Lake Street Bridges

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LAKE STREET BRIDGE #2

Chicago Tribune, April 13, 1859

To the Mayor and Aldermen of the City of Chicago in common council assembled:

Your committee on Harbor and Bridges, to whom was referred the several bids, for building bridge across the Chicago River at Lake street, having had the same under advisement, beg leave to report that we have carefully examined all the proposals for said bridge at Lake street, and are satisfied that the bid of Newton Chapin, of thirteen thousand four hundred and sixty-five dollars (less one hundred and seventy-five dollars for old bridge), is not only the lowest bid for the whole work complete, but in qll probability secure the completion of the same at a lower figure than to divide the work into separate contracts, and by so doing leave open an opportunity for extra charges, which on the final footing up, generally overrun all previous expectation.

Chicago Tribune, July 2, 1859

Passengers passed over the new Lake street Bridge yesterday. The structure opens very readily, and seems to give general satisfaction. The work has been quickly and trust, well done.

Chicago Illustrated May 1866
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We give in this view a section of the South branch of the Chicago river, lying between Randolph and Lake street bridges. It is generally more crowded with vessels of all kinds than now presented. The bridge is just south of the junction of the North and South branches. It is not crossed by any of the lines of street cars, and as Lake street, on the east from the lake, and west to Halsted street is graded, and is paved with Nicholson blocks, it is the favorite crossing to and from the west side of the river for equestrians and for vehicles of all kinds. The bridge is comparatively new; it is wooden, turns on a central pivot, and is substantially built.

These several views of the river will be seen through this entire work, and thus the reader will be able to trace the river from the mouth to the fork, and then the two branches in all their extent, North and South. In this way, the volume will embrace all the bridges, and every point in the river having the least public interest, or necessary to give a view of our immense extent of wharfage and shipping facilities.

James W. Sheehan
May 1866

LAKE STREET BRIDGE #3

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Chicago Tribune, October 25, 1885

LAKE STREET BRIDGE
Progress Making in Removing Old Structure.
The work of removing the old Lake street bridge (#3) is now almost completed so far as the bridge proper is concerned. All that remains is about a quarter of the protection, and about 250 of the central piles which formerly supported the turntable. These piles are about forty-five feet long, and the work of removing them is necessarily slow and tedious, only one being drawn out at a time. A pile-driving machine is used to drive a circular-saw which is attached at the end of a long shaft, which cuts off the piles about fourteen feet below the city datum, or about seventeen feet below water. These sawed off pieces are hauled out by another pile-driver and placed on a scow preparatory to being taken away. The piles remaining in the water will serve as the foundation for the caisson of the new bridge. The bottom is made of 12×12 inch timber, and upon this ground the concrete will will be built. The caisson is expected to be placed in position Monday. About fifty feet of the West Side approach, including one stone abutment, have been removed, and five new piles driven in the water-front as a guard. The east approach has not yet been touched. Inspector E. E. Napier, who looks after the city’s interests, stated that he did not think the work would be completed within the specified four months, but did not think it would be exceeded by more than one month. He thought all possible dispatch was being made, the men working twelve hours every day in the week including Sunday. There were yesterday about twenty-five men at work upon the pile-driving machines.

LAKE STREET BRIDGE #4

Chicago Tribune, June 13, 1886

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The new Lake street bridge is a beautiful structure, and, although similar in construction to the Rush street bridge (#4) that was completed two years ago, it has improvements over the latter in several points. The superstructure is of wrought iron throughout and is 220 feet long, having two street car tracks, two roadways each twenty-one feet wide, and two sidewalks each eight and one-half feet wide, making a total width of fifty-nine feet. It is twenty-eight feet high in the center and at each end. The bridge is supported on a drum at eighteen points, the drum being forty-eight feet in diameter. It is turned on eighty wheels, each eighteen inches in diameter and eight-inch thread, on steel tracks. This part of the machinery turns the enormous weightof about 700 tons. The superstructure work was done by Fitz-Simons & Connell—the same firm who did the Rush street bridge—and is one of the most difficult and satisfactory pieces of structure work done in Cook County. When it is considered that all foundations here must be artificial, as it is impossible to reach a rock stratification, the work of laying piers to support a 700-ton bridge is not an easy task for even such skilled engineers as are employed by this firm.

The work was begun Oct. 5, 1885, and continued under many outside difficulties, such as keeping river and street traffic open and removing the abutments of the old bridge. The foundations of the centre pier are made by driving 300 piles, each forty-five feet in length, down seventeen feet below the water-level within a radius of sixty feet. These piles are then cut off by ingenious machines perfected by this firm, consisting of a circular saw carried by an upright arbor, counterbalanced so that, notwithstanding the oscillation of the boat, each pile was cut off at a point indicated by the cross-line in an engineer’s level, a point on the saw-arbor being brought to coincide with the instrument at the commencement of each cut. In this manner a perfectly level surface seventeen feet below the water line was obtained, upon which a platform of oak timbers two feet in thickness and sixty feet in diameter finally rests. A caisson was then built upon this platform to exclude the water and to form retaining walls for the mass of which the pier is composed. This is concrete, thoroughly mixed by machinery and carefully rammed into place, forming an immense monolith equal to anything that can be constructed of a conglomerate character. The estimated weight of this pier is 4,000 tons; not the slightest sinking or uneven settlement under the load can be detected by the finest instruments.

The end piers are in like manner founded upon piles cut off at the same level with timber platforms, are built of concrete similar to the centre pier. The foundations of this bridge are a fine piece of engineering work, and also reflect credit upon the contractors, who have completed most thoroughly and satisfactorily a public contract. The machinery consists of two boilers of the locomotive type, double engines for swinging, double engines for wedging up the ends when closed, and an engine to run the dynamo, together with necessary pumps and water tanks to take water from the river and city mains. The engines are uniform in style, with upright frames and entirely open on one side. All shafting is of steel and gearing of bronze. The machinery comes from Vulcan Iron-Works of this city, which also furnished the swinging engines for Rush Street bridge and the Chicago & Evanston Railroad bridge, are also making those for the new Chicago & Great Western Railroad bridge.

Lake street bridge is handsomely lighted by seven arc electric lights furnished by the Van Depoele Electric Manufacturing Company. This light cannot be excelled for brilliancy, and is a general favorite as an outside light. The city has tried several kinds of arc lights, and have selected this as the best in use.

Engineering News-Record, 1886, Vol. 15

Lake Street Bridge. The iron swing bridge over the Chicago river at Lake street, Chicago, is completed, but the viaduct and approaches are not yet finished The bridge is 220 feet long. 23 feet high in center, and 20 feet high at ends; it has a width of 60 feet, composed of two 21-feet roadways and two 7-feet sidewalks: the floor will carry a weight of 125 pounds per square foot: The drum on which the bridge turns is 48 feet in diameter, and rests on 74 solid iron wheel-, 18 inches diameter and 8 inches wide on face: the gearing is of phosphor bronze. The bridge will be turned by a steam engine with a pair of 8-in. by 12 in. cylinders, and a 7-inch cylinder engine will be used to drive the electric light plant: the engine-house is on top of the structure. The bridge will cost $145,000, divided equally between the city and the West Division Street R. R. Co.: the viaduct will cost $55,000. paid by the railroads interested: total cost, $200,000. Work was commenced in November last.

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LAKE STREET BRIDGE #5

Engineering News, November 4, 1915

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SYNOPSIS—The new Lake St. bridge over the Chicago River will be a double-leaf bascule of 215 ft. span, carrying an elevated railway on the upper deck and a roadway (with car tracks) and side walks on the lower deck. The bridge itself is of interest, and its construction involved specially interesting and difficult problems, since the elevated railway had to be kept in operation over the old swing bridge during the construction of the new bascule bridge.

The Lake St. bridge, on one of the main thoroughfares entering the business district of Chicago, crosses the south branch of the Chicago River just south of the turning basin at the junction of the north and south branches with the main stem of the river. The present bridge has a three-truss swing span, which was built as a single deck structure in 1888 and strengthened in 1893 to carry an upper deck for the Chicago & Oak Park Elevated R.R.

The river channel is 235 ft. wide at Lake St., but the swing bridge interferes seriously with navigation, giving a clear channel width of only 65 ft. on each side of the center pier. The United States War Department ordered the removal of the bridge several years ago, as an obstruction to navigation, but owing to the desirability of avoiding interruption to elevated-railway traffic and the difficulty of arranging for a temporary means of crossing the river, the city authorities procured an extension of time. Before this was done, however, studies were made for an incline from the elevated structure to the street level just west of the river, the trains crossing the river on the Washington St. bridge (two blocks south) and then rising again to the elevated structure in North Market St. This scheme was abandoned, as it would be too dangerous to run five-car trains on the streets in the busy district.

It was decided therefore to construct the new bridge in such a manner that the elevated traffic could be continued over the old swing bridge, except occasionally for a few hours at a time and when the inconvenience to passengers would be at a minimum. Plans for this new bridge were well-advanced by the end of 1912 and provided for three railway tracks, but later the elevated railway company decided to have only two tracks. The changed plans and specifications were finished in June, and bids were opened on Sept. 18, 1913, but the lowest bid exceeded the estimate for the bridge.

Owners of patents for movable bridges then claimed that a more economical bridge could be built on their plans, and a commission of three engineers was selected in accordance with a resolution passed by the Finance Committee of the City Council’ on Oct. 24, 1913. This
commission consisted of John Ericson, City Engineer; J. E. Greiner, Consulting Engineer, of Baltimore, Md., representing the elevated railway, and W. H. Finley, Chief Engineer of the Chicago & Northwestern Ry. Mr. Finley was selected by the other two members. Competitive plans and estimates were received by this commission for various types of bridges which could be erected without materially interfering with the operation of the existing bridge. These included a double-deck lift bridge and double-deck single-and-double-leaf trunnion bascule
bridges.

The lift-bridge design placed the towers straddling the elevated structure on the approaches. The lift span could be erected in place in the open position or erected at the north side of the turning basin and floated into place on scows. The bascule bridges could be erected in the open position without interfering with the swing bridge, by omitting part of the floor system, thus allowing the trains to pass between the trusses. When the bridge was ready to be lowered, traffic would be interrupted long enough to complete the floor system and remove the swing bridge.

The commission recommended a vertical-lift design submitted by the city. On considerations of public policy, however, the City Council recommended the double-leaf bascule bridge (according to the city’s plans somewhat revised). Accordingly, the various bids were rejected and
the plans and specifications were revised.

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Fig. 1.

Description of the New Bridge
The new bridge (Fig. 1) will have the following main dimensions: 245 ft. c. to c. of trunnions, 217 ft. c. to c. of bearings; clear width of channel, 195 ft. ; clear distance between masonry piers, 209 ft. 3 in. ; length of counterweight arms, 39 ft. ; truss spacing, 42 ft. c. to c. ; width’ over side walks, 70 ft.; depth of trusses at center, 30 ft.; clear headway over the water, 16 ft. 6 in. for a width of 164 ft. The lower deck, 70 ft. wide, has two 16-ft. walks and a clear roadway of 38 ft. with two lines of street car tracks. The upper deck carries the double-track elevated railway.

This type of bridge was chosen mainly because it could be treated architecturally better than any other type, being symmetrical and having the counterweight under the roadway. The counterweight lowers into a tailpit between the river pier and anchor pier. The operating machinery will be placed under the sidewalks at each corner of the bridge and will be inclosed with concrete walls treated with suitable ornamentation.

The new bridge is located symmetrically about the center of the present swing bridge and is being erected in the open position. During the construction, traffic on the lower (street) deck of the present bridge is discontinued, street cars being diverted to the Randolph St. bridge, one block south.The new substructure consists of a tailpit and an abutment on each side of the river. This will be described in a separate article.

Temporary Supports for Elevated Approaches
After the street-railway company had removed trolley wires, rails, etc., from the swing span and approaches, the sidewalk brackets of the swing span were cut off with the acetylene torch, in order to obtain a wider channel with the bridge opened. The operator’s house, situated over the sidewalks, had to be removed and a new one erected on the roadway of the lower deck. This involved no great amount of work as the bridge is operated electrically. The old protection (which was almost all broken away) was removed, and a new protection constructed to suit the new channel lines on each side of the center pier.

The approach spans on the street level were removed, the steel being cut with the acetylene torch and removed from] the site by scows. Excavation was then started on both approaches back of the old abutment. The center part of the old east abutment was removed first. The ends of the abutment were left in place temporarily, as the columns of the elevated structure rested on them.

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FIG. 2. TEMPORARY SUPPORTS FOR END OF THE EAST APPROACH OF ELEVATED RAILWAY

Timber bents were then erected under the elevated structure, as shown in Fig. 2, which illustrates the east approach. Bents were erected just back of the river pier and in front and back of the abutment. These bents consisted of 12xl2-in. posts directly under each girder of the elevated structure, which rested on piles capped just above the water-level surface. Old foundation piles un covered during the excavation were used for supporting the bents, if suitably located. These were first tested by placing jacks between the bottom of the 12xl2-in. posts and the piles. The piles were observed for settlement under this load, and if none occurred during an interval of about a day they were considered suitable for use.

The number of these old piles was due to the fact that, previous to the construction of the present bridge (1888), there had been at least two bridges, both supported on pile foundations. These piles were of a kind not common today, ranging from 18 to 24 in. in diameter at the butt. They were in a remarkable state of preservation, being practically as good as when driven, which must have been nearly 50 years ago. The bents were capped with 12×12- in. timbers, braced with 2xl2-in. sway bracing. A batter pile was used in the bent at the river pier.

The columns of the elevated structure were supported on girders spanning the space for the tailpit. These girders rested on groups of piles driven in line with the first and second bents of the elevated structure east of the swing span, as shown in Fig. 3. Each girder consisted of two separate plate girders connected by cross-bracing. Each girder had a 96×1/4-in. web plate and four angles 6x6x-7/16 in.; it was stiffened at points of local load and about every 4½ ft. at other parts, by 5x3x3/8-in. stiffener angles. Webs were spliced for moment. The overall length of these girders was 78 ft. The double girder for the rear bent was placed first, the abutments having been entirely removed. The girders supporting the front bent and the end of the swing were placed when it was convenient to close elevated traffic for a few hours, as the masonry of the old river pier had to be removed when the swing bridge was open and the bridge could not be closed again for traffic until a new end bearing could be provided.

This work was done July 3, 1914, traffic being closed on the elevated structure from 9 a.m. to 4 p.m. Passengers used the Canal St. station, two blocks west of the river. As soon as the girders were in place, the temporary timber supports under the elevated structure (Fig.2) were removed.

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FIG. 3. METHODS OP SUPPORTING THE ELEVATED-RAILWAY APPROACH AT TWO STAGES OF THE WORK

After the construction of the tailpit, temporary timber bents were erected to support the elevated structure on the east side (Fig. 2). These rested on timbers laid on the pit floor. When these were ready for the elevated structure the box girders were transferred to similar positions on the west side. The girder under the first bent was transferred Dec. 29, when traffic was shut off on the elevated for 7½ hr. The temporary timber bents were removed as soon as the girders were in place.

The contractor for the superstructure started on Jan. 13, 1915, to erect falsework for the erection derrick on the east side and had this practically finished on Jan. 30. This falsework, or tower, required careful study, as the position of supports was not only limited by vertical headroom over the elevated structure, but by lateral clearances of a car swinging around the curve into the North Market St. branch (Fig. 1). This derrick is shown in Fig. 4.

The structural steel began to arrive at the site on Feb. 8. It was delivered on flat cars and unloaded at the railway yard on the north side of the turning basin (just north of the bridge site) where it was stored until needed. Thence it was delivered on scows.

The contractor started as soon as possible to erect the steel of the fixed parts upon which the movable structure rests. These parts consist of two carrying trusses, 48 ft. c. to c, parallel with and just outside the movable trusses.

The machinery girders are 7 ft. back from and parallel with the carrying trusses. The carrying trusses and machinery girders span from river pier to anchor pier, a distance of 53 ft.

The carrying trusses are the supports for the cross-girders (Fig. 5). They also carry the gear trains which are located opposite the racks in the rear arm truss members. The cross-girders are located 14 ft. back of the river pier; they carry the entire dead-load of the bridge, and have a span of 48 ft. c. to c. of carrying trusses, spanning the entire distance across the tailpits.

At the time the superstructure contractor began work on the east side the elevated structure was supported on timber bents resting on the floor of the pit (as shown in Fig. 2). These bents were so placed that the contractor could erect the carrying trusses and machinery girders without difficulty. These trusses and girders, being outside of the elevated structure, could be handled by the derrick. The erection of the cross-girder, on account of its weight and its position under the elevated structure, was more difficult.

Additional falsework was built to place the cross-girder. This consisted of A-frames resting on the floor of the tailpit. On the frames were placed two 15-in. channels, forming a runway for sliding the girder across the pit. The girder was lowered from the A-frame to its final position on the carrying trusses by means of jacks.

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PIG. 4. STIFF-LEG DERRICK OVER THE ELEVATED RAILWAY APPROACH

The fixed portion of the new elevated structure over the tailpits will be supported on new columns, which rest on the carrying trusses about 7 ft. from the center line of the anchor pier (Fig. 1). These columns are in the same place as the old floor-beams, but are located a greater distance out from center line of structure. The old floor beam was therefore lengthened in order to provide a connection for the new columns.

The steel columns in the bent at the river pier were also moved out, lengthened by splicing on portions of the old columns, removed from the bent near the anchor pier and carried down to a bearing on the carrying truss, the floor-beam of the elevated structure being lengthened as before.

The temporary timber bents under the elevated structure were then removed and the elevated structure carried on the new steel. The erection of the tail end of the bridge was then started, and part of the trusses had been assembled at- the time a strike of the structural iron workers was called at the end of April.

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FIG. 5. ONE OF THE TRUSSES OVER THE TAILPIT

During the week ending Apr. 17, 1915, the contractor began erecting his derrick on the west side. This was not placed over the elevated structure but in the tailpit, the mast resting on the floor and the stiff-legs being anchored to the sidewalls of the pit. A strike stopped the work in April and from that time until work was resumed on July 8, 1915, the elevated structure on the west side rested on two temporary cross-girders, and on the east side on the new carrying trusses with the permanent columns in place for the bent near the anchor pier and temporary bent in place near the river pier.

The leaves will be erected in the open position, a portion of the floor system being omitted to permit of passage of trains. When the leaves are lowered the two spans of the elevated structure over the pits will be removed and the floor system on the upper deck completed.

ENGINEERS AND CONTRACTORS
The work is under the Department of Public Works, the head of which is W. R. Moorhouse, Commissioner of Public Works. The City Engineer, John Ericson, is head of the Bureau of Engineering, and Thomas G. Pihlfeldt is Engineer of Bridges and Harbor. The final plans were
prepared in the Designing Section, under the immediate direction of A. von Babo, Engineer of Bridge Design, and the writer. The construction is supervised by the Construction-by-Contract Section, under Clarence S. Rowe, Assistant Engineer, and the resident engineer on the work is William A. Mulcahy, Assistant Engineer.

The contract for the substructure was awarded to the FitzSimons & Connell Dredge and Dock Co., of Chicago, on Mar. 14, 1914. The contract for the erection of the superstructure was let Mar. 18, 1914, to the Ketler-Elliott Erection Co., of Chicago. The contract for the steel was let to the American Bridge Co.

Engineering News, November 11, 1915

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SYNOPSIS—Foundation work on one of the heaviest drawbridges ever built, a double-deck double-leaf bascule. Anchor piers in open wells. Steel sheet-pile coffer-dam for main piers.

The double-deck double-leaf bascule bridge now being built across the river at Lake St., Chicago, was described by the writer in Engineering News, Nov. 4, 1915. The substructure consists of a tailpit and an abutment at each side of the river. The tailpit is a concrete box resting iu four cylinder piers carried down to solid rock, the walls of the pit acting as beams. The piers are spaced 34 ft. laterally so as to provide for a possible future double-track subway on Lake St. North of the tailpit are foundation walls for the operators’ houses. These rest on pile foundations. The abutments are supported on groups of piles driven on each side of the street, and act as beams, spanning the space that would be occupied by a future subway.

The depth of excavation for the tailpit necessitated special care to protect adjacent buildings and the elevated railway structure. Work did not proceed simultaneously on both sides of the river due to the fact that the scows for delivering material and removing excavated material effectually blocked the channel adjacent to the pier under construction, and it was necessary that one draw be left clear for the passage of the river traffic. Work was started Mar. 30, 1914, by the Fitzsinioiis & Connell Co., contractors for the subway.

Genehal Method of Working
The general method of conducting the work on the east side was as follows : Excavation was carried down to a general elevation of about 3 ft. above datum, giving about 38 to 40 ft. clear headroom under the elevated structure. A land piledriver was rigged up to clear the elevated structure, and all piles were driven. It was occasionally necessary to dig a hole for the point of the pile, in order to get the butt in under the hammer. By doing this piles about 25 ft. long could be driven.

As the four-story brick building on the north side apparently rested on floating foundation, steel sheeting was driven to protect it. The contractor braced the structure by tying the outside walls together by means of rods connected to timbers on the outside faces. During the excavation a reinforced-concrete wall inclosing the sub-sidewalk basement of the building on the south side of the street had to be removed. This was broken up by light charges of dynamite without any accident. The foundation piles under the operator’s house on the north side of the street were also driven.

The coffer-dam was next constructed. This consisted of a double row of Lackawanna steel sheet piling for the portion in the river and a single row of steel or wood piling for the portion on land. Where channel clearances permitted, two rows of sheeting were driven about 7 ft. apart; but the rows for the front wall of the coffer-damb were 3 to 5 ft. apart. The two rows were tied together with rods and the space between filled and puddled with clay dredged from the river. The sewer on the north side was diverted through a trough outside of the coffer-dam.

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FIG. 1. CONCRETING PLANT AND TOWER
The materials are delivered on scows. The view shows the west end of the old swingbiidge, with the columns of the elevated railway approach carried temporarily on a box girder spanning the tail-pit of the now bridge

A derrick was then erected on the north side to handle the excavation from the coffer-dam. Its mast was carried by a group of piles near the north support of the rear girders supporting the elevated structure, and the stifflegs were anchored to the coffer-dam. The derrick hoist was erected on a pile foundation outside the coffer-dam.

As the excavation for the tailpit proceeded the coffer dam was braced by four horizontal tiers of 12xl2-in. cross-bracing. One tier of bracing was placed about 18 in. above datum; the others were 6″, 13 and 19 ft. below datum. The bracing was supported by means of old piles and partly by suspension rods from the temporary box girders carrying the columns of the elevated approach. The material was loaded into buckets, which were lifted out by the derrick and dumped into a scow alongside the coffer-dam. The excavation was rushed day and night, with men working in three shifts.

When the excavation for the tailpit was practically completed, that for the subpier wells was started. The 8-ft. anchor-pier wells were started first and were dug as open wells, being excavated about 5 ft. at a time and then lined with 3×6-in. tongned-and-grooved maple lagging in lengths of 4 ft. 8 hi., each length being held in place with two or three rings of lx-t-in. steel. These rings were made in two sections, with a lug bent on the end of each for bolting together. The wells were excavated in this manner to solid limestone rock, the bottom of the well extending 1 ft. into the rock to insure a good bearing.

The material encountered in these wells was blue clay from 20 ft. (where the well started) to about 60 ft. below datum. This ranged from soft clay at the top to very stiff clay at the bottom. From 60 to 75 ft. below datum the material was a mixture of tough blue clay with gravel and boulders ; from 75 to 90 ft., a mixture of soft clay and sand; from 95 to 105 ft., gravel and sand. At 105 ft. a water-bearing stratum of sand was encountered, extending to rock at 107 ft. below datum. The quantity of the water was not enough to necessitate an air-lock, the water being removed by a centrifugal pump ; but progress was much retarded. It took from Aug. 14 to 28 to excavate these two wells.

CONCRETING PLANT ERECTED
While these wells were being put down the concreting plant was erected. The mixer plant was placed alongside the dock of the building at the south side of the street, on a pile foundation. In front of the mixer was erected a tower, similar to that shown in Fig. 1 (which is the tower at south side of west coffer-dam), for elevating the concrete to metal chutes that distributed the concrete to the forms. Handling concrete in barrows was unnecessary except for minor parte of the work beyond the reach of the chutes. These chutes were supported from the elevated structure by means of tackle and blocks, and were easily adjusted. Material was delivered to the river plant on scows, being wheeled from the scows in barrows to the mixer hopper.

When the excavation of the wells was completed the concrete filling was started. The concrete was mixed wet and dropped through pipes into the well. The work was inspected at regular intervals during the pouring of the concrete to see that it was being properly filled around the reinforcement and that too much water was not accumulating on top. As the concreting proceeded, the lagging and rings were removed, except for the bottom 15 to 20 ft. of the well. The concreting of the anchor-pier wells was completed on Aug. 31.

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Fig. 2.

EXCAVATION STARTED
The excavation for the 12-ft. wells for the river pier was started Aug. 31, as soon as the anchor-pier wells were concreted, and proceeded uninterruptedly until Sept. 10, the wells having been carried down to 95.5 ft. below datum. Work was then suspended temporarily, as the contractor encountered some difficulty in getting proper sand for concrete, and decided not to finish the well to rock until the proper materials were available. After a short delay excavation was again started, and rock was reached Sept. 15. Fig. 2 shows the rings and lagging in place, the line of electric lights in the well to illuminate it, and the pump for keeping the well dry.

Concreting was started immediately after the excavation was completed and concrete brought up to 93 ft. below datum, when work was again suspended due to the rejection of the sand by the inspector. This was lake sand from the eastern shore of Lake Michigan, and was finer than that called for in the specifications. After a delay of about a day suitable sand was procured and delivered in cars to a dock a short distance from the bridge, from which place it was brought to the site on scows. The work was then started again, the wells being concreted to the top. The lagging in these wells was left in place from\ the bottom up to 90.4 and 91.6 ft. below datum for the north and south wells respectively. The wells were completed on Sept. 21.

A bad leak in the south wall of the coffer-dam was noticed on Sept. 14; and it required considerable pumping to keep the water low enough to continue to work. The water entered at the connection of the double row of steel sheeting with the dock, and then through the wood sheeting which forms the part of the coffer-dam on the land. Considerable material was dumped in the river along the dock where the leak started, and finally stopped the leak, on Sept. 24.

Forms for the tailpit proper were prepared at the time the piers were being constructed, and as soon as these piers were finished (Sept. 29) the concreting of the tail-pit was started. The floor of the pit, a 5-ft. slab, 62×64 ft., was finished Oct. 3. The construction of the floor requires all piles and other supports for the bracing of the coffer-dam to be cut off above the top of floors, in order to avoid holes in the slab. The bracing is made to hold itself by trussing. The side walls and the river and anchor piers (forming the end walls) of the pit were then brought up to an elevation 1 ft. below datum, and were completed on Oct. 22. The overhanging parts of the side walls were temporarily omitted, so as to clear the piles under the girders supporting the elevated structure. The outside walls for the operator’s house were also brought up to the bottom of the cross walls joining them to the tailpit.

In order to make the pits watertight, a 6-in. layer of cement mortar, made of 1 part portland cement and 2 parts fine aggregate, was placed in the floors and on the outside faces of the walls, up to above datum. The mortar facing on the walls was applied by means of a mortar board, used as a form, which was placed inside the wall forms at the proper distance to give the required thickness of facing, the board being raised as the facing course was carried up with the concrete. The mortar was made in a mechanical mixer, and was delivered in chutes to a box, from which it was carried to the forms in coal scuttles or pails. The concrete was delivered by chutes
directly into the forms. From the time the coffer-dam was first pumped out until the concreting was finished the work was carried on continuously, the men working in three shifts, except on Sunday (midnight to midnight), when no work was done.

EAST AND WEST ABUTMENTS
At this stage of the work excavation was started for the west abutment, and the excavation for the east abutment was finished and the forms were constructed. After the concrete in the tailpit had set the girders supporting the elevated structure were shored up on the masonry, as described in the previous article (and shown at A in section CC of Fig. 3). The piles were cut off so that the overhanging walls and to]) of the walls under the operator’s house could be finished. This work was finished on Nov. 12. The concreting of the east abutment was started Nov. 13 and finished Nov. 25. The concrete plant was then moved to the dock on the west side of the river (Fig. 1). Foundation piles for the west abutment were then driven in the same manner and under the same conditions as those for the east abutment.

The forms for the east tailpit being removed, the space between the coffer-dam and tailpit was filled with water. Under full head of water the pit showed a small leak in the north wall at an elevation of about 1 ft. below datum at the junction of the side wall and overhang. This stopped as soon as silt filtered into the crack, and the pit was then accepted by the city. The coffer-dam was then removed and the channel dredged of all excess material, such as puddling and excavation.

At this same time the west coffer-dam was being constructed and foundation piles for the operator’s house were being driven. Excavation was also made for the new portion of the 5-ft. sewer on the west side, and the sewer constructed up to the abutment, where a temporary bulkhead was placed and an outfall constructed= under a freight house into the river.

WORK ON THE WEST PIER
Pumping out of the west coffer-dam started Jan. 11, and as the excavation proceeded the dam was braced as described for the east dam. Excavation for the foundation wells under the west anchor pier was started Jan. 23 and for the river wells Jan. 25. On Jan. 31, due to a rise in the river, the water overflowed the puddle wall of the coffer-dam and partly filled the wells, which were then pumped out. Excavation in the anchor-pier wells was done after the river-pier wells were finished. Water was encountered in the wells at 101 ft. The excavation for the river-pier wells was completed Feb. 7, having been carried to a depth of 109 ft. below datum and 1 ft. into solid rock. Concreting was finished in these wells on Feb. 12,, the lagging below 94 ft. and 87.25 ft. below datum being left in place.

The excavation for the north anchor-pier well was completed on Feb. 10 and the south well Feb. 11. They were immediately concreted, work being finished Feb. 15. The lagging was left in place below 82 ft. and 80 ft. below datum for these walls. The tailpit forms were then constructed and concreting commenced Feb. 16. The floor was finished Feb. 20, and by Mar. 6′ the walls were brought up to about 1 ft. below datum.

On Mar. 5 a leak developed in the south wall of the coffer-dam adjacent to the building, and this flooded the coffer-dam to river level. This break was repaired and the dam pumped out again.

During the time that excavation for the operator’s houses was proceeding the forms for the west abutment were erected and the wall was concreted. This work was started Mar. 12 and finished Mar. 19. The box-girder supports of the elevated structure were then blocked up on the masonry and the overhanging walls and operator’s house walls concreted, finishing Mar. 29. As a precaution against freezing the finished work was covered with tarpaulins.

The test of the west pit was made Mar. 31, and the coffer-dam was removed Apr. 2. The plant was then removed, docks were repaired where they had been cut for the coffer-dam, backfilling was placed, the permanent pier protection constructed, and the site cleaned up. The substructure contract was completed Apr. 28, or about 13 months after starting work. The girders supporting the elevated structure on the west side were left in place.

Engineering News, December 30, 1915

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The new double-deck bascule bridge and the old center pier double-deck swingbridge over the Chicago River at Lake St are shown in the accompanying view, which rep resents the condition of work a month ago.

The old swingbridge is kept in service to carry the elevated-railway trains, but the roadway is closed to traffic. The bascule bridge was erected with its leaves in the raised position, the’ deck and bracing of one panel in each leaf being omitted to allow trains to pass through until the bridge is ready i’or operation. Then traffic will be stopped for a short time while the old bridge is removed and the floor system of the new structure is completed.

The bridge is of the trunnion bascule type, with a span of 215 ft. c. to c. of trunnions, giving a width of 209 ft. between the piers for a channel 195 ft. wide in the clear.

The old bridge gives two channels only 65 ft. wide. The trusses are spaced 42 ft. c. to c. and are 30 ft. deep at the center. On the lower deck are a 38-ft. roadway (with car tracks) and two outside 16-ft. walks; on the upper deck is a double-track railway between the trusses.

The bridge was designed and built under the direction of John Ericson, City Engineer, and Thomas G. Pihlfeldt, Engineer of Bridges and Harbor. The contractors were the Fitzsimons & Connell Dredge and Dock Co. for the substructure, the American Bridge Co. for the steelwork, and the. Ketler-Elliott Erection Co. for the erection. The steel was stored on the dock shown beyond the center pier and was floated into place on lighters.

The bridge and its construction were described fully in Engineering News, Nov. 4 and 11, 1915.

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Old and New Drawbridges Over the Chicago River at Lake Street.

MUNICIPAL JOURNAL, VOL. XL, No. 11, March 16, 1916

The first double-deck bascule bridge ever constructed has been practically completed and put into partial service in Chicago. It replaces the old Lake Street drawbridge, which was condemned by the Secretary of War because it obstructed navigation in the Chicago River. The lower deck was closed to traffic (street cars, vehicles and pedestrians) when work was commenced on the substructure of the new bridge in March, 1914. Traffic on the upper deck, which is used by the trains of the Chicago & Oak Park Elevated Railroad, has not been interrupted, however, throughout the construction of the new bridge, except for the work from February 27 to March 4, during which the old bridge was dismantled to permit the two leaves of the new bridge to be swung down, ties and rails laid on the upper deck and other details attended to.

When it was decided to erect a new bridge at Lake Street a clear unobstructed span of 200 feet had to be provided, and a lift bridge with hoisting towers at each end as first proposed as the simplest means of taking care of a double-deck structure. The rather sad experience of the city with this type of bridge at South Halsted street caused further study of the problem. After prolonged consideration the design chosen was declared to be entirely feasible, even though never attempted for a double deck bridge heretofore. It is a two-leaf trunion bascule bridge. The total length of the steel work between extreme abutments is 355 feet.; the distance from center to center of trunnions is 245 ft. 3 in.; the width of the steel work over all is 70 ft. The lower deck has a 38 ft. roadway and two 14 ft. sidewalks. Sub-piers for the bridge are of concrete resting on solid rock about 110 ft. below river surface. About 7,200 cubic yards of concrete was used for the sub-piers, main piers and abutments. The sub-piers are so spaced as to permit of the possible future construction of a passenger subway.

The erection of the bridge has taken nearly two years. Delays were caused by the necessity for maintaining elevated train service· uninterrupted, by a two-months’ strike of bridge and structural iron workers, and by difficulty in obtaining flawless forgings for the large shafts. Each leaf was erected in upright position over the elevated= tracks, to accommodate which the floor beams and stringers in two panels of each leaf were omitted until the bridge was lowered in place on February 28. That date the old drawbridge was swung open and its ends blocked up and then its entire center section cut away with oxy-acetylene blow pipes. The remainder of the old bridge was dismantled at leisure before the close of the week and entirely removed except the center pier. At the same time the double-deck viaduct over the tracks of the Chicago, Milwaukee & St. Paul Railway directly west of the bridge, was bodily moved south about four feet to allow erection of the north half of a new and longer viaduct required for increased trackage for the new Union Station now under construction. It was planned to take the old bridge ouf and put the new bridge into commission with an interruption in elevated train traffic of only about 64 hours, but unforeseen difficulties lengthened this to 6 days, 14 hours. During this time, however, passengers from the Chicago and Oak Park trains were able to reach the “Loop’: or main business district, by transferring to trains of the Metropolitan Elevated Railway so that no very serious inconvenience was entailed.

It is expected to have the new Lake Street bridge entirely completed early in May. Its total cost will be about $650,000, of which part is borne by the Chicago & Oak Park Elevated Railroad. The design and construction has been under the general supervision of John Ericson, city engineer, and Thos. G. Pihlfeldt, city bridge engineer; Wm. A. Mulcahy, assistant .engineer of bridge construction, was in local charge: The contractor for the substructure was the Fitzsimons & Connell Dredge & Dock Company; the contractor for the superstructure was the Ketler-Elliott Erection Company.

Chicago Tribune, October 30, 1916

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A new barrier gate guaranteed to stop any automobile at any speed will be tried out at the Lake street bridge, according to a letter which Commissioner of Public Works W. R. Moorhouse has written to The Tribune. The gate is designed to prevent accidents such as the one at the Twelfth street bridge, where an automobile plunged thorough the open draw bridge into the river.

The gate is so constructed, Mr. Moorehouse, says, “that a drunken or careless chauffeur crushing through the first or guard gate will strike a sixteen inch boom and slide it against what is known as friction resistance for such a distance as either stop the machine or, if the speed of the machine is unreasonable, wreck it beyond repair.”

Calls Criticism Unwarranted.
In the course of the letter Mr. Moorhouse declares the public safety commission was incorrect in many of the statements criticising conditions at the bridges. Among the points he makes are these:

The South Halsted street bridge, which was said to have no guards has, as a matter of fact, two powerfully constructed steel gates which disappear when the bridge is closed.

Throop street, Canal street, and Cortland street bridges are all of the bascule type and form an effective barricade against traffic when raised.

The physical characteristics at the approach of the Addison street bridge are such that it is impossible to operate guards.

The Sunnyside avenue bridge, which was also criticized is under the jurisdiction of the sanitary district.

Urges More Care in Driving.
In conclusion Mr. Moorhouse makes an appeal to automobile drivers to pay more attention to signals at bridge crossings instead of trying to “run by the signals and cross a bridge after the signal has been displayed which is now the universal custom.” He points out that the average motorist will obey the whistle of the traffic policeman, where there is little or no danger to life, but will make every effort to disregard bridge signals, though there is imminent danger he will plunge through the draw and drown.

LAKE STREET BRIDGE #2

LAKE STREET BRIDGE #3

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LAKE STREET BRIDGE #5

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