Structural and health assessment of historic timber roofs from the Convent of Christ in Tomar

Abstract

Before coming up with any important decision of intervention in the restoration process of existing buildings, the assessment of the conservation state is required as regards heritage timber structures, and especially, for those that suffered a lack of maintenance in their service life. In that context, three timber roof structures from the Convent of Christ in Tomar, Portugal, have been selected and investigated. To this end, a research methodology has been introduced and applied to these case studies into four main steps: (i) Visual inspection; (ii) Non-destructive wood diagnosis; (iii) Structural safety evaluation; (iv) Prevention and intervention measures. For the visual inspection, every element and joint constituting the roof structures have been received scrutiny through stressing the wood species, the different construction stages, and last but not least, their respective geometry. As regards the encountered pathologies, structural disorders (e.g. accidental failure, serviceability defects...) and wood-deteriorations due to biological agents (e.g. wood-destroying fungi or insects) have been reported, which ineluctably leads to a likely decrease of the mechanical performances of the roof structure. In order to estimate the residual element cross-section and elastic modulus, wood diagnosis has been carried out through using three relevant non-destructive tests: (i) Ultrasonic Pulse Velocity; (ii) Drilling Resistance; (iii) Impact penetration. From the collected data, the three timber roof structures have been modelled on a commercial software in order to check their safety and integrity. Based on those outcomes, some prevention and intervention measures haves been lastly proposed case by case.

On-Site Risk Assessment Methodology of Historic Timber Structures: The Case Study of Santa Cruz Church

“…This research provides useful tools to face with the real behaviour of old frames and their pieces. More recently, other authors published new methods to approach structural assessment using the finite element method calculation system [26,27]. Others have established relevant safety evaluation guidelines to be applied to specific heritage timber frames [21].…”

“…The method to calculate and model the structural behaviour of historical timber frames has been treated by Argüelles [24] and Verbist [27], who considered the damages caused by the different degrading agents in order to be able of make structural simulations of the real wood behaviour, obtaining safety factors values. Other numerical assessment models were performed in [21,26], where a comparison was developed between the structural state at the beginning and the current time. However, they did not provide a simplified process to simulate and reproduce the timber state and its structural performance.…”

“…Therefore, the pieces that have not passed the quality filter of the standard would be rejected. This would make sense in the case of erecting parts in the new building [45], but in the case of inspection of existing structures, it is not logical to reject pieces, as it is proven that they are structurally working [26]. In this case, the particularity was more remarkable because one of the rejected pieces was a main ridge rafter (Figure 17c) that collects the joints of numerous rafters reaching the ridge beam and configuring one of the main lines of the structural frame, which shows its good behaviour as a bearing piece to consider.…”

Structural Vulnerability Assessment of Heritage Timber Buildings: A Methodological Proposal

“…Timber roofs are mostly vulnerable to wind risk, and several studies have been carried out to assess the vulnerability of heritage timber roofs subjected to wind load [21,98,[123][124][125][126][127][128]. For this purpose, a linear analysis is performed on a numerical model of the roofs in order to evaluate the critical elements and derive the displacement of the structure.…”

Evaluation of white rot decay in phenol-formaldehyde resin treated European beech (Fagus sylvatica L.) LVL by drilling resistance measurements

“…One of the main application areas for DR measurements is the detection of internal defects, decay, insect damage, hidden parts or the evaluation of wood properties in timber structures (Kappel and Mattheck 2003;Rinn 2012;Imposa et al 2014;Li et al 2019;Wang et al 2019). Drilling resistance measurements were applied for utility poles inspection (Gezer et al 2015;Reinprecht and Šupina 2015;Sharapov et al 2020a) and assessment of structural conditions of wooden bridges as well as historical and modern constructions and buildings (Imposa et al 2014;Brashaw et al 2015;Nowak et al 2016;Frontini 2017;Branco et al 2017;Ross et al 2018;Verbist et al 2019).…”