434 CHAPTER 15 Bending of Open and Closed, Thin-Walled Beams
Fig.15.9
Notation and sign convention for forces, moments, and displacements.
Fig.15.10
Internal force system.
system.Theformersystem,whichweshalluse,hastheadvantagethatdirectandshearloadsarealways
positiveinthepositivedirectionsoftheappropriateaxeswhethertheyareinternalloadsornot.Itmust
berealized,though,thatinternalstressresultantsthenbecomeequivalenttoexternallyappliedforces
andmomentsandarenotinequilibriumwiththem.