PSI - Issue 55

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Dulce Franco Henriques et al. / Procedia Structural Integrity 55 (2024) 214–221 Henriques et al. / Structural Integrity Procedia 00 (2019) 000 – 000

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Fig. 1. Flowchart summary of the methodology to be adopted in the assessment of in-service wooden structures.

Before rehabilitating a building, the main concern is to recognize the structural and physical condition of its constructive elements. This can be a complex process, especially in timber structures, due to the diversity of deterioration mechanisms to which they can be subjected. Wood is susceptible to physical, chemical, and biological degradation agents. The agents that are most active in leading to wood degradation inside the building are biological agents. The process of assessing the hazard of biological degradation in construction considers two parameters: use class (EN 335-1:2013) and natural durability (EN 350-1:2016, Maxime et al., 2019). While the former deals with the types and intensity of biological degradation depending on the conditions to which the structure is exposed, the latter refers to the "intrinsic resistance of wood to attack by destructive organisms" (EN 350-1:2016). It is therefore important to know in advance what types of degradation we are likely to be looking for at each location in the structural timber element. A fundamental aspect in identifying the biological agent of degradation is the distinction between dry and damp wood, since rot fungi and subterranean termites only affect damp wood, with moisture content values above 20 percent. Inside buildings, you should expect all the wood to be dry. Cruz & Nunes (2012) point to an equilibrium value for water content in interior applications of old buildings (dry wood), which is in the range of 14 to 18 percent. Excessive humidity will only appear in the event of anomalies, which may be due to design, manufacture or lack of maintenance. In these situations, it is common to observe symptoms, such as stains, which suggest the continuous existence of water, both in the past and in the present. Visual inspection covers all the global analysis actions, such as a general survey of the structure and the causes of the damage (active or extinct water intakes, overloading, design errors, among others), the location of the degradation, its level of severity and extent, and an assessment of the state of the connections. The intensity of the degradation, when it is caused by biological factors, can be assessed by directly analyzing the wood with a knife or another sharp object, detecting the presence of soft, crumbly material and looking for the area of intact material in the cross-section, i.e., the effective or residual cross-section. This includes an initial inspection, with the aim of characterizing the system structurally and assessing its general condition. A detailed inspection will be carried out later, if it is considered that there are reasons to gain a deeper understanding of the timber structure (repairs due to visible poor behaviour, change of use of the building, among others). A distinction needs to be made between historic structures and other existing structures, even though many of the assessment methods are common to both. For historical structures, reinforcement should be considered as a last resort. If such intervention becomes necessary, it should be minimal and may necessitate the use of more precise and sophisticated techniques compared to those employed for other existing structures. This could lead to additional costs that would not typically be justified, as can be read in Cruz et al. (2015). This study presents an example of a reliable approach using inspection and diagnosis based on accessible documents, for application to ordinary buildings.