In Austria, Germany and Switzerland, Lignoloc treenails are already successfully used as an alternative to aluminum nails in the production of CLT. During the gluing process in the vacuum press, they keep layers from slipping out of place and protect the vacuum film from being damaged by protruding nail heads.
When used correctly, new findings in research and development as well as in the field of dimensioning models lead to an increased fire safety in buildings. The low conductivity of wood and the charred layer, which forms during a fire, protect the inside of the wooden cross section which does not even “notice” that it is on fire.
However, CLT has one disadvantage compared to massive wood: Due to the high temperatures, the glue between the single layers can soften and the protective charred layer can fall off which then results in a higher burning rate. “If the glued layers were secured additionally with Lignoloc treenails, the burning rate would be further reduced. Metal connectors, on the other hand, would have the opposite effect because they conduct the heat even faster to the inside of the panel”, explains Stefan Siemers, head of research and development at Beck.
In cooperation with the ETH Zurich and Swiss Timber Solution and headed by Dr. Michael Klippel, Beck’s engineers designed an experiment designed to test this hypothesis on CLT panels of equal dimensions. Panel A served as a reference panel without additional fixing of the layers and was subjected to fire at a maximum of 1000°C. The panel burnt in a cascade-like manner: Once the panel was reduced to a certain thickness, the glue failed, the layers fell off one by one and exposed a fresh layer without charring. The average burning rate was 0.97 mm/minute (duration of the fire: 120 minutes).
Panel B was additionally nailed with four Lignoloc treenails per board crossing. The first layer burnt away rather quickly. However, from the second to the third layer this panel showed a fire performance similar to that of massive wood. The Lignoloc treenails thus prevented the falling off of the charred layer in substantial manner. As to the second and third layer, the burning rate was 0.62 mm/min which is that of massive wood.
In conclusion: During the fire performance experiment, Lignoloc treenails were able to hold together the layers, support the glue and guarantee a fire performance similar to that of massive wood. These findings form the basis for further research done by Beck, which the company makes available in the collaboration with CLT manufacturers – with the goal of minimizing the spread of fires as much as possible.
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