Behavior of single headed anchors placed in plastic hinge zone of reinforced concrete columns (Phase V)

Concrete members are expected to develop cracks and concrete spalling in an earthquake, as observed in laboratory tests and previous earthquakes. On the other hand, the current building codes and design guidelines for anchors are based on experimental tests of anchors cast/post-installed in concrete that experiences controlled minor damage (i.e., crack opening up to around 0.04 in.). Therefore, engineers are left with no guidance when designing the embedded connections in concrete walls, where substantial concrete damage is expected, as the Appendix D of ACI 318-11 states, “The provisions of Appendix D do not apply to the design of anchors in plastic hinge zones of concrete structures under seismic loads.” The tests in Phase II and Phase III of the NEES-Anchor project indicated that the key role of reinforcement, in addition to carrying the forces from the anchors, is to protect concrete around the anchors from splitting, breaking out, and crushing. This understanding has led to alternative designs and detailing for the anchor reinforcement. The focus of the Phase V tests were to 1) observe the behavior of anchors in plastic hinge zones the proposed anchor reinforcement; 2) verify the load transfer mechanism of the anchor reinforcement; and 3) identify the key parameters for the desired performance of anchors in plastic hinge zones.