KCI provided construction engineering and inspection services for the Maryland Department of Transportation State Highway Administration’s first project using a self-propelled modular transporter (SPMT) for the $4.6 million rehabilitation of the substructures and replacement of the superstructures of the bridges carrying West Nursery Road over MD Route 295 (Baltimore Washington Parkway) Northbound and Southbound. The common means and methods for this type of construction consist of closing a road or modifying traffic patterns (staged construction) to demolish the superstructure and all or portions of the substructure. After demolition activities are completed, the construction of the proposed structure can begin. This project constructed the superstructure independent of the existing substructure in the staging area located in the median of MD Route 295. Then the team moved each bridge, weighing approximately 500 tons, into place onto the existing abutments. Utilizing these means and methods for construction allowed for substructure abutment repairs and components scheduled for replacement along with existing superstructure demolition to occur concurrently with the construction of the proposed superstructure.
The benefits of these new means and methods include, but are not limited to;
- A compressed construction schedule
- A safer environment for the contractor and travelling public
- Reduced manipulations of traffic patterns
- An overall decrease to the inconvenience of the public
- A completed structure requiring very little maintenance due to the necessity to replace superstructure components that would not be replaced using conventional means and methods
To begin the project, the prime contractor, Wagman along with multiple subcontractors, started with the installation of sediment and erosion controls along with temporary maintenance of traffic measures, which included a roadway widening and changes to the existing traffic pattern to establish the proposed work zones and staging areas. Contractors utilized day shifts to construct the temporary bents, which simulate the existing abutments, for the proposed superstructure construction while utilizing night shifts to perform substructure and partial superstructure demolition activities. Once the temporary bents were built, the construction of the proposed superstructure began. This consisted of erecting fabricated structural steel, placement of SIP forms and steel stud shear developers, installation of reinforcing steel, bridge deck concrete placement, and constructing the parapet walls.
Over the course of two weekends in October (one weekend per structure) the SPMT arrived to remove the existing superstructure and set the new superstructure in place. Demolition of the old structure took place in the median while roadway approaches were constructed. Finally, the temporary bents were removed, proposed landscaping was installed, and the traffic patterns returned to their permanent configuration.
Disaster struck during the first scheduled lift. Just after midnight, the existing bridge carrying West Nursery Road over northbound MD 295 shifted off the SPMT and lodged itself on the west abutment.
The project team rallied to first ensure the load was stable and the SPMTs weren’t damaged, and then to identify alternatives that would restore traffic as quickly as possible. By noon, specialty subcontractors had dispatched more than 30 trucks carrying the parts and weights needed to assemble four massive cranes, and by early evening, crews were inching the superstructure back into its original position. Two weeks later, the SPMT executed the first of several perfect lifts, moving the existing structure onto temporary bents in the median. With only feet of wiggle room on either side, the new span was maneuvered and lowered into place the following night.
The project also included substructure repair work including rebuilding beam bearing pads, roadway approach work, restoration of the MD 295 median back to its pre-construction state including extensive, landscaping, roadway pavement markings, and construction of three stormwater management ponds.