Despite that piezoelectric ceramic lead zirconate titanate (PZT) has been used for structural health monitoring (SHM) in various engineering systems, limited work has been conducted on real size concrete structures. Beam-column connections are critical regions in reinforced concrete (RC) moment-resisting frame structures. The vulnerability of RC beam-column joints has been identified from structural damage investigations over the past decades, especially in the area of earthquake engineering. In the context of a terrorist bomb attack, the beam-column joints are very vulnerable, especially when the perimeter columns lose their load carrying capacity due to damage and the beam-column joints become one of the crucial load transfer mechanism of the structural frame. To avoid catastrophic failures, it is important to monitor beam-column joints under existing gravitational loads. In this paper, an experiment is carried out on four real size concrete frame structures with different detailing subjected to gradually increased loads. A number of PZT sensors are bonded to the frame structure to acquire PZT electro-mechanical (EM) admittance signature. The structural mechanical impedance (SMI) is extracted from the PZT EM admittance signature and its sensitivity is compared with that of the EM admittance. The relations between the damage index and the loading step and tip deflection of the concrete structure are obtained. Finally the sensitivity of the PZT sensors in detection of the critical loading level is discussed. The results show that the PZT sensors are capable of monitoring the integrity and behavior of the real size concrete structures.