THE USE OF CONCRETE-FILLED STEEL TUBE STRUCTURES IN THE RECONSTRUCTION OF DESTROYED FLOOR SLABS IN LARGE-PANEL BUILDINGS

The full-scale military invasion of Ukraine by the Russian Federation in February 2022 caused widespread damage to civilian  infrastructure, including large-panel residential buildings constructed primarily in the late Soviet period. These structures are  prevalent in urban districts like Saltivka, a densely populated area of Kharkiv located near the state border. Due to their  modular design and proximity to frontline hostilities, many of these buildings experienced either partial or complete  destruction, particularly affecting floor slabs.This study investigates the restoration of floor systems in damaged large-panel buildings and proposes a practical, innovative  reinforcement method based on tubular concrete (concrete-filled steel tubes) enhanced with a specialized infill composition.  The solution involves constructing a steel subframe integrated with a modified concrete core that includes steel fiber and  mineral additives to improve mechanical performance. Structural analysis and experimental  tests demonstrated that this  configuration significantly improves  the stiffness and strength  characteristics of floor elements while allowing for a reduction in  slab thickness. Compared to traditional solutions, the proposed system offers up to 50 % less deformation than empty steel  sections and about 30 % better performance than standard concrete-filled tubes.From a construction standpoint, the design allows for efficient assembly within existing buildings, maintaining room height and  minimizing the impact on architectural ergonomics. Additional central beams redistribute loads more effectively, transforming  the floor into a system supported along its entire perimeter, which reduces bending moments and enhances load-bearing  capacity.This method addresses critical challenges in post-war reconstruction by providing a costeffective, scalable approach to  residential rehabilitation. Its compatibility with prefabricated panel housing makes it particularly valuable in regions where  restoring living space quickly and safely is essential. The findings confirm that tubular concrete elements with optimized infill  materials can serve as a reliable alternative to traditional slab replacement techniques in the context of modern structural  retrofitting.