Problem 5.8-10A simply supported wood beam of rectangular crosssection and span length 1.2 m carries a concentrated load Pat midspan inaddition to its own weight (see figure). The cross section has width 140mm and height 240 mm. The weight density of the wood is 5.4 kN/m3. Calculate the maximum permissible value of the load Pif (a) theallowable bending stress is 8.5 MPa, and (b) the allowable shear stress is0.8 MPa. Solution 5.8-10Simply supported wood beam 334CHAPTER 5Stresses in Beams (Basic Topics)Maximum bending moment occurs under theconcentrated load.518,680 lb-ft 5224,200 lb-in.FROMAPPENDIXF: Select 8 310 in. beam (nominal dimensions)A571.25 in.2S5112.8 in.3s5MSÊSreq5Mmaxsallow5224,200 lb-in.2500 psi589.7 in.3tmax53V2AÊAreq53Vmax2tallow53(6407 lb)2(150 psi)564.1 in.25(6407 lb)(3 ft)212(120 lb/ft)(3 ft)2Mmax5RBd2qd22(b) CONSIDERING THE WEIGHT OF THE BEAMqBEAM517.3 lb/ft (weight density 535 lb/ft3)Vmax56485 lb8 310 beam is still satisfactory for shear.
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