Design and Validation of a Fiber-Reinforced Polymer Cable-Stayed Pedestrian Bridge: Human-Induced Actions vs. Comfort Levels.

The investigation into advanced structural materials, such as composite materials, has revealed numerous possibilities within the field of bridge engineering. Glass-fiber-reinforced polymers (GFRPs) are notable among these materials, particularly in footbridge construction, encompassing both arch and cable-stayed designs. While GFRPs boast advantages, such as their high strength-to-weight ratio, they may exhibit some deficiencies, particularly when subjected to dynamic loads induced by wind or pedestrian forces. Two noteworthy global examples are the Lleida arch bridge (Spain, 2001) and the Aberfeldy cable-stayed bridge (Scotland, 1992). These structures have recently undergone comprehensive studies by the authors to assess their behavior when subjected to specific conditions regarding pedestrian traffic and vibrations induced by under-passing trains, as far as Lleida is concerned. The methodologies employed in these studies are detailed herein, incorporating the relevant scientific literature and technical regulations that provide guidance on fundamental principles for bridge design, pedestrian modelling, and acceleration thresholds aimed at minimizing discomfort. While the framework of principles is clear, the regulations are extensive, requiring designers to have a comprehensive understanding of the diverse outcomes achievable through various approaches. Therefore, the provided state-of-the-art overview serves as a roadmap for assessing the performance of an innovative cable-stayed bridge recently proposed by one of the authors. Initially designed with six spans, this prototype has been reconfigured here as a three-span train station overpass. The analyses conducted allowed for the assessment of induced accelerations. According to current accredited standards, the resulting comfort classification is considered minimal, even if, for crowded conditions, more specific studies are required.

Vibration Serviceability of the Aberfeldy Footbridge under Various Human-Induced Loadings.

Developing new structural materials, such as composite materials, has provided many opportunities in bridge engineering. Among these materials, glass-fiber-reinforced polymers (GFRPs), in particular, have found applications in footbridges. However, some of the commonly recognized advantages of GFRPs, such as the high values of the strength/weight ratio, can also be considered disadvantageous for certain realizations, particularly when the composite material used in a footbridge is, for example, subjected to dynamic actions such as those that are induced by wind and walking and/or running users. The induced accelerations can reach high values in comparison to recommended thresholds. Further, the natural frequency decays during the service life, reducing the capacity of the frequencies to move toward the frequency content of the pedestrian step. In this framework, the presented research is devoted to the dynamic comfort assessment of a pioneering cable-stayed GFRP pedestrian bridge, Aberfeldy, which was assembled in 1992 in the eponymous small town, which is located in Scotland (UK). The assessment was numerically performed through a finite element (FE) model, which was tuned based on the literature data concerning geometry, structural details, and in situ-acquired frequencies. The analyses carried out in this study include the evaluation of the accelerations' time histories, which were induced when simulating a set of pedestrian path scenarios, and the dynamic actions that occur during pedestrian traveling. Specifically, different values of velocity and step frequency were considered as well as the inclusion of walking and running movements. Then, based on the acceleration values, the assessments of comfort criteria for the current standards were elaborated while also recognizing that the peak accelerations-usually attained for short periods-cannot be the only parameters considered in evaluating the pedestrian bridge capacity. This investigation allowed a dynamic comfort rating to be established for the Aberfeldy footbridge.

Impact of Dynamic Soil-Structure Interaction on Performance of a Single Span Footbridge with Overhangs Subjected to Mining-Induced Shocks.

The impact of the dynamic soil-structure interaction (DSSI) on the response of a single-span footbridge to mining-induced shocks was assessed. Firstly, the eigen values, modes and damping of the footbridge were evaluated based on in-operation field tests. Then, natural frequencies were determined numerically by a model usually used in static calculations, i.e., a simple supported beam with overhangs. The numerical natural frequencies turned out to be inconsistent with the experimentally determined values. In turn, the model, assuming the overhangs' ends translationally restrained, gave natural frequency values closer to the experimental ones. However, for the third mode, that is lateral, the frequency error (~26%) can be considered greater than usually accepted values. Hence, the three-dimensional numerical model of the footbridge was tuned by considering the DSSI between the overhangs and the ground, and implementing springs (in three directions) at the overhangs' ends. To estimate the impact of DSSI on the dynamic performance of the footbridge, time history analyses were carried out for the model with fixed overhang ends and for the model with additional springs. Two different types of mining-induced tremors were used as excitations. Those two tremors (narrow and wide band) induced different dynamic responses in the models with and without the springs. Hence, the impact of the DSSI on the dynamic footbridge performance needs to be considered to predict the effect of mining-induced shocks.

A Split-Wedge Anchorage for CFRP Cables: Numerical Model vs. Experimental Results.

Fiber-reinforced polymers (FRPs) are widely used within civil structural applications either for structural retrofitting or new constructions. This is due to their appreciable mechanical properties such as high stiffness and strength, resistance to environmental effects, as well low density. Through the years, such peculiarities have encouraged researchers to apply FRP cables within the design of prestressing systems, where steel cables are systematically adopted. However, the brittleness intrinsic to FRP materials necessitates additional efforts to design the anchorage devices. In fact, tendons are here subjected to stress peaks, which need to be controlled in order to prevent the premature failure of the cable. Following this goal, authors recently studied an optimized split-wedge anchorage, for 12 mm-diameter pultruded-carbon-fiber-reinforced polymer (PCFRP) tendons, adopting double-angle (DA) wedges, and compared its performance with a single-angle (SA) wedge configuration. Tensile tests were performed on 3 SA and 2 DA prototypes, respectively, through a universal testing machine: the DA configuration exploited the average cable capacity (257 kN) once, denoting a maximum efficiency. The obtained experimental results are utilized, in the framework of the present work, to calibrate contact parameters of nonlinear finite element models. The presented numerical results helped to assess benefits of the proposed configurations and the behavior of the anchorage components: the DA configuration turned out to satisfactorily avoid stress peak superpositions on the cable, with a reduction in pressure in the loading end of the cable with respect to the SA model.