The Iowa Department of Transportation (Iowa DOT) has added a series of RS40-10 rolled steel beam bridge standards to its acceptable bridge design configurations.
Gary Novey, assistant bridge engineer for the Iowa DOT, says that he believes these off-the-shelf rolled steel beam standards make it easier for bridge engineers to specify steel beams, may drive better costs from fabricators as designs are built from standard templates, and will reduce overall maintenance due to the use of integral abutments, weathering steel girders and low maintenance bearings.
Developed by Stanley Consultants in cooperation with the Iowa DOT, the new RS40-10 rolled steel beam bridge standards replace the previous short span design standards. The new standards cover multiple spans for bridges up to 340′-0 in length and include base sheets and bridge standards designed for LRFD specifications. The standards cover pile bent piers, tee piers, skew bridges (0°, 10°, 20°, 30° and 45°), 160’-0 to 340’-0 bridge lengths and symmetrical/unsymmetrical 40’ wide bridge decks.
Larry Badtram, principal structural engineer with Stanley Consultants, Inc. explains. “Ninety percent of the design is complete,” Badtram says. The engineer still has to deal with geometry and coordination, but the templates should reducedesign and construction time. The goal is that the only documentation necessary to design a bridge is a cover sheet that references the appropriate bridge standard sheet number, a quantity sheet, top of slab and maybe one other sheet for unique criteria at the specified site.”
For instance, to call out a 40-foot-wide, 300-foot-long bridge on a 20-degree skew, the bridge engineer puts together a cover sheet that references the appropriate bridge standard sheet numbers. Follow-up sheets might include upgrades to substructures and foundations. The contractor pulls these same sheets from the Website to determine quantities.
The Iowa DOT feels these standards should allow contractors and fabricators to develop consistent techniques and practices that will produce economies of scale. Since bridges are typically designed based on site conditions and an eye on longevity and durability, as well as cost, the availability of these rolled steel beam standards should also drive greatercompetition.
The bridge standards are available to county engineers as well. Since the bridge standards are approved by the chief bridge engineer of thestate, the DOT believes the standardization of bridge design components will give all parties confidence in the performance and durability of bridges constructed throughout Iowa.
According to Calvin Schrage of the National Steel Bridge Alliance (NSBA), who has collaborated with Iowa DOT on the development of the standards over the past decade, the Iowa rolled steel beam standards encompass the following individual span arrangements that combine to meet the desired total span length.
|TOTAL SPAN LENGTH||INDIVIDUAL SPAN ARRANGEMENTS
|160′ long||48′ + 64′ + 48′ spans|
|180′ long||54′ + 72′ + 54′ spans|
|200′ long||60′ + 80′ + 60′ spans|
|220′ long||66′ + 88′ + 66′ spans|
|240′ long||72′ + 96′ + 72′ spans|
|260′ long||78′ + 104′ + 78′ spans|
|280′ long||84′ + 112′ + 84′ spans|
|300′ long||90′ + 120′ + 90′ spans|
|320′ long||96′ + 128′ + 96′ spans|
|340′ long||102′ + 136′ + 102′ spans|
All Iowa DOT bridge designs, whether steel or concrete, make use of standards defined by the DOT and available on its Website, http://www.iowadot.gov/bridge/v8ebrgstd.htm.
The Short Span Steel Bridge Alliance (SSSBA) took the Iowa standards into account in the development of a national standard for short span steelbridges that is now being finalized. The standards may be used to constructcost-effective short span bridges, providing solutions for corrugated steelpipe, structural plate, rolled beam, and plate bridges.
The standards are expected to be available soon at the Short Span Steel Bridge Website, www.ShortSpanSteelBridges.org.