Estimation of Effective Stiffness of Infill Panels At Damage Limitation Limit State for Low- and Mid-Rise Infilled RC Frames

Abstract eng:
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 (e.g. L'Aquila 2009, Lorca 2011, Emilia 2012). In this paper, the attention is focused on the Damage Limitation Limit State (DL LS), defined as dependent on displacement capacity limit directly related to the damage to infill panels. Although inelastic (post-cracking) displacement demand in RC members at this LS can be quite low, infill behavior can be already strongly non linear, if a diffuse state of cracking has begun to arise in infill panels. Thus, based on 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 to be used in a linear analysis in order to obtain a displacement demand at DL LS (i.e., maximum Interstorey Drift Ratio) which is approximately equal to the demand evaluated through non linear dynamic analysis on the same model. To this end, Incremental Dynamic Analyses (IDAs) 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. Influence of number of storeys and design typology on the obtained effective stiffness is also analyzed.

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