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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]

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.

Many Tibetan heritage buildings in China are opened to tourists recently. The crowd load has become a significantly concern to the structural safety of the structures. The beams of these wooden structures are easily deformed or cracked under the crowd load. The condition assessment of the timber beam in a Tibetan heritage building under crowd load has become a new challenge. Convention statistical evaluation method making use of monitored strain data require a threshold value which is determined with no physical meaning. This paper separates the monitored strain into temperature-induced strain and crowd-induced strain. An analytical model of the timber beam including the semi-rigid connections at its ends is formulated for the calculation of different material stresses under crowd load. The condition of the beam is then quantitatively evaluated against the residual strength of material. The shear stress at any point of the beam can then be calculated from limited number of sensors for evaluating the more popular shear crack damage which is not monitored in most existing ancient structures. [ABSTRACT FROM AUTHOR]

Grandstands are structures which are regularly subjected to dynamic loads generated by crowd motions. It is a dangerous situation when spectators induce rhythmic jumping, dancing, stamping, etc. If the synchronized movement of spectators excites a natural frequency of the structure, resonant response might occur. To avoid such situations, temporary steel grandstands are commonly strengthened using additional elements that create bracing system which is selected depending on the size of the structure, type of the event, acting load, etc. It was proved that not only the use but also the arrangement of such structural members is crucial for the dynamic structural resistance. The aim of the present study is to determine the most effective arrangement of bracing system for a typical example of the temporary steel grandstand which is exposed to dynamic load induced by spectators. Three different arrangements of bracing systems have been analysed using five criteria recommended in the literature. The results of the study clearly show that the dynamic parameters of the grandstand are substantially different for various types of bracing systems. The largest improvement in the structural behaviour has been obtained for the grandstand equipped with the bracing system satisfying all proposed criteria. The peak accelerations for this case have been found to be nearly twice as low as for structures with other bracing arrangements. The application of such a system for the grandstand which is exposed to human-induced vibrations allows for safe use of the structure as well as improves comfort of spectators. [ABSTRACT FROM AUTHOR]

Research on modeling the walking-induced dynamic load and its effects on structures has been increasing in recent years. Existing standards for estimating the acceleration response excited by crowd takes ( is the number of walking persons in a crowd) times the single pedestrian load as the crowd load, neglecting uncertainties in the related parameters. This paper proposes a method for predicting the crowd-induced structural acceleration response based on the Bayesian theory. Parameters of the crowd include the distribution of stepping frequency, the interval of arriving time and the weight of pedestrians. By combining the existing methods for calculating the structural response to a pedestrian load and the Bayesian theory, the root-mean-square acceleration along with the crowd parameters are obtained. A field investigation is conducted to study the walking characteristics of pedestrians, including the distribution of stepping frequency, walking velocity and step length. The case of a crowd moving across a simply supported beam bridge is taken for illustration. The acceleration response under the crowd load with different stepping frequencies is calculated. A comparison between the results from the Bayesian method and the design standards is conducted. The proposed method is found to yield acceptable results, and is then applied to estimating the acceleration response of a typical Tibetan heritage building, with the result compared with a field measurement. [ABSTRACT FROM AUTHOR]

A field testing study was conducted on the concourse floor structure of Xi’an High-Speed Rail Station. Using accelerometers installed on the floor and data acquisition and analysis system, vibration measurements were taken during train arrival and departure, and under crowd-induced excitations. The study was aimed to investigate structural vibration responses under different load cases, human-structure interaction and the effects of walking mode and frequency on structural vibration. The results indicate that the floor does not incur excessive vertical vibration during train arrival and departure, and passenger boarding. Under different cases of crowd excitations, the maximum equivalent sinusoidal peak acceleration can reach 609.99mm/s2 when resonance occurs. Human-structure interaction can be observed from the responses under resonance. People in different modes of walking have different perceptions of the same floor vibration. Spectrum analysis indicates that responses have large magnitudes at the walking step frequency and its multiples. The first three orders of crowd walking excitation have the greatest contribution to floor vibration responses, hence it shall be sufficient to consider only the first three orders of crowd walking excitation in comfort analysis.The peak acceleration will overestimate acceleration response and ESPA is suggested to be adopted for vertical comfort evaluation. [ABSTRACT FROM AUTHOR]

The study of the probabilistic response of pedestrian-excited structures as well as their reliability analysis need to take into account the influence of a large number of uncertain parameters ascribed to structural characteristics, single pedestrian walking features and pedestrian traffic phenomena. Although pedestrian traffic is characterized by an intrinsic high variability and plays a key role in determining the pedestrian load, its probabilistic description remains scarce in literature. The present work aims at contributing to the probabilistic evaluation of the pedestrian traffic across footbridges. First, a categorized state of the art focused on sources of uncertainty is provided. Second, a new modeling framework for the probabilistic evaluation of pedestrian traffic is introduced in general and conceptual terms. The framework is conceived in analogy to the approach developed in another engineering field, i.e. wind engineering, on the basis of the phenomenological features of the pedestrian traffic. In order to put the framework in practice, each of its main modeling components is specified. We introduce a statistic approach to evaluate the incoming traffic and a microscopic traffic model to simulate the propagation along the footbridge of the uncertain pedestrian entrance. In order to prove its technical feasibility, the proposed framework is finally applied to an ensemble of real world crowd events and to two ideal footbridges with differently shaped walkway. As a final result, the pedestrian density along the footbridge is described as a random field in terms of its joint and unconditioned probability density functions and correlation lengths. [ABSTRACT FROM AUTHOR]

Tibetan heritage building has attracted attention from many people who have interest in its historical and cultural value. Many of these buildings are opened to visitors in recent years, and the live load from tourist becomes a problem with increasing number of visitors. A monitoring system has been installed in a typical ancient Tibetan timber building to collect data on the material stresses and deformations of structural components. Based on the data collected, a strategy is proposed to evaluate the component of structural response induced by crowd load. A statistical relationship is obtained between the effective temperature change and the recorded strain increment. Results show that the measured strain is closely related to the number of visitors, and this may form the basis for a method to further evaluate the safety and integrity of the structure. An experiment was conducted on a corridor of the building with random pedestrian loading to validate the proposed strategy with encouraging results. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

In the analysis of vibration of footbridges in vertical direction, for crowd situations, there is evidence in the literature that the whole effect of pedestrian action is not well modeled when applying current force-only models to represent such an action. In these models, the action of each pedestrian is represented by a pulsating force applied on the structure. In this paper, a crowd load model is proposed for sparse and dense crowds (with densities up to around 1.0 pedestrian/m2) in which biodynamic models are added to represent the whole action of pedestrians. The focus of the investigation is on vibration effects in vertical direction. Comparisons with measurements on a prototype footbridge were carried out and made it possible to identify differences in the structural response when applying force-only and force-biodynamic models to represent the pedestrian action. The latter (proposed) model resulted in a better agreement with the measurements. [ABSTRACT FROM AUTHOR]

With the opening of ancient Tibetan structures to visitors worldwide, human load has become the principal live load on these structures. This project studies the properties of the floor structure of an ancient Tibetan building and its behavior under human-induced load effects. Tests were conducted with static and dynamic crowd load, including stepping and jogging by people at a fixed position. The tests show that the floor structure does not behave as a continuous slab. It takes the load from local areas with minimal load transference properties. The acceleration response shows significant peaks when the footstep frequency is close to the natural frequency of the structure, but the human jogging excitation frequency does not have any obvious effect on the structural response. The elastic modulus of the Agatu material is estimated to be close to zero from the measured natural frequency of the slab. The Agatu material is concluded to be a discrete compacted material with insignificant contribution to the structural rigidity of the floor slab. [ABSTRACT FROM AUTHOR]