Sec. area, bottom flan ere ins. X depth ins. / Length in feet. - X 2 = Breaking weight, tons.

If the metal exceeds 1 inch in thickness deduct l-8th.

If above 2 inches deduct 1-4th.

This description of beam is of the strongest form, when the sectional area of the bottom flange is six times that of the top flange.

In designing this description of beam, the bottom flange may be from 1 -'2 to 1 1-2 the depth of beam; the top flange from l-4 to l-3 the width of the bottom one, and 2-3 to 1-2 the thickness of it; the feather being made at the top a little thicker than the top flange, increasing to the bottom to nearly the thickness of the bottom flange; in this way avoiding any sud-den variation in the thickness and saving weight; many engineers, however, prefer keeping the same thickness throughout in every part. The vertical brackets for stiffening the girder should not be made straight, but hollowed out something like the sketch, as thus they are much less liable to crack and all the corners should be well filled in.

In most cases it is necessary that the beam should be of uniform depth throughout; it will, however, save weight, without diminishing the strength of the beam, if the width of the bottom flange be reduced very considerably towards the ends; 1-2 of the width of the middle being quite sufficient; care being taken to maintain a sufficient surface for bearing,if the beam has to be carried on a wall,

Fig. 1.

Cast Iron With Feathers Or Flanges To Find Their S 53

Fig. 2.

Cast Iron With Feathers Or Flanges To Find Their S 54