DYNAMICS ANALYSES OF COMPOSITE MATERIAL FOOTBRIDGE UNDER ACTION OF PEDESTRIAN WALKING

Resumo

This work aims the optimization of a design of footbridges made of pultruded glass fiber
reinforced polymer (GFRP) profiles, under the dynamic effect of pedestrian walking. First, a footbridge
with a structural arch associated to trusses was designed, respecting the ultimate and serviceability states
for static analysis. The accelerations found in the dynamic analysis, was considerate intolerable for
human comfort according with the design guides. Therefore, it was necessary to design a synchronized
passive dynamic attenuator (SDA) to mitigate the excessive vibrations. Besides this first one, others
structural conceptions using truss beams and inverted queen post truss were analyzed aiming the most
efficient structural behavior. A computation program considering a two-dimensional model was
developed to integrate the equation of the movement taking into account the pedestrian crowd load. The
dynamics properties used in the two-dimensional model were obtained from one three-dimensional
model using a finite element method. Since the pultruded profiles are lightweight, it was considerate the
interaction between pedestrians and the structure by increasing the mass and the damping ratio. It was
noticed that without considering the pedestrian versus structure interaction the accelerations were found
to be excessive high showing that for very light structures, this consideration is extremely important.
Also, it was seen that modifying the structural design increasing the stiffness and mass resulted in
comfortable structures without the necessity of use SDA.