| Basic principle of Material Mechanics pointed out that the shearing modulus ofelasticity of cross section of the web （G, in brief） may affect the bending deflection of asimply supported beam; but this effectiveness for a steel beam can be neglected if the ratiobetween its span and height is over10. However, according to the Science of Wood andWood Products, G of the web of wood I-beam （IB） is weaker than that of steel and is easyto be changed by moisture so as to influence the IB’s bending deflection. In view of thispoint, this paper, by means of systematic experiments and analyses, approached the Gsincluding those changed by moisture of wood oriented strand board （OSB）, bamboowaferboard （BWB） and wood structural plywood and their effctiveness on bendingdeflection of the IBs webbed with those panel composites respectively. Meanwhile, inorder to make recognizing of the web property easy, bending modulus of elasticity （E, inbrief）, which is a common index in China National Standards, and its relationships with theG of the web panels were also studied in this paper.Results from the two-rail shearing test of OSB, BWB and SPly showed that there is adifference in the cross-section shearing failure performance between the panel composedwith wafer or strand and plywood. Unlike the plywood whose characteristic of the shearingfailure was similar with that of steel, the appearance of the shearing failure of both OSBand BWB was that there became bulging along the shearing line due to the failure ofgluepoints between the wafer or strand. The order of the G of these three panelcompositeswas: SPly （1666MPa）> BWB （1610MPa）> OSB （999MPa）. Generally, it isappropriate that G of IB’s web is little bit more than1200MPa.Analysis results of the relationship between the bending deflection of those IBs andthe Gs of those webs indicated there were negative relationships between G and both theshearing deflection and the total deflection of the IB, with the respect regression equation△i=9.7334G-0.0949and△s=464.15G-1.0044. The deflection by shearing occupied6.4%ofthe total deflection in bending averagely for the IB whose span-to-depth ratios was18:1,however, it was was42.9%for the IB whose span-to-depth ratios was4:1. Thus it can beseen that both the G of web and the span of IB played a comprehensive role on the bendingdeflection of IB.G of BWB-webbed and OSB-webbed IB with the constant temperature and humiditytreatment were tested in different moisture content ranging form air-dry moisture （10.9%）to fiber saturation point of panels. The results pointed out that the fiber saturation point ofBWB and OSB in this test was about25%; there was a negative relationship between the moisture content of BWB and OSB below the fiber saturation point., but their slope weredifferent; the value of G decreased significantly in a moisture content above15%; thethickness of BWB of10mm. thickness increased by9.93%and that of OSB increased by20.84%, respectively. G due to a decline in thickness brings the total decline in account theamount of G30.2%. Moisture absorption sheet can be seen on the sheet thickness swellingproduced significant effects on G is the bending deflection of water affect the IB one of theimportant factors.Based on the result of the test on detecting E of panels under the same ambienthumidity condition, the impact of moisture on E was the same as that on G, and there wassa great positive linear relationship between E and G（y=0.5572x+1740.4，R2=0.95）,Therefore, we can use the E of panels as the basis of selection for the web materialperformance when there was lack of national standard for G in China.The G, E and thickness swelling can be controlled by the adjustment of themanufacturing process condition of panels, by which, the bending deflection of IB also canbe controlled.Based on these results suggested:1) Specifications should be added to the structure Gwith a wooden plate test indicators and methods （recommended two-rail shear test methods）in our board, wooden structures and other national standards;2) Modify only consider thebending moment deflection of the IB method for the design deflection of bending andshear deflection includes IB, including the design method of bending deflection and thecorresponding limits in our Wood structure and wooden construction materials relevantstandards and specifications.The innovation in this study is the finding of the relationship between G of web andthe deflection in static bending. The theoretical value of this study was that the scientificrelationship between material properties and its structure performance was revealed. Thevalue in engineering application of this research is providing sufficient and reliabletechnical basis or reference for either the manufacturing of web or designing,manufacturing and applying of IB. |
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