Pre-1970 RC Corner Beam-Column-Slab Joints: Seismic Adequacy and Upgradability with CFRP Composites

Abstract eng:
This paper investigates experimentally the adequacy of corner beam-column joints in pre-1970 reinforced concrete buildings and determines the efficacy of carbon fiber-reinforced polymer (CFRP) composites for both pre- and post-earthquake retrofit of such joints. Four full-scale corner beam-column-slab specimens built with pre-1970 reinforcement details were subjected to a reverse-cycle bidirectional displacement history consisting of alternate and simultaneous cycles in the two primary frame directions before and/or after retrofit. Two of the specimens were first subjected to severe and moderate levels of damage, respectively, then repaired by epoxy injection, and strengthened by adding a #7 reinforcing bar within the clear cover at the column inside corner and by externally bonding multiple layers of CFRP to the beams, columns, and joint. Two other specimens were strengthened in their as-built condition. The results indicated that pre-1970 corner joints are severely inadequate to survive drift ratios of around 2% typically envisioned to occur during design earthquakes, and they cannot meet the FEMA 356 Life Safety and Collapse Prevention performance levels. It was shown, however, that such joints can be upgraded regardless of the level of existing earthquake damage to achieve a “rigid” joint behavior up to drift ratios of at least 2.4% applied simultaneously in both primary directions (i.e., 3.4% bidirectional drift) and to achieve joint shear strength factors larger than that used with seismically designed, codeconforming corner joints.

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