Design and Construction of Post-Tensioned Straddle Bents for US 301 over SR 1, New Castle County, Delaware

摘要

Section 1 of DelDOT's US 301 project in New Castle County, Delaware, includes the final design of 5.5 miles of limited-access toll highway. The structural design includes eleven new highway bridges, one bridge widening, eight major culverts, three retaining walls, and seven sign structures. One of the most complex design elements of the project is the interchange of the new US 301 with existing SR-1 and US 13. The flyover bridge carrying northbound US 301 over SR-1 includes two precast, post-tensioned concrete straddle bents (the first of their kind in the State of Delaware) with a maximum span length of 106 feet and total weight of 750 tons. The straddle bents were constructed and partially post-tensioned while supported on falsework within the median of SR-1 and subsequently transported, lifted, and erected into their final positions. A second stage of post-tensioning was performed after erection to provide the ultimate strength of the bents and to support the anticipated superstructure loads. Due to the caps' concrete volume, a mass concrete provision was introduced along with a thermal control plan to constrain the core temperature due to hydration and to prevent the formation of potential cracks. The theory of the straddle bent cap beam design and its structural analysis during casting, construction staging, transporting, and erection are examined.