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Blockhaus structural systems are obtained by assembling multiple timber logs able to interact with each other by means of simple mechanisms (e.g. contacts, tongues and grooves, and carpentry joints, also referred to as ‘corner’ joints). Although these systems have ancient origins, the structural behaviour of Blockhaus systems under well-defined loading and boundary conditions is still complex to predict. The paper focuses on the assessment of the typical buckling behaviour and resistance of in-plane compressed timber log-walls. The effects of various mechanical and geometrical aspects such as in-plane rigid inter-storey floors, load eccentricities, different types of lateral restraints, openings (e.g. doors or windows) or additional metal stiffeners, are investigated by means of full-scale buckling experiments. Results are then critically discussed and preliminarily assessed via analytical formulations taken from classical theory of plate buckling and column buckling. Although further advanced studies are required for the development of a generalized buckling design method, it is shown that several mechanical and geometrical aspects should be properly taken into account to correctly predict the structural capacity of Blockhaus systems under in-plane compression.

Blockhaus systems represent a traditional construction technology where structural resistance is attained by direct contact between multiple timber surfaces obtained via carvings, notches, and ancient carpentry joints. Although this technology is frequently used in practice for the construction of buildings (Fig.1), due to the complexity of various phenomena (loading perpendicular to the grain, effect of friction, influence of gaps in the joints, creep, etc.), their structural behavior under specific loading/boundary conditions is not completely known. The interaction between multiple logs, as well as the restraint effectiveness of carpentry timber joints and the anisotropy of timber, can strongly affect the load-carrying capacity of these structural systems [1][2][3][4]. The paper focuses on the assessment of the typical buckling behavior and resistance of vertically compressed timber-log walls. The effects of various mechanical and geometrical variables such as possible geometrical imperfections, openings (e.g. doors or windows), fully flexible or in-plane rigid inter-storey floors are investigated by means of advanced finite-element (FE) numerical models [5] validated on experimental results. Comparisons with analytical solutions are presented and critically discussed, in order to assess the applicability of existing formulations to Blockhaus structural systems. Finally, a simplified design approach suitable for implementation in the new Eurocode 5 is proposed for the stability check of timber log-walls under in-plane compressive loads.