PSI - Issue 55

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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1. Introduction Rehabilitating the old buildings that fill the centers of most cities in Europe is a concern of growing importance that is recognized by decision-makers, both from a social, heritage and tourist point of view. Intervention in ancient residential buildings, most of which date from the late 18 th century to the early 20 th century, requires specific techniques and knowledge. In Portugal, most of these buildings are made up of masonry and timber as structural members. Timber is found in floors, stairs, and roofs, as well as inside the walls, creating an earthquake-resistant braced structure. However, the lack of a pragmatic approach to assessing wooden members in traditional buildings has led to a lack of interest in keeping this original construction technique by many technicians responsible and the consequent choice to demolish the existing structures as the best way to avoid any inconvenience. To avoid this misconception, the right intervention approach should include a reliable assessment of timber structural condition that avoids the removal of many of the wooden elements in our heritage. In order to achieve redundancy in the assessment of timber members, correlation between non-/semi-destructive testing (NDT/SDT) techniques and wood properties are currently under significant scientific development, as can be seen in essential publications in literature as Kasal &. Tannert (2010), Dietsch & Köhler (2010) and Machado et al. (2015). Regarding the type of NDT/SDT techniques that exist or are being developed, they can be characterized as mechanical, acoustic, and imaging. The mechanical methods, which are all less recent and well-established, are represented by drill resistance, penetration resistance, screw withdrawal and core drilling technique. The effectiveness of these methods is very well proven by science and practice, and they are very reliable, inexpensive, simple to apply in situ and to interpret the results (Piazza and Riggio, 2008; Tannert et al., 2014, Kloiber et al., 2014, Feio & Machado, 2015, Nowak et al., 2016; Frontini, 2017; Shaparov et al., 2019; Parracha et al., 2019). On the other hand, the most recent methods, which are already well implemented or under development, are mostly represented by acoustic or imaging tests. These include ultrasonic echo methods, ground penetrating radar, sonic or ultrasonic tomography, ultrasonic time-of-flight measurements, X-ray radioscopy, NIR spectroscopy or laser scanner, among others (Dackermann et al., 2014, Riggio et al., 2015; Wedvik, 2016; Cabaleiro et al., 2019; Vössing & Niederleithinger, 2018; Linke et al., 2019; Shabani et al., 2020, Rodrigues et.al., 2021). Although mechanical, imaging, and acoustic methods are being tried and used in practice, Visual Strength Grading (VSG) still remains the established basis for assessing timber structures. It was the first non-destructive testing method and is still considered a fundamental tool for assessing timber structures (Cruz et al., 2015; Kasal & Tannert, 2010, Piazza & Riggio, 2008). Reasons for this are its apparent simplicity of application, no need for any special equipment, long experience gained from its use and its establishment in wood classification standards. Most of these methodologies were designed for new wood, prior to their one-site application. However, these strategies can also be adapted for use in existing buildings, with the necessary modification (Cruz et al., 2015). For all the reasons explained above, it is considered that the combination of information from different sources is the more accurate way to assess the condition of timber members in service. This combination of information can be done using direct readings to calibrate the indirect readings taken in situ, which includes the validation of previously obtained regression models (Kandemir-Yucel, 2007; Henriques et al., 2011; Machado et al., 2015; Feio & Machado, 2015; Parracha et al., 2019; Morales-Conde, 2014, among others). Linke et al (2019) argue that to determine material properties accurately and reliably, VSG should always be combined with NDT or SDT methods. This paper presents a methodological sequence for assessing timber members in service and developing, in somewhat detail, a case study of the assessment of a beam integral to a floor of a 19 th century building. This assessment uses direct and indirect readings from visual inspection, penetration resistance testing, moisture content and core extraction for laboratory analysis. Finally, visual strength grading is carried out and all data collected are integrated together. 2. Assessment methodology Flowchart in figure 1 summarizes the interactions between techniques, processes, and results within the scope of the recognition of timber structures in service. The 2 nd part, corresponding to "Structural Analysis" is not under the scope of this article but is shown in the flowchart in figure 1 as it is the sequence to be followed by the previous actions.