Question

Review The joists of a floor in a warehouse are to be selected using square timber beams made of oak The allowable bending stress is allow 42 ksi and the allowable shear stress is allow 125 poi (Figure 1) Part A If each beam is to be designed to carry 95 lb/ft over a simply supported span of 26 ft determine the smallest dimension of its square cross section Express your answer to three significant figures and include the appropriate units. Figure 1 of 1 HA Osa? Tulue in Submit RA Part B Cepele Pour

Answer 1

given "allow = 4.2 ksi Tallow 125 psi HI9Sb load (w) = 95 1b/ft length. 26 ft 2665 1 RA Ra = wie 95,2€ = 1235 16 Shear force is maximum at support Vx= 1235-95 x Vmax = 12 35 lb (at 2:o) Moment equation Mr = (1235a 95.22) 15.44 at mid span max Moment for udl is Mmax 8027.5 lb.ft = 13ft

Mmax = 96.33 kip.in shear stress checks Tavg 3 Vmax Σ Α Az a' = : 1235 x10-3 2 125 x10 3 a= 3.849 in Bending stress check M I M adla Mmax= Z Sallow 96. 33 4.2 ſze a%) a= 5.163 in smallest dimension az max (5.163, 3.849 in) a=5.163 in