The current trend toward lighter and slender pedestrian structures, with new aesthetic requirements and highperformance materials, has resulted in structures with increased susceptibility to vibration. Notable vibrations under human-induced excitations might appear, and the vibration serviceability requirements might not be accomplished. The Valladolid Science Museum Footbridge (Spain) is an example of a lively structure that might achieve excessive vertical acceleration under walking or running excitation. The control of excessive footbridge vibrations via passive and active devices is dealt with in this work. More specifically, this paper is concerned with the design and experimental implementation of a passive tuned mass damper (TMD) and an active mass damper (AMD) to mitigate human-induced vibrations on this in-service footbridge. The TMD, with a mass ratio of 1%, is designed by a numerical method based on H ∞ controllers. The AMD consists of a proof-mass actuator, with a mass ratio of approximately 0.2%, controlled by a strategy based on acceleration feedback with a phase-lag network. The performance of both devices has been assessed. structure to reduce the human influence, a proportional increase of stiffness being also necessary; and (iv) increasing the damping of the structure with special devices. Taking into account that stiffening the structure and increasing the mass are usually complicated and involve significant structural and non-structural changes, the alternative option of including damping devices to the structure seems to be the easiest way of improving the vibration performance of footbridges. Typical passive damping systems [6] are metallic dampers, friction dampers, visco-elastic dampers, viscous dampers, tuned mass dampers (TMDs) and tuned liquid dampers (TLDs). Among passive control devices available for implementation in footbridges, TMDs [7,8] (including parallel multiple TMDs [9] and series multiple TMDs [10]), TLDs [11] and fluid-viscous dampers are the most effective and, hence, the usual adopted solution [12].An alternative procedure to cancel footbridge vibrations is the use of active devices. Moutinho et al. [13] have recently implemented an active vibration control (AVC) on a stress-ribbon footbridge using a proof-mass actuator together with direct velocity feedback control (DVFC) with saturation. This actuator generates inertial forces in the structure without need for a fixed reference. The velocity output, which is obtained by an integrator circuit applied to the measured acceleration response, is multiplied by a gain and feeds back to a collocated actuator. The term collocated means that the actuator and sensor are located physically at the same point on the structure. The merits of this method are its robustness to spillover effects due to high-order unmodelled dynamics and that it is unconditionally stable in the absence of actuator and sensor (accelerometer with an integrator circuit) dynamics [14]. Nonetheless, when such dynamics are considered, the stability for high gai...

Evaluación de la predicción de aceleraciones debidas al tránsito peatonal en una pasarela en servicio

<p> This paper describes the dynamic analysis and vibration serviceability assessment of an in-service steel-plated stress-ribbon footbridge sited in Valladolid (Spain). Because of ist slenderness and singularity, this footbridge is a typical lightweight structure sensitive to dynamic excitation produced by pedestrians. A continuous vibration monitoring system which measures the acceleration and the environmental factors has been installed. The data collected have been used to identify the dynamics of the structure and assess ist vibration serviceability under in-service pedestrian traffic. Firstly, peak-acceleration-based test for single-frequency excitations are undertaken. Secondly, standards ISO 2631 and ISO 10137, suitable for general human exposure evaluation to whole-body vibrations, are used to evaluate the long-term vibration serviceability since they take into account the duration of the vibration exposure as well as the frequency content of the excitation.</p>