Investigation of the concrete parameters of existing RC buildings by operational modal analysis

This study is performed to answer the question: can the concrete class of an existing reinforced concrete (RC) building be determined by operational modal analysis (OMA)? The answer to the question is important since the performance assessment of an existing building starts with a material investigation performed with several concrete coring depending on the size of the building. This part is probably the most intrusive especially for the owners of the buildings. In the past three decades, OMA became the main non-destructive testing activity for the determination of dynamic characteristics of existing structures and its results were used for different aims including one, examining the elastic modulus of materials contributing to the stiffness of the systems. Although the direct relationship between the modulus of elasticity and compressive strength for concrete gives the sign of the possibility of using OMA to evaluate the concrete class in RC buildings, some aspects stand as a barrier to limiting its application. The first one is related to the definition of the elastic modulus of concrete which is not constant in nature. The second one is the stiffness contribution of infill walls and other nonstructural elements which affect the dynamic characteristics of the existing buildings. In this study, after elaborating on these aspects, the regular procedure has been applied in two different phases of two existing RC buildings. The independent evaluations performed for each phase of the buildings gave misleading results while an interactive algorithm working on two phases of each building gave better outcomes. The results also indicated some possibilities in using the OMA results for an estimation of concrete parameters in RC buildings.