Usage of Albizia lebbeck (L.) Benth. and Samanea saman Merillas Components in Wood Structures
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The Research of this paper to propose the usage of Albizia lebbeck (L.) Benth. and Samanea saman Merill are fast-growing commonly found in Thailand. However these species of wood could not be utilized as structural components either economically or safely due to the lack of recommended values for their engineering properties. Therefore the objective of this research was to study their physical and mechanical properties based on statistical data obtained from 11 series of tests in accordance with ASTM 0-143. 0-198 and 0-1037. The number of samples for each test was large enough to ensure 99% interval of confidence. Then goodness-of-fit tests were performed for each set of data to achieve at least 95% level of confidence. Buildings analyzed included residences, offices, and schools. The buildings were limited to two-storeyed buildings with f1oor-to-f1oor height of 3.00 meters. Given to joists and beams were simply supported. Values of structural reliability were obtained by using accurate methods. Results from testing showed that engineering properties of both species of wood could be represented well by normal distribution. Reliability analyses and designs of wood sections for joists. beams and columns showed that designs of Joists and beams wWe controlled by deflection; whereas those of columns were controlled by buckling. Based on these reasons the governing basic variable for designs of wood sections was the modulus of elasticity (E). If the accepted value of failure probability (P,) for serviceability limit states was set to be 10-4. the corresponding upper limit coefficient of variation (COV) of E would be 0.269. Similarty if the accepted value of P, for Ultimate limit states was set to be 10~. the corresponding upper limit COY of E would be 0.210. Since COY of E for both species of wood were lower than limit COY mentioned above. they could be used safely as structural components. Proposed design procedures were similar to Working Stress Methods. The only difference from E.I.T. standard was live load. Instead of nominal live loads for residence. office and school as stated In the Municipal law. mean Ifve loads based on data gathered in Thailand were recommended. Wood sections obtalnec from numerical procedures proposed were as large as those obtained from WCCAL Software. Furthennore recommended wood sections and factor of safety (FS) were summarized in appendices. It was also interesting to note that the value of E for compression and tension parallel to grain of both species of wood could be used to predict the corresponding value of E for bending.
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