Experimental assessment and damage modelling of hybrid timber beam-to-steel column connections under cyclic loads

Abstract

This paper presents an experimental and numerical study on the behaviour of timber beam-to-steel column connections under cyclic loads. Special attention is given to the accumulation of damage in the timber components and to its simulation. To this end, the fundamental nonlinear cyclic response of three specimens involving different configurations of top and seat angle connections with long bolts is examined. The experimental set-up, connection details and material properties are introduced first, followed by a detailed account of the testing procedure and results. The experimental outcomes enable a direct comparative assessment of the connection strength, hysteretic response, joint ductility, failure mode and energy dissipation capacity. In addition, finite element analyses employing a newly proposed damage-plasticity constitutive model of wood are presented together with a detailed description of the adopted modelling approach. The numerical output of these simulations at the local level, expressed in terms of strains and damage indices, is discussed and compared against the experimental measurements of local damage in the wood obtained through Digital Image Correlation (DIC) techniques. It is demonstrated that the connections under consideration are able to sustain their bending capacity without a significant deterioration in their stiffness or strength even up to large levels of deformation and several repetitions of loading cycles. Besides, the results and discussion presented in this paper support the conventional definition of global failure as a post-peak strength reduction higher than 20% of the capacity but so long as the strength measurements are obtained from the stabilized envelope curves of the specimens. The applicability of damage mechanics concepts to provide a reliable prediction of crack zones and damage accumulation in timber structures under the action of cyclic loads is also highlighted.Finally, general recommendations for avoiding brittle failure modes in this type of connection are given.