Influence of mechanical properties of modified mortar on In-plane and Out-of-plane seismic performance of RC frame structure with infill walls

The reinforced concrete (RC) frame structures with infill walls are severely damaged under earthquakes. Therefore, enhancing the seismic performance of infill walls is essential to improve a building's seismic resis-tance. Experimental investigations were carried out in this paper to enhance the mechanical properties of modified mortar using liquid nano-SiO2, polyethene acrylic acid (SA) emulsion, and polypropylene (PP) fibers as an additive. The results show that the flexural strength, compressive strength, tensile bond strength and shear strength of mortar along through joint were increased by 8.3%, 4.5%, 60.3%, and 60.8%, respectively, when adding 1% liquid nano-SiO2. The addition of SA emulsion improved the tensile bond strength but reduced the compressive strength and shear strength of the masonry along through joint. Adding PP fibers to mortar can improve the flexural and compressive strength but reduce masonry's tensile bond strength and shear strength of the masonry along through joint. A finite element model of the infill wall-RC frame structure was established in ABAQUS, and the influences of modified mortar's mechanical properties on in-plane (IP) and out-of-plane (OOP) seismic performance were analysed. The optimum percentage of liquid nano-SiO2 based on the simulation results was 1%. Compared with ordinary mortar, the initial stiffness of IP and OOP were increased by 8.45% and 13.3%, respectively, and the ultimate bearing capacity of IP and OOP were increased by 9.4% and 5%, respectively, when the containing of liquid nano-SiO2 was 1%. The IP and OOP initial stiffness and ultimate bearing capacity of the infill wall-RC frame structure with the SA emulsion mortar were lower than ordinary mortar. The IP and OOP seismic performances of the infill wall-RC frame structure with the PP fibers mortar were similar to ordinary mortar. The addition of nano-SiO2 emulsion improved the cement's hydration performance and significantly enhanced the IP and OOP seismic performance of the infill wall-RC frame structure.