Since its construction in 1929, Modjeski and Masters has been deeply involved with the Ambassador Bridge. Ralph Modjeski, the firm’s founder, was the bridge owner’s consulting engineer. He oversaw design and construction of, what was at the time, the world’s longest suspended span of 1,850 feet.
In the many decades since, through multiple owners and its growth into the busiest international trade border crossing in North America, Modjeski and Masters has worked to keep the bridge maintained for current conditions and prepared for what the future may hold. The latest Ambassador Bridge project continues this trajectory, but with a new, innovative twist to project delivery.
Started in November 2014, the current project is another facet of the bridge owner’s asset management plan. It includes inspection and evaluation of the suspended span’s main cables, design and inspection of the span’s miscellaneous steel repairs and construction. While the project details are important, it is the project delivery model that sets it apart.
For this work, Modjeski and Masters heads a unique engineer-led design-build project delivery model. To date, this type of project delivery model has been rare in the construction industry. In more typical design-build or design-bid-build models, the contractor takes the project lead during the project’s construction phase.
In an engineer-led model, the contractor, in this case Piasecki Steel Construction Corporation, is part of the engineer’s team from project inception. With engineer and contractor on the same team, the relationship is non-adversarial. The engineer develops the design with input from the project owner and the contractor. During the construction phase, the contractor is less likely to request change orders for construction document errors and omissions because they participated in creating those documents alongside the engineer during the design phase.
The collaborative design process means that projects are more cost effective to construct. It streamlines plan delivery and eliminates the need for multiple revisions that prolong schedules and drive up costs. Construction risks also are minimized.
How do you get to the point where this delivery model is even considered? It’s all about relationships.
In this particular case, Modjeski and Masters has been the engineer for the owner of the Ambassador Bridge, the Detroit International Bridge Company (DIBC), for close to two decades. Over those years, we have built a high level of trust with the DIBC on a variety of projects including annual condition inspections, load capacity ratings, and design of bridge redecking and miscellaneous steel repairs. So, instead of bringing in someone new to lead the continuation of its asset management plan, DIBC entrusted Modjeski and Masters to lead the current project.
Previous relationships with the contractor are also important for this particular delivery model. An engineer shouldn’t expect to lead a project with a contractor with whom they are working for the first time. Since both partners must adapt to a reversal of traditional project hierarchy, management, and roles, a solid foundation of trust is key to avoid scope creep and mistrust.
The project owner also plays a role in whether an engineer-led delivery model is possible at all. Many governmental owners are regulated to use a certain delivery model. Since the DIBC is the private owner of the Ambassador Bridge, it may select any delivery model that fulfills its and the project’s needs. It found that the engineer-led model saves time and money.
It’s our expectation that the engineer-led project delivery model is on the cusp of gaining wider recognition and implementation. Just as public-private partnerships have gained traction and shown to be more effective for certain projects, engineer-led represents a new and efficient method for project delivery.
As mentioned, the current project work is part of the DIBC’s asset management plan for the Ambassador Bridge. These investigations and construction improvements will help extend the bridge’s life for a significant amount of time. It will also maintain an open and fully operational border crossing that carries more than a quarter of all trade between the United States and Canada.
Modjeski and Masters brings considerable cable inspection expertise to the evaluation of the bridge’s two main suspension cables. Each cable is comprised of 37 strands, with each strand containing 218 wires. In total, that’s more than 8,000 wires per cable (more than 16,000 overall) and 7,500 feet of cable.
To minimize disruption to the more than 9,000 commercial vehicles that cross the Ambassador Bridge on a daily basis, the cables are inspected above traffic without the need to close lanes or reroute travelers. Proper safety devices and procedures are in place both at and under the cable locations where the work is conducted.
Engineers select specific panels of the cables to inspect. At each panel, inspectors remove the outer cable wrappings and coverings to evaluate the interior wires for corrosion, cracking, or unusual wear and tear. To inspect inside the bundle of wires, wedges are inserted into the cable at predetermined locations around the cable’s perimeter to expose more of the interior wires.
Corrosion stages of the individual wires are catalogued along with any observed wire breaks. Wire samples are removed for laboratory testing and new wires spliced in place. After compiling all the necessary data, engineers will determine the strength of the cables and the need for additional specialized monitoring or rehabilitation.
Also included in this round of maintenance are rocker link replacements at the main span stiffening trusses’ four corners; wind tongue rehabilitation; tower and stiffening truss bracing upgrades (plate, angle, lacing member, stiffener, and rivet replacement); toe plate installation at the top of the towers; longitudinal inspection walkway railing replacement and extension; and new transverse inspection walkway installation at each end of the main span.
Unlike many bridges, the Ambassador Bridge has been maintained well. At more than 85 years of age, it shows no signs of falling into disrepair. A vigorous ongoing maintenance plan has ensured its current health and will help extend the structure’s life well into the future.
By Michael Britt, PE - President / Chief Executive Officer