Concentric versus eccentric strut models in the seismic response of masonry infilled reinforced concrete frame structures using nonlinear dynamic analysis

The influence of masonry infills on the seismic response of reinforced concrete (RC) frame structures is evaluated based on comparative procedure between concentric and eccentric strut models. For this purpose, a four-story reinforced concrete frame structure was selected and designed according to Algerian seismic design code RPA 99/version2003. Comparisons were carried out with the variation in the mechanical characteristics of infills. To this end, three types of masonry infills were considered, defined as weak, intermediate and strong. A series of nonlinear dynamic analyses using a set of three time-history earthquake records were performed with the bare and regular infilled frames structural configurations. Results from nonlinear analyses furnish information on the interaction between the concentric/eccentric strut models and the surrounding structural elements, and their impact on the global and local responses. It is concluded that, at global level, the concentric strut model gives much stiffer response than the eccentric strut model and may be of some practical interest in the design of seismic gaps between adjacent structures; at local level, the concentric strut model is not able to reproduce the increasing of forces in columns due to infills and this increasing phenomenon is particularly relevant in the case of shear force for the strong masonry infill. This paper provides some limitations concerning the number of studied parameters; it can be extended through the consideration of wider set of parameters, such us infill thickness, number of stories, number of bays and irregular infill distribution, in particular soft first story.