Reinforced Concrete Frame Connections Rehabilitated by Jacketing

Sergio M. Alcocer and James O. Jirsa


Little experimental work has been conducted to verify the performance of concrete jacketing of frame elements and it suitability as a rehabilitation technique. Designers of this scheme have faced the dilemna of analyzing and designing rehabilitated structures without guidelines. An experimental program was developed to evaluate the effectiveness of jacketing of frame elements. Four reinforced concrete large-scale frame connections with flexible columns were tested after being repaired or strengthened by jacketing only columns, or both columns and beams. The subassemblages represented an existing structure designed according to Mexican and American practices typical of 1950's construction with non-ductile detailing. The specimen condition prior to rehabilitation and the layout of the column longitudinal reinforcement were also varied. The subassemblages were tested to large deformation level applying a bidirectional cyclic loading history.

The prime objectives of the study were as follows:
1. The effect of jacketing on the hysterertic response of the subassemblages, especially with regard to stiffness degradation and energy dissipation.
2. The mechanism of joint shear resistance in rehabilitated connections with a special structural steel cage used to provide joint confinement.
3. The effect of damage due to prior loading on the response of a jacketed beam-column joint.
4. The influence of the layout of the column longitudinal steel, in particular with respect to bond along bars bundled or in the corner of the column jacket or distributed along the face of the column.
5. The slab participation in the positive and negative moment capacities of the floor system.
6. The constructability of the jacketing scheme.

The program was part of the coordinated research effort between Mexican and American engineers implemented after the 1985 Mexico earthquake, and sponsored by the National Science Foundation (USA) and Consejo Nacional de Ciencia y Technologia (Mexico).

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