Health monitoring of civil infrastructures has achieved considerable importance in recent years, since the failure of these structures can cause immense loss of life and property. This paper presents the health monitoring of a plate girder of an observation tower located at Chennai. The observation deck was constructed over 94m above the ground level with concrete stem and large cantilever steel composite floor decks forming a bowl shape at the top. There are five floors, in which the fifth floor is having a butterfly shaped truss and each floor consist of 14 girders. The strains in the radial steel girders located at 102 m level due to upper floor construction were measured using electrical strain gauges. Readings were taken for a total duration of 500 days.