Monitoring the dynamic properties of a reinforced concrete building through its seismic strengthening

Ambient vibration surveys have been applied on a five-story reinforced concrete residential building during its seismic retrofit. Inadequate seismic performance of the building has been upgraded by the conversion of its single footing to a mat foundation, the addition of shear walls as two separate cores, jacketing of columns and beams, and the addition of a layer over the existing slabs. Five columns of the building have also been removed due to added cores. Starting from the original phase of the building, eleven sets of acceleration measurements have been recorded and analyzed until the completion of all construction works. Frequency domain methods have been used for system identification. The findings clearly showed the frequency decreases as the result of structural operations decreasing the stiffness of the building, such as partition wall demolition and column removal, while the seismic strengthening works, such as column jacketing and core addition increased the dominant frequencies of the building. The comparisons between the extracted modal frequencies revealed the effects of the performed construction works on the dynamic behavior of the building. Finite element models were also constructed for the original and retrofitted phases of the building. Thereby, the main aim of the study was accomplished by quantified experimental and numerical findings.