ASPIRE is a quarterly magazine published by PCI in cooperation with the associations of the National Concrete Bridge Council. The editorial content focuses on the latest technology and key issues in the Concrete Bridge Industry.
Issue link: http://www.aspiremagazinebyengineers.com/i/306885
The Raspberry Island Bridge features five spans of cast-in-place concrete slab girders. The bridge ties in with the nearby Hariett Island trail system and the River Walk, and features "St. Paul Rail" designed hand rails. C I T Y St. Paul Creates Replacement Plan by Kevin L. Nelson, City of St. Paul, Minn. T he collapse of the I-35W bridge in the Twin Cities region brought increased attention to the condition of Minnesota's bridge infrastructure, beginning a process to increase the available funding for replacement projects and rehabilitation. Most of our recent bridge and retaining wall projects have been concrete structures, and we expect that will continue for the future. The additional funding, especially through the state matching-funds program, is a welcome addition. It is being financed by a bond fund supported by an increase in the gasoline tax— the first such increase in 25 years. Minnesota had fallen behind other states in increasing this funding as there was no way to include an inflation factor in our budgeting. This caused us to fall behind in our construction. This program will help us to catch up and update bridges more quickly. In all, the city has 331 bridges within the right-of-way of the city, county, and state with 110 of those being concrete. The City of St. Paul has 12 structurally deficient bridges, according to our current bridge inventory. All are programmed for replacement in the next 5 years, with three to be replaced in 2008. The city also has nine Mississippi River crossings, including three concrete arch bridges and a segmental box girder bridge. All have been rebuilt or constructed new within the past 15 years. When we replace or build a new bridge, most often, we use the standard Minnesota Department of Transportation precast, prestressed concrete I-girders, although the state recently developed new standards that include a solid box beam design and an inverted T-beam. We have not yet designed with those components, but we will be using them once we see how best to apply them. Cast-in-place concrete decks are used on most of the bridges. We use concrete on our new bridges today because it fits our needs. It is a versatile material, providing a variety of ways that we can mold it and color it. It is economical and readily available. It also offers high durability and strength that will provide a service life of 50 to 100 years. The Earl Street Bridge is a multi-span design featuring precast concrete beams that replaces a deteriorated structure on the site. The railings feature the St. Paul Standard Ornamental rail and Lantern style lighting. EDitoR'S NotE If your city has a high percentage of concrete bridges or some interesting and innovative concrete bridges and would like to be featured in ASPIRE™, please let us know at info@ aspirebridge.org. Two of the three bridges being replaced this year will be replaced with concrete bridges. We anticipate replacing the remaining deficient bridges at a rate of two bridges per year. Most of these are local roads crossing railroads, and some of them are as much as 100 years old. The bridges being replaced this year were constructed in the 1950s. One of our most notable recent bridges was the Raspberry Island Bridge, which is the only land link to the island for vehicles and pedestrians. The five-span, cast-in-place concrete slab bridge was built during a difficult spring flood, which slowed falsework and forming procedures. The bridge features two 50-ft-long end spans and three 75-ft-long center spans. Ornamental steel railings and a colored concrete overlay on the deck panels were used to add visual appeal to the bridge. City engineers work closely with the state on achieving design goals and coordinating work so that designs are complementary, efficient, and cost-effective. Concrete designs ensure that those goals are met for us. _____________________ Kevin L. Nelson, P.E., is the bridge division manager for the Public Works Department of the City of St. Paul, Minn. In the wake of tragedy, more funding helps expand bridge program Aspire_sum08.indb 50 6/24/08 1:48:56 PM