Dynamic Properties of Low-Rise Concrete Walls Reinforced with Conventional Reinforcement or Steel Fibers

Experimental modal analysis allows characterizing the dynamic properties of structures from measurements of both the input forces and the structural response, which is known as the multiple input multiple output method (MIMO). This paper assesses the change of dynamic parameters obtained experimentally as a function of the maximum drifts and the type of web shear reinforcement of reinforced concrete (RC) and steel-fiber reinforced concrete walls emulating the first-story of a two-story house. The modal identification was carried out using the MIMO system, transfer functions—TF, and time window transfer functions—TWTF methods. The experimental program includes the response measured during shaking table tests of twelve isolated concrete walls subjected to acceleration records representing earthquakes with moment magnitudes of 7.1, 7.7, and 8.3. Six of the concrete walls were conventionally reinforced in the web using deformed bars or welded-wire mesh, and six concrete walls were reinforced with steel fibers. Results showed that the average differences in the identified natural frequencies with the MIMO system and the TF and TWTF methods were 2% and 4%, respectively. The frequencies of the walls estimated using the three methods ranged approximately between 6.5 and 3.5 Hz for drifts of up to 0.35%. It was observed that the level of drifts affected the fitting accuracy for the MIMO system, being more significant in RC walls. Therefore, dynamic parameters estimated using the MIMO system should be carefully verified for drifts higher than 0.7%.