L’effetto della variazione di rigidezza in elevazione sui massimi drift d’interpiano IDRmax per edifici esistenti in CA

The maximum interstorey drift IDR max experienced during an earthquake is a significant parameter for the assessment of potential seismic damage on buildings. Considering Reinforced Concrete RC buildings, both the structural elements and part of the nonstructural elements and building contents are drift sensitive and can be damaged for excessive IDR. There exist a number of proposals in literature for the simplified assessment of IDR max . However, they generally refer to tall buildings with uniform stiffness in elevation, or with gradual variation along the height. On the other hand, existing gravity load designed RC buildings are generally irregular in elevation due to stiffness variation; also when the infills contribution to the stiffness is considered, the presence of irregular openings may determine significant stiffness variation along the height. This paper studies the effect of stiffness varia tion along the height on the maximum expected IDR and evaluates the effectiveness of existing simplified methods for its prediction. Referring to a class of Gravity Load Designed buildings, it was observed that the approach proposed by Miranda (1999) yield s generally good results if the buildings are uniformly infilled, corresponding to uniform stiffness in elevation. However, when the possible variation of stiffness in elevation is considered, due e.g. to the variation of opening percentage in the infilled panels, the simplified approach by M i randa tends to underestimate IDR max . In general, d epending on the storey where the variation is concentrated and on the entity of lateral stiffness variation a major or minor error of those models is observed.