Reinforced Concrete Rocking Walls With Energy Dissipating Devices and Base Armoring

John Barkley

doi:10.7273/000005150

Conventional reinforced concrete walls are designed to yield and sustain damage at the base but have sufficient deformation capacity not to fail in design-level earthquakes. While this approach is intended to provide life safety, the damage to the wall during earthquakes may result in the need to repair the wall. A low-damage concrete wall concept was the focus of this study. In this concept, the wall was discontinuous at the base, which allows for rocking. Base armoring at the toes mitigates concrete crushing and a replaceable energy dissipating connector at each end of the wall connects it to the footing. Post-tensioning was not used. A test was conducted on an energy dissipater using demands from a standard reversed-cyclic protocol used for seismic tests. The individually tested energy dissipater reached a strain before fracture that was estimated to correspond to 4.0% wall drift. Minimal pinching and cyclic strength degradation was observed in the stress-strain hysteresis for the dissipater. Following the dissipater test, a wall was designed, constructed, and tested under fully reversed cyclic lateral loading. The wall was half-scale with two curtains of transverse and longitudinal reinforcement, satisfying ACI 318-19 minimum reinforcement ratios. It was tested as a cantilever with constant axial gravity load of 0.09Agf’c. 4.0% drift was reached with minimal damage observed in the wall. Fracture of an energy dissipater occurred during the negative excursion of the first cycle at 4.0% drift. The extent of base armoring, which was intended to include the length of the compression block and height of the plastic hinge, was sufficient to prevent crushing of toe concrete without the use of special boundary element reinforcement. The load-displacement hysteretic response was flag-shaped. Strength loss was not observed, with the exception of minimal strength loss for repeated cycles at a given drift increment. An analysis of the backbone curve also showed that post yield effective stiffnesses of the wall was similar to other post tensioned walls with dissipating devices. The favorable performance of the tested wall suggests that longitudinal post-tension tendons are not needed, although use of post-tensioning can provide re-centering. Exclusion of post-tensioning simplifies the design, reduces construction costs, and eliminates the need for inspection of the post-tension anchorages during the lifetime of the structure.

Reinforced Concrete Rocking Walls With Energy Dissipating Devices and Base Armoring

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