ASPIRE Summer 08 - Aspire - The Concrete Bridge Magazine

CITYIn the wake of tragedy,more funding helps expand bridge programSt. Paul CreatesThe Raspberry Island Bridge features five spans of cast-in-placeconcrete slab girders. The bridge ties in with the nearbyHariett Island trail system and the River Walk, andfeatures “St. Paul Rail” designed hand rails.Replacement Plan by Kevin L. Nelson, City of St. Paul, Minn.The collapse of the I-35W bridge in theTwin Cities region brought increasedattention to the condition of Minnesota’s bridgeinfrastructure, beginning a process to increasethe available funding for replacement projectsand rehabilitation. Most of our recent bridgeand retaining wall projects have been concretestructures, and we expect that will continue forthe future.The additional funding, especially throughthe state matching-funds program, is a welcomeaddition. It is being financed by a bond fundsupported by an increase in the gasoline tax—the first such increase in 25 years. Minnesotahad fallen behind other states in increasingthis funding as there was no way to include aninflation factor in our budgeting. This caused usto fall behind in our construction. This programwill help us to catch up and update bridges morequickly.In all, the city has 331 bridges within theright-of-way of the city, county, and statewith 110 of those being concrete. The City ofSt. Paul has 12 structurally deficient bridges,according to our current bridge inventory. All areprogrammed for replacement in the next 5 years,with three to be replaced in 2008. The city alsohas nine Mississippi River crossings, includingthree concrete arch bridges and a segmental boxgirder bridge. All have been rebuilt or constructednew within the past 15 years.When we replace or build a new bridge, mostoften, we use the standard Minnesota Departmentof Transportation precast, prestressed concreteI-girders, although the state recently developednew standards that include a solid box beamdesign and an inverted T-beam. We have not yetdesigned with those components, but we will beusing them once we see how best to apply them.Cast-in-place concrete decks are used on most ofthe bridges.We use concrete on our new bridges todaybecause it fits our needs. It is a versatilematerial, providing a variety of ways that wecan mold it and color it. It is economical andreadily available. It also offers high durabilityand strength that will provide a service life of 50to 100 years.Two of the three bridges being replaced thisyear will be replaced with concrete bridges. Weanticipate replacing the remaining deficientbridges at a rate of two bridges per year. Mostof these are local roads crossing railroads, andsome of them are as much as 100 years old. Thebridges being replaced this year were constructedin the 1950s.One of our most notable recent bridges was theRaspberry Island Bridge, which is the only landlink to the island for vehicles and pedestrians.The five-span, cast-in-place concrete slab bridgewas built during a difficult spring flood, whichslowed falsework and forming procedures. Thebridge features two 50-ft-long end spans andthree 75-ft-long center spans. Ornamental steelrailings and a colored concrete overlay on thedeck panels were used to add visual appeal tothe bridge.City engineers work closely with the state onachieving design goals and coordinating workso that designs are complementary, efficient, andcost-effective. Concrete designs ensure that thosegoals are met for us.The Earl Street Bridge is a multi-span design featuringprecast concrete beams that replaces a deteriorated structureon the site. The railings feature the St. Paul StandardOrnamental rail and Lantern style lighting._____________________Kevin L. Nelson, P.E., is the bridge division managerfor the Public Works Department of the City of St.Paul, Minn.Editor’s NoteIf your city has a high percentage of concretebridges or some interesting and innovativeconcrete bridges and would like to be featuredin ASPIRE, please let us know at info@aspirebridge.org.