THE 2012 EARTHQUAKE: AN ABACUS OF SURVEYS AND INTERVENTIONS IN MANTUA CHURCHES

Abstract. After the earthquake of 2012, the ecclesiastical heritage of Mantua was so damaged to render unusable many buildings. Especially churches show a higher vulnerability in relation to their architectural features. From a recognition after the seismic event, more that 40% of the churches of Mantua were damaged with different intensity.

After the first phase of expeditious damage detection, a methodical analysis has allowed to know the real state of conservation of many architectures.

The Diocese of Mantua commissioned to the Mantua Campus of Politecnico di Milano the survey and digital documentation of 25 churches differently affected by the seismic event. The goal of the survey was double:

a) realize the documentation necessary for the shoring and protection of damaged structures;

b) prepare the drawing for the following interventions on the buildings such as restoration, reconstruction and retrofitting.

Five years after the earthquake, many interventions of those identified were completed and concluded. Numerically, 129 churches were damaged and, nowadays, 115 have been restored and now they are fully open.

The paper aims to illustrate the operational criteria used in the survey activity and repair operations carried out in order to identify guidelines that can direct operators in cases of new consolidation measures.

All these directions were based on this premise: for historic structures, it is appropriate to accept a level of awareness with seismic risk higher than for ordinary structure, rather than act in the manner contrary to criteria of preservation of cultural heritage.

In these years, we tried to identify the forms of dependence between observed damages, construction types and the conservative state before the earthquake. The goal in fact is to understand the cause of the wide loss of ecclesiastic heritage. The reason can be searched in the unfamiliarity of construction practices, techniques and materials with earthquakes or the inability of existing building to resist the seismic stress because badly maintained.

These two possibilities conditioned the repair choices applied on the churches. The interventions regard different techniques which were optimized not only to be applied on buildings damaged by the earthquake but also on those that gradually show the necessity of accommodation measures. It is important, in order not to miss the operational experience gained in these years, to maximize the economic resources deployed by focusing the results achieved and verify if the followed path has been consistent and, if not, adjust the direction followed.

In summary, the solutions adopted are for example: ties and anchor elements, repair works on vaults with mesh and plaster, repair works on vaults with addiction of lightweight ribs; repair works on cracked vaults with wood, steel wedges and injections of natural hydraulic lime, filling in the gaps of the masonry structure to reduce vulnerabilities.