Class No. 1.

Masonry piers should be used for important railroad bridges and for very large highway bridges, where first-class stone can be obtained at reasonable cost. If good stone is not obtainable at a fair price, it is better to use one of the other classes. The proper way to proportion a masonry pier is to determine the least size under coping to support either the pedestals themselves or the pedestal-blocks, as the case may be, leaving a small margin on the exterior and ample room between pedestals or pedestal-blocks to allow for variation in erection, then batter the pier all around not less than one-half inch to the foot, or as much more as investigation shows to be necessary. The coping should project all around about six inches, the amount depending upon the magnitude of the pier and the thickness of the coping course, which should be from eighteen to twenty-four inches.

The batter for the sides is to be determined in the following manner: Compute for both the loaded and the empty structure the greatest longitudinal components of the total wind-pressure that can come upon the pier from the two spans which rest thereon, upon the assumption that the friction at the roller ends of the spans is zero.

The direction of the wind which will give the greatest longitudinal thrust on the structure is forty-five degrees in respect to its longitudinal axis. As the cosine of this angle is approximately seven tenths, the longitudinal component of the wind-pressure per lineal foot of span will be seventy per cent of the assumed said wind-pressure.

Find also the greatest traction thrusts from braked trains on the assumptions that, first, the greatest live load is on the structure, and, second, that the least live load, or one thousand pounds per lineal foot, is on same. Now find the values of the following combinations:

1. Thrust from wind load on empty bridge.

2. Thrust from heaviest braked train.

3. Thrust from wind load with lightest live load on the spans.