@article{article4352029e,
title   = {Multiple scales analysis of nonlinear oscillations of a portal frame foundation for several machines},
author = {Brasil, Reyolando Manoel Lopes Rebello da Fonseca},
year = {1999},
doi = {10.1590/s0100-73861999000400007},
journal   = {Revista Brasileira de Ciências Mecânicas}
}