| 1. Introduction |
| 2. General Characters |
| 3. Peculiar Characters |
| 4. Investigation Methods |
| 5. Instrumental Methods |
| 6. Conclusions |

The first attempts of systematic study in this field, as far as I know, have only been made in the first half of the XIX c., of course taking advantage of the studies carried out by Leonardo da Vinci and Galilei in this specific field; but only later the rupture modalities were investigated and recorded, which proves that scholars and technicians were aware of their usefulness. In a text book by Giovanni Curioni, a Professor in The Regia Scuola di appplicazione per Ingegneri di Torino are exposed the results of a large experimentation on a few compressed and bent specimens of wood of various dimensions: all the possible deformations and cracks occurring to the specimens, are listed and extensively shown (fig. 3).
Colours, working and dressing, kind of fittings, connections etc. are the other elements on which we base our considerations.
Therefore it is possible to catalogue the signs, make institutional the language used by structures to communicate. As a consequence, we ought to learn to understand this language, or better re-acquire its knowledge, in order to interpret the same structures, recognize the pathologies they are affected by, evaluate the state of efficiency and reliability, start a solid knowledge base suitable to plan, coherently with the constructional peculiarities and the planned utilizations, their conservation.
In other words the achievement of the fundamental task of studying the existing structures is the response to two general instances, the first has mere gnosiological character, the second practical, because it allows to fulfil the documentation of the complex, to assess its load bearing capability, to judge the reliability to the present use according to the Integrate Conservation, as stated by the Amsterdam Declaration; at the same time, to build up a base of data for the planning of the repair.
The load bearing structures of the monumental buildings and the structures of the same kind which can be classified as monuments carry not only the aesthetic and the documental or historic values but, in addition, some peculiar ones, their technological quality.
The latter are the product of the human invention of new shapes, steadier configurations, more suitable materials, more advanced techniques, innovative building processes, wider applications; therefore, every specimen is a precious witness of the efforts of conceptual and practical nature the men made; on the other hand, in every one traces of the human inventiveness can be found.
Every specimen is one ring of the chain with several branches that signs the stages of the Engineering Mechanics history; hence the care each one of them deserve and the strong reasons for our engagement in its conservation.
Unfortunately, in the Charters of Athens and Venice as well as in the following official documents on conservation this concepts are not to be found because at the time the aesthetic and historic values were considered essential and prevailing.
A specific “Charter” with the Principles for the Preservation of Historic Timber Structures, anyhow, has been elaborated and adopted by the Wood International Committee of ICOMOS (Datong, China, June 1998) and accepted by the ICOMOS General Assembly (Guadalayara, Mexico, October 1999): the fundamental values of the heritage are recognized and indications for the conservation are given, with attention to the material and cultural consistence of the structures as well to the building process. The Author of this paper, as a member of the Committee, was one of the compilers of the Charter and gave specific contributions on the concepts of the most rigorous conservation of the ancient structures. The Charter marks the significant passage, in the field of conservation, from the general concern for the material, the wood, to the wider consideration of the bearing structures in timber.
The acquaintance of the ancient timber structures is started with the aim of improving and making deeper the knowledge on them, as individuals and as a set. This is already an acknowledgement of the cultural values they carry and, at the same time, a primary measure of safeguarding.
In comparison with the survey, Acquaintance is meant as a more comprehensive intellectual, technical and scientific activity, including the concern and the search for cultural implications in the ideation of the structure. The second important task of the acquaintance is to collect all the necessary data to allow the formulation of a judgement on the reliability of the structure to perform its bearing function in safe conditions. Third, to allow a scientifically based consolidation, if necessary.
The aims of investigation are to determine the general and the peculiar characters.

General Characters of the Timber Structures

Hierarchy and Configuration...
Essential aims when studying a timber structural complex is the identification of the kind of hierarchic organization existing between the systems, the units, the members and the connections present. A wider, related, fundamental concept is that of the configuration of the various structural units at the various level of the hierarchy (see Tampone, Rec. & Cons., on Connections, n° 30, 1999; idem, on Sistemi strutturali lignei, n° 35, 2000).
Configuration of a structural unit (frame, truss, floor) as part of a structural system is an abstract concept related to the geometry of the mechanical device and of its components (as span, bay, height; number, shape and position in the space, normally the plane, of the members, dimensions and ratio between them), the connections of various nature between the members, which determine the relations between the elements and any other structural system connected. The configuration is devised to bear a given system of forces and withstand the foreseen actions thus ensuring strength, equilibrium, stability to the architectural organism (figg. 4, 5).
Indeed the configuration, the result of an ideation activity, is the essence of the structure, it carries its most exclusive and characterizing features; it is the element that deserves deeper investigation and more careful conservation.
Both concepts, hierarchy and configuration, have an actual connotation, i.e. they must be assessed as planner’s conception, real primitive condition, also later and present situation, according to the behaviour kept by the structure and to the variations (in loading, for instance).
Also necessary is to determine, for every part directly deputed to the strength, the real role it plays in the whole complex. For the supported parts it must be determined whether they have any structural role in a broad sense, that is whether they contribute in any way to the equilibrium or to the general stability of the system, for instance as deformations and translations inhibitors.
For every unit are to be identified the members component and the connections.
Other important elements to determine are the relations of the timber structural complex with the other structural systems present in the building as the bearing walls for a covering, the soil for a timber framed construction; these are started, performed, settled by the external ties. This means to recognize and to classify the various structural systems present in a building and to determine the relations between them.
Bearing, joints, connections are other very important elements of the structure and of the configuration. It is essential to determine design, nature, degree of movement freedom they allow to the concurring members, effectiveness and efficiency.

...and Alterations
A set of great importance both theoretical, to establish the history of the uses of the building, and practical, to record the changes in the behaviour of the structure, are the alterations which have been introduced to the initial configuration, the degradations occurred, the consolidation interventions; besides, the dates of the single events or, at least, their progression. Hence the possibility to determine also occurrences connected with the utilization of the building also depending on exceptional loadings, such as earthquakes, soil settlements, floods, thunderbolts, fires etc. It is possible in these cases, at least to a certain extent, to establish links between causes (ordinary loadings and extraordinary peaks, non mechanical actions), effects (damages, failures) and measures adopted (propping, stiffening, integrations, consolidations, replacements).
The initial configuration and therefore the behaviour of the structure could be greatly modified by the cited events; hence the importance of their detection.

Planner, Executors; Age
The question of the identity of the planner arises only for the most important and widest timber complexes where the stability has been a major concern or where relevant innovative characters, as revealed by the survey of the structure, are present. It is the case of the original trusses planned and realized by Giorgio Vasari to carry the heavy false ceiling in the Salone dei Cinquecento in Palazzo Vecchio in Florence, the very original bridge on the Cismon River designed by Andrea Palladio (Funis, 2000, cit.), the catena dé castagni (the tie made of chestnut-wood) planned by Filippo di ser Brunellesco to circle all the Santa Maria del Fiore’s dome, others.
On the contrary, we must suppose that the big majority of the wooden complexes was described by the planners to contractors only in the main lines together with some essential indications such as the required species and the quality of the timber: the executors were committed to choose the characteristics of the materials (the stock, the dimensions, especially the length), the design of the connection and other details depending on the skill of their workers. We ought to think that only by the second half of the XIX c. the structures, mainly the biggest ones, where the object of accurate description and determined (shape, configuration, dimensions) by means of calculation.
Nevertheless we have very interesting drawings, with plenty of details, from the Middle Age and the Renaissance on: the most interesting are those by Villard de Honnecourt, Taccola, Serlio, Leonardo da Vinci (fig. 6), Antonio da Sangallo il Vecchio, Francesco di Giorgio Martini, Palladio, …, Diderot and d’Alembert, Rondelet, Cavalieri di San Bertolo, Valadier, Emy, Curioni, Mazzocchi, Breymann, …, in which the research on configuration and connection is clearly the main task.

Figure 6: Leonardo da Vinci, built-up beam

Models and maquettes of course were also extensively used as it is know by the many specimen still surviving and by the documental survey on some major monuments. Even if they represented the whole architecture and not only the structure, they were extremely useful to discuss the solutions adopted, the constructive elements such as vaults, domes, trusses etc., and for the bidding. The role played by executors was essential, therefore it is important to investigate on their identity and composition, provenance, other realizations.
Chronological data of the structural complex, i.e. when it has been conceived, planned, built, repaired and, on the other hand, the timber purchased, which were the characteristics of the stock (which vary in time and place according to the necessities of the market), which operators were acting at the time in the place, are very useful also to establish the variations in typology, the external influences etc.; besides they are essential for the reconstruction of the whole history of the building. With regard to the matter of structural typologies, demanding researches are required on dated specimen or drawings, information and descriptions, types reported by handbooks and treatises of the time. Datation can have an other specification too, i.e. the period in which the trees of the timber have been cut; a reliable datum post quem.
Datation is also a necessary investigation activity because the same reliability of the structure depends on age, as specified below.

Innovations
The identification, in the investigated structure, of any design innovation of the structural types currently in use at that time and in that place, is of major importance in the general research on the history of the timber carpentries; actually, every structure has some innovative elements that represent a step of the continuous attempt to save costs, increase the distance between the supports (say increase the span and the bay of every structural unit), improve the general efficiency.
Some fundamental stages are the invention, by part of two contemporary architects, GiorgioVasari (false ceiling of Salone dei Cinquecento in Palazzo Vecchio, 1563) and, more clearly, Andrea Palladio (Ponte sul Cismon, around 1560), of the lattice girders based on a disposition of the members as in a net made of triangular stitches, which are not deformable, and ensure therefore to minimize deformability of the structure also saving material and costs. The interesting ceilings made with wooden ribs and lath or ruler mesh were introduced, in the same years, by Philibert de l’Orme inspired by the Vitruvians “concamerationes”, an effective response to the needs of articulated interior space postulated by the Mannerism and later the Baroque: their use became universal in Italy and elsewhere in Europe up to the XX century.
The Portuguese “Gajola”, a framed scheme studied by military engineers to be used in the reconstruction of the city of Lisbon severely damaged by the terrible earthquake of 1755, has perhaps far ancestors like the roman opus craticium and the framed timber construction as was, for instance, the Fachwerkbau in use in Germany since the Middle Age, but the Portuguese issue has a much more intentional, clear and effective disposition of the members, besides the use of members very small in size but very densely positioned so that they can also give a contribution to the stiffness, the presence of built-up vertical posts, the generalized use of the wind bracings
The improvements to this scheme, introduced at the end of the same century for Calabria and Sicilia in Italy, which have the same seismic problems, by Vivenzio first and later by Pesso with the so called “Casa baraccata”, were the care for the balance of the whole building, the use of packaged boards to make the vertical posts, the rational and widespread use of the wind bracings. All these elements are present in the Balloon Frame (around 1839), one variant of the so called Chicago Constructions, but with the mere use of boards, the diffuse use of the nails industrially produced, therefore cheaper and more easily available, since the beginning of the century which made possible the nailed connection in place of the very complicate, and of course expensive, jointing of the past.
Other important innovations are the so called “Belgian Truss” invented in 1839 by Polonceau who used, together and in the most appropriate way, timber, cast iron and puddled iron, the arched, large span structures by Emy, who used packages of boards bent to suit the planned shape, the different systems of glue-laminated timber which allows large span structures, and, more recently, the parallam, the microllam for special uses, the interesting built-up beams called Kreuzbalken by the configuration, if I may say so, of the section, the reinforced timber beams, the light floors made of two distanced layers of multilayered panels for structural purposes for new constructions and for repair of ancient floors (Tampone, 1996, cit.).

Construction Techniques and Process
The timber construction technique was mainly centred on the bond, i.e. the art of connecting the member extremities in the best way according to the chosen configuration. Up to the beginning of the XIX c., when many industrial processes were invented for the production of cylindrical nails and these became available and cheap, mortise by means of hollow and tenon or, at least, conjugated shapes of the parts to be faced, were the normal kind of connections, sometimes with the aid of iron fittings such as nails, collar ties, clamps etc.
Joints really fixed, anyway, were not available with this kind of connections because of the characteristics of the wood tissues, so the use of struts became necessary to ensure stiffness. In a similar way, struts were used to avoid point loading in the slender members.
These simple rules have been universally followed.
It is interesting to note that they are at the base of the iron construction techniques as they started to develop at the end of the XVIII c., from the Ironbridge onwards.
In the acquaintance of bridges and large structural complexes, especially in presence of vaults and domes, of great interest is to reconstruct ideally (sometimes physically too) the succession

of phases held by the builders, that is to say the building process, which in the timber structures is generally shown by the structural hierarchy and by the relative position of the members, in the sense that the upper parts are, generally speaking, placed at last, but in a few cases this is not so evident. The same question arises usually for the oriental timber constructions characterized by several kinds of connection which trap the members and prevent them from moving once in service, as a powerful mean to contribute in providing stability to the construction; this makes also impossible to remove them without disassembling the entire structure. It is important to note (Larsen, 1994, cit.) that the building process, in the Asiatic Countries and especially in Japan, is a more important value in the conservation tasks than the original materials, for the high social, technical, organizational, traditional meaning it has. In the Chinese and Japanese architecture, for instance, the process is conceived as a sequence of phases and it is codified by tradition.
A very interesting and famous example is constituted by the Palladio’s timber bridges, namely the Ponte sul Cismon and the Prima Invenzione described with text and drawings in his Treatise (Tampone, 2000, cit.; Funis, 2000, cit.). With the invention of a special iron bolt (fig. 11) the Author manages to achieve a high degree of prefabrication for the first bridge (Tampone, 2001, cit.; fig. 12); progressive forwarding of rafters from the banks allows, in the second, the construction without false work (Funis, 2000, cit.).

Environment
The environment has great influence on the conservation of the structure. The most relevant factors are pollution and, of course, humidity and temperature because of the dimensional variations they produce, the variations in the same strength of the wood, the predisposition to biotic attacks.
We ought to remember, anyway, that wood has an higher resistance to chemical attacks than other materials as steel and reinforced concrete, a conclusive factor in the choice of the timber as building material for the construction of chemical plants of very high architectural interest in Italy in the Thirties of the last century.
Occasional factors as malfunctioning of the gutters, humidity in the bearing walls of a covering, lack of aeration and ventilation as well as scarce use of the room, presence of water-proof and insulated covering or caps of the structures as well as occasional condensations, exposure, heating systems and conditioning are responsible of damages, also to the metallic components of the structure, that need detection and survey.
At the same time with specific investigations the main characteristics of the environment are to be determined, i.e. Temperature and Relative Humidity, consequently, temperature and humidity of the wood, pollution factors etc.

Peculiar Characters

Materials
For every member, the peculiar characters as the botanic species, the quality of the timbers (with specification of the ring thickness, the grain, the defects, the effects of the shrinkage and other damage), the position of the piece in the shaft, the workings, the mechanical and biotical decay, investigations must be carried out.
It is important to note that differences detected in one or more of these characters usually mean differences of construction period, workers etc. which must be the object of further analysis to achieve proper interpretation.
It is not true that wood does not undergo significant changes of the chemical composition and of the physical properties of the tissues with the time and under loading. It is true, on the contrary, that some changes occur, their importance depending on the age of the wood, the regimen of the loads, the environmental factors etc. Decrease of the cellulose, and therefore of the ratio between cellulose and lignin, increase of amount of inorganic components inside the wood if the humidity exchanges with the setting were consistent, decrease of the cristallinity of cellulose and consequent increase of water sorption, damages of the cellular walls are the most common changes (ref. to Technical Association for Pulp and Paper Industry). As a consequence the mechanical properties and the carrying capability are shortened.
The reduction of transversal adhesion between fibres caused by ageing, for instance, reduces the strength to longitudinal compression and to bending.
The results of the researches to carry on the matter are extremely important in consideration of the fact that many ancient structures realized more than thousands years ago still survive and are on duty. For these structures we ought to think to reduce progressively the duty loading for the safety of the structure itself and for the utilizers.

Mechanical properties
The assessment of the strength of the materials, although in a statistic and probabilistic way, is one of the most difficult tasks because it is not possible to deduce one or more members from an ancient structure for direct testing on structural scale samples, as it would be advisable.
The common procedure is to determine the medium stock’s properties (grading) and then to refer to tables; besides, the observation of the behaviour of the structure (see below).
The presence and the relations with other structural systems, for instance masonry supports, are other main investigation objectives.

Working and dressing
These are the operations from the cut in the forest, flotation or transport with other means, rough shaping, final hewing or sawing, preparation, placing, assembling etc.; besides, planing, protective treatments, varnishing, decoration. The investigations must include the progression of the operation which can vary considerably according to the organization of the work, the equipments and the tools used. Special attention must be put in the detection of the patinas, for documentation and for the conservation.

Defects
Knots too big, too numerous in a restricted area, dead and loose knots, ring-shakes (fig. 14), irregularities of the direction of the fibres, ill-formed tissues, brittle heart are the most common defects of the wood.
The shrinkage of the wood, which occurs because of the hygroscopicity of the tissues when the rate of internal humidity decreases, is a process which starts internal tensions and produces solutions in the continuity that are called checks or shakes. These are not a defect of the wood. They become, anyhow, a defect of the timber when this is used as a construction material because their presence reduces the mechanical strength of the member, predisposing to fracture.
The checks in the members are generally triggered off by knots where the grain is irregular, are placed along the longitudinal axe of the shaft, because the shrinkage rate is maximum in the tangential direction, and follow the grain although with some transition from one fibre to the other. Their shape in the transversal section is a V but it stops at the heart. The separation of the tissues and the moving away of the separation surfaces in a relative rotation have the effect (Tampone, 2000, cit.) of distorting into a concave surface each one of the two sides in which the full side shared and also all the three other sides of the beam. Besides, and it is the effect one can detect better, the side with the solution of continuity becomes, in the complex, convex.

In the beams with a rectangular section placed with the maximum dimension in the vertical plane, I observed that the check is generally on the lateral face and close to the hearth.
They are single in the majority of the cases because the formation of an only one is in general sufficient to release the internal tensions caused by the volume changes; sometimes this is accompanied by a similar one on the opposite face of the member but only one is prevailing in width and depth; rarely they are multiple. They are placed in different planes.
There is no connection between checks and forces even, as said, the presence of checks can negatively influence the behaviour of the beam.

Failures
The detection of the mechanical degradations of the structure, i.e. the failures, is a fundamental task: the manifestations must be looked for with the maximum care.
The most important and recurring are semi-permanent or permanent deformations (twisting or lateral buckling, sinking, sagging, contraction, dilatation, elongation, crushing, embedding, folding, …), rupture, tear, splitting, crack at the level of members, displacements (translations and rotations) at the member and unit level; disconnections, deformation (changes in geometry, rotations, piling up,…), loss of equilibrium etc. at the unit level; loss of stability at the general level of the system.
The cracks have direct, recognizable relation with the mechanical actions present, have no direct relation with the direction of the grain although an irregular disposition of the fibres and the presence of checks can spoil the behaviour of the member when loaded. In general they occur where the strains reach their maximum, the position of which in the geometry of the beam can be influenced by the presence of smaller or weaker sections.
The cracks of the members are quite different according to the nature of internal tensions caused by compression or tension or bending, shear, or torsion, and also to the absence or presence of decay agents such as beetles and fungi. They are frayed, irregular and progressive if the wood tissues are sound, on the contrary sharp, straight and instantaneous (sudden) if the tissues are affected by biotic decay.
The most dangerous are the transversal ones caused by tension; being the last stage of a severe failure, they precede collapse.
Peculiar interest deserve, in the bending, the cracks of excessive compression, which in general in the wood precede those to tension: they are characterized by a plastic consistence of the tissues affected and the bulging of the same tissues with the presence of small longitudinal cracks. The diagram of the compression-tension strains in the transversal sections is not bi-triangular.
In order to distinguish the two described types of solutions of continuity due to mechanical stresses and to shrinkage, it is convenient to remember, in short, that cracks are accompanied by other manifestations of mechanical nature and are a part of a wide frame, checks are an isolated effect of a well defined phenomenon.
When the structure is in poor conditions further analyses are requested to ascertain whether the failure is still active or it is extinguished, the factors of decay or failure, the period in which it occurred, the mechanical processes of failure, the members and the joints affected, the extension of the decay, the measures taken etc.
Failure of the structures can also occur because of the progressive malfunctioning of the connections, a disease which can affect every element of the hierarchic organization.
Loosening of the joints, twisting or breaking of the ends of the members are the usual disconnections.
Factors of disconnection are those of mechanical nature (excessive or anomalous stresses at the ends of the members), fungal attacks, alternative changes in dimensions (mostly size) of the members, inaccurate or faulty design of the joint, corrosion of the metallic devices, embedding of the holes in the wood etc.
They occur more frequently of the cracks of the members. They alter the configuration and can produce collapse.
Joints must be inspected carefully.
All the collected data have to be put in relation with the configuration and the loads. Physical and chemical decay and structural failures of the ancient structure often require maintenance or consolidation interventions; in these cases the analyses carried out in order to formulate the diagnose constitute a good base for a set of further investigations necessary for the project of the intervention.
At the end of the research process the anamnesis is accomplished and the diagnosis becomes possible.

Aesthetic values
Timber structures belong own peculiar aesthetic values such as: bi- or tri-dimensional geometry, proportions of the members, sequential position, chiaroscuro, weight, colour, decorations, symbolisms and others. In the acquaintance all these values are to be investigated and recorded,

also interpreted, and attempts are to be made to imagine and give, by means of restoration (descriptions, drawings, audiovisuals etc.), the look the structure had at the beginning of his life and in other significant moments, if any, in relation with the whole space and the other structures: in fact very often the structure has been altered and, more, hided by coatings, ceilings and similar. The interiors of the Romanesque and Gothic Churches, for instance, were changed and completely re-shaped in Baroque times and later, in an unitary view of the space which included floors, walls, ceilings, furniture, hangings.
Decorations anyhow are of different kind and manufacture, they include engraving, carving, varnishing, gilding, paintings (tempera or oil), chamfers, bas- or full relief sculpture, application of material or decorative objects, especially in the ceilings and false ceilings, such as fillets, ovoli, rosettes, others. Cantilevers of beams and trusses are generally made of a more valuable wood, oak, walnut or similar, often with foliage sculpture.

Reliability
The acquaintance always includes the need for assessing the conditions of the structure in order to determine its efficiency level and reliability to perform its service and to forecast the further phases.
Mathematical instrument can help considerably with verifications of the strength of the material in the most solicited sections of the members, of the balance of the units, of the stability of the whole system.

Investigation Methods

General considerations
Therefore, according with the aim of the research, the methods and the level of investigation vary considerably. The same progression of investigation is completely modified when the decay and the structural failure are severe and the risk of sudden collapse is high.
Due to the number of members in a structure, always high and sometimes enormous, all the aforesaid investigations must have a statistic character.
The investigation range, the methods, the instruments and the same number of tests vary accordingly.
The acquaintance of the carpentry is progressively achieved with inspections in situ; unavoidably, in a professional approach, the first concern is for stability and configuration.
During the inspections observations and analyses are made, that ease the first assessments and allow to plan the following instrumental analyses. These are made on the spot, in the laboratory, in the archives; non destructive tests for the analyses are of course preferable, except the unavoidable, justified exceptions. Loading tests are always problematic.
Further series of assessments could be required, on the base of the first results.
Mathematical calculations and models follow; due to the statistic methods used to collection the data, the mathematical models have no deterministic value.
Sometimes it is advisable to define the features common to the various components first, statistically assessing their constancy and the peculiarities, and carefully surveying later the parts with different features. These parts are to be considered deviations and interpreted as exceptions or as elements alien to the primitive edition of the complex, i.e. added later; for instance, these circumstances and the related questions arise when woods of different species are found in the analyzed structure.
The composition of the structural complex must be investigated in its general organization and articulation individuating each one of the structural systems present (in the big coverings, for instance: the masonry structure, the timber structure, etc.), or of the structural units of a complex nature (floors of big span, for instance)..
In the most general cases, once the sets of structural units has been determined, it is advisable to examine analytically the structural units, which are the real basic reference of every further investigation, in their configuration and, as for their constituting members, in the composition, geometry, connections, alterations, repair; besides, botanic species, stocks, quality, defects (ring shakes, deviations of the grain) and the knots too big, too numerous in a restricted area or loose or placed in the tended parts.
The further phase is the determination of he relations, in their history, between the units present, the other sets present and the structural complexes of a different nature like the soil, the masonry bearing structures and similar.
Essentially, the cited relations are the transmitted strains and the reactions to them.

Direct investigation methods
It is of fundamental importance to recognize, anyhow, that the visual analyses approach is the most important in any case.
Elasticity of timber members is a very interesting property of the wood for both applications, practical and theoretical, for the speculations it allowed at the past and present time.
The high level of deformability of the timber structures, more than the others, is mainly due to two factors, the elasticity of the members and also the ductility of the connections. Therefore deformations, dislocations and solutions of continuity could be essential symptoms of a general disease of the structure or, simply, they can put it in a critical situation. It is also possible to maintain, even only roughly and in a general way, that the more deformed the members are the more they are stressed; besides, that the more deformed members are more stressed than others of the same size but less deformed
On the other hand the presence of severe deformations in some regions of the member is enough to foretell that breakings will occur and that this will happen in those regions. Forecasting the whole behaviour of the member and the real position of the cracks can be disturbed by biotic decay, especially fungal, which cuts down the strength of the wood affected and even alters the character of the cracks.
An other very important reason for preliminary visual observation of the said symptoms is the fact that for the Architects and Builders, before the modern times, when no analytical, say mathematical, criteria were available to form reliability judgements concerning an existing timber structure, the only way they had was the physical inspection in order to observe its behaviour.
In the same way this exercise provided, with the deductive method, analogical criteria, the only available, for the dimensioning of the members, the understanding of the distribution of the stresses etc. in the planning of the structures to be made.
Special credits to this method come from the studies and the experiments carried out by Leonardo da Vinci, G. Galilei (the “experimental method”), and the observations of J. Leupold and, from the principle of the virtual works, known since the Middle Age, and the theorems of the deformation work.
Hence the importance, especially in the first phases of the acquaintance, of the visual method, which proves to be universal, and the necessity of adequate instruments for its application.
The thickness of the rings, the grain, the position in the shaft, the defects of the wood are generally recognized with simple observation, may be with the help of some samples (transversal cores, especially for the rings).
The close observation of the solutions of continuity aims to recognize cracks from checks or shakes.
The checks are identified by the elements of the formation process mentioned before: long and continuous line along the grain even if with some transitions to other fibres, V-shaped cross sections with vertex on the duramen, concavity of all the external surfaces.
The depth and the shape of the internal surfaces are measured with needle-probes, the concavities are evidenced by means of skimming or grazing light side-light and rulers. With the checks also the grain and its irregularities can be detected. The operations have to be repeated in several sections.
Failures of the structures, from complexes to single members, show manifestations which are peculiar to the hierarchic level and to the configuration.
Symptoms of bad conditions are the sinking of the top and the slopes of the roof, that means depression of the ridge and of the joists, the disorder of the coating, of the gutters etc., what means that rain water enters under the coating of the roof and in the walls: the probable affection of the timber carpentry by biotic attacks is to be detected looking for the presence of spots.
In the frames and the trusses typical failure manifestations are the loss of planarity and verticality (rotation on the horizontal axe passing trough the bearings) (fig. 18), the sagging of the rafters and the cracks in the more advanced phases of the degradation, the sagging of the chord combined with its sliding along the masonry seat and rotation, the disconnection of the joints (especially those rafter-chord), the sliding of the rafter along the chord, with consequent rotation of the rafter in the vertical plane and deviation of joists and small joists, the rotation of the ancons on the bearings, even bigger than that of the chord, when the collar-ties are missing or not in the right position, the loss of strength at the heads of the connections caused by rottenness when wood is encased into the masonry or cups. (fig. 20). At the level of set of units, the piling up.
Symptoms of failure of the structure of the floors, complex structural units, are the loss of elasticity of the whole unit, the sinking of some parts, some ruptures of the floor covering, the deformation of the principal and secondary beams which can be caused by insufficient dimensions in relation not only to the loads acting but also to the span or the bay. In very ancient structures and, for opposite reasons, also in those of the XIX c., visco-elastic deformations can have occurred because of loading, if the members are dimensioned with mere strength criteria and with little concern for stiffness.

Beams of large and very large section, usually of mature wood obtained by old trees, can be affected by “brittle heart” and undergo “size effect” cracks (Spinelli, cit.).
In the light vaults made with lathing kept in the desired shape by ribs of packaged boards, depressions at the key along with longitudinal cracks are rather frequent and are the effect of the deformability of the board centrings which, in its turn, is caused by the small section of the centrings and the high number of joints with progressive loosening. Besides, at the side sections of the centrings, where bending is inverted, some breakings at the extrados of the boards may occur
The signs of the workings and dressing are revealed in the same way and they allow to recognize the kind of tools adopted.
Addition and replacement timbers are recognizable by differences in colour, quality, size, working, often botanic species too. In these cases the investigation must be enlarged to include also the iron fittings and the other elements of connection to the ancient members and the results are to be put in the general frame for appropriate, extensive interpretation. Their importance, in general, is given by the information they can supply on the past behaviour and failures of the structure.
The modifications to the autograph configuration are investigated identifying the changes of geometry, the actual movements that connections allow, the presence of alien elements of timber, metal, other materials; besides, generally speaking, by high hyperstaticity and a confused organization of the members in redundant number.

Instrumental Methods

Application of the exact methods of the wood anatomy on small samples must follow the visual determination of the botanic genus, using the Scanning Electronic Microscope which allows, with close observation of the tissues, the use of the dichotomic key and the comparison with known specimens, to find out the status of them and the species. Some small transversal cores (also very useful for dendrochronological determinations) are necessary to investigate on the growth rings.
About the design of the connections, the Author (Tampone, Sordella, 2001, cit.) is tempting a new approach by means of Radiography. The use of this method is well attested for the study of the paintings, specially on wood. Present favourable circumstances as the availability of small size portable equipment, safer operational conditions, wider range than in the past of suitable films, the advantage of getting not diagrams but real images give many opportunities to develop the study of the connections.
In the last decades the method of the elastic waves has been widely tested and extensively applied for the grading of new timber; many applications have also been made to the ancient structures, with the aim of determining a dynamic modulus of elasticity from which, in a very approximate way, the static one is deduced, and finding out discontinuities, with qualitative results limited anyhow in their validity by the physiological heterogeneity of the wood. Simple, very advanced, extremely handy devices are available today, generally constituted by a small hammer as wave generator and a receiver, such as Pundit, Silvatest etc. They are modern, instrumental version of the ancient method quoted before. Leon Battista Alberti was able, as early as the half of the XV c., to suggest a similar method, still in use, based on percussion and direct acoustic reception.
Better performances are obtained when it is combined with other methods, for instance the measurement of the resistance to penetration of a drill (Resistograph) in the whole section of the member.
Several non-direct methods have been proposed so far and used for the determination of the mechanical strength of the timber; they are based on the measurement of the superficial hardness of the wood or the superficial resistance to penetration. With the latter, as application to wood of the sclerometer-type instruments (Pylodin), the strength to compression of the wood is deduced by the depth reached by the probe.
The age of the complex is determined with cross-datation with the methods of the documental and historic research, with the attribution of the typology, with the dendro-chronological and xilological determinations on the timbers, the Radio-carbon method for the most ancient specimens, dating the metal fittings, dating the decorations, identifying peculiar signs on the structure.
Dendrochronological determinations allow to establish a terminus post quem, relying on the assumption that every piece tested was incorporated in the construction after the date provided by the analysis. Usually the utilization of the timber was made very soon, within a few years after the cut of the trees, the necessary time for seasoning. Accessible cross sections are needed for the application of the method otherwise thin radial cores, as said, are to be made for the exact measurements of the thickness of every three rings. The analyses to be made in the laboratory are carried on with calibrated magnifying glasses and comparison with the master chronology.
The decorations, on the contrary, allow to establish a terminus ante quem with the methods of the Art history. The carpentry has been built after or at least during the time decorations were made. In the very interesting example of the Saint Catherine’s church roof carpentry in the Sinai, where the most ancient trusses survive in service (half of the VI c., Emperor Justinian), the carvings of the chords of the trusses are made on boards which cover the structural member and are bonded to this before the final placing. On the other hand many examples show that decoration has been provided also a few centuries later.
When more than one decoration layer is present on a structure, direct investigation is supported by radiography and the other scientific methods commonly used.
Quantity of Heat and Humidity of the setting and their changes can be determined by means of simple standard fixed apparatuses to be positioned in significant places of the rooms, punctual values on the surface of the wood can be read with a different kind of portable apparatus which allow speedy readings of temperature and moisture percentage. Problems still today arise for the determination of values in the wood and, of course, of the gradients.
Readings, to be continued over a long period, at least one meteorological year, are to be conveyed in a general frame, which includes the parameters of the atmosphere in the place, in order to allow correlative interpretation.
In presence of affected tissues, the elements to assess are shape and size of the holes, calibre, depth and extension of the galleries, bore dust and frass and, of course, the larvae as identification elements of the species of the beetles; besides, whether the attack is going on or extinguished, the severity of damage and, finally, the real reduction of the resistant sections of the structural members together with the aesthetic damage on the surface (see bibliographical references, in particular Gambetta, Liotta, Ridout). No chemical damage occurs.
In the timber structures, mostly the fungal attacks hit the parts which are in contact with wet masonry walls or other elements of the building where the ambient moisture produces condensation water, besides in the depth of the connections. Therefore the parts affected are not always in sight so that they are not detectable: it is necessary to carry out inspections planned on a probabilistic ratio, with adequate instruments, starting from the parts of the structure which show an higher moisture content.
The survey of the structural failures – permanent deformations, cracks, dislocations, collapse either partial or total etc. – includes shape, allure of the cracks, extension of the affected regions, depth and amplitude of the cracks, whether the tissues are decayed by biotic factors and whether the failure is still active; in this last case, progression ratio and trend.
A new approach is started (Tampone, 2001, cit.) with the reconstruction of the kinematical behaviour of the units and members, which is the object of further studies for the extension to the structural systems. The kind of step-by-step analysis requested relies on experimental observations with models and on mathematical modelling.

References
Tampone, G. (1996), Il restauro delle strutture di legno, Milano: Hoepli
Larsen, K. E. (1994). Architectural Preservation in Japan, Trondheim-Paris: Tapir Publishers/ICOMOS Wood International Committee
Larsen, K.E., Marstein, N. (2000). Historical Timber Structures. An ecological approach, Oxford: Butterworths- Heinemann
Spinelli, P. (1983). Verifica delle strutture in legno: problemi strutturali e normativi, in Atti (G. Tampone ed.) del I Congr. Naz. sul Restauro del Legno, II vol., Firenze: Palutan
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Tampone, G., Macina, F., Rachello, M. (1990). Bibliografia annotata sul restauro delle strutture lignee, 2° Congr. Naz. su “Il restauro del Legno”, Firenze 1989, in 2° Vol. di Atti, Firenze: Nardini ed.
Tampone, G. (1995) Uso, controllo e manutenzione delle strutture portanti lignee degli edifici monumentali, in Atti del II Conv. naz. A.R.Co. “Manutenzione e recupero nella città storica”, Roma: Gangemi ed.
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Relevant contributions published in the Rubrica “Gennaro Tampone: Le strutture di legno, Analisi e Conservazione” in the fortnightly magazine “Recupero e Conservazione”, De Lettera ed., Milano:
1. Testate di travi e di incavallature. Cause e meccanismi di degrado, n. 28, 1999
2. Collegamenti. Degradazione e restauro, n. 30, 1999
3. Solai. Storia, tipologie, materiali, n. 31, 2000
4. Solai. Decorazione e degrado, n. 32, 2000
5. Solai. Degradazioni generali e restauro, n. 33, 2000
6.I sistemi strutturali lignei. Degrado e conservazione, n. 35, 2000
7. Copertura e contro-soffitto lignei tardo-ottocenteschi del Salone delle feste di Villa Demidoff a Firenze. Ricerca, analisi, diagnosi. Restauro. Didattica, n. 36, 2000
8. Rilevazione delle strutture di legno, n. 38, 2001
9. Rappresentazione delle strutture di legno antiche, n° 40, 2001
Tampone G. (1999). Tipologie degli edifici danneggiati dal sisma, in Gurrieri F. (a cura di), “Manuale per la riabilitazione e la ricostruzione post-sismica degli edifici”, Roma: Regione dell’Umbria, DEI - Tipografia del Genio Civile
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