In 2020, Manafort Brothers, Inc. (MBI) was the lowest bidder and was awarded a contract by RIDOT to replace the proposed bridge carrying Glenbridge Avenue Bridge over Route 6 in the City of Providence. The proposed plan to replace the bridge included two construction phases. Due to the high traffic volumes and the proposed impact of staged construction to the adjacent community and travelling public, RIDOT requested MBI speed up construction by incorporating Accelerated Bridge Construction (ABC) using the lateral slide method. CHA, a national leader in ABC and one of ENR’s top 25 bridge design firms, was engaged by MBI in the spring of 2020 to redesign the proposed bridge to incorporate this method of construction.
Instead of building the proposed bridge in two separate construction stages and maintaining a single lane of traffic at all times on the structure, CHA proposed constructing the new superstructure to the west of the existing bridge and sliding the new structure into place during a short duration closure of Glenbridge Avenue. The general construction approach was as follows:
- Construction of temporary substructures to support the proposed superstructure.
- Installation of temporary falsework structures parallel to the abutments and pier. This falsework was located a few feet in front of both the abutments and adjacent to the pier.
- Construction of the new superstructure on the temporary substructure. The new superstructure included the steel girders and concrete deck, sidewalks, and barriers.
- Installation of temporary falsework parallel to the existing pier to temporarily support the existing bridge and allow for reconstruction of the new pier while the bridge maintained vehicular traffic.
- Short duration closure of Glenbridge Ave to complete the following:
- Demolition of the existing superstructure, abutments, and wingwalls.
- Installation of precast abutment stems and precast pedestals on the new pier wall.
- Sliding of the new superstructure onto the new substructures. This move necessitated an overnight closure of Route 6 and detour of traffic.
- Installation of precast wingwalls, approach slabs, pavement, and barrier connections.
- Re-opening of Glenbridge Ave.
The 2018 AASHTO LRFD Guide Specifications, authored by CHA Chief Bridge Engineer, Michael Culmo, served as the basis of design for the lateral slide. CHA’s goal was to work in conjunction with MBI to facilitate a bridge slide that minimized the number of proposed changes to the bridge that had been previously designed by others. New details were required at the abutments, pier, and deck ends to facilitate the accelerated construction. CHA’s proposed changes to the bridge included:
- Re-designing and re-detailing the abutment and girder end diaphragms. The new abutment seat details were coordinated with Mammoet, MBI’s heavy lift subcontractor to ensure their slide equipment would work with the proposed details.
- Replacing the proposed strip seal joints with Emseal expansion bridge joints.
- Replacing the proposed multi-column pier bent with a sold wall pier bent to facilitate support for the jacking forces used during the lateral slide.
- Using precast pier stems to allow for the new pier wall to be constructed beneath the existing bridge and then installing the precast stems to support the new slid bridge once the existing superstructure was demolished.
Figure 1 - Collision damage to exterior girder
In August 2021, several weeks before the new superstructure was slated to be slid into its permanent position, an oversized truck traveling in the eastbound direction collided into the bridge and caused significant damage to the fascia girder. The timing of the bridge strike could not have come at a worse time since the new bridge deck and barrier concrete had been poured several weeks previously and mostly finished curing. The bridge strike was significant, and the impact distorted the bottom flange and web of the steel girder approximately 8 ½ inches to the east over a length of approximately 40 feet (see Figure 01). Several diaphragm connection plate welds were cracked, and several diaphragm connection bolts sheared off from the collision (see Figure 02). The new bridge superstructure was actually set with the low chord approximately 8 inches higher than the existing superstructure. It’s unfortunate the truck wasn’t travelling westbound and had struck the existing bridge!
Figure 2 - Collision damage to interior diaphragm
CHA worked with MBI to repair the bridge. The new bridge’s steel girders consisted of two sections that were connected with a bolted field splice. Since most of the distorted girder and web flange were located on one section of the girder, CHA initially proposed replacing the section of girder with the impact damage and most of the distortion. The diaphragm connections were removed, and the new concrete deck and end diaphragms were removed through the first interior bay. Once the first section of girder was removed, CHA could assess if the remaining section of girder would move back into place or if the steel yielded, continue to replace the remaining section of girder and concrete deck, sidewalk, and barrier. Unfortunately, following the removal of the first section of steel girder, the existing remaining section still had out of plane distortion by several degrees in both the bottom flange and web (see Figure 3). The decision was made by RIDOT to replace the remaining section of girder, instead of trying to use jacking or heat-straightening to get the girder back into place.
Figure 3 - Remaining section of deformed girder
In the end, the vehicle collision ended up delaying the bridge’s construction by an entire year. The new superstructure’s exterior girder, concrete deck, sidewalk, and barrier were constructed in the spring and summer of 2022. At the end of September and beginning of October, the existing bridge was demolished, and precast abutments and pier stems were installed during a week shutdown of Glenbridge Ave (see Figure 04). During the overnight hours of October 4th into the 5th, Route 6 was detoured, and the new bridge superstructure was slid into place (see Figure 05). It’s important to note, in the end, this project didn’t utilize a true later “bridge slide”. Based on equipment availability, Mammoet subsequently decided to use a combination of slide jacks on tracks at the abutments and a self-propelled modular transporter at the pier to lift the bridge and move it into place.
Figure 4 - Erection of precast substructure
Figure 5 - New superstructure slid into place
The new bridge abutments were backfilled over the next couple of days and approach slabs were installed. Paving and other related roadwork was completed during the following weeks. While the overall project construction ended up taking longer than anticipated due to the vehicle collision, the actual traffic impacts to Glenbridge Ave and Route 6 were significantly lessened using ABC and sliding the new bridge into place.