The article “Load-Carrying Capacity of Lengthwise Cracked Wood Beams Retrofitted by Self-Tapping Screws” (J. Struct. Engr. 2017) provides data on the maximum load (kN) of J = 5 specimens of I = 4 types of wood beams used in housing: intact beams (L1), long, centered cracks (L2), short, centered cracks (L3), and long, offcenter cracks (L4).

Use a significance level of .05 to test the null hypothesis of no difference in true average maximum load for these four beam types.

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Beam type LI L2 L3 L4 Maximum load (kN) 32.53 19.18 7.50 18.18 21.89 13.15 10.62 6.75 16.08 14.12 13.25 18.52 12.02 18.83 12.80 26.95 13.19 11.55 24.63 23.63