Since the levee system is critical for protecting the downtown region, there was a strong desire to leave the existing floodwalls and levees intact. Appropriately, the bridge abutments were designed to penetrate the levee on both river banks while still maintaining flood protection for the city, with the new bridge abutments sized to match the loca- tions of the floodwalls. To minimize excavation and disturbance to the existing floodwalls, large portions of the original massive abutments were left in place. The new prototypical, semi-integral abutments were developed to account for the pile fixity caused by the rigid connection/ incorporation into the existing abutments. Due to the limited ability to raise the roadway, the Shuck-Britson engineers worked closely with the U.S. Army Corps of Engineers (USACE) and the Iowa Department of Natural Resources (DNR) to modify the existing hydraulic model, as well. With the pier footings for the new bridge supported on steel piles extending to bedrock, one less pier was required, increasing the flow area of the river by nearly twenty percent. Additionally, the bridge is designed to withstand the hydraulic effects of a 200-year frequency flood event and the intense water pressure acting against the bridge fascia. Expert Coordination & Collaboration Lead to Aggressive Build Schedule Following the demolition of the previous structure at the end of 2016, construction began on a new bridge. The shallow river depth allowed for the use of temporary causeways during construction with a minimal impact on the environment. All plans were submitted on time, allowing the Iowa Department of Transportation (DOT) to let this comprehensive project on sched- ule. Shuck-Britson’s estimate of probable cost for the project was $8,612,304.00, with an estimated bridge cost of $7,749,615.00. The actual bid price for the project was $9,060,752.68, with an actual bridge bid cost of $8,379,396.23. The difference in the original cost estimate versus the bid cost is mostly attributed to site difficulties and aesthetic components. In November of 2017, a mere 12 months after construction began, the bridge opened to one lane of vehicle traffic in each direction with partial pedestrian traffic. The project was substantially completed in Spring 2018.
The Shuck-Britson team, along with parent company Snyder & Asso- ciates, made the project possible by collaborating to provide the devel- opment of project concept statement, preliminary bridge and roadway plans, hydraulic analysis and documentation, final bridge and roadway design plans, as well as the extensive coordination and development of aesthetic details. Also, the design team provided rapid response service for issues that arose during construction. These included addressing unanticipated site conditions, pile driving inquiries, and general con- struction observation. Award-Winning Bridge Project The success of the new Grand Avenue Bridge led to a similar design for the Locust Street Bridge location (currently under construction) with plans in the works to let the Walnut Street Bridge in 2022. The innovative aesthetics on the new bridges is viewed as a visual comple- ment to the Iowa Women of Achievement Bridge located just upstream from Grand Avenue and helped to transform the downtown river area for a new generation. Shuck-Britson and their client, the City of Des Moines, were awarded the 2019 Honor Award for Engineering Excellence in the Transportation category by the American Council of Engineering Companies of Iowa (ACEC-IA) for the Grand Avenue Bridge project. About Shuck-Britson Shuck-Britson specializes as a full-service structural engineering and consulting firm serving clients throughout the Midwest and beyond since 1966. With a focus on diverse client needs, we perform engi- neering for inspection, evaluation, repair, rehabilitation, strengthening, design, and load rating for all types of bridges and structures. After decades of working closely together, Shuck-Britson became part of the Snyder & Associates family in 2008 to deepen and expand the full-service capabilities of both firms. Together we provide extensive civil and structural engineering services grounded in over 90 years of experience. From historic preservation to new construction, Shuck- Britson brings your vision to life through smart, right-sized solutions. Watch the video here.
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csengineermag.com
october 2020
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