@Article{ 
  pertom07,
  author = { Percivale, Danilo and Tomarelli, Franco },
  title = { A variational principle for plastic hinges in a beam },
  journal = { Math. Models Methods Appl. Sci. },
  year = { 2009 },
  volume = { 19 },
  number = { 12 },
  pages = { 1-34 },
  URL = { http://cvgmt.sns.it/paper/1281/ },
  note = { cvgmt preprint}
}