Resonance monitoring is an established method for detecting deteriorat
ion in materials in accelerated aging tests. Current ASTM practice mon
itors a single resonance. If more than one resonance is monitored it b
ecomes possible to distinguish localized deterioration from general de
terioration, to identify the specific locations of deterioration, and
to recognize anticipated deterioration events. Data on location of det
erioration is important in durability tests for assemblies where a dis
tinction between materials failures and failures due to stress concent
ration is needed. Relations for the interpretation of changes in reson
ance as location of deterioration are developed A laboratory study of
condition monitoring by resonance in fatigue loading of a welded steel
frame is reviewed. A potential application for resonance monitoring i
n building assemblies is outlined.