  The main purpose of the present paper is to compare two different kinds of
approaches in modeling the deck of a suspension bridge: in the first approach
we look at the deck as a rectangular plate and in the second one we look at the
deck as a beam for vertical deflections and as a rod for torsional
deformations. Throughout this paper we will refer to the model corresponding to
the second approach as the \textit{beam-rod model}. In our discussion, we
observe that the beam-rod model has more \textit{degrees of freedom} if
compared with the isotropic plate model. For this reason the beam-rod model is
supposed to be more appropiate to describe the behavior of the deck of a real
suspension bridge. A possible strategy to make the plate model more efficient
could be to relax the isotropy condition with a more general condition of
orthotropy, which is expected to increase the degrees of freedom in view of the
larger number of elastic parameters. In this new setting, a comparison between
the two approaches becomes now possible.
  Basic results are proved for the suggested problem, from existence and
uniqueness of solutions to spectral properties. We suggest realistic values for
the elastic parameters thus obtaining with both approaches similar responses in
the static and dynamic behavior of the deck. This can be considered as a
preliminary article since many work has still to be done with the perspective
of formulating models for a complete suspension bridge which take into account
not only the deck but also the action on it of cables and hangers. With this
perspective, a section is devoted to possible future developments.
