Human-structure Interaction Research Articles

A frequency-domain approach to model vertical crowd-structure interaction in lightweight footbridges

Load models that account for Human-Structure Interaction (HSI) may be preferable to accurately predict the dynamic response of lightweight footbridges subjected to pedestrian actions. Representing each person within a crowd may not be practical in engineering design calculations as time-variant models with a large number of degrees of freedom have to be managed. In addition, high computational time may be required to achieve the steady-state response. In this sense, this paper proposes a novel approach to calculate the vertical steady-state response of footbridges from a time-invariant coupled crowd-structure system. Considering the model of the structure and a feedback model of the crowd, a total closed-loop Transfer Function (TF) of the coupled system is derived. Based on this frequency-domain interacting methodology, a step-by-step procedure is set to asses the vibration serviceability of lightweight footbridges due to harmonic excitations through simple algebraic operations. The proposal is used to study a Fibre Reinforced Polymer footbridge subjected to two streams of walking pedestrians. For this structure, a good compromise between experimental and numerical results is obtained in terms of vertical vibrations and TFs. To further validate the proposed approach, a pre-stressed concrete laboratory facility is also analysed, obtaining a satisfactory agreement between the experimental and numerical TFs. Thus, the proposed approach allows to evaluate lightweight footbridges under crowd-induced loads considering HSI in a simple and accurate manner, which is clearly geared to practice.

Using Full-Scale Observations on Footbridges to Estimate the Parameters Governing Human–Structure Interaction

Using Full-Scale Observations on Footbridges to Estimate the Parameters Governing Human–Structure Interaction

Vertical human-structure interaction of a simply-supported steel-glass composite footbridge under both standing and moving pedestrians

For lightweight footbridges, there are evident vertical coupling effects among standing pedestrians, moving pedestrians and the footbridge. To further clarify the vertical human-structure interaction, the effects of a single standing pedestrian, a single moving pedestrian, as well as both a single standing pedestrian and a single moving pedestrian on a simply supported steel-glass composite footbridge model are investigated in this study, respectively. Experimental results show that the effects of standing and moving pedestrians on the structural natural frequencies are different. The Fourier spectrum of the footbridge is sensitive to the relationship between the natural frequency of the coupled system and the walking frequency of the moving pedestrian. Moreover, at the same monitoring point, the vertical velocity of the footbridge is significantly less than that of the centroid of the standing pedestrian. Finally, a corresponding theoretical model is presented in this study. It is found that the theoretical model can well predict vertical dynamic responses of the human-structure coupled system, and the relative relationship of the vertical dynamic response between the footbridge and the standing pedestrian is clarified. This study can provide valuable references for vertical human-structure interaction and vibration serviceability assessment of the footbridge.

Active control of human-induced vibrations on lightweight structures via electrodynamic actuator dynamics inversion

The active vibration absorber represents an effective means to mitigate excessive vibrations in low-damping structures. Nevertheless, the dynamics of the actuators employed in such systems may negatively affect their performance and stability restricting their operational frequency range. This article presents an application of dynamics inversion techniques to the force control of electrodynamic proof-mass actuators employed as active vibration absorbers in lightweight pedestrian structures. The dynamics inversion approach is applied to enhance the classical direct velocity feedback scheme. Additionally, a novel method relying on dynamics inversion is presented: the Broadband Force Cancellation Algorithm. This procedure consists in estimating, in real-time, the equivalent force acting on the system to later apply it back to the structure with the opposed sign. The effectiveness of the proposed methods is assessed via numerical simulations carried over a realistic model of an existing lightweight footbridge and an electrodynamic proof-mass actuator. Two load cases are analyzed: a fixed swept-sine force and a walking load. Both cases account for the actuator-structure interaction. The human-structure interaction is considered in the latter scenario due to its importance when dealing with lightweight pedestrian structures. Simulation results demonstrate that the dynamics inversion techniques effectively cancel out actuator dynamics leading to an excellent tracking of the reference force output by the suggested or other vibration control algorithm. The proposed schemes are proved promising since they substantially outperform the widespread direct velocity feedback approach. In particular, the Broadband Force Cancellation Algorithm minimizes the action of the external forces within their estimation frequency range, thus being especially suited to tackle broadband excitations, important in lively pedestrian structures, whereas the velocity feedback methodology performs best at the structural resonant frequencies.

Análisis por condición de servicio causado por vibración vertical inducida por peatones en estructuras

Civil engineering structures such as grandstands, slabs, footbridges and staircases have reported unacceptable vertical vibration when they are affected by human activities. Even when most of these structures are designed according to current guidelines and design codes, there are still misunderstandings in the human-structure interaction effects that, in some cases, may increase the vibration response compromising the structural serviceability performance. As a result, the serviceability load conditions due to pedestrian activities control, in most cases, the design for these structures. Therefore, a systematic overview regarding vertical pedestrian-structure interaction is carried out to demonstrate the need for a realistic analysis to properly incorporate these effects toward more rational structural designs. The discussion establishes a body of knowledge regarding pedestrian loads and structural responses, yielding the potential for more rational approaches to improving the analysis and design of pedestrian structures.

Coordinated distribution of stadium electric load unloading based on artificial intelligence

The Stadium’s Electricity (SE) is cost-effective and critical to meeting the stadium’s size requirements. Because of their complex internal operations and extensive functionality. Stadium energy efficiency improvements are demanding and time-consuming due to the large and diverse electricity loads that can be managed. The stadium source of information is unloaded and turned off after sports. During sports, the system is ready to be deployed in case of an electricity outage. Several of these issues must be carefully evaluated, starting with accurate representations and human-structure interaction models, and determining acceptable facility vibration serviceability limitations of crowd activities. Due to various factors, stadiums like those used for athletic or entertainment events are distinct from other civil engineering constructions. Stadiums are susceptible to both the coordinated and random motion of huge crowds, which presents several issues. In computer science, Artificial Intelligence (AI) refers to the development of machines that can simulate human mental processes. AI can be used in various ways, from natural language processing to speech recognition to computer vision. This paper introduced a new method for (SE-AI) in addition to enhancing stadium control capabilities in various functional areas. The intelligent stadium development effectively enables it to handle construction equipment in an integrated manner. In the stadium’s electrical design, the smart sports model is structured. An investigation of the stadium’s electrical design system to provide helpful information for the stadium’s electrical design work based on engineering design principles. Advanced technology is mirrored in the stadium’s equipment, which is moving toward informationization and intelligence due to the advancement of science and technology, especially digitalization. If the research results can be a helpful guide for bettering the electrical planning of stadiums can be a more substantial impact on society. Stadiums are investing in Wi-Fi and distributed antenna systems to boost connection. This allows viewers to follow the game throughout the stadium and helps scattered personnel communicate.

Reconstruction of the Vertical Dynamic Running Load from the Registered Body Motion

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.

A frequency-domain procedure to design TMDs for lively pedestrian structures considering Human–Structure Interaction

The use of advanced low-density high-strength materials, such as Fibre Reinforced Polymers (FRPs) or aluminium alloys, has enabled to construct lightweight and slender footbridges, which structural design may be governed by the Vibration Serviceability Limit State (VSLS) under human-induced loads. These structures may be excited in resonance by higher and less energetic harmonics of human actions in contrast to footbridges built with traditional construction materials. Additionally, Human–Structure Interaction (HSI) may be relevant on the dynamic response of these type of pedestrian structures. A solution for the aforementioned issues may be the installation of Tuned Mass Dampers (TMDs) in the bridge. Thus, this paper presents a frequency-domain procedure to design TMDs for lively pedestrian structures based on a coupled Human–Structure–controller system. The proposal, which accounts for uncertainties associated to the structure and the interaction phenomenon, is applied to design passive inertial control systems for an FRP footbridge. Also, the implications of HSI in the design of TMDs are discussed, and the performance of the designed devices is assessed considering two human actions, bouncing and walking. Since the peak value of the steady-state response of a pedestrian structure can be fast assessed through algebraic operations, the proposed approach is suitable to design robustly control systems against human-induced vibrations. As a result, structural elements and controllers can be properly dimensioned, leading to further cost-effective footbridge projects.

Experimental calibration of a one degree of freedom biodynamic model to simulate human walking-structure interaction

Human-structure interaction (HSI) is a key issue in the behavior of lightweight and low-damping footbridges displaying vertical bending vibration mode frequency within the range of human walking pace. To address HSI, researchers have been developing biodynamic models to represent the pedestrians moving along the structure, according to different methodologies. This paper proposes a biodynamic model based on the single degree of freedom spring-mass-damper system subjected to base excitation, as this formulation is consistent with that of the motion equations of the coupled system composed by the pedestrian and the structure. The parameters of the biodynamic model are expressed by three regression equations and were calibrated with the aid of experimental tests with pedestrians walking on a rigid platform and on a flexible one under harmonic vibration. A comparison between the obtained parameters of this biodynamic model and those of other models from the footbridge literature is presented, pointing out the differences in range variation. Finally, the results of tests conducted aiming to validate the calibrated model are compared to theoretical simulations showing good correlation.

Time-domain numerical analysis of single pedestrian random walks on laminated glass slabs in pre- or post-breakage regime

Mechanical performance assessment of load-bearing elements under ordinary design actions is a priority when material degradation or even severe damage may be experienced. This is especially the case of unconventional constructional materials, or assembled systems like laminated glass (LG) solutions, in which multiple load-bearing components may suffer of different mechanical issues. This turns out in potential risk for customers, and in the need of specific design assumptions to address the problem. For load-bearing elements with direct interaction with final users (as pedestrian systems), a reciprocal modification of mechanical and dynamic parameters should be properly taken into account in the early design process.This paper explores the sensitivity of human-structure interaction effects and performance indicators for LG slab modules subjected to various walking paths of single pedestrians. An extended set of Finite Element (FE) nonlinear dynamic numerical simulations is presented, in which the variation of conventional performance indicators (such as acceleration peaks, deflection, vibration frequency) is investigated for two in-service LG modular units with intact (LGU) or partially fractured (LGF) glass layers. Walking scenarios are described with the support of consolidated deterministic method in use for pedestrian loads, in which walking features do not account for the features of structural background. The comparative analysis of numerical results with earlier experimental outcomes for two reference LG slab modules subjected to random walking conditions shows that time-domain nonlinear simulations with simplified pedestrian loads can efficiently capture some major effects of pedestrians, as well as the presence of damage in glass. At the same time, it is shown that fractured glass layers in LG pedestrian modules can still provide partial post-breakage contribution to the resisting section.

Design of a Semiactive TMD for Lightweight Pedestrian Structures Considering Human–Structure–Actuator Interaction

Lightweight pedestrian structures constructed with high strength-to-weight ratio materials, such as fiber-reinforced polymers (FRP), may experience large accelerations due to their lightness, thus overcoming the serviceability limit state. Additionally, uncertainties associated with human–structure interaction phenomena become relevant. Under these circumstances, variations in pedestrian actions could modify the modal properties of the coupled human–structure system and classical approaches based on passive Tuned Mass Dampers (TMD) do not offer an effective solution. An alternative solution is to use a Semiactive TMD (STMD), which includes a semiactive damper that, when properly designed, may be effective for a relatively broad frequency band, offering a robust solution when significant uncertainties are present. Thus, this paper presents a design methodology for the design of STMDs applied to lightweight pedestrian structures including human–structure and actuator–structure interaction. A multiobjective optimization procedure has been proposed to simultaneously minimize structure acceleration, inertial mass, and maximum damper force. The methodology has been applied to a lightweight FRP footbridge. Realistic simulations, including system uncertainties, interaction phenomena, nonlinear damper model, noise-contaminated signals, and the practical elements (in-line digital filters) needed for the successful implementation of the control law, validate the methodology. As a conclusion, the STMD is more effective than its passive counterpart in both, canceling the response or achieving similar performance with significant lower inertial mass.

Nonlinear rotational inertial double-tuned mass damper for reducing human-induced floor vibration with frequency detuning

This study proposes a novel nonlinear rotational inertial double-tuned mass damper (NRIDTMD), which introduces a cubic stiffness element into the inerter-based passive control system RIDTMD, by exploiting the frequency insensitivity of nonlinear energy sink to overcome the frequency detuning problem in human-induced floor vibration control. Due to its nonlinear nature, the complexification-averaging technique is adopted to obtain the approximate steady-state response of the coupled floor-NRIDTMD system, and the number of the solutions and stability of the responses are discussed. Based on the genetic simulated annealing algorithm, the design parameters of the proposed NRIDTMD are optimized, and the empirical design formulation and response prediction equation are further proposed. Considering the effect of frequency detuning caused by human-structure interaction, floor stiffness degradation and mass increase, a numerical model of an experimental floor is used to verify the vibration mitigation performance of the proposed NRIDTMD, and compared with those of TMD and RIDTMD. The results reveal that the empirical formulation and prediction equation exhibit excellent accuracy and applicability, and the proposed NRIDTMD can minimize the acceleration response increment of the floor in frequency detuning, exhibiting better frequency robustness than those of conventional linear dampers.

Experimental Evaluation of the Driving Parameters in Human–Structure Interaction

Many studies in the literature have already evidenced that pedestrians are able to change the dynamic properties of slender structures (e.g., footbridges and staircases). The aim of this paper is to analyse which pedestrians’ features mostly affect the structure behaviour, in order to properly account for them in a human–structure interaction problem, while disregarding the less relevant ones. This is accomplished by measuring the apparent mass (i.e., the frequency response function between the vibration of the structure at the contact point and the consequent force exerted by the pedestrian to the structure itself) curves of human bodies and coupling them to the dynamics of a slender structure. In more detail, this paper aims at analysing which factors must be accounted for among intra-subject variability (i.e., the dynamic behaviour of the same subject can change because it is characterised by a natural dispersion), inter-subject variability (i.e., different subjects have different dynamic behaviours) and the posture (i.e., the same subject changes posture during motion and this causes a change of his/her dynamic features). The influence of the apparent mass properties on the modal parameters of the hosting structure is addressed by means of a modal approach.

Status of vibration serviceability design methods for lightweight timber floors

Since the 1970s occupant complaints about vibration serviceability performances of lightweight timber floors have risen in many countries. Initially concerns commonly centered on behaviours of joisted floors in non-commercial buildings. Empirical design methods were developed, but those methods sidestepped generalize understanding of the issues. Subsequent evolution of building construction techniques and material options often exacerbated inadequacies of empirical design methods. Consequently, interest in understanding why vibration serviceability problems occur and how to avoid them has reemerged as a priority research topic. This paper discusses technical issues associated with predicting vibration serviceability performances of lightweight timber floors, and identifies best current analysis and design practices. Emphasis is on ability to handle the full range of variables associated with 21st century lightweight construction methods. This includes capability to address effects of architectural and construction design choices, and effects types of building occupancies have on dynamic loads and motion responses of floor systems. Need to utilize capabilities of modern numerical engineering analysis tools is also emphasized. Ongoing R&D activities are mentioned, including need to address Human-Structure Interaction effects commonly important to proper design of lightweight building superstructures.

A spring-loaded inverted pendulum model for analysis of human-structure interaction on vibrating surfaces

Human-structure interaction (HSI) issues have gained increasing attention from researchers. In the present paper, a 3-D spring-loaded inverted pendulum (SLIP) model is established for modeling human running on vibrating surfaces. PD control for the leg force and foot moment is employed to achieve the desired values for the height and forward running speed of the center of mass, and P control is used to maintain limited lateral speed. Numerical results show the robustness of the control methods which are stable even subjected to large disturbances, and the effects of different control parameters are analyzed. Shaking table tests were conducted in which the participants ran on a treadmill excited laterally or longitudinally by a shaking table. The test results show that the HSI increased with the excitation level, and synchronizations were observed mainly in the cases of longitudinal excitations. The HSI can be interpreted as an equivalent additional mass and negative damping for the lateral direction, while additional mass for the longitudinal direction. The numerical simulations are compared with the experiments, and it demonstrates that the model describing human behaviors agrees well on both the stationary and moving treadmill (i.e. subjected to excitation).

Human-structure interaction: convolution-based estimation of human-induced vibrations using experimental data

This article addresses the estimation of the effects of human-structure interaction on the dynamic behaviour of slender structures. The paper proposes a method able to provide predictions of human-structure interaction effects in cases in which no models of human dynamic behaviour can be used/are available and only experimental data have to be used. The proposed approach describes the coupled system composed by the structure and the people on it, splitting the action of people into two components: passive and active forces. The sum of the two provides the global action of each person on the dynamics of the structure. Furthermore, an analytical treatment based on modal coordinates and convolution operations is proposed in order to use experimental data, related to the dynamic behaviour of humans, for predicting the vibration level of the occupied structure. An experimental campaign on a slender staircase provided data employed to validate the approach discussed in the article.

Prediction of structural responses induced by single-person jumping through a physical principle based on transfer functions

The vibration caused by human excitation has become a key factor at the structural design stage of large-span structures including footbridges, sport stadia, and high-rise buildings. As the structures tend to become slenderer and lighter, the mass of the crowd is not negligibly small compared with the mass of the structure. In such cases, the crowd and the structure form a coupling system through a mechanism known as human–structure interaction (HSI). Researchers found that the structural responses with and without HSI are different. However, the interaction effect on the structural responses has rarely been quantitatively evaluated from the perspective of human system parameters. In this paper, a novel method using a physical principle to predict jumping-induced structural responses is proposed, in which the structural response is expressed as the multiplication of a series of transfer functions representing human system and structural dynamic properties. Structural responses of a large-span concrete structure under jumping excitation are predicted using the proposed method and identified human system parameters. Comparison with measured responses shows satisfactory agreement. The proposed method provides a solution to consider HSI effect on the calculation of structural responses in the vibration serviceability design for large-span structures.

Identification of a Human-Structure Interaction Model on an Ultra-Lightweight FRP Footbridge

Due to the high strength-to-weight ratio of fibre reinforced polymers (FRPs), human-induced vibration problematic remains as a subject to be fully comprehended in order to extend the use of composites in Bridge Engineering. Thus, this paper studies an ultra-lightweight FRP footbridge, which presents excessive vertical vibrations when the fourth harmonic of a walking pedestrian is synchronised with the structure’s fundamental frequency. Focusing on the vertical bending mode, at 7.66 Hz, the bridge dynamic behaviour was assessed under the action of a single pedestrian crossing the facility at a step frequency of 1.9 Hz. As an over prediction of the footbridge response was computed using a moving force (MF) model available in a design guideline, a mass-spring-damper-actuator (MSDA) system was adopted to depict a walker. Hence, Human-Structure Interaction (HSI) phenomenon was considered. Employing the experimental results, parameters of the MSDA system were identified, leading to a HSI model that considers the first fourth harmonics of a walking human. Additionally, a parametric analysis was carried out, determining that the damping ratio of the human body and the load factor associated to the fourth harmonic are the most relevant parameters on the estimation of the response. The identified HSI model may be used as a first approximation to accurately predict the dynamic response of ultra-lightweight composite structures and should be extended to account for crowd-induced loads.

Semi-active control of walking-induced vibrations in bridges using adaptive tuned mass damper considering human-structure-interaction

Tuned mass dampers (TMDs) are used to control pedestrian induced vibrations of pedestrian bridges as traditional vibration control devices. A TMD can have a good control effect when it is tuned to the natural/vibrational frequency of the primary system. However, a traditional passive TMD is sensitive to the frequency deviation. Actual human-induced excitations can cover a wide frequency range and are stochastic virtually, which will cause a decrement in its control effect. The human-structure interaction (HSI) can also change the structural characteristic and lead to a mistuned TMD. To propose a more robust and effective TMD in solving the serviceability problem, a semi-active independent variable mass TMD (SAIVM-TMD) is introduced in this study. Wavelet transform (WT) is used to identify the structural instantaneous frequency, then, the mass of SAIVM-TMD is adjusted according to the WT - based control algorithm by actuating devices in real time. To highlight the control effect of SAIVM-TMD, a simply supported pedestrian bridge is carried out as a case study. The bridge is simplified to a Euler–Bernoulli beam according to an in-situ test and model analysis. Then, its dynamic responses under different controllers are analyzed and compared under single pedestrian periodic and stochastic walking-induced excitations. HSI is considered and a pedestrian is modulated as a moving spring-mass-damper (SMD) model. Then, a case under crowd-induced stochastic excitation is proposed. A passive TMD optimized for a pedestrian bridge under moving loads is used for comparison. Results show that SAIVM-TMD always has the best performance because it can adapt to the structural vibrational frequency changes efficiently and retune.

The Influence of Human-structure Interaction on Structural Dynamic Properties

For large-span flexible structures, human-structure interaction is obvious, but designers do not have a clear understanding of whether human-structure interaction should be considered in structural design. In this paper, the pedestrian Spring-Mass-Damper (SMD) model and dynamic parameters are used to study the influence of human-structure interaction on structural dynamic properties by using ANSYS finite element calculation software to calculate and compare 70 working conditions. The results show that when the structure-human frequency ratio is less than 1 and slightly greater than 1, the human-structure interaction has a greater influence on the dynamic properties of the structure. As the structure-human frequency ratio increases, the influence of the human-structure interaction on the dynamic properties of the structure decreases. When the structure-human frequency ratio is greater than 2, the human-structure interaction can be ignored.