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Since the occurrence of pedestrian-induced large lateral vibration of the London Millennium Bridge in 2000, scholars have realized the complexity of pedestrian-induced lateral vibrations. Despite extensive research spanning over two decades, the underlying mechanisms between pedestrians and footbridges remain incompletely understood. Currently, there are two main popular models for explaining the pedestrian-induced lateral vibration of the footbridge: the synchronization lock-in model and the self-excited force model. Among existing studies, the inverted pendulum model (IPM) essentially belongs to the self-excited force model, has gradually gained recognition. This model assumes that pedestrians maintain a constant step frequency and suggests that footbridge lateral vibration divergence can occur through pedestrian-bridge interaction without synchronization. Although the IPM theoretically elucidates the mechanism by which pedestrian-bridge interaction leads to self-excited forces, it still has its shortcomings: it overestimates the critical number of pedestrians required for triggering vibration divergence of the footbridge. The underlying cause of this problem stems from the inverted pendulum model’s inherent limitation as a single-mechanism framework, which fails to consider the adjustments of pedestrian’s step frequency and instead solely relies on the adjustments of pedestrian’s step width. Consequently, this results in an underestimation of the virtual equivalent damping coefficient that is in phase with the vibration velocity of the footbridge. This study proposes a generalized-inverted pendulum model (G-IPM), in which the pedestrian walking phase evolution is effectively combined with the IPM, thereby the adjustments of pedestrian’s step frequency and step width can be considered simultaneously. Compared to the single-mechanism-based IPM, the numerical simulation results indicate that the proposed dual-mechanism-based G-IPM requires fewer pedestrians to trigger the bridge vibration divergence, which is closer to the actual results. Additionally, parameter analysis reveals that varying pedestrian characteristic parameters exert different impacts on the vibration response of bridge. The proposed model pioneers the use of a dual-mechanism-based model, which is of significant theoretical importance in revealing the underlying mechanism of pedestrian-induced lateral vibrations of the footbridge. [ABSTRACT FROM AUTHOR]

The remarkable lateral oscillatory occurrences observed in renowned footbridges, such as the Solferino Bridge in France, the Millennium Bridge in the UK, and the Oda Bridge in Japan, have garnered widespread attention. The intricate nature of pedestrian-induced lateral vibrations necessitates a comprehensive investigation into their underlying mechanisms, with the crux lying in the identification of the lateral excitation model. Presently, most prevailing detection approaches predominantly rely on contact-based equipment, such as force sensors and displacement sensors. However, these approaches suffer from two main drawbacks. Firstly, contact measurement necessitate a substantial number of sensors and entail higher experimental costs. Secondly, when extending contact-based measurements to accommodate multiple individuals, complications arise, including cumbersome installation, heightened technical complexity, and escalated experimental costs. Therefore, we present a novel approach, based on visual technology, to expeditiously recognize the lateral excitation induced by pedestrians. Termed the Dual Perspective of Mediapipe (DPM), this method harnesses the power of Mediapipe, coupled with dual camera models, to precisely unravel pedestrian gait particulars and lateral forces. The efficacy of the proposed approach is validated through a comparative analysis with existing pedestrian gait data. It is noteworthy that this approach offers significant advantages: non-contact with the test pedestrians, thereby ensuring the accuracy of gait information; convenient and straightforward arrangement of measurement equipment; and low experimental costs. [ABSTRACT FROM AUTHOR]

Footbridges are analyzed in terms of dynamic response for pedestrian comfort. This problem is solved mainly on light and at the same time rigid constructions, which are easily oscillated by pedestrian load. It is often solved on steel footbridges, but with the technological development of UHPC, we are capable nowadays to build relatively light and long span concrete footbridges. Behaviour of a thin concrete cross-section with its geometry is closer to steel structures, but at the same time we have to deal with rheological effects such as creep and shrinkage. There are many influences on the structure that can affect the dynamic behavior of the structure, including the non-linear behavior of the cable system. This paper presents an initial entry into the computational issues of more complex constructions that have more input influences. [ABSTRACT FROM AUTHOR]

This paper presents a maintenance prioritisation framework for Taiwan's 1268 pedestrian bridges. It aims to standardise their inspection and maintenance, as Taiwan's current bridge management specifications and manuals only apply to its highway and railway bridge infrastructure. It is designed to assess the structural safety and serviceability of six pedestrian bridge types by visual inspection. To assign weight factors to the structural safety and serviceability components of the identified bridge types, two rounds of Delphi method interviews with bridge experts were conducted. The framework is centred on a weighted average condition assessment method that integrates expert-determined weight factors with visual inspection results to calculate a condition index (PBCI). Pedestrian bridges are ranked and classified based on their PBCIs to set appropriate inspection frequency and scope, and to inform maintenance resource allocation. The application of the framework to five pedestrian bridges in Taoyuan City demonstrated its practicality and value for bridge authorities tasked with managing large inventories of pedestrian bridges. [ABSTRACT FROM AUTHOR]

This study evaluates the dynamic performance of a reference footbridge under human–structure interaction (HSI) effects using real-time hybrid simulation (RTHS). The footbridge, designed with precise multi-axial dynamic sensitivity, is tested under pedestrian gait velocities of 1.20, 1.50, and 1.80 m · s − 1 . The RTHS framework involves an analytical continuous model of the footbridge as a numerical substructure and real human gait loads as the experimental substructure. The results reveal significant dynamic coupling between pedestrian-induced loads and the responses of the structure. Lateral vibrations exhibit a fundamental frequency of approximately 1.0 Hz, whereas vertical vibrations peaked near 2.0 Hz. Dynamic synchronization, particularly at higher gait velocities, amplified the structural vibrations, with lateral loading increasing by up to 300% in the middle span. Vertical loads show substantial amplification and attenuation depending on gait velocity and footbridge location. Lateral accelerations display a dispersion of approximately 15.0%, whereas vertical accelerations showed higher variability, with dispersions reaching up to 20%. The RTHS technique demonstrates high fidelity and accuracy, with global errors below 2.95% and delays of less than 2.10 ms across all evaluated directions. These results emphasize the critical importance of accounting for HSI effects in the design of pedestrian footbridges because human-induced vibrations can significantly impact structural serviceability and user comfort. This study offers important insights into optimizing footbridge design to mitigate the risks of excessive vibrations and ensure both safety and functionality under typical pedestrian loads. [ABSTRACT FROM AUTHOR]

Copyright of Chinese Journal of Applied Mechanics is the property of Chinese Journal of Applied Mechanics Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Sky Bridge 721 was opened on 13 May 2022. It is located in the area of the Kralicky Sneznik mountain massif in the area of the Dolni Morava Mountain Resort. It was built in two years and spans the valley between the two ridges Slamnik and Chlum with a length of 721 metres. It has become a new landmark of the region, although in reality it is almost invisible when viewed from a distance. It winds like a thin thread below the horizon of the mountain ridge, suspended between the sky and the ground, so that it does not interfere with the view of the surrounding countryside. It was a real challenge to bridge such a wide valley at a height of nearly 100 metres and to achieve a subtle line of the footbridge that would not disturb the silhouette of the mountain massif. This is the story of the whole process, from the design to the statics, construction, design and implementation, that the TAROS NOVA a.s. team had to overcome during the implementation of the footbridge. [ABSTRACT FROM AUTHOR]

Cracks, common indicators of deterioration in bridge frameworks, frequently stem from wear and rust, leading to increased local flexibility and changes in the structure's dynamic behavior. This study examines how these cracks affect the dynamics of footbridges when subjected to loads generated by walking individuals. The pedestrian is modeled as a linear oscillator, while the cracked bridge is represented by a simply supported beam following Euler–Bernoulli's theory. The use of the Dirac delta function allows for the precise representation of the localized stiffness reduction at the crack location, facilitating the calculation of analytical expressions for the beam's vibration modes. The research suggests that the presence of cracks minimally affects the bridge's mid-span displacement. However, with a limited depth of cracks, the appearance of cracks notably amplifies the mid-span acceleration amplitude of the bridge, leading to a pronounced concentration of energy at the third natural frequency of the bridge in the acceleration spectrum. As the depth and number of cracks increase, the acceleration amplitude continues to decrease, but the corresponding spectrum remains almost unchanged. The study's outcomes enhance the comprehension of how cracks affect the performance of bridge structures when subjected to loads from pedestrians, offering insights for the monitoring and evaluation of the condition of cracked footbridges. [ABSTRACT FROM AUTHOR]

The inverted pendulum model is currently a widely accepted pedestrian lateral force model in the study of pedestrian-induced lateral vibration. The inverted pendulum model proposes that pedestrians walking on a laterally vibrating structure maintain their balance and comfort by adjusting their lateral foot position rather than their stride frequency. In other words, the stride frequency of a pedestrian is unaffected by the lateral vibration of the structure. This viewpoint directly contradicts the synchronization theory, which suggests that pedestrians adjust their stride frequency to adapt to the lateral vibration of the structure. The observed phenomenon of phase drift in Bocian's experiments provided validation for the effectiveness of the inverted pendulum model. However, the simultaneous observation of phase pulling indirectly refuted the underlying assumption of the inverted pendulum model: that pedestrians' stride frequency remains unaffected by the lateral vibration of the structure. Bocian's experimental findings shattered the artificial boundary between the inverted pendulum model and the synchronization theory, indicating the existence of a hybrid mechanism in the pedestrian lateral force model. Regrettably, to date, no specific model for this hybrid mechanism has been developed. This study employs the Kuramoto model to describe the phase evolution of a pedestrian under the influence of structural lateral vibration. Based on the traditional inverted pendulum model (IPM), the phase evolution inverted pendulum model (PE-IPM), which takes into account the adjustment of pedestrian lateral stride frequency (or stride time), is developed to explain the potential hybrid mechanism in the pedestrian lateral force model. To validate the effectiveness of PE-IPM, detailed comparisons are made between its numerical simulation results of pedestrian lateral gait and Bocian's experimental findings, the results of which are in good agreement. The validation demonstrates that PE-IPM can capture the detailed characteristics of pedestrian lateral gait well and effectively address the issue of an underestimated equivalent damping coefficient in IPM, confirming that PE-IPM can be used as an improved pedestrian lateral force model for further investigations into pedestrian-induced lateral vibration. [ABSTRACT FROM AUTHOR]

Copyright of Space & Form / Przestrzeń i FORMA is the property of West Pomeranian University of Technology, Department of Architecture & Urban Planning and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In order to investigate the effects of jumping loads on structural vibrations. Firstly, an improved semi-sine model was proposed, and characteristic parameters for the crowd jumping load model were suggested. Next, an analytical solution for the dynamic response of a simply supported beam under a single person's jumping load was derived. Finally, using a pedestrian footbridge in Jingzhou City as an example, the experimental and numerical results of the structural acceleration response under jumping loads were compared to validate the applicability of the improved semi-sine model. The results show the improved semi-sine model exhibits a maximum error of 2. 8% when compared to experimental measurements. In contrast, the semi-sine and semi-sine squared models exhibit corresponding maximum errors of 23. 4% and 7. 1%, respectively. At a jumping frequency of 2. 3 Hz, the jumping load frequency closely approximates the first-order natural frequency of the structure, resulting in resonance within the structure. In the mid to high-frequency range, the response results of the improved semi-sine model closely align with experimental measurements. These results hold valuable insights for accurately simulating jumping loads. [ABSTRACT FROM AUTHOR]

Numerous studies have investigated the long-term monitoring of natural frequencies, primarily focusing on medium–large highway bridges, using expensive monitoring systems with a large array of sensors. However, this paper addresses the less explored issue of monitoring a footbridge, examining four critical aspects: (i) sensing system, (ii) frequency extraction method, (iii) data modelling techniques, and (iv) damage detection. The paper proposes a low-cost all-in-one sensor/logger unit instead of a conventional sensing system to address the first issue. For the second issue, many studies use natural frequency data extracted from measured acceleration for data modelling, the paper highlights the impact of the input parameters used in the automated frequency extraction process, which affects the number and quality of frequency data points extracted and subsequently influences the data models that can be created. After that, the paper proposes a modified PCA model optimised for computational efficiency, designed explicitly for sparse data from a low-cost monitoring system, and suitable for future on-board computation. It also explores the capabilities and limitations of a data model developed using a limited data set. The paper demonstrates these aspects using data collected from a 108 m cable-stayed footbridge over several months. Finally, the detection of damage is achieved by employing the one-class SVM machine learning technique, which utilises the outcomes obtained from data modelling. In summary, this paper addresses the challenges associated with the long-term monitoring of a footbridge, including selecting a suitable sensing system, automated frequency extraction, data modelling techniques, and damage detection. The proposed solutions offer a cost-effective and efficient approach to monitoring footbridges while considering the challenges of sparse data sets. [ABSTRACT FROM AUTHOR]

This study evaluates the dynamic performance of a reference footbridge under human–structure interaction (HSI) effects using real-time hybrid simulation (RTHS). The footbridge, designed with precise multi-axial dynamic sensitivity, is tested under pedestrian gait velocities of 1.20, 1.50, and 1.80 m·s−1. The RTHS framework involves an analytical continuous model of the footbridge as a numerical substructure and real human gait loads as the experimental substructure. The results reveal significant dynamic coupling between pedestrian-induced loads and the responses of the structure. Lateral vibrations exhibit a fundamental frequency of approximately 1.0 Hz, whereas vertical vibrations peaked near 2.0 Hz. Dynamic synchronization, particularly at higher gait velocities, amplified the structural vibrations, with lateral loading increasing by up to 300% in the middle span. Vertical loads show substantial amplification and attenuation depending on gait velocity and footbridge location. Lateral accelerations display a dispersion of approximately 15.0%, whereas vertical accelerations showed higher variability, with dispersions reaching up to 20%. The RTHS technique demonstrates high fidelity and accuracy, with global errors below 2.95% and delays of less than 2.10 ms across all evaluated directions. These results emphasize the critical importance of accounting for HSI effects in the design of pedestrian footbridges because human-induced vibrations can significantly impact structural serviceability and user comfort. This study offers important insights into optimizing footbridge design to mitigate the risks of excessive vibrations and ensure both safety and functionality under typical pedestrian loads.

Cracks, common indicators of deterioration in bridge frameworks, frequently stem from wear and rust, leading to increased local flexibility and changes in the structure’s dynamic behavior. This study examines how these cracks affect the dynamics of footbridges when subjected to loads generated by walking individuals. The pedestrian is modeled as a linear oscillator, while the cracked bridge is represented by a simply supported beam following Euler–Bernoulli’s theory. The use of the Dirac delta function allows for the precise representation of the localized stiffness reduction at the crack location, facilitating the calculation of analytical expressions for the beam’s vibration modes. The research suggests that the presence of cracks minimally affects the bridge’s mid-span displacement. However, with a limited depth of cracks, the appearance of cracks notably amplifies the mid-span acceleration amplitude of the bridge, leading to a pronounced concentration of energy at the third natural frequency of the bridge in the acceleration spectrum. As the depth and number of cracks increase, the acceleration amplitude continues to decrease, but the corresponding spectrum remains almost unchanged. The study’s outcomes enhance the comprehension of how cracks affect the performance of bridge structures when subjected to loads from pedestrians, offering insights for the monitoring and evaluation of the condition of cracked footbridges.

Objective: As a major safety intervention, infrastructural facilities such as footbridges, underpasses or signals are provided for pedestrians to remove their direct interactions with vehicles and consequently ensure safe crossing as they attempt to cross roadways. Interestingly, it is evident that even within the proximity of footbridges or underpasses, some individuals are more willing to take the risk of crossing at-grade even where there are no signals or crosswalk markings to separate their movement from vehicles. These crossing alternatives may have different utilization depending on location and road user types. Therefore, sustainable crossing facilities are needed to meet pedestrian needs. This study attempts to investigate the factors that influence pedestrians to avoid provided footbridges and engage in at-grade crossing behaviors. Methods: The crossing point preference is an interpersonal behavior which is a multifaceted and complex phenomenon involving conscious (intentions) and subconscious (habits) factors. This study employs Triandis' Theory of Interpersonal Behavior (TIB) as a theoretical framework and structural equation modeling to achieve study objectives. Pedestrians were intercepted randomly and socio-demographics, trip characteristics and perceptions data collected through a stated preference survey. Results: Perceived consequence, affect, and social factors were found as significant antecedents of at-grade crossing intentions. Habits and facilitating conditions significantly moderate the impact of crossing intentions on actual at-grading crossing behavior. Pedestrians' perceived consequence was found to significantly mediate the impact of social factors and affective factors on intention to cross at-grade. Apart from gender, age, satisfaction with footbridge features, work trips, and crossing frequency were all significant determinants of actual crossing at-grade behavior. Conclusions: The study findings can help road safety agencies provide acceptable sustainable facilities that will be used by pedestrians to ensure that the purpose of investments toward pedestrian crossing safety is achieved. Effective road safety education and awareness campaigns on negative consequences of crossing at-grade, while highlighting the benefits of using provided footbridges are suggested to be undertaken by government agencies. [ABSTRACT FROM AUTHOR]

Digital fabrication with concrete (DFC) is fast becoming an attractive alternative for components (i.e., façades, urban furniture) and structural typologies (i.e., short‐span footbridges, columns, floor systems) for which complex geometries derived from particular aesthetical criteria and/or construction time constrictions are governing parameters. Additionally, some authors claim that this process allows improving the sustainability of structures, as less material is necessary compared to traditional concrete solutions, thus reducing greenhouse gas emissions linked to material consumption. Nonetheless, the environmental implications of DFC are still under scrutiny and remain objectively unquantified. In this study, a sustainability assessment model to allow decision‐makers to evaluate and compare concrete footbridge alternatives—from the sustainability perspective—including those constructed by means of 3D printed concrete (3DPC) techniques, is presented. The proposed approach is based on the MIVES method. For this purpose, the most representative criteria and indicators of sustainability identified are measured and weighted‐aggregated in a decision‐making tree. The sustainability index (SI) of each alternative is the outcome derived from the application of the model, and the SI was used as reference for evaluating the alternatives. The sustainability of 3D‐printed footbridges is quantified and compared to other concrete‐based solutions: traditional reinforced cast‐in‐place and precast concrete, as traditional solutions, and ultra‐high performance precast concrete and textile‐reinforced concrete, as innovative alternatives. The results of the analysis lead to conclude that 3D‐printed footbridges have positive impacts on environmental and social indicators, but economic indicators still need to be improved to attain a competitive solution. The approach proposed herein to assess the sustainability of footbridges can be extended to other cases and stakeholders' preferences by adapting the components of the method to sensitivities and particular boundary conditions of other scenarios. [ABSTRACT FROM AUTHOR]

Abstract This article aims to study the influence of random crowd loading on the perceived vibration response of pedestrians. Firstly, a vertical vibration response analysis method considering pedestrian perception was established based on the random crowd walking model. Secondly, change rules of maximum vibration response of pedestrians, occurrence time and position interval under different random walk models were compared and analyzed. Finally, the vibration response reduction factor was defined by studying the correlation between the maximum vibration response of pedestrians and the peak acceleration of the structure, and the approximate calculation method of the maximum vibration response of pedestrians was proposed. The results show that the maximum acceleration perceived by pedestrians obeys the normal distribution under the four crowd walking models, the response distribution of ordered arrangement model (OAM) is larger than that of the other three models; The location and occurrence time of the maximum response depend on the distribution of pedestrian locations on the footbridge, and there is no significant change with the increase of population density. In addition, the distribution of OAM and stochastic arrival model (SAM) are consistent, which is concentrated in the middle of the total time-history. In contrast, the distribution of stochastic distribution model (SDM) and dynamic equilibrium model (DEM) are relatively uniform. The maximum error between the calculated acceleration maximum value and the actual acceleration value felt by the pedestrian is less than 5%. These results can provide reference for quantitative evaluation of pedestrian-induced vibration comfort.

The topic of this paper is an experimental analysis of the dynamic behaviour of stays of an existing footbridge focusing on determination of the tensile forces in stays. The examined structure was the footbridge across the Vltava river in Lužec nad Vltavou. It is a cable-stayed footbridge, the horizontal load-bearing structure consists of UHPC components, which are prestressed by a pair of external cables. The horizontal load-bearing structure is suspended on a 39.85 m high A-shaped steel pylon by means of a system of 17 pairs of stays. As a part of the work the tensile forces in stays were determined using the vibration frequency method. The method is based on the knowledge of natural frequencies of the stays, which were investigated by the experimental analysis.

This article aims to study the influence of random crowd loading on the perceived vibration response of pedestrians. Firstly, a vertical vibration response analysis method considering pedestrian perception was established based on the random crowd walking model. Secondly, change rules of maximum vibration response of pedestrians, occurrence time and position interval under different random walk models were compared and analyzed. Finally, the vibration response reduction factor was defined by studying the correlation between the maximum vibration response of pedestrians and the peak acceleration of the structure, and the approximate calculation method of the maximum vibration response of pedestrians was proposed. The results show that the maximum acceleration perceived by pedestrians obeys the normal distribution under the four crowd walking models, the response distribution of ordered arrangement model (OAM) is larger than that of the other three models; The location and occurrence time of the maximum response depend on the distribution of pedestrian locations on the footbridge, and there is no significant change with the increase of population density. In addition, the distribution of OAM and stochastic arrival model (SAM) are consistent, which is concentrated in the middle of the total time-history. In contrast, the distribution of stochastic distribution model (SDM) and dynamic equilibrium model (DEM) are relatively uniform. The maximum error between the calculated acceleration maximum value and the actual acceleration value felt by the pedestrian is less than 5%. These results can provide reference for quantitative evaluation of pedestrian-induced vibration comfort. [ABSTRACT FROM AUTHOR]

In view of in-field applications, this paper introduces a methodology that uses the registered body motion to reconstruct the vertical dynamic running load. The principle of the reconstruction methodology is to use the time-variant pacing rate that is identified from the body motion together with a generalized single-step load model available in the literature. The methodology is reasonably robust against measurement noise. The performance of the methodology is evaluated by application to an experimental dataset where the running load and the body motion were registered simultaneously. The results show that a very good fit is found with the measured forces, with coefficients of determination of 95% in the time domain and 98% for the amplitude spectrum. Considering a 90% confidence interval, the fundamental harmonic is shown to be reconstructed with a maximum error of 12%. With nearly 90% of the energy concentrated around the fundamental harmonic, this harmonic is the dominant component of the running load. Due to the large inter-person variability in the single-step load pattern, a generalized single-step load model does not arrive at a good fit for the higher harmonics: the reproduction errors easily exceed 50% for a 90% confidence interval. Finally, the methodology is applied to reproduce the dynamic running load induced during full-scale tests on a flexible footbridge. The tests are designed such that the structural response is governed by the (near-)resonant contribution of the fundamental harmonic of the running load. The results show that even when a 12% uncertainty bound is taken into account, the structural response is significantly over-estimated by the numerical simulations (up to 50%). These results suggest a non-negligible impact of other phenomena, such as human–structure interaction, that are not accounted for in current load models.

The Cheadle Center at UCSB manages the North Campus Open Space (NCOS), which is a project that has restored 136 acres of upland and wetland habitats that existed before the area was converted into the Ocean Meadows Golf Course in the 1960s. The NCOS restoration project began in 2017 with a fine-scale grading of the site in order to recreate the salt marsh and use the excavated soil to rebuild the upland habitats to the southwest, which are now called the NCOS Mesa. In addition to re-establishing native biodiversity, a key goal of the restoration is to utilize the site as an educational, scientific, and recreational resource. This archived version of the May 2018 newsletter includes updates on snowy plovers and other birds using the habitat, as well as bridge installation. The feature story focuses on invasive plant control, which allows native plants to thrive and provides restoration experience for students. Community photos include Western Snowy Plovers (Charadrius nivosus), White-Faced Ibis (Plegadis chihi), Cliff Swallows (Petrochelidon pyrrhonota), and a juvenile Pacific Chorus Frog (Pseudacris regilla).

The Cheadle Center at UCSB manages the North Campus Open Space (NCOS), which is a project that has restored 136 acres of upland and wetland habitats that existed before the area was converted into the Ocean Meadows Golf Course in the 1960s. The NCOS restoration project began in 2017 with a fine-scale grading of the site in order to recreate the salt marsh and use the excavated soil to rebuild the upland habitats to the southwest, which are now called the NCOS Mesa. In addition to re-establishing native biodiversity, a key goal of the restoration is to utilize the site as an educational, scientific, and recreational resource. This archived version of the April 2018 newsletter marks the first anniversary of the grant-funded restoration project and includes updates on spring wildflowers, bridge and boardwalk construction, planting progress, and weed control by solarization. The feature story focuses on the performance of the hydrology improvements with recent rainfall, which was in line with predictions and avoided flooding in the surrounding neighborhood. Community photos include American Avocet (Recurvirostra americana), Cinnamon Teal (Spatula cyanoptera), and Rock Wren (Salpinctes obsoletus).

In order to overcome the problem that the comfort evaluation results of the footbridge design specification are too conservative. Firstly, randomness of parameters in walking force was taken into account to construct random walk model, and the cumulative probability distribution of the maximum acceleration of the structure and pedestrian feelings were obtained through time history analyses. The reduction coefficient of vibration response was defined by studying the correlation between the vibration response of footbridge and the vibration response of pedestrian feelings. Meanwhile, the maximum response of pedestrian feelings was recommended as the comfort evaluation index. Secondly, the annoyance model was established based on the improved membership function, and the annoyance curves under different use environments were given. Finally, the vibration comfort evaluation method was proposed based on pedestrian sense of reality and improved annoyance model, and the comfort evaluation of a pedestrian overpass in Jingzhou City was carried out. The results show that the peak acceleration has a significant correlation with the maximum vibration response of pedestrian feelings, and the corresponding relationship can be established according to the reduction coefficient of vibration response. The maximum error between the fitting curve of annoyance and the calculation result curve is less than 3%, and the influence of variation coefficient is not more than 1%. Compared with peak acceleration, the calculated value of annoyance considering pedestrian feelings is closer to the experimental result. The results have reference significance for quantitative calculation of footbridge vibration comfort. [ABSTRACT FROM AUTHOR]

The topic of this paper is an experimental analysis of the dynamic behaviour of stays of an existing footbridge focusing on determination of the tensile forces in stays. The examined structure was the footbridge across the Vltava river in Lužec nad Vltavou. It is a cable-stayed footbridge, the horizontal load-bearing structure consists of UHPC components, which are prestressed by a pair of external cables. The horizontal load-bearing structure is suspended on a 39.85m high A-shaped steel pylon by means of a system of 17 pairs of stays. As a part of the work the tensile forces in stays were determined using the vibration frequency method. The method is based on the knowledge of natural frequencies of the stays, which were investigated by the experimental analysis. [ABSTRACT FROM AUTHOR]

The impact of the dynamic soil-structure interaction (DSSI) on the response of a single-span footbridge to mining-induced shocks was assessed. Firstly, the eigen values, modes and damping of the footbridge were evaluated based on in-operation field tests. Then, natural frequencies were determined numerically by a model usually used in static calculations, i.e., a simple supported beam with overhangs. The numerical natural frequencies turned out to be inconsistent with the experimentally determined values. In turn, the model, assuming the overhangs' ends translationally restrained, gave natural frequency values closer to the experimental ones. However, for the third mode, that is lateral, the frequency error (~26%) can be considered greater than usually accepted values. Hence, the three-dimensional numerical model of the footbridge was tuned by considering the DSSI between the overhangs and the ground, and implementing springs (in three directions) at the overhangs' ends. To estimate the impact of DSSI on the dynamic performance of the footbridge, time history analyses were carried out for the model with fixed overhang ends and for the model with additional springs. Two different types of mining-induced tremors were used as excitations. Those two tremors (narrow and wide band) induced different dynamic responses in the models with and without the springs. Hence, the impact of the DSSI on the dynamic footbridge performance needs to be considered to predict the effect of mining-induced shocks. [ABSTRACT FROM AUTHOR]

As a public space and building, the footbridge is not just a physical concrete building but also carries people's life experiences and beliefs. In Hong Kong, however, footbridges are a joint product of the government and property developers to control people and drive consumption. Taking the footbridge as an example, this article explores the relationship between public space and the power of discourse. The article first discusses how the government and property developers manipulate footbridges as a social control tool. This article draws on case studies of the use of public space during and after Hong Kong's social movements in 2019 to discuss how people tried to regain their power of discourse in urban space, and how the government and the bourgeoisie suppressed such attempts. This paper argues that footbridges serve as marginal spaces, and demonstrate power and control by providing a space for people to discuss public affairs and be used to demonstrate power and control, especially in social movements. The footbridges traditionally used are challenged in a social event at the same time, brought under the gaze of planning and management from authorities, on the meaning of public space, the footbridges are narrowed or even prohibited in Hong Kong. [ABSTRACT FROM AUTHOR]

Current codes and guidelines for the dynamic design of footbridges often only specify the pedestrian-induced excitations. However, earthquakes may occur during the passing stage of pedestrians in earthquake-prone regions. In addition, modern footbridges tend to be slender and are sensitive to vertical ground motions. Therefore, we investigate the effects of vertical ground motion on pedestrian-induced vibrations of footbridges. A total of 138 footbridges with different materials, dimensions, and structural types are considered as the target structures. The classical social force model combined with the pedestrian-induced load is used to simulate crowd loads for the scenarios with six typical pedestrian densities. Furthermore, 59 vertical ground motions with four seismic intensities are taken as the seismic inputs. An amplification factor is introduced to quantify the amplification effects of vertical ground motion on human-induced vibrations of footbridges. Four machine learning (ML) algorithms are used to predict the amplification factor. The feature importance indicates that the scaled peak ground acceleration, the pedestrian density, and the bridge span are the three most important parameters influencing the amplification factor. Finally, the vibration serviceability of the footbridge subjected to both crowd load and vertical ground motion is assessed. [ABSTRACT FROM AUTHOR]

The last few decades new trends in the design of pedestrian bridges have resulted in lighter and more slender structures. This leads to a reduction in natural frequencies and increased flexibility, and thus a greater possibility for structures to become more exposed to excessive vibrations caused by pedestrians. The lager amplitudes of vibrations occur if the pace frequency of excitation load approaches one of natural frequency of footbridge. The vibration of high proportions may cause pedestrians to feel uncomfortable, sick or unsafe while crossing the bridge. In modern pedestrian bridge design, human-induced vibrations have become an important issue. Footbridge vibrations occur in vertical, lateral and longitudinal direction, and torsion of the bridge deck is also possible. The main types of pedestrian action on the bridge are walking and running, while jumping, bouncing, swaying are considered to be intentional, or sometimes even vandal excitation. Pedestrian-induced loads are difficult to model since pedestrians may have different weight, various number in the groups randomly distributed over the bridge deck. Also, the walking velocity may vary from a pedestrian to a pedestrian. The load models appropriately set up are of great importance for understanding the response of the bridge. Principles of modeling of the human-induced load and some characteristic models of pedestrian loads, described in proposals and codes, are presented in this paper. Some results of Serviceability Limit State analysis, in terms of human-induced vibration, of the pedestrian bridge over the Nišava River in Niš, are also presented.

Relevance. This work is the first in a series of publications on the selection of a suitable analytical surface for implementation as a self-supporting structure for a thin shell footbridge. The study on the influence of concrete strength, live load position and support types on the stress-strain state of a hyperbolic paraboloid (hypar) shell is presented. Objective - to define the initial design parameters such as the appropriate concrete strength and the support type that generates the best structural behaviour to perform the subsequent structural design of a thin shell footbridge. Methods. The static finite element analysis was performed for 4 compressive strengths of concrete (28, 40, 80, 120 MPa) which correspond normal, high and ultra-high resistance concrete, 5 different live load arrangements and 3 different support conditions. Results. The shell model with pinned (two-hinged) supports shows the same vertical displacements as the model with fixed supports (hingeless). For the studied shell thickness, in terms of stress behaviour, the model with pinned ends is more efficient. The combination of two-hinged supports with 80 MPa concrete strength shows a better structural performance.

Pedestrian-induced loads may cause vibration serviceability or safety issues in slender structures such as long-span floors and footbridges. Although some models for crowd walking loads have been established, the synchronization among pedestrians and interaction with the structure have not been fully expressed. This study proposes a Fourier series model with a series of equivalent dynamic load factors (EDLFs), which are adaptive to different crowd-dominant walking frequencies, structural damping ratios, crowd sizes, and pedestrian traffic conditions (unrestricted, restricted, and exceptionally restricted). Using the power spectral density for the crowd walking loads proposed in a previous study, the structural responses of different single-degree-of-freedom systems are calculated via numerical simulations of approximately 20 million variations, and the EDLF for crowd walking loads is obtained after back-calculating the structural responses. This modeling method weighted the energy around the dominant walking frequency. The results show that the EDLFs are stable for crowds of over 30 pedestrians. The proposed model was compared with three modeling methods for dynamic load factors and five codified models for crowd walking loads from different aspects, and the feasibility of the EDLF is verified based on a benchmark footbridge and an as-built floor structure. The EDLF is convenient for design purposes because it is compatible with the single-person model currently adopted in major design codes and software. [ABSTRACT FROM AUTHOR]

The vibration comfort evaluation is a control standard other than strength and deflection, but the general comfort evaluation method only considers the response of the mid-span position and does not consider the difference in the vibration response of different positions at the same time. It is crucial to study how pedestrians actually feel when they walk on footbridges. The computer vision-based vibration comfort evaluation method is a novel method with advantages, such as noncontact and long-distance. In this study, a computer vision-based method was used to evaluate the global vibration comfort of footbridges under human-induced excitation. The improved Lucas–Kanade optical flow method is used for multitarget displacement identification of footbridges. Additionally, the YOLOv5 algorithm for pedestrian detection is used to obtain the position information of pedestrians on the footbridges. Then, according to the pedestrian position information, the structural responses of different pedestrian positions corresponding to time periods are extracted from the displacement responses of each point, and they are combined to obtain the structural global displacement. The global acceleration can be obtained by calculating the global displacement. The rms value can be calculated based on the global acceleration and compared with the standard for comfort evaluation. The global comfort evaluation method is validated by pedestrian walking experiments with different frequencies on a laboratory footbridge. The experimental results show that the computer vision-based global comfort evaluation method for footbridges is feasible and is a more specific and real-time comfort evaluation method. [ABSTRACT FROM AUTHOR]

Dynamic forces generated by human locomotion, including walking, jumping and running, can lead to excessive vibrations of slender structures and result in severe vibration serviceability issues. This has led to the development of load and prediction models. For running, however, the existing load models are limited to single person load models calibrated on a rigid surface. The aim of this study is to address this gap by exploring the influence of low-frequency vertical vibrations on the running motion, known as active human–structure interaction. A measurement campaign was conducted using a transportable measurement setup that was placed on both a rigid and a vibrating surface. The results demonstrate the presence of active human–structure interaction during running on a vertical vibrating surface. Key findings include changes of the peak contact forces influenced by the relative phase and frequency difference between the runner and the structure. • Treadmill running tests were conducted on a rigid and vertical vibrating surface. • A method to analyze the running gait on a vibrating surface is proposed. • No active guidance of the pacing rate is observed. • The frequency difference between runner and structure determines the contact force. • An influence range of active human–structure interaction for running is determined. [ABSTRACT FROM AUTHOR]