivity scan, with a robust proposed parameter set for small-to-moderate detuning. The study is restricted to elastic time-history analyses under frequent-earthquake-level excitation, three ground-motion records and a fixed-base assumption; nonlinear response, larger record sets and soil–structure interaction effects are explicitly identified as scope limitations and are left for follow-up work. Full article

Concrete vibration quality has an outsized effect on structural durability, but construction sites have no reliable way to monitor it in real time. Compounding this, vibration machinery has no self-awareness of its own operating state, so failures and degradation tend to go unnoticed until something goes wrong. The proposed system integrates a Raspberry Pi controller and a hybrid neural network model within the vibrator apparatus itself. The model pairs a 1D CNN with a Kolmogorov–Arnold Network (KAN). The CNN initially conducts the majority of the computational workload: it systematically reduces dimensionality and extracts salient features from extensive time-series data, thereby circumventing the convergence challenges that a KAN encounters when processing unrefined high-dimensional sequences independently. Subsequently, a B-spline-based classification module supersedes the conventional fully connected layer. This innovation is noteworthy; the module is capable of identifying minute damping variations and frequency alterations during the process of concrete liquefaction, accurately distinguishing between states such as “adequate compaction” and “over-vibration,” which may appear nearly indistinguishable in their dynamic responses. The achieved accuracy in vibration state classification was 97.55%, while recognition of no-load conditions reached 98.17%. The system provides millisecond-level active protection against hazardous impacts, effectively reducing equipment wear. With a low implementation cost of approximately 800 RMB and a projected 20% improvement in construction compliance, this work provides reliable technical support for ensuring controllable construction quality and extending equipment service life, offering an efficient solution for the intelligent upgrade of building equipment. Full article

Damping modeling significantly influences the numerical seismic response of buildings, something that, despite being repeatedly emphasized in earthquake engineering research, is still overlooked even by seismic codes. It is a fact that, for simplification and ease of application, modern seismic design provisions assume damping for buildings entirely composed of a single material, e.g., reinforced concrete or structural steel. The current codes offer no guidance on damping assumptions for so-called mixed buildings comprising a lower part (stories) of reinforced concrete and an upper part (stories) of structural steel. Despite the growing use of mixed reinforced concrete-structural steel buildings, damping modeling of their seismic response remains almost unexplored. This study aims to contribute to this field by investigating the effect of different damping models on the elastic and inelastic seismic response of realistic three-dimensional mixed buildings. Modal response spectrum and time-history analyses served for this purpose. Key seismic response parameters, including interstory drift ratios, floor accelerations, and base shear demands, are extracted and systematically compared for the examined damping models. The results highlight the sensitivity of computed seismic demands to the assumed damping model. Guidance on selecting a damping model for the seismic analysis of mixed reinforced concrete-structural steel buildings is provided. Full article

In tunnel engineering, the integration of aseismic materials and structural designs has become a prevalent strategy to reduce earthquake-induced damage. However, previous studies on the seismic performance of tunnel structures predominantly employed deterministic methods, overlooking the spatial variability of the surrounding rock mass. This oversight often leads to an overestimation of structural performance, posing potential risks to the project. This study develops a probabilistic framework based on random field theory to evaluate the aseismic performance of tunnel linings incorporating a rubber–sand–concrete (RSC) constrained damping layer. The analysis systematically evaluates the aseismic performance of RSC across varying peak ground acceleration (PGA) levels and tunnel depth conditions. The findings are compared with results from traditional deterministic approaches. The probabilistic analysis indicates the following: (1) a reduction of approximately 70% in the dispersion of maximum principal stresses across various PGAs; (2) a decrease in RSC’s aseismic performance with greater burial depths, though it remains substantial overall, and (3) a reduction in the failure probability from 31.8% to 16.3% at PGA = 1.2 g. Furthermore, deterministic methods tend to produce overly optimistic estimates of tunnel aseismic performance, highlighting the need for probabilistic analysis. Full article

This study presents an experimental investigation into the repair and seismic performance enhancement of earthquake-damaged reinforced concrete (RC) frame structures using high-strength cement mortar and viscous dampers. A 1/4-scale, four-story RC frame model—designed according to a seismic fortification intensity of 8 degrees (corresponding to 0.2 g PGA in China’s seismic code)—was subjected to shaking table tests under increasing levels of artificial seismic excitation. Following the first round of loading, the damaged structure was repaired using high-strength mortar infill, and 12 viscous dampers were installed for seismic upgrade. The second round of identical seismic loading was applied to evaluate the effectiveness of the repair strategy. Comparative analysis of structural responses before and after repair reveals that the combination of high-strength mortar and viscous dampers improved damping capacity. The initial natural frequencies of the repaired structure increased by 6% (X) and 24% (Y), and damping ratios rose—reaching 12.75% and 10.78% under rare ground motions (1.34 g). Peak acceleration and inter-story drift ratio (IDR) were effectively reduced under moderate seismic levels, although some increase in IDR was observed at higher intensities, all drift values remained within the seismic code limits. The viscous dampers significantly altered the inter-story deformation mechanism, reducing the deformation concentration factor (DCF) of the frame structure and resulting in a more uniform distribution of story drifts. In addition, the energy dissipation capacity of the dampers increased progressively with the intensity of seismic excitation. The results validate the feasibility and efficiency of integrating viscous dampers with high-strength mortar for seismic repair and retrofitting of RC frame structure. Full article

In this paper, a hidden ring beam (HRB) joint suitable for steel-tube-reinforced concrete (ST-RC) composite columns is proposed. The seismic performance was evaluated experimentally by hysteresis loading tests on reinforcement anchorage construction and reinforced concrete (RC) slabs, which was evaluated by several indices to assess the strength, ductility, stiffness degradation and energy dissipation capacity. The results showed that the HRB joints have reliable seismic safety performance. The ultimate failure of all the specimens occurred in the plastic hinge regions of the RC beams. The specimens with different reinforcement anchorage construction methods exhibited excellent anchorage performance, maintaining effective anchorage between beam longitudinal bars and ring bars under cyclic loading. The RC slab increased the joint strength and the initial stiffness, with only a reduction in the ductility coefficient, and the average equivalent viscous damping coefficient reached 0.155. In addition, a joint numerical model was established, and the accuracy was validated against the test results, with the predicted strength differing from the test results by no more than 6%. A parametric analysis using numerical simulations revealed that the ring–longitudinal ratio, bearing stirrup diameter, RC slab constraints and axial load ratio were critical factors influencing the seismic performance of the joints. On the basis of the results of the parametric analysis, a moment capacity calculation method is proposed for HRB joints, providing a practical reference for seismic design in engineering applications. Full article

Conventional buckling-restrained braces (BRBs) with rectangular steel tube confinement suffer from stress concentration and inefficient material utilization, limiting their seismic performance. To address these limitations, this study proposes a novel non-rectangular concrete-filled steel tube BRB system incorporating elliptical and corrugated cross-sections. Comprehensive finite element simulations using ABAQUS are conducted to systematically investigate the influence of key geometric parameters—wall thickness (1–14 mm), corner radius (40–55 mm), and corrugation angle (30–75°)—on hysteretic behavior, load-bearing capacity, and failure modes. The results demonstrate that optimized non-rectangular sections achieve load-bearing capacity comparable to conventional rectangular designs (e.g., elliptical section with 12 mm wall thickness reaches 10.02 MN, a 75% increase over 1 mm thickness) while significantly improving material efficiency. Corrugated sections exhibit enhanced weak-axis performance, with equivalent viscous damping ratios exceeding the NIST-recommended threshold of 0.25. Parametric analyses reveal that wall thickness above 12 mm yields diminishing returns; corner radius reduction to 40 mm triggers local buckling yet increases peak capacity; and corrugation angles exceeding 50° induce instability. All non-buckling models satisfy AISC compression strength adjustment factor requirements (β ≤ 1.3). This study systematically evaluates non-rectangular BRB geometries, filling a critical gap in the literature and providing design guidelines that leverage shape optimization to enhance both seismic resilience and material economy. Full article

Accurate estimation of structural damping is essential for seismic performance assessment and design for earthquake-resistant buildings. From a sustainability perspective, reliable evaluation of dynamic properties is crucial in extending the service life of existing structures and reducing the need for material-intensive interventions. Ambient vibration measurements enable non-invasive identification of damping characteristics, supporting sustainable assessment of the built environment. This paper presents an analysis of the dynamic response of a four-story reinforced concrete structure. Ambient vibration recordings are obtained with Geodas Aquisition Station and one-second velocity sensors made by Butan Service And Tokio Soil Ltd., available from CERS (Seismic Risk Assessment Research Center) research center from TUCEB (Technical University of Civil Engineering of Bucharest). The sensors were installed at the top level of the analyzed structure. The method used for estimating the damping ratio is the Random Decrement Technique (RDT). The influence of the several parameters involved in the method is investigated, such as the triggering value, the dimension of the time window sub-samples, and the number of cycles considered within a window relative to the natural period of the structure. For the analysis of the parameters specific to the RDT method, computational routines were developed using syntax compatible with OCTAVE/MATLAB R2019b. Filters were applied to isolate the natural vibration modes. The variability in the parameters demonstrates that the developed method is robust. Full article

This study investigates the energy dissipation efficiency of structures equipped with nonlinear viscous dampers under seismic excitation. It aims to address the lack of a clear quantitative relationship between the energy dissipation ratio (the ratio of energy dissipated by dampers to the total seismic input energy), ground motion intensity, and damper parameters by systematically examining the underlying energy dissipation mechanism and parameter influence laws. First, an analytical model for a single-degree-of-freedom (SDOF) system controlled by the nonlinear viscous damper is established based on random vibration theory. An explicit analytical formula for the energy dissipation ratio is then derived by incorporating the statistical properties of the velocity response, which reveals a power-law relationship with the peak ground acceleration (PGA), damping coefficient (C), and damping exponent (α). Subsequently, this analytical model is extended to multi-degree-of-freedom (MDOF) structures using the mode decomposition method, leading to an engineering-oriented approximate formula for the energy dissipation ratio under the assumption of first-mode dominance, with its applicability conditions specified. Finally, a six-story reinforced concrete frame is employed as a numerical case study to evaluate the accuracy and engineering applicability of the proposed model through nonlinear time history and sensitivity analyses under various damper parameter combinations. The results indicate that PGA, C, and α all have a significant impact on the energy dissipation ratio and structural response, with C exerting a more direct influence on the overall energy dissipation level. The energy dissipation ratio is demonstrated to be a key performance indicator for damper parameter selection and seismic performance evaluation, providing a theoretical basis and practical reference for the damping design of structures incorporating nonlinear viscous dampers. Full article

This paper investigates an abstract fractional Cauchy problem with damping formulated in the sense of the Caputo derivative, where the derivative orders satisfy $0<\delta <\gamma \le 1$. By introducing the concept of a Caputo fractional $(\gamma ,\delta ,k)$ resolvent and systematically analyzing its fundamental properties, together with key features of the generalized Mittag–Leffler (ML) function, we establish the uniqueness and existence of strong solutions for this class of damped fractional-order evolution equations. Under more restrictive assumptions on the underlying operators, the solution admits an explicit representation in terms of ML-type functions associated with fractional exponents. Furthermore, we demonstrate that the proposed abstract framework can be effectively applied to concrete models, including fractional diffusion equations with damping. These results highlight the relevance and necessity of fractional damping models in accurately describing complex dynamical phenomena, such as vibration processes and anomalous diffusion. Full article

Damage to tunnel structures under seismic action severely affects engineering safety and post-earthquake rescue, making it crucial to enhance the seismic capacity of tunnels. Current seismic approaches for tunnel engineering mainly include seismic isolation (shock absorption layer technology), damping, and anti-seismic, among which shock absorption layer technology has attracted considerable attention due to its economic efficiency and effectiveness. However, existing research has primarily focused on single shock absorption layer materials, lacking systematic classification frameworks and multi-dimensional comparative analyses, making it difficult to provide comprehensive guidance for material selection and engineering applications. This paper systematically reviews the research status of tunnel shock absorption layers. First, it elucidates three core mechanisms through which shock absorption layers function: wave-impedance mismatch and energy reflection, material damping and energy dissipation, and system stiffness reduction with natural period elongation. This study proposes categorizing the existing materials for tunnel shock absorption layers into five main types: foam concrete, other types of concrete, polymer materials, asphalt materials, and porous metallic materials. A detailed introduction is provided for each material category, covering their physical properties, shock absorption performance, advantages and disadvantages, as well as relevant optimization studies conducted to address material limitations. By comprehensively comparing the mechanical properties, shock absorption performance, durability, constructability, recyclability, and economy of these five types of materials, revealing their unique advantages and applicable limitations in tunnel shock absorption. Finally, the limitations of existing research are summarized, development directions for tunnel shock absorption layer materials are proposed, and the future research trend of tunnel damping layer technology is envisioned. This paper provides a reference for the research, selection, and standard formulation of tunnel shock absorption layer materials. Full article