When in 2011 we launched the BHIMM (Built Heritage Information Modeling Management) project, which involved six Research Units and had been awarded to the Politecnico di Milano by the Italian Ministry of University and Research, available literature concerning the implementation of digital informative modeling on historic buildings was definitely poor.
The developments in the field that we can see and glean from the literature now, only five years later, are simply amazing. The technological transfer of BIM from the construction field to the world of cultural heritage seems to be a more and more appealing subject for academic researchers, but many doubts and problems arose looking for the most effective road to a real implementation on this very peculiar market.
Several important Italian monuments have been used to test BIM techniques as implemented in the heritage domain: for instance, Milan Cathedral, the huge complex of Albergo dei Poveri in Genua (Figure 1); the church of S. Maria di Collemaggio in L’Aquila that was damaged by the 2009 earthquake (Figure 2); and Masegra Castle in Sondrio in the Alpine region (Figure 3), to name just a few. In the course of these implementations, different solutions were explored, and almost all the activities that follow each other along the cyclic management process of an historic building, acknowledged and as such protected, have been explored with the perspective of making them digital and interoperable as much as possible.
The specific nature of the conservation process of built cultural heritage is radically different from the construction process, and therefore poses substantial challenges in implementing BIM on these projects.
The available tools, which have been developed to design and assemble serial building components, can hardly deal with the irreducible variety of ancient buildings, still in use although well beyond the limits of their service life, recognized as heritage to be conserved complying with the complex criteria of authenticity (which, in accordance with the Declaration of San Antonio—the result of a symposium held in Texas in 1996 on the subject of authenticity in the conservation and management of cultural heritage—means material authenticity).
As it is often the case when innovation happens by means of technological transfer from one sector to another, the new tools tend to be adopted in a frame of accustomed attitudes, in a rush, and often even without changing the targets, wasting or underutilizing the potential of the procedures and techniques.
The many pilot research BIM implementations that were carried out under the aegis of the BHIMM project on several Italian historic buildings demonstrated that the transition from the traditional representation by 2D views associated with a restoration project to a 3D parametric model cannot be just a matter of tools and procedures to be customized: instead, it is necessary to understand the use of parametric tools to renovate the whole heritage conservation and valorization process.
The transition from drawing to BIM is parallel with the transition from restoration as an event to conservation as a process (we used to speak of planned conservation). Therefore, it is a transition from a scheme that used to see restoration as a constructive process (on existing premises instead of on free land), to the vision of a long-term process, in which many different activities (management, maintenance, monitoring, conservation, heating, restoration, etc.) are carried out by different actors, who need to exchange a lot of information overcoming asymmetries and cognitive gaps.
It is prudent, therefore, to approach the topic of Built Heritage Information Modeling, or Historic BIM, by an analysis of the processes well before working on the question on the development of the tools.
It is well known that the precondition for the ability of 3D models to support the management of existing buildings has been the evolution of acquisition tools in the Geomatics field (also known as surveying engineering or geospatial science). Point-clouds became familiar to architects and conservators, as the costs of automatic surveying became competitive with the costs of direct measurements.
Generally, three basic problems are pointed out when dealing with the step from point-clouds to parametric models suitable for architectural conservation, and these topics have been largely dealt with in the framework of BHIMM as well.
First, in order to be used operationally for conservation , the data that is collected cannot be limited to the external surfaces of the objects, which have to be investigated and in some way represented by their thickness, layers and internal features. In a BIM environment therefore, the problem arises of characterizing elements as three-dimensional not only from the geometric point of view, but also for materials and techniques.
Second, the point-cloud has to be converted to a model made of discrete and significant objects, corresponding to the operations that have to be carried out for design, computational or documentation purposes. The issue has already been posed as a geometric problem, because of the irregular shapes of historical buildings. The use of NURBS (non-uniform rational B-splines) curves and surfaces has supplied a satisfactory solution to this problem, which helps to overcome the lack of basic libraries offered by commercial software and avoid wasting the level of geometric detail obtained using advanced surveying techniques. But as stated above, information and details to be investigated and filed are far more varied.
Third, BIM models, as provided by parametric software available today, use typified components, downloaded from libraries, which can be enriched and customized, but any historic building is the outcome of construction processes, besides changes and layering in progress of time, which produce the variety that is just the core of the recognition of authenticity, and therefore of value. The question of harmonizing the oneness character with the typology approach is surely not new, as this was one of the most discussed topics for Conservation theory. The solution of producing individual objects embedded in the model, rather than in the software library, has been successfully explored, but it entails giving up a series of possible automations.
On this point, it would be worthwhile to point out that there are already several products available with ready-made families of elements typical of historic architecture, classified by periods, often coming from the plates of architectural treatises. You can find on the market Renaissance BIM, Gothic BIM, Regency BIM, or any period BIM. Using these products can certainly help to make 3D models more realistic and better-looking, but these models should serve to enhance data sharing, not simply build sceneries fit for videogames. The risk is to consolidate a rough level of detail, more than good for some purposes, but not exhaustive for the whole process.
The trend nowadays, also from the industry side, is to bridge the gap between survey and parametric modeling, empowering the most popular software tools. Nevertheless, the intent of this step has to be clarified, by means of some reflections on operational needs, on the required levels of description and information.
Being definitely different from the design of a new building, the work carried out on an existing building, especially when it is dealt with as a heritage object to be conserved and not just retrofitted, is not a simple progression: it’s a matter of reverse engineering or downloading from data banks. If we are able to imagine the ideal process developed up to its regime, we see that the need of information sharing does not point to the unique perfect model, suitable for any function, used by all the actors, as the best option to strive for.
For the Italian norm UNI 11337, we have suggested a definitely different approach to LODs, overturning the parallelism with the progressive LODs described for the design of new constructions. (LOD stands for “Level of Development” and is a specification that defines the scope and detail of a BIM model at different stages and for different purposes.) Conservation works on existing buildings declared of cultural importance, and therefore protected, entail continuity in knowledge management, so that they require at any time a high level of information and description. In the best case, the scientific report produced by a previous intervention should be available, implemented by following maintenance and management activities. In case of starting up without previous documentation, nevertheless the survey and connected investigations, such as energy or structural monitoring if needed, should from the beginning tend to the same (high) level of detail and richness of data; any design choice needs to be based on the level of information corresponding to an as-built model, also enriched by maintenance and monitoring data.
Such a high level of detail in models for cultural heritage may not be needed in some technical domains. For example, single domains such as structural analyses, energy simulations, behavioral studies, cost computation, etc. could refer to simplified versions of the detailed model. However, sometimes even single technical activities require an advanced level of detail, as well as different definitions of the parametric objects. For example, a structural or energy analysis may need to sometimes take into account an entire element, such as a wall or a column, and sometimes just its layers, parts, stones, etc. At other times, the entire level of detail of the model would be required for other kinds of analyses.
It is worth remembering that there is a parallel to this dichotomy in the traditional 2D process, where the design sheets describe the building by means of plans, facades and cross-sections, differently from the breakdown of the same building in the frame of a maintenance plan.
Reasoning about the inversion of the elaboration flow leads, therefore, to a point already underscored by BIM research—the conceptual distinction between the (unique) interoperable model and the platform, which enables data exchange among several “domain specific” BIMs. Domain specific models (i.e., BIM for architectural design, structural analysis, energy analysis, construction and site design, cost analysis, management, maintenance, etc.) will undoubtedly perform better than the huge single model, which should be also the exchange platform.
For each model, an individual recognition of BIM objects can be carried out; each specific model should download from the general data base just the useful data, and upload its output in order to make it available for other domains through the platform.
This vision of BIM has been argued, e.g. by Arto Kiviniemi, as the way to ensure the highest interoperability. It is also the way to carry out a very important change in the heritage field, as the required anticipation of detailed investigation, as well as the availability of tools enabling a continuous control, will enhance the quality of the whole process.
Stefano Della Torre is an academic in the field of Restoration, full professor since 2001 in the Politecnico di Milano, where he currently serves as the Director of the Department of Architecture, Built Environment and Construction Engineering. He is also the President of buildingSMART Italy, the Italian Chapter of buildingSMART International. He is the principal investigator of several national and International conservation and heritage projects including "Knowledge of historical building techniques: protocols and innovative tools for diffusion and applicability to preservation process" (research project granted by the Italian National Ministry, 2005/2006); "Built Heritage Information Modelling/Management – BHIMM" (research project granted by the Italian National Ministry, 2012-2015); and "Cultural Heritage Activities: New Goals and benefits for Economy and Society" (European project JPI-Heritage+, 2015-2017). He is also a consultant of the Cariplo Foundation for the "Cultural districts" project and has been the coordinator of a set of research projects promoted by Regione Lombardia about preventive conservation and planned maintenance of Built Cultural Heritage.
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