Case Study of Local Damage Indicators for a 2-Bay, 6-Storey RC-Frame subject to Earthquakes

A simulation study of a 2-bay, 6storey model test RC-frame(scale 1:5) subject to earthquakes is considered in this paper. Based on measured (simulated) storey accelerations and ground surface accelerations several indices for the storey damage, including interstorey drift, flexural damage ratios, normalized cumulative dissipated energy, Park and Ang's indicator, a low-cycle fatigue damage index and a recently proposed local softening damage index estimated from time-varying eigenfrequencies are used to evaluate the damage state of the structure after the earthquake. Storey displacements are obtained by double time-integration of the measured accelerations, and the storey shear forces are calculated by using a simple shear model, where the shear force at a given storey is determined as the summation of inertial forces in the storeys above. All the mentioned methods except for the latter require measurements at all storeys, whereas the time-varying frequencies can be estimated form a single measurement by using system identification in combination with a moving window technique. The estimated values of the various damage indicators are the compared with damage indicators calculated by the simulation program SARCOF from the time-varying stiffness matrix of the FE-model. Good correlation was found between the SARCOF damage indicator and the considered low cycle fatigue damage indicator, the flexural damage ratio, The Park and Ang indicator and the local softening damage indicator. In the considered case, the damage state of the two lower storeys can be characterized as very servere and in general this is displayed by the various damage indicators except for the normalized cumulative plastic deformation which shows far too low a damage level in the second storey.