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Structures such as long-span footbridges, floors, and long cantilevers are vulnerable to vibration serviceability problems under crowd walking, which should be taken into consideration during the structural design, operation, and maintenance stages. Standards have been developed to enable designers to assess the vibration serviceability of structures using simplified load models that simulate crowd-induced loading. To facilitate engineers in quickly selecting appropriate standards for vibration serviceability design, ten current standards were collected which deal with the assessment of structural vibration serviceability under walking loads, including the French "Assessment of vibrational behavior of footbridges under pedestrian loading" (2006), the German "Design of footbridges guideline" (2007), the Chinese "Technical standard for human comfort of the floor vibration" (2019), etc. The ten standards were reviewed and evaluated from three aspects including the crowd loading model, structural response calculation method, and vibration serviceability evaluation standard in this paper. Through summary and comparison between standards, three directions for future improvement and perfection of the standards were proposed: the challenges of the improvement of the standards focus on the establishment of the refined stochastic load model, the analysis of the crowd–structure coupling system, and the modelling of multifactor coupling serviceability evaluation indexes. [ABSTRACT FROM AUTHOR]

Structures such as long-span footbridges, floors, and long cantilevers are vulnerable to vibration serviceability problems under crowd walking, which should be taken into consideration during the structural design, operation, and maintenance stages. Standards have been developed to enable designers to assess the vibration serviceability of structures using simplified load models that simulate crowd-induced loading. To facilitate engineers in quickly selecting appropriate standards for vibration serviceability design, ten current standards were collected which deal with the assessment of structural vibration serviceability under walking loads, including the French “Assessment of vibrational behavior of footbridges under pedestrian loading” (2006), the German “Design of footbridges guideline” (2007), the Chinese “Technical standard for human comfort of the floor vibration” (2019), etc. The ten standards were reviewed and evaluated from three aspects including the crowd loading model, structural response calculation method, and vibration serviceability evaluation standard in this paper. Through summary and comparison between standards, three directions for future improvement and perfection of the standards were proposed: the challenges of the improvement of the standards focus on the establishment of the refined stochastic load model, the analysis of the crowd–structure coupling system, and the modelling of multifactor coupling serviceability evaluation indexes.

Recently several light‐weight, long span floors are built (e.g. steel‐framed structural systems), where the design is governed by vibration control. In these cases the acceleration due to human‐ or machine‐induced vibration can be very high, which may cause human discomfort. Long rectangular plates subjected to concentrated loads are often investigated by a replacement beam with a so called "effective width", and the amplification factor is calculated according to a SDOF system, which in the case of resonance is equal to 1/2ξ, where ξ is the damping ratio. Since damping in lightweight, steel‐framed structural systems is very low (1–3%), dynamic amplification (calculated according to an SDOF system) can be rather high. However, the steady‐state dynamic response of beams and long plates subjected to periodic loads are significantly different. The steel‐framed floors are mechanically long even in that case when the ratio of the sides of the floor is around one due to the high orthotropy. For long plates, the response and the amplification factor are substantially different from those of beams. Hence, design based on effective width may lead to 2‐4 times higher acceleration than the real values. As an example the roof of a gymnasium under construction is examined, where different sport activities (walking, running, aerobic) will take place. The natural frequency of the floor supported by steel joists is small, close to the frequency of walking, therefore a detailed vibration analysis was performed. [ABSTRACT FROM AUTHOR]

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Human induced dynamic forces on structures are of interest in the area of human-environment interfaces. The research community is interested in characterizing human decisions and providing information on the consequences of human actions to control those human forces more effectively. Dynamic structures can vibrate under human motion. In the context of human–structure interactions (HSI), dance induced vibrations can be quantified with sensors. This data can provide a unique opportunity for dancers to understand the quality of their dance with objective metrics. Previous work in capturing dance moves required wearable sensors attached to the dancer’s body. Often an intrusive process, this method is not scalable if dancers are not familiar with technology and it limits their participation without access to special studios or facilities. If simple, deployable technology could be available to dancers, they could monitor their dance without engineers. This research integrates dancers’ interest in qualifying dance motion and engineering curiosity to study human induced vibrations. As a part of the framework, researchers used two indexes to differentiate between a well synchronized group dance from asynchronous moves. The two indexes are the Harmony Index and the Coordination Index, respectively, and are validated against the Visual Index, a qualitative index obtained from an expert who judged dance moves based on one video capture. The indexes were derived from measurements of the movement of the structure dynamically excited by the dancers, hence quantifying dance coordination. These two indexes are based on time history data obtained from sensors installed on a wooden bridge where dancers performed at different levels of proficiency. The results of this research show that the two indexes sort effectively the quality of the dancers, when validated with the Visual Index. As a result, this research proposes using Low-cost efficient wireless intelligent sensor (LEWIS) to objectively sort different levels of dance quality which could be expanded to study the HSI for design and assessment of the structural systems used for dancing, such as performance halls and ballrooms.

Copyright of Revista Sul-Americana de Engenharia Estrutural is the property of Revista Sul-Americana de Engenharia Estrutural 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.)

Current vision-based displacement measurement methods have limitations such as being in need of manual targets and parameter adjustment, and significant user involvement to reach the desired result. This study proposes a novel structural displacement measurement method using deep learning-based full field optical flow methods. The performance of the proposed method is verified via a laboratory experiment conducted on a grandstand structure with a comparative study, where the same data samples are analysed with a commonly used vision-based method, and a displacement sensor measurement is used as the ground truth. Statistical analysis of the comparative results show that the proposed method gives higher accuracy than the traditional optical flow algorithm and shows consistent results in compliance with displacement sensor measurements. Image collection, tracking, and non-uniform sampling are investigated in the experimental data and suggestions are made to obtain more accurate displacement measurements. A field-validation on a footbridge showed that the measurement error induced by the camera motion is mitigated by a camera motion subtraction procedure. The proposed method has good potential to be applied by structural engineers, who have little or no experience in computer vision and image processing, to do vision-based displacement measurements. [ABSTRACT FROM AUTHOR]

Progress in understanding human-structure interaction (HSI) on footbridges has been hampered by the shortage of quality data collected in realistic environments. This paper reports a novel experiment conducted on a naturally-swaying 7 m footbridge of frequency 0.67 Hz and amplitudes up to 125 mm. Subjects crossed the bridge while wearing infrared motion-tracking markers and pressure-sensing insoles. The bridge was fitted with bespoke force plates, allowing investigators to simultaneously record kinematic and kinetic reactions to the structure's motion, which was assumed simple harmonic. The bridge was naturally excited by the test subjects, who were allowed to walk at a comfortable self-chosen pace. The data show that the subjects adopted a fixed-in-space Centre of Mass (CoM) strategy but their Centres of Pressure (CoP) were highly correlated to the position of the bridge deck within its lateral oscillation cycle (henceforth 'bridge phase'), allowing for the prediction of wide and crossed steps. Ground forces generally correlated to CoM-CoP separation, which reflected the phase of the bridge at the previous heel-strike. Instantaneous step width was correlated to the bridge phase and is proportional to the offset in the Medial-Lateral (M-L) ground force between consecutive steps. The Inverted Pendulum Model (IPM) was evaluated using the data, exhibiting a limited fit to the recorded ground forces. Finally, the pedestrian-induced work on the bridge and system stability boundaries are also calculated, revealing mechanisms for bridge instability to occur. [ABSTRACT FROM AUTHOR]

Human induced vibration is a common problem in the design of planking levels as both flooring or decking. The source of the vibration is the so-called “human induced loading (HIL)”. Models are available for a single exciting person and for a dense aggregation of persons. Small groups of persons should also be considered in view of serviceability limit state design. This paper introduces a model for the time variant stochastic fields of forces induced by the walking of a small group of persons. A numerical example is presented dealing with the evaluation of vertical and transversal accelerations at nodes of a finite element model of an existing wood footbridge. The example considers different idealizations of the human induced excitation and the results of these models are compared to actual records. [ABSTRACT FROM AUTHOR]

Crowd induced dynamic loading in large structures, such as gymnasiums or stadiums, is usually modelled as a series of harmonic loads which are defined in terms of their Fourier coefficients. Different values of these Fourier coefficients that were obtained from full scale measurements can be found in codes. Recently, an alternative has been proposed, based on random generation of load time histories that take into account phase lags among individuals inside the crowd. This paper presents the results of some studies carried out in order to compare the existing load models used to simulate periodic jumpings and develop a new load model. Generally the testing is performed on platforms or structures that can be considered rigid because their natural frequencies are higher than the excitation frequencies associated with crowd loading. But in this paper, to validate these load models test have been performed on a structure designed to be a gymnasium, which has natural frequencies within that range. Test results have been compared with predictions based on the load modelling alternatives with quite good agreement. A calibrated finite element model of the structure has been used for this purpose. The new model provides a clear improvement in the energy contained within higher frequencies. [ABSTRACT FROM AUTHOR]

We present a novel framework for measuring the body motion of multiple individuals in a group or crowd via a vision-based tracking algorithm, thus to enable studies of human-induced vibrations of civil engineering structures, such as floors and grandstands. To overcome the difficulties typically observed in this scenario, such as illumination change and object deformation, an online ensemble learning algorithm, which is adaptive to the non-stationary environment, is adopted. Incorporated with an easily carried and installed hardware, the system can capture the characteristics of displacements or accelerations for multiple individuals in a group of various sizes and in a real-world setting. To demonstrate the efficacy of the proposed system, measured displacements and calculated accelerations are compared to the simultaneous measurements obtained by two widely used motion tracking systems. Extensive experiments illustrate that the proposed system achieves equivalent performance as popular wireless inertial sensors and a marker-based optical system, but without limitations commonly associated with such traditional systems. The comparable experiments can also be used to guide the application of our proposed system. [ABSTRACT FROM AUTHOR]

• The vibration comfort test of smart phone structure is proposed. • The comfort evaluation methods of ordinary building structures and long flexible structures are supplemented. • The specific limits of displacement and velocity for evaluating the comfort of different structures are verified. In view of the lack of portability and real-time performance of traditional instruments, the monitoring module based on smartphones which can achieve the acquisition of structural acceleration is developed. The accuracy and performance of smart phone through dynamic test is verified. Aiming at the shortcomings of the comfort evaluation method in the scope of application and evaluation parameters, the idea of displacement and velocity limits is put forward, and the evaluation limits applicable to different structures are given. The results show that the limits of displacement and velocity can be used as supplementary indexes for comfort evaluation of flexible structures. [ABSTRACT FROM AUTHOR]