Experimental and analytical study of seismic damage and retrofit of lightly reinforced concrete structures in low seismicity zones

A one-third scale model of a typical gravity load designed low-rise reinforced concrete frame building (lightly reinforced concrete structure) in the Eastern and Central United States was tested on the shaking table at the State University of New York at Buffalo Earthquake Simulation Laboratory. No considerations were made for seismic resistance and the general non-seismic detailing provisions of ACI-318 were used for the design. The model is a three story, one-bay by three-bay, office building and represents the critical interior bay of the prototype building. A series of varying intensity ground motions were performed on the shaking table using the scaled Taft N21E accelerogram to represent minor, moderate, and severe earthquakes. The dynamic characteristics of the model after each seismic event were determined from a white noise identification shaking table test. It is shown that gravity load designed structures have some inherent strength for resisting seismic forces. However a weak column-strong beam behavior is evident in the response and large story drifts, beyond 2% of the story height (exceeding current code recommended limits), develop during strong earthquakes.;Analytical models are developed to predict the seismic response of the model building based on identified member properties from engineering approximations, component tests, and an experimental response fit. It is shown that the response predictions based on integrating the behavior from component tests provide adequate correlation of the seismic structural response behavior, thus verifying the importance of component testing.;A damage evaluation of the model is performed analytically to assess structural integrity after the induced ground motions in terms of damage states. A modified damage model is proposed to incorporate the additional damage from P-delta effects in columns.;Several local and global retrofit techniques are proposed for repair and enhanced seismic resistance of lightly reinforced concrete frame structures. An analytical seismic evaluation is performed for each retrofit alternative on the existing damaged model based on member properties from engineering approximations. One retrofit alternative is performed on the model based on the analytical seismic performance and retrofit constructability. The retrofitted model was then tested on the shaking table under the same moderate and severe earthquakes previously performed. It is shown the retrofitted model performed adequately and was governed by a desirable strong column-weak beam behavior during the shaking.;An analytical model is developed to adequately predict the seismic response of the retrofitted model building based on integrating the identified member properties from retrofitted component tests. An analytical damage evaluation of the retrofitted model is also performed.