Page 356 - Aircraft Stuctures for Engineering Student

9.9 Effect of idealization 337

Siniilarly the resultant of q12. parallel to the y axis is
SJ = q12b2. - Yl) (9.77)
Thus the resultant: in a given direction, of a constant shear flow acting on a web is the
value of the shear flow multiplied by the projection on that direction of the web.
The resultant shear force S on the web of Fig. 9.53 is

s = Js:.s;l= q12 J(x2 - x1)2 + b2. - yl) 2

i.e.
s = 412L12 (9.78)
Therefore, the resultant shear force acting on the web is the product of the shear flow
and the length of the straight line joining the ends of the web; clearly the direction of
the resultant is parallel to this line.
The moment My produced by the shear flow q12 about any point 0 in the plane of
the web is, from Fig. 9.54

(9.79)
in which A is the area endosed by the web and the lines joining the ends of the web to
the point 0. This result may be used to determine the distance of the line of action of
the resultant shear force from any point. From Fig. 9.54
Se = 2Aq12

from which

Fig. 9.54 Moment produced by a constant shear flow.