Experimental Study of Fire-Induced-Delamination of Cross Laminated Timber
Daniel Brandon, Birgit Ostman, Joseph Su, Amanda Kimball, Matthew S. Hoehler
Cross Laminated Timber (CLT) is increasingly used as a structural material for tall buildings, due to its structural properties and low carbon footprint. CLT is a mass timber product, which is made by crosswise gluing layers of timber lamellae. Recent architectural trends include having visible CLT surfaces, which, in the event of a fire, can become involved in the fire and act as fuel to the fire. A study by the Fire Protection Research Foundation (FPRF; USA), National Fire Protection Agency (NFPA; USA), National Research Council Canada (NRC-CNRC; Canada), Research Institutes of Sweden (RISE; Sweden) and National Institute of Standards and Technology (NIST; USA) has focused on the contribution of exposed CLT to compartment fires. The study included a review of previous compartment fire tests, full-scale fire tests of compartments with and without exposed CLT structures, the development of design methods for engineers and intermediate scale fire tests to identify high-temperature resistant adhesives for CLT. The full-scale compartment tests showed the undesirable consequences of CLT delamination during a fire (i.e. fall-off of exposed lamellas), which occurred due to weakening of the CLT adhesive. These consequences included fire regrowth after a period of decay or a continuation of a fully developed fire. This can make self-extinction of a compartment fire not possible, implicating that the fire will lead to collapse if the fire is not manually extinguished or extinguished by sprinklers. In order to achieve self-extinction of flaming combustion in compartments with exposed CLT it is important to avoid fire-induced delamination. It was shown that fire-induced-delamination can be avoided using high-temperature-resistant adhesives. A test method was developed to identify adhesives that are not prone to fire-induced-delamination under relevant fire conditions. A summary of the test methodology, evaluation and results is discussed in this article.