EXPERIMENTAL TESTING OF A LIGHTLY REINFORCED CONCRETE SHEAR WALL

This project report summarizes the findings of a half-scale laboratory test on a slender lightly reinforced concrete (LRC) shear wall subjected to cyclic loading. LRC shear walls, specifically those of pre-1980’s type design, have longitudinal and horizontal reinforcement ratios near the code minimum, while often lacking confinement in the wall end-zones. These walls are thought to exhibit brittle compressive failure mechanisms such as rebar buckling or concrete crushing based on observations from past earthquakes. Non-ductile concrete buildings are a large contributor to earthquake losses around the globe, as noted in the San Fernando (1971) and Christchurch (2011) earthquakes, to name a few. In the U.S., buildings constructed before the 1976 UBC are at risk for collapse and pose a significant threat to occupant life-safety and community resilience. Thus, there is pressure among structural engineers to create feasible and economical design solutions to address these non-ductile concrete performance issues. The wall test performed in this paper reproduced a unique failure mechanism of LRC walls tested at the University of Auckland, University of Illinois, and the University of Canterbury where there is limited distribution of plasticity, such that there are few, wide primary cracks and secondary cracks do not develop. Also, several of these tests (Cal Poly and Auckland) exhibits higher than anticipated displacement ductilities due to rocking at the wall-foundation interface. The experimental test results from this project enable the examination of current industry practice for conducting a nonlinear analysis of LRC walls as discussed in Doan & Williams (2020)

Feasibility of a Fiber Reinforced Polymer Retrofit for Non-Ductile Concrete Walls

A significant number of pre-1980’s non-ductile reinforced concrete (RC) structures in California have been identified as deficient, many of which utilize RC shear wall systems to resist earthquake lateral forces. These non-ductile wall systems are typically lightly reinforced and lack adequate boundary element detailing. Engineers suspect these walls to susceptible to brittle, compression-controlled failure modes due to damage from concrete crushing and bar buckling. As a result, one approach designers are taking is to seek fiber reinforced polymer (FRP) retrofit solutions that improve the compression capacity of high-stressed wall end zone regions based on effectiveness of these approaches with columns. This paper presents the initial results from a lightly reinforced RC shear wall test without boundary elements intended to be representative of a vintage wall. The experimental test showed that the expected compression-type damage mechanisms were not the primary contributors of wall failure. Rather the failure was attributed to the development of few, large crack planes near the base of the wall and the fracture of most longitudinal bars at the wall-foundation interface. Additionally, the drift capacity was greater than anticipated. Therefore, the original proposed fiber reinforced polymer (FRP) retrofit developed by the authors in collaboration with industry input – wrapping the wall end zones with FRP sheets and thru-wall splay anchors to improve the compression capacity of these regions – may not be a viable approach. The research findings suggest that additional investigations into FRP solutions are necessary for different classes of non-ductile walls and their respective failure types