A simply supported beam, 10 ft long, consists of three 4-in. by 6-in. planks that are secured by bolts spaced 12 in. apart. The bolts are tightened to a tensile stress of 18 ksi. The beam carries a concentrated load at its midspan that causes a maximum bending stress of 1400 psi. If the coefficient of friction between the planks is 0.3, determine the bolt diameters so that the shear between planks can be trans- mitted by friction only. 6 in.- 12 in. FIG. P5.95