A floor pan assembly is disclosed that includes a side sill extending in a longitudinal direction that has a lower portion and a top surface. The floor pan may include a weld flange having a height H1 that is welded to the lower portion along a full length of the floor pan and an extended weld flange having a height H2 that is higher than H1 and welded to the top surface of the side sill along a limited length of the floor pan. The floor pan may also include a corrugated area integrally provided in the floor pan that includes a plurality of furrows and ridges that extend obliquely relative to the longitudinal direction.