Abstract
This paper aims at pointing out some misconceptions concerning the evaluation of the walking-induced dynamic response of footbridges, and their impact on design procedures. First, a review of the existing Code provisions is briefly presented. In particular single-walker models and multiple-walker models are addressed; in doing so, models originally presented in different forms are made homogeneous for the purpose of comparison; their limits of applicability and advantages are pointed out. Then, the response of six steel box girder footbridges with different spans is evaluated following the provisions of existing Standards and Guidelines, and compared with allowable comfort levels. The comparison showed a wide scatter of the results, revealing some inconsistencies of the procedures, and underlining a clear need for their critical revision.
Highlights
Footbridges, especially if built within urban areas, are taking an ever-growing importance both from the functional aspect point of view and for the role of architectural icons they are often given.The modest live loads considered in the design process allow sizing extremely slender structures, with low stiffness and low damping; this brings the risk of unacceptable pedestrian-induced vibrations
Natural walking frequency is reasonably described by a Gaussian distribution with a mean of 2 Hz and a Standard Deviation of approximately 0.20 Hz (Matsumoto et al 1978, Ricciardelli, Pansera 2010)
There is still need for clarifying what real improvements have been achieved in design procedures, as current approaches lead
Summary
Footbridges, especially if built within urban areas, are taking an ever-growing importance both from the functional aspect point of view and for the role of architectural icons they are often given.The modest live loads considered in the design process allow sizing extremely slender structures, with low stiffness and low damping; this brings the risk of unacceptable pedestrian-induced vibrations. The necessity follows from providing the structural engineer with methods of dynamic analysis and reliable comfort criteria. The issue of the evaluation of the dynamic response of footbridges subjected to human-induced loads was first introduced more than a century ago by Tilden (1913). This was a pioneering work, where most of the aspects of human loading of structures seem to have already been recognized, though not quantified. For many following decades most of the design procedures have been exclusively based on the application of static vertical loads
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