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Traditional retrofit methods typically focus on increasing strength/stiffness of the structure. This may increase seismic demand on the structure and could lead to excessive damage during a seismic event. This paper presents an alternative retrofit method which integrates concepts from selective weakening and self-centering (rocking) to achieve low seismic damage for substandard reinforced concrete shear walls. The proposed method involves converting traditional cast-in-place built shear walls into rocking walls, which softens the structure, while allowing re-centering. Laboratory tests were performed to validate the retrofit concept on a benchmark wall specimen designed to pre-1970s standards. Observations from the test showed minimized damage and excellent recentering in the retrofitted wall. Additional testing was carried out to verify a novel anchorage scheme for post-tensioning elements, required to implement the proposed retrofit. Ultra-High-Performance Concrete (UHPC) was judiciously used to minimize damage and optimize the retrofit process. 

Precast concrete shear walls with unbonded post-tensioning, which resist seismic loads have attracted the attention of researchers over the past 20 years. This study provides a database of a special subset of precast concrete shear walls tested under monotonic or cyclic loading: rocking walls, hybrid walls, and walls with end columns. These shear walls experience joint opening, undergo rocking motion over the foundation, and utilize unbonded post-tensioning to self-center after load removal. Seismic energy is dissipated in distinct ways that vary from nonlinearity of concrete and post-tensioning strands (rocking walls) to yielding of mild steel reinforcement or external energy dissipaters (hybrid walls and walls with end columns). The experimental drift capacity, strength, and damage sequence of walls from the literature were compiled. Onsets of cover concrete spalling, yielding of energy dissipaters, yielding of post-tensioning strands, fracture of energy dissipaters, and crushing of confined concrete were reported. ACI guidance on shear walls were evaluated by comparing the lateral drift and strength measured by testing and predicted by ACI. 

This paper describes the fabrication and assembly of tessellated precast reinforced concrete shear walls. These walls are being constructed and tested as part of an NSF-funded research project designed to demonstrate the concept of Tessellated Structural-Architectural (TeSA) systems. The over-arching goal of this research is to explore tessellation patterns that can be implemented on a large scale, are architecturally appealing, and provide structural function. TeSA systems are comprised of individual tiles arranged in tessellations, or repeating geometric patterns. Tiles are topologically interlocking, which means that they transfer forces due to their interlocking geometry rather than through a bonding adhesive. The benefit of such a system is the ability to localize failure and rapidly repair the individual damaged tiles, rather than the entire system. The specimen discussed in this paper is a precast concrete shear wall constructed from individually cast I-shaped tiles. Shear wall tests are forthcoming; this paper focuses instead on documenting technical solutions to difficulties faced during design, fabrication, and assembly of the test specimen. This paper is intended to provide lessons learned to others who are designing and building TeSA walls and thereby facilitate the benefits of these novel systems.