http://orcid.org/0000-0003-3864-2052
Robust and reliable assessment of existing structures, require extensive knowledge to determine their current health condition, safety level and useful residual life. Accurate assessment of current performance conditions is essential to design cost effective and durable repair, strengthening or upgrading measures. This is true of all existing structures, but particularly true of structures made of timber, an organic material with complex mechanical characteristics, which is particularly affected by environmental agents and subjected to ageing processes. This difficulty is compounded by the lack of guidance found in current codes and regulations for the assessment of existing and historic timber structures.
COST is an intergovernmental framework for European Cooperation in Science and Technology, allowing the coordination of nationally-funded research on a European level. The COST Action FP1101 (website: http://www.costfp1101.eu/) ‘Assessment, Reinforcement and Monitoring of Timber Structures’, is a research network established under the umbrella of the COST domain ‘Forests, their Products and Services’. The major aim of COST Action FP1101 is to increase the acceptance of timber in the design of new structures and its longevity in historic and existing structures by improving the robustness of methods to assess, reinforce and monitor such structures, and facilitate the dissemination and uptake of these methods.
Within the Cost Programme, a major tool to improve and disseminate knowledge is the organisation of Short Term Scientific Missions (STSMs), where researchers of different institutions pair together to develop particular research tasks, exploiting complementary skills and resources.
The outcomes of the missions undertaken during the 3 years of the Cost Action FP1101 were presented at the FP1101 Final Conference on 8th September 2015 in Wroclaw, Poland, in conjunction with the 3rd International Conference on Structural Health Assessment of Timber Structures (SHATIS3). A selection of the most promising presentations were then invited to submit full manuscripts, which underwent a thorough review and are now brought together to define the state of the art on life cycle assessment, testing and characterisation, within this special issue.
The topics covered by the nine manuscripts that we present in this special issue vary to cover the broad remit and scope of the FP1101 Cost Action. The first activity to determine the residual life of an existing timber structure is the in situ assessment and visual strength grading. An assessment methodology and data collection protocol for the analysis and assessment of historic timber roof structures is proposed by Serafini et al. (2017) who spent her STSM at CNR IVALSA Institute working with Dr Riggio.
In existing timber buildings the decay of the wood exposed to environmental conditions is a critical factor in determining their residual life and their need for repair or replacement. While initially weathering mainly affects the external surface of wooden facades it may lead to more advanced degradation such as wood cracking, checks and consequently penetration of the wood-decaying agents into the material. The goal of the research carried out by Sandaket al. (2017) through an STSM at the Department of Mathematical Sciences and Technology of the Norwegian University of Life Sciences, was to investigate the kinetics of the degradation rate of wooden samples by exposing different types of wood to the same weathering exposure in 15 different locations in Europe. Two approaches for image analysis are presented.
The uniqueness and specific aging that any given timber building would experience, given the specific environment it is exposed to, means that very often the research process need to start at the end of the particular and proceed towards generalisation, rather than the other way round. Hence findings from specific case studies are very valuable in this context.
Timber decay is the subject of the paper by Filippo Frontini, ‘In-situ evaluation of a timber structure using a drilling resistance device. Case study: Kjøpmannsgata 27, Trondheim (Norway)’ (Frontini 2017). This study uses impact sounding and drilling resistance measurements to determine the state of conservation of the columns of an early eighteenth century warehouse built on the riverbank of the Nidelva in Trondheim. Results from the methods compare well with visual inspection and notwithstanding the high content of moisture, elements which were not permanently in water showed good resistance to drilling.
In the paper entitled ‘Seismic Resistance of Traditional Timber-Frame Himiş Structures in Turkey: a Brief Overview’ (Aktas 2017), Dr Aktas, who has worked on the subject with Dr Turer from METU University, demonstrates how careful observation and interpretation of the construction details, together with experimental racking test, can be used to prove and quantify the seismic capacity and performance of these structures.
Helder Sousa reports on the application of in situ survey and visual grading to determine the state of conservation of a particular building in Portugal, ‘Visual assessment and diagnosis of a timber railway station warehouse in Foz do Tua’ (Helder Sousa 2017), working within the timber research group at the University of Minho, Portugal.
Knowledge on the fracture properties of materials is essential to assure structural integrity and proper design of mechanical connections in timber constructions. Measurement of this property is, however, a very challenging task. Sandak et al. (2017) propose a simple and reliable testing method based on the measurement of the cutting forces and chip thickness to determine fracture toughness and of the shear yield strength. The procedure was developed during an STSM at Gdansk University of Technology, in collaboration with Professor Kazimierz Orlowski.
Fracture propagation is also the subject of Jowker et al. (2017) experimental work carried out during an STSM at Lund University, Sweden. This work compiles a review of test methods and experimental results to investigate the difference in brittle failure of timber as determined on small clear specimens as per standards’ requirements as opposed to real size structural members in the presence of nots.
Timber structures are composed of several structural elements which interacts through joints. Notwithstanding the critical role of connections in the robustness and integrity of existing timber structures, relatively modest attention is paid to a thorough analysis of the behaviour of traditional carpentry joints.
Jan Siem, spent his STSM at Technische Universiteit Eindhoven, working with Prof Jorissen. The objective this collaboration was to produce a critical understanding of the design rules for carpenter joints available in EC5, based on tracing them back to original national standards and comparing them with observed and assumed failure modes. The paper ‘The single step joint - a traditional carpentry joint with new possibilities’ (Siem 2017) included in this special issue focusses on the very common single step joint.
Finally, the STSM carried out by Coralie Avez at Lund University, Sweden, under the supervision of Pro Crocetti, investigates a large diameter single dowel connection reinforced by a steel plate glued on a rubber layer. It aims to gain knowledge on this reinforced connection by using a finite element method with the software ABAQUS and by calibrating the model with test results. The paper ‘Large Diameter Single Dowel Joint: Finite Element Modelling of a Reinforced Joint’ (Avez et al. 2017), explores the capability of the finite element method to fully represent the behaviour of such joint and provides insight in the parameters affecting its load bearing capacity. The parametric analysis allowed to refine the design of the connection.
We hope that this relatively modest but insightful compendium of manuscripts shows the breadth and depth of the subjects delved in by the members of the COST action FP1101 and provides an overview of the needs for continued and future research in the field of Assessment, Reinforcement and Monitoring of Timber Structures. The editors are indebted to the COST Action FP1101, and to the members that participated in the production of this special issue, either as authors or reviewers.
ORCID
Dina D’Ayala http://orcid.org/0000-0003-3864-2052