ArticlePDF Available

Assessment of Timber Structures Using the X-Ray Technology


Abstract and Figures

The assessment of timber structures is a permanent task to check the normal function of individual structural timber elements. Non-destructive testing methods are preferred but the value of the information is limited due to the performance of the applied assessment method. However, X-ray is a technology which allows a view into the structural member or the connections. The mobile X-ray technology has been used in laboratory tests and practical situations at existing structures and led to excellent results which allowed detailed analyses. The method and its possibilities for non-destructive testing of timber structures will be presented. The results reached show a high potential for an effective assessment of existing structures including connections and structural timber members.
Content may be subject to copyright.
Assessment of timber structures using the X-Ray technology
Steffen Franke
, Bettina Franke
, Florian Scharmacher
Bern University of Applied Sciences, Architecture, Wood and Civil Engineering,
Solothurnstrasse 102, CH-2504 Biel/Bienne, Switzerland
Keywords: Timber, Connections, Nondestructive testing, Assessment, X-Ray
Abstract. The assessment of timber structures is a permanent task to check the normal function of
individual structural timber elements. Non-destructive testing methods are preferred but the value of
the information is limited due to the performance of the applied assessment method. However,
X-ray is a technology which allows a view into the structural member or the connections. The
mobile X-ray technology has been used in laboratory tests and practical situations at existing
structures and led to excellent results which allowed detailed analyses. The method and its
possibilities for non-destructive testing of timber structures will be presented. The results reached
show a high potential for an effective assessment of existing structures including connections and
structural timber members.
The structural assessment of timber structures is caused by different reasons, such as regular
inspections, structural modifications, changes in serviceability or historic preservation. The
assessment of timber structures always begins with the visual inspection of the complete building
for the analyses of the supporting structure. The following assessment of the single members,
connections or specific details will take place only after this step. An advantage in assessing timber
structures is that abnormalities are normally relatively easy to detect due to discoloration, cracks or
plastic deformations. Especially in combination with the measurement of the moisture content, first
specification can already be done. Depending on the abnormalities found, specific testing methods
are available and can be used. The test methods can generally be classified into nondestructive, less
destructive and destructive test methods. For the detailed survey of the building and assessment, an
overview of common methods is given in Table 1. Further explanation can be found in e.g. Aicher
[1], Görlacher [2], Kasal & Tannert [3], Köhler et al. [4], Rinn [5], Steiger [6] and Vogel et al. [7].
Non-destructive testing methods are preferred, but the value of the information is limited due to
the performance of the applied assessment method. Especially the occurrence of internal damages
like cracks, holes, fitting inaccuracy or plastic deformations of mechanical fasteners cannot be
detected reliably with these common methods. However the X-ray technology allows a view into
the structural member or connections. The application of the X-ray technology on wooden
structures was investigated and the results and limitation are presented.
Common assessment methods for timber structu
testing methods
Less destructive
testing methods
testing methods
Visual inspection
Moisture content
Crack detection and mapping
Ultrasonic wave or echo
Chemical investigations
Resistance drilling
Penetration resistance tests
Withdrawal resistance test
Drill core specimens
Test of glue line quality
Mechanical testing for strength
Advanced Materials Research Vol. 778 (2013) pp 321-327
© (2013) Trans Tech Publications, Switzerland
All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of TTP, (ID:,15:37:51)
X-ray technology
Method. The X-ray technology is known from the medical use. Nowadays there are also mobile
X-ray systems available which are used for the in-situ assessment of structures, as shown in [8], [9],
[10], [11], [12], [13]. The adoption of this technology provides the possibility to look inside the
member with a high accurate resolution according to the measuring area of 30 by 40 cm for the film
used. The X-ray technology is a non-destructive testing method and works quasi contactless. The
use of a mobile X-ray technology in combination with the specific digital scanner allows in-situ
assessment of existing structures.
The safety requirements for the use of the mobile X-ray system do not limit the practical use on
existing timber structures. The mobile X-ray system used works with hard X-ray impulse generator
but with a very low dose as against stationary X-ray systems known. Furthermore the exposure
transmitter is only active, meaning X-rays are only generated, while ”taking” the picture. This
process takes only a few seconds and before and after no X-ray exposure happens. In practical use,
the safety zone is specified as follows: 3 meters around the transmitter, 30 meters in measuring
direction and 11 meters perpendicular to it. The users carry a personal dosimeter to register any
Theory and Calculation. X-rays are a form of electromagnetic radiation. The X-rays are absorbed
depending on the material respectively their density. The X-ray absorption parameter is defined by
the Beer-Lambert law as follows:
 = 
∙ 
Where I is the intensity after radiography in [W/m
], I
the intensity before radiography in
], d the thickness in [m] of the material and µ the X-ray absorption coefficient in [m
]. For
wood, the X-ray absorption coefficient is defined as follows:
= ′ ∙  (2)
With µ’ as the mass absorption coefficient in [m
/kg] and ρ the density of the material in [kg/m
The absorption capacity depends on the density of the material, the atomic mass, atomic number
and the depth of the material, [14].
The X-ray radiography depends on the impulse intensity of the X-rays, the distance of the test
object to the transmitter as well as to the film plate and also the thickness of the material. The
principle of the process is shown in Fig. 1, where the test object is located between the X-ray
Fig. 1 Principle process of X-ray technology and investigations
X-ray system RadiogramTest object Film plate
322 Structural Health Assessment of Timber Structures
transmitter and the film plate. The X-rays transmitted travel through the test object and will be
absorbed with different intensities before they hit the film plate. The material specific absorption of
the X-rays leads to the so called radiogram which will finally be transferred in a grayscale picture.
The volume of the three dimensional test object will be reproduced as a two dimensional picture.
Applications and limits of the mobile X-ray technology
Laboratory analyses of the system. The principle of the X-ray process is similar to taking a
picture with a photo camera. The quality of the photo depends on the depth of field, sharpness of
movement and focus. These parameters are not comparable for X-ray systems. Here the impulse
intensity, the distances of the test specimen between the transmitter and the film plate and the
thickness respectively density restrict the results, resolution and accuracy of the method.
According to Eq. (1), the intensity I on the film plate increases linear with the intensity of the
transmitter I
. The gray value of one pixel behaves proportional to the intensity and will increase.
Fig. 2 shows the radiograms taken with different numbers of impulses from a steel screw tip
inserted in wood block as test object. The test object had a constant thickness d of 70 mm.
Increasing the thickness increases the absorption of the X-rays, so that for radiograms with
comparable quality, the number of impulses has to be increased as well. The effect of the number of
impulses was analyzed for two different thicknesses and is shown in Fig. 3.
Furthermore the distance a between the transmitter and the test object and the distance b between
the test object and the film plate, see Fig. 1 was verified related to the accuracy and sharpness of the
radiograms. The same test object with the steel screw inserted in a wood block with a thickness of
70 mm was used. The increase of the distance b results in a smaller projected area where the object
is enlarged compared to the original size, as shown in Fig. 4. On the other hand, the reduction of
distance a leads to a clear “burned” spot and unusable radiograms. A minimum distance a of about
1 meter was necessary for the test configuration with a film plate of 30 by 40 cm. The relation
between the two distances a and b is summarized in Fig. 5.
Finally the thickness of the test object was verified from 70 mm up to 350 mm. Hereby constant
parameters for the number of impulse, distances of the test object to transmitter and film plate were
used. The radiograms of the test object with the metal screw inserted in the wood block with
different thicknesses are shown in Fig. 6. The contrast of the radiogram reduces with the increase of
the thickness of the test specimen. The typical structural elements of wood on macro scale level are
visible for thicknesses up to 200 mm. For greater thicknesses, only major differences are visible in
the radiogram like parts of steel or wood. As summary, the relation between the mean gray value
and the thickness is shown in Fig. 7.
Fig. 2 Radiograms with different number of
Fig. 3 Effect of number of impulse, the shadowed
area marks the not useful configurations
0 50 100 150 200 250 300 350
number of impulse [-]
Advanced Materials Research Vol. 778 323
Assessment of wood and connections. The first investigations are done in the laboratory with
samples of historical wood to wood connections or with mechanical connections. Fig. 8 shows a
wood to wood connection with an internal hardwood dowel. Not only the two wood species,
European spruce and beech, can be clearly distinguished but also differences within one material
like knots and even the annual grow rings are visible. Furthermore the fitting accuracy of such a
connection can be checked. In this case gaps are clearly detectable. As a practical application, a
historical timber construction in a chateau was investigated. Wooden nails could be detected during
the assessment of a multi layered beam construction, as shown in Fig. 9.
The assessment of timber connections with mechanical fasteners is shown in Fig. 10 for a
dowelled connection with inner steel plate. The test specimen shown was loaded/unlodaded in
certain steps at the laboratory and X-rayed after each load step. For every case, the visual inspection
of the outside area (heads of the fasteners) do not indicate any irregularities. But the radiograms
show that inside the connection plastic deformations according to the Johansen theory, [15] already
occurred, as shown in Fig. 10c)-d). The plastic deformations of the fasteners indicate an
overloading and a failure of the connection. The connections have to be repaired in this case.
Fig. 4 Radiograms with different distances, top
row distance a and bottom row distance b
Fig. 5 Effect of distances of impulse, the shadowed
area marks the not useful configurations
Fig. 6 Radiograms with different thicknesses of
the test object
Fig. 7 Effect of thickness, the shadowed area
marks the not useful configurations
Fig. 8 Wood to wood connection with hardwood dowel
0 10 20 30 40 50 60 70 80 90
Distance [m]
Distance [m]
mean gray value [%]
0 50 100 150
thickness [mm]
324 Structural Health Assessment of Timber Structures
Assessment of restored glue lines and fungal/insect decay. Glulam is a common used engineered
wood product for large span timber constructions. The assessment of these structures is a permanent
task in order to ensure the integrity and performance. In some cases, the glue lines or cracks have to
be restructured or supports and high stressed areas have to be reinforced. The assessment of
restructured glue lines was therefore investigated with the mobile X-ray system within a research
project. A glulam member with two restructured cracks was X-rayed in different directions to check
the restoration. In the first radiogram, taken in a direction perpendicular to the glue-line planes and
shown in Fig. 11b), a clear failure at the outside of the beam can be seen. But the allocation to one
of the glue-lines or even the evaluation if there are more failures in the same direction is not
possible. Fig. 11c) shows the final radiogram inclined to the glue-line plane. Here, the two
restructured glue-lines can be separated from each other and the failure spots and injection holes are
clearly visible for each glue-line. In this case, both glue-lines show the failure at the same position.
Furthermore, the assessment of this member also shows voids and bubbles along the glue-line plane
as well as in the injection holes. Depending of the size of these defects, the structural capacity of the
beam and the strength of the restructured glue-line can be influenced. In a practical application, also
voids and bubbles within a glued-in rod connection could be detected.
a) b) c)
Fig. 9 Historical wood nail in multi layered wooden member, a) position of X-ray shot, b) original
radiogram, c) wooden nail marked in radiogram
a) b) c) d)
Fig. 10 Connection with mechanical fasteners, a) Test specimen, b) unloaded connection, c) and d)
connection with plastic deformations
Advanced Materials Research Vol. 778 325
In general fungal or insect decay can be observed within the visual inspection. But in some cases
structural elements are covered or only viewable from one side, so that the mobile X-ray system can
be used for detailed analyses or specification of assumptions. Fig. 12 shows as example of a glulam
member with fungal decay in the top layers. The typical cubic failure structure is visible in the
radiogram observed and allows estimating the dimension of the decay.
Discussion and conclusion
The X-ray system has been used in laboratory tests and practical situations at existing structures and
led to excellent results which allowed detailed analyses going further as common non-destructive
assessment methods. It was shown that the mobile X-ray technology offers a high potential for an
effective assessment of existing structures including connections and structural timber members.
Deformations of mechanical fasteners like the formation of plastic hinges due to overloading are
visible as well as the macroscopic structure of wood, knots or different wood species. Also glued
connections like finger joints or restructured glue-lines were checked for quality and/or damages.
Voids or bubbles but also cracks due to overloading could clearly be detected.
The practical examples presented, give an overview of the ability and the limits of this method
and show that the mobile X-ray system is a novel successful non-destructive testing method of
timber structures. With increase of the differences of the density of the investigated materials, the
contrast is getting more and more intensive. However, reliable analyses of the resulting radiograms
should be done by people who have experiences with the system and are professionals in timber
structures in order to be able to identify irregularities from inaccuracies even in less contrast
a) b) c)
Fig. 11 Gulam member with two restructured cracks, a) test specimen, b) X-ray direction
perpendicular to the glue-line (top view),
c) X-ray direction inclined to glue-line
a) b)
Fig. 12 Fungal decay in X-ray, a) test specimen, b) radiogram
326 Structural Health Assessment of Timber Structures
We would like to thank the master student Mr. Scherler for his effort and contribution to these
results within his project paper.
[1] S. Aicher, Verfahren und Aussagemöglichkeiten bei der Begutachtung von Holzkonstruktionen
in Fachtagung Bauwerksdiagnose, Berlin, Germany, 2008.
[2] R. Görlacher, Hölzerne Tragwerke: Untersuchen und Beurteilen in: Sonderforschungsbereich
315: Erhalten historische bedeutsamer Bauwerke, Verlag Ernst & Sohn, Berlin, Germany,
[3] B. Kasal, T. Tannert, In situ assessment of structural timber, State of the art report of the Rilem
technical committee 215-AST, Springer Verlag, Dordrecht, Heidelberg, London, New York,
[4] J. Köhler, G. Fink, T. Toratti, Assessment of failures and malfunctions, Publication of COST
Action E55-Modelling of the performance of timber structures, Shaker Verlag GmbH, Aachen,
[5] F. Rinn, Chancen und Grenzen bei der Untersuchung von Konstruktionshölzern mit der
Bohrwiderstandsmethode, Bauen mit Holz, 94/9 (1992).
[6] R. Steiger, Zustandserfassung und Zustandsbeurteilung, in EMPA/HSR-Conference,
Rapperswil, Switzerland, 2009.
[7] M. Vogel, T. Tannert, H. Hansen, D. Kehl, S. Kraus, Überprüfungsmethoden geschädigter
Holzkonstruktionen, Research report, Bern University of Applied Sciences, Biel, Switzerland,
[8] M. Vogel, F. Scharmacher, Qualitätskontrolle von Holzkonstruktionen – Mobiles Röntgen.
Holzforschung Schweiz 2012/1, (2012), pp. 9-11.
[9] B.K. Brashaw, V. Bucur, F. Divos, R. Goncales, J. Lu, R. Meder, R.F. Pellerin, S. Potter, R.J.
Ross, X. Wang, Y. Yin, Nondestrucitve testing and evaluation of wood: A wordlwide research
update, Forest Products Journal 2009/59, pp.7-14.
[10] Q. Wei, B. Leblon, A. La Rocque, On the use of X-ray computed tomography for determining
wood properties: a review, Can. Journal for Res. 2011/41, pp. 2120-2140.
[11] B.J. Pease, G.A. Scheffler, H. Janssen, Monitoring moisture movements in building materials
using X-ray attenuation: Influence of beam-hardening of polychromatic X-ray photon beams,
Construction and Building Materials 36 (2012) pp. 419-429.
[12] T. Kruglowa, In-situ assessment of density and material proberties in timber structures by
non-destructive and semi-destructive testing, Thesis, Chalmers University of Technology ,
Gothenburg, Sweden (2012).
[13] T. Lechner, Assessment of density in timber using X-ray equipment, International Journal of
Architectural Heritage, 2013/7, pp. 416-433.
[14] M. Purschke, Verbesserung der Detailerkennnbarkeit in Röntgendurchleuchtungsbildern durch
digitale Bildrestauration, Doctoral thesis, Technical University of Berlin, Germany, (1989).
[15] K.W. Johansen, Theory of timber connections. Int. Association for Bridge and Structural
Engineering (IABSE) Publications, 9 (1949), pp. 249-262.
Advanced Materials Research Vol. 778 327
... extremely snow load or an accident by car crash at timber bridges. In these cases, even small plastic deformations as well as fitting accuracy can be easily checked, as shown in [14] Further assessments of timber structures using the X-ray radiography are reported e.g. in [14][15][16][17][18]. ...
... extremely snow load or an accident by car crash at timber bridges. In these cases, even small plastic deformations as well as fitting accuracy can be easily checked, as shown in [14] Further assessments of timber structures using the X-ray radiography are reported e.g. in [14][15][16][17][18]. ...
... It can be assumed that using a typical setting of portable X-ray system (e.g. 150 KVP and X-ray dose per pulse of 0.026-0.040 mSv as reported in [14]) and test object made of Norway spruce (P. abies) with a density of 480 kg/m 3 and a moisture content of $15%, the X-ray unit can be used assuming the following: ...
... In the forest and wood products sector, numerous investigations have been undertaken to assess the internal characteristics of wood in non-destructive ways (Bucur, 2003). Examples include the use of X-ray for solid wood (Franke et al., 2013, Charwat-Pessler et al., 2014, Lechner et al. 2013; and, the use of thermal imaging for monitoring moisture content and imaging subsurface defects (Keoa et al., 2014, López et al., 2013, Conde et al., 2012. Detecting defects in wood by non-destructive ultrasonic methods has also been investigated by some researchers in certain tree species. ...
Effective non-destructive methods for identifying poor quality and knotty timber in standing trees can contribute to higher quality timber reaching the appropriate processing mills and to a reduction in transport costs of harvested timber. Eucalyptus nitens is a major temperate plantation hardwood species primarily used in paper production. More recently it has also been considered as a potentially suitable source to produce high quality sawlogs. One important aspect of the economic viability of this sawlog business is being able to differentiate between pruned (higher quality) and unpruned (lower quality) plantation eucalyptus. Low quality stems contain higher percentages of features such as knots and/or branch traces that lessen the quality and value of logs that can be produced. Unfortunately, it is not possible to visually discriminate between pruned and unpruned standing trees and while wood processors do use large x-ray image machines during processing, finding ways to reduce transportation costs by enhancing timber quality remains a major challenge. This research presents results from ultrasonic and thermal testing to non-destructively detect internal defects in 17 year old E. nitens grown in Tasmania, Australia. For the investigation, 12 samples (billets) from different parts of the trunk of an E. nitens tree were selected and conditioned to levels of forest moisture content of 120% (70% water content). The samples were scanned by two ultrasonic techniques through-transmission and pulse-echo. In the through-transmission method, the waves were propagated at 10 cm intervals in the longitudinal direction and at 45 degree angle spacing in the circumferential direction. In the pulse-eco method, the surface of the billets were scanned in 10cms intervals around the billets. Unpruned billets were also evaluated for moisture content using a thermal camera to examine the effect on ultrasonic wave propagation. The ultrasound revealed significant differences between recorded ultrasonic waveforms propagated through unpruned billets and pruned ones. Unpruned billets produce a much larger effect on ultrasonic waves when compared with the waves propagated by the pruned billets tested. The thermal camera highlighted that wet knotty wood tends to have higher moisture content than clear wood except when the timber is air dried which produces a slightly lower moisture content being detected in knotty timber over clear wood. Results provide evidence that in-field non-destructive techniques for standing trees internal structural assessment are viable and could be operationalised within Tasmanian E. nitens plantations.
Shipworms (Bivalvia: Teredinidae) are considered one of the main agents of wood bioerosion in the marine environment. They dig tunnels inside the wood they feed on, causing its progressive weakening. X-rays are a widely used non-destructive technique to assess wood biodeterioration (e.g. EN 275). However, an X-ray is a two-dimensional projection, with the possibility that some of the objects overlap and obfuscate each other. The higher the density of the shipworms, the more difficult is to count and measure the single tunnel. The aim of this work was to find a straightforward method for calculating the volume of shipworm tunnels based on the size of shipworm shells, which are always clearly identifiable on the X-rays. Some wood test panels attacked by ship-worms were analysed, with two distinct geometric methods being applied to estimate the tunnels volume based on radiographs. An allometric model was then introduced linking the volume to the shell diameter, which allows an easy estimation of the actual bioeroded volume from conventional two-dimensional radiographs. This technique allows to evaluate the bioerosion after the first growing season, shortening the exposure time and reducing costs. The model can be applied even when the tunnels are difficult to distinguish from each other, i.e. overlapped , folded or covering the whole surface of the radiograph.
Full-text available
Bamboo is an organic material that has its durability dependent on environmental interactions when used in construction. Durability is largely defined by the way in which the material was used in a building. Therefore, the aim of this research is to identify the decisions made during the design phase, which affect the durability of bamboo elements; through the analysis of the pathological manifestations and the decay processes that affect this material in buildings. Seven bamboo structures, constructed between 2009 and 2016 in southern Brazil, were analyzed – two in Santa Catarina, two in Rio Grande do Sul and three in Paraná. Data were collected through interviews with the designers and builders, as well as surveys of buildings. In all cases, it was necessary to carry out a planimetric survey of the buildings before beginning the inspection procedures. For the surveys, an adaptation of the technique of visual inspection was used to identify and register the pathological manifestations in bamboo elements. Users and owners of the buildings were also interviewed to obtain information about the use and maintenance phase. The characteristics of each building were registered, including the specifications related to the species of bamboo used, the treatment and the constructive technique. In the diagnosis of the condition of the bamboo elements, the characteristics of the pathological manifestations, the mechanisms of occurrence and the probable causes and origin were explained. Eight different bamboo species were used in the case studies, Phyllostachys pubescens were the most widely used. The analyzed buildings are located in very humid regions and were designed by professionals who had experience with the material. Bamboo was used as a structural element in open spaces; the culms are protected from direct contact with the soil and, in most cases, from contact with the rains. Only two cases had complete formal projects prior to construction, in four cases the execution was based in physical or virtual 3D models and one of them only in the designer’s guidelines. The cracks were the type of pathological manifestation that appeared in a greater quantity of culms in the structures, its origin occurs mainly in the phases of design and construction; the second most frequent occurrence was the stains and changes of color of the culms, appearing predominantly in the stages of design and use of the building. Finally, the perforations identified in the culms were originated in the design, construction and use phases. In most cases, the pathological manifestations originated in the construction and in the planning phases, were caused by the deficiency in the execution of the constructive details or by decisions related to the treatment or location of the culms in outdoor areas. This is related, on the one hand, to the lack of a formal project to guide implementation and, on the other hand, to the lack of skilled labor in bamboo work. Several occurrences had their origin or worsened during the phase of use and maintenance of the buildings, in some cases the users did not know how to carry out the maintenance activities. Finally, based on the analysis of the occurrences, practical suggestions were made to assist the designers in making decisions in the design and execution of buildings with bamboo aiming at greater durability of the material, among them the elaboration of a user manual.
Full-text available
It is currently known that using stress wave and drilling resistance to detect the internal damage in the ancient timber structure is not a highly precise process. To improve the detection precision of this process, a simulation test was used to detect the internal damage of poplar and elm in ancient buildings. In this empirical study, we compared the detection precision of these two detection methods. Based on the idea of variable weight, we introduced three combined forecasting models based on the IOWA operator, IOWGA operator, and IOWHA operator to predict the internal damage in the ancient timber structure. The results show that the combined forecasting model based on the IOWA operator is more effective in predicting compared to a single detection method and other combined forecasting models. To be more specific, the results show that the detection precision of the combined model is increased by 25.8% and 4.7%, respectively, compared to the precision of the stress wave and drilling resistance tests. The error indicators of the combined forecasting model based on the IOWA operator are better than those of the other combined forecasting models. In addition, the analysis results based upon cross-validation theory show the combined forecasting model based on the IOWA operator has the best applicability, which provides a new practical method for evaluating internal damage of timber components in ancient buildings.
Full-text available
Die Akzeptanz und das Vertrauen in Ingenieurtragwerke unterschied-licher Materialien hängt neben einer weitestgehend schadensfreien Erfüllung der Tragwerksfunktionen wesentlich davon ab, welche Aussagemöglichkeiten Begu-tachtungsverfahren bei Inspektionen der Konstruktionen aus gegebenem Schadens-anlass oder bei routinemäßigen Kontrollen ermöglichen. In dem Beitrag werden aus der Menge aller bekannten Begutachtungsverfahren insgesamt sechs der wichtigsten Methoden für die Begutachtung von Holzkonstruktionen erläutert und die Aussage-möglichkeiten basierend auf quantitativen Bewertungskriterien, sofern vorhanden, dargestellt. Neben der rein visuellen Inspektion, den Feuchtemessungen sowie den Rissgrößen-und Risslagebestimmungen wird das zerstörende Verfahren der Bohr-kernentnahme mit Scherfestigkeits-und Faserbelagsprüfungen sowie die quasi zer-störungsfreie Bohrwiderstandsmeßmethode dargestellt. Aus dem Bereich der zerstö-rungsfreien Methoden werden die Ultraschall-basierten Verfahren angeschnitten und der neueste Stand der Technik betreffend Detektion klaffender Risse und Fehlver-klebungen bei Holzkonstruktionen aufgezeigt. 1 Einleitung Der Anlass für die Begutachtung einer Holzkonstruktion kann wie bei Tragwerken aus an-deren Materialien unterschiedliche Gründe haben. Zum einen kann die Begutachtung ohne Vermutung oder effektives Vorliegen eines akuten Schadens routinemäßiger Natur sein (Brückenbauten, Hochbauinspektionen gemäß Empfehlungen der Gebäuderichtlinie). Zum anderen, und bislang überwiegend, erfolgen Begutachtungen in Verbindung mit bekannt gewordenen Schäden. Die für die (Schadens-)Begutachtungen eingesetzten Verfahren und die damit verbundenen Aussagemöglichkeiten hängen sodann wesentlich von der Art des speziellen Holzbaustoffs (u. a. Vollholz, Brettschichtholz, plattenförmige Holzwerkstoffe, Brettsperrholz und Holzverbundbauteile), vom Bauwerk und von den jeweiligen Schadens-arten ab, die bezüglich Ursache und Auswirkung sehr unterschiedlich sein können. Im fol-genden werden nach einem Abriss über Schadensarten und –merkmale insgesamt sechs der wichtigsten Begutachtungsverfahren und deren Aussagemöglichkeiten basierend, sofern vorhanden, auf quantitativen Bewertungskriterien behandelt. 2 Schadensarten und –merkmale
Full-text available
Timber is an intriguing structural material and the only one that is truly renewable. Being biodegradable, hygroscopic and non-isotropic, it presents special challenges when assessing its integrity in structures. The presented paper outlines the major issues related to in-situ evaluation of structural timber and summarizes the work of the RILEM Technical Committee 215-AST “In-situ assessment of structural timber”. The committee was established in 2005 to bring together leading scientists and practitioners in the field of evaluation of timber in existing structures. Timber structures have been investigated for decades using numerous techniques that have been either developed specifically for the material or were transferred from other fields of investigation. A state-of-the-art report describing existing and emerging technologies and methods was prepared by the RILEM committee. The report describes the principles, the applications and the limitations of major evaluation techniques for in-situ assessment of timber. A brief discussion of codes standards and future research needs shows that much needs to be done in this area. As a present activity, harmonized test procedure recommendations are being prepared that will provide the engineering community with valuable guidance when evaluating timber structures.
Full-text available
X-ray attenuation measurements are commonly used as a non-destructive method to monitor internal concentration changes of moisture (i.e., moisture content) and other chemical compounds in porous building materials. The technique provides direct measurements of moisture content changes through analysis with a composite model consisting of a dry porous material and a thickness of water equivalent to the moisture content of the material. The current formulation of this composite model relies on certain assumptions, including a monochromatic X-ray photon beam source (i.e., X-ray photons of a single, consistent energy) and that interactions between the X-ray photons and the materials (water and porous material) are independent. However, X-ray sources typically used by researchers in this field of study produce X-ray photon beams over a spectrum of energy levels, or polychromatic X-ray photons. Implications of this inconsistency are introduced and discussed. This paper presents both an overview of fundamental descriptions of the X-ray attenuation measurement technique and results from a parametric experimental study of various porous construction materials, including calcium silicate board, aerated autoclaved concrete, clay brick, cementitious materials, and wood. Results from the parametric investigation indicate the attenuation coefficient of water is dependent on the type and thickness of the porous material.
Full-text available
Some of the significant non-destructive testing (NDT) and non-destructive evaluation (NDE) research efforts being conducted by international forest products research community are discussed. The international NDT/NDE research community aims to organize a series of technical symposia for the exchange of technical information for researchers. The International Nondestructive Testing and Evaluation of Wood Symposia Series is aimed to provide a technical and scientific forum for researchers to present and share their latest research efforts. Published proceedings from each symposia consist the research and development efforts presented during the symposium. Researchers and industry representatives are now using this symposia as a platform to present their research work. NDE technologies can be used to evaluate the forest operational value chain and to ensure public safety by detecting defects in urban trees.
Full-text available
In several processes of the forest products industry, an in-depth knowledge of log and board internal features is required and their determination needs fast scanning systems. One of the possible technologies is X-ray computed tomography (CT) technology. Our paper reviews applications of this technology in wood density measurements, in wood moisture content monitoring, and in locating internal log features that include pith, sapwood, heartwood, knots, and other defects. Annual growth ring measurements are more problematic to be detected on CT images because of the low spatial resolution of the images used. For log feature identification, our review shows that the feed-forward back-propagation artificial neural network is the most efficient CT image processing method. There are also some studies attempting to reconstruct three-dimensional log or board images from two-dimensional CT images. Several industrial prototypes have been developed because medical CT scanners were shown to be inappropriate for the wood industry. Because of the high cost of X-ray CT scanner equipment, other types of inexpensive sensors should also be investigated, such as electric resistivity tomography and microwaves. It also appears that the best approach uses various different sensors, each of them having its own strengths and weaknesses.
Wood density has a strong relationship with several mechanical properties, such as strength and stiffness. An x-ray image calibration procedure, which enables the determination of density properties for the in situ assessment of timber structures, has been developed. This nondestructive method is useful for evaluating the internal condition for global assessments of the structure. For this study, 14 wood specimens with significant density differences were exposed to x-rays. The specimens were set up in a number of image configurations. The images were analyzed and evaluated using an image toolbox. A similar procedure was applied to six built-up blocks with different thicknesses in order to calibrate the thickness of the specimens. Finally, a calibration wedge was set up to verify the procedure. The density calibration procedure from x-ray images was verified on a timber beam specimen, resulting in good agreement and an average accuracy of 97%. The values obtained from the image calibration presented a very good linear correlation between the measured density and the grayscale from x-ray images with coefficients of determination (R2) ranging from 0.90–0.98. The main advantages compared with conventional techniques are the detection and quantification of internal damage, defects, disturbances, and deterioration that may reduce the mechanical properties of the structure. This study shows good potential when it comes to the development of a viable tool for in situ assessments of timber structures. This technique could be used indirectly in analyses of structural behavior.