A growing attention has been addressed to the influence of infills on the seismic behavior of Reinforced Concrete buildings, also supported by numerical and experimental analyses, and by the observation of damage to infilled RC buildings after recent earthquakes. In this paper, the attention is focused on the Damage Limitation Limit State, defined as dependent of displacement capacity limit directly related to the damage of infills. Although inelastic displacement demand at this LS can be quite low, infill behavior can be already strongly non linear, if a diffuse state of cracking began to arise in infill panels. On the basis of the results of several non linear dynamic analyses, a reduction factor of the initial elastic stiffness of infills is estimated, in order to obtain an effective stiffness of infill panels such that a dynamic linear analysis of the infilled numerical model leads to a displacement demand at DL LS (maximum Interstorey Drift Ratio) which is approximately equal to the same demand evaluated through non linear dynamic analysis on the same model. To this end, Incremental Dynamic Analyses are performed on four- and eight-storey infilled frames, designed for seismic loads according to the current Italian technical code and for gravity loads only according to an obsolete technical code.
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