Helena Cruz

Guidelines for On-Site Assessment of Historic Timber Structures

In the scope of European Cooperation in Science and Technology–Wood Science for Conservation of Cultural Heritage (COST IE0601–WoodCultHer) (available at http://www.woodculther.org) it was agreed to produce Guidelines for the Assessment of Historic Timber Structures, covering the principles and possible approaches for the safety assessment of old timber structures of historical relevance that could be used as the basis for possible European Standards, as discussed with CEN/TC346 (Conservation of Cultural Heritage). This approach was targeted at all those concerned with the conservation of heritage buildings. These guidelines should also help decision-making regarding the need for immediate safety measures. The aim is to guarantee that inspection and assessment measures provide the necessary data for historical analysis, structural safety assessment, and planning of intervention works, while having minimal impact on the building fabric (the original materials, structural systems, and techniques).This article provides information on the criteria to be used in the assessment of load-bearing timber structures in heritage buildings. It covers the preliminary assessment (desk survey, preliminary visual survey, measured survey, structural analysis, and preliminary report), as well as the detailed survey of timbers (with a special emphasis on visual strength grading on site) and carpentry joints. The subsequent diagnostic report and the detailed design of repairs are outside its scope.

A non-linear 3D FEM model to simulate timber-concrete joints

This paper, presents 3D non-linear FEM models developed to predict the mechanical behaviour of timber-concrete joints made with dowel-type-fasteners. They consider isotropic behaviour for steel and concrete and orthotropic behaviour for timber, all the materials are modelled with non-linear mechanical behaviour. Besides, the interaction between materials is modelled using contact elements associated with friction. The results obtained in the numerical simulations are evaluated and compared with results obtained in laboratory shear tests. The model developed showed the capacity to simulate the behaviour of the joints if the materials used are properly modelled. Nevertheless further research is still necessary to improve the modelling of the materials particularly timber.

Interlayer Influence on Timber-LWAC Composite Structures with Screw Connections

Timber-concrete composite structures are often used as upgrade solutions for existent timber floors. The timber cross section is maintained and a concrete layer is poured over the floorboard surface. Floorboards help with loading distribution on the beams. The study presented is based on laboratory tests that used specimens made with a lightweight aggregate concrete (LWAC). The use of this type of concrete, compared with normal weight concrete (NWC), has the advantage of lower dead weights, and might be very important in many cases, namely, when the supporting structure has limited strength. Many design works of timber-concrete composite connections do not take into account the timber interlayer, which is known to reduce the load-carrying capacity and the stiffness of the connection. Previous investigations of NWC found that the inclusion of the interlayer leads to average reductions of 30% and 50% for the load capacity and slip modulus, respectively. The current investigation with LWAC found that such re...

A Review of Adhesion Promotion Techniques for Solid Timber Substrates

The use of primers, coupling agents, and other surface treatments to enhance adhesion is now common in the aerospace, automotive, and plastics industries, where they are used to develop highly durable bonds to metals, advanced composites, ceramics, and plastics. However, such treatments are virtually non-existent in the wood products industry although they could solve important adhesion problems. In particular, adhesion promoters can enhance the environmental durability of epoxy bonded joints, and they can enhance the reliability of bonds to timber treated with wood preservatives. A review of current findings is provided that attempts to gather the scarce and disperse information available in the literature about adhesion promotion techniques for bonded solid timber joints. A general overview of the research needs on this topic is also given.

Adhesives for On-Site Rehabilitation of Timber Structures

The use of adhesives to produce assembled structural joints in the building industry is increasing, particularly in the context of on-site rehabilitation of timber structures. On their own or together with steel or fibre reinforced polymer composite connecting materials, adhesives can provide low intrusive, fast, versatile and effective on-site repair or reinforcement interventions to timber structures. Most common applications involve sealing and repair of cracks, drying fissures and delamination of glued laminated members; replacement of decayed beam ends; strengthening of timber members; and repair and strengthening of mechanical timber joints. The performance of bonded joints highly depends on their design and detailing, surfaces preparation, selection and application of adhesives, and full compliance with their cure schedule. Therefore, the work should be carried out by well-informed, trained and certified operators following a Quality Assurance Program to ensure satisfactory end-product strength and durability. Despite some recent developments, the exploitation of the full potential for on-site bonded joints is mainly restrained at present by the lack of structural design guidance, standards for durability assessment and onsite acceptance testing. This article discusses briefly the use of adhesives on the construction site in the context of structural repair and reinforcement; the requirements and practical difficulties in the work on site with regards to the strength and durability of the rehabilitated timber structure; and the consequent need for quality control. It also highlights the characteristics and requirements that must be fulfilled by structural adhesives and reinforcing materials; factors affecting performance and durability of bonded joints; and ways to improve adhesion and durability. Finally, it points out some research needs and future developments identified by the authors.

Fire resistance tests on timber beam-to-column shear connections

Purpose This paper aims to present the results of an extensive experimental programme on the fire behaviour of timber beam-to-column shear connections, loaded perpendicularly to the grain. Design/methodology/approach The experimental programme comprised tests at normal temperature and loaded fire resistance tests on beam-to-column connections in shear. Twenty-four full-scale tests at normal temperature were performed covering nine different connection typologies, and 19 loaded fire resistance tests were conducted including 11 connections typologies. Findings The results of the fire resistance tests show that the tested typologies of steel-to-timber dowelled connections reached more than 30 and even 60 minutes of fire resistance. However, aspects such as a wider gap between the beam and the column, reduced dowel spacing, and the presence of reinforcement with self-drilling screws all have a negative influence on the fire resistance. Originality/value The experimental programme addressed the fire behaviour of timber beam-to-column shear connections loaded perpendicularly to the grain in a systematic way testing a wide range of common connection typologies significantly enlarging their experimental background.

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.

Reaction to Fire of Existing Timber Elements Protected With Fire Retardant Treatments: Experimental Assessment

Fire safety is an important issue of building safety, especially when the building’s fire load contents enhance the risks of fire deflagration. When existing timber structures are involved, the most usual way to improve its reaction to fire is to treat wood with fire retardants. This study focuses on the surface protection of existing timber roof structures against fire, through the use of fire retardant (FR) treatments applied on site. An experimental investigation was carried out to study the effect of FR treatments on timber reaction to fire, with a special emphasis on timber members with biological deterioration and previously treated with preservative products. The behaviour and effectiveness of intumescent and non-intumescent treatments was also investigated. The study showed that the application of FR treatments improved the reaction to fire of timber, even in the presence of previous preservative treatments. However, the choice of the specific FR treatment should take into account the substrate conditions. In addition, test results suggest that protection systems involving multi layers (intumescent and non-intumescent) with different functioning modes each are likely to have a good global performance on the protection of timber elements against fire.

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.