Joint Research Conference
June 24-26, 2014
Wooden I-joists are manufactured by adhering oriented strand board webbing into the groove of a laminated flange. I-joists are tested for strength at the production plant by a destructive stress. This measure is called ultimate load at failure and is the force (lbs) required to break the I-joist. I-joist products have different mixes of web depths and flange widths. Each joist depth and flange width combination has an associated “resistive shear load”. The ultimate load divided by the resistive shear load yields the specific strength ratio. The I-joist plant experienced more strength ratio failures during the one year than previous years. Production lots that did not meet shear load specification were scrapped.
The data set analyzed contained the stress test results, as well as information about the product type. Regression trees (JMP) were used to explore the nominal data and its relationship to the shear load result. Reliability and probability plotting (Minitab) were used to understand and verify the groupings discovered by the regression trees.