Some bridges we travel daily without giving it a second thought. Other times, the majesty of one captures our attention immediately. Have you ever wondered how the type of bridge is selected? There are numerous factors that affect bridge type selection, and the process is as varied as the environments around them. So what drives these choices?
You might be familiar with some of the main bridge types: tied-arch, cable-stayed, truss, cantilever, girder, suspension, and arch. However, some bridges, particularly large structures, are usually comprised of a combination of types. Furthermore, within each major bridge type category, there are many variations such as building materials and geometric configurations. Bridges may also be fixed in place or designed to move to accommodate the passage of vessels. Often the primary focus is on the type of structure you see being built, but the choices go far beyond that.
Where will the bridge touch down? How will it tie into the existing roadways and affect the flow of traffic through the surrounding communities. Will it be an iconic symbol that is synonymous with the region, or will it blend into the background to avoid distracting from a natural setting?
The decision process begins when a client identifies a need. That need could be a new structure, replacement of an aging one, or a major rehabilitation. The nature, scale, and funding of the project can determine who has input into the final decisions. In some cases, both the owner and the public may influence the design. Transparency is key during this process and identifying stakeholders who will be affected is critical to identifying and addressing concerns.
Engineers at M&M like to think of each bridge selection as a unique story that has yet to be written. We get to know the participants involved and the needs and desires that drive them. We learn the setting and community of where this story takes place. Factors like environmental, historical, and cultural impacts; traffic projections and disruptions; effects on commerce and local businesses during construction; multimodal opportunities beyond vehicular traffic; and the overall future vision for the community or land use may be early chapters of the story. Geometric constraints, navigation channels, railroad clearances, budget, funding, schedule, and materials availability or preferences may follow.
Ultimately, M&M wants to partner with our clients through every step of the process. Well selected and maintained bridges can last more than a lifetime. Many bridges designed more than a hundred years ago by our founder, Ralph Modjeski, are still standing today.
Choosing the wrong bridge type at the start can cost bridge owners more money in the long run because of higher maintenance costs or premature functional obsolescence. That’s why we present a thorough report with options during the first phases of each project — so the client makes an educated decision armed with an understanding of all the factors involved.
We do not jump to the end of the story with preconceived conclusions of what type of bridge or alignment is best. Building the right bridge takes the right considerations paired with technical expertise. Each bridge has its own story and each decision we make during the build process shapes the final result. We wait for the story to unfold like a good book – one with a great ending that leaves behind a unique legacy.