Acceleration Levels Research Articles

Impact of early-age vibration on the permeability and microstructure of mature-age concrete

Dynamic excitation in early-age significantly impacts the performances of mature concrete in underground structures, such as tunnels beneath railways supported by cast-in-place concrete. This study explores the impact of early dynamic excitation on properties of mature concrete. Vibration tests at a fundamental frequency of 114Hz, with peak acceleration levels ranging from 0.1g to 0.4g, were conducted using shaking table. Specimens underwent 33seconds of dynamic excitation every 15minutes over the initial 48hours, excluding a night break from 0-6am, totaling 114 vibration cycles. Various lab tests were employed to assess the properties and microstructure of mature concrete post-vibration, including water penetration resistance, capillary water absorption, Coulomb electric flux, scanning electron microscopy (SEM), mercury intrusion porosimetry (MIP) and Nitrogen adsorption-desorption measurement (NAM). The results proves that vibration causes water secretion and air bubbles discharge before the initial setting of concrete, thereby enhancing the hydration reaction. The relationship between vibration loads with varying peak accelerations and the cohesion resulting from hydration reaction influences the microstructural evolution of concrete, leading to the weakening and strengthening of permeability of mature concrete. Under the vibration spectrum and test conditions described in this paper, vibration loads with peak values less than 0.234g decrease the total volume of large and middle pores (>20nm) by up to 50% and increase the total volume of small pores (<20nm) by up to 200%. Due to these changes in pore structure, the permeability coefficient (Sk), cumulative capillary water height (i) and Coulomb electric flux decrease by up to 47.84%, 39.5% and 31.6%, respectively. However, when the amplitudes of vibration loads exceed 0.234g, the total volume of large and medium pores (>20nm) increases, and that of small pores (<20nm) decreases, leading to a reduction of the impermeability of mature concrete. Additionally, the SEM analysis corroborates these microstructural variations.

Behavior of Polymeric Substrates and Sintered Silver Printed Hybrid Electronic Assemblies Subject to Extreme Acceleration Levels and Elevated Temperatures

Abstract This paper focuses on the response of printed hybrid electronic (PHE) assemblies with polymeric substrates and additively manufactured sintered silver electrical traces subject to extreme mechanical shocks (up to 100,000 g) and high temperatures (up to 150 °C). The substrates are hemispherical domes of injection-molded polycarbonate and polysulfone thermoplastics. Trace deposition onto the domes is accomplished by a novel process that combines conventional milling with extrusion printing to recess silver traces and dielectric insulation within the surface of the substrate. Mechanical shock testing is performed using an accelerated-fall drop tower equipped with a dual mass shock amplifier (DMSA) able to generate accelerations from 10,000 g up to 100,000 g with pulse durations of ∼0.05–0.1 ms and impact velocities of 6.5–20.5 m/s. Specimen performance is characterized by electrical and physical testing before and after testing. While polycarbonate domes survive multiple drops at all acceleration levels and temperatures, they are sensitive to heat and susceptible to warping and structural deformation at 150 °C which can compromise trace performance. Polysulfone domes can survive these temperatures without issue, but are less shock resistant and only survive 3–4 drops at 100,000 g (compared to 30+ for polycarbonate domes). Trace resistance is used as a metric to assess trace performance. All traces exhibit progressive long-term degradation over the course of multiple shocks, followed by instantaneous discontinuity during the final shock event. Trace failure (defined as the doubling of static trace resistance) occurs at ∼105–106 J/kg cumulative impact energy for all acceleration levels.

A Study of Sliding Base Isolation System: A Review

Seismic isolation systems are crucial for protecting structures by minimizing the transmission of acceleration during seismic events, and among the various types, the resilient sliding system, which combines restoring springs and sliders, is highly effective in mitigating seismic impacts. This system controls structural responses by balancing stiffness and friction, ensuring safety while maintaining the functionality of buildings. However, optimizing the design of this system requires carefully selecting combinations of stiffness and the coefficient of friction to achieve low acceleration levels, while simultaneously managing the relative displacement within the isolation system to protect both the structure and its occupants. Excessive displacement may compromise the integrity of the isolation system or cause damage to the structure it is meant to protect. The challenge lies in finding the optimal friction and stiffness levels that provide sufficient energy dissipation and restore forces without allowing displacement to exceed acceptable thresholds. Studies show that restoring forces generated by springs help limit excessive displacements, while sliders dissipate seismic energy, and adjustments in these parameters must account for variations in ground motion intensity and frequency. Thus, a balance between flexibility and resistance is essential in sliding systems to ensure maximum structural safety and occupant protection during earthquakes. This paper reviews different sliding isolation systems which fulfils the requirements of controlling the earthquake and functioning accordingly. It include systems such as PF, FPS, VFPI , CFPI,VFPS,PFPE, VCFPS,VFFPI etc.

Impact of Vertical Vibration on Group Piles During Earthquake Loading: Experimental Findings

This study presents novel research on the impact of vertical vibration on the dynamic response of pile groups embedded in stratified soil under seismic loading conditions. An experimental setup was employed wherein the piled machine foundation was subjected to vertical vibrations at three operating frequencies (10, 20, and 30 Hz) and subsequently exposed to four levels of seismic acceleration (0.1 g, 0.34 g, 0.77 g, and 0.82 g). Piles with a length-to-diameter ratio of 25 were embedded in a stratified soil profile, with an upper loose layer (30% relative density) and a lower dense layer (80% relative density) acting as end-bearing. Measurements and analyses of horizontal and vertical accelerations, and amplification factors were conducted using the Fast Fourier Transform (FFT), spectral acceleration (Sa), and variation of acceleration with depth. The results demonstrated a significant reduction in horizontal acceleration, with a peak ground acceleration (PGA) reduction of up to 64% in average, particularly at higher frequencies such as 30 Hz. The mitigation efficiency at 30Hz improved with increasing PGA, showing reductions of 42, 68, 75, and 63% for seismic accelerations of 0.1 g, 0.34 g, 0.77 g, and 0.82 g, respectively. The analysis further revealed harmonic resonance and higher mode effects at lower frequencies, with nonlinear soil behavior affecting the resonance and amplification patterns. Additionally, the results demonstrate that the far-field accelerations exceeded the near-field accelerations within the pile group, particularly in the surface layer. The results indicated that the initial vibration amplitudes exceeded the safe operating limits outlined in ACI 351.3R-18 under seismic loading, particularly at higher seismic acceleration levels and lower frequencies. Additional modified charts were presented to account for these conditions. The results presented promising evidence for using vertical vibrations as an earthquake-mitigation strategy. However, avoiding operating at frequencies less than 10 Hz is recommended because of the potential resonance and interaction with horizontal accelerations during earthquakes. Doi: 10.28991/CEJ-SP2024-010-010 Full Text: PDF

Reliability of brain volume measures of accelerated 3D T1-weighted images with deep learning-based reconstruction.

The time-intensive nature of acquiring 3D T1-weighted MRI and analyzing brain volumetry limits quantitative evaluation of brain atrophy. We explore the feasibility and reliability of deep learning-based accelerated MRI scans for brain volumetry. This retrospective study collected 3D T1-weighted data using 3T from 42 participants for the simulated acceleration dataset and 48 for the validation dataset. The simulated acceleration dataset consists of three sets at different simulated acceleration levels (Simul-Accel) corresponding to level 1 (65% undersampling), 2 (70%), and 3 (75%). These images were then subjected to deep learning-based reconstruction (Simul-Accel-DL). Conventional images (Conv) without acceleration and DL were set as the reference. In the validation dataset, DICOM images were collected from Conv and accelerated scan with DL-based reconstruction (Accel-DL). The image quality of Simul-Accel-DL was evaluated using quantitative error metrics. Volumetric measurements were evaluated using intraclass correlation coefficients (ICCs) and linear regression analysis in both datasets. The volumes were estimated by two software, NeuroQuant and DeepBrain. Simul-Accel-DL across all acceleration levels revealed comparable or better error metrics than Simul-Accel. In the simulated acceleration dataset, ICCs between Conv and Simul-Accel-DL in all ROIs exceeded 0.90 for volumes and 0.77 for normative percentiles at all acceleration levels. In the validation dataset, ICCs for volumes > 0.96, ICCs for normative percentiles > 0.89, and R2 > 0.93 at all ROIs except pallidum demonstrated good agreement in both software. DL-based reconstruction achieves clinical feasibility of 3D T1 brain volumetric MRI by up to 75% acceleration relative to full-sampled acquisition.

Analysis of Road Roughness and Driver Comfort in 'Long-Haul' Road Transportation Using Random Forest Approach.

Global trade depends on long-haul transportation, yet comfort for drivers on lengthy trips is sometimes neglected. Rough roads have a major negative influence on driver comfort and increase the risk of weariness, distracted driving, and accidents. Using Random Forest regression, a machine learning technique well-suited to examining big datasets and nonlinear relationships, this study examines the relationship between road roughness and driver comfort. Using the MIRANDA mobile application, data were gathered from 1,048,576 rows, including vehicle acceleration and values for the International Roughness Index (IRI). The Support Vector Regression (SVR) and XGBoost models were used for comparative analysis. Random Forest was preferred because of its ability to be deployed in real time and use less memory, even if XGBoost performed better in terms of training time and prediction accuracy. The findings showed a significant relationship between driver discomfort and road roughness, with rougher roads resulting in increased vertical acceleration and lower comfort levels (Road Roughness: SD-0.73; Driver's Comfort: Mean-10.01, SD-0.64). This study highlights how crucial it is to provide smooth surfaces and road maintenance in order to increase road safety, lessen driver weariness, and promote long-haul driver welfare. These results offer information to transportation authorities and policymakers to help them make data-driven decisions that enhance the efficiency of transportation and road conditions.

Seismic fragility analysis and reliability evaluation for ancient stone pagoda using distinct element method

This study presents an application of performance-based assessment to establish fragility functions and evaluate the seismic reliability of an ancient stone pagoda in Korea. The pagoda was constructed of stone elements which were stacked over each other in layers without bonding material. To account for the discrete nature of this kind of structural configuration, the distinct element method is used to perform the incremental dynamic analysis to develop fragility functions. Three performance levels are specified on the capacity curve which is established based on non-linear pushover analysis. The randomness in seismic demand generation was considered when exciting the pagoda by a set of 23 input ground motion records, which were scaled into different intensity levels. The seismic response of the pagoda under different ground motions at several peak ground acceleration levels shows that the predominant frequency of the excitation is closely related to the behavior of this kind of structure. Ground motions with lower predominant frequency values induce stronger distortion to the pagoda than the ones with higher predominant frequency. The fragility functions estimated by maximum likelihood method show that earthquakes with peak ground motion of 0.469 g have a 50% probability of causing a collapse on the pagoda in the most conservative assessment. The probability of the pagoda collapsing within 50 years is 1.65% for the most earthquake-vulnerable site among the sites considered in the study.

A 2 : Towards Accelerator Level Parallelism for Autonomous Micromobility Systems

Autonomous micromobility systems (AMS) such as low-speed minicabs and robots are thriving. In AMS, multiple Deep Neural Networks execute in parallel on heterogeneous AI accelerators. An emerging paradigm called Accelerator Level Parallelism (ALP) suggests managing accelerators holistically. However, there lacks a specialized and practical solution populating ALP for an AMS, where the varying real-time requirements under different working scenarios bring an opportunity to dynamically tradeoff between latency and efficiency. Furthermore, accelerator heterogeneity introduces enormous configuration space, and the shared-memory architecture results in dynamic bandwidth interference. In this paper, we propose A 2 , a novel AMS resource manager optimizing energy and memory space efficiency under variable latency constraints. We gain insight from prior Learn&amp;Control scheme to design an Analyze&amp;Adapt scheme specialized for heterogeneous AI accelerators under shared-memory architecture. It features analyzing the system thoroughly offline to support two-step adaptation online. We build a prototype of A 2 and evaluate it on a commercial edge platform. We show that A 2 achieves 32.8% improvements in power and 13.8% in memory compared with control-based methods. As for timeliness enhancement, A 2 reduces the deadline violation rate by 9.2 percentage points (12.8% → 3.6%) on average compared to directly porting Learn&amp;Control methods.

Basis-independent quantum coherence and its distribution under relativistic motion

Recent studies have increasingly focused on the effect of relativistic motion on quantum coherence. Prior research predominantly examined the influence of relative motion on basis-dependent quantum coherence, underscoring its susceptibility to decoherence under accelerated conditions. Yet, the effect of relativistic motion on basis-independent quantum coherence, which is critical for understanding the intrinsic quantum features of a system, remains an interesting open question. This paper addresses this question by examining how total, collective, and localized coherence are affected by acceleration and coupling strength. Our analysis reveals that both total and collective coherence significantly decrease with increasing acceleration and coupling strength, ultimately vanishing at high levels of acceleration. This underscores the profound impact of Unruh thermal noise. Conversely, localized coherence exhibits relative stability, decreasing to zero only under the extreme condition of infinite acceleration. Moreover, we demonstrate that collective, localized, and basis-independent coherence collectively satisfy the triangle inequality. These findings are crucial for enhancing our understanding of quantum information dynamics in environments subjected to high acceleration and offer valuable insights on the behavior of quantum coherence under relativistic conditions.

Characteristics of environmental stress cracking of PE-HD induced by biodiesel and diesel fuels

In the context of the increasing effect of carbon dioxide emissions on the global climate biodiesel produced from renewable sources has emerged as a promising contender replacing fossil fuels, especially in long-range transport vehicles, using existing engines and infrastructure.High-density polyethylene is one of the prevailing materials for pipe and container applications for storage and transport of such fuels, both, from fossil and renewable resources. The contact with the respective fuels raises questions concerning material compatibility as biodiesel exhibits significant differences compared to conventional diesel fuel affecting its sorption and plasticization behavior in polyethylene. In this study, its behavior with respect to environmental stress cracking, considered one of the most frequent damage mechanisms leading to failure of polymer parts and packaging, was evaluated using the well-established Full Notch Creep Test. This approach allows for a detailed fracture surface analysis using imaging techniques, such as optical and laser scanning microscopy, as well as infrared spectroscopy. Comparing the environmental stress cracking behavior in standard surfactant solutions with that in biodiesel and diesel, respective crack propagation rates, showing different levels of acceleration, were determined and details of the underlying mechanisms could be revealed. Furthermore, the specific infrared absorption of the biodiesel's ester functionality allows its semi-quantitative determination on the fracture surface of the tested specimens after failure. Thus, a preferred uptake of sorptive fluids in the fracture zone due to local morphological changes of the polyethylene could be directly evidenced by infrared spectroscopy.

Extended version—to be, or not to be stateful: post-quantum secure boot using hash-based signatures

AbstractWhile research in PQC has gained significant momentum, its adoption in real-world products is slow. This is largely due to concerns about practicability and maturity. The secure boot process of embedded devices is one scenario where such restraints can result in fundamental security problems. In this work, we present a flexible hardware/software co-design for HBS schemes which enables the transition to a post-quantum secure boot today. These signature schemes stand out due to their straightforward security proofs and are on the fast track to standardisation. Unlike previous work, we exploit the performance intensive similarities of the stateful LMS and XMSS schemes as well as the stateless $$\text {SPHINCS}^{+}$$ SPHINCS + scheme. Thus, we enable designers to use a stateful or stateless scheme depending on the constraints of each individual application. To demonstrate the feasibility of our approach, we compare our results with hardware accelerated implementations of classical asymmetric algorithms. Further, we outline the use of different HBS schemes during the boot process. We compare different schemes, show the importance of parameter choices, and demonstrate the performance gain with different levels of hardware acceleration.

Towards automatic identification of ship-ice contact using acceleration measurement

When a ship navigates in ice-covered areas, its hull experiences motion and vibration responses due to ship-ice contact. The magnitude of such responses can be represented well by acceleration, which is easy to measure onboard ice-going ships. The level of acceleration is determined by the environmental and operational conditions through excitation via the ship-ice contact. Conversely, it is possible to infer excitation and environmental conditions using acceleration measurements via appropriate methods. Accelerations associated with such responses can also affect the functionality of the onboard equipment and therefore, should be quantified. Nevertheless, studies on shipborne acceleration measurements in ice fields and their links to prevailing excitations and environmental conditions are rare. This study explores the feasibility of using shipborne acceleration measurements to infer the corresponding excitations (i.e., ship-ice contacts) as a first step towards the inference of ice conditions via acceleration measurements. An automatic identification method for ship-ice contact is proposed that can effectively separate ship-ice contact events from acceleration measurement signals. The acceleration signals are decomposed in the time-frequency map obtained through a short-time Fourier transformation (STFT). An improved detection transformer (DETR) model was used to automatically identify ship-ice contact events and achieved good accuracy in the validation set. This model was then applied to automatically identify ship-ice contacts using acceleration signals under various environmental and operational conditions. The frequency of the identified ship-ice contact reasonably reflects its dependence on prevailing environmental and operational conditions, which confirms the validity of the proposed methodology.

Vibration control and transmission mechanism of super high-rise building located on subway based on spring vibration isolation system

This study focuses on the vibration control effect of the spring vibration isolation system (SVIS) on a super high-rise building located on the subway (BLS) and the transmission mechanism of vibration in super high-rise BLS. Firstly, the 1:35 scale shaking table test model of super high-rise BLS is designed, the rationality of the shaking table test model is verified, and the shaking table test is implemented. Secondly, the finite element model (FEM) is established and verified based on the results of the shaking table test. Finally, based on verified FEM, the vibration control effect of SVIS on super high-rise BLS and the vibration transmission mechanism of super high-rise BLS is analyzed. The results show that the vibration response of the BLS show amplification trend along the height direction. The amplification of vibration response of BLS is effectively controlled by SVIS. The higher the floor, the greater the reduction coefficient, and the better the control effect. The reduction coefficient above 10F is mainly distributed above 0.80 due to the SVIS. The BLS equipped with the SVIS maintains the degree of Z-direction vibration and 1/3 octave vibration acceleration level that is within the limits stipulated by the specifications. The first-order vertical frequency of BLS equipped with the SVIS is adjusted from 65 Hz to 8 Hz, far from the favorable frequency range of the subway wave.

Commuter Experience: An Assessment of Metro-Train Comfort Amidst Operational Vibroacoustic Conditions

This study investigates the impact of different passenger rolling stock structures and train configurations on vibrations and noise generated during operation. Vibroacoustic measurements were performed during acceleration, constant speed, and braking phases to analyze the effects using statistical analysis according to the relevant standards, revealing a statistically significant relationship between the equivalent noise level and vibration dose. In the context of the expanding Warsaw metro network, which is adding new lines and modern rolling stock, trends in the development of metro rolling stock were analyzed using five different types of metro vehicles, from the oldest to the newest designs. Vehicle performance was ranked in the context of ride comfort using standards and combined vibration and noise measures. The research results allowed for a collective comparative assessment of the construction of individual types of passenger rolling stock in terms of vibroacoustic phenomena, thanks to which it is possible to assess the impact of modern solutions and the justification for investing in modern rolling stock. Newer trains generally record significantly lower vibration and noise levels. The difference between the oldest and the most modern vehicle types is 57% for the vibration acceleration level (0.08 ms−2 RMS) and 66% for the noise level (2.2 dB LAeq).

A self-powered spring-based triboelectric vibration sensor

Abstract Self-powered vibration sensors have gained attention due to their versatility. However, a limitation of many existing self-powered sensors is their single-direction functionality, which hinders their effectiveness in capturing multidirectional human movement’s swinging motions. To address this, this study introduces an innovative self-powered vibration sensor based on the triboelectrification effect of an inverted pendulum metal ball. This novel sensor excels at detecting micro-vibrations through the freestanding sliding electrification of a metal ball using Kapton tape. The generated charge is transferred through interdigital electrodes arranged in a spiral pattern. To ensure adaptability to various motion types, the metal ball is affixed to a spring and configured as an inverted pendulum. This setup allows the sensor to detect both linear and rotary motions across a range of acceleration levels. The fabricated sensor exhibits remarkable sensitivity, measuring 0.203 V/mm. It was affixed to the human body to detect low-frequency vibrations, particularly those below 20 Hz. Impressively, it can detect millimeter-scale vibrations, even up to 3 mm, at different rotational angles (0°, 30°, 60°, and 90°). This outcome highlights the promising performance of our vibration sensor in the field of human motion monitoring, making it a significant advancement in the realm of self-powered vibration sensors.

Study on the vibration characteristics of double-row tapered roller bearings for high-speed rail axle box

PurposeThe purpose of this paper is to establish a dynamic model considering the actual operating conditions of the train and to study the dynamic performance and vibration characteristics of axle box bearings under different operating conditions.Design/methodology/approachIn this paper, based on the internal contact characteristics of double-row tapered roller bearings, a dynamic model considering the actual operating conditions of the train is established. The correctness of the model is verified by the vibration test of the bearing. Comparative analysis was conducted on the effects of axial force, radial force and rotational speed on the angular velocity of the cage, slip rate and vibration acceleration level of the inner ring.FindingsAs the force increases, the slip rate of the cages on both sides decreases, and the vibration acceleration level of the inner ring increases. With the increase of rotational speed, the cage slip rate of the axle box bearing increases and the vibration acceleration level of the inner ring increases.Originality/valueA dynamic model is established considering the actual operating conditions, and the dynamic performance and vibration characteristics of the axle box bearing under different operating conditions are analyzed by numerical method. The research content can provide reference for the parameter design of high-speed railway bearings.Peer reviewThe peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-03-2024-0085/

Framework for Seismic Vulnerability Assessment of Nonstructural Elements Inside an Inflatable Lunar Habitat

The pursuit of knowledge and curiosity are once again driving humanity to seek a human presence on extraterrestrial bodies. While numerous challenges must be overcome on the moon to achieve this goal, the moonquake hazard has often been overlooked. Using NASA’s Moon to Mars Architecture requirements for surface habitation and accounting for the midterm/long-term mission duration, a framework for vulnerability assessment is developed for essential nonstructural elements (NSEs) inside an inflatable habitat subjected to moonquakes. The aim of this study is to develop an approach to assess the vulnerability of typical NSEs that support essential equipment, such as the environmental control and life support system, under a paucity of information related to the seismic hazard. We also emphasize that the launch dynamic environment and lunar seismic environment exhibit notable differences in their characteristics, which can lead to higher lateral acceleration levels than initially expected. This acceleration may be linked to high-occurrence seismic events. However, due to the lack of information regarding the frequency of these events, the risk of NSEs being subjected to unforeseen loads increases. It is imperative to equip future lunar habitats with seismic mitigation measures until additional seismometers are deployed near upcoming surface human outposts.

A new formulation of the understeer gradient and stability margin to analyse vehicle steady-state cornering behaviour

The understeer gradient is a measure that describes a vehicle's cornering behaviour as either understeer, neutral, or oversteer. Several formulations of this measure have been developed, all of which are reviewed in this paper. It has been found that all of these formulations rely essentially on the lateral acceleration of the vehicle. While the understeer gradient provides a useful connection to vehicle stability, its reliance on lateral acceleration can result in numerical instability and error at high levels of lateral acceleration. To address this issue, a new formulation of the understeer gradient is proposed in this paper. This new formulation is based on vehicle speed and is suitable for all maneuvers. Unlike previous formulations, it does not rely on lateral acceleration or provide a direct connection to vehicle stability. To address the issue of vehicle stability, a new measure called the stability margin is also proposed in this paper. The stability margin provides a more precise measurement of a vehicle's stability than the understeer gradient alone. By combining the stability margin with the new formulation of the understeer gradient, a more comprehensive picture of a vehicle's cornering behaviour and stability can be obtained.

Effect of material characteristics of lead rubber isolators on seismic performance of box girder bridge

Near-field (NF) earthquakes have distinct ground motions, forward directivity pulses, and fling-step motions, causing structural responses to differ from far-field (FF) earthquakes. Seismic isolation is regarded as a developed and successful technology that may be applied to enhance a structure’s functionality and safeguard it against catastrophic earthquake effects. The variation in mechanical properties of seismic isolation also significantly influences bridge seismic response. The study investigates the influence of lead rubber (LRB) isolators and the characteristics of ground motions on seismically isolated bridges, aiming to determine optimal parameters for minimal earthquake response. Key parameters include ground motion characteristics, characteristic strength (Q), and isolator flexibility. The study modeled the force-deformation behavior of isolators using bilinear behavior, reflecting the Bouc-Wen hysteric model. CSI Bridge was used to model seismically isolated steel box girder bridges, with eight natural accelerograms assessing a 2% probability of exceedance in 50 years. The peak responses of pier displacement (MPD), isolator hysteric energy (HED), base shear, and deck acceleration are chosen as the response parameters for the comparison. To evaluate the response parameters, the earthquake data are scaled to the three studied peak ground acceleration (PGA) levels of design level (0.2 g), extreme level (0.4 g), and rare-extreme level (0.8 g). The findings offer insight on the relevance of isolator stiffness and its influences on the seismic performance of isolated bridges. The study identifies minimum values for pier displacement, hysteric energy, deck acceleration, and base shear at specific Q/weight sustained by isolator (W) and time period (T) values. Recommendations are made for the preliminary seismic isolation design of bridges with LRB isolators, highlighting the importance of PGV to PGA ratio in earthquake damage assessment.

Field measurement of track vibration induced by full-load and empty-load condition in curve section of underground metro line

In order to compare the differences in vibration before and after wheel re-profiling and assess the vibration impact of train under full-load and empty-load condition, the field vibration measurement was conducted on an underground metro track components (including rail, sleeper, and track-bed) by using a specific testing car. The results indicate that wheel re-profiling is effective in reducing track vibration, within the frequency range of 31.5–1250 Hz, the vibration acceleration levels of the track after wheel re-profiling were notably lower than those prior to re-profiling and the vibration acceleration levels of the rail, sleeper, and track-bed decrease by 4.7 dB, 6.6 dB, and 6.7 dB, respectively. In the frequency domain, the characteristic peak frequencies of the three track components, whether under full load or empty load, align closely with the frequencies associated with track irregularities. Full-load condition primarily affects the vibration acceleration at lower frequencies, with minor influence on higher frequencies. The vibration acceleration levels of all three track components are higher under full load than empty load. Additionally, under full-load condition, the transmission loss from the rail to the sleeper increases, while the transmission loss from the sleeper to the ballast remains nearly constant. The results of vibration acceleration levels obtained from routine vehicle operations validate the limited impact of axle load on track components vibration.