Special Issue on Load Modeling and Experimental Studies on Lively Pedestrian Bridges

Pedestrian bridges traditionally have functioned as arteries in urban areas, transporting people to and from high-density transportation hubs and stadia. They recently have begun to play an important architectural and cultural role in redefining the landscape and character of cities. Pedestrian bridges are built to emphasize the architectural character of their surroundings, and hence, they appear in many interesting shapes and configurations. In addition to making an architectural statement, pedestrian bridges often serve as important landmarks and as a platform to showcase design creativity.

Interest in architecturally appealing structures such as cable-stayed bridges and in using lightweight materials such as aluminum for pedestrian bridges has resulted in many lively structures. Since the Millennium Bridge incident in London, there has been extensive research activity to gain an understanding of the interaction between structures and their occupants. Scores of laboratory and full-scale measurements have followed. Improved models for both individual pedestrian loads and crowds have been proposed in the literature. New methods for controlling pedestrian-induced vibrations have also been proposed and validated in the field. A large number of laboratory and field studies have been undertaken on lively pedestrian bridges in Europe and the Americas.

Despite the volume of research activity in this area, there are significant differences among popular design models in various jurisdictions. There are also gaps in the fundamental characterization of pedestrian loads, including human–structure interaction, and verifying them by using field observations. This special issue is aimed at synthesizing the state of the art in the area of pedestrian bridges and addressing these gaps while highlighting new understanding in the area of load modeling and experimental characterization of lively pedestrian bridges. Ten articles, selected from more than 30 submissions via a thorough peer-review process, are included in this special issue. These papers include two review papers, two articles focused on load modeling, four articles focused on design aspects, and two papers on experimental modal analysis and vibration assessment.

In their review paper titled “A Conceptual Review of Pedestrian-Induced Lateral Vibration and Crowd Synchronization Problem on Footbridges,” Fujino and Siringoringo provide several examples of past bridge failures. In addition, they review popular force models, excitation mechanisms, and stability criteria for dealing with lateral vibrations. Furthermore, they also review popular guidelines currently being used for design purposes and point out key limitations in our understanding in general and design criteria in particular.

Ricciardelli and Demartino, in their paper “Design of Footbridges against Pedestrian-Induced Vibrations,” present a critical review in which background hypotheses, field of applicability, and results obtained through various loading and evaluation methodologies are compared. They also provide a comprehensive review of load models for a single pedestrian, multiple pedestrians, and interaction and instability models.

In their paper titled “Biomechanically Excited SMD Model of a Walking Pedestrian,” Zhang et al. present a force model that consists of a spring-mass-damper along with a pair of biomechanical forces to model human–structure interaction in the vertical direction. Using a motion-capture system on a rigid floor, the biomechanical forces and the model parameters are estimated by using measurements.

Jiménez-Alonso et al., in their paper “Vertical Crowd–Structure Interaction Model to Analyze the Change of the Modal Properties of a Footbridge,” propose a vertical crowd–structure interaction model that consists of two submodels, (1) an interaction subsystem, which accounts for the change in the modal properties caused by a pedestrian, and (2) a multiagent submodel for modeling the crowd behavior that results from the individual interaction model. This model focuses on the vertical direction and is compared with crowd-data measurements obtained from the Viana Footbridge in Portugal.

In their paper titled “Performance of Pedestrian-Load Models through Experimental Studies on Lightweight Aluminum Bridges,” Dey et al. study the performance of the widely used periodic (Fourier) load model in predicting the serviceability of lightweight aluminum bridges. The authors evaluate the performance of this model to predict serviceability for nonresonant (with the fundamental mode) cases and when the higher harmonics of walking may be nonresonant or near resonant with the fundamental mode in the vertical direction.

Dall’Asta et al., in their paper titled “Design and Experimental Analysis of an Externally Prestressed Steel and Concrete Footbridge Equipped with Vibration Mitigation Devices,” discuss key design aspects of a 142-m three-span continuous externally prestressed steel and concrete footbridge in Italy. Their paper presents an interesting design that consists of a combination of high-damping rubber material and tuned mass dampers (TMDs) to enhance the overall system damping of the bridge.

In their paper titled “Numerical and Experimental Evaluation of the Dynamic Performance of a Footbridge with Tuned Mass Dampers,” Van Nimmen et al. evaluate the performance of a steel pedestrian bridge using both simulated and experimental data specifically to evaluate the effectiveness of TMDs mitigating peak responses during pedestrian loading. The authors study provisions from two design guidelines, Sétra (AFG 2006) and HiVoSS (Heinemeyer et al. 2009), with an aim of evaluating and comparing predictions for this bridge. Their results underscore the sensitivity of damper parameters to the loading characteristics on the bridge.

A similar study is presented in the paper “Human-Induced Vibrations on Two Lively Footbridges in Milan,” in which Tubino et al. assess the serviceability of two bridges with and without TMDs under different loading conditions. Both footbridges discussed in this paper are very interesting from a dynamic point of view, in that the fundamental natural frequency (vertical) is approximately 2 Hz. The authors carry out comparisons between measurements and analytical predictions.

Ni et al., in their paper titled “Series of Full-Scale Field Vibration Tests and Bayesian Modal Identification of a Pedestrian Bridge,” present an experimental comparison of estimated modal properties of a bridge located on the City University of Hong Kong campus. Results from three modal identification methods encompassing ambient and forced excitation cases are critically compared, and their relative merits are discussed. In addition, an uncertainty analysis was performed to ascertain the accuracy of the identified modal parameters.

In their paper titled “Vibration Monitoring of a Steel-Plated Stress-Ribbon Footbridge: Uncertainties in the Modal Estimation,” Soria et al. present modal identification results from 1 year of continuous monitoring of a steel-plated stress-ribbon footbridge in Spain. They correlate their results with environmental factors and provide statistical models for the modal frequency estimates. The authors conclude that, after correcting for environmental effects, such statistical models can serve as valuable tools for diagnosing structural health.

The articles in this special issue cover important aspects of all three components of pedestrian bridges: load modeling, design, and experimental analysis. In addition, there are two review papers included in this special issue. Ten high-quality papers highlight important advances in the field of pedestrian bridges while outlining major challenges in the area. Although it is by no means an exhaustive treatment of all aspects and challenges encountered in the design and analysis of pedestrian bridges, the guest editors hope that this special issue brings to the fore key challenges to be addressed in the near term and continues to spur interest among researchers and practitioners to work in this exciting area of structural dynamics and experimental analysis.