UNIVERSITÉ LIBRE DE BRUXELLES
ÉCOLE POLYTECHNIQUE DE BRUXELLES /BRUSSELS SCHOOL OF ENGINEERING
BUILDING,ARCHITECTURE AND TOWN PLANNING DEPARTMENT
T HEORETICAL AND EXPERIMENTAL STUDIES ON EARLY REINFORCED CONCRETE STRUCTURES
CONTRIBUTION TO THE ANALYSIS OF THE BEARING CAPACITY OF THE HENNEBIQUE SYSTEM
A
RMANDEH
ELLEBOISA DISSERTATION SUBMITTED FOR THE DEGREE OF DOCTOR IN ENGINEERING SCIENCE
ACADEMIC YEAR:2012–2013
SUPERVISOR:PROF.BERNARD ESPION -Université libre de Bruxelles
Printed by Presses Universitaires de Bruxelles (P.U.B.) Avenue Paul Héger, 42 – 1000 Brussels
www.ulb.ac.be/pub/
Copyright of the cover illustration:
François Morellet – 2006 – Reinforced concrete (0°-10°-80°) – fer à béton non rouillé – 30 x 30 x 4 cm – Ref. artiste: 06025 – Private collection. Courtesy: Galerie Jean Brolly, Paris
Committee members
PROF.PHILIPPE BOUILLARD - Chairman Université libre de Bruxelles
PROF.EUGEN BRÜHWILER
École polytechnique fédérale de Lausanne
PROF.RIKA DEVOS- Secretary Université libre de Bruxelles
PROF.BERNARD ESPION – Supervisor Université libre de Bruxelles
PROF.WERNER LORENZ
Brandenburgische Technische Universität Cottbus
PROF.JEAN-CLAUDE VERBRUGGE
Université libre de Bruxelles
PROF.INE WOUTERS – Member of the scientific advisory board Vrije Universiteit Brussel
This research was supported by the
Fonds National de la Recherche Scientifique F.R.S. - FNRS
Acknowledgments i
ACKNOWLEDGEMENTS
I have been fortunate to work with a large number of people during my PhD whom I would like to acknowledge.
I am thinking specifically of my supervisor Prof. Bernard Espion for his valuable advice, for sharing his expertise and for his confidence. Many thanks also to Prof. Philippe Bouillard for giving me the opportunity to start a PhD within the BATir Dept. and for supporting me from the beginning, and to Prof. Ine Wouters for her involvement in my PhD. Over the years, I have also counted on the help of Michel Provost (thanks so much for your positive attitude), Prof. Rajan Filomeno Coelho, Prof. Jean-Claude Verbrugge, Prof. Yves Rammer, Prof.
Arnaud Deraemaecker, Prof. Thierry Massart and Prof. Stéphanie Staquet. My thanks also to my ULB colleagues for creating such a nice work environment! It was a real pleasure working with you, from the 3rd floor to the 5th floor! I am particularly grateful to David Attas, Dominique Pierson, Benoit Descamps and Benoit Mercatoris for the interesting and relaxing talks...
Furthermore, several researchers were also present during my PhD, so thank you especially to Dr Michael De Bouw (Artesis), Prof. Rika Devos (ULB), Dr Stéphanie Van de Voorde (VUB), Prof. Inge Bertels (VUB), Dr Leen Lauriks (Artesis), Quentin Collette (VUB) and Koen Verswijser (VUB).
Thank you also to Gilles Vanhooren and Olivier Leclercq for their essential technical support at the LGC; to CRIC-OCCN and particularly to Dr Christian Pierre, Dr Olivier Germain, Dr Stéphane Wirgot, Paul Van Audenhove and Michel De Lanève for several laboratory experiments; to Dr Jean Dille and Loïc Mallet (4MAT-ULB) for their help in steel determination; to Vincent Fiquet (Orex) for the loan of the Ferroscan; to Prof. Alain Préat (ULB) and Marc Delogne for the petrographic analyses; to Jean-Claude Mongay for the help with the patents database. Many thanks as well to Simon Vaillant for his availability and kindness in the Hennebique archives, to the engineering offices: Origin Architecture &
Engineering (especially Charlotte Nys), Greisch (especially Alain Lothaire and David De Wolf), Ney & Partners (especially Henry Philippot and Olivier Gallez), bureau Matriche (especially Roger Matriche and Philippe de Grasse) and to Dr Anne Van Loo (CRMS), Dr Sara Wermiel (MIT), Yannik Van Praag (La Fonderie), Raymond Balau (La Cambre), Ghislain Claerbout (Monument), Guido Vanderhulst, Jean-Jacques Van Mol, Prof. Jean- Marie Bleus (ULg) for their help in finding information about early reinforced concrete structures in Brussels. I am also particularly grateful to Prof. Jean Christophe, Anne-Marie Camps and Prof. Patrick Burniat for so kindly allowing me access to the family archives of Paul Christophe. I also would like to express my gratitude to Graham Buik and Isabelle Toussaint for the friendly and efficient English proofreading of my thesis.
ii Acknowledgments Finally, I would like to thank my best friends for their positive encouragement all the way through. Last but not least, my most grateful thanks to my family for their understanding and dynamic support. I am indebted to them for finally being able to complete my PhD. And I would like to thank my husband Antoine for making me better and for his constant love and support for so many years...
Armande
Brussels, May 2013
Summary iii
SUMMARY
In the framework of the conservation of early reinforced concrete structures from the last third of the 19th century up to 1914, this research deals with superstructures (excluding foundations, roads, pipes, etc.) in reinforced concrete (in the modern sense of the term – i.e.
concrete made with artificial cement and rebars supplying tensile strength; thus, the combination of a metal profile embedded in concrete is excluded). The development of reinforced concrete as a building material started around 1880 and became widespread around the time of the First World War. Some of the structures concerned are listed as heritage properties today. Therefore they deserve specific and careful study to ensure long- term preservation of their historic, architectural, technical and socio-economic value. They bear witness to a period in construction history when reinforced concrete was a new material.
The outbreak of the First World War marked the end of the initial period of innovation, exploration and experimentation. By then, reinforced concrete had become widely accepted and adopted as a suitable and effective building material. However, present-day attempts at restoration often prove inadequate, due to incomplete understanding of this period of construction and the characteristics of the first generation of reinforced concrete. If the causes of degradation are incorrectly diagnosed, the repairs are likely to be inappropriate.
Moreover, the number of reinforced concrete structures requiring repair work is currently increasing with the natural ageing of the material. This phenomenon will continue to grow in the coming years.
With this in mind, the present research aims at identifying the specific structural characteristics of reinforced concrete structures erected before the First World War. Several axes of investigation were pursued in this PhD research and have resulted in the main observations detailed below.
- Based on a case study of the region of Brussels (Belgium), a database of structures built in reinforced concrete prior to 1914 was drawn up in order to place the material in its historical and geographical context. The inventory currently contains 507 examples and provides a panorama of the uses of reinforced concrete, ranging from numerous foundations and slabs to a complete structure from the end of the 1890s. This list is supplemented by a survey of a total of 605 patents filed for reinforced concrete in Belgium before the First World War. The early development of reinforced concrete was strongly related to national patenting, with a considerable number of systems being patented by private inventors for commercial purposes. Reinforced concrete profoundly transformed the building industry. All the professions working with the composite material had to change their approach, from the planning stage through to execution on the site. From the viewpoint of construction history, all these modifications make the time of the advent of reinforced concrete a particularly fruitful period to study.
iv Summary - From the survey of early reinforced concrete structures in Brussels and the database of Belgian patents, the supremacy of the Frenchman François Hennebique and his system on the Brussels market for reinforced concrete (and, by extension, on the Belgian market) before 1914 is incontestable. This commercial achievement resulted from a combination of factors: an efficient structural system, meticulous attention to the quality of on-site reinforced concrete execution, and the commercial acumen to develop the business through advertising and other media. The well-known Hennebique system represents a monolithic structure including slabs, beams and columns. In fact, this system changed over the decades of operation of Hennebique’s company, not so much in relation to the design methods (his original semi-empirical method continued to be used) but particularly in practical terms (the type and location of the rebars among others). The evolution of the system is analysed by means of technical drawings from about 30 Belgian projects designed by Hennebique between 1900 and 1930.
- After the building contractors, who had been the first to believe in the structural and economic potential of reinforced concrete, engineers invented the calculation models and architects started developing new shapes. The Belgian engineer Paul Christophe was among the first theorists of reinforced concrete. The publication of his book Le béton armé et ses applications in 1899 is internationally recognised as a milestone in the rational modelling of structural reinforced concrete elements. Prior to the present study, details of his life and work remained largely uninvestigated, but the discovery of large parts of his personal archives has allowed clarification of his role in the popularisation of reinforced concrete, especially at the theoretical level.
- Reinforced concrete structures around the beginning of the 20th century were initially governed by empirical models of calculation (and execution) developed by the individual constructors. Gradually, reinforced concrete standards, published between 1904 and 1923 and based on working stress analysis and elastic modular ratio theory, replaced the utility of the patented systems. The different theoretical approaches are briefly described in this research. Mastering the theoretical assumptions and calculation methods used at the time represents the first step towards an appreciation of the structural behaviour and the possible weaknesses that can be expected.
- A review, based on literature published at that time, of the properties of the components of reinforced concrete allows identification of the characteristic materials used in the concrete matrix and the metal reinforcements. The execution process and the available technological tools for erecting a reinforced concrete structure are also addressed, as these would have had a direct influence on the quality of construction. Non-destructive and destructive experimental laboratory tests were performed 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 reinforcements. Comparing the results obtained using different techniques also makes it
Summary v possible to determine the extent to which these techniques are reliable for the appraisal of early reinforced concrete structures.
- The structural efficiency of the Hennebique system is assessed based on an understanding of the principles of Hennebique’s semi-empirical method of calculation, but also – and primarily – by means of observations from experimental tests carried out on full-sized beams removed from the Colo-Hugues viaduct. Analysing and understanding the behaviour of the new composite material was a critical issue for promoting the use of reinforced concrete at the beginning of the 20th century. Today, what is required is a re-assessment of its structural behaviour. Three bending tests up to failure in simply supported conditions were performed at the BATir Department of the Université libre de Bruxelles on T-beams from the Colo- Hugues viaduct. This case study is representative of the majority of Hennebique structures, because the typical continuous straight T-beam is the main structural element of any Hennebique structure (bridge, building, etc.). The first test is 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 through yielding of the reinforcements followed by crushing of the concrete at mid-span. The second and third tests are 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 the adhesive bond between rebars. The results of these three experiments combined reproduce the actual behaviour of the viaduct in service. The bearing capacity of the Hennebique system in service and at ultimate has been demonstrated, at least for one loading case. 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. Two strengthening solutions are suggested as supplementary information.
- The pathologies observed in early reinforced concrete structures (honeycombs, corrosion of the rebars, and so on) are mainly attributable to the tools and techniques that the builders had at their disposal (handmade compaction, high water-to-cement ratio, etc.) and by the limited contemporary knowledge of the physical and chemical phenomena, especially with regard to long-term effects. In fact, the concrete quality of the viaduct is surprisingly satisfactory despite its great age, due to the fact that the whole structure was covered with plaster, like the majority of reinforced concrete structures designed at that time.
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. Working on existing buildings often requires a multidisciplinary and holistic approach. The present study could thus be extended in various areas. For example, other structural aspects could be studied more in depth, such as demonstration of the shear
vi Summary strength of the Hennebique system or detailed consideration of the reinforcements (low adherence, particular anchorage devices, etc.).
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.
Résumé vii
RÉSUMÉ
C'est dans le cadre de la conservation, au sens large du terme, que s'inscrit cette recherche sur les constructions en béton armé de première génération, c'est-à-dire de la fin du 19ème siècle au début du 20ème siècle. Cette recherche traite uniquement des superstructures, à l'exclusion des fondations, routes, tuyaux, etc., et en béton armé au sens moderne du terme, c'est-à-dire un béton réalisé à base de ciment artificiel et dont les armatures interviennent surtout pour reprendre les efforts de traction, ce qui exclut par exemple les utilisations de poutrelles métalliques enrobées de béton. Certains de ces ouvrages, réalisés entre 1880 et 1914, font aujourd'hui partie intégrante du patrimoine bâti, pour leurs valeurs architecturale, historique, technique ou aussi socio-économique. Ils jalonnent désormais l'histoire de la construction comme témoins d'une époque où le béton armé était un matériau nouveau. La Première Guerre mondiale marque la fin de cette période de premières innovations, d'explorations et d'expérimentations. Elle entérine l'acceptation et la diffusion du béton armé comme matériau de construction à part entière. Cependant, ainsi que le montrent certains projets de restauration actuels aux interventions inadéquates, il y a encore une méconnaissance des spécificités du béton armé de cette époque. Les causes de leurs dégradations mal diagnostiquées sont traitées de façon inappropriée. Or, dans les prochaines années, nombre de structures en béton armé construites dans la première moitié du 20ème siècle seront amenées à subir une rénovation suite au vieillissement naturel du matériau. C'est pourquoi pour conserver au mieux ces structures, il est indispensable d'étudier en détails leurs caractéristiques techniques pour ensuite intervenir, si nécessaire, de façon précise et adaptée.
Ce doctorat s'attèle donc à identifier les particularités des constructions en béton armé construites avant l'avènement de la Première Guerre mondiale, et plus spécifiquement à étudier leurs aspects structuraux. Plusieurs axes de recherche ont été développés et ont abouti aux principaux résultats suivants.
- Basé sur le cas de la région de Bruxelles-Capitale (Belgique), un inventaire des interventions en béton armé, construites avant 1914, a été dressé pour replacer le matériau dans son contexte historique et géographique. Cette base de données, comprenant 507 biens jusqu'à présent, illustre les types d'utilisation du béton armé dans la construction au début du 20ème siècle, d'abord des fondations ou simples planchers, jusqu'à une structure monolithique complète dès la fin des années 1890. Cet inventaire est complété par le relevé détaillé des brevets, au nombre de 605, déposés à ce sujet en Belgique avant la Première Guerre mondiale. Les brevets ont joué un rôle fondamental dans le développement du béton armé. Celui-ci était, en effet, régi par un foisonnement de systèmes commerciaux, majoritairement brevetés. L'introduction du béton armé a transformé en profondeur le secteur de la construction et notamment les professions liées tant à la phase de conception qu'au
viii Résumé chantier lui-même. Du point de vue de l'histoire de la construction, toutes ces mutations font de l'avènement du béton armé une période historique riche.
- A la lecture du panorama offert par les inventaires des constructions et des brevets, la prééminence de la compagnie du Français François Hennebique, et donc de son système, sur le marché bruxellois (et par extrapolation sur le marché belge) du béton armé avant 1914 est indéniable. La réussite commerciale de Hennebique résulte d'une combinaison de facteurs: un système efficace sur le plan structural, une qualité d'exécution de béton coulé en place fiable et méticuleuse ainsi qu'un sens développé des affaires, en maîtrisant l'art de la promotion et de la publicité notamment. Le système bien connu de Hennebique comprend un ensemble monolithique formé par des dalles (hourdis), poutres et colonnes. Ce système a, en réalité, évolué dans le temps, pas tant d'un point de vue théorique (les calculs de dimensionnement sont les mêmes) mais plutôt pratique (positionnement, type d'armatures, etc.). Cette évolution a été observée par l'étude d'une trentaine de cas pratiques exécutés par Hennebique entre 1900 et 1930 en Belgique.
- Après les entrepreneurs, qui ont été les premiers à croire aux nouvelles possibilités constructives qu'offre le béton armé ainsi qu'à son succès commercial, les ingénieurs en inventent les principes de calcul et les architectes en révolutionnent les formes. L'ingénieur belge Paul Christophe fut parmi les premiers théoriciens du béton armé. La publication de son ouvrage Le béton armé et ses applications en 1899 constitue une étape importante, et internationalement reconnue, pour le dimensionnement rationnel d'éléments structuraux en béton armé. Jusqu'à la présente recherche, sa vie et son œuvre étaient restées assez confidentielles mais la découverte d'une partie de ses archives personnelles a permis de clarifier son rôle dans la diffusion, surtout théorique, du béton armé.
- Les structures en béton armé d'avant la Première Guerre mondiale furent d'abord gouvernées par des méthodes empiriques de dimensionnement (et d'exécution) développées par chaque constructeur. L'apparition des premières règlementations entre 1904 et 1923, basées sur une analyse en contraintes admissibles et la théorie du coefficient d'équivalence, remplace ensuite peu-à-peu l'utilité des systèmes brevetés. Les différentes approches théoriques sont brièvement décrites dans cette recherche. Maitriser les hypothèses et les méthodes de calculs employées à l'époque est, en effet, une première étape pour comprendre le fonctionnement structural prévu et les potentielles défaillances de dimensionnement.
- A travers une lecture attentive de la littérature publiée à cette période, les matériaux intervenants dans la fabrication du béton armé (c'est-à-dire le béton et les armatures) et utilisés couramment au début du 20ème siècle ont été identifiés ainsi que les moyens disponibles à cette époque pour produire des structures en béton armé. Des méthodes d'essais non-destructives et destructives ont été appliquées principalement, sur le viaduc Colo-Hugues (1904, Braine-l'Alleud, système Hennebique) afin d'évaluer les caractéristiques mécaniques, les propriétés chimiques et la durabilité tant du béton que des renforcements
Résumé ix métalliques. Comparer les résultats de ces différentes méthodes permet d'aborder les limites d'utilisation de ces techniques, lorsqu'il s'agit d'évaluer structuralement des bétons armés de première génération.
- Grâce à la compréhension des principes, semi-empiriques, de dimensionnement appliqués par le bureau Hennebique en son temps mais surtout grâce aux observations déduites des essais expérimentaux réalisés sur des poutres de grandeur réelle, prélevées sur le viaduc Colo-Hugues, le fonctionnement structural réel du système Hennebique est évalué.
Comprendre et modéliser le comportement du nouveau matériau composite fut une problématique fondamentale pour accroître l'usage du béton armé au début du 20ème siècle.
Actuellement, il s'agit de réévaluer le comportement de ces structures. Trois essais jusqu'à rupture ont été menés, au département BATir de l'Université libre de Bruxelles, sur des poutres à gousset en T provenant du viaduc Colo-Hugues en conditions isostatiques et soumises à flexion. Ce viaduc des chemins de fer vicinaux est un cas d'étude représentatif de la majorité des constructions Hennebique, car la poutre de section en T est la structure typique du système Hennebique, utilisée tant dans les ouvrages d'art que dans les bâtiments. Le premier essai est une flexion 4 points sur une travée complète du viaduc (6 m de portée) pour obtenir la réponse en zone de moment maximum positif. La rupture ductile a eu lieu par plastification des armatures suivie d'un écrasement du béton en zone centrale, c'est-à-dire dans la zone la plus sollicitée. Deux éléments identiques de longueur de 4 m ont été essayés en flexion 3 points pour représenter le comportement sur appuis. La rupture de ces deux dernières expériences s'est produite suite à un glissement des armatures sur appuis (goussets à côté de la colonne). Il s'agit donc d'une rupture à caractère fragile. Les trois essais combinés représentent correctement la structure hyperstatique du viaduc dans son fonctionnement en service. La capacité portante réelle du système Hennebique en service et à l'état limite ultime, du moins dans un cas de chargement, a pu être expliquée.
Ces essais fournissent les données essentielles pour estimer l'efficacité structurale du système Hennebique et identifier ses faiblesses. Deux solutions de renforcement sont proposées en complément d'information.
- Les pathologies observées dans les bétons armés datant du début du 20ème siècle (nids de graviers, corrosion des armatures, etc.) sont, la plupart du temps, causées par les outils sommaires à la disposition des constructeurs (vibration à la main, rapport eau/ciment plus élevé qu'aujourd'hui, etc.) et par une connaissance limitée des phénomènes physiques et chimiques, surtout à long terme. En fait, la qualité du béton du viaduc Colo-Hugues est particulièrement satisfaisante malgré l'âge avancé du béton, grâce notamment à l'enduit recouvrant l'ensemble du viaduc, ce qui est le cas pour la majorité des structures de la période étudiée.
Cette recherche démontre que les constructions en béton armé datant de 1880 à 1914 diffèrent des ouvrages postérieurs en béton armé et qu'il serait utile pour leur restauration de
x Résumé tenir compte de ces spécificités. La connaissance approfondie des particularités des constructions en béton armé de première génération permettra, espérons-le, de contribuer à leur longévité en intervenant le moins possible sur les structures d'origine. Etant donné que l'étude des structures existantes nécessite le plus souvent une approche pluridisciplinaire, ce travail pourrait être poursuivi dans plusieurs domaines variés. Il resterait notamment à approfondir d'autres aspects de stabilité, comme par exemple la démonstration de l'efficacité à l'effort tranchant du système Hennebique ou encore la prise en considération plus détaillée des armatures (adhérence limitée, forme d'ancrage particulier, etc.).
Mots-clés
Béton armé, fin 19ème – début 20ème siècle, région de Bruxelles-Capitale, histoire de la construction, conservation et restauration du patrimoine, F. Hennebique, P. Christophe, essais expérimentaux en flexion, capacité portante, structure, dimensionnement, matériaux, béton armé durci, armature.
List of publications by the author xiii
LIST OF PUBLICATIONS BY THE AUTHOR
Peer reviewed journals
[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(8), 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), (accepted).
Chapters in books
[1] Hellebois, A., & Espion, B. (2014). Paul Christophe. In Nouvelle Biographie Nationale, published by the Académie Royale des Sciences, des Lettres et des Beaux-Arts de Belgique, 13, (in press).
[2] Hellebois, A. (2013). Première génération de béton armé: le règne des brevets, entre systèmes commerciaux et normes naissantes. In Denoël, J.-F., Espion, B., Hellebois, A., &
Provost, M. (Ed.), Histoire de béton armé: Patrimoine, durabilité et innovations, Brussels, 20- 25.
[3] Hellebois, A., & Espion, B. (2013). Conclusions. In Denoël, J.-F., Espion, B., Hellebois, A., & Provost, M. (Ed.), Histoire de béton armé: Patrimoine, durabilité et innovations, Brussels, 146-149.
[4] Hellebois, A. (2011). 13 notes. In Attas, D. & Provost, M. (Dir.), Bruxelles, sur les traces des ingénieurs bâtisseurs, Brussels: CIVA, 68-69, 72-73, 78, 91-92, 97, 108-109, 160-161, 185, 196-197, 198, 208, 209-210, 210.
[5] Hellebois, A. (2010). Les Trois Canadas, une villa pittoresque à Watermael-Boitsfort. In Van Mol, J.J. (Dir.), L’avenue Van Becelaere au passé recomposé, Brussels: Histoire et Science à Watermael-Boitsfort, 160–161.
Conference proceedings
[1] Espion B., Pierre C., Germain O., Lebon B., & Hellebois A., (2013). Characterisation of new ternary cements with reduced clinker content. In Sakai, K. (Ed.), Proceedings of the 1st International Conference on Concrete Sustainability, 145-152.
[2] Hellebois, A., & Espion, B. (2012). Insight into technological aspects of the evolution of the Hennebique reinforced concrete system. In Jasienko, J. (Ed.), Proceedings of the 8th International Conference on Structural Analysis of Historical Constructions, 2, 1160–1170.
[3] Hellebois, A., Rammer, Y., & Verbrugge, J.-C. (2012). Concrete Piling: Major Developments in the Historical Practice of Pile Foundations. In Carvais, R., Guillerme, A.,
xiv List of publications by the author Nègre, V., & Sakarovitch, J. (Ed.), Nuts & Bolts of Construction History. Culture, Technology and Society. Proceedings of the 4th International Congress on Construction History, Paris:
Picard, 2, 581–591.
[4] Hellebois, A. (2012). Technique et architecture, une alliance féconde. Arcs, voiles minces et parements en béton. In Le patrimoine d’ingénierie: 150 ans d’innovations structurales à Bruxelles, Ministère de la Région de Bruxelles-Capitale, Administration de l’Aménagement du Territoire et du Logement, 19–24.
[5] Hellebois, A., & Espion, B. (2011). Material properties of reinforced concrete at the turn of the 20th century: a review of original literature. In Rostislav, D. (Ed.), Proceedings of the 2nd WTA (Building Materials and Building Technology to preserve the Built Heritage) PhD Symposium, 248–260
[6] Hellebois, A., & Espion, B. (2011). Concrete properties of a 1904 Hennebique reinforced concrete viaduct. In Brebbia, A. & Binda, L. (Ed.), Proceedings of the 12th International Conference on Structural repairs and maintenance of architectural heritage, 589–600.
[7] Hellebois, A., & Espion, B. (2010). Domination of commercial patents in the evolution of early reinforced concrete. Case-study of the region of Brussels. In Gu, X. & Song, X. (Ed.), Proceedings of the 7th International Conference on Structural Analysis of Historical Constructions, Advanced Materials Research, 133, 119–124.
[8] Hellebois, A., Dewolf, D., & Provost, M. (2010). Structural assessment of the vaulted masonry ice storage Glacières Royales (1874) in Brussels. In Gu, X. & Song, X. (Ed.), Proceedings of the 7th International Conference on Structural Analysis of Historical Constructions, Advanced Materials Research, 134, 549–554.
[9] Hellebois, A., Germain, O., & Espion, B. (2010). Reinforcement assessment in early reinforced concrete constructions. In Forde, M. (Ed.), Proceedings of the 13th International Conference on Structural Faults and Repair, Edinburgh: Engineering Technics Press, 98–
108.
[10] Hellebois, A. (2009). The influence of rock-workers on early reinforced concrete constructions. Study case of the villa of Alphonse Vasanne in Brussels. In Schuermans, L.
(Ed.), Proceedings of the 1st WTA (Building Materials and Building Technology to preserve the Built Heritage) PhD Symposium, 33, 99–116.
Non peer reviewed journals
[1] Hellebois, A., & Espion, B. (2011). Réflexions sur la conservation des premières constructions en béton armé (1880-1914), Les Nouvelles du Patrimoine 132, 11–14.
[2] Hellebois, A., & Van de Voorde, S. (2011) Histoire de l'architecture en béton en Belgique (1920–1975), Les Nouvelles du Patrimoine 132, 15–18.
List of publications by the author xv [3] Hellebois, A. (2011). Reprise en sous-œuvre et patrimoine culturel immobilier, une journée d'étude riche en enseignements techniques, Les Nouvelles du Patrimoine 131, 44–
45.
[4] Hellebois, A. (2010). Le Stade des jeux, une construction en béton armé de première génération. In Balau, R., Urbanisation de Namur-Citadelle, de Lainé à Hobé: œuvre inachevée, potentiel sous-estimé, Les Cahiers de L'Urbanisme, 74, 59.
[5] Hellebois, A. (2010). Le béton armé, un matériau novateur pour les ponts en arc.
Exemples sur Meuse. In Balau, R., Namur 1893–1913. La SA Namur Citadelle et le projet urbain de Georges Hobé. Etudes et documents. Aménagement et Urbanisme (SPW-DGO4), 9, 80–81.
[6] Hellebois, A. (2010). Inventory of early reinforced concrete constructions in the region of Brussels (prior to 1914). Study of their conservation and restoration problems. Raymond Lemaire International Centre for Conservation of Monuments and Sites Newsletter, 23–24.
Other
[1] Espion, B., & Hellebois, A. (2010/11/06). Le Béton Armé. Emission de télévision RTBF:
Télétourisme – Institut du Patrimoine Wallon. Available for consultation at http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/67336
Table of contents xvii
TABLE OF CONTENTS
ACKNOWLEDGEMENTS I
SUMMARY III
RÉSUMÉ VII
LIST OF PUBLICATIONS BY THE AUTHOR XIII
TABLE OF CONTENTS XVII
ABBREVIATIONS AND SYMBOLS XXIII
INTRODUCTION 1
RESEARCH CONTEXT 3
AIM AND SCOPE OF THE THESIS 4
METHODOLOGY OF THE SOURCES 5
OUTLINE OF THE THESIS 8
CHAPTER 1
FROM REINFORCED CONCRETE PATENTS TO PRACTICE: THE BRUSSELS CASE STUDY 15
1.1.CONTEXT OF THE EARLY DEVELOPMENT OF REINFORCED CONCRETE 17 1.1.1. Influence of rock work on the birth of reinforced concrete 17 1.1.2. Breakthrough of reinforced concrete as a structural building material 19 1.2. METHODOLOGY FOR DRAWING UP THE DATABASES OF PATENTS AND REALISATIONS 23
1.2.1. Legal framework for patent submission in Belgium before 1914 23
1.2.2. Peculiarities of reinforced concrete patents 27
1.2.3. Reinforced concrete interventions in the region of Brussels 30
1.3.RESULTS AND ANALYSIS OF THE TWO DATABASES 33
1.3.1. Expansion of the types and uses of reinforced concrete structural elements 33 1.3.2. Significant reinforced concrete patents and interventions 41
1.3.3. Evolution of the Hennebique system 68
1.3.4. Impact of reinforced concrete among professionals in the building sector 76
1.4. CONCLUSIONS 87
xviii Table of contents CHAPTER 2
MATERIALS IDENTIFICATION FROM ORIGINAL COMPOSITION TO LONG-TERM PROPERTIES 91
2.1. INTRODUCTION 93
2.2.MATERIALS ANALYSIS DEDUCED FROM THE LITERATURE REVIEW 94 2.2.1. Identification of the mix constituents of concrete 94
2.2.2. Concrete mix design 101
2.2.3. Type of metal reinforcements 104
2.2.4. Mixing, tamping and casting reinforced concrete onsite 107
2.2.5. Controlling the quality of the materials 111
2.3.EXPERIMENTAL PROGRAMME 113
2.3.1. Description of the tested specimens 114
2.3.2. Methods of testing applied to hardened concrete 118
2.3.3. Methods of testing applied to steel samples 121
2.4.RESULTS AND ANALYSIS OF GENUINE REINFORCED CONCRETE MATERIAL 124 2.4.1. Attempts to reveal the actual composition of the Hennebique concrete 124 2.4.2. Mechanical performance and ageing process of the concrete 129
2.4.3. Cover thickness measurement with covermeter 135
2.4.4. Characteristics of the metal rebars 138
2.5.DISCUSSION 141
2.5.1. Relationships between concrete compressive strength and its composition141 2.5.2. Localisation and identification of the reinforcement 145 2.5.3. Comparison with other similar Hennebique case studies 147
2.6.CONCLUSIONS 149
CHAPTER 3
DESIGNING REINFORCED CONCRETE ELEMENTS AT THE TURN OF THE 20TH CENTURY 153
3.1. REINFORCED CONCRETE ACCIDENTS AS INITIATORS OF THEORETICAL RESEARCH 155 3.2.THE ROLE OF CHRISTOPHE IN RATIONAL REINFORCED CONCRETE MODELLING 160
3.2.1. Biography of the Belgian engineer Paul Christophe 160 3.2.2. The ins and outs of Le béton armé et ses applications 167 3.2.3. The reinforced concrete network of Paul Christophe 175 3.3. PRINCIPLES OF THE COMPUTATION METHOD PROPOSED BY THE FIRST STANDARDS 183 3.3.1. Introduction of reinforced concrete as a public domain material 183 3.3.2. The establishment of the working stresses theory 186 3.4.LONGITUDINAL STRESSES IN ELEMENTS SUBJECTED TO BENDING 192
Table of contents xix
3.5. SHEAR STRESSES IN PIECES SUBJECTED TO BENDING 207
3.6. COMPRESSION OF COLUMNS 214
3.7. CONCLUSIONS 218
CHAPTER 4
LOADING TESTS UP TO FAILURE OF TYPICAL REINFORCED CONCRETE HENNEBIQUE T-BEAMS 221
4.1.INTRODUCTION 223
4.2. PREVIOUS EXPERIMENTAL STUDIES ON HENNEBIQUE T-BEAMS 224
4.3.EXPERIMENTAL PROGRAMME 227
4.3.1. Description of the specimens and material properties 227
4.3.2. Test methods and measurements 230
4.4. RESULTS 232
4.4.1. Test 1: behaviour at ultimate 232
4.4.2. Tests 2 and 3: behaviour at ultimate 234
4.5.ANALYSIS AND DISCUSSION 237
4.5.1. Combination of the three tests 237
4.5.2. Serviceability limit state analysis 238
4.5.3. Ultimate limit state analysis 240
4.6. CONCLUSIONS 243
CHAPTER 5
PROSPECTIVE ISSUES FOR ENGINEERING PRACTICE 247
5.1.PARTICULAR RISKS OF DURABILITY OF EARLY REINFORCED CONCRETE STRUCTURES 249 5.2. REPAIR METHODS APPROPRIATE TO HISTORIC REINFORCED CONCRETE IN A NUTSHELL 255
5.2.1. Remedial action for reinforced concrete structures 256 5.2.2. Conservation strategy for significant reinforced concrete structures 260 5.3.BASIC TECHNICAL PROPOSALS FOR STRENGTHENING THE HENNEBIQUE T-BEAM 262
5.3.1. Available strengthening products for reinforced concrete beams in flexure 263 5.3.2. Experimental studies performed on reinforced concrete beams in flexure 267 5.3.3. Strength assessment of the retrofitted reinforced concrete beam 270
5.4.CONCLUSIONS 278
CONCLUSIONS AND PERSPECTIVES 281
BIBLIOGRAPHY 291
xx Table of contents
APPENDICES A
A. REINFORCED CONCRETE PIONEERS A
A.1. France B
A.2. Germany G
A.3. The Netherlands I
A.4. Other countries J
A.5. Lists of Belgian professionals M
B. DATABASES OF REINFORCED CONCRETE PATENTS AND REALISATIONS (BEFORE 1914) R C. CONTEMPORARY ISSUES WITH THE ARCHIVES OF FORMER CONSTRUCTORS R D. PAUL CHRISTOPHE: PUBLICATIONS AND PROJECTS ON REINFORCED CONCRETE S
Abbreviations and symbols xxiii
ABBREVIATIONS AND SYMBOLS
Abbreviations
AAM = Archives d’Architecture Moderne
ABEM = Association Belge pour l’Etude, l’Essai et l’Emploi des matériaux ACI = American Concrete Institute
AIA = American Institute of Architects
AIPC-IABSE = International Association of Bridge and Structural Engineers An. = Anonymous
ASCE = American Society of Civil Engineers ASTM = American Society for Testing of Materials ATPB = Annales des Travaux Publics de Belgique AVB = Archives de la Ville de Bruxelles
BATir = Building, Architecture and Town Planning Department of the Université libre de Bruxelles
B&E = Beton und Eisen
BNF = Bibliothèque Nationale de France
BTSR = Bulletin Technique de la Suisse Romande CCE = Concrete and Constructional Engineering CFRP = carbon-fibre reinforced polymer
CRIC-OCCN = Belgian Center for scientifical and technical researches for the cement industry
DT = Destructive Test e.g. = for example EB = Externally Bonded
SEM-EDX = Scanning Electron Microscope- Energy Dispersive Spectroscopy
Febelcem = Fédération de l’Industrie Cimentière Belge/Federatie van de Belgische Cementnijverheid
fib = Fédération International du Béton FRP = Fibre Reinforced Polymer GL = Gazette de Lausanne i.e. = that is
ICE = Institution of Civil Engineers
Icomos = International Council on Monuments and Sites
IFA-FH = Cité de l’architecture et du patrimoine, Institut Français d’Architecture, Centre d’archives d’architecture du 20ème siècle, Fonds Bétons armés Hennebique
KBR = Bibliothèque Royale de Belgique KUL = Katholieke Universiteit Leuven
LBA = Le Béton Armé, organe des Concessionnaires et Agents du système Hennebique
xxiv Abbreviations and symbols LGC = Civil Engineering Laboratory of the Université libre de Bruxelles
LVDT = Linear Variable Differential Transformer NACU = National Association of Cement Users NDT = Non-Destructive Test
NSM = New-Surface Mounted (or Mounting) OPRI = Office Belge de la Propriété Intellectuelle RC = Reinforced Concrete
RIBA = Royal Institute of British Architects
RILEM = Reunion Internationale des Laboratoires et Experts des Matériaux, Systèmes de Construction et Ouvrages
S.n. = Unidentified – without the name of an author SLS = Serviceability Limit State
UGent = Universiteit Ghent UK = United Kingdom
ULB = Université libre de Bruxelles ULS = Ultimate Limit State
USA = United States of America
Symbols: capital letters total section of the element water absorption
total section of the stirrups used in a transversal section of the beam
concrete section inside the reinforcement frame concrete section
area of FRP
the fictious section of the spirals section of steel in tension
area of reinforcement in tension
area of reinforcement in compression
section of the bolt
section of one stirrup
section of the whole strands of shear force stirrup cement content
chloride content
grain size distribution nature of aggregates
Young modulus of concrete
Young modulus of CFRP external sheets
Abbreviations and symbols xxv Young modulus of steel
bending stiffness at the uncracked or cracked stage depending on the analysed section
strength of the steel plate to lateral pressure resultant compression
force in the FRP resultant tension
distance of the haunch from the tensile steel section to the surface
depth of the haunch
the second moment of area of the homogenised section calculated in the uncracked state (Chapter 3)
second moment of area of the section calculated in the uncracked state second moment of area of the concrete
second moment of area of the existing unstrengthened section in the cracked state
second moment of area of the strengthened cracked section second moment of area of the steel
safety coefficient (Chapter 3) , , , empirical constants
energy absorbed during the Charpy impact test span of the beam
distance between two ribs bending moment
saturated mass dry mass
statically indeterminate negative moment at intermediate supports
statically indeterminate positive moment at mid-span
design ultimate moment
resistant bending moment obtained experimentally resistant bending moment
acting bending moments at the critical section in Test 2
acting bending moments at the critical section in Test 3
acting bending moment at mid-span acting bending moment
distribution of bending moment in the reference system due to a unit bending solicitation acting at hinge
bending moment at mid-span for a simply supported beam
maximum bending moment measured experimentally at the critical section Test 2
maximum bending moment measured experimentally at the critical section Test 3
xxvi Abbreviations and symbols theoretical cracking bending moment at the critical section Test 2
theoretical cracking bending moment at the critical section Test 2
theoretical cracking bending moment at the critical section Test 3
theoretical cracking bending moment at the critical section Test 3
theoretical cracking moment at mid-span
bending moment when strengthening at mid-span at the serviceability limit state bending moment in strengthened section at steel yield
maximum axial load that the column can bear (Chapter 3) variable loads (Chapter 4)
design shear strength
shear strength of bolt
local crushing of concrete
critical load
applied loads during loading test
maximum resistance that the stirrups can bear (permissible shear or tensile steel stresses) static moment
shear force in the bolts
maximum tensile force in the CFRP shear force
volume of voids (Chapter 2)
difference between shear force at ultimate and at the applied load when strengthening cement paste volume
design shear force
water content for fresh concrete
water content for fresh concrete
Symbols: lower-case
effective width (Chapter 4) width of the slab or the flange
width of adhesive
effective width width of the FRP
width of the flange
width of the steel plate width of the web
concrete cover
quantity of cement (Chapter 2)
Abbreviations and symbols xxvii concrete cover of the compressive steel section
depth of carbonation (Chapter 2) depth of the slab or the flange
nominal diameter of the bolt (Chapter 5) the effective depth
diameter of the hole
exact cover depth
measured cover average depth of the slab
distance between bolts and the end of the steel plate average compressive strength of concrete
in-situ characteristic concrete compressive strength deduced from EC2
in-situ characteristic concrete compressive strength deduced from EN 13791
characteristic cylinder compressive strength of concrete
concrete compressive strength at 28 days
concrete compressive strength resulting from the Schmidt hammer test
concrete compressive strength resulting from the Schmidt hammer test including carbonation correction
normalised concrete compressive strength on cylindrical cores
concrete tensile strength
average calculated tensile strength of concrete characteristic tensile strength of CFRP external sheets
ultimate steel strength for bolt
ultimate steel strength
ultimate steel strength of the plate average yield strength of steel
yield strength of bolt
design value of the strength of the transversal reinforcements superimposed loads
depth of the beam or the slab
distance between the steel rebars in tension and the upper fibre (Chapter 3) height of the bolt into concrete (Chapter 5)
buckling coefficient (Chapter 3) number of the stirrup
geometry factor
minimum anchorage length required anchorage
xxviii Abbreviations and symbols coefficient depending on the type of concrete (Chapter 3)
equivalent factor, modular ratio
number of bolts for half steel plate (Chapter 5) permanent loads (Chapter 4)
uniformly distributed external loads dead load
distance between bolts
spacing between transversal rebars spacing between stirrups
age (Chapter 2) thickness of the plate
thickness of the FRP
thickness of the steel plate volume of water
water-to-cement ratio position of the neutral axis
position of the neutral axis
neutral axis at the uncracked stage
position of the neutral axis in the strengthened section point in the span where the FRP is no longer required distance of the resultant compression from the neutral axis internal level arm
distance between centre of gravity of the inferior and superior elements of the truss
distance between neutral axis and the centre of gravity of the rebars in tension
distance of the compressive steel section from the neutral axis
Symbols: Greek letters
geometrical coefficient (Chapter 5) safety factor
partial safety factor for modulus of elasticity of FRP
partial safety factor for manufacture of FRP
partial safety factor for FRP strength
partial safety factor for strain of FRP partial safety factor for concrete
partial safety factor of the bolt partial safety factor for steel
bending moment at mid-span due to 75% of the variable loads.
interspacing of the stirrup
Abbreviations and symbols xxix interspacing of the previous stirrup
length along the beam between position of maximum and moment at first yield at the steel stress increase for steel after strengthening
stress increase for concrete after strengthening strain
concrete strain
ultimate compressive strain of concrete
design rupture strain of FRP
characteristic failure strain of FRP
FRP strain at maximum design moment
maximum strains in the yield zone yield strain of steel
yield strain of steel (Chapter 5)
factor in the relationship between the resistive bending moment and the geometry of the slab
density of concrete or standard deviation
allowable concrete compressive strength
concrete stresses before strengthening concrete stress
concrete tensile stress
failure stress of the material
FRP stress at maximum design moment
FRP stress at steel yield
maximum stress in the critical section
limit stress of spiral reinforcement (Considère design)
allowable tensile strength of steel
steel stresses before strengthening steel stress
longitudinal shear stresses at the plate ends (Chapter 5) tangential stresses
design bond strength of the connection
total maximum longitudinal shear stress within the yield zone
allowable concrete in shear
limiting longitudinal shear stress in concrete
limiting longitudinal shear stress in the yield zone mean longitudinal shear stress in the yield zone
xxx Abbreviations and symbols shear steel allowable stress
local longitudinal shear stress at crack positions
factor in the relationship between the percentage of steel reinforcement and the geometry of the slab
diameter of rebar
plastic rotation required in Test 2 rotation required in Test 3
actual rebars diameter
plastic rotation at the plastic hinge i
actual rebars diameter
Symbols: chemical elements Al = aluminium
Al2O3 = aluminium oxide Ca = calcium
CaO = calcium oxide CO2 = carbon dioxide Cr = chromium Fe = iron
K2O = potassium oxide MgO = magnesium oxide Mn = manganese
MnO = manganese oxide Na2O = sodium oxide Ni = nickel
P = phosphorus S = sulphur Si = silicon
SiO2 = silica dioxide
INTRODUCTION
INTRODUCTIONCHAPTER 1CHAPTER 2CHAPTER 3CHAPTER 4CHAPTER 5APPENDICESBIBLIOGRAPHY
CONCLUSIONS AND PERSPECTIVES
Introduction 3 | 326
RESEARCH CONTEXT
Concrete is widely used around the world and has become part of the surroundings in our daily life. However, this building material, so common nowadays, only appeared in construction during the second half of the 19th century. Indeed, the two materials constituting reinforced concrete (RC), i.e. concrete and steel, were then available in large and uniform quantities as a result of the progress in the cement industry and metallurgy. This research studies RC structures of the first generation, namely those built before 1914. This period, around 1880–1914, constitutes a turning point between on the one hand RC considered as a system of construction, defined by commercial patents, and on the other hand RC considered as a new structural material, governed by standards and open to widespread utilisation. The different names commonly employed to describe RC at that time also reveal the experimental and innovative aspects of this system of construction. At the turn of the 20th century, RC emerged as an appealing material for any application in civil engineering or building construction, from foundations to a complete bridge, house, factory or public building. The suggested attributes in favour of RC are its fireproofing quality, strength, durability (protection of steel against corrosion), watertightness, hygienic advantage, and possibly economy of construction. After the First World War, RC became a material in the public domain that anyone could produce.
Enthusiasm and interest for the study and preservation of the first generation of RC structures is rather new. The interest in RC structures and their history has grown extensively over last three decades. Many studies have been dedicated to early RC buildings, from the point of view of architectural history (Giedion, 1928; Onderdonk, 1928; Collins, 1959; Fanelli
& Gargiani, 2008), construction history (Lemoine, 1991; Elliott, 1992; Barjot, 1999; Deuten, 2003; Simonnet, 2005), and concrete conservation (de Jonge, 1997; Macdonald, 2003;
Macchi, 2006; Reed et al., 2008; Heinemann, 2013). But RC plays a major role not only in the history of architecture but also in the history of structural and civil engineering. However, a minority of studies (Alford, 1990; Gori, 1999; Jürges, 2000; Mezzina et al., 2010) have concerned the structural analysis of early RC and an assessment of the efficiency of the different systems in use before 1914. Moreover, many studies on early RC material are carried out in a national context, including, to cite only a few per country: France (Lemoine, 1991; Simonnet, 1992; Delhumeau, 1999; Bosc et al., 2001), Germany (Haegermann et al., 1964; Kurrer, 2008; Stegmann, 2009), the Netherlands (Disco, 1990; Deuten, 2003;
Heinemann, 2013), the United Kingdom (Cusack, 1981; Stirling, 2001; Newby, 2001;
Sutherland et al., 2001), Italy (Nelva & Signorelli, 1990; Gori & Muneratti, 1995; Iori, 2001), Portugal (Sena-Cruz, 2013), Spain (Burgos Núñez, 2009), Switzerland (Gubler, 1985; Gubler
& Neuenschwander, 1985; Jost, 2006), the United States (Slaton, 2001; Wermiel, 2009).
Few related to the Belgian context (Baes, 1932; Fredricx & De Meyer, 2004; Van de Voorde,
4 | 326 Introduction 2011; Espion, 2013a). However, the local context is essential for understanding the uses of early of RC and its expansion in connection with the international context, with interrelations between countries and pioneers.
The early RC masterpieces are witnesses to a period of construction and today are recognised as part of our heritage. They represent specific building technologies, responding to the needs and desires of the population at the beginning of the 20th century. The preservation of early RC buildings thus aims to recognise their social, cultural, architectural and technical significance. Therefore, these buildings deserve specific and careful study to preserve their qualities in the long term. However, many structural analyses carried out today ignore the characteristics of old RC due to limited knowledge of the RC materials and structures from the first decades of the 20th century (also observed by (Heinemann, 2013)).
Therefore, intervention in the framework of a restoration or rehabilitation project is often inadequate, due to a misunderstanding of this period of construction. Moreover, the repair methods do not sufficiently take into consideration the concepts underlying concrete conservation. Nevertheless, the number of RC structures requiring repair work, whatever the date of construction, is currently increasing with the natural ageing of the material. This phenomenon will continue to grow over the coming years. Indeed, the majority of repair and maintenance worldwide relates to the durability problems of RC structures (fib Bulletin 40, 2001). Therefore, it is necessary also to deal with the repair, strengthening and upgrading of RC, including the early RC structures. The approach towards preservation of existing structures is also part of the concept of sustainability, reducing waste, energy consumption, etc. (Foster et al., 2007).
AIM AND SCOPE OF THE THESIS
The prime objective of this study is to identify the specific characteristics of early RC structures (1880s–1914) built in Brussels and, by extension, in Belgium. RC is basically defined as a combination of metal rebars embedded in a concrete matrix, where steel supports mainly tensile stresses and concrete resists compressive stresses. The goal of this research is to understand as much as possible of the original construction, in order to be able to preserve it on a long-term basis. It is intended to analyse the characteristics of early RC structures by means of theoretical and experimental research and compare information available in the literature with real and current data, taking into account the ageing of the material. The majority of the experimental tests presented in this research were carried out on a Hennebique monolithic structure (T-beam), as this was the most common system used at that time.
Accordingly, five issues are addressed in this PhD research. Chapter 1 deals with the
Introduction 5 | 326 submissions of RC patents, the types of RC interventions and the actors in RC propagation
in Brussels before 1914. It aims at representing the Belgian context of RC development, by identifying the structural types and systems commonly used at that time. Chapter 2 presents the materials, methods and tools used for erecting RC structures at the turn of the 20th century. All these parameters play a role in the durability of RC structures. The findings are compared with material analysis carried out today on early RC structures, with special attention to the Hennebique system. Chapter 3 details the basis of designs and calculation models developed at that time. It also includes an extensive biography of Paul Christophe, an influential figure in the theoretical development of RC in Belgium and abroad. Chapter 4 approaches the structural qualities and deficiencies of the early Hennebique beam-and-floor system by means of three full-scale experimental tests up to failure. These experiments were performed on the Colo-Hugues viaduct, built in Braine-l’Alleud in 1904 and designed by Hennebique. A girder bridge with a typical T-beam as the main structural element, this case study is representative of Hennebique RC production at the turn of the 20th century. Chapter 5 summarises the most common pathologies of early RC structures and reviews possible actions for suitable conservation. Two appropriate solutions for strengthening the Hennebique T-beam are also proposed.
In addition to the clear interest for construction history, studying the technical characteristics of RC structures built at the turn of the 20th century will certainly help to contribute to proper preservation of this type of heritage. Hence, this research fulfils the requirements of a holistic approach to heritage preservation, from acquisition of data to structural analysis, diagnosis of the state of conservation and safety evaluation aiming at defining relevant remedial measures (Victoria Falls Icomos Charter, 2003). The ambition is also to guide decision- makers dealing with early RC to perceive the particular issues of this worthy heritage, and thus to take relevant decisions concerning its preservation. Deep historical and structural understanding of the first phase of RC is actually crucial for correctly estimating the efficiency of these structures. Hopefully, this will lead to limited intervention when restoring old RC structures, based on relevant, and even sustainable, conservation.
METHODOLOGY OF THE SOURCES
At the end of the 19th century and the beginning of the 20th century, RC innovations were mainly publicised through numerous journals, international congress proceedings, manuals, handbooks, university lectures, specification books, standards and advertisements. The topics addressed in the literature, either from before 1914 or recently published, are diversified in terms of the types of information that the present research covers, such as material definitions, standards, architecture, calculation and modelling, repair, techniques of appraisal, etc. The dates indicated in the thesis for early RC invention, construction, testing,
