The Theoretical Prediction of Collapse Mechanisms for Masonry-Infilled Steel Frames

The masonry infills in infilled steel frames are generally considered non-structural elements and are neglected in design by different codes. In fact, the presence of these infills should have a decisive influence on the mechanical properties such as lateral stiffness and ultimate strength. In the present work, a new macro-model has been proposed to model the masonry infill by two equivalent pin-jointed diagonal struts connecting the beams and the columns, respectively. To show the infill effect, the theory of plastic hinges has been adopted as an appropriate approach. In this parametric study, the prediction of the nature of failure mechanisms of structures subjected to a combined loading system has been presented, including their collapse loads with information about the location and order of plastic hinges. The model has been validated by theoretical and experimental predictions. In addition, interaction diagrams, λV-λH\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\lambda V{-}\lambda H$$\end{document}, were constructed. From the result, the factors that have a direct influence are the infill thickness and the values of α\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\alpha $$\end{document}. By comparing the collapse loads for the infilled frames to their corresponding open frames, it was found that the lateral stiffness and the vertical strength were considerably increased. It can be said that the two-strut model proposed can realistically capture the collapse mechanisms of infilled frames and can more accurately estimate the local effects due to the infill–frame interaction. Finally, important conclusions about the failure modes of the infilled frames and their corresponding collapse loads were drawn from this work.