Harried Brown Line commuters returned to their normal routine today, as “L” service resumed between the Merchandise Mart and the Loop. Service was suspended last week, giving the city time to replace half of the aging Wells Street Bridge, which carries the Brown Line across the Chicago River. Still, it’s a bit early to breathe a sigh of relief. In April the city will shut down the bridge again, in order to replace its northern half.
That lull should give you time to digest this incredible fact: The last time the city replaced the bridge in 1922, “L” service was suspended for just three days.
Backing up, the hulking burgundy section of bridge that workers shipped away on a barge this past week was not, in fact, the original Wells Street Bridge. That bridge – a floating one – was destroyed in a flood in 1849. Its replacement, a hand-operate wooden truss bridge, was incinerated by the Great Chicago Fire in 1871.
Wells Street got its first steel bridge the following year. It was a swing bridge, which was then replaced by a steam-powered swing bridge in 1888, which was then converted to run on electricity about a decade later. A second deck was added in 1896, giving the Wells Street Bridge its special burden: even today it’s just one of two bridges that carries elevated trains across the Chicago River.
This built history is laid out in a 1999 engineering survey conducted by preservationists at the National Park Service – who probably had no idea what commuting headaches they were foreshadowing when they wrote the following: “Because traffic on the elevated lines could not be diverted without great expense, replacement of double-decked bridges presented the engineers with the difficult task of maintaining elevated service during construction.”
Sound familiar, Brown Line folks? The citizens of 1909 Chicago felt your pain: City engineers were faced with just such a task when the U.S. Department of War ordered Chicago to replace its swing bridges with ones that made river navigation easier that same year.
The city began with the bridge over Lake Street, and handed the reigns to Thomas G. Pihlfeldt.
The Norwegian-born engineer “admitted that the problem of replacing the bridge initially had him stumped,” according to the authors of the 1999 report. And here’s why: “In a twelve hour period, between seven in the morning and seven at night, 3,180 motorized vehicles, 1,000 elevated trains, 850 horse teams, and 7,000 pedestrians passed over the bridge.”
Those numbers sound quaint now, but the solution Pihlfeldt came up with is impressive even by today’s standards:
Essentially, they left the existing swing bridge in place as long as possible, and built the new bascule around it, in a fully vertical, elevated position. In this manner, elevated service was maintained across the old swing bridge and through the raised trusses of the new bridge under construction. As the replacement project neared completion, the old swing was cut away, and the leaves of the new bridge were lowered to the closed position so work could begin on the decking. Construction of the upper decking and elevated rails suspended rail service for only one week, and the project was hailed as a great success.
When plans began in 1916 to replace the Wells Street Bridge, “Pihlfeldt merely reapplied the formula that had worked so well at Lake Street.”
Of course, no one counted on World War I interrupting the city’s construction plans – and draining its coffers. It was another five years before the city could afford to tackle Wells Street.
When the city finally did move to replace the bridge in December of 1921, it did so under what the engineering study authors called a “tightly controlled construction process”:
At 7:00 p.m. Friday evening, the work crew closed the old bridge, and began to remove the elevated rails. Floodlights lit the construction site as darkness approached, and the flooring of the new bridge moved toward completion. Nearly round-the-clock work succeeded in cutting away the central portion of the swing bridge, installing new rails, removing approaches and adding new approaches in time to resume elevated service for the Monday morning rush hour.
Catch that? Elevated train service was interrupted for just three days (although pedestrians, cars and other vehicles weren’t allowed back on the bridge until February).
While playing the slideshow, push "X" for full screen. "Show info" displays captions.
Dan Burke, the Chicago Department of Transportation’s Deputy Commissioner and Chief Engineer, said he and his colleagues were very impressed by the last renovation of the Wells Street Bridge.
“What they did was ingenious. It was fantastic how they were able to build the new larger structure around the old one,” Burke said. “It set the bar pretty high.”
Unfortunately, conditions near the river were quite different in 2013, making it impossible to take the same approach. “The original swing bridge wasn't landlocked,” he said. “You didn’t have buildings abutting all four corners.”
“We found by taking a piece off, floating it away and installing the next piece, we were able to get it to a fairly tight closure window,” Burke said.
In the 1940s, city engineers calculated the lifespan of a moveable Chicago bridge at about 40 or 50 years. The Wells Street Bridge was in service for nearly twice that, and it’s hardly the only bridge that will need attention.
“A lot of those structures are going on 80, 90, 100 years old,” Burke said. “We currently have 40 movable bridges. . . to keep up with that pace you’re trying to do at least one a year.”
Luckily most of Chicago’s other bridges will be less complicated to renovate. Because they don’t carry “L” cars they can be shut down for longer periods of time. And because they’re historic structures they’ll likely be cared for in a more piecemeal way; Burke and his team can repair individual components rather than replace all the supporting trusses at once. “They’re iconic structures, and they’re still very serviceable,” he said. “In all likelihood we’ll maintain them in perpetuity.”
Next up, Burke has his eye on the bridges that cross LaSalle and Van Buren Streets. Here’s wishing him and his team speedy construction.