Evaluate the maximum positive moment in the right span
Equate MB to the true plastic-moment capacity of the W21 x 55. Evaluate the maximum
positive moment ME in span BC, and locate the point of contraflexure. Therefore,
MB = -36(125.4)712 = -376.2 ft-kips (-510.13 kN-m); ME = 169.1 ft-kips (229.30 kN-m);
BF= 10.2 ft (3.Um).
Select a section to resist the plastic moment
The moment to be resisted is ME. Thus, Z = 169.1(12)736 = 56.4 in^3 (924.40 cm^3 ). Use
W16 x 36 with Z= 63.9 in^3 (1047.32 cm^3 ).
The design is summarized in Fig. 27/ By inserting a hinge at F, the continuity of the
member is destroyed and its behavior is thereby modified under gradually increasing
load. However, the ultimate-load conditions, which constitute the only valid design crite-
ria, are not affected.
