Influence of anti-seismic strengthening schemes on the load-bearing capacity and lateral stiffness of reinforced concrete frames of multi-story buildings

Abstract

The object of research is a reinforced concrete frame of a multi-story building strengthened by various anti-seismic methods. The problem solved is the lack of comparative experimental data on how different strengthening techniques affect the load-bearing capacity and rigidity of such frames under lateral loading. Frame models were built at a 1/3 scale using extended similarity theory, both unreinforced and reinforced with carbon fiber fabrics (Russian and Turkish), steel profile jackets, steel corner stiffeners, X-shaped steel braces, and brick infill. A test methodology and a strain-gauge measuring system were developed; static load was applied by a 50 tf hydraulic jack at the top of the frame and recorded with a dynamometer. The results show that, of all methods considered, X-shaped steel braces and brick infill provide the highest load-bearing capacity: the failure load rose from 14000 N for the unreinforced frame to 33000 N, and bending stiffness increased by 59 percent (from 661600 to 1597100 N/m). This is explained by the braces and infill engaging the frame as a stiff diagonal load path that redistributes lateral forces and limits displacement. A distinctive feature of the work is the direct experimental comparison of six reinforcement schemes on identical scaled frames under the same loading conditions, which made it possible to rank them objectively. However, brick infill increases the structural mass and thus the seismic inertial load on the floors, adversely affecting overall seismic resistance. The results provide an objective basis for choosing between strengthening schemes in the seismic retrofitting of existing multi-story frame buildings in high-seismicity regions, favoring lightweight, high-stiffness solutions