Use of a Standard Parabola for Drawing Diagrams of Bending Moment. . 667 
the bending moment diagram drawn. The same procedure applies to each 
span in turn ; so that the complete diagram is obtained at once. 
§ 6. Another problem in which the method can be used is that of deter- 
mining the adjustment of supports so that the maximum bending moment 
be as little as possible. To secure this we should have maximum positive 
bending moment numerically equal to the maximum negative moment. 
Between two supports, at one of which the moment is zero, we have to 
adjust the position of the parabola till the negative value on the second 
support is equal numerically to the maximum positive value for the span. 
The position of the parabola may readily be got by trial, and this completely 
solves the problem for a uniform beam supported at the ends and at an 
intermediate point. 
Fig. Ill shows the adjustment for a whole length of 60' divided into two 
equal spans, the weight being 100 lb. per foot run. 
The same solution would apply to a 3-span girder if the middle span is 
sufficiently short. If the middle span is long, the parabola can be adjusted 
first to the middle span, arranging it so that the negative end values of the 
bending moment are equal to the maximum positive moment throughout 
the span. 
Fig. IV shows the diagrams for a beam of 80' length, 100 lb. per foot run, 
supported at the ends and at points 20' from the ends, the middle span being 
thus 40'. 
