Loading models and response control of footbridges excited by running pedestrians

Abstract

New trends in the architectural design of footbridges feature an unprecedented slenderness, especially when these are located in the urban environment. For this reason, static analyses and a design towards the ultimate limit state have proven inadequate in many circumstances, and the main objective in the structural design is becoming that of assessing the serviceability limit state through dynamic analyses. On the other hand, the key issue of dynamic analyses is the availability of reliable models for the structure and for loads, and in the particular case of pedestrian action the lack of commonly accepted models for walking, running and jumping has become the weak link in the whole structural design process. In a first stage of the present work, vibration measurements were taken on a recently built cable-stayed footbridge, whose second vibration mode was excited by runners. As a second step, a dynamic loading model for the vertical component of the running-induced force was developed, which was used for the finite element analyses of the footbridge. Finally, tuned mass dampers (TMDs) represent a quite mature technology for reducing the resonant response of flexible structures, but their effectiveness is heavily dependent on the tuning ratio. In the case of footbridges, pedestrians can act as a significant part of the vibrating mass; thus, varying the vibration frequency, which makes it difficult to properly tune the damper frequency. Semi-active TMDs can be looked at as passive devices able to adjust their dynamic parameters according to a given control logic. A physical description of a control algorithm is given in the paper, and its performance is discussed.

Application of an Artificial Fish Swarm Algorithm in an Optimum Tuned Mass Damper Design for a Pedestrian Bridge

“…According to [47][48][49][50], a vertical force can be simulated considering of three different frequencies.…”

Study on Adaptive-Passive and Semi-Active Eddy Current Tuned Mass Damper with Variable Damping

“…According to [60,61], a vertical force is often modelled as a sum of a static and a dynamic component as Equation (16).…”

“…In order to verify the effect of semi-active ECTMD further, human-induced vibrations of 1.8 Hz, 2.0 Hz and 2.2 Hz are simulated. According to [60,61], a vertical force is often modelled as a sum of a static and a dynamic component as Equation (16 The comparisons of structural response under 2.0 Hz walking, running and jumping excitations are shown in Figure 13. The detailed results of the harmonic and human-induced excitation simulations are shown in Table 6.…”

A Review of Human Induced Vibrations on Footbridges

“…The successful application of fluid viscous dampers to earthquake resistant design has also been extensively discussed many years ago by Constantinou (1994). In addition, semi-active TMDs are developed by Occhiuzzi et al (2008) by adjusting their dynamic parameters based on a magnetorheological fluid-control strategy by varying the intensity of the magnetic field, while different combinations of viscous and friction types of behavior can be achieved. The effectiveness of semi-active TMDs is also presented in Demetriou et al (2015).…”