José S. Machado

Non-Destructive Evaluation of the Mechanical Behavior of Chestnut Wood in Tension and Compression Parallel to Grain

This article addresses the evaluation of the strength and stiffness of chestnut wood, in tension and compression parallel to the grain, using different non-destructive techniques (ultrasounds, Resistograph® and Pilodyn 6J). Approximately 200 timber specimens (divided into compression and tension tests) were tested up to failure, comprising recently sawn timber (which is now available on the market for structural purposes) and what was called old wood, obtained from structural elements belonging to ancient buildings. The possibility of predicting wood properties by application of non-destructive techniques is discussed based on simple linear regression models. Extrapolation of regression models obtained from recent cut wooden material to that obtained from old timber beams is analyzed. The results show reasonable correlations between mechanical elastic properties and non-destructive techniques (ultrasounds, Resistograph® and Pilodyn 6J). New and old wood mechanical data exhibited a scattered cloud of points, implying in terms of assessment of properties of timber elements in service by regression models that these models should not be supported only on data from recently sawn wood. Therefore, models combining information from new and old wood specimens are proposed based on lower 95% confidence limits of regression lines.

Cork as a building material: a review

This review focuses on cork as a natural, renewable and sustainable construction raw-material. Cork has an unusual combination of properties making it suitable for application in buildings and infrastructures, for example insulation, wear-resistance and durability. The material properties combined with a favourable ecological footprint allow designers, architects and engineers to meet some of the Green Building demands. A summary on cork production, structure, chemistry and properties was made. The processing into cork-based products, for example cork agglomerates and composites, is detailed as well as their properties and applications in construction. The aptitude of cork-based products for compliance with sustainability and energy efficiency criteria is also addressed.

In Situ Evaluation of the Reference Properties of Structural Timber Members. Use of Available Tools and Information

Survey of existing timber structures often includes the need to allocate mechanical properties to structural timber members. This task has to take into account the huge variability of timbers properties (within and between species), characteristic that differentiates this material from other structural materials (e.g. concrete and steel). For many decades, and still now, the application of visual strength standards is the main or only procedure used for this task. Despite the large number of other non and semi-destructive technique developed their regular application to in situ assessment of timbers mechanical properties is still almost non-existent. The present paper discusses possible ways to use and combine information from visual grading standards and non and semi-destructive techniques to predict the reference properties of timber members in service. The discussion has in mind studies conducted over the last years and the information provided by different guidelines, standards or papers recently published.

Structural Connections for Small-Diameter Poles

AbstractIn Portugal, given the large proportions of natural regeneration pine stands, a large amount of young trees must be removed from the forest, to assure the quality of mature trees and to decrease the risk of fire. With this problem in mind, a national study was launched to investigate the use of maritime pine small-diameter poles in structural applications. The study had two different tasks. The first task comprised the determination of mechanical properties and the establishment of visual and mechanical strength grading procedures and is already completed. The second task concerns the development of connections. This paper presents results within the second task. Three types of connections, regarding failure load and stiffness, were studied: connections using central plates; glued-in rods; and dowel nuts. The glued-in rods showed the highest mean failure load and, especially, stiffness. Indeed, the glued-in rods showed a mean stiffness around six times higher than the one obtained for the other st...

Effects of Beetle Attack on the Bending and Compression Strength Properties of Pine Wood

One major difficulty one has to face in the assessment of old timber structures concerns the assessment of the effective strength of timber cross sections with biological damage.Its effects may generally be considered, either by assuming a reduced cross section or by assuming reduced mechanical properties for the apparent cross section.Where beetles attack produce a “diffuse” damage, i.e. their tunnels spread in most of the cross section surrounded by a significant amount of undamaged wood, the assumption of a reduced cross section may not be the best approach.To assess the effect of diffuse damage by beetles to pine timber, damaged timber was collected from an old structure and tested in bending and compression in small “clear” wood specimens (cross sections of 2cm x 2cm). The varied degrees of biological damage were assessed in terms of the “holes” area measured in the cross section surface with the help of image processing analysis. Bending and compression strength were correlated with biological damage. Test results suggest that, although very high levels of insect destruction have an impact on the timber strength, timber density still is the governing factor.

Properties of multilayered sandwich panels with an agglomerated cork core for interior applications in buildings

Four types of sandwich panels with multilayered designs were produced using wood veneer of Aleppo pine as face and inner sheets, and cork agglomerate as core, intended for use in construction as panelling or partition walls in interior applications. These multilayered sandwich panels were characterized regarding static hardness and dimensional stability when facing changes in relative humidity and when subjected to a deformation. The panels showed a considerable increase in dimensional stability and shear strength with the increase of the number of layers. The results suggest that the correct design choice, for example number of inner wood sheets and thickness of cork core layers, allows these sandwich panels to be used as non-structural construction elements such as partition walls.

Impact of drywood termites in the Islands of Azores

Summary The detection in 2002 of drywood termites in the islands of Azores has became an urgent issue to be coped with given the fast degradation that structural elements can show after a short period of installation of the colony. In the United States control costs associated with drywood termite degradation are estimated to exceed 300 million dollars annually. A recent study indicates drywood termite presence in over 43% of the buildings of Angra do Heroismo city, and timber structures surveys conducted so far points to strong levels of degradation of timber elements and structures. The impact of this infestation is even stronger while affecting a historical city as Angra do Heroismo (inscribed on the World Heritage List). A strong effort should be put on the rehabilitation of structures already affected, implementation of control procedures for restraining the spread of new colonies into so far sound buildings and alteration of traditional practices (namely choice of wood species and protection treatments) regarding timber utilization in construction. This document presents some of the most relevant facts regarding drywood termites presence in two Azorean cities, degradation problems already detected and preliminary proposals already made to the Working Group nominated by the Azores Regional Government to deal with this problem.

Feasibility of automatic detection of knots in maritime pine timber by acousto-ultrasonic scanning

In order to assess the lengthwise variation of mechanical properties of maritime pine (Pinus pinaster Ait.) a study on the possibility of automatically detecting knots by ultrasonic readings across the grain was carried out. A through-transmission acousto-ultrasonic (AU) setup was implemented allowing acquisition of AU profiles along the central mid-third of each specimen. An algorithm was proposed and successfully implemented for enhancing variations on the AU profiles due to knot presence. Discriminant analysis was applied to the AU profiles. The results show the possibility of automatically differentiating clear wood zones from zones with a knot area ratio value above 20% or 30%, with a success rate of 75% to 83% depending on the dimension of the specimens tested.

Performance of Expanded High-Density Cork Agglomerates

AbstractPrototype boards of high-density expanded cork agglomerates (230 and 290  kg m−3) were produced and tested for tensile strength (before and after moisture resistance cyclic tests), hardness, thermal conductivity, and reaction to fire. Increases in tensile strength and dimensional stability were observed with the increase in density. No significant change in thermal conductivity was noticed. The application of a varnish resulted in a noticeable increase in hardness for the higher-density cork agglomerate. Reaction to fire was improved from class Efl to class Cfl. The improvement of properties of expanded cork agglomerates from densification can enhance their application in the building sector.

Selected solutions for rehabilitation of wooden structures : some portuguese case studies

Timber is one of the most used materials in the roofs and floors of monumental constructions in Portugal. The geometry is defined by elements that occupy a limited and well defined part of the tri-dimensional space, with a clear evidence of the hierarchy of the components. Timber elements are often visible, which allows easier conservation, identification of the wood species, characterization of details and evaluation of deterioration. Complex timber structures, such as those belonging to the roofs of large monuments, are often not easy to understand in a expedite way. As the coverings of monuments as cathedrals, public buildings, mansions or villas show very complicate features, not easy to be understood during the first inspection. This is not only due to the fact that the system is very elaborate and to the large number of members but also due to continuous changes and repair past works, mostly with additional stiffening or propping. The typical result of the history of the construction is the increase in the number and the heterogeneity of the members, together with a multiplicity of connections and diversity of supports. This means that the original must be distinguished from the additions and the replacements. This complexity makes the field of conservation of historical timber structures not only a challenge but a field much in need of modern research. The objective of this paper is to present some of the Portuguese experience in this field, showing how the rehabilitation solutions can be supported by the inspection techniques and by an extensive knowledge about the constituent material from which the structure was made, both from the mechanical point of view and from the physical point of view. A number of case studies will be presented to illustrate common conservation problems, and design problems as well as the possibilities and limitations of several solutions and to discuss the suitability of several intervention methods.