Influence of different damping components on dynamic response of concrete rocking walls
Precast concrete rocking walls with unbonded post-tensioning, as a seismic resilient system, dissipate energy imparted to them during an earthquake through inherent viscous damping, impact damping due to the wall rocking on top of the foundation, and any available hysteretic damping. A shake table study on eight rocking walls designed with different quantities of hysteretic damping ratio varying between 4% for a Single Rocking Wall (SRW) to 15% for a rocking wall system, known as PreWEC, with supplemental hysteretic dampers, i.e., O-connectors, generally demonstrated their satisfactory seismic performance during design-level and higher intensity earthquake motions. The test results confirmed lower participation of energy dissipation due to impacts as the hysteretic component increased. Larger hysteretic damping also led to a reduction in the maximum drift of rocking walls as well as the number of large drift excursions after the first peak of response. Using the area enclosed by the force-displacement hysteresis response of O-connectors, recommended design values for hysteretic damping of PreWEC systems are presented in this paper. While larger displacement amplitudes were achieved for the walls with lower hysteretic damping (i.e., SRWs), it is shown that the duration of their dynamic responses was reduced due to a negative rate of input energy in these rocking walls, which favorably removed a part of the seismic energy imparted to the system. Contrary to a common belief that rocking walls without additional damping devices are not dependable lateral load resisting systems, this paper concludes that these walls attract less seismic input energy and perform satisfactorily with a small amount of inherent damping, suggesting their potential application in seismic resistant structures.