Relevant findings on experimental behavior of exterior beam-column joints reinforced with plain bars under cyclic actions

One of the main challenges in framed Reinforced Concrete (RC) structures under seismic loads is the behavior of beam-column joints, as these elements experience high stresses during seismic events, which can lead to unexpected collapses due to brittle failure mechanisms. In Italy, many RC buildings constructed before the mid-1970s exhibit significant structural vulnerabilities, having been designed solely for gravity loads. Key deficiencies include the use of plain reinforcing bars, inadequate anchorage details, and the absence of horizontal reinforcement in the joints. Specifically, the use of plain bars for RC structures was prohibited only with the introduction of the 2008 Building Code. This study provides an overview of the seismic performance of exterior beam-column joints reinforced with plain bars, based on experimental results from cyclic load tests found in the literature. The reviewed tests examine key parameters that influence joint behavior, such as the amount of horizontal reinforcement, column axial load, and anchorage details. The overview provides a comprehensive framework for understanding the behavior of exterior joints reinforced with plain bars and their failure mechanisms. The study highlights the shortcomings of specific reinforcement arrangements and details in the tested joints. It provides a critical discussion on the damage patterns and failure mechanisms observed, focusing on the effects of reinforcement details and the influence of key parameters, such as the impact of column axial load on joint shear stress at failure. Given the lack of similar studies in the literature, this analysis establishes a foundation for a thorough understanding of the behavior of joints with plain bars. This knowledge is crucial for upgrading these joints and developing effective retrofit solutions for buildings constructed before 2008.