How do you rehab a 65-year-old bridge that serves as a key point of traffic relief and a route directly into downtown St. Louis with limited original structure information? This is a challenge the Illinois Department of Transportation (IDOT) and Modjeski and Masters Inc. faced during a recent project on the Martin Luther King Bridge.
The Martin Luther King Bridge has connected St. Louis, Mo., with East St. Louis, Ill., for more than 65 years. This 4,000-ft, three-lane bridge stretches over the Mississippi River, connecting I-55 and I-64, U.S. 40, and Martin Luther King Drive with the downtown streets of St. Louis. The bridge’s 34 spans are composed of a variety of superstructure types including continuous multi-beam spans, simple multi-beam spans, deck truss spans and a three-span cantilevered through truss.
The structure was originally owned by the city of East St. Louis and operated as a toll bridge. Today, IDOT shares ownership of the bridge with the Missouri Department of Transportation (MoDOT) and is the lead agency in charge of maintaining it.
Following the tragic 2007 collapse of the I-35 West Mississippi River Bridge in Minnesota, and the new federal mandate on the inspection and load capacity rating of gusset plates, IDOT proactively brought Modjeski and Masters on as a consultant to perform an extensive load capacity rating of the structure, which included the gusset plates. This was an aggressive approach not all states were taking at the time.
Inspection and load capacity ratings
The load capacity rating of the Martin Luther King Bridge had some initial complications due to unavailable design or shop drawings for certain members, particularly the gusset plates. Without having all of the original structure details, the ratings could not be immediately completed. Missing information had to be gathered from the field. To limit the disruption to traffic while improving the accuracy of the field measurements, photo-imaging was employed to obtain the needed gusset plate information. This was easily completed during a scheduled National Bridge Inspection Standards (NBIS) condition inspection Modjeski and Masters was already under contract to perform.
Photo-imaging technology works by utilizing inspection photos to create scaled CAD drawings. To accurately scale the image, a standard reference target is magnetically attached to the gusset plate. Using a high-resolution camera with a flat-field focus lens, photos of the gusset plate with the attached reference target are taken, and the distance from the camera to the target is recorded. Field measurements of the perimeter of the plate are taken in order to have additional reference dimensions to confirm the processed images. The thickness of the plate also is measured in the field to provide a complete depiction of the plate geometry.
To process the pictures, graphic editing software is used to correct the perspective and straighten the image. After editing the image, it is uploaded to MicroStation and final adjustments are made to create a CAD drawing that can be scaled to match the reference dimensions obtained during the inspection. Exact dimensions can then be obtained from the drawing for all geometric data required to complete the load capacity rating analysis of the gusset plates.
Based on the results of the load capacity ratings and the inspected condition of the structure, IDOT decided rehabilitation of the Martin Luther King Bridge was necessary. For this rehabilitation project, we worked with sub-consultant Lin Engineering Ltd. was brought on to provide preliminary and final design and construction engineering services for IDOT to increase the load-carrying capacity of the bridge, repair areas of deterioration, and ultimately extend the life of the structure.
Priorities and concerns
One of the top priorities of the rehabilitation was to increase the bridge’s load-carrying capacity. Results of the load-capacity ratings indicated that certain members had inadequate capacity to support the design live load at inventory levels. Per IDOT’s load rating procedures, the design live load used for the rating analysis was an HS20 live load. However, the Martin Luther King Bridge was originally designed for an H20 live load in accordance with the design code of that era. Because the bridge was designed to support a lighter load than what is required today, it is not surprising some members needed to be strengthened. Strengthening of select members including floor beams, stringers, gusset plates and steel bent caps was performed to achieve this project goal.
Another concern was the existing condition of the 725-ft suspended-span grid deck system. Defects had been observed on the grid deck during a previous wearing surface replacement project. The severity of these defects warranted the replacement of the grid deck system during this rehabilitation project. The existing grid deck was welded to the stringer system in the suspended span. To facilitate the replacement of the grid deck, the stringer system in this span also was replaced.
Controlling the weight of the replacement deck was a top priority. The new grid deck could not weigh more than the existing grid deck to ensure it did not negatively impact the structure’s load-carrying capacity. Therefore, the replacement deck was designed and detailed to be as light as possible. Advances in grid deck system technology were researched to alleviate concerns of repeat wearing surface and grid deterioration issues. Modjeski & Masters recommended a half-filled galvanized steel-grid deck with a lightweight concrete overfill wearing surface.
The deck system outside of the suspended span consisted of 3,275 ft of reinforced concrete slab. Deterioration was noted in various locations throughout the slab during the inspection. In order to accurately estimate the construction time and cost to repair the concrete deck, IDOT requested that Modjeski & Masters better define the areas of concrete deterioration in order to refine the quantity of repairs required.
Infrared thermography was used to delineate the isolated areas of the deck needing repair. By using this method to document the concrete deck conditions, IDOT was able to limit the impact on traffic while gathering the data. Other, more traditional methods of documenting the condition of a concrete deck, such as hammer sounding or chain drag procedures, are time-consuming and would have caused tremendous traffic disruption on this busy commuter thoroughfare.
Designers contracted Penetradar Corp. to perform infrared thermographic deck testing using ThermaMap IRT vehicle. This vehicle includes a high-resolution infrared radiometric camera, a distance measurement instrument, and PC-based image analysis hardware and software. The IRT vehicle collected data while traveling each lane of the bridge at nominal speeds of 15-25 mph during non-peak hours. The infrared thermography produced a thermal image of the deck surface, which was then digitized, providing a mapped-out analysis of the deck with the delaminated concrete areas highlighted. The technique is based on unequal heating rates of materials. Therefore, deteriorated concrete creates a thermal anomaly that can be detected and quantified. The results were utilized to map out and quantify the repairs in the rehabilitation plans.
Miscellaneous repairs were performed to address a number of structural defects observed during the NBIS inspection. The structure’s splash zone and other identified problematic areas were cleaned and painted. Leaking expansion joints were replaced throughout the structure, with the exception of the finger plate expansion joints, where only the troughs were replaced. The hinges in one of the west approach spans were reset to better align the girders in the direction of the overall movement of the span.
Modjeski and Masters also coordinated with the U. S. Coast Guard to bring the bridge’s navigation plan to current standards, which required installation of an additional navigation light and several reflective panels. New LED navigation light fixtures also were installed throughout the structure to increase the efficiency of the lighting and decrease maintenance requirements.
MLK Bridge St. Louis
With numerous other projects such as the new I-70 Bridge, the Arch grounds renovations, the Eads Bridge rehabilitation, and the upcoming Poplar Street Bridge reconstruction taking place in and around the St. Louis area which were impacting traffic flow, coordination of project timelines between MoDOT and IDOT was crucial.
Before the rehabilitation of the Martin Luther King Bridge began, IDOT coordinated the project schedule with the city of St. Louis and MoDOT. The required closure period of the bridge for the rehabilitation was scheduled to begin after other ongoing projects in the downtown area were substantially completed. This plan relied on the newly opened I-70 Stan Musial Veterans Memorial Bridge to be used as part of the detour to relieve traffic congestion in the area during the closure period.
IDOT awarded the contract to Keeley and Sons Inc. to perform the construction services required for this complex rehabilitation. Modjeski and Masters and Lin Engineering provided construction support to IDOT when needed. This consisted of working with Keeley and its subcontractors, including L.B. Foster, which provided the contractor’s steel grid deck; reviewing numerous shop drawings; answering questions during construction; and reviewing the analysis of the structure under construction loads.
Throughout both the design and construction phases of this project, routine bridge inspections continued. Additional maintenance repairs were added to the rehabilitation due to new or advanced defects noted during these inspections. Cleaning the existing steel during construction also exposed additional areas of deterioration which required repair. Because of this, the rehabilitation project had an evolving scope, which Modjeski & Master and Keeley and Sons were able to accommodate.
Road to success
The Martin Luther King Bridge has served as a key point of traffic relief for over 65 years. Even with the new I-70 Stan Musial Veterans Memorial Bridge and the existing Eads and Poplar Street Bridges, the Martin Luther King Bridge is still a vital connection needed to efficiently move traffic through these communities. This rehabilitation project has helped to ensure the bridge will be able to continue playing this role for years to come.
In total, the structure was closed for five months, from July 6, 2015, to Dec. 18, 2015, when it was reopened to traffic.
By implementing photo-imaging and infrared thermography, IDOT was able to reap the benefits of leveraging new technology that is available to document the existing structure conditions and supplement the existing information available. These technologies followed in line with the project priorities of maintaining and extending the life of the bridge, while improving the driving experience and safety for everyone in the St. Louis and East St. Louis area.
The rehabilitation of the Martin Luther King Bridge demonstrated how innovation, coordination and collaboration can lead to saving time and money, and reducing negative impacts on traffic while maintaining a safe connection for the surrounding communities.
By Jerilyn Hassard, PE, SE - Senior Associate