Stiffness and damping of infilled steel frames

This paper presents the results of an experimental and numerical investigation on 15 masonry, concrete and multilayer infill specimens. Two types of frames are considered. The first one, having pinned connections, has a small-scale and is composed of very stiff beams and columns. The second has a medium-scale and has rigid connections. The frames represent lower storeys of high-and medium-rise buildings, respectively. The effects of reinforcement and bond beam on masonry infill panels are investigated. It is shown that the efficiency of horizontal reinforcements and bond beams on the behaviour of infill panels depends on the dominant cracking pattern. The results show that adding the steel fibres to the material of infill corners can considerably increase the ultimate strength of concrete panels. It is also concluded that the behaviour of multilayer or fibrous concrete panels is better than single-layer panels and they are preferred when strengthening buildings against lateral loads. A new explanation for infill stiffness, named practical stiffness, is proposed and a new formula is suggested to estimate stiffness of the specimens. Eventually, damping ratios of all specimens are presented. The results show that damping ratios of specimens are indicators of structural damage.