The theoretical approach was based on the theory of bending of orthotropic thin plates was used to obtain the governing differential equation. The strain energy stored in a plate element due to bending, twisting and the mid-plane force was obtained. Expressions of the exact frequency equations for stiffened plate model having a straight line array of spot welding with and without the effect of residual stresses for the cases: C-C-C-C, C-S-C-C, C-S-C-S, S-S-S-S, S-C-S-S, C-S-S-C, C-F-C-C, C-F-S-C, S-F-S-C were obtained. A numerical analysis of spot welding process using finite element method...