Fire Resilience of Load-Bearing Wall Made of Hollow Timber Elements

During a fire load, a charred layer forms on the timber elements, which is a natural protection against fire, so that a certain level of fire resistance could be achieved by using elements with a larger cross-section. However, this modus of fire protection is not always suitable. One of the most commonly used fire protection systems are fire protection boards. In this work, a large-scale fire test was carried out on a protected load-bearing wall made of hollow elements under the effect of sustained mechanical loads and fire exposure. Different stages of charring were observed. The test was aborted at the 91st minute due to a decrease in the load-bearing capacity and integrity criteria. The allowable average temperature rise on the non-exposed side of the specimen (140 K) was not exceeded until the 91st minute of the test, and the allowable maximum temperature rise on the non-exposed side of the specimen (180 K) was not exceeded until the 90th minute of the test. The loss of specimen integrity occurred at the 90th minute of the test. For surfaces protected by fire-resistant panels, it should be considered that the onset of charring is delayed until a certain time. According to EN 1995-1-2, charring can start before the fire protection is removed, but at a lower charring rate than the rates up to the time of failure of the fire protection. The expression proposed in EN 1995-1-2 shows relatively accurate results for certain systems and thicknesses of fire protection linings. However, it does not consider the presence of more than one lining layer or the full range of lining thicknesses themselves. For the wall described in this paper, the predicted failure time of the fire boards would therefore be 41.5 min, which is not consistent with the results of the experiment (51 min). The results of the calculation model according to EN 1995-1-2 did not fully agree with the results of the fire test on the protected load-bearing wall.