A simplified method to account for vertical human-structure interaction

This is the final version. Available on open access from Elsevier via the DOI in this recordTo account for vertical human-structure interaction (HSI) in the vibration serviceability analysis, the contact force between the pedestrian and the structure can be modelled as the superposition of the force induced by the pedestrian on a rigid surface and the force resulting from the mechanical interaction between the structure and the human body. For the case of large crowds, this approach leads to (timevariant) models with a very high number of degrees of freedom (DOFs). To simplify analysis, this paper investigates the performance of an equivalent single-degree-of-freedom approach whereby the effect of HSI is translated into an effective natural frequency and modal damping ratio for each mode of the supporting structure. First, the numerical study considers a footbridge structure that is modelled as a simply-supported beam for which only the fundamental vertical bending mode is taken into account. For a relevant range of structure and crowd parameters, the comparison is made between the structural response predicted by the simplified model and the more accurate reference model that accounts for all DOFs of the coupled crowd-structure model. Where the simplified model is found to underestimate the structural response, although to a limited extent, this is compensated for by introducing a correction factor for the effective damping ratio. Second, the performance of the simplified method is evaluated through the application on a real footbridge. The results show that the simplified method allows for a good and mildly conservative estimate of the structural acceleration response that is within 10-20% of the predictions of the reference crowd-structure model.Research Foundation Flanders (FWO

Advanced Fourier-based Model of Bouncing Loads

This is the author accepted manuscript. The final version is available from Springer via the DOI in this record36th IMAC, A Conference and Exposition on Structural Dynamics 2018Contemporary design guideline pertinent to vibration serviceability of entertaining venues describes bouncing forces as a deterministic and periodic process presentable via Fourier series. However, fitting the Fourier harmonics to a comprehensive database of individual bouncing force records established in this study showed that such a simplification is far too radical, thus leading to a significant loss of information. Building on the conventional Fourier force model, this study makes the harmonics specific to each individual and takes into account imperfections in the bouncing process. The result is a numerical generator of stochastic bouncing force time histories which represent reliably the experimentally recorded bouncing force signals.The authors would like to acknowledge the financial support provided by PRIN 2015-2018 “Identification and monitoring of complex structural systems” and National Natural Science Foundation of China 347 (51478346) and State Key Laboratory for Disaster Reduction of Civil Engineering (SLDRCE14-B-16)

Pedestrian-Induced Vibrations of Footbridges: An Extended Spectral Approach

The vibration serviceability assessment of footbridges under pedestrian traffic requires a probabilistic approach considering the uncertainty in the dynamic behavior of the structure and the variability of multiple load parameters, such as the pedestrians' arrival time and step frequency. In view of engineering applications, a major challenge lies in the development, verification, and validation of efficient prediction models. With this challenge in mind, this paper uses a spectral approach to predict the dynamic response induced by unrestricted pedestrian traffic. A spectral load model available in the literature is extended to account for multiple harmonics of the vertical walking load and for application to arbitrary mode shapes. Furthermore, a closed-form expression is proposed to estimate the variance of the multimode structural response taking into account both resonant and nonresonant contributions. The performance of the proposed approach is evaluated for a simply supported beam as well as a real footbridge where multiple modes considerably contribute to the overall structural response. The results show that the proposed approach allows a good and mildly conservative estimate of the structural response to be obtained

Identification and modelling of vertical human-structure interaction

Slender footbridges are often highly susceptible to human-induced vibrations, due to their low stiffness, damping and modal mass. Predicting the dynamic response of these civil engineering structures under crowd-induced loading has therefore become an important aspect of the structural design. The excitation of groups of pedestrians and crowds is generally modelled using moving loads but also the changes in dynamic characteristics due to human-structure interaction are found to significantly affect the footbridge response. The present contribution investigates the influence of the presence of the pedestrians onto the dynamic characteristics of the occupied structure by means of an extensive experimental study on a footbridge in laboratory conditions. The analysis shows that the natural frequencies slightly reduce due to the additional mass but more significant is the observed increase in structural damping. Similar observations are made on a in situ footbridge. This interaction is simulated using a coupled human-structure model in which the human occupants are represented by simple biomechanical models

Verification of Joint Input-State Estimation by In Situ Measurements on a Footbridge

An existing joint input-state estimation algorithm is extended for applications instructural dynamics. The estimation of the input and the system states is performed in a minimum-variance unbiased way, based on a limited number of responsemeasurements and a system model. The noise statistics are estimated, as they areessential for the joint input-state estimation and can be used to quantify the uncertainty on the estimated forces and system states. The methodology is illustrated using data from an in situ experiment on a footbridge.Offshore Engineerin