Search Results (310)

In this work, we investigate tensor perturbations in a de Sitter background within the framework of Chern–Simons modified gravity. We introduce transverse-traceless perturbations and analyze how the Chern–Simons Cotton tensor induces parity-violating modifications to gravitational wave propagation, while the Pontryagin density vanishes at linear order. Using a mode decomposition of the scalar background field, we derive the sub- and super-horizon limits of the wave equations and uncover chiral corrections in the dispersion relations of tensor modes. The resulting birefringence exhibits both amplitude and velocity components, alternating with the phase of the scalar field. Particular solutions sourced by the scalar background show helicity-dependent amplification and a characteristic scaling of the radiated flux that reduces smoothly to the Minkowski limit. The accumulated phase difference between right- and left-handed modes grows quadratically inside the horizon and becomes frozen outside, leaving a permanent parity-violating imprint in the primordial tensor spectrum. Finally, by promoting the Chern–Simons field to a massive dark matter candidate, we demonstrate how its mass-dependent dynamics connect gravitational birefringence to axion-like dark matter phenomenology. Full article

This study investigates the seismic retrofit of historic single-nave churches through the optimization of roof diaphragms designed to enhance energy dissipation. The proposed strategy introduces a deformable box-type diaphragm above the existing roof, composed of timber panels and steel connectors with a cover of steel stripes, where energy dissipation is concentrated in the connections. The retrofit design is guided by the estimation of Equivalent Damping Ratio (EDR) instead of the usually adopted resistance criterion, considering an energy-based approach to improve global seismic performance while preserving architectural integrity. In this way, the retrofitted configuration of the roof can be considered a damper. Three numerical phases are presented to assess the effectiveness of the equivalent damping-based intervention. In the first one, the seismic response of the initial non-retrofitted configuration is implemented using a 3D linear finite element model subjected to a response spectrum. Subsequently, nonlinear equivalent models subjected to spectrum-compatible accelerograms are implemented, simulating the possible retrofitted configurations of the roofs to detect the optimum damping and finding the corresponding roof diaphragm configuration. In the third one, the response of the detected retrofitted configuration is also evaluated by nonlinear 3D model subjected to accelerograms. The three phases with the relative numerical approaches are here applied to a case study, located in a high seismic hazard area. The results demonstrate that the EDR-based methodology can optimize the retrofitted roof diaphragm configuration; the nave transverse response is improved in comparison with that designed with the traditional approach, considering only the over-strength of the interventions. Comparisons about the approaches based on the EDR and the strength criteria are presented in terms of lateral displacements, in-plane shear acting on the roof diaphragm, and in-plane stresses on the façade. Full article

Across the Baltic Sea region, areas situated in climate-sensitive water zones are increasingly exposed to environmental and socio-economic challenges. Gdańsk, Poland, is a prominent example where the rising threat of climate-related hazards, particularly connected with flooding, coincides with growing demand for resilient and adaptive housing solutions. Located in the Vistula Delta, the city’s vulnerability is heightened by its low-lying terrain, polder-based land systems, and extensive waterfronts. These geographic conditions underscore the urgent need for flexible, climate-responsive design strategies that support long-term adaptation while safeguarding the urban fabric and the well-being of local communities. This study provides evidence-based guidance for adaptive housing solutions tailored to Gdańsk’s waterfronts. It draws on successful architectural and urban interventions across the Baltic Sea region, selected for their environmental, social, and cultural relevance, to inform development approaches that strengthen resilience and social cohesion. To achieve this, an exploratory case study methodology was employed, supported by desk research and qualitative content analysis of strategic planning documents, academic literature, and project reports. A structured five-step framework, comprising project identification, document selection, qualitative assessment, data extraction, and analysis, was applied to examine three adaptive housing projects: Hammarby Sjöstad (Stockholm), Kalasataman Huvilat (Helsinki), and Urban Rigger (Copenhagen). Findings indicate measurable differences across nine sustainability indicators (1–5 scale): Hammarby Sjöstad excels in environmental integration (5/5 in carbon reduction and renewable energy), Kalasataman Huvilat demonstrates strong modular and human-scaled adaptability (3–5/5 across social and housing flexibility), and Urban Rigger leads in climate adaptability and material efficiency (4–5/5). Key adaptive measures include flexible spatial design, integrated environmental management, and community engagement. The study concludes with practical recommendations for local planning guidelines. The guidelines developed through the Gdańsk case study show strong potential for broader application in cities facing similar challenges. Although rooted in Gdańsk’s specific conditions, the model’s principles are transferable and adaptable, making the framework relevant to water sensitivity, flexible housing, and inclusive, resilient urban strategies. It offers transversal value to both urban scholars and practitioners in planning, policy, and community development. Full article

Within the present paper, Physics-Informed Neural Networks (PINN) are investigated for the analysis of frame structures in two dimensions. The individual structural elements are represented by Euler–Bernoulli beams with additional axial stiffness. The transverse and axial displacements are approximated by individual neural networks and the differential equations are considered by minimizing a joined global loss function within the simultaneous training process. The boundary conditions at the supports of the structure and the coupling conditions at the element connections are considered in the global loss function and specific weighting factors are defined and tuned within the training. The combination of several structural elements within one analysis by training a set of neural networks simultaneously by a joined loss function is the main novelty of the current study. The formulation of coupling conditions for different scenarios is illustrated. Additionally, a nondimensionalization approach is introduced in order to achieve an automatic scaling of the individual loss function terms. Several examples have been investigated as follows: a simple beam structure first with quadratic load and second with varying cross-section properties is analyzed with respect to the convergency of the networks accuracy compared to the analytical solutions. Two more sophisticated examples with several elements connected at rigid corners were investigated, where the fulfillment of the consistency of the displacements and the equilibrium conditions of the internal forces is a crucial condition within the loss function of the network training. The results of the PINN framework are verified successfully with traditional finite element solutions for the presented examples. Nevertheless, the weighting of the individual loss function terms is the crucial point in the presented approach, which will be discussed in the paper. Full article

This work presents a numerical study of side boundary effects in pore-scale digital rock flow simulations, where the side boundaries are often treated as no-slip walls. While the capillary end effects from inlet and outlet boundaries are well known, the influence of side boundaries has not been systematically studied, especially for two-phase flow. We employ a well-established three-dimensional color-gradient lattice Boltzmann model to simulate immiscible two-phase flow on both real and synthetic rock samples. Our results reveal significant artifacts in small samples caused by side boundaries, leading to non-representative saturation profiles, even though absolute permeability remains consistent with larger samples. In drainage, non-wetting phase saturation is substantially lower near the side boundaries due to increased trapping of the wetting phase, while in imbibition, the wetting phase preferentially flows along the walls, forming steep V-shaped saturation profiles near the side boundaries. Increasing sample size can reduce boundary influence, but this is often impractical for certain samples, owing to, for instance, high computational demands. Enforcing periodic boundary conditions directly on the side boundaries only marginally improves saturation near the boundaries for the drainage cases, as poor pore connectivity across quasi-periodic boundaries remains a limitation, especially in low-porosity media, while the approach causes unphysically high wetting phase saturation near the side boundaries during imbibition. An alternative approach is to generate synthetic rock samples that are inherently periodic in the transverse directions, enabling more representative two-phase flow simulations. By comparing simulations with no-slip and periodic boundary conditions on a low porosity synthetic rock sample, the side boundary effects can cause more than 10% differences in steady-state saturation. Thus, synthetically generated periodic digital rock samples offer a promising solution for pore-scale studies of low-porosity media. Full article

Scaffolds, as temporary structural support systems in civil engineering, play an essential role during construction. Independent steel scaffold systems, typically composed of assembled steel tubes, can be erected and function as standalone supports without mutual interference. This feature offers notable advantages over conventional scaffolding, including easier dismantling and higher reusability efficiency. However, the absence of specific design and construction codes for this type of scaffolding has hindered its broader application, underscoring the need for further research into its structural reliability. This study investigates the stability of basic load-bearing units in independent scaffolding through vertical loading tests on three specimens with varying heights and end conditions. The failure modes of the specimens are systematically compared, and the load-transfer mechanism and mechanical behavior of the scaffold units are analyzed. Experimental results, validated against ABAQUS finite element simulations, reveal that the critical region under axial compression lies at the junction between the inner and outer tubes. As specimen height increases, a plastic hinge develops in this region under load. In shorter specimens, the inner and outer tubes interact in a nearly fixed-end condition, without failure of the connecting pins. All three specimens failed by instability, and reducing the specimen height significantly enhanced the load-bearing capacity. When the top of the specimen is pin-supported, the material’s compressive strength is not fully utilized. To improve the axial stability of independent scaffolding, several structural improvements are proposed: replacing the pinned top with a plate-supported end to enhance compressive stability; integrating transverse bracing at the ends to connect individual units into an integrated system, thereby improving overall stability without compromising spatial flexibility; and applying mechanical reinforcement with external collars at the inner–outer tube interface to increase local bending stiffness and reduce initial imperfection, thus strengthening the global buckling resistance of the independent scaffolding system. Full article

Modular barges are increasingly applied in inland and nearshore operations for their transportability and flexible assembly, yet the reliability of their connections remains insufficiently studied. This study presents a finite element analysis of a 15-ton-class modular barge in service, focusing on bolted and interlocking joints under still-water and wave-induced loads. A detailed three-dimensional model with explicit contacts was developed, and four load cases combined hydrostatic and deck loads with longitudinal and transverse crest/trough scenarios. Results showed that the highest stresses occurred in central stiffeners and lower interlocking joints, but all were below allowable limits, ensuring adequate safety margins. Bolted joints exhibited low stress, confirming their robustness and redundancy within the hybrid system. By analyzing an operating barge under realistic conditions, this study demonstrates the structural adequacy of the modular concept and provides a basis for future guidelines and larger modular floating platforms. Full article

This study presents a new formulation for laminated composite thick shells by incorporating the discrete Kirchhoff–Mindlin triangular (DKMT) element into the vector form intrinsic finite element (VFIFE) method. This integration enables the accurate modeling of transverse shear effects, which are difficult to capture using conventional VFIFEs. In this framework, the shell is discretized into particles whose motions are analyzed over discrete time intervals, referred to as path elements. Euler’s law of motion governs particle dynamics, while triangular elements connect the particles and describe local deformation and internal forces. Quaternions represent rigid body rotations within the convected material frame, and internal forces are obtained from the shape functions of the VFIFE–DKMT element. The formulation is validated through numerical examples involving geometrically nonlinear displacements, dynamic responses, and large deformations in isotropic and composite shells. The results demonstrate the accuracy and robustness of the proposed method in predicting the nonlinear motion of thick shell structures. Full article

One of the main goals of the Compressed Baryonic Matter (CBM) experiment at the Facility for Antiproton and Ion Research (FAIR) is to investigate the properties of strongly interacting matter under high baryon densities and explore the QCD phase diagram. Fluctuations of conserved quantities like baryon number, electric charge, and strangeness are key probes for phase transitions and critical behavior, as are connected to thermodynamic susceptibilities predicted by lattice QCD calculations. In this paper, we report on up-to-the-fourth-order cumulants of (net-)proton number distributions in gold–gold ion collisions at the nucleon–nucleon center of mass energies $\sqrt{s_{NN}}$ = 3.5–19.6 GeV using the Parton–Hadron-Quantum-Molecular Dynamics (PHQMD) model. Protons and anti-protons are selected at midrapidity ($\left|y\right|$ < 0.5) within a transverse momentum range 0.4 $<p_T<$ 2.0 GeV/c of STAR experiment and 1.08 $<y<$ 2.08 and 0.4 $<p_T<$ 2.0 GeV/c of CBM acceptances. The results obtained from the PHQMD model are compared with the existing experimental data to undersatand potential signatures of critical behavior and to probe the vicinity of the critical end point in the CBM energy range. The results obtained here with the PHQMD calculations for $\kappa {\sigma }^2$ (the distribution kurtosis times variance squared) are consistent with the overall trend of the measurement results for the most central (0–5% centrality) collisions, although the calculations somewhat overestimate the experimental values. Full article

Offshore platforms need to be made, from the start of their construction, to withstand the extreme environmental conditions they will be facing. This study investigates the welding-induced residual stress and distortion in a Y-shaped tubular joint extracted from an offshore wind turbine jacket substructure. While similar joints are commonly used in offshore platforms, their welding behavior remains underexplored in the existing literature. The joint configuration is representative of critical load-bearing connections commonly used in offshore platforms exposed to harsh marine environments. A finite element model has been developed to simulate the welding process in a typical offshore tubular joint through thermal and mechanical simulation. Validation of the model has been achieved with results against reference experimental data, with temperature and distortion errors of 3.9 and 5.3%, respectively. Residual stress and distortions were analyzed along predefined paths in vertical, transverse, and longitudinal directions. A mesh sensitivity study was conducted to balance computational efficiency and result accuracy. Furthermore, clamped and free displacement boundary conditions are analyzed, demonstrating reduced deformation and stress for the second case. Full article

Unidirectional carbon fiber-reinforced polymer (UD-CFRP) composites demonstrate superior tensile creep strain and stress relaxation behavior along fiber orientation. However, prolonged transverse compressive loading in structural connection zones induces significant interfacial stress relaxation and creep deformation, primarily driven by resin matrix degradation and interfacial slippage under thermal-mechanical interactions, and remains poorly understood. This study systematically investigates the transverse stress relaxation characteristics of UD-CFRP through controlled experiments under varying thermal conditions (20–80 °C) and compressive stress levels (30–80% ultimate strength). Post-relaxation mechanical properties were quantitatively evaluated, followed by the development of a temperature-stress-time-dependent predictive model aligned with industry standards. The experimental results reveal bi-stage relaxation behavior under elevated temperatures and compressive stresses, characterized by a rapid primary phase and stabilized secondary phase progression. Notably, residual transverse compressive strength remained almost unchanged, while post-relaxation elastic modulus increased by around 10% compared to baseline specimens. Predictive modeling indicates that million-hour relaxation rates escalate with temperature elevation, reaching 51% at 60 °C/60% stress level—about 1.8 times higher than equivalent 20 °C conditions. These findings provide crucial design insights and predictive tools for ensuring the long-term integrity of CFRP-based structures subjected to transverse compression in various thermal environments. Full article

To increase and optimize the use of wood in structural elements, a deep understanding of its mechanical behavior is necessary. The transverse material properties of wood are particularly important for mass timber construction and for utilizing wood as a strengthening material in timber connections. This study experimentally determined the stiffness and strength of Scots pine wood under compression perpendicular to the grain and rolling shear loading, as well as their dependence on the annual ring structure. A previously established biaxial test configuration was employed for this purpose. The modulus of elasticity in the radial direction was found to be about twice that in the tangential direction (687 vs. 372 N/mm²), although the strength in the tangential direction (5.19 N/mm²) was comparatively higher than that in the radial direction (4.70 N/mm²). For rolling shear, especially for the rolling shear modulus, a large variation was found, and its relationship with annual ring structure was assessed. The obtained RS modulus ranged from 50 to 254 N/mm², while RS strength was found to be between 2.14 and 4.61 N/mm². The results aligned well with previous findings. Full article

Spun piles adjacent to the pile cap need sufficient confinement to ensure the formation of plastic hinges during severe earthquakes. However, the high confinement ratio required for precast piles according to ACI 318-19 results in tightly spaced spirals, which are difficult to implement. Since higher confinement is only needed at specific regions of the pile, external transverse reinforcement using steel jacketing has been proposed as an alternative solution. An experimental and numerical study was conducted to evaluate the effectiveness. The experimental results showed that the jacket enhanced both the strength and energy dissipation of the connection, but had only a minor effect on its ductility. A parametric study using finite element analysis was performed to investigate the parameters influencing connection behavior. The results indicated that variations in jacket thickness did not significantly impact the connection’s performance. A jacket height equal to 1.53 times the pile diameter was found to be the maximum effective height. It was also observed that higher axial loads led to a sudden loss of connection strength, thereby reducing ductility. Partial bonding between the jacket, grout, and pile was found to be acceptable within a certain range. The numerical analysis found that the steel jacket increases the ductility. Full article

Erosion monitoring was carried out between 2003 and 2022 using a hydrological station with a Thomson overflow, a water gauge, and a limnigraph installed at the outlet of the Kolonia Celejów gully system. The study area is located in the north-western part of the Lublin Upland in the Nałęczów Plateau mesoregion (SE Poland). The total amount and intensity of precipitation were measured using an automatic station and water runoff and suspended sediment yield (SST) were also continuously measured. High variability in water runoff was observed during this period (max. of about 76,000 m³ and mean > 26,000 m³), and as a result of numerous heavy rains, a significant increase in SST (max. of about 95 Mg to about 1200 Mg and mean of 24 Mg to about 215 Mg) was noted in the second half of the measurement period. Most of the material removed at that time came from the cutting of the gully bottom and from the redeposition of material transported from the catchment used for agricultural purposes. In order to determine the volume of material delivered to the slope–gully cascade system in November 2012, a second station was installed at the gully head, which only operated until June 2013. However, the measurements covered all snowmelts and summer runoffs, as well as the June downpours. At the same time, these measurements represent the first unique attempt to quantify the delivery of material from the slope subcatchment to the gully system. The year 2013 was also important in terms of water runoff from the loess gully catchment area (about 40,000 m³) and was a record year (SST > 1197 Mg) for the total amount of suspended material runoff (7.6% and 33.5% of the 20-year total, respectively). During the cool half of the year, 16,490 m³ of water (i.e., 42% of the annual total) flowed out of the gully catchment area, and during the warm half of the year, 23,742 m³ of water (59% of the annual total) flowed out. In contrast, 24,076.7 m³ of water flowed out of the slope subcatchment area during the year, with slightly more flowing out in the cool half of the year (12,395.9 m³ or 51.5% of the annual total). In the slope and gully subcatchment areas, the suspended sediment discharge clearly dominated in the warm half of the year (98% and 97%). The record-breaking SST amount in June was over 1100 Mg of suspended sediment, which accounted for 93% of the annual SST from the gully catchment area and over 94% in the case of the slope subcatchment area. The relationships in the slope–gully cascade system in 2013 were considered representative of the entire measurement series, which were used to determine the degree of connectivity between the slope and gully subsystems. During summer downpours, the delivery of slope material from agricultural fields accounted for approx. 15% of the material removed from the catchment area, which confirms the predominance of transverse transport in the slope catchment area and longitudinal transport in the gully. The opposite situation occurs during thaws, with as much as 90% of the material removed coming from the slope catchment area. At that time, longitudinal transport dominates on the slope and transverse transport dominates in the gully. Full article

As the core component of electrified railway power supply systems, the fatigue performance and reliability of catenary support structures are directly related to the operational safety of high-speed railways. To address the problem of structural fatigue damage caused by increasing train speed and high-frequency operation, this study develops a refined finite element model including a support structure, suspension system and support column, and the dynamic response characteristics and fatigue life evolution law under train operation conditions are systematically analyzed. The results show that under the conditions of 250 km/h speed and 100 times daily traffic, the fatigue lives of the limit locator and positioning support are 43.56 years and 34.48 years, respectively, whereas the transverse cantilever connection and inclined cantilever have infinite life characteristics. When the train speed increases to 400 km/h, the annual fatigue damage of the positioning bearing increases from 0.029 to 0.065, and the service life is shortened by 55.7% to 15.27 years, which proves that high-speed working conditions significantly aggravate the deterioration of fatigue in the structure. The reliability analysis based on Monte Carlo simulation reveals that when the speed is 400 km/h and the daily traffic is 130 times, the structural reliability shows an exponential declining trend with increasing service life. If the daily traffic frequency exceeds 130, the 15-year reliability decreases to 92.5%, the 20-year reliability suddenly decreases to 82.4%, and there is a significant inflection point of failure in the 15–20 years of service. Considering the coupling effect of environmental factors (wind load, temperature and freezing), the actual failure risk may be higher than the theoretical value. On the basis of these findings, engineering suggestions are proposed: for high-speed lines with a daily traffic frequency of more than 130 times, shortening the overhaul cycle of the catenary support structure to 7–10 years and strengthening the periodic inspection and maintenance of positioning support and limit locators are recommended. The research results provide a theoretical basis for the safety assessment and maintenance decision making of high-speed railway catenary systems. Full article