A damage analysis of steel-concrete composite beams via dynamic methods. Part I: Experimental results

This paper is an experimental investigation on damage-induced changes in modal parameters of steel-concrete composite beams subject to small vibrations. Dynamic tests have been performed on two pairs of composite beams, whose connections have different linear densities, and three damage configurations for each beam have been analyzed. Damage was induced by removing concrete around some elements connecting the steel beam and the reinforced concrete slab and consequently causing a lack of structural solidarity between the two beams. Experiments revealed that: (i) unlike axial frequencies, flexural frequencies show a rather high sensitivity to damage and therefore can be considered as a valid indicator upon a diagnostic analysis; (ii) induced damage causes the nodes of flexural vibration modes to displace towards the damaged area; (iii) in addition to hindering relative sliding on the concrete-steel interface, the elements connecting the slab and the metallic beam play a key role in reducing transversal motions between the two beams. These experimental results were crucial to outline an accurate analytical model of the dynamic behavior of composite beams with damaged connectors and to formulate a diagnostic problem from dynamic test data. Part II of this research will deal with mechanical modeling of damaged composite beams and damage identification.