This paper summarizes the application of a rational methodology for the structural assessment of existing reinforced concrete Tunisian structures which include bridges and wheat silos. This methodology is based on ambient vibration measurement of the structures, identification of the modal signature and finite element model updating. Detailed finite element models of the structures were first created to determine judicious locations of the measurement points. Ambient vibration tests were then conducted using a data acquisition system with nine force-balance accelerometers placed at selected locations. The Enhanced Frequency Domain Decomposition (EFDD) technique was applied to extract the modal signature of the structures. The finite element models were updated in order to obtain a reasonable correlation between experimental and numerical modal properties. The primary objective of the paper is to demonstrate the use of the EFDD technique to extract the dynamic characteristics of the selected structures from available operational response measurements. A secondary objective is to combine the measured modal signature with model updating for assessing the structural condition of the selected structure. The proposed methodology was applied to two case studies.