Collapse assessment of concrete buildings : an application to non-ductile reinforced concrete moment frames

Existing reinforced concrete buildings lacking details for ductile response during earthquake shaking represent prevalent construction type in high seismic zones around the world. Seismic rehabilitation of these existing buildings plays an important role in reducing urban seismic risk; however, with the massive inventory of existing concrete buildings and high costs of seismic rehabilitation, it is necessary to start by identifying and retrofitting those buildings which are most vulnerable to collapse. The collapse of most non-ductile concrete buildings will be controlled by the loss of support for gravity loads prior to the development of a side-sway collapse mechanism. “Gravity load collapse” may be precipitated by axial-load failure of columns, punching-shear failure of slab-column connections, or axial-load failure beam-column joints. In this dissertation, system-level collapse criteria are developed and implemented in a structural analysis platform to allow for a more accurate detection of collapse in these existing moment frames. Detailed models for primary components, which may precipitate gravity-load collapse of the concrete moment frame, are first required to achieve this objective and develop the collapse assessment framework. An analytical model based on mechanics is developed to reliably capture the lateral load–deformation response of a broad range of reinforced concrete columns with limited ductility due to degradation of shear resistance, either before or after flexural yielding. The robust collapse performance assessment could be used for many structural applications. In this dissertation, it is used to identify collapse indicators, design and response parameters that are correlated with “elevated” collapse probability. The collapse assessment framework is also used to identify the relative collapse risk of different rehabilitation techniques. Finally, the framework is used to estimate the impact of collapse criteria on the expected financial losses for existing concrete frame buildings in high seismic zones. This dissertation includes important contributions to (1) modeling techniques for components in existing concrete frames through the development of a mechanical model for existing concrete columns, (2) development of system-level collapse criteria, and (3) application of collapse fragilities in defining collapse indicators, improving loss estimation of existing concrete frames, and differentiating the collapse performances of existing and retrofitted concrete frames.