## 1 Introduction  
In the last decades, there has been strong interest worldwide in developing codes for buildings focused on the Performance Based Seismic Design (PBD), rather on prescriptive criteria [1]. As a general rule, the PDB procedure allows designing structures able to satisfy a specific performance level, for a desired seismic hazard [2]. The design philosophy is based on the collapse prevention and the reduction of repairing costs, thus bringing social and economic benefits. The PBD goals can be reached through different design strategies, such as the Force-Based Design (FBD) or the Displacement-Based Design (DBD) calculation processes.  
Despite the FBD procedure has been implemented in standards for earthquake-resistant buildings (i.e., the current edition of the International Building Code [3]), however, some of the seismic design provisions in use (see for example the ASCE 41-17 [4] and ASCE 7-16 [5] documents) still do not respect the general PBD strategy, due to several intrinsic issues. For a given building object of analysis, these issues come upon the FBD basic hypothesis, namely the assumption of the initial elastic stiffness and the adoption of a specific force reduction factor to predict the inelastic force distribution. As also discussed in [6], for most of the buildings of technical interest, it is thus not possible to fully exploit the FBD goals (and achieve an optimal design target). It is in fact reasonably expected that two different structures (still being constructed according to the same technology) can exhibit different levels of damage under the same input seismic action. Moreover, according to standards in use, the actual seismic design of structures is carried out with a uniform-hazard spectrum for a fixed return period, hence leading to uncontrolled values of failure probability, which in turn can usually vary with the structural and location features [7].  
The DBD procedure, in this regard, is a multi-level design approach based on the displacement response spectrum as a cornerstone for calculating the base shear demand. In most of the cases, the inter-story drift is chosen as a key parameter to control the global level of damage, and its limit values strictly depend on the structural system to verify. Deformations or strains are generally recognized to better assess the damage evolution, given that they are expected to go beyond the elastic range. The DBD procedure follows, as the FBD, the \"Capacity Design\" principles, i.e., the \"Hierarchy of Resistances\", to ensure that plastic hinges occur only at pre-established points. However, the DBD procedure has been basically developed to overcome the FBD limitations, hence allowing achievement of consistent performance levels for structures with different properties, through the definition of uniform-risk design maps [7].  
In this paper, the original Modal-DBD calculation steps are further extended from their formulation and adapted to the structural typology of timber Blockhaus (or log-house) systems. They represent one of the oldest construction typologies, being based on overlapped (solid or glu-lam) timber logs that are interconnected by carpentry joints. Based on a multi-story case-study building of technical interest, key issues for the application of the Modal-DBD approach to Blockhaus structures are thus discussed. Major advantage for the overall calculation process, as shown, is derived from refined Finite Element (FE) numerical simulations carried out on single log-wall portions under in-plane lateral loads, so as to collect the key mechanical parameters that are of primary interest for the definition of the required backbone curves. The accuracy of calculation results is then assessed with the support of a Push-Over (PO) analysis of the multi-story case-study building.