Project

STA CLT Special Interest Group

Goal: The Structural Timber Association Special Interest Group has been formed to address challenges in the sector, through a series of work packages to provide both guidance and evidence to support the fire safe design of mass timber High Rise Residential Buildings (HRRB) and commercial buildings.

Cross Laminated Timer (CLT) is increasingly adopted as a structural framing solution due to its sustainability benefits and impact on reducing construction programme. CLT is formed of a series of timber lamellae arranged orthogonally to give improved homogenous stiffness and stability. As an engineered timber product in residential applications, it is common to have all apartment and/or room bounding surfaces formed as CLT, i.e. the CLT not only forms elements of structure, but also serves a separating function.

In most instances in residential applications, the CLT is lined in some manner, plasterboard for example. For commercial projects, the scale of the fire enclosure is much larger, with the CLT generally only forming an exposed ceiling / slab structure.

For HRRB and similar types of purpose groups, the Building (Amendment) Regulations 2018 set out new statutory requirements in respect of the materials forming external walls and specified attachments which have been taken into account with this research.

The programme of fire performance experiments has been undertaken by leading CLT manufacturers including Binderholz, B&K Structures, Eurban, Henkel, KLH, OFR and Stora Enso, to provide test based evidence of behaviour which will enable specifiers and the market in general use CLT in the knowledge it is a safe building material.

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Danny James Hopkin
added a research item
This paper provides understanding of the fire performance of exposed cross-laminated-timber (CLT) in large enclosures. An office-type configuration has been represented by a 3.75 by 7.6 by 2.4 m high enclosure constructed of non-combustible blockwork walls, with a large opening on one long face. Three experiments are described in which propane-fuelled burners created a line fire that impinged on different ceiling types. The first experiment had a non-combustible ceiling lining in which the burners were set to provide flames that extended approximately halfway along the underside of the ceiling. Two further experiments used exposed 160 mm thick (40-20-40-20-40 mm) loaded CLT panels with a standard polyurethane adhesive between lamella in one experiment and a modified polyurethane adhesive in the other. Measurements included radiative heat flux to the ceiling and the floor, temperatures within the depth of the CLT and the mass loss of the panels. Results show the initial peak rate of heat release with the exposed CLT was up to three times greater when compared with the non-combustible lining. As char formed, this stabilised at approximately one and a half times that of the non-combustible lining. Premature char fall-off (due to bond-line failure) was observed close to the burners in the CLT using standard polyurethane adhesive. However , both exposed CLT ceiling experiments underwent auto-extinction of flaming combustion once the burners were switched off.
Danny James Hopkin
added a research item
https://www.sfpe.org/publications/sfpeeuropedigital/sfpeeurope23/europeissue23feature4
Danny James Hopkin
added a research item
Mass timber in the form of cross-laminated timber (CLT) panels has become a popular design option for the construction of buildings across the UK. However, there is currently concern amongst designers and approval bodies that the performance of CLT panels from different suppliers varies sufficiently such that each design necessitates specific consideration of the source of the CLT, with the underpinning fire strategy only holding where the mass timber elements are procured from a specific supplier. To assess whether such concerns are founded, this paper compares the in-depth temperature profiles, the mass loss rate, and charring depths of CLT panels from three major CLT suppliers, in a vertical (wall) configuration. The experimental campaign studied four different variables: (1) the effect of the lamella thickness, (2) the difference exhibited when using a polyurethane non-heat resistant adhesive or a modified polyurethane heat resistant adhesive, (3) the influence of having non-edge-glued joints of the laminations within the first lamella vs edge-glued, and (4) the CLT supplier. The samples were exposed to an incident heat flux of 50 kW/m 2 for 60 min using a radiant panel. The results indicate that the performance of the samples from the suppliers does not show a statistically significant difference for the same combination of parameters (adhesive type, lamella thickness and edge-glue). Thus, subject to parameters being consistent, i.e., adhesive, edge-gluing condition and lay-up, CLT can be specified in a generalised manner, improving confidence in the performance of the products and easing their procurement.
Danny James Hopkin
added a research item
Concerns about the environmental impact of building construction is leading to timber being more commonly used. However, it often faces scepticism regarding its safety in the event of fire. This article provides a point of reference on the fire performance of cross-laminated timber through a review of large-scale tests. Although adequately protecting CLT can make its contribution to fire insignificant, some of the internal surface of an enclosure can be exposed whilst still achieving adequate fire performance. Natural fire tests show that the charring rate and zero-strength layer thickness are higher than commonly used in guidance documents. The type of adhesive used to bond lamellae influences performance where delamination can lead to secondary flashovers, particularly in smaller enclosures. Structural elements can potentially collapse without self-extinction and/or suppression intervention. Tests to date have focussed on a residential context and knowledge gaps remain regarding larger enclosures, such as office-type buildings.
Danny James Hopkin
added 3 research items
This paper summarises a systematic experimental study to evaluate what, if any, differences in fire performance characteristics of cross-laminated timber (CLT) are apparent between samples manufactured by three different leading European suppliers. This element of the study focuses on samples in a ceiling orientation, subject to a constant incident heat flux of 50 kW/m2 imposed via a radiant panel (from below) at the centre of the sample, for 60 minutes. Experiments are conducted on samples with varying lamella thickness (20 or 40 mm), adhesive type (heat resistant [HBX] vs. non-heat resistant polyurethane [HBS]) and edge-gluing procedure (edge vs. non-edge-glued). In-depth temperature, charring depth, mass loss rate (MLR) and heat release rate (HRR) form the basis of comparison. It is observed through a statistical assessment (ANOVA) that limited differences exist between suppliers when panels have the same characteristics, e.g., lamella thickness, adhesive type and edge-gluing procedure. Differences are marginally more pronounced for MLR vs. charring rate.
Danny James Hopkin
added a project goal
The Structural Timber Association Special Interest Group has been formed to address challenges in the sector, through a series of work packages to provide both guidance and evidence to support the fire safe design of mass timber High Rise Residential Buildings (HRRB) and commercial buildings.
Cross Laminated Timer (CLT) is increasingly adopted as a structural framing solution due to its sustainability benefits and impact on reducing construction programme. CLT is formed of a series of timber lamellae arranged orthogonally to give improved homogenous stiffness and stability. As an engineered timber product in residential applications, it is common to have all apartment and/or room bounding surfaces formed as CLT, i.e. the CLT not only forms elements of structure, but also serves a separating function.
In most instances in residential applications, the CLT is lined in some manner, plasterboard for example. For commercial projects, the scale of the fire enclosure is much larger, with the CLT generally only forming an exposed ceiling / slab structure.
For HRRB and similar types of purpose groups, the Building (Amendment) Regulations 2018 set out new statutory requirements in respect of the materials forming external walls and specified attachments which have been taken into account with this research.
The programme of fire performance experiments has been undertaken by leading CLT manufacturers including Binderholz, B&K Structures, Eurban, Henkel, KLH, OFR and Stora Enso, to provide test based evidence of behaviour which will enable specifiers and the market in general use CLT in the knowledge it is a safe building material.