BIM (Building Information Modelling ) are three-dimensional models of buildings. Their application has for many years been relegated to the design of new buildings. However, in countries like Italy, where the existing historical heritage is a peculiarity of the Bel Paese, it is essential to deal with its redevelopment and preservation over time. This is where HBIM comes from, i.e., the need to use digitization by applying BIM to historic buildings as well, which, by their very nature, often turn out to be the result of stratifications of evolutionary phases, materials and architectural changes that have followed one another over the years.
All this information is difficult to assimilate through a traditional type of management, which denotes a high risk of loss of important data needed in subsequent phases of intervention. In this regard, think, for example, of the importance of having available the documentation that might concern the diagnostics of a historic building made over the years, or the consolidation interventions made in previous years, and so on.
H-BIM – What is Heritage Building Information Modelling ?
It is precisely in order to collect various historical information about a building that the acronym “H-BIM” was born: Historical or Heritage Building Information Modelling, i.e., that process applied to existing buildings or monuments that aims not only at the mere restitution of the three-dimensional model, but especially at the creation of so-called “intelligent models.” The latter are rich in geometric information and inclusive of the state of preservation of materials, in which all components are parametric objects with a well-defined semantics and capable of containing all historical information derived from appropriate documentary analysis.
The term HBIM was coined in 2009, first used in a scholarly article by Professor Maurice Murphy of the Dublin Institute of Technology; since then the topic has grown in scope, finding considerable acceptance among practitioners and academics in the field.
This discipline, although relatively young, has enormous potential. Think, for example, of the vast number of buildings of great historical, architectural and monumental value in our country. But that’s not all: HBIM is a process applied to existing buildings of any type, so both to monuments and works of cultural or historical value, and also to simple houses from the 1950s.
In the first case, HBIM is used for the preservation, management and documentation of historical works, enabling the acquisition and analysis of detailed data on buildings and supporting restoration, maintenance and preservation activities of architectural heritage.
In the second case, it is worth mentioning that in Italy, about 60 percent of buildings are more than 40 years old. This underscores the growing importance of promoting the rehabilitation of existing buildings through energy upgrading, restoration and rehabilitation.
HBIM: potential and application areas
HBIM is an excellent alternative to traditional representation methods, enabling the creation of a complete digital model with all building information. This model can be used for building restoration, maintenance, and management, just as it is in new construction. Despite the obvious differences between the two fields, the advantages offered by BIM can be successfully exploited in both cases.
The “digital reconstruction” of the building by object modeling follows a logic similar to that of a traditional BIM model, but with the integration of information specific to historic buildings.
This information includes, for example, the evolution of the building over time, its state of preservation, functional integrity, and other historical documents and images that complement the digital representation of the building. All of this is critical for the subsequent management and maintenance of the building.
In essence, with HBIM, it is possible to obtain BIM models of existing buildings that contain a variety of information and are easily updated, replaceable, and integrated.
The goals of the HBIM process
The goal of the HBIM process, then, is to generate an information model that is congruent and geometrically consistent with reality, where most of the information gathered up to that point is contained, as if it were a digital “catalog” that can be queried when needed.
Below we summarize all the steps of the HBIM process.
Acquisition of the historical-constructive information of the artifact
The correct approach to HBIM involves researching all available historical and recent paper and digital documentation available from state archives, local governments, libraries, and any archives that may have information related to the building. This action is the first step in the proper application of the process, with a view to recovery and restoration consistent with the building’s history.
Survey phase
At the basis of modeling for graphical restitution must necessarily take place a survey, which is usually conducted digitally through the use of tools such as laser scanners or a camera for terrestrial photogrammetry, which allow obtaining the so-called point cloud, that is, a set of points referenced to each other in space that contain information of a geometric character (their coordinates in a known reference system) and of a colorimetric character, in that each point is associated with a relative color obtained from a photo taken by the instrument during scanning.
It will be at this stage that information will be returned with acquisition methods capable of focusing and describing each detail effectively and completely.
A cloud is managed with software dedicated to loading the formats in which the survey is saved and displaying it according to specific parameters (intensity of points, height above the ground, representation of thematics), which allow operations to transform them. There are several, including open source ones: for years now Autodesk Recap has been very popular, which processes clouds to save them in a format known as RCP that can be imported or linked to files in AutoCAD, Revit, Naviswork and other design products. In Recap, in addition to defining its visualization, a cloud can be decomposed and georeferenced to share its spatial coordinates, along with the model that will be derived from it. It also comes in handy to dissect it according to cutting planes of different orientations to derive the planimetric distribution of the building. It means that in many cases, the parts being represented are isolated, hiding the surrounding building. At the same time, however, the context should then be isolated and saved in a dedicated layer, because it can be reused as a scenario in which to place the modeled building.
Model creation
The next step is the creation of the model using the usual Authoring Software. Through the creation of specific libraries of parametric objects, the previously described information content is enriched to thus compose the complete BIM model of the artifact.
In fact, from a three-dimensional surface (consisting of the texture of millions of points that make up the cloud) depicting the surveyed work, it is necessary to create a parametric BIM model.
Considering then that existing buildings almost never exhibit features of regularity and repetitiveness, the modeling of such artifacts becomes a rather complex operation with a considerable expenditure of time and resources.
BIM modeling is the most delicate and complex phase that must go hand in hand with the BIM objectives previously defined within an information management plan.
The two-dimensional profiles obtained from AutoCAD (such as those available on archweb) provide a basis for being able to more accurately model AEC objects, or at least those that are customizable with their Boolean input: operations between solids, essentially wall inserts, but also classical balustrades, frames and stringcourses of openings, roof bands, and other forms of decorations and stylistic features present in the monument to be surveyed. It is important to note this aspect, because in the modeling that is generally implemented for these types of forms, generic in-place models are used, then set directly on the cloud sections on appropriate reference planes. In summary, then, in the first case we have data with little modeling potential, while in the second case we have greater potential to reproduce the shapes but with a paucity of data.
Populating documentation information within the model
The HBIM model can only be considered complete when correlations are in place within the multitude of data that allow the user to interrogate the model from a historical documentary point of view, from the point of view of graphic/digital elaborations and in exporting abacuses of quantities necessary for quantifying costs or materials of related interventions.
Of fundamental importance, moreover, is the possibility of integrating the information within the model over time, which will be able to be matched throughout the life of the building and make it possible to keep track of any interventions or additions over the years.
Use of CDEs
The integration of model information can be implemented through the use of CDEs (Common Data Environment), which allow different types of documentation organized by appropriate directories to be stored in a shared cloud, of which it will be possible to manage access according to the roles held.
Once the necessary is placed within the CDE, communication between the different actors will be much easier, and the possibility of loss of information (if used in the correct manner) is very limited to the benefit of the continuous taking of the design evolution.
The advantages of the HBIM process
In summary, the use of an HBIM process in interventions on the legacy building fabric has many advantages:
- the obligatory path to follow in HBIM involves a much deeper knowledge of the artifact given by extensive research of historical documentation and detailed graphic restitution guided by the digitally performed survey.
- the presence within a single data collector, represented by the BIM model, of all the information related to the artifact and usable by different professional figures, allows to centralize in a single virtual environment the trace of all the activities on the building.
- speeds up the retrieval of the history of the artifact on the basis of which to carry out new intervention strategies.
- the construction of a BIM database of existing buildings, both historic and non-historic, makes it possible to carry out in a more organic way numerous evaluations of urban planning and historical relevance, allowing to calibrate macro-interventions on an urban scale starting from the structural stratifications and volumetric expansions that have followed one another over time.
Successful examples
There are numerous successful examples of HBIM projects applied to historic buildings. For example, on the Italian territory, models have been made of important historical universities with hundreds of thousands of square meters that have started the process first of surveying with laser scanning and then constitution of the BIM model for the efficiency and optimization management of their real estate assets.
Internationally, the restoration of Notre-Dame Cathedral in Paris after the devastating fire in 2019. HBIM enabled rapid mapping of damaged elements and precise planning of restoration work.
HBIM in the European scene and even more so in the Italian one is a topic of primary importance for the historical conservation and management of the existing architectural and artistic heritage.
Conclusions
HBIM represents a revolution in historic preservation and the management of old buildings. With its ability to accurately capture and represent architectural and historic features of buildings, BIM is enhancing our understanding of the past and helping to preserve our heritage for future generations.
