Characterization of fish-bone type RC wall buildings througth analytical fragility functions

The seismic behavior of reinforced concrete (RC) buildings during the last decade has been successful in terms of preventing the overall or partial collapse and protecting human life. However, high-intensity earthquakes have produced significant damage to this kind of structures. For example, after the 2010 Chile earthquake, extensively localized brittle damage was observed in RC wall buildings. This rupture mechanism was characterized by concrete crushing and buckling of the vertical reinforcement. Most of the damage occurred in the lower stories of medium-rise buildings constructed after the year 2000 and was due in part to the use of thin unconfined RC walls subjected to high axial load ratios. Although significant damage was observed in only approximately 2% of the stock of RC wall buildings taller than nine stories, there are many other buildings with almost identical structural characteristics to the damaged ones that presented minor damage, or that did not present damage at all. Therefore, it is necessary to understand and quantify the vulnerability of this large number of buildings that may be prone to suffer the same type of brittle failure by future
seismic events.

This research is focused on medium-rise RC wall buildings with floor plans commonly used for residential buildings in Chile and other seismic countries. These buildings have a plan configuration that resembles that of a “fish-bone” structure, with long corridor walls in the longitudinal direction and perpendicular walls in the transverse direction. Although this typology is widely used in seismic regions around the world, its characterization through analytical or empirical fragility and vulnerability functions is poor. Available characterizations are based mainly on over-simplified models that cannot accurately represent the complex 3D behavior of this type of buildings. Thus, this research aims to develop analytical fragility functions based on simplified but accurate models validated with sophisticated 3D inelastic finite element models of a real building.

Analytical fragility functions are built from inelastic finite element models of representative building slices modeled using the software DIANA. Two different building conditions are analyzed in this study. First, the typical Chilean buildings constructed between 2000 and 2010 are considered, characterized by thin unconfined RC walls. Second, confined RC wall buildings are evaluated, which represent the new constructions built after the changes in Chilean seismic code in 2011, are evaluated. Incremental dynamic analysis is performed with the use of a series of ground motion records from the 2010 Chile earthquake. Engineering demand parameters are calculated and related to damage measures, in order to obtain fragility functions, considering various damage states: slight, moderate, extensive, and complete. The results of this research could be used to develop a robust analytical framework for vulnerability
assessment of RC wall buildings constructed before and after the 2010 earthquake and evaluate the effects of the changes in Chilean seismic code.