Restrepo and Rahman 2007
A jointed precast cantilever wall is studied for is capability to rock about the foundation without loss of structural integrity. Current design recommends anchoring walls causing plastic hinges to form in response to inelastic behavior. This can result in costly repairs due to structural damage during a seismic event. The proposed system allows uplift upon the foundations which is countered by gravity loading and prestressed unbonded tendons. Energy dissipation is also provided by longitudinal mild steel reinforcement crossing the joint between the walls and the foundations.
System Concept
Rocking hybrid walls, which are assembled with energy dissipators, allow for a nonlinear elastic response and display a stable flag-shaped hysteretic response. Lateral displacements force a separation gap at the wall-foundation beam connection. Longitudinal Mild steel reinforcement provides significant energy dissipation during this uplift and the gravity load and prestressed unbonded tendons provide the self-centering capabilities.
The energy dissipating devices are labeled as “dog-bones” which consist of machined mild steel reinforcing bars. Energy is dissipated through the section of the bar which is machined at a smaller diameter over a specified length in order to yield at a specified force. The bars are cast into the foundation and grouted into the walls during erection.
The life safety performance objectives for the research are as follows: prevent sliding shear at the wall base, preclude yielding of the tendons, avoid fracture of an energy dissipation device, prevent loss of integrity of the wall, and minimize significant loss of stiffness.
Experimental Study, Results and Discussion
Three half-scale precast concrete wall specimens were created to represent a wall in a 4-story building. Two of the three specimens were cast with energy dissipators. The walls were subjected to quasi-static reversed cyclic loading.
All of the performance objectives for the rocking hybrid walls were closely met. The rocking hybrid system allowed minimal structural damage during a major EQ without residual drifts. The efficiency of energy dissipation was exemplified by a 14% equivalent viscous damping ratio.
Reference
Restrepo, J. and Rahman, A. (2007). ”Seismic Performance of Self-Centering Structural Walls Incorporating Energy Dissipators,” Journal of Structural Engineering, 133, SPECIAL ISSUE: Precast-Prestreesed Concrete Structures under Natural and Human-Made Hazards, pp. 1560–1570.