Load-carrying capacity test of a long-span timber truss Jorge M. Branco PhD Assistant Professor, ISISE, Department of Civil Engineering, University of Minho, Guimarães, Portugal (corresponding author: jbranco@civil.uminho.pt) Humberto Varum PhD Full Professor, CONSTRUCT-LESE, Faculty of Engineering (FEUP), University of Porto, Porto, Portugal Vitor Ramisote MSc Engineer, Department of Civil Engineering, University of Aveiro, Aveiro, Portugal Aníbal Costa PhD Full Professor, Department of Civil Engineering, University of Aveiro, Aveiro, Portugal The aim of this work was to study the behaviour of existing timber trusses in order to improve the knowledge that may support engineers in the definition of more adequate restoration interventions in old buildings, particularly of long-span timber structures, as industrial or monumental constructions. For this purpose, a cyclic load-carrying test was carried out on a full-scale timber planar truss rescued from an old industrial roof structure. Before the tests, an accurate geometrical characterisation was performed and the biological condition of the timber elements was evaluated by non-destructive tests to determine their effective cross-section. The results of the destructive load- carrying test were used to calibrate a numerical model with the aim of assessing the effect of the effective cross- sections of the truss components and the axial stiffness of the joints on the overall response observed during loading. The full-scale test performed proved the importance of this type of testing in assessing the behaviour of existing timber trusses. It is essential to assess the damage of the joints and to model correctly their behaviour so as to numerically reproduce the overall behaviour of timber trusses. Notation A heel strap cross-sectional area of heel strap E steel modulus of elasticity of steel E α wood elastic modulus in direction forming an angle α with the fibre E 0 modulus of elasticity in direction along fibres E 90 modulus of elasticity in orthogonal direction of fibres G shear modulus k ax axial stiffness of joints k ax,hs axial stiffness of tie beam–post connections L longitudinal direction L nominal notch length, where compression deformation occurred l heel strap length of heel strap R radial direction S nominal notch area T transversal direction δ maximum vertical displacement of truss υ Poisson ratio 1. Introduction The assessment of existing timber structures requires, and relies upon, the determination of the mechanical properties of the individual timber members, as well as the behaviour of joints and structural system effects (Cruz et al., 2015; Dietsch and Kreuzinger, 2011; Frühwald, 2011; Uzielli, 2004). In existing timber structures, the first step in safety assessment is evaluation of the actual mechanical properties of the material (Riggio et al., 2013). Despite significant effort in the development of non-destructive testing, the strength of timber members can only be rigorously determined by destructive tests, which is often unacceptable in the case of historic build- ings and other existing timber structures (Calderoni et al., 2010; Kasal, 2010). In practice, it is the lack of knowledge about the mechanical properties of these materials and their structural behaviour that normally leads to the replacement of existing wooden structures, instead of their retrofitting, to comply with the safety and serviceability requirements proposed in recent codes and recommendations. Moreover, inaccurate characterisation of the behaviourof traditional timber roof structures can result in adverse stress distribution estimates in the members, as a result of inappropriate strengthening adopted in joints, in terms of stiffness and/or strength (Descamps et al., 2014; Drdácký et al., 1999). Thus, laboratory tests on scaled or full- scale specimens of members, connections and trusses are recognised as instruments that can provide valuable infor- mation for a better understanding of the behaviour of tra- ditional timber roof structures (Bertolini-Cestari et al., 2013; Del Senno and Piazza, 2003). Portuguese traditional buildings are normally constituted by timber roof systems, with the truss as the main structural 373 Structures and Buildings Volume 169 Issue SB5 Load-carrying capacity test of a long-span timber truss Branco, Varum, Ramisote and Costa Proceedings of the Institution of Civil Engineers Structures and Buildings 169 May 2016 Issue SB5 Pages 373–387 http://dx.doi.org/10.1680/jstbu.15.00006 Paper 1500006 Received 05/01/2015 Accepted 06/11/2015 Published online 18/12/2015 Keywords: maintenance & inspection/rehabilitation, reclamation & renovation/timber structures ICE Publishing: All rights reserved Downloaded by [] on [12/01/17]. Copyright © ICE Publishing, all rights reserved.