Page 139 - Handbook of Civil Engineering Calculations, Second Edition

1.122 STRUCTURAL STEEL ENGINEERING AND DESIGN

FIGURE 27

5. Evaluate the maximum positive moment in the right span
Equate M B to the true plastic-moment capacity of the W21 55. Evaluate the maximum
positive moment M E in span BC, and locate the point of contraflexure. Therefore,
M B –36(125.4)/12 –376.2 ft·kips (–510.13 kN·m); M E 169.1 ft·kips (229.30
kN·m); BF 10.2 ft (3.11 m).
6. Select a section to resist the plastic moment
3
3
The moment to be resisted is M E . Thus, Z 169.1(12)/36 56.4 in (924.40 cm ). Use
3
3
W16 36 with Z 63.9 in (1047.32 cm ).
The design is summarized in Fig. 27f. 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.