Lateral Strength of Steel Frames with Masonry Infills Having Large Openings

This paper describes an experimental program to investigate the in-plane seismic behavior of steel frames with unreinforced masonry infills having large window openings. Test parameters included the masonry pier width and the number of wythes. Infill strength and stiffness deterioration seemed to be independent of the pier width or the number of wythes. Results indicate that the ultimate shear strength of these infills ranged between 0.82 and 1.08 MPa (120 and 157 psi). Stiffness deterioration for each infill was almost identical. By 0.20% drift each infill lost more than 70% of its original effective stiffness, with the remaining stiffness degrading by 2.0% drift. Ductility of these tested masonry infills depended on the pier width and the number of wythes. Narrow piers tended to be more ductile than wide piers, resulting in less observable damage in the brick at large-amplitude drifts. Similarly, the double wythe infills tended to be more ductile than single wythe infills. This research was directed toward possible use in the evaluation methodologies of ATC-33.