고체역학 (Beer) — Analysis and Design of Beams for Bending: Problem 5.93

5.93 A uniformly distributed load of 66 kN/m is to be supported over the 6-m span shown. Knowing that the allowable normal stress for the steel used is 140 MPa, determine (a) the smallest allowable length l of beam CD if the W460 x 74 beam AB is not to be overstressed, (b) the most economical W shape that can be used for beam CD. Neglect the weight of both beams.