You will find information about the stability of steel box beams in
Guide to Stability Design Criteria for Metal Structures
5th ed.
Theodore V. Galambos
Wiley.
The current prevalent approach seems to be to ensure bracing action at panel points and then the longitudinal stiffeners plus compressed plate be checked as a column.
If you simply want to design steel box beams not requiring nor transversal nor longitudinal stiffeners nor related considerations, then the LRFD specification might be enough. You can download it for free from
