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logo LGC Photo AHs_2011_4 Photo AHs_2011_2   Construction history in relation to the preservation of engineering and architectural heritage
   
Contact Bernard Espion, Armande Hellebois
   
Keywords

Reinforced concrete, late 19th – early 20th century, Brussels, construction history, heritage conservation, F. Hennebique, P. Christophe, full size experimental tests, structural assessment, material properties, hardened concrete, reinforcement.

   
Title of the PhD research

Theoretical and experimental studies of early reinforced concrete structures. Contribution to the analysis of the bearing capacity of the Hennebique system.

   
Description of the research project

This research deals with early reinforced concrete structures from the last third of the 19th century up to 1914 with a view to ensuring their sustainable conservation. As shown by many inadequate interventions in restoration projects, misunderstanding of the characteristics of this first generation of reinforced concrete is still common. Therefore, this doctoral research aims at identifying the specific structural characteristics of reinforced concrete structures erected before the First World War. Several axes of investigation were pursued, resulting in the following main observations:

- Based on a case study of the region of Brussels (Belgium), a database of 507 examples prior to 1914 was drawn up and provides a panorama of the uses of reinforced concrete. This list is supplemented by a survey of a total of 605 patents filed on this topic in Belgium before the First World War. The early development of reinforced concrete was strongly related to national patenting.

- From the survey and the database, the supremacy of the Hennebique system on the Brussels reinforced concrete market before 1914 is incontestable. The well-known Hennebique system actually changed during the decades of the company's operation. The evolution of the system is analysed by means of technical drawings from about 30 Belgian projects from 1900 up to 1930.

- Until the present study, the biography and bibliography of the Belgian engineer Paul Christophe, one of the first theorists of reinforced concrete, remained uninvestigated. The discovery of large parts of his personal archives allows clarification of his role in popularising the rational modelling of structural reinforced concrete elements.

- The different theoretical but empirical approaches are briefly described in this research and are compared to the first reinforced concrete standards, published between 1904 and 1923. Mastering the assumptions and calculation methods used at the turn of the 20th century is a first step towards understanding the expected structural behaviour and possible weaknesses.

- The properties of the components of reinforced concrete and the execution process commonly used at the turn of the 20th century can be identified through a review of the contemporary literature. Non-destructive and destructive experimental tests were carried out on original samples, mainly removed from the Colo-Hugues viaduct (1904, Braine-l'Alleud, Hennebique system), in order to assess the mechanical properties, chemical features and durability issues for concrete and ferrous rebars.

- Three bending tests up to failure were performed on beams removed from the Colo-Hugues viaduct at the BATir Department. The first test was a four-point bending test on a complete span (6 m) of the viaduct to obtain the response of the central part under positive bending moment. The flexural failure was ductile and occurred though yielding of the reinforcements followed by crushing of the concrete at mid-span. The second and third tests were three-point bending tests on 4 m long specimens centred on the column, representing the behaviour of the beam around the supports. These showed a sudden slipping failure due to loss of adhesive bond between rebars. These experimental tests provide essential data for a better understanding of the mechanisms of failure and reveal the main weaknesses of the Hennebique T-beam.

This research establishes that reinforced concrete structures from 1880 to 1914 differ from later reinforced concrete structures. Taking into consideration the features of early reinforced concrete structures will contribute to ensuring sustainable conservation with limited intervention, thus preserving as much as possible of the original structure when restoration work is undertaken.

     
Support

This project was funded by the Fonds National de la Recherche Scientique (F.R.S.-FNRS) between 2009 and 2013.

     
Selected publications

[1] Hellebois, A., & Espion, B. (2013). Test up to failure of a typical RC Hennebique T-beam. Proceedings of the ICE - Structures and Buildings, 166(9), doi:10.1680/stbu.12.00036.

[2] Hellebois, A., Launoy, A., Pierre, C., De Lanève, M., & Espion, B. (2013). 100-year-old Hennebique concrete, from composition to performance. Construction and Building Materials, 44, 149–160. doi:10.1016/j.conbuildmat.2013.03.017.

[3] Hellebois, A., & Espion, B. (2013). Structural weaknesses of the Hennebique early reinforced concrete system and possible retrofitting. Structural Engineering International, 23(4).