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SUMMARYThis paper addresses the elastic dynamic response of simply supported bridges to ground motion in their transverse direction. The interaction between superstructure and support #exibilities is studied in a systematic manner for symmetric spans. The bridges are modelled as beams with uniformly distributed mass and elasticity, simply supported at the ends by elastic springs. It is shown that a dimensionless sti!ness index, which re#ects the relative sti!ness of the superstructure compared to the sti!ness of the substructure, completely de"nes the dynamic mode shapes of the model. Useful closed-form expressions, based on approximate shape functions, are derived for the dynamic parameters of the "rst mode, and their accuracy is assessed. The e!ect of the sti!ness index on these dynamic parameters is investigated. Numerical case studies are presented to illustrate the use of proposed equations in the seismic analysis of bridges.

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/npsi/ctrl?lang=en http://nparc.cisti-icist.nrc-cnrc.gc.ca/npsi/ctrl?lang=fr Access and use of this website and the material on it are subject to the Terms and Conditions set forth at http://nparc.cisti-icist.nrc-cnrc.gc.ca/npsi/jsp/nparc_cp.jsp?lang=en NRC Publications Archive Archives des publications du CNRCThis publication could be one of several versions: author's original, accepted manuscript or the publisher's version. / La version de cette publication peut être l'une des suivantes : la version prépublication de l'auteur, la version acceptée du manuscrit ou la version de l'éditeur. For the publisher's version, please access the DOI link below./ Pour consulter la version de l'éditeur, utilisez le lien DOI ci-dessous.http://dx.doi.org/10.1061/(ASCE) 0733-9445(2001)127:5(554) Journal of Structural Engineering, 127, 5, pp. 554-560, 2001-05-01 Local versus global ductility demands in simple bridges Alfawakhiri, F.; Bruneau, M. Local Versus Global Ductility Demands in Simple BridgesBy Farid Alfawakhiri 1 and Michel Bruneau, 2 Member, ASCE Abstract : This paper addresses the inelastic dynamic response of simply supported bridges to ground motion in their transverse direction. The effect of the relative substructure-superstructure flexibility on the inelastic response of bridges is studied for symmetric spans. The bridges are modeled as beams with distributed mass and elasticity, simply supported at the ends by elasto-plastic springs. An analytical extension of the common generalized single degree of freedom model into the inelastic range is presented. Flexibility of the capacity-protected structural elements is shown to add significantly to the ductility demand of the energy dissipating components of bridge systems. A simple method is developed to account for these flexibilities when assessing bridge response beyond its elastic range. Numerical case studies are presented to illustrate the new analytical tool.