Converting the Aerial Transfer Bridge to the Aerial Lift Bridge

The crew of the Kansas City Bridge Company, who converted the Aerial Transfer Bridge into the Aerial Lift Bridge, including one gentleman seated in the front row, smoking a cigarette, who looks remarkably like actor Sean Penn. (Image: Lake Superior Maritime Collection.)

By August 10, 1929, the aerial bridge had been stripped of its gondola and the girders that suspended it from the bridge’s upper truss. Workers (the entire crew is pictured here) then set about the task of preparing the bridge structure for its most dramatic change: extending it 41 feet higher so that, with the roadway span raised, the bridge allowed a clearance of 135 feet for passing vessels. Workers with the KCBC put up “false work,” wooden scaffolding to bolster the bridge during construction, when its span would be separated from the old north and south towers. They also erected another set of taller towers within the framework of the old bridge; the raised span would rest atop the new towers, which would also carry the massive pulleys and counterweights that allowed the bridge’s deck to raise and lower.

A crowd estimated at five thousand gathered near the bridge on the morning of Saturday, October 19, to watch as workers armed with acetylene torches cut straps and rivets, freeing the bridge’s entire overhead truss—all 410 tons of it. They then began to slowly raise it into its new position, winching it into place by 10:30 a.m. The crowd was never bored. A seaplane pilot flew his plane under the bridge as the span was being raised, and at least one steel worker mugged it up for the crowd, at one point standing on his head atop the bridge’s tallest point, kicking his feet in the air. Even a film crew was on hand to capture the moment.

With the top span in place and the steel work on the new towers complete, the largest unfinished job was the lower span, the roadway that would lift out of the way to allow marine traffic through the canal. Its framework was built in sections between the towers at roughly the height of the old bridge. Workers slung sections of trestle under the overhead truss by cables or cantilevered them from the new towers. By November 7, workers had the first unit in place, reaching toward the middle from the south tower. Work progressed from the north tower a week later. Before the month’s end, workers set the framework’s last piece in place and began permanently fixing it to the new lifting machinery. Not once did construction hamper canal traffic.

The construction proceeded slowly. KCBC had promised an operational bridge by the end of 1929, but it wasn’t until January 6, 1930, that the lower span was lowered into place at street level for the first time, ready for its nine-hundred-ton roadway’s installation. The company asked for and received a contract extension, with the bridge’s final touches now due on March 15. Bridge use, however, started at 8 a.m. on January 12, 1930, the first moment cars traveled over the span, which was limited to one lane as workers paved the other. No one recorded who drove the first automobile across the bridge. The first streetcar over the canal began its journey at 5:28 a.m. on March 12. About a week’s worth of minor details still had to be worked through, and the bridge still needed a coat of paint. Otherwise it was complete. To celebrate the bridge’s opening, the Community Club held a banquet at the Park Point School and a dance at the Park Point Community Clubhouse at Lafayette Square; admission was seventy-

five cents for the food and fifty cents to dance.

Regular Operations Begin

Like its predecessor, the Duluth Aerial Lift Bridge stood as a marvel of engineering, especially considering that the new bridge was built without completely destroying the old. The original bridge’s head span, raised forty-one feet, now provided little more than wind bracing: the new towers carried the moveable road span and massive counterweights. In its new life the head span was adapted to carry electric conduits and gas and water mains across the ship canal. The power to raise and lower the roadway span came from four electric motors, each of ninety-five horsepower, located in the upper level of the two-story operators house positioned above the road span. Any two of the motors could power a lift. The power came from storage batteries located beneath the South Pier approaches, kept charged by city electricity accessed by both a direct line and by tapping into trolley cables that ran along the top of the lift span (two generators stood by for emergencies). The same room housed a gasoline engine that could move the lift span should electricity completely fail. In the operators house’s lower room, operators controlled the bridge and a host of safety devices positioned at various points on the bridge and its approaches—mechanical and electric interlocks, traffic gates, bells, signal lights, pneumatic horns, and both telephone and radio communication—to insure safe movement by land and water. With the engines directly above them, lifting and lowering the bridge was loud work for the operators.

The bridge’s most intriguing engineering aspect was how the lift span and its counterweights worked. The 900-ton span was balanced by two 450-ton concrete weights, one on each end of the bridge. The span and its counterweights were connected by twelve 1 7/8-inch cables that ran over four sheaves—wheels twelve feet in diameter and weighing 14 tons each—one at each top corner of the structure. As the span went up the counterweights came down. The cables, in turn, were so heavy that they too had to be balanced. This was accomplished by attaching chains to each of the two concrete counterweights; they resemble extremely large bicycle chains measuring 81 feet long and weighing approximately 259 pounds per foot. The bridge was so well balanced that when the first paint job was applied—tinted “Essex” green, a dark green similar to forest—the counterweights had to be adjusted to compensate for the weight of the paint. (See the appendix for diagrams of how the bridge works.)

Numerous inspections and test lifts continued until March 29, 1930, when the Corps of Engineers tug USS Essayons passed outbound to officially test the bridge’s readiness, becoming the first vessel to pass beneath the completed bridge. The first big carrier to pass beneath the bridge, the F. E. Taplin, did so on April 24. Near the end of April the City Council adopted an extensive set of rules for the bridge’s operation that covered right of way, loitering, warning signals, special consideration for emergency vehicles, how close a car could come to the bridge when it was raised, and others mostly to do with safe operation. Pedestrian rides were strictly forbidden, and violating any of the rules was a misdemeanor punishable by a fine of up to $100 or eighty-five days in jail. A few days later the KCBC notified the City Council that they considered their job complete. A contingency of city officials including the mayor, all five city council commissioners, the city attorney, and the city engineer followed up their biweekly meeting with an inspection of the bridge. It took nearly a month to work out some minor issues based on requests of the War Department, but on June 5, 1930, Duluth took possession of its aerial lift bridge.

Unlike the myriad troubles the aerial transfer bridge experienced its first year, the months after the new bridge began operation seemed relatively problem free. Operators noticed some cable fraying, which they easily corrected. The emergency gasoline engine was used once, but this was traced to an operator’s mistake. But Bridge Superintendant Leonard Green found plenty wrong with the bridge: the back-up engines were too slow for emergencies, four hundred rivets were missing, the shifting gear was impractical and did not allow for quick shifting, the operators house’s windows weren’t weather-tight, the height indicator was falling apart, the main shaft’s coupling was loose, and the oilless bearing sheaves and working cables screamed from a lack of grease, which leaked from the counterweight sheaves. He made his complaints known to the City Council, which decided to withhold $27,500 it still owed KCBC to address these issues and to cover the financial responsibility for changes requested by the War Department that the builders had not completed.

Harrington, Howard & Ash quickly came to the KCBC’s defense, claiming that most of Green’s issues were unfounded. Not a single rivet was missing, let alone four hundred, and the fact that the height indicator had “fallen to pieces” was an issue of maintenance, and therefore the City’s fault. They did admit that keeping the sheaves greased remained a problem, and recommended that the city simply hire someone to clean and replace the grease “as often as necessary.” This proved impractical. Eventually Chicago’s Viscosity Oil Company came up with an exceptionally heavy grease that did the job. The reason Green thought the emergency gearing was too slow, the company said, was that it “was never intended for general operation but only when the span might be covered with ice, increasing the load to be lifted.” It had a different gear ratio to handle the larger load, and therefore worked more slowly. But more important than Green’s complaints was that Major Bullard of the Engineers agreed with them—and wanted a faster emergency gear if the bridge was to sit over his canal. In December Bullard, upon witnessing the bridge raise faster than he had seen before, told city commissioners that if all the operators were trained to handle the bridge like that, he would drop his request for alterations. The newspaper joked that the bridge operators were being sent to “school to study gear shifting.”

Each issue was either addressed or eventually settled. In October W. A. Anderson & Co. put the final touches on the bridge: a fresh deep Essex green paint job over the bridge’s old towers.