Keywords: structural analysis, irregular geometry, 3D virtual models, close range digital photogrammetry, heritage.

Surroundings altered by human activities stand as a remarkable testimony of human adaptability to the environment where they have lived. Several issues arising from the analysis of a structure belonging to such an environment, the so-called traditional industrial construction, will be discussed in this paper. Problems such as dereliction, alteration or sheer disappearance and how structures of this sort in Galicia (Spain) may eventually be thus affected is one of the main areas of discussion. Some solutions to mitigate the fact that we keep on losing our heritage wealth are put forward, above all that of using techniques that will enable us to record and document data before actual buildings completely disappear forever.

The objective of this work is to contribute to preserve this type of structures, locating key areas where stress is critical, and therefore the risk of failure greater. In order to carry out this analysis it is necessary to determine the geometry of the elements these structures are built with. In case of roofs, the construction material is generally sawed trunk wood, whose geometry can be relatively irregular, rendering conventional measuring methods difficult. The technique proposed to solve this problem falls within the scope of close range photogrammetry [1].

This technique allows to obtain geometric and visual information. Its utilisation as an easy, low-cost method is analysed [2]. The suggested method is based on the use of monoscopic digital photogrammetric stations complying with the directives of the International Committee for Architectural Photogrammetry (CIPA). The studies are presented with the obtained numerical results and the graphical results, as well as three-dimensional models of the structures, rendered with their original textures, as a proposal for their documentation and conservation. Once the digital data is filed, the full document can be accessed through the internet, metric information of the constructions can be obtained, and making 3-D models or developing photo-models using realistic textures are all tasks that can be performed with ease.

The methodology developed will help us get to know the shape and size of the analysed structure, using geometric data obtained by means of photogrammetry. The metric three-dimensional model of the structure is built using a set of flat sides defined by means of the identification of different points belonging to the surfaces of the structural elements being considered.

The process followed in the analysis is as follows: field work and laboratory work (generating 3-D model of the superficial contour of the structure and analysing the stress of structural elements [3]).

Areas where sections are most reduced or where critical stresses are at work can be located [4,5].

The method proposed to acquire the structural geometry has the further advantage of not needing to be directly in touch with the constructive or structural elements analysed, for which it is particularly useful in circumstances where gaining access proves difficult. Moreover, it enables geometric resistant parameters to be obtained, even when the geometric shape of the piece is irregular, and these can be directly transferred to a CAD system so that they can be processed directly on the computer, all of which is a significant step forward when compared to conventional measuring techniques.

From the analysis made it is possible to assess the load capacity of the total structure and its factors of safety, as long as there is enough information on the material obtained after lab tests to add to the geometric information already available

1

P. Arias, C. Caamaño, H. Lorenzo, A. Badaoui, "Fotogrametría digital de objeto cercano: una técnica alternativa para el conocimiento y conservación del patrimonio rural", VII Congreso Internacional de Rehabilitación del Patrimonio Arquitectónico y Edificado, Yaiza - Lanzarote, 2004.

2

P. Arias, "Simple methods for close range photogrammetry. Application to the study of tradicional agroindustrial constructions", PhD Thesis, University of Vigo, Pontevedra, Spain, 2003.

3

M. Vázquez, "Resistencia de materiales", Editorial Noela, Madrid, Spain, 1994.

4

R. Argüelles, F. Arriaga, "Estructuras de madera. Diseño y cálculo", AITIM, Madrid, Spain, 1996.

5

Eurocódigo 5, "Proyecto de estructuras de madera. Parte 1.1: Reglas generales y reglas para la edificación", Norma experimental UNE ENV 1995-1-1.

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