The situation originated from structural failures analyzed in the Domus Tiberiana is very complex. The architectural stratification noticeable is difficult to read because the building has a long history, made of transformations and additions, has suffered several earthquakes, has been excavated for archeological purposes and reinforcements have already been performed in past restoration works.
In general the structures are damaged by diffuse fractures, out of plumb walls, detachments and degradation of materials. The vaults as well as the foundations have cracks, most of which are severe and parallel to the slope. The two fronts of the building are detached from the spine walls, where cracks can be observed running from foundations to the top of the terrace of the Orti Farnesiani. From the analysis of the crack map, it looks like that the movement of the structure is mostly linked to the slippage of the lower side of the building toward the valley, with a slight rotation toward the mount. This structural failure is not due to vertical loads because they are modest; instead, it is to blame to the concentration of stresses due to the different responses given to horizontal forces by the different bodies. In fact, the seismic vulnerability of the building is mostly due to the structural discontinuity of the slope, to the different levels of foundations and to the lack of homogeneity of the ground on which the structures were built.
The seismic retrofitting has been performed applying the minimum alteration, taking advantage of the strength of the existing structures and developing a good box action between all the elements of the building. The consolidation was based on a diffuse intervention, rather than small punctual operations, because these would have applied major concentrations of stresses and therefore lead to possible local damages. The restoration works concerned the repair of cracks of the spine walls and of the vaults, sealing them with materials that were compatible with the existing ones chemically and physically, and the positioning of tie rods that increased tensile resistance of masonries. Moreover tie rods were inserted parallel to the front of the Via Nova in order to remove phenomena of overturning failures of the front wall, which once was probably contrasted by a vault that originally covered the ramp. To complete the configuration of the box action, it has been performed the reconstruction of the vaults and the terrace’s slabs that cover the complex of the Domus. The new structures were built with irregular blocks of tuff set in a mortar bed prepared with natural hydraulic lime. In order to bring the terraces’ floor at the same level of the Orti Farnesiani, it was constructed a new slab made of steel and corrugated sheet that is able to offset the difference between the level of the extrados of the vaults and the Orti’s floor. In all passages that connect the different rooms of the Domus the lintels and relieving arches were restored, with integrations or reconstructions using masonry with the aid of falseworks.
[by Alessandro Bozzetti, Studio Croci e Associati, and Maria Grazia Filetici, Superintendence for Archeological Heritage, Rome - text Alessandra Ledda]