Study on Interaction between Rocking-Wall System and Surrounding Structure

Abstract

Reinforced concrete (RC) special structural walls have proven to be an effective means of resisting lateral loads in structural systems. They are detailed to dissipate energy through the development of plastic hinge regions. Although few buildings with special structural walls have collapsed in recent earthquake events greatly limiting the number of casualties, tremendous economic loss has been encountered due to irreparable structural damage. Compared to special structural walls, rocking-wall systems have demonstrated superior seismic performance with excellent self-centering and greatly reduced damage. This innovative structural system was proposed decades ago, but limited effort had been put into investigating the interaction mechanism between rocking-wall systems and the surrounding structure (e.g. floors and columns). This limitation has prevented this system from becoming popularized in practice. Two large-scale structural assemblages, which consisted of rocking-wall systems and surrounding structures, were tested under quasi-static loading to investigate the interaction mechanism. A PreWEC (Precast Wall with End Columns) system was used as the rocking-wall system in the two tests. The PreWEC system consisted of a rocking wall and end columns adjacent to the wall with energy dissipating elements “O-connectors” connecting the two components together. A surrounding rigid-connected structural system constructed using cast-in-place concrete was used in test specimen PFS1. The structure was designed to investigate an upper bound interaction between the PreWEC system and the surrounding structure. It featured gravity columns and an unbonded post-tensioned floor system with rigid wall-floor connections. PFS1 exhibited reasonable self-centering characteristics and excellent energy dissipating capabilities. Although some localized damage occurred to the floor adjacent to the wall ends, fast re-occupation of the structure was possible with little damage to the wall and structural integrity of the floor maintained. Three-dimensional constraint effects of the floor on the rocking wall were found to be significant in the test, especially when transverse constraint from parallel structural elements existed close to the wall. A three-dimensional numerical model of the unbonded post-tensioned floor was proposed and validated using the test data. Design recommendations for the rigid wall-floor connections were proposed to alleviate the damage to the floor. A surrounding precast structural system was used in test specimen PFS2 designed to minimize the interaction between the PreWEC system and the surrounding structure. It featured precast edge columns and a floor system formed by precast untopped planks. Special precast wall-floor connections that isolated the floor from the vertical movement of the wall were used in PFS2. The existence of the end columns provided a unique gravity load transfer path toward the wall frame line, while isolating the floor from the wall. This greatly increased the flexibility in floor-plan layout and space planning of the building. PFS2 was almost “damage-free” and “self-centered” after the design drift (2%), thus immediate re-occupation of the precast structure might be feasible after seismic events. Design recommendations were proposed for the end columns, the special wall-floor connections and the plank-beam connections, which were key components in the precast rocking-wall structure. Although the base moment of the PreWEC system used in PFS1 was similar to that used in PFS2, the strength and the energy dissipation capacity of PFS1 were much larger than those of PFS2. The gravity load transfer path and constraint effect from surrounding structure were the two key factors that contributed to the difference. A general criterion that accounts for both factors is proposed to ensure the self-centering of rocking-wall structures. The advantages and disadvantages of using the rigid or the special isolation wall-floor connections are summarized. Design recommendations for rocking wall panels, energy dissipating elements, and the interface grout layer are presented.