OCCI's CSX Bridge at MP 172.3 is a double-track railroad bridge located near Cumberland, Maryland and spans the North Branch of the Potomac River at the West Virginia – Maryland boarder. The bridge sees approximately 20-30 trains per day and is a key component to the CSX East coast network.
The pre-existing bridge was originally constructed in the early 1900’s and was a four-span structure with two 48’-8” girder spans and two 166’-0” through Pratt truss spans. It was replaced with three-150’-0” Deck-type Plate Girder (DPG) spans with all new piers and abutments.
Model collaboration allowed multiple parties to be involved during the bid, design, fabrication, erection and bridge closure phases of the project. During bid stage, we were able to use Tekla BIMsight as a tool to visually show CSX Railroad and HDR, Inc. exactly how the bridge change-out would take place.
Due to the size, complexity, and age of the existing structure, it was necessary to immediately begin taking field measurements to fully understand the existing bridge geometry. A field survey was necessary to locate the West Virginia abutment in order to design a temporary “jump-span” that would allow train traffic to continue while the demolition of the existing abutment and construction of the new abutment occurred. Layout points and layout lines were directly imported from the Tekla model into surveying equipment to locate the “jump-span” falsework. Survey data imported from the field and exported from Tekla was frequent throughout the completion of the fabrication, erection, and bridge change-out processes.
The use of a 3D Tekla Model and BIMsight was invaluable when it came to designing the falsework. Working hand in hand with Genesis Structures, we were able to design significant temporary falsework structures that would allow us to support the new DPG spans prior to closure, assist in sliding both the existing trusses out to be demolished and the new DPG spans in to their final resting position during a 34-hour bridge closure window. With the use of Custom Components, we are able to accurately model standard falsework that we use and reuse on future jobs. With this library of inventoried assemblies, we are able to cut down on remodeling these items in future jobs. This substantially increased time savings during the design phase when we were trying to consider different falsework structures in different construction scenarios.
Fabrication of the new spans was a complex operation. Weighing roughly 900-tons per span and spanning 450’-0” long, the three span DPG structure was modeled and fabricated by Prospect Steel. We were able to convert Prospect Steel’s 3D Tekla model into .ifc file format and reference them in our model which fast-tracked falsework design and erection sequence by accurately displaying their spans sitting in pre-closure and final resting positions. Missouri Fabricators fabricated all the unique falsework items required for the project.
To simulate the complex lifting sequences prior to the closure, the 3D Tekla model was directly imported into 3D Lift Plan, a CADD based critical lift planning software. Communication between these programs resulted in a quick and accurate method to develop documentation necessary to perform the critical lifts of erecting the contract steel.
The new DPG spans were pre-assembled in a laydown yard on site, and transported across the river using Self Propelled Modular Transporters (SPMTs). They were then loaded by crane onto the falsework structures where they waited for the closure to start. With the existing trusses properly reinforced, and new DPG spans ready for installation, it was time for the closure.
During the closure, the existing bridge was jacked up to clear the existing concrete pedestals and slid downstream onto the temporary falsework where it would be demolished at a later date. With the existing structure out of the way, the new DPG spans were simultaneously slid into place and set down in their final position. The closure was finished 9 hours ahead of schedule totaling 34 hours from when the last train rolled through on the old bridge to the first train rolling through on the new bridge.
