Urban Bridge Design Considerations | Part I by: Steve Kathol, P.E.,S.E.

Designing bridges in urban areas can present multiple challenges that are not as common in more rural settings. Urban bridges are often constructed in locations with limited setback to other properties or buildings; are often required to carry a high volume of arterial or collector street traffic; are often critical to maintaining access to a business, residential development or other facility that is significant to the community; and often involve some level of aesthetic enhancement to better align with a city’s urban development plan. In the eyes of the public, successfully addressing each of these considerations may be the difference between the success or failure of a project.

Two important aspects, among several, that are considered as part of Schemmer’s normal design practice for urban bridge projects are the following:

Noise - The construction of most bridges can be a noisy process that is disruptive to urban functions, but there are alternative components that can often be designed to reduce this nuisance construction noise. For example, driven piling is often used for deep foundation support of bridge piers and abutments. The installation of driven piling requires a large hammer on a crane mast to pound each pile into the ground. This results in a noisy rhythmic pounding of steel that can take several months or longer, depending on the length of the bridge. In areas where retail, office, school, hospital or other facility of significance is nearby, this nuisance noise is not easily tolerated by the public. In these cases, a drilled concrete shaft foundation could be considered as an alternative to driven piling. Drilled shafts are augured into the ground, creating substantially less noise. On the U.S. 6, Broadway Viaduct project in Council Bluffs, Iowa (designed by Schemmer), drilled shafts were used to reduce noise and vibration, and a method known as Post Grouting or Base Grouting was also utilized to allow shorter shaft lengths. This allowed the shafts to be terminated approximately 20 feet above bedrock. By implementing this method, our team significantly reduced shaft length and the time that was required for installation.

Vibration - Typical construction practices on bridge projects will create vibration within the immediate area of the project location. If historic buildings or other structures are nearby, damage from vibrations could result. To prevent such damage to these structures, vibration thresholds, based upon building material type, can be determined and monitored during the construction process. If the vibration threshold is reached, alarms will sound and the Contractor is required to stop work and remedy the activity creating the excessive vibration.

There are various other design aspects that Schemmer applies innovative practices in producing a quality urban bridge design for clients and communities to enjoy for years to come.

Stay tuned for Urban Bridge Design Considerations | Part II coming soon!