Defining the structurally compatible uses of ancient vaults: A comparison between traditional and modern modelling approaches

The conservation of historical architectural heritage cannot be limited only to a series of isolated interventions on materials and structures, but must include also the maintenance or insertion of compatible uses, which can guarantee a continuous upkeep. The exploitation of heritage, nevertheless, is a wedge issue, as it involves new loads, more wear, different environmental conditions, which can induce changes in their behaviour which are hard to foresee. This contribution aims to analyse in particular the structural issues involved in the use changes or in the adaptation of a pre-existing use to new functional or normative requirements. Indeed, for a correct management of the built heritage, the choice of the structurally compatible uses cannot disregard a specific analysis aimed at the identification of the structure bearing capacity and focusing on the indications to combine functional and structural needs. The proposed case study, on which the approach is applied, regards the Pilotta National Museum, in Parma, that is undergoing a reorganization of the visit paths and a reconsideration on the uses allocated to some spaces. More specifically, a vaulted room over a long barrel vault is asked to host new functions and carry new loads, whose compatibility with the preservation of the monumental structure must be assessed. For the assessment of the structural compatibility levels, different modelling approaches have been tested, in order to compare their results and to analyze their pros and cons in this type of evaluation. On one side, traditional methods were chosen: the graphic Méry method and the Heyman limit analysis have been applied to a system of 2D arches composing the vault. On the other side, the edge cutting ChronoEngine Distinct Element Model have been also tested, under the same conditions. In all cases, calculations have been made changing both values and positions of the loads, depending on the requests for the new use of the vault. The results are compared both in terms of stresses inside the masonry and in terms of deformation of the structural elements, evaluating the types of information and detail that the different approaches can supply. The results of the numerical method allow to assess the validity of the traditional approaches. On the other side, the possible contribution of the traditional methods to the calibration of the parameters for the numerical models is also discussed. The results, at last, will be adopted to propose limitations to the possible uses and to give specific indications about the setting up of the museum exhibitions.