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Assessment of Timber Structures
Abstract and Figures
In timber construction, the last decades were characterized by significant technical advances and developments, widening the range of application of timber structures in the building sector. This resulted in the fact of timber being increasingly used for e.g. wide-span structures. Consequently this led to a growing importance of the assessment of wide-span timber structures, naturally resulting in an increased interest of the professional community in assessment methods for existing timber structures.
Many methods exist to assess location and degree of damages in structures. In a more narrow sense, this is also true for the observation of failure mechanisms by appropriate monitoring systems or by inspections e.g. visually or by means of non-destructive measurements.
The current practice of the assessment of existing timber structures however might not be considered suitable to facilitate confident decisions about the reliability of structures.
Any method allows only to assess certain types of failures, making it necessary to combine different methods to derive a full picture about the residual performance of the structure.
Many methods assess certain properties of the structure non-destructively and deliver results in form of measurements. To date it is often not possible to relate these measurements to strength and stiffness related properties of the timber components with sufficient certainty and therefore do not allow a quantification of the reliability of the structural component under consideration.
The objective of this task group was to collect feasible assessment methods and to evaluate each of them with regard to the following objectives:
− What can be determined / what can not be determined?
− How exact and valid are the results (e.g. degree and size of damage;
local/global results)?
− How complex and time consuming is its application (on-site,
(non-) destructive)?
− Which combinations of methods are useful to derive a clear picture
of the structural integrity of the assessed structure?
− How are the test results related to the properties of interest?
The data received from an assessment should be incorporated into probabilistic models. These models can be used to carry out analyses of the remaining load-bearing capacity and reliability of the structure as well as a basis for the planning of inspection and/or monitoring strategies.
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... Fundamenter av andre materialer, for eksempel betongpeler, stålpeler og grunne betongfundamenter er ikke vurdert her. 4 Tilstandsvurdering av trepeler kan vaere et element av en helhetlig vurdering av tilstanden til en bygning. Flere standarder og retningslinjer eksisterer på nasjonalt og internasjonalt nivå, noen dokumenter dekker trekonstruksjoner spesielt (for eksempel, [3,4]). ...
... Fundamenter av andre materialer, for eksempel betongpeler, stålpeler og grunne betongfundamenter er ikke vurdert her. 4 Tilstandsvurdering av trepeler kan vaere et element av en helhetlig vurdering av tilstanden til en bygning. Flere standarder og retningslinjer eksisterer på nasjonalt og internasjonalt nivå, noen dokumenter dekker trekonstruksjoner spesielt (for eksempel, [3,4]). ...
... • Banking på pelen med en hammer kan benyttes for å få et inntrykk av den innvendige tilstanden [4]. c. ...
... Some types of rot form hidden damage that cannot be observed in visual evaluation. Therefore, in practice, non-invasive or partially invasive instrumentation methods are used for the diagnostics [7][8][9][10]. The principles of heritage conservation emphasize minimum intervention in the element assessed; this is fulfilled in the case of resistance micro-drilling, which also provides a very precise interpretation of wood properties at the drilling spot [11,12]. ...
... Sensitive and careful structural repairs of a protected timber polygonal barn are presented in the form of three functional samples. The extent of hidden damage was investigated using a resistance micro-drill Resistograph, based on measurement procedures presented in [8,9]. Micro-drilling meets the heritage conservation requirement to minimize interference with the element assessed; additionally, it provides a reliable interpretation of wood properties (especially when looking for cavities and holes), which can be further enhanced by a higher number of drilling holes within an assessed element, as confirmed by [11,12]. ...
The paper describes a method of structural repair to damaged elements of protected timber houses. Emphasis is laid on minimum intervention in the valuable material that needs to be preserved to the maximum possible extent, especially without larger interventions in the visible parts. The designs will find application in situations where it is not possible or appropriate to use common building methods, and it is necessary to carefully fill out or substitute bio-damaged parts of structural elements. The material for the production of fillings of structural elements corresponds to the originally used wood species; in the case of contact with the ground, oak is the choice due to its durability. Small caverns are filled with earth-based mortar with lime, casein, and chopped wheat straw. Such mortar mixtures were subjected to laboratory tests, which have shown that earth-based mortar (E) and earth mortar with lime putty modification (EL) have very similar physical, mechanical, and hygric properties. The properties significantly changed when curd cheese/casein was added to fresh mortar (ELC): the mechanical strength of hardened mortar increased substantially, and the diffusion of water vapours dropped, which is very beneficial for careful repairs of timber elements. The combination of timber and mortar filling provides a suitable means of repairing locally decayed timber members.
... Assessment of conditions of timber foundations can be an element of an overall assessment of the conditions of a structure. Several standards and guidelines does exist at national and international level, some documents cover timber structures in particular (for instance, [3,4]). ...
... • Tapping or sounding. Tapping using hammer can be used to obtain a reference to the inner conditions of a wood element [4]. The sound which comes when beating on the wood may signalise presence of serious damage due to decay of material. ...
... Nevertheless, the original strength class, the load history, the environmental exposure, and the transport and storage conditions of salvaged timber might be unknown. In this case, a sufficient assessment is needed (see, e.g., [21,22] for assessment methods and approaches). ...
Salvaged timber elements often have length limitations, and therefore, their reuse in structural products normally would require additional processing and end-to-end joining. This increases the costs of reusing such materials, which makes them even less attractive to the timber sector. In the presented research, a new approach is proposed for reusing short, salvaged timber elements combined with new (full-scale) timber boards to fabricate dowel-laminated timber (DLT) panels without significant processing or end-to-end joining or gluing. In this approach, salvaged timber elements are pressed in the system in such a way that they can contribute to the bending performance of the DLT panels by resisting compression stress. In order to evaluate the effectiveness, several small-scale and large-scale DLT panels were fabricated. Salvaged plywood tenons were used as connectors. The bending stiffness of the small-scale DLT panels and the first eigenfrequency, damping ratio, bending properties, and failure modes of the large-scale DLT panels were evaluated. The results exhibited that by using the proposed approach, the short, salvaged timber elements can contribute substantially to the bending stiffness of the DLT panels without requiring end-to-end joining or gluing. On average, about a 40% increase in the bending stiffness could be achieved by pressing in the salvaged timber elements, which results in relatively similar stiffness properties compared to conventional DLT panels. One further characteristic is that the failure of the panels, and therefore the panel's strength, is mainly governed by the quality of the full-scale timber boards instead of the salvaged ones. This can be beneficial for practical use as the qualitative assessment of the strength properties of salvaged timber becomes less critical.
... To assess the condition of an engineered timber structure, sound knowledge about material and material-specific load-carrying mechanism is needed. Expert engineers utilize numerous methods for inspection, from historical documentation, visual inspection, measurements of material moisture and crack development up to drill resistance or ultrasound transmission, just to name a few [2,3]. However, little guidance exists about a specific course of action, only fundamental guidelines are available [4,5]. ...
Numerous large-span, load-bearing structures, e.g. for public venues, sports halls or industrial
facilities, utilize glued-laminated timber (glulam) due to its versatility and aesthetic appearance.
Since glulam is an organic and composite material consisting of wooden lamellas joined with glue,
mistakes during planning, fabrication and use of the structure can lead to deficiencies or even
damages. Following a visual inspection suitable to detect surface deterioration, further holistic
investigation of the glulam material is necessary to appraise structural safety or estimate the need
for restoration. Besides the integrity of the wooden lamellas, the glue bond of the lamellas is vital
for the operational reliability of glulam. A currently practiced, semi-destructive assessment method
to revalue the condition of the glue lines consults a shear test on drill core samples with included
glue line. The presented paper links this method to medium-scale shear tests and large-scale
3-Point bending-shear tests representing a practical loading situation. To provoke shear failure
during bending, reinforcements of the specimens at critical tension and compression zones included
glued-on beech veneer lamellas and self-tapping screws, respectively. Executed on the same
sample material, shear resistance was determined for all three testing formats. The sampling included
aged and new glulam. Published values derived from comparable test programs augmented
the database. Based on the evaluated test results of the drill cores under shear loading, suggestions
regarding the drill core extraction and the implementation of the valuation method of EN 14080
are outlined. After incorporating a size effect to account for varying dimensions of the bendingshear
specimen, their shear resistance values correlated well with the obtained values from the
drill core tests. This adumbrates the possibility to derive the shear resistance of structural members
from shear values of drill core samples taken from an existing glulam structure.
... In this course, the publications of the COST Action E55 ("Modelling of the Performance of Timber Structures", e.g. [20]), COST Action IE0601 ("Wood Science for Conservation of Cultural Heritage -WoodCultHer", e.g. [21]) and COST Action FP1402 ("Basis of Structural Timber Design -from Research to Standards") have to be named as pioneers. ...
In Germany, general building regulations regarding planning and execution of structures in
compliance with public safety requirements are valid for both, the erection of new and the
preservation of existing structures. However, the regulations within current Eurocodes have been
developed for new structures. The evaluation of load-bearing capacities of existing structures
necessary due to alterations or damages must be performed based on current codes. Especially
for existing structures, the application of these standards can cause difficulties and safety issues.
What is more, the evaluation of load-bearing capacities in compliance with codes and standards
developed for the erection of new structures requires detailed knowledge regarding the technical
characteristics of the historical construction at hand. Thus, a comprehensive assessment and
evaluation of the actual state to investigate the load-bearing capacity of an existing structure are
necessary requirements.
Codes and regulations for the assessment and evaluation of existing structures have been developed on an international – especially European – level within the last 15 years. Switzerland can
be seen as a pioneer since a whole series of standards for the evaluation of existing structures
has been introduced in 2011. These standards belong to the first ones containing regulations for
the evaluation of existing structures. Further developments to be considered are current Italian
standards, ISO 13822:2010 and the JRC Science and Policy Report 2015.
The following contribution summarizes these developments. Besides, the state of the art and of
the standardization in Germany is analysed regarding their applicability on the evaluation of existing timber structures. The comparison between the international and national state of the art
shall contribute to the development of a common approach for harmonized European standards
for the assessment and evaluation of existing structures.
... El ultrasonido es un método de carácter no destructivo, práctico y económico, empleado para caracterizar el comportamiento mecánico de la madera (Pellerin y Ross, 2002). El módulo dinámico, derivado de las pruebas de ultrasonido, puede ser utilizado como índice comparativo de la calidad en una especie particular; y como parámetro de ingeniería necesario para el análisis estructural probabilístico y sísmico de estructuras de madera (Joint Committee on Structural Safety, 2006) (Dietsch & Köhler, 2010). ...
La madera es un material combustible. De tal forma que la industria fabricante de productos de madera requiere de información experimental sobre la resistencia al fuego de las diferentes especies empleadas en ingeniería. El objetivo de la investigación fue determinar y comparar la densidad aparente, la velocidad de onda y el módulo dinámico de cinco maderas mexicanas, antes y des-pués de ser sometidas al fuego. La metodología consistió en estudiar cinco especies mexicanas: Tabebuia rosea, Andira inermis, Juglans pyriformis, Quercus spp y Cordia elaeagnoides. Para cada especie se prepararon 35 probetas de pequeñas dimensiones y se les realizaron pruebas de ultrasonido y de resistencia al fuego. Los resultados del análisis estadístico indicaron que cada espe-cie se comporta de manera diferente. La densidad aparente de la madera correlaciona bien con la pérdida de masa. La densidad aparente de la madera después de la exposición al fuego, presenta una fuerte correlación con la densidad de la madera antes de ser expuesta al fuego. En cambio, la velocidad de onda y el módulo dinámico no se correlacionan bien. Los resultados de la investiga-ción son particulares para las condiciones experimentales de este estudio de caso. Para sugerir de manera más general un compor-tamiento de la madera expuesta al fuego, son recomendables estudios intensivos con métodos normalizados. Palabras Clave: Densidad aparente, material combustible, módulo dinámico, pruebas no destructivas, velocidad de onda.
Abstract
Wood is a combustible material. The industry of wood products requires experimental information on the fire resistance from the different species which are used in engineering. The objective of the research was to determine and compare the apparent density, wave velocity and dynamic modulus of five Mexican woods before and after being subjected to fire. The methodology consisted of studying five Mexican species: Tabebuia rosea, Andira inermis, Juglans pyriformis, Quercus spp. and Cordia elaeagnoides. For each species, 35 specimens of small dimensions were prepared and ultrasound and fire resistance tests were carried out. The results of the statistical analysis indicated that each species behaves differently. The apparent density of the wood correlates well with the loss of mass. The apparent density of the wood after exposure to fire has a strong correlation with the density of the wood before being exposed to fire. In contrast, the wave velocity and the dynamic module do not correlate well. The results of the research are particular to the experimental conditions of this case study. In order to suggest wood fire behavior in a more general way, intensive studies with standard methods are recommended.
... El módulo de elasticidad derivado de pruebas de vibraciones transversales, produce información que puede ser utilizada como índice comparativo de la calidad de una especie en particular y como parámetro de ingeniería necesario al análisis estructural probabilístico y sísmico [4,5]. ...
Resumen
El objetivo de la investigación fue determinar la densidad y el módulo de elasticidad de madera de Guazuma ulmifolia, Spathodea campanulata y Abies religiosa y observar el efecto del proceso de impregnación con sales de boro sobre estas propiedades. Se estudiaron lotes de 35 probetas normalizadas y se impregnaron con una solución con una concentración del 3 % con el método baño caliente-frío. Antes y después del tratamiento de impregnación se realizaron pruebas de vibraciones. Los valores promedio de la densidad, frecuencia natural y módulo de elasticidad son proporcionales a los reportados para maderas mexicanas. Cuantitativamente, los resultados de retención son comparables con los de la bibliografía. Considerando que las tres especies fueron sometidas al mismo tratamiento de impregnado y probadas con un método de carácter no destructivo, se concluye que cada especie de madera responde mecánicamente de manera diferente e independiente al proceso de impregnación con sales de boro.
Palabras clave: Densidad; Módulo de elasticidad; Absorción; Retención; Baño caliente-frío.
Abstract
Retention of Salts of Boron in Three Mexican Woods. Mechanical Assessment by Vibrations
The goal of the research was to determine the density and the modulus of elasticity of Guazuma ulmifolia, Spathodea campanulata and Abies religiosa wood and to observe the effect produced by a boron salts impregnation process on these properties. Thirty-five sets of standard specimens were studied, and impregnated with a 3 % concentration solution with a hot-cold bath method. Before and after the treatment, transversal vibration test were realized. Average values of density, natural frequency and modulus of elasticity are proportional to Mexican woods previously reported. Quantitatively, results of boron salts retention were comparable with the ones reports in the bibliography. Considering that the three species were exposed to the same treatment of impregnation and tested with a non destructive method, the research concluded that each wood species mechanically reacts in a different and independent way to the process of impregnation of Boron salts.
Keywords: Density; Modulus of elasticity; Absorption; Retention; Hot-cold bath.
... For their reconstruction, it is necessary to locate degraded parts to prepare the reconstruction plan. Recently, a few guidelines and methodologies for timber constructions inspection have been published, supported by several international committees such as RILEM, COST E55, COST IE0601 (Kasal and Tannert 2011;Cruz et al. 2015;Dietsch and Köhler 2010). The fundamental and commonly used diagnostic method is a visual inspection that provides general information and certain qualitative data about surfaces of inspected structure (Calderoni et al. 2010;Piazza and Riggio 2008). ...
A reconstruction of historical timber structures requires precise diagnostics of mechanical properties of particular structural members, which would subsequently underlie a reliable plan of the reconstruction. Mechanical properties of wood are determined most exactly using destructive techniques, but often they cannot be used in historical constructions. This calls for using nondestructive or semi-destructive techniques that are still reasonably exact, not too invasive and can be profitably used in situ. This work examines a new nondestructive diagnostic tool that enables to determine strength and stiffness parameters of wood parallel to the grain in situ. The function of the instrument was verified using standard compression tests parallel to the grain that correlated with the instrument well (r = 0.92). Complicated stress state in the drilled hole was examined by contact finite element analysis and revealed high contribution of longitudinal elastic moduli in force measurement (r = 0.96).
Tópicos en Tecnología de la Madera presenta los resultados de los trabajos de investigación desarrollados en el Laboratorio de Mecánica de la Madera, de la Facultad de Ingeniería en Tecnología de la Madera, de la Universidad Michoacana de San Nicolás de Hidalgo, en Morelia, Michoacán, México. El Libro está formado por investigaciones originales e independientes cuyos resultados fueron divulgados durante el periodo de 2015 a 2016 en la revista Investigación e Ingeniería de la Madera, ISSN: 2395-9320, publicación cuatrimestral editada por la Universidad Michoacana de San Nicolás de Hidalgo.
1 Introduction.- 2 Ionizing Radiation Computed Tomography.- 3 Thermal Imaging.- 4 Microwave Imaging.- 5 Ultrasonic Imaging.- 6 Nuclear Magnetic Resonance.- 7 Neutron Imaging.- References.- List of Notations.- Color Plates.
Wood in service can be attacked by a variety of biological organisms. Such organisms feed on the constituents of wood, thereby reducing its ability to carry load and serve in an engineering capacity. This paper presents the results of a study that investigated the use of longitudinal stress wave nondestructive evaluation to assess the strength of wood members exposed to biological attack. Clear southern pine specimens were exposed to attack by wood-destroying decay fungi and termites under field conditions in southern Mississippi. The speed of stress wave transmission and attenuation characteristics of the specimens were determined using longitudinal stress wave techniques after exposure. These nondestructive parameters were then incorporated into a multivariable regression model and used to predict the parallel-to-grain compressive strength of the specimens. Excellent agreement was found between predicted and actual compressive strength values.
The joint distribution of strength of materials is derived in terms of a set of conditional distributions to be used in studies on structural reliability. Bayes theorem of probability theory is used to update prior distributions for the parameters of Gaussian sequences by direct observations and/or by compliance tests. Maximum-Likelihood estimators are given for the efficient quantification of prior information. The formulae are applied to concrete production judged by standard tests. It is shown that statistical uncertainties must not be ignored in structural reliability studies.
380 p., graph. In general, this book is concerned with capital budgeting and decision theory. Specifically, it centers around a singular uncertainty decision - the decision by oil and gas operators to drill, or not to drill, a well. Actually, a sequence of decisions must precede this final action, but each one of these preliminary decisions is principally directed toward the final payoff question: Should we invest money in this well? If so, how much should we risk, and how much of the risk should we share with others? The objective of this book is twofold. The first objective is to describe the nature of decision problems in drilling for gas and oil, a business situation where uncertainties are exceptionally great, and to describe how businessmen actually make drilling decisions in the face of these uncertainties. This descriptive section, of great interest in its own right, then provides the foundation for the second objective, which is to explore the possibilities of applying "decision theories" to such decisions. This second objective is normative or prescriptive in its attempt to provide the driller with better guides to consistent action to meet his own goals. The presentation of the applications of mathematical theories is kept clear and simple, and the methods suggested for dealing with these problems can be understood by a reader with only a working knowledge of arithmetic and high school algebra. This book should be of interest to several audiences, among whom are the following: ( 1 ) people in the oil industry; (2) people in other industries who are actively interessed in finding ways of making better decisions in situations of risk and uncertainty; and (3) people whose interests are perhaps inore academic and who are concerned with both theory and practice in the area of decision making.
Nondestructive Testing of Large Bridge Timbers
- R Emerson
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- J Ross
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K., J., Ross, R., J. and Pellerin, R., E., Nondestructive Testing
of Large Bridge Timbers. In: Proc. 11 th International Symposium on Nondestructive Testing of Wood, Madison, WI, pp.
175-184, 1999
Diagnostic investigations of wooden structures using ultrasonic-echo technique
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1 st International RILEM Symposium On-Site Assessment of
Concrete, Masonry and Timber Structures, Varenna, Italy,
2008
Testing Of Wooden Construction Elements with Ultrasonic Echo Technique and X-Ray
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- M Krause
[Hasenstab 2006] Hasenstab, A., Osterloh, K., Krause, M., Testing Of Wooden
Construction Elements with Ultrasonic Echo Technique and
X-Ray. In: Proc. 9th European Conference on NDT, September 25-29, 2006
Methods of Structural Safety
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Methods, Wiley, Chichester, UK, 1996