Question

Four wheel loads of 6 kN, 4 kN, 8kN and 5 kN cross a girder of 20 m span followed by uniformly distributed load of 4 kN/m and 4 m long with the 6 kN load leading. The magnitude of bending moment at a section 8 m from the left support for the given positions of loads is kNm.

• A. 86.4
• B. 80.8
• C. 119.2
• D. 108.4

Answer 1

The correct option is D 108.4


Ordinate of influence line for BM at $C=\frac{8\times 12}{20}=4.8m$
$Ordinateunder6kNload=\frac{4.8}{12}\times 7=2.8m$
$Ordinateunder4kNload=\frac{4.8}{12}\times 10=4.0m$
$Ordinateunder5kNload=\frac{4.8}{8}\times 6=3.6m$
$OrdinateunderheadofUDL=\frac{4.8}{8}\times 4=2.4m$
$\therefore M_C=(6\times 2.8)+(4\times 4)+(8\times 4.8)+(5\times 3.6)+(\frac{1}{2}\times 2.4\times 4\times 4)$
$=108.4kNm$