Dynamic behaviour of cracked granite and marble columns retrofitted with steel collars

Granite and heavy stone circular columns could often be found in the cultural heritage among ancient churches and historical buildings in all the Mediterranean area. Their good strength properties allow them to carry big load values, while their bright colours and aesthetical characteristics were used by a lot of architects in the past to achieve structural solutions with great visual impact.Though such materials have great compressive strength values, environmental effects, especially long term effects, can damage the structural members, by cracking them. In this way the slenderness of the column increases, and the presence of an imposed ground motion can be very dangerous, since the column will be more vulnerable to rocking motion, which in critical cases could lead to overturning or material crushing due to stress concentration.This paper focuses on the behaviour of cracked granite and heavy stone columns subjected to rocking motion due to pulse type ground shaking. In this field, the effect of the presence of circular collars is analysed and discussed. The overturning spectra are determined, including the presence of the collars, showing their effectiveness in reducing the overturning risk. Comparisons are shown with numerical analyses and a simplified analytical procedure is proposed.