Disproportionate collapse prevention analysis for post and beam mass timber building

Abstract

Disproportionate collapse prevention of mass timber buildings is becoming a relevant design consideration due to the increasing height of these buildings. Linear static alternative load path analysis (ALPA) is well-established with extensive details and worked examples for concrete, steel, and light-frame wood buildings. The research presented herein illustrates its application to a mass timber building with floors supported by beams and columns, referred to as ‘post and beam’ system. The performance of a six-storey post and beam mass timber building, using predominantly wood-to-wood bearing-type connections, following three notional element removal scenarios (removals of ground floor internal, edge, and corner columns) is investigated. It is evaluated whether the case study building’s structural system can trigger floor collapse-resistance mechanisms by checking if its primary elements and connections satisfy disproportionate collapse acceptance criteria, defined by the demand-to-capacity ratio after element removals. The results demonstrated that: i) element removal analyses should be conducted in 3D and should include all primary structural elements, with floor carrying its own weight at every level; ii) compressive arching is dominant for members with small span over depth ratios, whereas catenary action governs for larger spans; iii) continuous beams and slabs help the floor system to cantilever over the removed elements; and iv) the considered connection detail may be improved by the addition of axial connectors to trigger catenary action.