Seismic analysis and retrofit of non-ductile reinforced concrete frame buildings

In many regions of the United States, especially the eastern and central regions, there exist thousands of non-ductile reinforced concrete frame buildings that were designed and constructed during the 1940's through 1960's primarily to resist gravity loads only or gravity plus wind loads. Many of the construction details in these buildings do not satisfy modern code requirements for earthquake resistance. Recent earthquakes in Mexico and Turkey caused severe damage of similar buildings. Therefore, it is a great concern that the strength, ductility, and energy dissipation capacity of these buildings may not be adequate to sustain earthquake-induced loads in these seismic regions. This research addresses how non-ductile reinforced concrete frame buildings behave and perform in an earthquake, whether they are adequate to resist earthquakes, and if not adequate, how to retrofit them for earthquake resistance.; The main objectives of this research are: (1) to identify structural details and features of non-ductile reinforced concrete frame buildings; (2) to study the inelastic seismic behavior and evaluate the seismic performance of non-ductile concrete buildings; (3) to evaluate ways to retrofit non-ductile concrete buildings to improve their seismic resistance; (4) to provide a method to evaluate the seismic performance and retrofit of non-ductile reinforced concrete buildings.; 3-story and 12-story prototype office buildings, designed using either the working stress design method or the ultimate strength design method were analyzed to study the inelastic behavior of the buildings under lateral forces. Methods for modeling non-ductile behavior were developed. The strength and ductility capacity of the buildings were determined. The seismic performance of each buildings was evaluated by comparing the ductility capacity with the ductility demands estimated from single degree-of-freedom design spectra. A seismic retrofit approach was established and evaluated.; It is concluded that the inelastic behavior of non-ductile reinforced concrete frame buildings is strongly affected by non-ductile behavior at local critical regions. The flexural strength and ductility of the columns control the overall strength and ductility capacity of the prototype frame buildings. Pullout of girder bottom longitudinal reinforcement from girder-column joints limits the base shear capacity of the 12-story prototype buildings. The seismic performance of the prototype buildings depends on the number of stories, design method, and soil conditions. Many existing column jacketing techniques are appropriate for the levels of ductility improvement required for seismic retrofit of non-ductile reinforced concrete frame buildings in the eastern and central United States. A procedure was established for seismic retrofit of the non-ductile buildings for practicing engineers engaged in the seismic retrofit of actual structures.