Temperature distribution and charring penetrations in timber assemblies exposed to parametric fire curves : Comparisons between tests and TASEF predictions
Abstract: Four furnace tests have been performed using two different parametric fire curves and the results are compared with computer simulations and Eurocode calculations. What differentiates the parametric fire curve from other fire curves is in particular the cooling phase, something that has proven to be hard to model for timber structures. A literature study and computer simulations were followed by experimental work performed at SP Wood Building Technology in Stockholm. The computer simulations were performed using the computer code TASEF. The predictions from TASEF were compared with measurements from the fire tests to evaluate how well the program can predict temperature distribution using a parametric fire curve. The four fire tests were executed at SP Wood Building Technology, glued laminated timber beams were used in all tests. When preparing the test specimens thermocouples were installed to measure temperature distribution, the thermocouples were installed in drilled holes. A deviation study regarding these drill-holes was performed as a part of the preparations. The temperature distributions measured during the tests were compared with the temperature distribution predicted by TASEF. Charring rate and charring depth were obtained from the fire tests, from the TASEF simulations but also by using equations given in the Eurocode. Since TASEF simulates temperature distribution and not charring depth, the 300 °C isotherm was assumed to represent the charring depth. The results from all three methods were compared and evaluated. The agreement between experiments and TASEF predictions regarding temperature distribution and charring depth were in general very good. Parametric fire curves with opening factors of 0.02 m1/2 and 0.04 m1/2 were used in four fire tests. TASEF performed more accurate predictions regarding the temperature distribution for the small opening factor but looking at the charring depth the predictions were better for the bigger opening factor. It is recommended to perform further studies and find out the reason for this behaviour. Comparing the charring depths measured at the tests with values calculated using Eurocode 5 there were some differences in charring depths. Charring depths for the horizontal direction of the beams were much alike, but when comparing the charring depths for the vertical direction there is a significant difference. The equations regarding charring depth for wood exposed to parametric fire curves in Eurocode 5 underestimate the charring depth. It is recommended to evaluate these equations further. For one of the timber beams delamination occurred, this has previously been assumed not to occur to glued laminated beams. More studies should be performed regarding delamination of glued laminated beams exposed to fire.
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