Letter to the Editor: Design Fires for Open-Plan Buildings with Exposed Mass-Timber Ceiling
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Letter to the Editor: Design Fires for OpenPlan Buildings with Exposed Mass-Timber Ceiling Egle Rackauskaite, Arup, London, UK Panagiotis Kotsovinos*, Arup, Manchester, UK David Barber, Arup, Washington, DC, USA Dear editor, Over the past decade, the design and construction of mass timber buildings using cross laminated timber (CLT) and glulam have significantly increased globally. This is mainly due to the benefits of timber construction in the global fight against climate change and a decarbonised economy. In addition, it meets architectural aspirations, can result in a reduced cost and improved speed of construction, in comparison to conventional, typically non-combustible construction forms. Many recent proposals by architects include high-rise mass timber buildings for office and public uses with large open-plan floor areas that are greater than 1000 m2 with aspirations of maintaining as much timber exposed as possible. For the structural fire design of high-rise buildings, a key issue to be addressed is the requirement for the building to withstand burn-out of a fully developed fire. When the load-bearing member is combustible and is exposed there is a feedback loop between the fire severity and structural response (through timber charring) resulting in more onerous fire conditions. The uncertainty of the types of fires that are therefore likely to occur in large-open plan compartments with exposed loadbearing timber, and how the timber may contribute to the fire, is a complex area that has not received enough attention from regulators, standardisation bodies, the industry or the research community. A conservative measure to mitigate the inherent risk combustible load-bearing elements pose, for design safety purposes is that of complete encapsulation of the timber. The purpose being to limit the additional contribution from the combustible structure to the fire throughout its duration. This is a relevant design safety assurance solution, once the encapsulation systems have been appropriately detailed, and fire tested for the specific application. It is important to understand the effect of the exposed mass timber on compartment fire dynamics to actively incorporate exposed load-bearing timber into a robust design solution; and this understanding is also relevant when determining the acceptable exposed area when quantifying the fire resistance of the structure, * Correspondence should be addressed to: Panagiotis Kotsovinos, E-mail: panos.kotsovinos@arup. com
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Fire Technology 2020 and when analysing if the compartment floors and walls are not compromised for the design fires being considered. In addition to the quantity of exposed timber area, the overall compartment fire dynamics may also be impacted by the number and orientation (e.g. walls vs. ceiling) of exposed mass timber surfaces [1]. However, this aspect is outside the scope of this letter, which focuses on the fire severity within buildings with a single exposed mass timber surface (i.e. ceiling).
1. The Compartment Timber Structures
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