Estimating the local and global effects of infills on steel frames by an improved macro-model

Abstract

Masonry infill panels change the seismic behavior and internal forces of surrounding frames and should be considered in analysis and design phases. Single equivalent strut model, the most common strut model, does not address the internal forces and therefore the multi-strut models are preferred. In this paper, the previously proposed three-strut model (model PD) has been improved to represent a more reliable prediction of both local and global infill effects. For this, an in-depth finite element sensitivity analysis is performed. It is shown that the new model estimates the bending moment and shear force distribution and predicts the stiffness and strength of the infilled steel frames more accurately than previously proposed models in the literature. Properties of the nonlinear hysteretic behavior of infilled frames including stiffness degradation and strength deterioration can also be determined precisely. Finally, the macro-model is further developed to capture the global seismic response and element force distribution of frames with a soft first story.