A box beam is fabricated from four boards, which are fastened together with screws, as shown in Figure P9.43b. Each screw can provide a resistance of 800 N. In service, the box beam will be installed...

A box beam is fabricated from four boards, which are fastened together with screws, as shown in Figure P9.43b. Each screw can provide a resistance of 800 N. In service, the box beam will be installed so that bending occurs about the z axis, and the maximum shear force in the beam will be 9 kN. Determine the maximum permissible spacing interval s for the screws. (See Figure P9.43a.)