In recent years much research has been done on the effect of infills on the behavior of structures. Most of research relates to infills with masonry materials. The use of sandwich panels has been developed with the development of new technologies in the building industry. Unfortunately, engineers in the design of structures ignore the influence of a variety of infills, including the sandwich panels. However, the observed damages in the infills indicates that the influence of these systems on the properties such as stiffness, strength, and plasticity of structures is significant.
Ignoring the effects of the infills on the behavior of structures in the process of analyzing and designing structures will not be reliable.Therefore, in this study, the seismic behavior of moment resisting steel frames (MRSF) including sandwich panel infills are investigated. In this regard, nonlinear static analysis were performed on 72 MRSF equipped with sandwich panel infills, by using SAP 2000 finite element software. The influences of the parameters such as opening dimensions, gap width in the interfaces, span length to story height ratio (L / H), and number of story on the behavior factor of MRSF including sandwich panel infills are investigated. The results show that the presence of sandwich panels as an infill in the MRSF increase stiffness, energy dissipation capacity and structural strength against the lateral load of the earthquake. The opening in the infills reduces seismic parameters and as the opening dimension becomes larger, the behavior of the infilled frame leads to the bare frame behavior. The results also show, the presence of interfaces gaps between the infills and structural elements reduced the stiffness, structural strength in comparison with the without gap models. In models including gaps, creating openings with 30% surface of the infill surface, improves the behavior factor. Finally, the behavior factor of the MRSFs including without gap sandwich panel infills can