A. Lorenzana

Adaptive Tuned Mass Damper for the Construction of Concrete Piers

In this paper the authors have studied and proposed a control system for an adaptive tuned mass damper (TMD) for self-climbing formworks to be used in some critical construction phases of concrete piers. This dynamic vibration absorber will move together with the formwork, and must change the tuned parameters (frequency, damping) for an optimal situation in each instant of the pier construction. With this device, the structural damping of the pier will increase and consequently personal comfort (e.g., sickness and acceleration levels) and structural security (stress level) will improve. The numerical results are based on a finite element model (FEM) for the 92 m concrete pier of La-Miel Viaduct (Nerja, Spain). This model has been adjusted by means of acceleration records obtained on the top of the pier. On the basis of this model several approaches of adaptive TMDs have been studied and finally a feasible solution has been suggested.

Modal and dynamic analysis of a footbridge in service

Obras de ingenieria civil como las pasarelas peatonales son estructuras cada vez mas esbeltas, ambiciosas y complejas en las que los efectos dinamicos producidos por las solicitaciones a las que estan sometidas (peatones) pueden inducir problemas de servicio y/o amplificaciones importantes o repetitivas de los esfuerzos y deformaciones. Esto junto con las actuales demandas sociales relativas a la percepcion y confort suscitan la necesidad de integrar el analisis y diseno asistido por ordenador en la evaluacion de las vibraciones generadas por las cargas a las que estan sometidas. El empleo de los programas comerciales de elementos finitos no ha proliferado tanto como en otros campos de la ingenieria por la existencia de metodologias simplificativas en numerosas guias y normativas nacionales e internacionales y por la dificultad de hacer modelos realistas en el caso de estructuras complejas. Sin embargo, el conocimiento generado por el analisis de este tipo de modelos numericos resultaria especialmente util en las fases mas tempranas del diseno de estructuras similares, tanto inicial como de las modificaciones necesarias para solucionar problemas dinamicos existentes, ya que es en estas etapas cuando se podria aplicar la mejor solucion desde un punto de vista tecnico y economico. En el presente articulo se describe el proceso de generacion y ajuste del modelo mecanico de una pasarela actualmente en servicio y la simulacion de la solicitacion de dos tipos de carga: una excitacion generada por un shaker y una carga peatonal, contrastando los resultados generados mediante el modelo numerico con los obtenidos experimentalmente.

Exact statement of the instability problem for frames and its direct numerical solution

A general approach for the systematic evaluation of the critical buckling load and the determination of the buckling mode is presented. The Navier-Bernoulli beam model is considered, having the possibility of variable cross-section under any type of load (including pressures and thermal loading). With this purpose, the equilibrium equations of each beam element in its deformed configuration under the hypothesis of infinitesimal strains and displacements is considered, resulting in a system of differential equations with variable coefficients for each element. To obtain the nonlinear response of the frame, one should impose the compatibility of displacements and the equilibrium of forces and moments in each beam-end, also in the deformed configuration. The solution is obtained by requiring that the total variation of potential energy is zero at the instant of buckling. The objective of this work is to develop a systematic method to determine the critical buckling load and the bucklingmode of any frame without using the common simplifications usually assumed in matrix analysis or finite element approaches. This way, precise results can be obtained regardless of the discretization done.

Quantifying Differences Between Walking Locomotion on Rigid and Flexible Pavements

This work explores the differences between walking locomotion on rigid pavement and a particular type of flexible pavements made of EVA75 foam having thickness of either 10 or 20 mm. The aim is to analyse how human movements, in terms of trajectories of different body parts, are influenced by rigidity of such pavements. This research line is ultimately directed towards evaluation of the influence of flexible pavement on the vibration perception by human test subjects walking over vibrating decks of lively footbridges and floors.

Discomfort Evaluation on Lively Footbridges with Soft-Rubber Pavement

This paper deals with the measurement of the pedestrian perception of the movement of lively footbridges. Several tests on a 80 m single span stress-ribbon footbridge are presented. This footbridge is very slender and has a very low structural damping and several modes under 3 Hz, resulting in sensible vertical movements. Despite of that, general users do not complain too much, probably because its pavement is made of a thick pour-in-place soft-rubber material.