Effect of infill walls reinforced with cement-based composite plates on the seismic behavior of reinforced concrete buildings

Living in a region that is both seismically active and highly vulnerable to earthquakes is a reality constantly reminded by the frequent occurrence of small and moderate seismic events. A historical overview reveals that large and destructive earthquakes have occurred frequently in this region, causing significant loss of life and property. In fact, even moderate earthquakes have sometimes resulted in severe damage within our country. The primary reason for this is the existence of an aging and largely unengineered building stock. Furthermore, data obtained from existing buildings shows that the use of poor-quality materials further exacerbates the destructive effects of even moderate seismic events. Being aware of this situation and seeking solutions to the [destructive earthquake–existing building] relationship has become a critical area of research for many structural engineers and academics. In light of these issues, this doctoral study investigates a new and practical strengthening method aimed at improving the performance of existing buildings. In this context, both experimental and analytical studies were conducted to assess the cause–effect relationship of strengthening infilled walls using Textile Reinforced Cementitious Composites (TRCC). TRCCs used for strengthening infill walls in this study are advanced composite materials produced by embedding high-strength, bidirectional, and woven textile meshes into a fine-grained cement-based matrix. These systems have been developed to overcome limitations commonly encountered in traditional reinforced concrete structures, such as corrosion, high weight, and limited deformation capacity. The textile reinforcement used in TRCC systems (e.g., AR-Glass, carbon fiber, PVA, or basalt fibers) can be integrated into the matrix as 2D or 3D woven fabrics, achieving high bonding and compatibility with the matrix. This allows the textile and the cementitious matrix to act together as a unified material. In this doctoral study, multilayer textile placement was used, which significantly improves the tensile and flexural performance of TRCC systems. This performance advantage leads to promising results when TRCCs are used as strengthening elements. The main objective of this study is to utilize TRCCs to strengthen infill walls in reinforced concrete buildings, transforming these walls from non-structural architectural elements into components that contribute to the structural performance under dynamic loads such as earthquakes. In other words, infill or partition walls, typically considered secondary elements, are turned into load-resisting components that enhance the lateral load-bearing capacity of buildings. To achieve this, four 1:3 scale single-story, single-bay reinforced concrete frame specimens were produced and tested as part of the experimental program. Among them, one was a bare frame without infill, one included only an unreinforced masonry infill, and the remaining two were strengthened using TRCC systems with different properties. The results obtained from these tests were compared to evaluate the effectiveness of TRCC-based strengthening. In addition, the experimental results of the reinforced concrete frame specimens were analytically examined within the scope of the TBDY-2018 and FEMA-306 codes, and the analytical results were compared with the experimental ones. It was observed that the experimental and analytical results yielded highly convergent values. Finally, using the strengthening techniques validated in the experimental study, a 14-story existing reinforced concrete building was retrofitted with TRCC composites. The effect of this strengthening approach on the building's seismic performance was evaluated. Pushover analyses were performed for both the retrofitted and unretrofitted conditions, and the results were compared to assess the improvement in structural behavior. This study proposes a novel strengthening material and method aimed at providing a faster, more practical, and cost-effective retrofit solution for many existing reinforced concrete buildings that are at risk of collapse in a highly seismically active country. The proposed strengthening technique, which can be easily applied to infill walls within reinforced concrete frames, allows for retrofitting without altering the building's existing architectural features or usage. Moreover, it eliminates the need for evacuation, demolition, or destructive interventions within the existing structure during the strengthening process.