The Natchez-Vidalia Westbound Bridge is a 4,205-foot-long through-truss structure that was built in 1940 and carries U.S. 84 westbound over the Mississippi River from Natchez, Mississippi, to Vidalia, Louisiana. The westbound portion is just one of a pair of twin bridges spanning the river.
As seen in the August 2020 Edition of the Journal of Protective Coatings and Linings (JPCL) and on PaintSquare.com
The westbound bridge was recently repainted as part of one of the largest bridge rehabilitation contracts that the Mississippi DOT has ever awarded. The project involved the removal and replacement of all existing coatings in conjunction with replacing six pins and links in the through-truss sections. This was the first attempt to complete all of this work in a single project.
This article discusses the project coordination and partnering process initiated by the contractor between all parties to realize a full one-year closure for completion. Schedule coordination was imperative as certain areas on the bridge were closed to all construction activities, including vehicles during the pin replacement process, when the bridge was locked down with no movement allowed in those areas. The surface preparation and painting revolved around the pin replacement activities, and weekly coordination was crucial. The project also involved constant communication between the contractor and the QA inspectors to meet the schedule.
BACKGROUND
In the mid-1990s, after finding pin cover plates missing, MDOT and its consulting engineering firm inspected the pins and determined that several had shifted. The consulting engineer developed plans and MDOT promptly let a project to press the pins back to the original locations. However, the project was canceled after numerous failed bid attempts, and MDOT elected to monitor the pins. In 2012, it was determined that the pins were continuing to move, requiring significant repair or replacement.
With the size and complexity of the bridge and pins, MDOT requested that the Federal Highway Administration poll other state DOTs to determine if a pin replacement of this magnitude had ever been completed, and no such project was found. The consulting engineer also contacted several railroad agencies and was able to obtain guidance.
Original containment before starting pin replacement
Because a pin replacement project of this size had not been conducted on a vehicular bridge, a preliminary project was developed and let in 2014 to replace only two of the pins, and that project proved to be highly successful. During the process, the paint system was evaluated and determined to be in a failed condition.
With the bridge being a major east-west route for both general traffic and commerce, MDOT and the Louisiana Department of Transportation and Development (LADOTD) decided that the remaining pins and paint system should be replaced. In 2017, a project that would close the bridge for one year to expedite the paint and pin replacements was let and awarded.
DESIGN CONSIDERATIONS
Pre-project design considerations began with looking at the successful replacement of the two pins and links in 2014, with the added difficulties of scheduling the painting and replacement operations so they would not interfere with one another.
When the bridge joints are “locked down” for the pin replacement operation, the bridge is in a vulnerable position because the joints cannot expand and contract as they were designed. Because the contractor was required to limit the time between when the temporary restraints supported the bridge and the new links were installed, a 96-hour time frame was established to complete each pin replacement. Temperature, wind and high-water levels were also considered when deciding when to “lock down” joints for replacement. The contractor was not permitted to engage temporary restraints when the forecasted 10-day temperature fluctuation was greater than 40 degrees, when the forecasted wind speed was expected to exceed 30 mph, or when an unusual high-water event was occurring or expected.
Strain gauges were installed on multiple truss members and the post-tensioning bars to ensure that the temporary restraints were properly transferring the load off the pin and link, as well as to evaluate any unforeseen losses in the restraints. The splice plates were also instrumented to evaluate stresses once the pins were removed. Because the temporary restraints would change the boundary conditions of the bridge to fixed (adding additional load in the truss and forcing the piers to flex), the piers were inspected prior to and after locking each joint. The initial inspection of the piers revealed numerous cracks, as expected for a mildly reinforced pier at 75 years of age. No crack growth was observed in the post-inspection.
The pre-project design considerations for the painting operations included developing an anticipated schedule of events centered around the pin replacement operations. MDOT had to consider how to prepare the surface and which coating system to use once the pin was removed on the interior of the casing. The MDOT standard, Special Provision 907-845-2, “Coating of Existing Structural Steel,” was referenced. Throughout the partnering process, project revisions were made that will be discussed later.
SUBMITTAL REQUIREMENTS AND AWARD CONSIDERATIONS
MDOT advertised a Request for Qualification to short-list qualified teams. The painting and structural contractors were required to submit their statements of qualification to perform the work. The following categories were graded for each team:
- Experience and qualifications of key personnel;
- The team approach to management of a contract; and
- Past performance on similar projects.
The “pin and link” replacement contractor was required to submit for MDOT Director of Structures approval, which details procedures and outlines means and methods for pin and link replacement operations, with consideration to the painting operations. The submittal included use of temporary restraints, staging of equipment on the bridge, schedule, sequence of construction and more.
In addition to cleaning and repainting work, the project included extensive pin replacements throughout the bridge.
Painting submittals included a contract QC plan per the SSPC-QP 1 requirements and a site-specific work plan. Environmental, health and safety plans were required to address pollution control, waste management and waste disposal. The containment plans were the most critical, as they had to accommodate the lockdown periods during the pin removal and replacement process. All parties reviewed the plan to ensure that it would not do any damage to the structure during the process. Other factors like ventilation, wind loading and verifying the containment was constructed to the requirements of the plans were carefully analyzed.
ACCESS AND CONTAINMENT SYSTEM
All coating operations, equipment and containment were not permitted to interfere with or slow down the pin and link replacement operations. A “no load zone” was set up for each corresponding link replacement location. Only approved link replacement equipment was allowed in the “no load zone.” Painting operations and equipment were not allowed in the “no load zone” from the time the post-tensioning bars were engaged until the new pins and links were installed; the length of the “no load zone” was up to 40% of the length of the truss. The contractor was also required to prepare a contingency plan addressing natural weather events such as tropical storms and unusually high river elevations, including the removal and reinstallation of the containment system.
The contractor had a 24-hour window from when the old link was removed to when the new pins and links were installed to set up containment and abrasive blast and paint the area inside the truss, which would become inaccessible once the new links were installed.
The specification required SSPC-SP 10/NACE No. 2, “Near White Metal Blast Cleaning,” and application of a single coat of inorganic zinc in these areas. The original plans called for a full three-coat system; however, once the decision was made to reinstall the pin after a 24-hour period (for safety), the decision to use a single coat of IOZ was made.
MAINTENANCE OF TRAFFIC
U.S. 84 is a major east-west route for both general and local traffic and commerce, with a detour length of nearly 200 miles when closed. During the 2014 project, traffic was detoured head-to-head on the adjacent bridge while the contractor was replacing the pins, and this traffic plan proved to be effective.
The same approach was used in 2017 by establishing crossovers at each end of the bridge and putting traffic head-to-head on the adjacent bridge. However, the closure duration was only one year. Oversized traffic was required to schedule a police escort to use both lanes of the eastbound bridge or detour. This proved to be successful with the local traffic easily navigating the closure. LADOTD, MDOT, the City of Vidalia and the City of Natchez worked together to inform the traveling public and commercial haulers of the closure. The agenda for all partnering meetings included MDOT issues. Reps from both the City of Natchez and the City of Vidalia attended these meetings, which proved to be quite useful in solving traffic flow issues.
SURFACE PREPARATION AND COATING OPERATIONS
As previously mentioned, the specification required “Near White Metal Blast Cleaning” and a surface profile that met the coating manufacturer’s recommendation of 2–4 mils. Early on, the surface profile depth was an issue, and the contractor changed grit size to conform to the specification. Due to frequent weather events in the area, the contractor decided to remove all existing coatings, then go back and re-blast to achieve the SSPC-SP 10 requirements before requesting a QA inspection. The QA inspector conducted preliminary inspections during lunches and breaks and advised the contractor QC inspector of missed/non-compliant areas, which helped the project schedule and avoided long inspections before primer application.
During the initial primer application, the contractor applied a thin “hold-coat.” However, this process led to missed areas and subsequent rusting, and was eliminated. Instead, the primer was applied within the specified range of 3–5 mils. There was also concern over excessive film-build around the rivets, so the stripe coat of primer was eliminated. Thorough QC and QA inspections were performed to ensure complete coverage of the primer. While time-consuming, the team considered this important and all agreed that it was worthwhile.
Safe bridge access was provided for painting, pin replacements and subsequent inspections.
The epoxy intermediate coat was applied at 5–10 mils. QA and QC inspection personnel performed the stripe coat inspection at the time of application to enhance productivity. Missed areas were also corrected. After drying, the dry-film thickness measurements and visual inspection reverted to the normal QA/QC process.
The topcoat was an aliphatic polyurethane applied at 3–6 mils. The final inspections entailed checking all areas for DFT, visual appearance and coverage, which was challenging at the pin replacement locations. The team delayed final inspections in these areas as some damage was noted each time. Access had to be reestablished for final inspections, which proved to be difficult. The team tried a drone inspection on the outside faces, but it did not work well due to the sheer number of visual defects noted. Different access was provided to verify DFT and visual inspection and to complete the final repairs.
PIN REPLACEMENT
As part of the contract plans, the contractor was required to submit a detailed sequence of construction demonstrating means and methods for removing the pins and links. The contract plans also provided a suggested sequence of construction that the contractor adopted with minor modifications.
A temporary bypass that locks the joint from moving in all directions was developed to remove the pins and links. It was important for the temporary bypass to have internal redundancy plus alternate load paths to mitigate the risk of any one component compromising the bridge when the pins and links were removed. A series of bypasses were used to lock the joint, while the pier was expected to flex under thermal loads.
Only one pin and link location was permitted to be locked down and replaced at a time. The following steps were employed for the pin and link replacement operations.
Step 1 – Tension Diagonal Bypass: The diagonal bypass bars were tensioned to remove the load in the existing truss diagonal member, link and pin. Stressing operations were conducted in increments and member stresses were observed to ensure that the bypass was functioning as anticipated. Although the entire load would not be released until the pins were removed, it was preferred to minimize the load in the existing link to avoid the pins from binding and prevent sudden movement resulting from pin removal.
Step 2 – Tension Upper Longitudinal Restraint: Both the upstream truss and the downstream truss upper longitudinal restraints were tensioned to prevent the joint from moving longitudinally. The upper longitudinal restraints were designed for a 60-degree temperature drop, but stressed to accommodate a 40-degree temperature drop based on the 10-day weather forecast.
Step 3 – Weld Templates and Field Drill Splice Plate: Once the bridge was locked from moving, the splice plate templates were welded together and used to field-drill the splice plates. Field-drilling and splice plate installation were challenging due to the 100-plus A490 bolts per gusset face, but was completed with minimal incidents.
Step 4 – Install Top Strut Plates: The two top struts were connected to provide lateral additional rigidity in the event there were any unexpected lateral forces when the link was removed.
Step 5 – Install Lower Longitudinal Restraints: Shims were installed between the two false chord members and post-tensioned together to ensure continuous bearing between members.
Step 6 – Remove Pins: Because of the difficulty in previous attempts to reset the pins in 1997, the contractor elected to cut the pins with a diamond-studded wire saw. After cutting the pins, minimal change in force was observed in the links. No movement was observed in either joint during removal of the pins.
Step 7 – Line Bore Gusset Plates: The contractor line bored a 10 ½-inch to 10 ¾-inch hole through the existing gusset plates to ensure that the new pins would bear properly and fit.
Step 8 – Install New Pins: Once the final hole dimensions and centerlines were measured, the dimensions were sent to the fabricator and the new pins and links were turned down to their final dimensions and delivered to the bridge. The new pins and links were able to be installed with minimal difficulty.
Step 9 – Remove Temporary Restraints: After the new pins were installed, the temporary restraints were disengaged, and load was transferred to the new pins and links.
PARTNERING FOR THE BEST PROJECT
With a project of this size, complexity and cost, it is critical that all parties communicate. The partnering process helped keep the project on schedule and helped avoid complications that would jeopardize the overall project. Also, because the project was a “one-of-a-kind” (other than the previous 2014 project, which did not include full removal and replacement of the existing coatings), an error could result in a bridge closure or a catastrophic collapse.
Despite all the risks and unknowns of the pin replacement process, the two-agency and five-firm team attributes preparation and communication as the keys to a well-run, successful project. Collectively, team members worked to add years of service life to the bridge. Though coordinating activities between two state agencies and multiple contractors is often a challenge, this project was different. The process went smoothly, and the project team gave a lot of feedback. Many of the contractor’s suggestions were considered and applied, particularly on issues such as thermal movement or monitoring as well as sequence of construction between pin and link replacement and painting operations.
Thanks to coordination from all parties involved, the project was successfully completed during the one-year closure period.
The contractor who was awarded the contract introduced an informal partnering process that benefited the entire project. The process was based on trust and an open, honest attitude in which all participants involved with the project recognized both common and individual objectives and worked to achieve those objectives through communication and cooperation.
The partnering process produced several outcomes that aided in completing a quality project on time and on budget. For example, decisions about the QA/QC inspection process for the painting were made that led to some side-by-side inspections, which accelerated the coating operations. Problems and challenges encountered were discussed to create workable solutions that did not impact the quality of the job.
CONCLUSION
The project went very well from MDOT’s prospective. In addition to the coordination and communication, other factors that proved critical included the successful completion of the previous “test” project, good contingency planning and having on-site structural engineers conducting the inspection of the pin replacements, along with an extremely experienced paint inspection firm.
One major lesson learned was the ability to adapt to changes and conditions discovered in the field. Though each pin and link panel point was similar, they were also very different and behaved differently. The pin and link replacement operations at each location had a different challenge arise that had to be overcome.
The amount of pre-planning, including open meetings with all bidders to discuss the project requirements, was also critical to the successful completion. The informal partnering meetings were a complete success to solve issues that arose during the project. The critical review of all submittals, shop drawings and containment plans in a timely manner kept the project on budget and on schedule.
ABOUT THE AUTHORS
Justin Walker is the Director of Structures, State Bridge Engineer at the Mississippi Department of Transportation. He joined MDOT in 1997 as a bridge design engineer and has since served as design team leader, design section engineer and Deputy Director of Structures–Assistant State Bridge Engineer. He is a member of the Mississippi Engineering Society and the Structural Engineering Association of Mississippi and is the Vice Chairman of T17 Welding AASHTO Subcommittee on Bridges and Structures. He is also currently the MDOT voting member of the AASHTO Subcommittee on Bridges and Structures. Walker is a graduate of Co-Lin Community College and Mississippi State University, where he holds a bachelor’s degree in civil engineering.
Patrick Roth is a Structural and Project Engineer and Bridge Inspection Team Leader with HNTB. He has more than 12 years of experience as a civil and structural engineer and bridge inspector in the New York City and Louisiana areas. He holds a bachelor’s degree in civil engineering from Louisiana State University and is a registered Professional Engineer in Louisiana, Mississippi, New York and Texas.
Greg Richards is the Southern Area Manager for KTA-Tator, Inc., where he has been employed for more than 20 years. He manages projects in Florida, Georgia, Alabama, South Carolina, Texas and Tennessee involving bridges and other industrial structures. Richards is an SSPC-certified Protective Coatings Specialist, Bridge Coating Inspector (Level II), Protective Coatings Inspector (Level 2) and a C-3 Supervisor/Competent Person for Deleading of Industrial Structures, as well as a NACE-certified Coating Inspector (Level 3). He also serves as an instructor for SSPC’s BCI course, as well as NACE courses.
ACKNOWLEDGMENTS
The authors would like to acknowledge those involved in the successful completion of this project, including John Korfiatis, Blastech Enterprises; Michael Belsky, Piasecki Steel Construction Corp.; and Mark Hudson, The Sherwin-Williams Company.