Assessment of the Dynamic Structural Response of Footbridges Subjected to Vandal Loads: Numerical and Experimental Modelling

Modern buildings increasingly utilize lightweight, high-strength materials and feature high-rise, large-span structural designs. These structures often exhibit low natural frequencies and are susceptible to resonance from low-frequency dynamic loads such as wind and pedestrian loads. This paper focuses on a large-span double-connected structure and analyzes its dynamic response under the combined effects of wind and pedestrian loads. First, a finite element model of the structure was created using ANSYS, and model validity verification and modal analysis were performed. Second, a Fourier-based pedestrian model was used to simulate pedestrian loads and generate time-range data. The pulsating wind speed was generated from the Davenport spectrum using the harmonic superposition method. Wind load time-range data were calculated for different heights using Bernoulli’s theorem. Finally, the solution yields information about the dynamic response of the structure. The study revealed maximum vertical comfort ratings in the connecting corridor were achieved when crowd density did not exceed 0.3 persons/m2. The connecting corridor’s most unfavorable horizontal comfort level was evaluated as a medium, except for the 0-degree wind angle condition. This paper provides experience in studying the dynamic response and vibration suitability assessment of the large-span double-connected structure under wind and pedestrian loads.

Evaluation of dynamic response and biomechanical properties of isolated blood vessels

A numerical model based on Navier-Stokes equations was used in conjunction with an experimental model in rabbits to study the effects of acute intracranial hypertension on basilar artery blood flow velocity. The hypertension was induced by pressure transmission via an epidural pressure sensor inserted into a parietal intracranial opening. A critical value of half of the diastolic arterial pressure for the intracranial cerebral pressure was determined by both numerical and experimental models. At this intracranial cerebral pressure level, the total input resistance and total input compliance, determined by the numerical model, exhibited an increase of 27% and 10%, respectively, and the tissular compliance a decrease of 25% from their physiologic baseline values. When the intracranial cerebral pressure reaches the level of the diastolic arterial pressure, a zero diastolic flow is observed into the cerebral vascular system. This study validates the theoretical model, which could be used in assessing intracranial cerebral pressure noninvasively in humans when O2 pressure can be stabilized.

Wave–current-structure blockage: Validation of one-way hydro-structural coupling with large-scale model tests of a stiffness-similar jack-up in elevated condition

The church of Saint Felix in Girona (Spain) is crowned by an octagonal bell tower with a stone pinnacle at each corner. It was built using dry-joint stone masonry, a technique that involves laying stones in a precise pattern to create a solid and durable structure. In order to strengthen the connection between the stone blocks of the pinnacles, a wooden bar was placed through a central hole carved in the stone structure. Today, the inner structure has completely disappeared. During maintenance and repair work, it was decided to restore the functionality of the disappeared reinforcement by installing a titanium bar in its place. Due to the uncertainty associated with the pinnacle’s behaviour and the lack of both, a proper numerical model of the monument, and an extensive characterization of the materials, a strategy based on multiple approaches was designed. The proposed strategy was based on combining numerical and experimental models, the final objective being to determine the length and mechanical properties of the metallic inclusion, considering the effects of gravity, wind, and seismic forces. A scale model of the pinnacle was evaluated in laboratory conditions. The results were used to calibrate a numerical model representing the scale specimen. After calibration, the results were extrapolated to a full-scale numerical model. The experimental and numerical results showed that the pinnacles needed to be reinforced along their entire height. The tensile stresses cause by wind and seismic forces at different levels, could not be compensated without the contribution of the titanium bar inserted into the pinnacle.

Approximate parameter for semi-rigid `Khorjinee' connections in dynamic torsional response of steel structures

This paper presents a progressive numerical model validation of a bowstring-arch railway bridge based on the analysis of experimental data from different structural response measurements, namely, static deformations under environmental actions, modal vibrations, and transient dynamic responses under traffic loads. This work also addresses an integrated approach that uses structural health monitoring (SHM) measurements in combination with FE modelling to understand the structural behaviour of a long-span complex bridge. A progressively phased in situ SHM system has provided a diverse set of data streams ranging from static and dynamic responses to the measurement of environmental and operational traffic loads. The first phase consists of defining a detailed baseline finite-element (FE) model of the bridge, envisaging the initial condition of the structure immediately after construction, and its validation using modal parameters (natural frequencies and mode shapes) derived from an ambient vibration test. Since overall in-service deflections in general do not exercise the non-linear regime of the bridge response, the second phase focuses on the analysis of static response data and temperature measurements to validate the non-linear behaviour of the structural system, particularly at the bearing devices, under slow actions. The third and final phase addresses the dynamic analysis under traffic actions, which provides greater sensitivity in the detection of non-linear behaviour due to the effects of high-amplitude actions induced by regular train loading profiles. To guarantee the accuracy of the baseline numerical model, particularly under temperature and traffic actions, it was necessary to use contact restrictions in some specific bearing devices. This improvement is in line with the structural changes detected in some bearing devices through visual inspections. As a result, an updated numerical model capable of reproducing the modal, static, and dynamic structural responses was achieved, showing a very good agreement between experimental and numerical data. In future applications, this updated numerical model will be useful for assessing the condition of the bridge under traffic loads, namely to identify damages and support the adoption of life cycle maintenance strategies based on the integration of SHM systems with (stochastic) load and failure models.

This study investigates the dynamic response characteristics of the tunnel bottom structure, focusing on a heavy-haul railway tunnel. To assess the condition of the tunnel bottom, geological radar and drilling core techniques were employed, along with on-site dynamic testing. The dynamic stress and acceleration response characteristics of the tunnel bottom structure, situated in grade V surrounding rock, were analyzed under axle loads of 25 t, 27 t, and 30 t. Both time-domain and frequency-domain analyses were conducted to explore the impact of structural defects on the dynamic response of the tunnel bottom. The results indicate that the dynamic response of the tunnel bottom structure increases linearly with increasing train axle load. In the presence of void-related defects at the tunnel bottom, the dynamic response of the structure is amplified, with an observed growth rate of up to 26.3%. Furthermore, the load exerted by heavy-duty trains on the tunnel bottom structure is predominantly a low-frequency effect, concentrated within the range of 0–20 Hz. Analysis of the 1/3 octave band reveals that the maximum difference in acceleration levels occurs at a center frequency of 31.5 Hz. Additionally, as the distance between the measurement point and the vibration source increases, the dynamic response induced by the void defect on the tunnel bottom structure weakens.

To investigate the influence of the casting speed on the flow field and the shape of the solidification front in an industrial bronze caster, numerical calculations have been performed and experimental flow field measurements were used to validate the numerical model. Both numerical and experimental model represented 1:1 the real caster geometry of 820 × 250 × 800 mm3. A steady-state calculation, considering solidification and turbulent flow, was performed. Furthermore, a 1:1 water model of the industrial bronze caster has been built and combined with a Particle Image Velocity (PIV) setup to measure the apparent flow fields. Amongst other parameters, the numerical model provided information on the influence of the casting speed on the solidification front shape. The water model gave the experimentalist the facility to adjust the shape of the solidification front to the one predicted by the numerical model and compare the resulting flow field with the numerical prediction. This work presents a comparison of the results of both numerical and experimental models for different casting speeds with the same numerical parameters and boundary conditions.

This paper provides examples of application of advanced numerical modelling to analysis of transformer operation and design optimization. Computer simulations are useful tools that help engineers in keeping the balance between the continuous pursuit of reducing the cost of transformers and assuring high quality performance. The presented examples refer to different types of transformers and different problems in their operation. They include analysis of thermal shock test of the dry transformer, analytical, experimental and numerical modeling for improvement of passive cooling in oil-immersed distribution transformers and seismic analyses of power transformers. In each case the numerical modelling approach is presented and the example results are shown. Simulations of thermal shock test indicate large temperature gradients that may have essential influence on mechanical behavior of the dry transformer coil. Further, the higher cooling efficiency of the new concept of passive cooling is validated using mathematical, numerical and experimental models. Finally, the proposed numerical methods of seismic analysis indicates that oil has an influence on structure dynamics and the whole transformer system must be taken into account during vibration analysis.

The nonlinear interaction of the high-steep waves with a bottom-fixed monopile is studied experimentally and numerically in this research. The predominance of the near-breaking waves in sea-bottom-effect waters where fixed structures such as wind turbines have been located drives the incentive of the endeavour. Hence, viscous fluid kinematics due to the interaction of regular and irregular wave regimes with the monopile is determined by using a three-dimensional viscous numerical model that takes advantage of an implicit finite volume to solve the Reynolds Average Navier–Stokes (RANS) equation. The volume of fluid method is exploited to treat the air–water interface. Moreover, the physical model test is carried out to record wave loads and kinematics of the free surface flow around the monopile. A range of nonlinear waves is considered for experimental and numerical models, from weakly nonlinear waves to near-breaking waves. The accuracy and convergence tests for different mesh sizes are conducted on the numerical model, and the numerical results are compared with the experimental data for verification. To reveal the nonlinearities of the shear force and the bending moment, the spectral analysis is run on the time-history of results. Furthermore, the fidelity of the numerical viscous model is evaluated for different sea states. The analogous study is replicated for a broad range of irregular waves to recognise the higher-order wave loads driven by the inertia forces and the diffraction.

Experimental and numerical models can be used to investigate saltwater intrusion (SWI) in coastal aquifers. Sea level rise (SLR) and decline of freshwater heads due to climate change are the two key variables that may affect saltwater intrusion. This study aims to give a better understanding of the impact of increasing seawater levels and decreasing freshwater heads due to climate change and increasing abstraction rates due to overpopulation using experimental and numerical models on SWI. The experimental model was conducted using a flow tank and the SEAWAT code was used for the numerical simulation. Different scenarios were examined to assess the effect of seawater rise and landside groundwater level decline. The experimental and numerical studies were conducted on three scenarios: increasing seawater head by 25%, 50% and 75% from the difference between seawater and freshwater heads, decreasing freshwater head by 75%, 50% and 25% from the difference between seawater and freshwater heads, and a combination of these two scenarios. Good agreement was attained between experimental and numerical results. The results showed that increasing the seawater level and decreasing freshwater head increased saltwater intrusion, but the combination of these two scenarios had a severe effect on saltwater intrusion. The numerical model was then applied to a real case study, the Biscayne aquifer, Florida, USA. The results indicated that the Biscayne aquifer is highly vulnerable to SWI under the possible consequences of climate change. A 25 cm seawater rise and 28% reduction in the freshwater flux would cause a loss of 0.833 million m3 of freshwater storage per each kilometer width of the Biscayne aquifer. This study provides a better understanding and a quantitative assessment for the impacts of changing water levels’ boundaries on intrusion of seawater in coastal aquifers.

Dynamic structural responses of long-span dome structures induced by tornadoes

Exposure to high doses of total body irradiation (TBI) may lead to the development of acute radiation syndrome (ARS). This study was conducted to establish an experimental rat model of TBI to assess the impact of different doses of TBI on survival and the kinetics of changes within the hematopoietic system in ARS. In this study, 132 Lewis rats irradiated with a 5Gy or 7Gy dose served as experimental models to induce ARS and to evaluate the hematopoietic response of the bone marrow (BM) compartment. Animals were divided into 22 experimental groups (n = 6/group): groups 1-11 irradiated with 5Gy dose and groups 12-22 irradiated with 7Gy dose. The effects of TBI on the hematopoietic response were assessed at 2, 4, 6, 8 hours and 5, 10, 20, 30, 40, 60 and 90 days following TBI. Signs of ARS were evaluated by analyzing blood samples through complete blood count in addition to the clinical assessment. Groups irradiated with 5Gy TBI showed 100% survival, whereas after 7Gy dose, 1.6% mortality rate was observed. Assessment of the complete blood count revealed that lymphocytes were the first to be affected, regardless of the dose used, whereas an "abortive rise" of granulocytes was noted for both TBI doses. None of the animals exhibited signs of severe anemia or thrombocytopenia. All animals irradiated with 5Gy dose regained initial values for all blood cell subpopulations by the end of observation period. Body weight loss was reported to be dose-dependent and was more pronounced in the 7Gy groups. However, at the study end point at 90 days, all animals regained or exceeded the initial weight values. We have successfully established a rat experimental model of TBI. This study revealed a comparable hematopoietic response to the sublethal or potentially lethal doses of ionizing radiation. The experimental rat model of TBI may be used to assess different therapeutic approaches including BM-based cell therapies for long-term reconstitution of the hematopoietic and BM compartments allowing for comprehensive analysis of both the hematological and clinical symptoms associated with ARS.

Simple SummaryHuman burns are diverse and the most difficult injuries to study in clinical settings. Numerous experimental burn models designed to study and compare different aspects of burns and their consequences and treatment are steadily progressing. This review summarizes the latest advances in experimental burn research as a guide to aid in the future design of studies.Experimental burn models are essential tools for simulating human burn injuries and exploring the consequences of burns or new treatment strategies. Unlike clinical studies, experimental models allow a direct comparison of different aspects of burns under controlled conditions and thereby provide relevant information on the molecular mechanisms of tissue damage and wound healing, as well as potential therapeutic targets. While most comparative burn studies are performed in animal models, a few human or humanized models have been successfully employed to study local events at the injury site. However, the consensus between animal and human studies regarding the cellular and molecular nature of systemic inflammatory response syndrome (SIRS), scarring, and neovascularization is limited. The many interspecies differences prohibit the outcomes of animal model studies from being fully translated into the human system. Thus, the development of more targeted, individualized treatments for burn injuries remains a major challenge in this field. This review focuses on the latest progress in experimental burn models achieved since 2016, and summarizes the outcomes regarding potential methodological improvements, assessments of molecular responses to injury, and therapeutic advances.