Effects of bending and heat on the ductility and fracture toughness of flange plate.
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2012-05-01
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Alternative Title:Project title: Performance and Effects of Punched Holes and Cold Bending on Steel Bridge Fabrication
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Edition:Technical report; Sept. 2003-Aug. 2006.
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Abstract:Bridge fabricators for the Texas Department of Transportation (TxDOT) have occasionally experienced the
formation of cracks in flange plate during bending operations, particularly when heat is applied. Bending the
flange plate is necessary for certain details used in the fabrication of steel highway girders such as dapped end
details. Heat is sometimes used to assist in the bending operation, particularly to help reduce the forces required
to bend the plate. This report documents the findings of a TxDOT-sponsored research project that investigated the
possible causes of the cracking and developed recommendations to prevent the occurrence of such cracking.
The research project investigated the cracking problem using both experimental and analytical studies. The
experimental study involved the use of small tensile specimens loaded to different strain levels under varying
temperature conditions. Strain levels up to 15 percent were investigated. Temperature conditions included testing
at room temperature, 450ºF, and 1150ºF. The results showed that strain levels above 10 percent generally reduced
the ductility and fracture toughness of the plate. Additionally, it was found that the application of heat during the
bending process significantly reduced ductility and was the major contributor to the formation of cracks. A finite
element study of the heating process was used to extend the results for the experimental study.
As a secondary study, the fatigue behavior of non-loaded bolted connection details was investigated along
with the influence of plate thickness. These details occur when gusset plates are bolted to flanges of girders.
Unlike flange or web splices where the load must transfer out of the main member, the load in these details passes
through the main plate, resulting in higher stresses around the bolt holes. Pre-tensioning the bolts normally shields
the bolt holes from fatigue damage due to the resulting compressive stress field. This study found that for plate
t hicknesses greater than 1.0 inches, a reduction in fatigue strength was warranted.
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