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/306864
S TAT E F or more than a century, Iowa has seen c o n c r e t e b r i d g e s b u i l t w i t h s t e a d i l y a d v a n c i n g t e c h n o l o g y — c a s t - i n - p l a c e (CIP); reinforced; precast, prestressed; high- performance (HPC); self-consolidating (SCC); post-tensioned; ultra-high-performance (UHPC); and combinations of technologies to accomplish accelerated bridge construction (ABC). The history of Iowa's concrete bridges began in the late nineteenth century with the first CIP reinforced concrete Melan arch bridge, built when arches were popular for their efficiency and beauty. Soon after the Iowa State Highway Commission (IHC) was established early in the twentieth century, the IHC developed plans for several series of standard CIP reinforced concrete slab and beam bridges. These standard plans were created in the same era as the proprietary and competing concrete arch designs of James Barney Marsh and Daniel B. Luten. Precast and Pretensioned Bridges In the early 1950s, the bridge office developed standard designs for several new concrete bridges, often in conjunction with the Iowa Highway Research Board (IHRB). There were the H1 and H2 CIP reinforced concrete girder and continuous girder series for spans to 67.5 ft and 100 ft, respectively, and the J10 precast reinforced concrete series (reinforced channel slabs) for spans up to 30 ft. In 1954, the bridge office recognized the advantages of precast, prestressed concrete beams with the H10-series for spans up to 42.5 ft. As with all of the state- developed standard bridges, these were built by counties and cities as well as by the state. Updated versions of the H-series are still in use today. The family of standard beams developed in the 1950s has grown to cover a wide range of span lengths and superstructure depths. The newest set of bulb-tee beams provides a competitive alternate for medium-span bridges. These bulb-tee beams have proven to be a perfect solution for many two-span overhead structures, multiple-span urban viaducts, and the approach spans of major river crossings. Attributes of the new beams include AASHTO Load and Resistance Factor Design (LRFD) compliance, low permeability (< 2500 coulombs), high strength (up to 9000 psi), efficient design with longer spans (up to 155 ft), wider beam spacings (up to 9.25 ft), and an aesthetically pleasing shape. It is interesting to note that the majority of Iowa bridges utilize precast, prestressed concrete beams. In fact, prestressed concrete was the material of choice for bridges over the interstate system. High-Performance and self- Consolidating Concretes In early 2000, as a part of the reconstruction of I-235 in Des Moines, the Iowa Department of Transportation (IowaDOT) introduced HPC and SCC. Although HPC and SCC have been used widely in the United States, deploying these mixtures in Des Moines was not a simple task. A group of IowaDOT engineers from various disciplines, along with the Federal Highway Administration (FHWA), collaborated on developing mix designs and construction specifications that were suitable for central Iowa. The HPC mix designs had to utilize locally available aggregates, and meet new design requirement s in terms of strength a n d p e r m e a b i l i t y. M a n y c h a l l e n g e s w e r e encountered along the way, including a lack of local experience in producing mixtures such as HPC; implementation of a new aggressive policy on star ting curing pr ocedur es for concrete within minutes after placing; and dealing with harsh winter conditions. The I-235 experience laid the groundwork for statewide implementation of HPC, which is currently being used on major reconstruction projects in western Iowa (I-29/I-80 in Council Bluffs) and eastern Iowa (I-74 in the Quad Cities and U.S. 20 in Dubuque). These projects include several Missouri River and Mississippi River crossings. Although HPC has not been officially adopted for statewide use, many elements of HPC are being added to traditional mixtures.This can be attributed to the successes achieved on the I-235 project. Furthermore, some changes to IowaDOT's constr uction specifications were made to take advantage of ADvANCES IN CONCRETE BRIDGES in Iowa by Ahmad Abu-Hawash, Norman McDonald, Kimball Olson, and Kenneth Dunker, Iowa Department of Transportation The Marsh rainbow arch bridge constructed in 1914 across the Raccoon River near Lake City has three 80-ft-long spans. Photos and drawings: IowaDOT. ASP10-1625.indb 52 6/21/10 12:20 PM