August 25 was a beautiful Saturday in Chicago – bright blue skies and not too hot. It was a nice day for a summer outing such as a visit to Lincoln Park Zoo or a picnic in Grant Park. Or how about watching a new 4.3 million-pound railroad bridge being rolled up a street and slipped onto its abutments? That's exactly how several people spent that day.
The new commuter railroad bridge is the first major milestone of a $101 million infrastructure project to increase the efficiency of the region's urban rail network and is also part of the city's "Building a New Chicago" infrastructure program. The bridge (thought to be the largest pre-assembled truss bridge ever moved into place) is the first step toward the reconfiguration and grade separation of the intersection of Chicago's Torrence Avenue and 130th Street, which will improve the traffic flow of all modes of transportation through this difficult and chronically congested intersection.
But months before that sunny Saturday, many people had already watched the bridge being virtually transported up the street and placed over the intersection – by means of a 3D infrastructure model and animation developed by consulting engineering firm Kapur & Associates using Autodesk Building Information Modeling (BIM) software solutions.
Grade separation project
The Torrence Avenue Grade Separation Project involves the complete reconstruction and realignment of the intersection. Torrence Avenue and 130th Street will be lowered 25 feet, allowing traffic to pass below two new bridges for the Norfolk Southern (NS) Railroad. This will eliminate the current at-grade crossings of these tracks and improve traffic flow to a nearby Ford Motor assembly plant.
The new bridge goes over ground-level NS freight lines and will carry commuter trains over the tracks and the sunken Torrence Avenue, replacing an existing bridge to its immediate north. The entire intersection reconstruction includes six new bridges and the realignment of the commuter railroad tracks and roads, as well as a new drainage system, retaining walls, lighting, traffic signals, a mixed-use pedestrian path, and extensive landscaping.
Walsh Construction, the project's general contractor, engaged Kapur & Associates to provide site construction layout, including all survey control. Kapur is a multi-discipline engineering firm with deep expertise in the use of 3D data modeling. Kapur used the Autodesk Infrastructure Design Suite of civil engineering software to develop an accurate 3D project model – data that is being used to support 3D machine control grading. The firm used AutoCAD Civil 3D software (part of the Autodesk Infrastructure Design Suite) to create the model based on point cloud survey data of the existing surfaces and final 2D design drawings. The model included all the road and rail alignments, as well as the bridge abutments.
Planning the truss bridge move
Once the project was underway, Walsh asked Kapur to work on an additional part of the project – designing a temporary path for the truss bridge move. "Typically a bridge this size is constructed in place," explained Curtis Luecke, Walsh project manager. "But that wasn't feasible for this bridge, given the constant flow of railroad traffic running beneath it."
The solution was to build offsite. Four self-propelled mobile transporters (SPMTs) carried the fully assembled, 394-foot-long, 67-foot-high bridge along the temporary path and up Torrence Avenue to its final position on new piers straddling the road.
Even using this accelerated bridge construction (ABC) strategy to minimize traffic disruption, the move caused several unavoidable closures. Torrence Avenue was shut down the evening before. The NS freight trains that cross Torrence Avenue were allowed an eight-hour outage on Saturday for the move. And the south tracks of the commuter rail (just north of the new bridge) were also closed as a precaution.
"We were under enormous pressure," Luecke said. "We were given eight hours to roll the bridge into place and faced $12,500 per hour of liquidated damages if we went beyond that window."
Leading up to the move, there was intense planning and coordination to ensure everything went smoothly that day, culminating in a large meeting of all the project stakeholders two months before the move to communicate the final strategy for the bridge placement. Approximately 40 representatives from the U.S. Department of Transportation, the State of Illinois, the City of Chicago, NS, Northern Indiana Commuter Transit (NICTD), and Ford attended the meeting.
"When you're standing in front of a room full of people and telling them you're going to jack up a 2,350-ton bridge and roll it 800 feet into position in eight hours, there's quite a bit of explaining to do," Luecke said.
Model-based project simulation
To support Walsh's communication efforts, Kapur suggested using project models it had already developed to simulate the move. Creating visualizations as part of the design process is a growing trend on infrastructure projects, helping companies visually communicate project proposals and individual project activities to clients, government agencies, and the public. Visualizations such as renderings and/or animations can be particularly effective during meetings where the audience contains a mixture of technical and nontechnical project stakeholders. For firms like Kapur that use model-based workflows, their civil infrastructure models can be repurposed to produce these visualizations.
"To support construction layout, we had already created a model of the existing terrain, the graded transport road, and the bridge abutments," explained Christopher Dietz, Kapur's project surveyor. "The only design component missing was a model of the bridge itself."
As luck would have it, Kapur had recently hired a college graduate who worked on the project as an intern the previous summer. "After that internship, I went back to school to complete my degree and continued modeling the project on my own time – exploring the use of BIM software and workflows for civil engineering projects. As a learning exercise, I used Autodesk Revit Structure to model the truss bridge from the structural engineer's 2D drawings," said Mark Peterson, the recently hired Kapur staff engineer.
Peterson also learned how to use Autodesk 3ds Max Design software – a 3D modeling, animation, and rendering tool that can be used to create animations from a variety of model data, including Civil 3D and Revit. All of these software packages are a part of the Autodesk Infrastructure Design Suite and were therefore available to Kapur.
"To generate the animation, I imported the Revit Structure and Civil 3D models into 3ds Max Design, and then used that software to simulate the complex movement for the truss," Peterson said. "The interoperability of Civil 3D, Revit, and 3ds Max Design made the process very efficient."
The final animation (watch it at www.youtube.com/watch?v=-jL0ygZ4UvA) shows the truss bridge, on the SPMTs, moving along the temporary road and up Torrence Avenue, being lifted up and aligned with the abutments, then slid over the bearing points and set into place. The movie includes details such as the pause needed to place temporary plates over the railroad tracks (providing the transporters a smooth surface) and the removal of the transporters once the bridge was set. There is even a captioned timeline of the major move components and rail outages.
"The simulation helped us clearly communicate our plan to everyone in the room and experience it as if they were actually there. We all saw exactly what had to be done to avoid glitches during the real move," said Luecke. "We had eight hours to move the bridge. We did it in six and a half."
"This is the first time we used our design model to create an animation like this, but it certainly won't be the last," Dietz said. "I was surprised to see how easy it was to reuse the models – which already contain very precise construction layout data – to create these project visualizations. This is definitely an approach we will be using more often to support our own, and our clients', communication efforts."
Daniel L. Kucza, survey group leader, Kapur & Associates (www.kapurengineers.com), has more than 26 years of experience with traditional survey methods as well as 3D data collection, control, creation, and distribution. With extensive knowledge of 3D scanning technologies and the construction project process He has worked effectively with municipal, state, and private clients, leveraging emerging technologies across the United States and Canada. Karen Weiss, P.E., is the senior industry marketing manager for infrastructure for Autodesk (www.autodesk.com). She worked 19 years in the transportation industry, holding engineering positions in the public and private sectors. For the last four years she has focused on developing industry focused marketing programs for infrastructure including roads and highways, rail, land, and water.
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