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22 MARINE REVIEW. [May 24, EIGHT-TRACK BRIDGE ACROSS CHICAGO DRAINAGE CANAL. The main drainage and ship canal of the Sanitary District of Chicago, forming the connecting link between the great lakes, the Mississippi river and the Gulf of Mexico, was constructed, not only to drain the Sanitary District of Chicago, but also with a view to securing an artificial highway for navigation. To accomplish this purpose, it was necessary that the railroads and highways across the canal be carried by movable bridges About 2,000 feet west of the junction between the main drainage channel and the Chicago river, virtually in the heart of the city, eight railroad tracks, side by side, cross the line of the canal. Four of these tracks are owned by the Pittsburg, Cincinnati, Chicago & St. Louis Railway, Thomas H. Johnson, chief engineer; two are owned by the Chicago Ter- minal Transfer Railroad, F. E. Paradis, chief engineer; and two by the Chicago Junction Railway, J. B. Cox, chief engineer. During the early construction of the canal, fixed plate girder spans were provided to carry these railroad tracks across the narrow channel then required for the passage of tugs and scows used in the construction of the canal. A con- tract was entered into between the interested railroad companies and the Sanitary District of Chicago, under which the sanitary district was to © Dood ms ooool, oo Se, opooo esq e nooo ollolfalfolfo| joooo FRR A ollolollollol joooo mae ololoaiollol joooe aljolollollo| joooo o| loo Be ea E r-- fal i Ni pier. These piers are each 48 feet wide, and are placed parallel to the center line of the canal. They rest on bed rock, 44 feet below city datum. The piers are not solid; in each pier there are four Cavities, which mate- rially reduce the amount of the required concrete and masonry, _ The contract for the construction of the bridge was entered into on August 10, 1898, but the contractors were greatly delayed in beginning the work because of the delay in diverting the railroad tracks to the tem- potary trestles. Two trestles were constructed on each side of the site of the bridge. Another temporary trestle has been constructed on the east side to accommodate the increased railroad traffic. The temporary tres- tles and cofferdams were constructed by the Sanitary District of Chicago. The cofferdams were built on each side of the site of the bridge, and the area covered by the excavation for the new bridge pumped dry. The Mc- Arthur Brothers Co. of Chicago had charge of the construction of the substructure, together with all excavation necessary therefor, and the ex- cavation for the full width of the channel at the site of the bridge. This work was started about May 23, 1899, and extraordinary efforts were made to hurry the completion of the work, so as to permit the opening of the toe Z "FS, pee bas goo o000aq r goo 80 oo qoo)}|O000 oooo = oooa 0% og oog oooag oooooga "5 oo ooa oooo oogooo00 io oooo oooogoo sa ooog ooo0ogog o OO oooo oooooog EIGHT-TRACK SCHERZER ROLLING LIFT BRIDGE AS IT WILL LOOK WHEN COMPLETED. furnish the railroad companies with an efficient, economical and satisfac- tory permanent movable bridge, the sanitary district to pay for the cost of constructing the same, and to pay to the railroad companies a sum of money, which, capitalized, would produce an income sufficient to maintain the bridge perpetually. STUDYING SOLUTION OF THE PROBLEM. Extensive studies. for the solution of the very difficult problem pre- sented by the large number of railroad tracks to be concentrafed on the proposed bridge were made by the engineers of the Sanitary District of Chicago, under the supervision of Mr. Isham Randolph, chief engineer, and Mr. W. M. Hughes, engineer of bridges. A four-track swing bridge had been constructed across the Harlem river, New York city, for the New York Central Railroad. A four-track bascule bridge of the Scherzer rolling lift bridge type had been constructed across the 'Chicago river and used by the Metropolitan West Side Elevated Railroad for a number of years. No eight-track movable bridge had ever been constructed. A swing bridge wide enough to accommodate the eight railroad tracks was objectionable to the railroad companies interested, because the center pier and protection pier of the bridge would fill a large part of the cross section of the existing channel, and the bridge, when open, would only leave two narrow channels for the passage of vessels, thereby greatly re- tarding their passage and delaying the very heavy railroad traffic. As all the tracks would be concentrated on one structure were the swing bridge in any manner disabled, especially in the moving mechanism, it wou!d 'have to be kept open to accommodate navigation until the necessary re- pairs could be completed, and the entire business of the railroad compa- nies at this point would be "'tied up." It was decided by the sanitary district to invite, by extensive adver- tisements, competitive designs and bids thereon, for the construction of a movable bridge to best fulfill the requirements of the situation. In re- sponse to these advertisements plans were received by the sanitary dis- trict from Mr. C. L. Strobel; Mr. Onward Bates, represented by the Edge Moor Bridge Works; Mr. M. G. Schinke, represented by the Milwaukee Bridge & Iron Works; Mr. J. A. L. Waddell, represented by the King Bridge Co.; Messrs. 'Wilmann and Franzen; Mr. William H. Breithaupt and the Scherzer Rolling Lift Bridge Co. The designs and plans of the Scherzer Rolling Life Bridge Co. were selected by the sanitary district, and approved by the railroad companies interested, and contracts were entered into between the Sanitary District of Chicago and the Scherzer Rolling Lift Bridge Co. for the construction of the substructure and super- structure of this bridge, as a fixed structure. A contract was also made under which the Scherzer Rolling Lift Bridge Co. were to act as super- vising engineers over the construction of the fixed bridge and also the movable bridge when contracts are let for the construction of these addi- tional parts of the bridge. Mr. Ralph Modjeski, member American So- ciety Civil Engineers, was retained as consulting engineer by the railroad companies interested. GENERAL DESORIPTION--THE SUBSTRUOTURKE. The bridge crosses the channel at an angle of 68 degrees 21 minutes 40 seconds. It provides a clear waterway for navigation of 120 feet be- tween the piers, at right angles to the center line of the canal. On each side of the waterway provided for navigation is placed a main supporting canal early in January, 1900. The substructure work was carried on both day aud night and was completed about Jan. 5, 1900. The main piers are composed of Portland cement concrete, capped by four 2-foot courses of Bedford stone. The abutments are composed of Portland cement concrete, faced and capped with Bedford stone. The Portland cement concrete was mixed by machinery, and composed of one part of cement, three parts of sand and six parts of broken stone, depos- ited in layers not exceeding 6 inches in thickness and thoroughly tamped and rammed. PARTICULARS OF SUPERSTRUCTURE. The superstructure of the fixed bridge will be built by the A. & P. Roberts Co. of Philadelphia. The superstructure was designed according to the general specifications of the Scherzer Rolling Lift Bridge Co., in SUBSTRUCTURE OF THE KIGHT-TRAOK BRIDGE IN APRIL, 1900. conformity with the specifications for railroad bridges of the Pennsylva- nia lines west of Pittsburg, dated April, 1897, the loading being 5,000 pounds per lineal foot of single track, with a concentrated load of 50,000 pounds at any one point of the track. hit The bridge consists of four independent double track Scherzer rolling ift bridges, placed side by side, with a clearance of 6 inches between the adjacent trusses. The spans may be operated either jointly or singly, as desired, by two Operators, one on each side of the canal. When the