Retrofitting strategies for vulnerable RC frames: Thin steel plate infill solutions

Seismic vulnerability in aging low-ductility reinforced concrete (RC) frames poses significant risks in earthquake-prone regions due to inadequate lateral load resistance and noncompliance with modern seismic codes. This study investigates the potential of thin steel infill plates as a practical alternative to enhance the seismic performance of low-ductility RC frames. Experimental testing and numerical modeling were conducted to assess the effects of different infill plate-to-boundary frame connection configurations on lateral strength, stiffness, and energy dissipation. Three RC frame specimens were tested under reversed cyclic lateral loads: one bare frame as a baseline and two frames incorporating thin steel infill plates with different connection schemes. In one configuration, the steel plate was fully integrated with the frame; in the other, it was attached only to the beam and foundation. Numerical models were developed in OpenSees, incorporating bond-slip mechanisms and the shear behavior of beams and columns. Experimental and numerical results, demonstrating strong correlation, indicate that the incorporation of steel plates into low-ductility RC frames significantly enhances their ultimate strength. The presence of steel infill plates notably improved the initial stiffness, energy dissipation capacity, and lateral strength of the frames. Furthermore, no abrupt strength degradation was observed throughout the testing, despite the development of shear cracks in the beams and columns of the specimens with infill plates, underscoring the effectiveness of the steel plates in mitigating seismic vulnerabilities.