jected to by most American railway engineers on account of the great deflection that it permits.

Deck Plate-Girder Spans

Although plate-girders are of necessity as unscientific structures as a bridge specialist ever has to design, they are without doubt the most satisfactory type of construction possible for short spans. Their superiority over articulated trusses is due to the following reasons:

First. Owing to their compactness they better resist shock and check vibration.

Second. They have fewer critical points where overstress is likely to exist because of faults of either designing or workmanship.

Third. A number of loose rivets lying close together will do far less harm in a plate-girder than in an open-webbed one.

Fourth. The cost of manufacture per pound of metal is a little less.

Fifth. Owing to the steady demand for plate-girder structures and the comparatively small number of the sections of metal used in their manufacture, it is easy to obtain quickly the materials required; and the work on the metal is of a simple character. For these reasons plate-girder spans can generally be purchased with less delay than open-webbed girders.

Sixth. The cost per pound for erection is decidedly less, excepting where the conditions are unusual, and the cost of painting is comparatively small.

Seventh. They can be overstressed without danger much higher than open-webbed girders.

Eighth. They are less liable to injury by accident than articulated trusses.

Ninth. They are more easily painted, and are more accessible to examination for rust.

Tenth. The cost of maintenance is less, owing to the absence of small parts and details that might work loose under traffic.

The ordinary limit of length of plate-girder spans is about one hundred (100) feet, but that limit has often been surpassed by twenty-five (25) or thirty (30) per cent for simple spans and by much more for swing spans. Usually it is the difficulty in shipping very long plate-girders from bridge shop to site that determines the superior limit of such spans. The loading of long girders on cars for shipment is quite an art, and it should be entrusted only to men experienced in such loadings; for, otherwise, the metal is liable to be injured in transit or the cars to break down, or some other trouble is likely to happen before they reach their destination. Some engineers believe that the liability to injury of long plate-girders in shop, transit, and field should limit their length to one hundred (100) feet; but the author is not of this opinion, for he thinks that by taking proper pre-