Structural performance of reversible discrete timber systems

Abstract

The construction industry accounts for a significant part (39%) of the global greenhouse gas (GHG) emissions, additionally it is accountable for 40% of all extracted materials, 40% of primary energy usage and 40% of the total waste generated. Adding up to CO2-emissions in the form of embodied or operational carbon. Meanwhile the temperature limit set in 2015 signed Paris Agreement with the purpose of reducing the global temperature increase, is being exceeded

If the global GHG-emissions are not reduced the global temperature rise will increase even more, and with that the severity of the climate change consequences. GHG emissions in the building sector can be decreased by reducing operational and/or embodied carbon. Since embodied carbon is getting increasingly higher but lacks in research and innovative solutions, this research explores the possibility of reducing embodied carbon by designing a reversible discrete timber system as alternative to a conventional structural timber element or system.

For this a joint that is reversible and applicable to discrete timber elements must be found and tested. Five joints from a larger list were selected based on simplicity. In order to determine the loads on the discrete timber system, a case study was set to be a post war apartment block in Rotterdam South. The selected joints were analysed to determine what would happen if a load is applied to this element. The load showed highly localized peak stresses in the joints, indicating that the joints might be the weakness of the discrete timber elements, the rest of the element showed expected behaviour. In the end a simple square cog joint is the most suitable.

Besides testing the discrete timber elements, the discrete timber systems also needed to be tested to see how they would react under the applied loads, and what the resulting maximum displacement and utilization values would be. Here various ways of aggregating discrete timber elements was tested. These aggregations were influenced by parameter such as the scaling factor (where a normal straight column, was scaled variedly into a mushroom-like column), dimensions of the base of the discrete system, the dimensions of the cross sections and the material of the discrete elements. The results from these tests showed the effects from the various parameters on the maximum displacement and utilization of the discrete timber system.

However, there are also some gaps with regards to which joints are suitable, moreover, can the joints be made in timber or should there be resorted to a reinforced joint in a different material than timber? One of the main strengths of a discrete timber system lays in its reversibility, and for the system to be reversible there must be a demountable joint.

Discrete timber systems can be a feasible alternative to conventional structural timber by ensuring that the discrete systems have strong, reversible joints that are simple in production and construction.