Resistenza della parete esterna del Colosseo alle azioni sismiche

The strength of the external wall of the Colosseum under out warding horizontal forces is evaluated by means of non-linear pushover analyses. Many different loading directions are considered in order to define the worst load condition for the monument. The analysis takes into account the properties of the different materials of the structure: the travertine masonry blocks and the roman concrete. The failure domains of the materials are evaluated and the cracking spreading on the wall at increasing forces is defined by means of an iterative procedure which modifies the membrane stiffness of the finite elements according to the actual state of stress. The application of horizontal loads parallel to the minor axes of the elliptic plan of the monument for a peak acceleration of 0.13 shown that the vertical cracks extend up to the extrados of the circumferential arches of the third order a vertical portion of the external wall can overturn outwards. The peak normal acceleration which gives the overturning of a strip delimited by vertical cracks is about equal to 0.14g. Therefore this value can be considered the ultimate horizontal peak acceleration of the monument in the actual configuration. The comparison with the result obtained in Coccia and Ianniruberto (2004) show the great reduction of the lateral strength respect to the original configuration. This reduction is mainly due to the lack of the third and fourth order ambulatory vaults that increases the height of the unrestrained part of the external wall and its vulnerability to horizontal forces.