Prior to the LRFD 4th Edition with 2009 interims, LRFD 5.9.4.2.1 required a Service I compression stress evaluation for live load and one-half the sum of effective prestress and permanent loads. This requirement effectively changed the DC load factor in the Service I limit state from 1.0 to 0.5. To avoid confusion, we added a new combination named Service IA. The Service IA limit state combination was used to evaluate the compression stress limitation.

AASHTO LRFD 4th Edition, 2009 interim provisions moved the previously mentioned compression stress limitation from LRFD 5.9.4.2.1 to LRFD 5.5.3.1. The limit state combination used to compute the compression stress was changed from Service I using half permanent loads (which we called Service IA) to Fatigue I.

For all intents and purposes, the Service IA and Fatigue I limit state are the same.