Evaluation of Seismic Retrofit of Reinforced Concrete Frame Structures: Part I: Experimental Performance of Retrofitted Subassemblages
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This report is Part I of a two part series on the evaluation of seismic retrofit methods for reinforced concrete frame structures. It deals with the experimental behavior of retrofitted reinforced concrete column elements and beam-column joint subassemblages under reversed cyclic lateral loading. A seismic retrofit/rehabilitation redesign methodology was developed, and validated in the present experimental study. Two column specimens, a one-way beam-column subassemblage and a two-way beam-column-slab subassemblage, all originally designed in accordance with AC1-318 for gravity loads only (1.4D + 1.7L), were retrofitted and tested at increasing drift amplitudes. The original specimens possessed relatively weak columns with respect to the adjacent beam strength. The retrofitted column specimens showed increased strength and a ductile post-yield behavior. Longitudinal bar buckling in the columns and low cycle fatigue failures as seen in the original/as-built specimen tests were entirely averted in the retrofitted specimens. The beam-column joint and the subassemblage retrofit, though distinct, were successful at converting the specimen failure mechanisms to a desirable strong-column/weak-beam one. Comparisons are made between the displacement response of the original/as-built specimen tests and the present retrofitted test results. Conclusions are drawn on the efficacy of the retrofit schemes and the failure mechanisms observed.