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/575053
CONCRETE BRIDGE TECHNOLOGY ILLINOIS GIRDER SHAPES OFFER DESIGN FLEXIBILITY by Kevin Riechers, Illinois Department of Transportation Earlier this year the Illinois Department of Transportation (IDOT) introduced a series of new precast, prestressed concrete (PPC) girder profiles to supplement their current PPC girder profiles. The goals were to create * sections that are capable of spanning further to compete with other materials, * robust top flanges to better resist damage during future deck replacements, * improved durability, * sections with sufficient lateral stiffness to accommodate use for longer spans, * a variety of functional bridge configurations, and * sections with future growth potential by utilizing higher concrete strengths. Before selecting the new beam sections, IDOT reviewed numerous beam configurations and designs from surrounding states and other leading concrete beam states throughout the country. The development process also included close coordination with the Precast/Prestressed Concrete Institute (PCI), concrete researchers, Illinois fabricators, and potential users/ owners. All available design options and fabrication techniques were reviewed and revisited to help IDOT achieve its goals. A total of 11 new beam sections were created. The following are some highlights of their characteristics: * Six beam depths: 27, 36, 45, 54, 63, and 72 in. * Narrow, thick top-flanges with two width options * Large bottom flanges * Curved flange-to-web transitions * Concrete compressive strength of 8.5 ksi at 28 days - increased from 7 ksi * 0.6-in.-diameter, Grade 270 strands * Epoxy-coated, welded-wire shear reinforcement with standardized spacing Compared to the new Illinois (IL) shapes, IDOT's current PPC I-beam and bulb-tee beams have smaller cross sections, but the same range in depths is available for both the new and current - 36 to 72 in. A new shallower IL-beam with a depth of 27 in. was created to expand the span range for new and replacement structures. Typically, wide and thin top-flange beams provide an efficient prestressed beam design. It's not uncommon to see a top-flange width of 48 in. that's less than 3 in. thick at the outside edges. However, wide and thin top flanges make future deck removal difficult, provide less space for deck drainage options, and offer less flexibility for locating stage lines and concrete closure placements for staged construction. The new IDOT sections have a maximum top-flange width of 38 in., with a minimum thickness of 5 in. The top flange can be reduced to 24 in. with a simple form block-out. These flange configurations help meet IDOT's goals of providing more flexibility and easier removal and replacement of existing decks. This was in line with IDOT's choice of durability and functionality as its top priorities when creating the new sections.