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Loai El-Gazairly Presents to ASCE Richmond.

Loai El-Gazairly, Ph.D., P.E., presented to ASCE Richmond about the design and construction of the post-tensioned straddle bents that were part of the US 301 over SR 1 project in Delaware. WRA is the Engineer of Record for this flyover (Contract 1B), which is part of seven contracts of the US 301 project with a total construction cost of $330 M. The US 301, Section 1 project in New Castle County, DE includes the preliminary and final design of the 5.5 miles of limited-access toll highway. One of the most complex design elements of the project is the interchange of the new US 301 with the existing SR 1 and US 13. The structure design includes 11 new highway bridges, one bridge widening, eight major culverts, three retaining walls, and seven sign structures. The US 301 over SR 1 flyover includes two pre-cast, post-tensioned straddle bents (the first in the State of Delaware) with a maximum span length of 116 feet and a total design weight of 750 tons. Due to the caps’ concrete volume, a mass concrete provision was introduced along with a thermal control plan in order to constrain the core rate of hydration and to prevent the formation of potential cracks. The straddle bents were cast and partially post-tensioned while being supported on falsework within the median of SR 1, then transported, lifted and erected into their final position. A second stage of post-tensioning was performed after erection to provide the bents with the ultimate strength to support the anticipated superstructure loads. The presentation discussed the caps' design philosophy, as well as their structural analysis during casting, construction staging, transporting and erection.