| Wood I-Joist (IJ), which is made of industrial fast-growing trees, is an efficient heavy-loading material for wooden buildings. It could be used as a substitute for solid wood beam in modern light frame wooden buildings. Though both the manufacturing and application of IJ have been popular in developed countries about half a century, it was blank in China now.End bearing capacity, end bearing length, lateral bulking performance and stiffness of the framed joist are the main structural properties of IJ. They not only affect the bearing capacity, stability and living feelings of modern light frame wooden buildings, but also influence the anticipated quality and manufacture control of IJ.The end of the IJ placed on the top board bear both the compression directly come from the loading of upper building, men, furniture and etc. and the shearing in the uniform bending come from loading of men, furniture and etc. Therefor, both vertical anti-compression capacity and anti-shearing capacity of the end of IJ are needed to be emphasized. However, the IJ placed on the metal connectors need only to consider the shearing from bending. Results from the tests and analyses of the IJ samples in this study, which were made with the poplar LVL whose tensile strength parallel to grain was 8,700Mpa and the web of bamboo waferboard whose horizontal shearing strength was 22Mpa, showed that the vertical anti-compression strength of the IJ was 5.70Mpa, the rupture loading from the uniform bending for the IJ placed on the metal connectors was 7.14kN without consideration of the edgewise stability of the web, the minimum bearing length of the IJ was 56.80mm and the shearing strength parallel to the glue line of LVL should be over 4.30Mpa. The calculated method to determine the minimum bearing length put forward in this paper solved the problem that that was usually determined with the experience of the constructor.The results from the tests and analyses for lateral buckling and stability showed that, though there was an advancing deflection, the lateral bulking behavior of the IJ still subjected to the basic law of the homogeneous beam so that the classical mathematics for critical loading on the lateral bulking of homogeneous beam could be applied to IJ; the deviation between calculated and measured value in this study was only 5%. Meanwhile, it was found that the method employing the lateral-stability coefficient and bending moment as a key factor for judging lateral stability of IJ was much more scientific and applicable than that employing the bending modulus of rupture of the whole IJ. The later-stability coefficient and critical bending moment of the IJ in this study were ? l=0.49 and M cr=3,595N.m respectively.Static bending stiffness of the joists composed with IJ and top panel could be acquired by either theatrical calculation or the testing and analyzing of the bending deflection. Results from both the calculation and tests showed that the value of the static bending stiffness of the composed joist determined with testing analysis was 10% greater than that with the calculation; the calculation for the deflection of a single IJ including that from shearing could not be applied for that of the composed joist. The static bending stiffness of the composed joist in this study was 26,4603 N.m2.All the fruits from the above research may be taken as necessary technical bases and references for application of IJ in modern light frame wooden buildings. |
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