1st Croatian Conference on Earthquake Engineering 1CroCEE 2021

Earthquake swarms are catastrophic events that affect the global strength, stiffness and ductility of existing reinforced concrete (RC) structures due to the effects of damage accumulation. Such multiple excitations can be more critical if RC buildings are exposed to highly aggressive environments. In this study, the seismic performance of a four-story RC framed structure exposed to corrosion and subjected to multiple earthquakes is assessed and compared in terms of fragility. A finite element model for the RC frame is adopted and implemented in an advanced software platform for seismic simulations. To provide a complete prediction and understanding of structural response uncertainties, the geometrical and the mechanical properties of steel and concrete constitutive models are defined independent random variables with specific probabilistic distributions. The long-term exposure to aggressive environments is simulated through the pitting corrosion with its probabilistic time initiation and propagation. Such pitting corrosion is applied to beams and columns.
Montecarlo simulations are then performed to investigate the seismic performance of the testbed RC frame through Incremental Dynamic Analyses (IDA). The chord rotation and shear forces of RC components, accounting for brittle and ductile mechanisms, are used as engineering demand and capacity parameters. The robust fragility assessment is then conducted for a range of seismic intensity, i.e., (a) the spectral acceleration for the first fundamental frequency of the structure and (b) the modified spectral acceleration intensity accounting for the elongation period. Finally, the fragility assessment of environmental marine exposure is presented and compared to the pristine structure.