Experimental investigations of connections for robustness of mass timber buildings

Recent growth in mass timber construction has raised concerns about preventing disproportionate and progressive collapse, emphasizing the need for performance-based design due to general lack of understanding the behaviour of mass timber connections under extreme load and deformations. The aim of the research presented was to expand on the current understanding of the mechanical properties of common floor panel-to-panel cross laminated timber (CLT) connections and subsequently floor systems under combined bending and tension, as typically observed under catenary action through experimental analysis. The thesis develops the methods for component-level and full-span substructure tests for CLT floors under extreme deformations that allow for distillation of the necessary parameters. The novelty of the study lays specifically in analysing the changes in these parameters due to increasing tension utilisation of the connections, which is instrumental for robustness performance analysis and has not been previously investigated. The component test developed uses a fraction of resources needed for the standard full-span testing while aiming to provide the same information about the connection behaviour, which can be used in design calculations and modelling alike. Full-span testing was performed to verify the component test results through numerical methods, as well as introducing further parameters such as continuous spanning panels and wall detailing. In total five types of CLT floor-to-floor connections were investigated, including four most commonly used currently in the industry as well as a novel tube connector

Experimental and numerical analyses of full-span floors and component level subassemblies for robust design of CLT floors

Tall mass timber structures are becoming increasingly prevalent and, with some now rising as tall as 81m (Abrahamsen, 2017) it is vital to consider design for structural robustness and disproportionate and progressive collapse prevention under accidental actions (Starossek & Haberland, 2012). The Eurocode 1-7 approach (European Committee for Standardization, 2006) focuses on material independent objective-based design. An inherent robustness through alternative load paths (ALPs), primarily catenary action, is targeted through introduction of vertical and horizontal ties. This is a prescriptive approach without the necessary physical basis when introducing novel construction methods

CLT Connection Behaviour Under Extreme Deformations:Influence on Structural Robustness in Large Timber Construction

Multi-storey timber construction has become increasingly popular over the past decades, largely due to its naturally low net carbon footprint. One of the important design considerations in structures of this scale is their robustness. Existing prescriptive design methods for robustness, generally developed for steel and concrete construction, cannot be directly applied to wooden structural systems without further research. Some experimental work is available on the catenary action formation in Cross-laminated timber (CLT) and Laminated Veneered Lumber (LVL), however, these tests focus on substructures and the results are difficult to generalise beyond the specific geometries and materials tested. This study focuses on developing a localised component test methodology of high repeatability which isolates the behaviour of individual elements and connections, and investigate their influence on the robustness of the structure as a whole. The experiments presented focus on two key components of CLT buildings: a continuous 5-ply CLT section and a half-lap floor joint. The solid section was tested under 3-point bending to investigate the deformations in CLT after rolling shear failure. Similarly, a 4-point bending test was performed on the half-lap joint to achieve the moment rotation curve. The force was applied until a drop of approximately 10% in the moment resistance was observed. The specimens were then transferred onto a tension testing rig. The study indicates that double span floors impede proprietary catenary formation and although the tested connections have the potential of forming catenaries, they have limited tensile and rotational capacities and may not be adequate for catenary formations in buildings above 4 storeys

Application of a Tube Connector for Catenary Actioni in CLT Floors

Multi-storey buildings require provisions to avoid disproportionate consequences after unexpected events, e.g. explosions or human error during design and construction. To prevent failure progression in the structure after an initial damage (loss of load-carrying elements), alternative load paths, like catenary action, should be provided. Catenary action supports the sagging structure after element loss by transferring the loads horizontally to the adjacent elements; this mechanism requires the connections to remain ductile under high load. Conventional dowel-type connectors in timber structures have limited potential to develop catenary action in beams or floors. A previously developed tube connector exhibited desirable behaviour to develop catenary action in cross-laminated timber floors; however, the tube exhibited and undesirable failure mode. In the present study, the behaviour of a newly designed variant of the tube connector was experimentally investigated under catenary action. The new connector design was tested in varying configurations, at both the component level and full-scale floor level, in Canada and Sweden. The results show that a more desirable behaviour of the adapted connector could be achieved compared to the previous design, with respect to catenary action. Funder: Government of British Columbia;ISBN för värdpublikation: 9781713873273, 9781713873273Främja ökat byggande av flerfamiljshus i träTallwoo