________________________________________________________________________ PROBLEM (11.9) The jib crane shown in Fig. P11.9 is of capacity W = 20 kN. For α = 30 o and a factor of safety of n s = 3, calculate the required minimum cross-sectional area for circular steel bar AB (E = 200 GPa). SOLUTION FBC ∑F ∑F 30o B FAB 20 = 40 kN sin 30o = 40 cos 30o = 34.64 kN y = 0 : FBC = x = 0 : FAB W=20 kN Pcr = FAB = So, I= π c4 π 2 EI f s L2 , I= 34.64 ×103 (3)(2.5) 2 = 0.329 × 10−6 m 4 2 9 π (200 ×10 ) = 0.329 ×10−6 , c = 25.44 mm 4 A = π c 2 = π (25.44) 2 = 2033 mm 2 Justification of the formula used: r = I A = 12.7 mm L r = 2500 12.7 = 197 O.K. Excerpts from this work may be reproduced by instructors for distribution on a not-for-profit basis for testing or instructional purposes only to students enrolled in courses for which the textbook has been adopted. Any other reproduction or translation of this work beyond that permitted by Sections 107 or 108 of the 1976 United States Copyright Act without the permission of the copyright owner is unlawful.