A framework for architectural heritage HBIM semantization and development. Part 1

S. Brusaporci, P. Maiezza, A. Tata

Part 1 ABSTRACT

Despite the recognized advantages of the use of BIM in the field of architecture and engineering, the extension of this procedure to the architectural heritage is neither immediate nor critical.

The uniqueness and irregularity of historical architecture, on the one hand, and the great quantity of information necessary for the knowledge of architectural heritage, on the other, require appropriate reflections.

The aim of this paper is to define a general framework for the use of BIM procedures for architectural heritage.

The proposed methodology consists of three different Levels of Development (LoD), depending on the characteristics of the building and the objectives of the study: a simplified model with low geometric accuracy and a minimum quantity of information (LoD 200); a model nearer to the reality but, however, with a high deviation between virtual and real model (LoD 300); a detailed BIM model that reproduce as much as possible the geometric irregularities of the building and is enriched by the maximum quantity of information available (LoD 400).

1. INTRODUCTION

Building Information Modelling, through an objected-oriented semantic modelling enriched by heterogeneous information, allows

the integration of all aspects of the building process into a single platform.

The working method that is developed, based on an integrated and interactive database, offers advantages and potentials of great interest for the architectural assets documentation.

However, the extension of the BIM process to historic buildings, which led to the creation of the Historical or Heritage BIM, is still an open question today.

The BIM approach, in fact, designed for the project of the new buildings, is hardly combined with the specific needs of the architectural heritage documentation.

There are two main problems:

the uniqueness of the historical buildings, due to the craftsmanship of its realization, the processes of modification and transformation occurred over time, the phenomena of degradation and deformation;
the great amount of information necessary for a complete and exhaustive knowledge of the architectural assets.

The objective of this paper is the definition of a methodology concerning the application of the BIM process to the architectural heritage: on the basis of the reflections imposed by the specificity and peculiarity of historical buildings, we want to develop a framework that, starting from the survey of the object of study, aims at the realization of BIM models useful for the documentation of historical buildings, and that can constitute the point of departure for the restoration project, maintenance and management of the architectural asset (Fig. 1).

Figure 1

2. BACKGROUND

The term HBIM (Historic Building Information Modelling) is born within the Dublin Institute of Technology (Murphy, M. et al., 2009; Murphy, M. et al., 2013).

HBIM is intended as a multidisciplinary system consisting in the construction of smart objects (parameterized on the basis of architectural rules and treatises) on the data deriving from the building survey.

These objects can be used in semi-automatic façade generation procedures, which combine elements from the library on the base of architectural proportions and rules. The façades thus created, as well as the individual elements, can then be modified through a graphic editing, to fit the survey data (Dore and Murphy, 2015).

Since the subject-matter of the HBIM process is the historical building in its current configuration, the survey represents the initial moment of the methodology (Fig. 2).

Figure 2

3. FRAMEWORK: FROM THE SURVEY TO THE HBIM FOR DOCUMENTATION

The use of BIM for historical buildings modelling remains problematic and still difficult (Logothetis et al., 2015).

The different methodological approach to the architectural heritage – based on a deep knowledge of the building – makes appropriate reflections necessary.

First of all, the application of a methodology based on standardization to buildings characterized by uniqueness and irregularity generates problems for their modelling.

Reducing the architectural elements of the building to typified objects leads to setting aside the peculiarities of the historical object, in favour of a less time-consuming workflow.

On the contrary, a greater correspondence of the model to the surveyed building leads to a reduction in the benefits of parametric modelling which, on the other hand, results to be greater for elements characterized by lower LoD.

Added to this is the question of information, characterised by two different aspects: on the one hand, there is the need to manage a large amount of data not always supported by current BIM platforms; on the other hand, there is the question of the availability or otherwise of information concerning the various themes (constructive technology, historical phases, etc.) and their interpretation.

However, despite the problems inherent in extending the BIM approach to built heritage, it represents an opportunity both for heritage documentation and for conservation management (Oreni et al., 2013).

Starting from these reflections, in this paper we proposed a general framework aimed at the realization of BIM models of historical buildings, including both the geometrical and the information aspects.

In order to overcome the problems posed by the BIM for historical buildings, the framework includes different solutions, varying according to the purpose of modelling and the characteristics of the object of study (Fig.3).

Figure 3

3.1 The framework

Based on the characteristics of the object of study and the aims, the building survey is made, from which, through the semantization of the components, the modelling process can start.

The characteristics of the HBIM models descend from the features of the architectural asset (for example roman building, renaissance palace, baroque church, etc.), the aims of the modelling (geometrical-dimensional survey, survey for the restoration, etc.) and the Level of Development (LoD) desired. Therefore, the framework includes three main types of model, each characterised by a different Level of Development (based on the definitions by the American Institute of Architects (AIA) for the project of new buildings but here re-used for the existing) and a specific modelling methodology.

The three different types are:

LoD 200, a simplified model of the building with a low geometric accuracy and a minimum quantity of information.
LoD 300, in which the amount of information is greater, i.e., through not only the use of family parameters but also the creation of new ones; the modelling is done creating parameterized and simplified families, by which we obtain a model nearer to the reality but, however, with a high deviation between virtual and real model.
LoD 400, which reproduce as much as possible the geometric irregularities of the building and is enriched by the maximum quantity of information (through an extended database in which also all the information from the historical-critical analysis are embedded).

The detailed modelling is obtained by using families created ad hoc (based on Boolean operations) or, in the case of particularly complex and irregular geometries, integrating the model with NURBS (Non Uniform Rational Basis-Splines) imported and parameterized.

Figure 4

Thus, we get the AS-BUILT BIM: a detailed model as close as possible to historical building, with a minimum deviation and characterised by a high definition from both an architectural and an informative point of view.

As an example, we present the three corresponding types of vault model (Fig. 4):

A model with LoD 200, with no structural interest; it is possible to model it in-place, realizing the vault as a single element, through extrusion and subtraction operations.
A model with LoD 300, in which there is also interest in a structural model. The only use of a stratified model in- place is not enough because it doesn’t have any structural value; it is therefore necessary to superimpose a structural floor, made as a single layer.
A model with LoD 400, detailed from both a structural and architectural point of view and inclusive of all constitutive layers.

In order to have a structural BIM object, it is necessary to superimpose a model in-place, which fulfils the architectural and informative task (a detailed model, complete with all the information available concerning each single layer of the vault), on a structural floor, created ad hoc, that coincides with the 3 -D architectural element (i.e. a floor of the maximum height of the vault, emptied into the underlying part).

The complete knowledge of the vault stratigraphy, which allowed the achievement of a similar LoD, was possible thanks to the restoration of the building, which led to the consolidation of the vault with glass fibers (Fig. 5).