Four wood boards 1 in. by 6 in. in cross section are stacked as shown and used as an 8-ft-long simply supported beam. A 400-lb concentrated load is applied at the center of the span. Neglecting the weight of the beam, calculate the following based on the full nominal (rough) dimensions:
(a) the maximum bending stress (boards not glued together)
(b) the maximum bending stress if the boards are glued together
(c) the maximum shear stress in the middle glued joint