In recent years, there has been a large body of research on the effect of infill panels on structural behavior. While research on the behavior of infill panels is ongoingly developing, engineers tend to exclude the infill panel effect in structural designs regardless of the type of infill panels. Previous research has been mostly focused on experimentally studying the behavior of the sandwich infill panels on a small scale; however, the effect of gaps in full-scale structures and the sensitivity analysis of the impacts of infill panel gaps have received less attention. The present research provides a nonlinear static analysis on 72 3D models of reinforced concrete moment frames with sandwich infill panels and 9 models of infill panel-free concrete moment frames. The targeted parameters include the effect of opening inclusion, the gap's width between the frame and the infill panel, the ratio of span length to story height (L/H), and the number of stories. A wide variety of models are investigated with 1.5, 2, and 2.5 L/H ratios and 3, 6, and 9 stories. The 0 and 30%-opening inclusion patterns are also considered. The opening's size in structures is defined as a percentage of the infill panel's size. The connection of infill panels to concrete frames is considered with the effect of 0, 20, 30, and 40mm gaps and evaluated as the research's main parameter. The nonlinear solution method is based on fiber plastic hinges. After the corresponding numerical method is validated and several numerical analyses are performed, the results are investigated. The findings imply that the inclusion of sandwich infill panels significantly affects structural seismic parameters, especially behavior factor and ductility factor, enhancing stiffness and ultimate strength against earthquake-sourced lateral loads. This research indicates that compared to infill panel-free models, zero-gap infill panel-included structures show a markedly different behavior, which is due to significant interact