Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: A qualitative explanation of the origin of torsional instability in
  suspension bridges   We consider a mathematical model for the study of the dynamical behavior of
suspension bridges. We show that internal resonances, which depend on the
bridge structure only, are the origin of torsional instability. We obtain both
theoretical and numerical estimates of the thresholds of instability. Our
method is based on a finite dimensional projection of the phase space which
reduces the stability analysis of the model to the stability of suitable Hill
equations. This gives an answer to a long-standing question about the origin of
torsional instability in suspension bridges.

34
The categories of this paper are: chem-ph
15
The categories of this paper are: nucl-ex
16
The categories of this paper are: stat
11
The categories of this paper are: hep-lat
22
The categories of this paper are: chao-dyn
19
The categories of this paper are: eess
30
The categories of this paper are: q-alg
3
The categories of this paper are: physics
32
The categories of this paper are: atom-ph
37
The categories of this paper are: supr-con
6
The categories of this paper are: astro-ph
12
The categories of this paper are: nucl-th
0
The categories of this paper are: hep-ph
1
The categories of this paper are: cs
8
The categories of this paper are: hep-ex
31
The categories of this paper are: ao-sci