Criteria and techniques for repairing and strengthening the architectural heritage
Research and applications
The preservation and valorisation, and then the use according current necessities, of architectural heritage are more and more becoming a major social and economic, besides cultural, issue in many countries. The consequent necessity of ensuring a “minimum accepted level” of structural safety to the involved construction typologies – far from being dealt with by structural engineers in the same way as they treat “modern structures” – is a real challenge, especially considering that they are frequently exposed to severe environmental hazards (like earthquake).
Problems in fact are raised ranging from the same definition and choice of the “conventional” safety level, to the tools and methodologies that can be used to perform reliable structural analyses and safety verifications – being clearly and universally recognised the strong reliability limits in this contexts of even the most sophisticated modern ones– and to the selection, design and execution of appropriate materials and interventions techniques aimed to repair and strengthen the built heritage while preserving as much as possible of its cultural, historic, artistic values.
Important lessons have been learned in this context in Italy from the effects of recent earthquakes (Friuli 1976, Irpinia 1980, Umbria-Marche 1997, L’Aquila 2009, Emilia 2012, Amatrice 2016), all having had destructive effects on historic centres, even when previously subjected to retrofitting interventions, thus demonstrating that even the most innovative solutions can be ineffective, and even dangerous, if not appropriately designed and executed.
Strong debates are still raised on all such issues, but some achievements are to be considered definitely accepted by the majority of the scientific and technical community as they have found appropriate recognitions in the most recent codes and recommendations at national (the Italian Guidelines for evaluation and mitigation of seismic risk to cultural heritage) and international levels (ICOMOS – ISCARSAH International Scientific Committee for Analysis and Restoration of Structures of Architectural Heritage: “Recommendations for the analysis, conservation and structural restoration of architectural heritage”, and ISO 13822: “Bases for design of structures - Assessment of existing structures” ANNEX I (Informative) Historic Structures).
The most recent advances of the research in the above mentioned fields, and the contents of the cited codes and recommendations are briefly presented, together with some practical case studies, making particular reference to a research project funded by the European Union in the ambit of the FP7, conducted by 18 partners from different European and non European Mediterranean area countries, and coordinated by the University of Padova (www.niker.eu).
A wide range of tools and methodologies are first of all available for the “assessment” phase of the real mechanical/structural characteristics of an historic building, ranging from in situ non destructive (NDT), minor destructive (MDT) and destructive tests (DT), to different structural modeling approaches (finite element models, discrete element models, rigid blocks analyses) and to combined numerical/experimental procedures (models identification and calibration, structural health monitoring).
Then the variety of intervention technologies comes, specifically tailored for strengthening typical structural components (masonry walls and piers, arches, vaults, floors, roofs) made of different materials (catted and rubble stones, clay bricks, timber, cast iron) and to improve the overall static and seismic performances of an historic building. (figures 16-24)
Case studies are then presented dealing with different structural typologies in different service conditions, like the Church in Venice or the fortress e in L’Aquila (figures 25-26).
[by Claudio Modena, University of Padova, Italy]