The San Antonio “Y” at 40, America’s First Span-by-Span Segmental Urban Viaduct
Abstract:
The elevated Downtown San Antonio “Y” Project was a bold undertaking by the Texas State Department of Highways and Public Transportation (SDHPT, now TxDOT) in the 1980s and early 1990s to develop an aesthetically pleasing, low maintenance solution to increase capacity and improve mobility where I-35, I-37 and I-10 converge in downtown San Antonio. TxDOT initially decided on a concrete “composite wing-girder” structure developed by T. Y. Lin for the San Francisco International Airport Upper-Level Viaduct and partnered with researchers at the University of Texas at Austin to test constructability and performance of the concept for the “Y” Project. At the time of project development, FHWA required alternative concepts (usually concrete vs. steel) for bridge projects above a certain dollar amount. However, they permitted TxDOT to utilize two concrete alternatives — the composite wing-girder alternative designed by TxDOT and a span-by-span segmental alternative designed by Figg & Muller Engineers. Subsequent contracts in the interchange, designed by Figg & Muller later TxDOT, did not require an alternative and were all built using span-by-span segmental construction. The various contracts introduced new refinements as overall deck widths increased, and gore area geometry posed challenges for variable precast box dimensions and transverse post-tensioning across longitudinal closure joints.
Valuable lessons were learned during construction that influenced detailing for both the later contracts in the interchange and future segmental projects around the country. The structures have performed well through the decades, but lessons are still being learned today concerning early era post-tensioning and segmental construction applications and the challenging task of large-scale infrastructure maintenance.
Presenters:
Brian Merrill, Wiss, Janney, Elstner Associates, Inc.
Christopher White, HNTB Corp.
Technical Director, Long-Span & Complex Bridge Lead: For over thirty-five years Chris White has been providing management, design and construction support services for major bridge projects throughout the United States and internationally. His expertise includes technical management and leadership for complex structures, including: post-tensioned segmental box girders and spliced I-girders; cable-supported, arch and truss bridges; heavy and light rail structures; displacement-based seismic design; vessel impact studies; redundancy focused steel substructure design; and complex finite element analyses of structures. His broad, hands-on experience spans the spectrum from bridge concept development to final design to contractor-support design during construction, and finally, to load rating and rehabilitation of existing structures. He has led bridge proposal pursuits, conceptual design and final design involving design/bid/build, design/build and construction-manager-at-risk (CMAR, CMGC) methods of contracting.
