city charge for water; and all other items of expense which a contractor would incur if the work had been done by contract. Charge for switching service is not included, nor are charges made for use and deterioration of tools. The switching service was comparatively small in amount, as the material was practically all unloaded from tracks assigned to us for this purpose.

The concrete work was begun about May 1st and the work planned for this year was practically completed Sept. 21st. In all about 8400 cu. yds. were mixed and placed. No attempt at speed was made, the plan being to merely keep pace with the elevation of the roadbed. In this, as in all of the work of the Bridge & Building Department in connection with the Track Elevation, our plans were made to suit the requirements of the Engineer of Track Elevation.

STEELWORK.

About August 1st the erection of the steelwork was begun. Eight of the four track subways are practically completed at this time, and the remaining three will be finished about Nov. 1st.

The plan followed in the erection was very simple. The fact that each track was up to grade at each crossing when the erection of the girders at that crossing was begun, was of material advantage. The girders, posts, castings, and floor material were shipped to the work as required, and were unloaded from the cars directly into place. The girders, shipped together usually, were so loaded on the cars that they reached the work right end to and placed on the right side of the car with reference to each other, when there was any difference in ends or sides.

The plan of erection was, after first placing all of the girders for a set of two or three crossings, to then remove the false work from and put in and rivet up the steel floor, of first one and then the other, of the two construction tracks at these two or three crossings. The traffic was then diverted to these two tracks and the same operations followed for the remaining two. The object in erecting a set of two or three crossings together was to reduce to a minimum the number of times that it was necessary to divert the traffic.

The erection was done with two 20-ton derrick cars built from plans made by the Bridge & Building Department. The manner of using them is shown in Fig. 489. The girders are picked from the cars on which they are loaded and landed on their bedplates, one on each side of the track on which the cars stand. The view shows an outside girder in place, and a girder in the hooks ready to be swung out and lowered on the opposite side of the track.

From 30 to 34 men, working eight hours per day, were engaged on this work, and the aim was, as far as possible, to keep one part of them erecting and the other part riveting continuously. It took an average of a little less than seven days to erect and rivet

up complete each 4-track crossing. The crossings weighed from 440,000 lbs. to 630,000 lbs., and averaged about 525,000 lbs. each. The tight floor necessitated a large number of 5g in. rivets. Each crossing averaged about 3,500 -in. and 17,000 -in. field rivets. Our rivet crews averaged about 325 -in. and 700 g-in. rivets during each day of eight hours.

The labor cost of erecting and riveting the first seven crossings complete has been about o. 175 cents per lb. of steel.

The metal, except the top of the floor plates, will be painted two coats of iron ore paint, mixed at the Railway Company's shops, and applied by our force. We are experimenting with a hot asphalt coating for the floor. The results so far have not been very satisfactory.

All the work described has been performed by employes of the Bridge & Building Department of this railway. In addition to this, the work of building catch-basins, man-holes and sewers; the laying and depressing of water mains; the paving of subways; the building of sidewalks and fences; the moving of buildings where extra right-of-way was purchased, has been done principally by contract, under the direction of the writer. This work is not yet completed.

In conclusion it may be stated that, with improvements in detail which have suggested themselves from time to time during the past season, the same general plan of work will be followed next year.

LII.

By ALBERT REICHMANN, MEM. W. S. E.*

Read October 5, 1898.

The structures on the line of the Chicago, Milwaukee & St. Paul Railway Company, spanning the streets of the City of Chicago, were built of open hearth steel with an ultimate tensile strength of 55,000 lbs. to 65,000 lbs. per square inch. They were designed to carry two 160 ton engines coupled together on each track. The girders, however, which carry a full track load, have their unit stresses increased 20 per cent over those carrying onehalf track load, which is equivalent to carrying one and two-thirds the load of one rail with the same unit stresses as the girders carrying one rail load.

There are two types of crossings, one with intermediate supporting columns and one without. The crossings with intermediate supporting columns have their end girders tapering toward the end of the bridge and the intermediate spans parallel, as shown

FIG. 491.

C.M&ST.PR

BRIDGE AND BUILDING DEPT.

CHICAGO TRACK ELEVATION.
FOUNDATIONS FOR PEDESTALS
AND ABUTMENTS.

PLAN OF FOUNDATIONS FOR PEDESTALS AND ABUTMENTS.

on Fig. 490. The supporting columns are braced transversely with latticed bracing of angle irons, and are secured to the girders with seven-eighth inch diameter bolts. They rest on cast iron bearing plates 1 foot 6 inches below the sidewalk at the curb line, as shown on Fig. 491. A cast sleeve passes over the end of same

I

*Assistant Engineer Bridges & Buildings, C. M & St. P. Ry.

which is flush with the top of the sidewalk and the sides of the curb.

The cast sleeves are filled with cement mortar so the water will drain from the columns. This construction takes up the minimum space on the sidewalk; besides, by going down under the sidewalk, a large bearing plate may be used, which is especially desirable where concrete is used, as the concrete very frequently is not given time to attain its maximum strength before its load is placed on it.

The other type of crossing consists of single span girders, as shown on Fig. 489. These girders have parallel flanges, with their ends rounded off to a radius of 3 feet. They rest on large bearing plates which are made in two pieces, and are so designed that the bottom castings may be set at any angle and at the same time allow for both lateral and longitudinal motion of the steel work. This is done by making a circular projection on the bottom main casting which fits into a circular recess in the top casting or cap. This recess in the top casting has one inch greater diameter than the circular projection on the bottom casting. The girders are spaced 13 feet centers when the track is on a tangent.

The Floor System consists of 12 inch 45 pound "I" beams spaced 15 inches centers. The "I" beams rest directly on the bottom flange angle of the girders, their bottom flanges being cut to a width of 31⁄2 inches at the ends to avoid the rivets in the horizontal leg of the bottom flange angle. Thus it was not necessary to make any rivet space in the horizontal leg of the flange angle greater than 41⁄2 inches.