Application of modal-displacement based design method to multi-story timber Blockhaus structures

Structures under seismic excitation undergo different inter-story drift levels that can be associated to damage of both structural and non-structural elements, and thus to the expected losses. The Modal-Displacement Based Design (DBD) procedure, in this regard, has been developed to fix major issues of Force Based Design (FBD) approaches, thus to design multi-story buildings in which the inter-story drift can allow one to control damage mechanisms. In this paper, the conventional Modal-DBD methodology is applied to multi-story timber buildings constructed using the Blockhaus technology. Given their intrinsic geometrical and mechanical features (i.e., stacking of logs, door/window openings, gaps and friction mechanisms, etc.), dedicated methods of analysis are required for them, compared to other wooden structures. A three-story case-study Blockhaus system of technical interest is thus presented for the assessment of Modal-DBD calculation steps. As shown, special care must be spent for the selection of convenient inter-story drift limits that in general should reflect the characteristics of the examined structural typology. The backbone parameters are thus collected for each shear-wall composing the 3D Blockhaus building, based on refined Finite Element (FE) analyses of separate log-walls. The overall results of the Modal-DBD process are thus finally assessed by means of a Push-Over (PO) analysis, carried out on a simplified 3D FE model of the examined multi-story structure. The comparison of FE predictions, as shown, demonstrates that reliable estimates can be obtained when the Modal-DBD procedure is applied to timber Blockhaus systems. In particular, base shear loads can be estimated with good accuracy, while the corresponding top displacements are slightly overestimated (with up to +10%-14% the expected values, for the collapse prevention performance level).