所有者：芝加哥运输部
Lead Design Firm/Civil Engineer:Aecom
总承包人：F.H. Paschen
Structural Engineer:Aecom
结构工程师（方法）：HBM Engineering Group
建筑工程师：TranSystems
钢制造商：希尔斯代尔制造商
钢弯曲专家：BendTec
Steel Erector:S&J Construction
第41街行人拱门桥项目团队克服了艰巨的任务，即在活动的铁路线，链条电线和芝加哥湖岸大道的所有八个车道上跨越1,470英尺。这座耗资2800万美元的行人和自行车桥采用扭曲方法，形成了巨型S，将布朗兹维尔社区的公园新月社区连接到第41街海滩。
根据今年的项目法官的说法，对道路和铁路的安全通道已成为工程艺术的功能性工作。他们补充说，将桥上桥的240英尺长的倾斜式钢拱与进近一样令人惊叹。
The primary obstacle—Lake Shore Drive—runs nearly 16 miles like an asphalt and concrete ribbon separating Chicago from a series of public parks, beaches and other amenities east of it. On the city’s South Side, the Metra commuter and Canadian National (CN) railroad lines run parallel to LSD, complicating locals’ efforts to enjoy the public assets that Chicago’s 19th-century urban planner Daniel Burnham had the foresight to include in his original plan of Chicago as land reserved for public use in perpetuity. Of the few existing bridges on the South Side, most were not wheelchair accessible and ADA compliant. In 2003, then-Mayor Richard M. Daley held an international design competition to try to connect the South Side to its parks.
“The bridge design competition was based off the South Lakefront Study, which looked at access to the lakefront compared to North Lake Shore Drive,” says Tanera Adams, a civil engineer in the Chicago Dept. of Transportation. “There was a connection to the lakefront [on the North Side] every quarter mile, whereas, on the south side, there were not quite as many connections. You could see [the lakefront], but you couldn’t get to it. You’d have to travel quite a few blocks. For the 41st Street bridge location, there was no bridge there at all at the time.”
该竞赛中的参赛者之一 - Aecom和Cordogan，Clark＆Associates（CCA）的团队，都提出了使用蛇纹石方法和双弓的想法。与典型的拱形桥（在水平和垂直方向上是对称的）不同，团队的设计要求在反向曲率和长冠曲线上进行跨度的跨度，在该曲线上，拱形之间的中心比拱门的外部端的拱门之间的中心高7英尺。拱门从垂直方向倾斜30°，甲板肋骨曲线在400英尺半径上，仅由一侧的衣架支撑。
What ultimately was built “really originated from that design competition, because they were looking for some smooth curves,” says Mike Eichten, vice president for central division transportation at AECOM. “It was really an aesthetic approach to it. It was all about the end user and a great experience whether that was bikes or pedestrians.”
The design competition resulted in five winners for five new bridges, including the AECOM/CCA team, chosen from among 67 entrants by a jury of experts.
Years would pass, however, before funding was lined up. Chicago finally received an $18.76-million Transportation Investment Generating Economic Recovery (TIGER) grant in 2014, and that’s when AECOM refined the details of how such a bridge could be built and moved the project forward as the lead design engineer. The rest of the money for the project eventually came from the Chicago and Illinois departments of transportation. A notice to proceed followed that year. TranSystems joined the team as the construction engineer, and F.H. Paschen was hired as the contractor. By June 2017, construction was ready to begin. Immediately, the team had to coordinate work with the various community stakeholders.
Eichten说：“这是一个通用方法的一个很好的例子”和Alderman，居民，分包商，CN，Metra和运输部门之间的协调。“似乎每个人都在全部，从一开始就有很大的买入。”
临时桥梁计划
The serpentine approaches were necessary, particularly on the western side, to facilitate a 5% grade ADA ramp and still squeeze the approach within a footprint that got it over the catenary electrical lines and their towers. The vocal Chicago cycling community also reacted positively to the longer approaches rather than ramps with setbacks or other options that would force riders to dismount to cross Lake Shore Drive.
该项目以北的第35街桥梁两年前开始建设，其延误试图围绕活跃的Metra和CN铁路线进行工作，并且必须在湖岸Drive上穿越75英尺。
During the 41st Street Bridge planning stage, Paschen, AECOM and TranSystems talked over the idea of using a temporary bridge during construction with their client, the Chicago Dept. of Transportation. All agreed that it was the way to go.
Paschen的高级项目经理Tim Bea说：“这是对铁路的影响最小的最佳解决方案。”“在我们走过的四个通勤者Metra线路和我们走过的两个CN铁路之间，总共有六行。您可能已经覆盖了结构，但是显然，您必须在轨道之间运行邮政岸并在轨道之间进行支撑。那将是一团糟。”
TranSystems project engineer Brian Racine says building the temporary structure was well worth the expense.
“We weighed the pros and cons of a temporary bridge or other erection methods, and putting in this temporary bridge was well worth the money to provide a safe platform for our workers,” he says, “but also to provide protection for the railroads and to eliminate the need to have the track shut down. So, after that, we had to design the new bridge a little higher over the catenary wires so we could squeeze in this temporary bridge. It was really a unique opportunity.”
得益于Paschen的强大预制计划以及以美国陆军工程兵团的建模的质量控制计划，该项目的子结构元素已于2017年11月完成，即在开创性的五个月后完成。3D Tekla和Revit型号用于协助制造商和钢架，以放置和制造拱门和甲板截面的钢管的放置和制造。提出了严格的要求，以确保弯曲的钢管从制造到田间保持其圆形和精确的几何形状。
To provide structural stability, part of the bridge’s design called for kicker ribs to be introduced at each end of the arch span in a basket handle configuration to provide lateral support to the main arch rib. Many of the structural challenges involved the connection details, including the box beam connection to the round deck ribs, a hold-down device to combat large uplift and torsional forces, hanger and arch base connections, and expansion bearings with large lateral resistance and lateral stop and jacking supports.
Paschen used LiDAR laser scanning of the foundations, which were then replicated at Hillsdale Fabricators’ St. Louis shop to meet the quarter-inch tolerances necessary for proper installation.
BEA说：“我们每周举行的钢款图纸发布的会议。”“我们将两个主要的制造商聚集在一起。我们将这种基调设定为一个团队，以互相负责。那是准时交付的重要组成部分。”
在运输之前，桥梁的大部分是在Hillsdale的商店组装的，以进行质量控制。Paschen’s ability to procure 1.2 million lb of structural steel and large diameter steel pipe and accurately fabricate it through Hillsdale and bending fabricator BendTec, all in an accelerated time frame, allowed the bridge to be constructed under budget and opened to the public six months earlier than the contract completion date of April 2019.
Community Reaction
社区对第41街行人拱门桥的反应是芝加哥行人和自行车桥的前所未有的。
人们对我说，‘哦，蓝桥。太棒了，’”艾希滕说。“它具有如此独特的美感，但是正如我们之前提到的那样，它是一种使用的乐趣。”
Bronzeville residents even put signs up thanking the contractors and the city for the bridge that connects them to their lakefront.
“I’m very proud of that structure,” says Adams, a Chicago Dept. of Transportation civil engineer. “It’s been a labor of love since the design competition. It’s been a long time coming, and it’s very rewarding to see it being built and to actually see people using it. It’s an asset to the community and to the lakefront.”
