The effect of post-tensioning force magnitude and eccentricity on the natural bending frequency of cracked post-tensioned concrete beams

Abstract

The effect of prestress force magnitude on the dynamic properties of uncracked prestressed concrete structures is something that has been widely debated among researchers to date. The effect of pre- and post-tensioning force magnitude on the natural bending frequencies of cracked prestressed concrete structures is something that is more established, and widely agreed upon. This paper describes the results of dynamic impact testing on damaged post- tensioned concrete beams. The natural bending frequency of the cracked beams were determined through experimental modal analysis. Dynamic impact response signals were obtained at different levels of post-tensioning force for the cracked beams. The Fast Fourier Transform was implemented and a peak picking algorithm was subsequently used to determine the natural bending frequencies of the beams. The relationship between prestressing force and natural frequency for both the cracked and uncracked beam sections was determined. The results for the cracked beams were compared to the results for the same uncracked beam sections. A marked difference in vibration behaviour was observed for the cracked beams between the nonfully prestressed and the fully prestressed case. Conclusions from the study are drawn and have profound implications in the fields of system identification and structural health monitoring in pre- and post-tensioned concrete structures.