In-plane, out-of-plane, and in-plane/out-of-plane interactional behavior of masonry-infilled steel MRFs with different frame components flexibilities and considering openings

In this paper, the in-plane (IP), out-of-plane (OOP), and IP/OOP interactional behavior of masonry-infilled steel moment-resisting frames (MRFs) are investigated through calibrated finite element modeling and analyses. Some of the key parameters influencing the response of masonry-infilled frames (MIFs), namely panel aspect ratio, size of central window opening, and steel frame components flexibility, are studied in a parametric study, covering a wide range of values for the parameters. The effect of each considered parameter on the IP and OOP response of MIFs are investigated. In addition, the suitability of various existing equations for predicting the IP and OOP strength of infills are evaluated, and based on the results obtained in this study, new formulae capable of predicting MIFs response characteristics are proposed. A novel non-uniform OOP force distribution pattern based on the first mode shape of free vibration of infilled frames is introduced and implemented, and OOP strength capacity of considered MIFs under this new force pattern are compared with those obtained from common uniform OOP force distribution method. For the IP/OOP interaction analyses, a novel loading protocol is introduced and adopted, and its suitability is compared with that of the common loading protocols used in the literature and discussed in detail. Finally, capacity of masonry infill walls subjected to simultaneous IP and OOP loadings were derived and, based on the results, a new interaction curve formulation was proposed. The results signified that the interaction curve formulation prescribed by ASCE/SEI 41-17 Standard is unconservative.