Historical overview on criteria and techniques for reducing timber structures deformability

ABSTRACT

Timber represents one of the first construction materials of mankind, thanks to its excellent mechanical, physical, as well as technological, characteristics. However, in addition to the other timber properties, a high deformability must be included. This is strictly conditioned by the intensity, direction and duration of the stressing load and by the constraints stiffness degree and arrangement. A behavior which was taken in account since the earliest constructions in recorded history, by introducing different bracing methods aimed at the structural stiffening. The advancement of science and a consequently deeper knowledge on timber rheological behavior, and in general on structural mechanics, implied the carrying out of ever more effective solutions for the deformability mitigation, regarding both vertical structures (i.e. timber frames) and roof carpentry. The wooden frames, throughout history, did not emphasize a high variability with regard to devices for limiting the in-plane deformability. Conversely, roof carpentry was characterized by an extreme richness of variants, in particular, in the buildings of northern and central Europe. Furthermore, studies concerned with the truss theory development, namely graphical tools and numerical formulations applied to the structure sizing and safety evaluations, are reported in this article.

KEYWORDS:

• Timber structure
• deformability
• bracing
• history of constructions
• truss theoretical studies

Disclosure statement

No potential conflict of interest was reported by the author.

Notes on contributor

Nicola Ruggieri, architect, PhD, specializes in historical timber structures and constructive techniques. He was the Italian delegate at the EU-COST ACTION FP1101/Assessment, Reinforcement and Monitoring of Timber Structures (Trento, Londra, Antalya, Praga, Trondheim, Wroclaw). He is creator and member of the scientific committee of the international conference HEaRT (Cosenza, 2013; Lisbona, 2015). He is the author of about 60 publications (monographs, scientific articles, conference papers, editorships). He has taught at the University of Calabria, Sapienza of Rome and at the University of Rome Roma Tre. Since 2015 he is member of the Segreteria Tecnica di Progettazione of the Parco Archeologico di Pompei.

Notes

1. Timber has, maintaining approximately unaltered its mechanical properties, an elevated durability if immersed in an environment with adequate temperature and humidity.

2. P. Gros, ed. Vitruvio De Architectura (Torino: Giulio Einaudi Editore, 1997).

3. According to the abbé Laugier that in 1753 published his Essai sur l’architecture, in which he referred how to discover the true principles of architecture.

4. The strongly hierarchical order that distinguishes the timber structures has been schematized by Professor Tampone in: elements, i.e. members (a first level) that are connected among them to form structural units (a second level) for example trusses; various structural units are connected to form a structural system (a third hierarchical level), for example the whole roof carpentry.

5. A. J. Evans, The Palace of Minos at Knossos, vol. I–IV (London, 1921–1935).

6. E. Tsakanika, ‘The constructional analysis of timber load-bearing systems as a tool for interpreting Aegean Bronze Age architecture’ (proceedings of the Symposium ‘Bronze Age Architectural Traditions in the Eastern Mediterranean: Diffusion and Diversity’, May 7–8, 2008, Munich).

7. Ibid.

8. The extreme difference of elastic module value between the two materials, timber and masonry, entails the absorbing of loads originating from floors almost entirely by the masonry.

9. An exception is represented by the monumental grave of Lefkas in Eubea of the tenth century bc. A construction characterized by a wooden colonnade with dimensions 47 × 10 m; a timber use that, however, did not have important repercussion on the constructive development of the Greek architecture, especially that of the Archaic period (Popham M. R., Calligas P.G., Sackett L.H., 1993, Lefkandi II: The Protogeometric Building at Toumba. The excavation, architecture and finds, British School of Archeology at Athens, Oxford.)

10. N. Ruggieri, ‘Timber Framing Wall in the Italic civilization’, in Historic Earthquake-Resistant Timber Frames in the Mediterranean Area, eds. N. Ruggieri, G. Tampone, and R. Zinno (Springer International Publishing Switzerland).

11. P. Gros, ed. Vitruvio De Architectura (Torino: Giulio Einaudi Editore, 1997).

12. V. Galliazzo, I ponti romani (Treviso: Canova, 1995).

13. G. A. Breymann, Trattato generale di costruzioni civili (Milano: Francesco Vallardi, 1885).

14. S. Stellacci, N. Ruggieri, and V. Rato, Gaiola vs Borbone system: A Comparison between 18th C Anti-Seismic Case Studies. International Journal of Cultural Architectural Heritage (2016); F. Pugi and S. Galassi, ‘Seismic Analysis of Masonry Voussoir Arches according to the Italian building code’, Ingegneria Sismica 3, (2013): 33–55.

15. The scientific literature presents opposed interpretations about the real contribution of bracings in masonry reinforced with wooden frames. Kouris e Kappos (L. A. S. Kouris and A. J. Kappos, ‘Detailed and Simplified Non Linear Models for Timber-Framed Masonry Structure’, Journal of Cultural Heritage no. 13 (2012): 47–58), for example, affirmed that the structural system stiffness is ensured by the timber bracings. In this case the masonry is only indirectly useful, preventing the instability phenomena of the diagonals, designed for guaranteeing a limited deformability of the system.

A different interpretative theory has been pointed out in a document written by ARUP Gulf Ltd (ARUP 2011 Report Seismic Performance Assessment of Dhajji Dewari Building System Non Linear Response History Analysis), in which, conversely, was reported that a strategic role in a stiffness response is uniquely played by the masonry infill of the frame. In order to support such deductions the ARUP engineers in collaboration with University of Engineering Technology (UET) di Peshawar have performed several numerical and experimental analysis, highlighting the ineffectiveness of the wooden diagonals in the deformability reduction under, in particular, earthquake actions. Therefore, the bracings would be necessary only in stabilizing the frame during the wall erection.

16. Even if there was no reference to the failure cause, such rupture mechanism has been described by Otto Warth at the end of the eighteenth century in the 2nd volume Die Konstruktionen in Holz, included in the Breymann's treatise: ‘ … statically the Saint Andrew's crosses do not cause any benefit, because when their faces are in the same plane, have to have a notch in their intersection point, and then lose much of their strength … ’, p. 54.

17. E. Poletti, G. Vasconcelos, and M. Jorge, ‘Full-scale Experimental Testing of Retrofitting Techniques in Portuguese “Pombalino” Traditional Timber Frame Walls,’ Journal of Earthquake Engineering 18, no. 4 (2014): 553–79.

18. A skeleton of big members.

19. N. Ruggieri, ‘The Borbone “Istruzioni per gli ingegnieri”. A Historical Code for Earthquake-resistant Constructions,’ International Journal of Cultural Architectural Heritage (2016). https://doi.org/10.1080/15583058.2016.1212128

20. It is the result of a joint research between Università della Calabria (Ruggieri Nicola and Zinno Raffaele) and National Research Council of Italy Trees and Timber Institute (Ceccotti Ario and Polastri Andrea).

21. N. Ruggieri, G. Tampone, and R. Zinno, ‘In-plane vs Out-of-plane ‘Behaviour’ of an Italian Timber Framed System: the Borbone Constructive System. Historical Analysis and Experimental Evaluation’, International Journal of Architectural Heritage 9 (2015): 1–16.

22. Ibid.

23. N. Ruggieri, 2015, L’ingegneria sismica nel Regno Di Napoli (1734–1799) (Roma: Aracne editore).

24. G. Tampone, Il restauro delle strutture di legno (Milano: Hoepli, 1996).

25. ‘ …  in order to these members do not inflect in every direction, they have to connect with the transversal elements AB, BC, CD, etc. by means of a half-lap joint, and replicate along their height  … ’ G. Vivenzio, Istoria e teoria de' tremuoti in generale ed in particolare di quelli della Calabria, e di Messina del MDCCLXXXIII (Napoli: Stamperia Regale, 1783).

26. Kostas C. Makropoulos and Vicki Kouskouna, ‘The Ionian Islands Earthquakes of 1767 and 1769: Seismological Aspects. Contribution of Historical Information to a Realistic Seismicity and Hazard Assessment of an Area’, in Review of Historical Seismicity in Europe, eds. P. Albini and A. Moroni (Milano: CNR).

27. E. Vintzeleou, et al., Earthquake Planning and Protection Organization (Public library of Lefkada, 2007).

28. Such a technical artifice relates back to the transversal junction element of the boat planking. From this it can be assumed, considered that Venetia occupation (from the fourteenth to eighteenth centuries) of the islands has deeply influenced the Lefkas culture, a derivation from the Italian shipwright constructive knowledge.

29. G. Tampone, Il restauro delle strutture di legno (Milano: Hoepli, 1996).

30. Ibid.

31. A. Trevor Hodge, The Woodwork of Greek roofs (Cambridge University Press, 1960).

32. G. Valadier, L'architettura pratica dettata nella Scuola e Cattedra dell'insigne Accademia di S. Luca (Società Tipografica, Roma, 1831).

33. ‘ … in contignationibus tigna et axes; sub tectis, si maiora spatia sunt, et transtra et capreoli, si commoda, columen, et cantherii prominentes ad estrema suggrundationem … ’ (IV, 2), Vitruvius was not particularly clear in the above description giving rise to different scholars’ interpretations.

34. R. Brandon and A. Brandon, The Open Timber Roofs of the Middle Ages, David Bogue 86 Fleet Street, London, 1849.

35. ‘ … L’Angleterre conserve ancore bon nombre de ces charpentes … ’ (‘ … England still conserves a number of these carpentries … ’) E. Viollet Le Duc,  Dictionnaire raisonné de l’architecture française du XIe au XVIe siècle, Imprimerie De E. Martinet, Rue Mignon, Paris. vol. III, 1875, p. 15

36. J. M. Fletcher and P. S. Spokes, ‘The Origin and Development of Crown-Post Roofs’, Medieval Archaeology 8, no. 1 (1964): 152–83.

37. A similar principle has been adopted in a strengthening solution with various possible configurations invented by Professor Messina. The Messina system consists in modifying the internal constraints of the truss by means of steel cables (G. Tampone and N. Ruggieri, ‘State-of-the-Art Technology on Conservation of Ancient Roofs With Timber Structure,’ Journal of Cultural Heritage (2016). 10.1016/j.culher.2016.05.011; a ‘harness’ that increases the in-plane stiffness of the structural unit and indirectly its strength. 

38. Differently from Serlio, many authors of treatises, as Pellegrino Tibaldi in 1621 and others of the sixteenth and seventeenth centuries, e.g. Fontana, recommended to separate the king-post from the tie-beam.

39. E. Benvenuto, La scienza delle costruzioni ed il suo sviluppo storico (Firenze: Sansoni, 1981).

40. R. Dugas, A history of mechanics (New York: Dover Publications, 1988).

41. F. Funis, Il ponte ligneo sul Cismon e le altre tre invenzioni di Palladio, in Bollettino ingegneri 12, Firenze, 2005, pp. 7–18.

42. R. Dugas, A History of Mechanics (New York: Dover Publications, 1988).

43. See his work of 1827, An Essay on Bridge Building, with useful indications on bridge execution.

44. The German engineer in the preface of his work Die Graphische Statik ascribed to Jean Victor Poncelet, engineer and professor at École de l’artillerie et du genie di Metz the role of precursor of the graphical statics.

45. S. P. Timoshenko, History of Strength of Materials (New York: Dover Publications, 1983).