The stress which the rivets connecting the web and flanges sustain is evidently due to the stress which is transmitted from one to the other. We have here two stresses to consider, and for whose resultant we proportion the number of rivets. The one is vertical, being due directly to the load resting on the flange of the girder, whence it is transmitted to the web through the rivets. It is difficult to find out what the amount of this stress will really be, as it depends upon the stiffness of the material intervening between the load and rivets. We will not be very far from the maximum effect if we take the weight of one driver, as distributed over the space covered by two cross-ties, making the vertical stress to be resisted by the rivet 12,000/24"=500 lbs. per inch run of the girder.

Fig. 20.

The weight of the track is inconsiderable. The other stress is horizontal and was found in the first chapter of the book given by the eq. (10), viz.:

S = Sx /hx.

This stress s, as already explained, is nothing but the maximum increment of flange stress at every section of the girder.

On page 60 we have given the maximum values of sx at the end, and at the sections a, b, c, d, e of the girder, from which we can now obtain. the values of s at these points.

At end s=69,500/4.5Ã--12=1,200 lbs. per.inch run.

a"=55,500/4.5Ã--12=1,000 " " "

b"=44,700/4.5Ã--12=810 " " "

c"=34,900/4.5Ã--12=640 " " "

d"=24,000/4.5Ã--12=440 " " "

e"=17,800/4.5Ã--12=320 " " "

The resultant of s thus obtained with the vertical stress of 500 lbs. is therefore the stress on the rivets, and we have:

The shear of rivet is double, consequently we take its bearing value, viz.: 4,700 lbs.

At the end, where we have the stress of 1,300 lbs. per inch run, we must therefore space rivets, 4,700/1,300=3« inches apart.

At a 4,700/1,120 =4 inches apart.

At b 4,700/950=6 " "

It is not necessary to calculate any further, as this last spacing already exceeds the distance which we have already taken as the maximum. It is true that the spacing, 4« inches, which we have taken as the maximum allowable, is for the flange, yet in order that the rivets in the two legs of the angle should stagger each other, both legs must have the same spacing. This staggering of rivets, so long as there is room enough for the riveter, after one rivet is in place, to rivet the other, is not necessary in the compression flange. But, as already said, in order that the rivet holes may lie in straight lines, vertical and horizontal, the top and bottom rows should be spaced alike. In the bottom flange angles the rivets must stagger completely, since we have deducted only one rivet hole out of each angle in calculating the net sectional area. In fact, the spacing in top and bottom flanges are made alike.