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Wytrzymałość na zginanie i niezawodność kompozytu drewnianego LVL w warunkach podwyższonych temperatur

Bednarek Z., Pieniak P., Ogrodnik P.

Zeszyty Naukowe SGSP / Szkoła Główna Służby Pożarniczej

2010

Nr 40

5--17

W artykule zostały przedstawione wyniki badań doświadczalnych wytrzymałości na zginanie tworzywa warstwowego LVL (Laminated Veneer Lumber). Badania zostały wykonane na specjalnie zaprojektowanym stanowisku badawczym z możliwością oddziaływania wysokich temperatur.

Composites based on LVL constitute the type of material which is more and more frequently used as construction elements in construction industry. Materials of this type can be characterized by other parameters as the ones used for raw wood. Their resistance properties are of key significance. In case of majority of construction materials, the exposure to temperatures in the conditions of fire affects the increase of resistance and reliability. The aim of the tests presented in the article has been to evaluate the influence of increased temperatures on resistance and reliability of LVL composite. Method: The experiment has been conducted on the specimens made from LVL according to PN-72/C-04907 norm. The specimens prepared to test resistance to static bending have been made in the form of cubicoids sized 20×20×300 mm. The test of bending strength has been performed on universal resistance machine – FPZ 100/1 (VEB Thuringer Industriewerk Rauenstein, Germany). The temperatures of fire environment have been simulated by means of the hot air blow (GHG 650 LCE). The evaluation has been made in the following ranges of temperatures: 20, 50, 100, 150, 200, 230°C. Results: The test has been carried out in the group of 66 specimens, 11 for each studied temperature. With respect to a considerable scatter of measurement results emphasized by other authors, descriptive statistics of test results have been calculated and “post hoc” HSD Tukey’s test has been performed to assess the differences in temperatures in the subsequent ranges of temperatures. Obtained standard derivations point out to the sufficient repetitiveness of test results. The increase in fluctuation of strength in higher ranges of temperatures has been observed and the differences in strength of specimens from subsequent ranges of temperature have been revealed. The obtained results have served as the basis for reliability evaluation. The probability of survival has been analyzed, that is absence of damage in the function of loading and temperature reflecting the plan of tests. The two-parameter Weibull’s distribution was used for the sake of analysis. Conclusions: Strength of LVL composite decreases statistically in the subsequent ranges of temperature. Dynamics of probability decrease was the highest after exceeding the temperature level of 150°C. The tests have proven the suitability of the post prepared in the Department of Applied Mechanics of SGSP for the comparative studies of timber based materials in the conditions of increased temperatures.